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DFMA report

The document provides a summary of a report analyzing the design for manufacturing and assembly (DFMA) features of an HP Deskjet printer. Key DFMA guidelines considered include minimizing parts, using standard parts, facilitating part handling, and encouraging modular assembly. The report examines the printer's design for automation and assembly, use of plastics, fastening methods, and sheet metal components. Figures are included to illustrate how the printer's design incorporates various DFMA principles such as pyramidal assembly, symmetry, and avoiding part jamming.

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DFMA Report The Design for Manufacturing and Assembly Features of a Deskjet Printer Kerrie Noble, 4th Year PDE, 200948192 11/5/2012 I declare that this submission is entirely my own original work. This is the final version of my submission. I declare that, except where fully referenced direct quotations have been included, no aspect of this submission has been copied from any other source. I declare that all other works cited in this submission have been appropriately referenced. I understand that any act of Academic Dishonesty such as plagiarism or collusion may result in the non- award of my degree. Signed …………………….…………………...Date 05/11/2012
Contents Introduction to Design for Manufacture and Assembly ...................................................................3 My ChosenProduct ...................................................................................................................... 3 Design for Automation and Assembly ............................................................................................ 5 Design for Plastics....................................................................................................................... 17 Design for Fastening and Other Joining Methods.......................................................................... 31 Design Considerations for Boring............................................................................................. 32 Design Considerations for Drilling............................................................................................ 34 Design Considerations for Soldering......................................................................................... 35 Design for Mechanical Fastening.............................................................................................. 36 Design for Sheet Metal and Presswork......................................................................................... 41 Conclusion ................................................................................................................................. 46 References................................................................................................................................. 47
Introductionto DesignforManufactureandAssembly In manyinstancesthe failure of acomponentorproduct can be traced back to the designof parts and assembly proceduresbeingused. DesignforManufacture andAssembly,more commonly abbreviatedtoDFMA,isthe processbywhichdesigns,assemblysequencesandproceduresare analysedandalteredinordertoincrease the effectivenessof automatedassembly. (unknown author,dora.eeap) The term‘increasingeffectiveness’,isdefinedasminimisingthe costof productionand/ortime tomarketfor a product,while maintaininganappropriate levelof quality. (Cook,C.,and Youssefi,K,) Thiscanbe expandedfurther,tothe pointwhere DFMA can alsobe definedasthe processof proactivelydesigningproductstooptimizeall the manufacturingfunctions: fabrication,assembly,test,procurement,shipping,delivery,service,andrepairwhile alsoassuring the bestcost, quality,reliability,regulatorycompliance,safety,time-to-market,andcustomer satisfaction. (Hamidi,M.,andFarahmand,K, 2008) To achieve the objectivesof DFMA,whichwere outlinedabove,there are some keyguidelinesto followduringthe design stage of anymassproducedproduct;  Minimize partcount  Make parts multi-functional  Reduce the numberof screwsand screw types  Facilitate partshandling  Use standardparts and hardware  Encourage modularassembly  Use stack assemblies/Don’tfightgravity  Designpartswithself-locatingfeatures  Minimize numberof surfaces  Assemble inthe open  Simplifyandoptimize the manufacturingprocess  Eliminate interfaces  Designforpart inter-changeability  Designtolerancestomeetprocesscapability These keyguidelinesleadtothe abilitytoidentifymanyfeatureswithinatypical massproduced product. (unknownauthor,smaplab) Toshow how DFMA is appliedinanindustrial settingIhave chosento lookat a mass producedproductwhere manyDFMA featurescan be highlighted. MyChosenProduct The product whichI have chosentoanalyse forthisstudyon DFMA is the HP DeskjetF4200 All-In- One seriesprinter. The Desk-topprinterwasfirstdevelopedin2007 and has since beenproducedin Chinafor the Hewlett-PackardDevelopmentCompany. Thisisamass producedproductwithinthe printerandcopierbusinesssector,andissoldworld-wide.
Ink-jetprintersare amulti-billiondollarindustryworldwide,andsince the introductionof the deskjetproductseriesinthe 80’s,the marketand competitionwithinithasgrownsignificantly. In the 90’s HP facedthe followingconflictionswhendesigningthe latestdesk-jetproducts;  Upholdingthe HPreputationforqualityandservice  Meetingthe increasingdemandforprintingproductsandincreasingthe company’smarket share  Achievingthe targetsforprofitandrevenue growth  Andalsosustainingthe ‘HPWay’ of management HP seta targetof producing300,000 printerspermonthfromthe productionline inVancouverwith the aid of an automatedmanufacturingsystem. The operationsreportproducedin2008, as a joint venture withthe Hewlett-Packardcompanyandthe MassachusettsInstitute of Technology,outlined the newsystemdesign forthe productionof the Deskjetproductandhighlightedthe successthe companywere havingwiththisatthat particulartime withinthe company’shistory. (Burman,M., Gershwin,S.B.,and Suyematsu,C,1998) ThisreporthighlightedthatDesignforManufacture andAssemblywasalarge considerationforthis company,as far back as 1998. Throughthe use of systemdesignthe companyappearedtohave re- assessedthe designforproductionneedswithinthe product,andhada large successwiththis. Asa resultIwas interestedinfindingoutif DFMA wasstill consideredindepthbythe companythrough the analysingof the designof one of theirmore recentDeskjetprintermodels. WithDFMA there are nine maindesignareaswhichshouldbe considered;  Designformachining  Designforcasting  Designforforging  Designforsheetmetal andpresswork  Designforwelding  Designforfasteningandotherjoiningmethods  Designforplastics  Designforassemblyandautomation  Faulttree analysis The four areaswhichhave beenhighlightedabove,designforsheetmetal andpresswork,designfor fasteningandotherjoiningmethods,designforplastics,anddesignforassemblyandautomation,
are the fourDFMA designareaswhichI will explore throughoutthe reportasI feltthese were key areas fordesignconsiderationwhichmainlyaffectedthe designoutcome of aDeskjetprinter. DesignforAutomationandAssembly The main aimof DesignforAssemblyistosimplifythe productsothatthe cost of manufacture is reduced. Thisincludesbothpartdesignandthe designof the whole productwithananalytical approach inorderto identifyanyassemblyproblemsearlywithinthe designprocess. (Chan,V.,and Salustri,F.A.,2005) There are a fewrecommendedguidelinesforthissmall areaof DesignforManufacture and Assembly;  Use pyramidassembly,avoidthe needtorepositionthe partiallycompletedassemblyinthe fixture  Designpartsthat have end-to-endsymmetryandrotational symmetryaroundthe axisof insertion  Designpartsthat, inthose instancesinwhichthe partcannot be made symmetric,are obviouslyasymmetric  Provide featuresthatwillavoidjammingof parts  Avoidfeaturesthatwill allowtanglingof parts  Avoidpartsthat are stickyor slippery  Reduce the numberof differentpartstoa minimum  Considerareductioninthe numberof separate parts  Introduce guidesandchamferstohelpwiththe placementof parts  Showconsiderationwithinthe designof difficultyof assemblyindirectionsother thanabove  Create a large base on whichthe assemblycanbe built. Featuresthatmake itsuitable for quickand accurate locationonthe workcarrier These are the mainDesignforAutomationandAssemblyguidelinesasgiveninareportby Wisconsin UniversityconcerningDesignforAssemblyguidelines. These are the featureswhichIwill analyse withinthe HPDeskjetprinter. Usepyramid assembly,avoid theneed to reposition thepartially completed assembly in thefixture – Figure 1 showsa planview of the hinge system whichisuse to attach the scanner/copiertopcover. The areas highlightedwithinthe picture clearly illustrate the ‘open-nature’of the hingesonthe outersurface of the product. Thismeansthat there are no sidesortop to the hinge allowingthe connectionfromthe coverto slotintothe correct place fromdirectlyabove,the maindirectionof insertionwhenusingapyramidal assembly. Within the red triangularsectionwhichIhave highlighted withinthe picture,the screw type usedfor assemblingthisproductcanbe clearlyidentified. AsFigure 1
thisscrewappearson the top surface of the printer,thisalsohelpstosuggestapyramidal assembly as the top of the screwappearsto be in the same plane asthe otherfeaturesidentifiedinthe product. If the screwtop had appearedtohave beenona differentplane tothe hinge systemwhich had beenpreviouslyidentified,thenIwouldnothave suggestedthe use of pyramidal assembly withinthisproduct. Thiswouldbe because of the needforseparate assemblyactionstooccur in manydifferentdirectionsduringthe entire assemblyprocess. However,asthispicture illustrates, separate componentshave beenlocatedintotheircorrectpositionandthensecuredinplace ina stackedassemblystyle,the maincharacteristicof pyramidal assembly. Thisisfurtherevidencedin figure 2 below. The colour coordinatedspotsinfigure 3highlightthe manydifferentcomponentlevelswithinthe printerbase,withgreenbeingthe highestplacedcomponentandreddenotingthe lowestplaced component. Thishelpstoshowthe obviousstructure withwhichthe printerwasassembled. The structure inthe centre of the picture illustratesthe blackplasticcasing,whichisusedforhousingthe inkcartridges,whichislocatedonslide railswhichare attachedtosheetmetal component. The only waythe assemblyforthese particularcomponentscanbe successful istoinsertthe componentsin the correct orderin a sequential fashion,where the nextcomponentisstackedontopof the other. I believethisshowsagoodexample of pyramidalassemblyasitclearlyillustratesthe stackingof the componentsandthe orderof componentinsertionhasalsohadto be consideredindetail. Figure 2 Figure 3 Figure 4 Figure 5
Thisfigure showsa closerviewof howthe componentswithinthe printerare stacked. This illustratesthe pyramidal assemblywhichwashighlightedinfigure 3. Figure 5 showshowthe stackingof componentscontinuestolowerlevelsthanthose whichwere highlightedinthe previousfigure. The arrow headin thisfigure ishighlightingthe rollerbarwhich existsbelow the ink-headassemblywhichwasdiscussedinthe previousfigure. Thisfurther highlightsthe extentof pyramidal assemblywhichisinuse withinthisproduct. Design partsthathaveend-to-end symmetry and rotationalsymmetry around theaxisof insertion – The Deskjetprinterhasmanycomponentswhichneedtobe insertedduringanyassembly procedure. Thistherefore meansthatthe inclusionof componentswithfeaturesthatallow forquick and easyassemblylocationare necessary. One suchfeature whichallowsforquickandeasy assemblylocationisthe use of componentswithcharacteristicsymmetryinmanydirections,to avoidconfusionoverthe orientationof the componentpriortolocatingthe componentwithinthe assembly. The componentinFigure 6, showsa bad example of partsymmetrywithinthis product. The dashedline depictsthe axisof insertionforthisparticularcomponent. Therefore there are manyfeatureswithinthe componentdesignwhichpreventthis componentfrombeingsymmetrical,ina rotational sense,aroundthe axisof insertion. There are manyfeatureshighlightedinthis figure whichall contribute tomakingthis componentnon-symmetrical. The firstof these featuresare the recessesonthe topedge of the component,these are large incomparison to the size of the componentandare all individuallysized. These recessesare alsonotreplicatedon the bottomedge of the component. The inclusionof rollerbearings onone side of thiscomponent alsocreatesa non-symmetrical partaroundthe axisof insertion. The bottomedge of this componentincludesridgeswhichhave been incorporatedintothe designinorderto increase the strengthdue tothe thinwall thickness of the part. The top edge of the componenthasa much largerwall thickness and therefore doesnotneedtheseridgesto provide supportorincrease strength,these featurestherefore alsoaddtothe non- symmetrical nature of the component. Thisis a particularlybadexample of end-to-endand rotational symmetrywithinpartdesign, however,there are alsogoodexamplesof Figure 6 Figure 7
part symmetrywithinthisproduct. The axle and rotatingbearings,infigure 7,are part of a largersub-assemblywithinthe product. The axisof rotationis againshownbythe dashedline whichhasbeenimposedonthe picture. Inthis instance itisclear to see thatthe bearingsandaxle are all cylindrical shapeswithnoaddedfeatures, thismeansthat the componenthasrotational symmetryaroundthe axisof insertion. Thisclearly demonstratesthisspecificguideline fordesigningforautomationandassembly. Inadditionthis componentalsohasend-to-endsymmetry,the blue dashedlinedenotesthe axisof symmetry aroundthe centre of the component. Thisfigure therefore clearlydemonstratesthe advantagesof componentdesignwithend-to-endandrotational symmetry. The benefitsof thistype of componentdesignwhenconsideringassemblyproceduresisnow clear,itiseasyto assume that, withthistype of component,assemblywillbe muchmore efficientdue toreductionof time needed to correctlyorientthe componentduringthe assemblyprocess. Withthistype of componentdesign the orientationisremovedasafactor of concern as the componentwill operate regardlessof its orientation. Design partsthat,in thoseinstancesin which the partcannotbe madesymmetric,areobviously asymmetric– Upon furtheranalysisof the Deskjetprinteritbecame evidentthatthe majorityof componentswithinthe productwere designedwiththisguideline asakeylimitingfactor. Some examplesfromthe productare shownbelow; In the example showninFigure 8,the mainoutline of thiscomponentis symmetrical aboutthe centre-lineaxis, shownhere inred. There are however, some small butsignificantfeatures incorporatedwithinthe designwhich make thiscomponentdeliberately asymmetrictoassistwithassembly operations. Some of the asymmetric featuresinclude the use of rounded cornerswithininsetswhichhave beencut intothe surface of the design,these featuresare highlightedinblue. A second asymmetricfeature incorporatedinthis designisthe use of an additional feature addedontothe face of the topsurface of the component,thisfeature isusedasa catch feature inorderto keepa hinged componentinplace whenthe printerisnot inuse. This feature ishighlightedinthe figure ingreen. These featureshelpto make the componentasymmetricinnature to ensure the componentcanonlybe insertedinthe correctorientationduring Figure 8 Figure 9
assembly. Similarfeatureshave alsobeenidentifiedinasecondcomponentwithinthe product, showninfigure 9. In thisfigure itiseasiertoidentifyanasymmetricfeatureandtovisualise how thishashelpedplace the componentduringassembly. The sheetmetal componenthighlightedinthe picture hasa side panel ononlyone edge of the component. Due to the positioningof othercomponentsrelativeto thispiece of sheetmetal,andthe inclusionof the side panel,ittherefore meansthatthisparticular componentcanonlybe fittedinone orientationduringassembly, thisisonlypossiblethroughthe use of thissimple asymmetricfeature. Providefeaturesthatwill avoid jamming of parts – Forquickand efficientassembly,itisimportant that any part doesnotjam while instorage before beingmovedontothe productionline. Thisis alsoan importantconsiderationatanearly stage of the designprocessforanycomponentof the Deskjetprinter. The figuresincludedabove show anumberof features,incorporatedwithin variouscomponentsof the Deskjetprinter,whichavoidthe jammingof partsbefore andduringthe assemblyprocedure. In Figure 10 the use of ribs has beenhighlighted. Aswithmostproducts,itisobviousthatfeatures such as ribsare primarilythere toaddstrengthandsupportto large,flatpolymersurfaces,however these featuressecondaryrole istopreventcomponentsfromjammingwhile containedinstorage Figure 10 Figure 11 Figure 12 Figure 13
before beingmovedtothe assemblyline. The inclusionof these featurespreventsidentical componentpartsbeingstacked andconsequentlybecomingjammedwhile beingstoredin respective batches. There are manyotherexamplesof manytypesof featuresaimedatavoidingthe jammingof parts duringstorage. In figure 11 you can see twoverydifferentfeatureswhichIbelieve alsohelppreventjamminginone of the variouscomponentswithinthe Deskjetprinter. The componentshownhere isthe coverused for the scanningcomponentof the printer. The twokeyfeatureshere are the use andshape of the hingesandalsothe differinglevelheightswhichhave beendesignedintothe component. The differentheightlevelspreventthe internal stackingof these components,forexample,plasticcups may be able to stack internallydue tothe conal shape of the product. Withthe componentshown here,thiscannothappendue to the lackof indentedsurface featuresandthe differingsurface heights. Alsobyplacingthe hingesonthe outeredge of the product,witha relativelylarge height, preventstwoof these componentsinstorage becomingjammed. The featuresinfigure 12 workin a similarwayto that of the ribs infigure 10. These three- dimensional featuresdirectlypreventthe stackingof componentswithinastorage situation. Finally, figure 13 showsan itemof trim usedforaestheticappeal withinthe Deskjetprinter. The design featuresoutlinedinthispicture are the outeredgeswhichhave suitablyroundedcornersandthe top-surface indentation. Fromexperience,componentstendtobecome jammedwhenflatsurfaces and sharpcorners are usedwithinthe designof the product. Thiscomponentdeliberately differentiatesthe topandbottomsurfacesbyincludingthe surface indent,ashighlighted,toprevent stacking. The roundedcornersalso helptolessenthe probability of componentsbecomingjammed or damagedduringstorage. Figure 14 Figure 15
The figuresabove are againhighlightingmore featureswhichIbelieve couldleadtothe jammingof parts,however,withthese featuresIbelieve the jammingismore likelytooccurduringthe assembly processratherthan duringstorage before beingusedforassembly. Figure 14showsthe mountedcircuitboardwithinthe assembly. Inthisfigure the wirescomingfrom the circuitboard have beenhighlighted. Thiscomponentdesignhasagood elementinthatthe wiresall leave the circuitboardinthe same directionsothat theycan be containedinone cornerof the assembly. Ido believe thatthisdesigncouldalsobe improved. Ibelieveitcouldbe possibleto include atrack withinthe designof the printerbase where the wirescanbe fedthroughduring assembly,thiswouldpreventthe wiresbecomingtangledwithothercomponentswhichare added to the assemblyafterthe circuitboardhas beensecured. Thiswouldhowever,needtobe consideredasthe time takentofeedwiresthroughanenclosedtrackwithinthe base would adverselyaffectthe total time takentoassemble the product. Figure 15 and16 showthe electronictape connectingthe print-headtothe circuitboard,thisis effectivelythe intelligence withinthe product. Infigure 15featureswhichhave beenspecifically designedforthistype of productto ensure the tape issecuredinplace andalsoto preventjamming whenthe printerisinuse and the preventionof tanglingwithothercomponentsduringassembly. I thinkthisissuccessful designasthe operationof the productisnotlimitedinanywaybut considerationhasalsoclearlybeengiventothe manufacturingprocess. Figure 16 howevershows howcloselythe tape issecuredtoothercomponentsconcernedwiththe movementof the print- headand the highpotential tanglingof these componentsdue tocompactand difficult circumstancessurroundingassembly. The electronictape issecuredinplace,howeverthe toothed beltwhichdrivesthe movementof the print-headhastobe insertedmanuallyalongside the tape. The space betweenthese twocomponentsisminimalandthereforethe riskof tangling andthe difficultyof assemblymustbe high. Figure 16
Avoid partsthatare sticky or slippery – Before disassemblingthe printertodiscoverthe designof the componentsbeingusedwithinthisparticularmodel Iassumedthatthisspecificdesignguideline may be hard to achieve withinthisproductdue tothe needformovingpartswhichare primarilyof metallicstructure. Thiswasprovedwhenthe componentswere analysedinmore detail. In figure 17 the arrow headis highlightingthe use of ametallicaxle, believedtobe steel,whichisusedto mountand secure the inkcartridge headwithinthe assembly. The ink cartridge headisthe principle moving componentwithinthe printerandit movesina horizontal motionalong thisaxle. Therefore,thiscomponent withinthe printerwill have toendure the highestlevelof force andfriction duringconstantuse of a sustained periodof time. Due to these requirementsitisimperativethatthe axle islubricatedtoovercome the frictioncausedbythe motionof the print-head. Thislubrication causesthe surface of the axle tobecome veryslipperyandtherefore makesthe assemblyof this componentdifficult. Thisisan unavoidableuse of astickyand slipperysurface becausetothe operational requirementsof the product,however,Ibelieve the axle placedinasub-assembly before beingplacedandfixedwithinthe mainbodyof the printer. Thisisdue to the nature of the othercomponentssurroundingthe axle,the fixturesbeingusedandalsothe experience Ihadwhen tryingto disassemble the componenttoanalyse the design. If thiscomponenthasbeenplacedin the mainassemblyaspart of a smallersub-assemblythenIbelievethisshowsthoughtwithinthe designprocessof howa difficultcomponentcanbe insertedintothe mainassemblywithmore ease. Thisis anotherexample of the use of a slippery/stickycomponentwithinthe printer. Aswiththe previouscomponent, the axle,thiscomponentisanecessitydue to the operational requirementsof the product. The difference betweenthis componentandthe axle isthe way in whichthisproducthas beenplacedinto the mainassemblyof the printer. The axle whichhas beendiscussedabove hasbeen placedwithinasub-assemblybefore being includedinthe mainassemblyprocedure. In thisfigure,itisclearto see that the component isnot part of a sub-assemblyandhassimplybeen placedintothe requiredpositionwithinthe component. Fromthispicture itisclearto see the amountof liquidincludedwithinthe texture of thiscomponent. Ibelieve thiscouldhave causedthe Figure 17 Figure 18
speedof the productionandassemblyof thisproducttoslow however,overcomingthisthrough designmaybe difficult. Ibelievethe onlypossiblesolutiontothisproblemwouldbe tolookintothe use of differentmaterialswhichsatisfythe criteriaof use duringthe product’slife-span. Reducethe numberof differentpartsto a minimum – As the Deskjetprinterisacomplex product, the numberof differentcomponentsinvolvedwill be higherthanmostothermassproduced products. Figure 19 showssome of the screwsusedto assemble the product. It is clearto see fromthe picture that all of the screwsare the same diameterandlength. Theyare alsothe same type of screw,all were removedfromthe product usingthe same,standardsizedAllen-key. Thisisa prime example of designingtominimizethe numberof different parts usedwithinthe assemblyof aproduct. Figure 20 illustratesthe all the componentswhichare partof the HP Deskjetprinterassembly. Aspart of thisassemblyIcountedapproximately 53 differentcomponentswithinthis product. Althoughthisisa complex productinvolvingthe use of many mechanismsandfixtures,itisalsoa small andcompact product soI believe thisisa large numberof different componentsforsucha small product. I believethisnumberof components adds tothe overall weightof the product. When comparingthe physical specificationsof thisproductwithanothersimilarmodel fromarival company,itiseasyto see howdesignandthe numberof differentcomponentswithinthe assemblymaymatter. Physical Specificationfor HP DeskjetF4200 All-in-One Series Height– 161.5mm Width– 437.5mm Depth– 290.4mm Weight– 4.9kg Figure 19 Figure 20
Physical Specificationsfor Epson StylusSX130 Printer,Scanner, Copier(argos, 2012) Height– 150mm Width– 436mm Depth– 365mm Weight– 3.9kg It isclear to see fromthiscomparisonthatthe two productsare verysimilarinsize butthe Epson printeris1kg lighterthanthe HP Deskjetbeinganalysedinthisreport. Ibelieveone of the main factors inthismustbe the numberof differentcomponentsbeingusedwithinthe design. Ibelieve that the numberof differentpartsbeingusedinaproductproportionallyaffectsthe weightof the product. However,toprove thisI wouldalsoneedtoanalyse the EpsonStylusSX130. Considera reduction in the numberof separateparts – It became clearduringthe disassemblyof this productthat sub-assemblieshadbeenused throughoutthe assemblyprocedure forthis product. Whenfirstlookingatthe product the overall impressionitcreatesisone of complexity, large numberof parts and time consuming assemblyprocedures. Thisiswhatisshown infigure 21. However,uponfurtheranalysis it became clearthatthe complex appearance of the productsoonbecame splitintomore manageable sub-assemblies. These are showninfigure 22 and 23. These are twoof the mainsub-assemblieswithinthe mainbase assemblyof the product. Whenthese sub- assemblieswere removedfromthe product there were fewcomponentsleftwithinthe mainbase of the printer. Those componentswhichwere leftwere small,lightcomponentswhichwere directlyfixedtothe plasticbase of the product. Figure 21 Figure 22 Figure 23
Introducechamfersand guidesto help with the placementof parts – Chamfersandguidesare essential forease of assembly,whichhelpstoreduce the time takentoproduce the product. There were manyexampleswithinthisproductof the use of chamfersandguides. In figure 24, the use of guidescanbe clearlyseen. The guideshere are situatedonthe side of the mainpolymerbase forprintertoaid the placementof the manysub-assemblieswhichare inserted duringthe mainassemblyprocedure. Uponinspectionof the sub-assemblieswhenIwasdis- assemblingthe productitwasevidentthatthese guideswere extremelyimportantinthe placingof the sub-assemblies. The guidespin-pointedthe exactpositionof eachsub-assembly,Ialsonoticed that itwas impossibletoplace anysub-assemblyintothe wrongpositiondue tothe designof these guidesandalsodue to the shape and size of the componentswhichwere beingusedthroughoutthe product. In figure 25, the simplicityof the designof the guidesusedforassemblyisshown. The designisa simple t-intersectionwiththe wall of the polymerbase. Althoughsimplisticthisdesignisaneasy and effective wayof placingcomponentswithinaproductand I feel itisusedwidely andsuccessfully withinthisproduct. Relativelylarge forcescanbe presentdue tothe movementof components withinaprinterbutthese guidessuccessfullysecure the componentsinplace withnoproblems occurringduringthe use of the product. Showconsideration within thedesign of difficulty of assembly in directions otherthan above – The figure usedabove alsodemonstratedthiskeydesignguideline,itiseasytosee fromthe ‘t’ designof the guide thatcomponentscan be insertedbyslidingthemintoplace fromdirectlyabovethe product. There were manyotherdesigncasesthroughoutthe productwhichalsoconsideredthis designforassemblyfeature. Figure 26 highlightsone of the bossesusedfor securingcomponents. Thisbossispositionedina vertical directionfromthe horizontalplane. This indicatesthatduringassemblyall componentsmustbe insertedfromabove tocoincide withthisdesignfeature, as thisindicatesthatscrewsare insertedina downward directionfromdirectlyabove the base of the product. Figure 24 Figure 25 Figure 26
Thiswas evidencedwithineverycomponentandsub-assemblywithinthe productandI thinkHP have fulfilledthisdesignguideline withgreatsuccess. There washoweveroninstance wherethe screw had beeninsertedinaverticallyupwarddirectionfromthe bottomsurface onthe under-side of the base. Thisis showninfigure 28 where the base of the product has beenturnedupside down. It isthenclear to see thata specificcomponenthasbeeninsertedinthe opposite directionfrom everyothercomponentwithinthe product. ThiswouldsuggestbaddesignandIthinkthe company needtoreviewthe designof the base of the printeranddecide if a separatelyattachedcomponent on thissurface isnecessary. In figure 27 there isanotherclearexample of designconsiderationforassemblyfromabove. The highlightedhinge componentispartof the frontpapertray whichcan be raisedandloweredduring the operationof the printer. Thishinge feature hasthree sides,one side hasbeenremovedtoallow tolerancingsothe tray can be closedwithoutinterference andcollisionswiththe othercomponent part. Thismeansthat the onlypossible directionof insertionduringthe assemblyprocedure isfrom directlyabove,asimple designsolutionwhichaidsthe assemblyprocess. Createa large baseon which the assembly can be built – This isthe final designguideline fordesign for automationandassembly. Thisparticulardesignguideline,Ifeel,isshowcasedwell withinthis product. Figure 29 showsthe bottomsurface of the polymerbase usedforthe Deskjetprinter. Whenthe base size was comparedtoother similarproducts(see page 11/12) itwas establishedthatthissize of base wasaverage for thistype of product,in termsof assembly it isa good size toavoidtryingto insert componentsintotightlypact,small spaces. Thispicture alsohighlightssome other featureswhichare importantforautomation duringassembly. The featureshighlightedare locatingfeaturesusedtosecure the product Figure 27 Figure 28 Figure 29
to the productionline sothe productdoesnothave to be moved,ordoesnotslipduringthe assemblyprocedure. These featureswill thereforeallow forself-locationwhichisidealforuse withinanautomated assemblyline. (homepages,Wisconsin) Howdo thesedesign guidelines relate to theoverall guidelines on DFMA? I believethe designguidelinesdiscussedinthissectionhelptoachieve thesemainpointsset-outby the DesignforManufacture and Assemblyguidelines; - Minimise partcount – reducingpartcount alsoreducesthe overall costof the product. It standsto reasonthat if the designissimplerandeasiertoassemblythenthe production time decreasesandthe productbecomescheapertoproduce asit isspendinglesstime on the productionline before beingsold. - Facilitate partshandling - Use standardparts and hardware The two pointsabove bothhelpachieve increasedreliabilitywithinthe product. If partsare designedwithhandlinginmind,eithermanual orautomated,thenthe assemblyprocedure becomesmore consistentandtherefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandlessopportunitiesforerrorsarise. - Encourage modularassembly - Use stack assemblies/Don’tfightgravity - Designpartswithself-locatingfeatures - Assemble inthe open By achievingthese DFMA pointsthe productwill alsobecomelessexpensive toproduce, howeveritwill alsoincreasethe qualityof the product. If the productiscomposedof smaller sub-assembliesthentheycanbe assembledwithmore attentiontodetail,if all components were insertedintoone mainassembly,the processwouldbecomerushedandleadtoerrors loweringthe qualityof the output. Italsoencouragesthe designertoconstantlytryto review the designandmake it lighterandmore compact,resultinginahigherqualityoutputforthe user. DesignforPlastics Due to the large quantitiesinwhichthisproductisproducedIbelieve thisproductwasproduced usinginjectionmoulding. Thiswasevidentwhenanalysingthe polymercomponentsused throughoutthe designof the productas some ejectionmarkswere evidentonthe surface of particularcomponents. Thisthereforemeansthatcertaindesignguidelinesforinjectionmoulding and plasticsmustbe consideredwithinthe productanditscomponentsfromanearlystage inthe designprocess. Accordingto a resource fromSan Jose State University the maindesignforplastics guidelinesare;(Youssefi,K.,unknownyear)  Provide adequate draftangle foreasierpartremoval fromthe mould(2˚minimum)  Minimize sectionthickness;coolingtimeisproportionaltothe square of the thickness. Reduce costby reducingcoolingtime. 0.065’’≤t≤0.5’’
 Keepribthickness60%of the part thicknessinordertopreventvoidsandsinks  Avoidsharpcorners,theyproduce highstressandobstructmaterial flow  Provide smoothtransitions,avoidchangesinthicknesswhenpossible  Keepsectionthicknessuniformaroundbosses  Use standardgeneral tolerances;donottolerance  Minimumthicknessrecommended;0.25inor0.65mm, up to 0.125mm for large parts  Roundinteriorandexteriorcornersto0.1 – 0.015 inradius(min.) topreventanedge from chipping  Be careful of interactionswithothermaterialswhichmaycause degradationof the plastic  Use transfersinsteadof embossingsothatparts are interchangeablebetweenproduct ranges  Re-entrantsorundercutsshouldavoided  Large flatsurfacesshouldbe avoidedastheytendtowarp Many of these are evidencedwithinthe designof the printerandare discussedbelow. Provideadequatedraftangleforeasierpart removalfromthemould (2˚ minimum) – This productis composedof manyinjectionmouldedpolymerparts,there wastherefore manyexamplesof the inclusionof draftangleswithinthe designof eachcomponent. The figuresbelowhighlightsome of these. Figure 30 showsone of the polymercomponentsusedforhousingrollerbearingswhichmovesthe paperthroughthe printingoperation. Thisisone of the more complex polymercomponentsused withinthe designof thisproduct, howeveritisstill viabletosee adraft angle withinthiscomponent design. The solidredlineswithinthispicture highlightthe angularnature of eachof the outeredges of the component,the dottedredlineshave beenaddedtorepresentthe angle of these edgesto the normal vertical line. Fromthese redlinesitistherefore easytosee the angularnature of the edgesusedwithinthiscomponentdesign,itisalsocleartosee that the draft angle ismore than the 2˚ minimumrequiredtohelpthe removal of the componentfromthe mouldduringthe manufacturingprocess. Figure 30 Figure 31
Figure 31 alsohighlightsthe use of draftangleswithinthe designof the mainbase designforthe printer. Thisisa side viewof the componentandagainthe solidredlineshighlightthe slope of the outeredges. Thisisanothergooddesignexample of the use of draftangleswithinthisproduct. Againitis easyto see thatthe draftanglesusedhere are greaterthan the minimumrequired. The final example of the use of draftangleswithinthe designof one of the componentsusedwithin thisproducthas beentakenfrom the front panel componentof the printer. This componentisthe maincomponentwhichcan be seenwhenthe printerisinuse,this componentalsohousesthe papertrayand allowsaccessto the print-headtoenable the changingof the inkcartridges. Thisisan example of the use of draftangleswithina componentwithaveryspecificandhigh surface finishspecification. Thisprovesthat regardlesstothe requiredtolerancingand finishingof the component,there isstillaneedfor draft angles. The draftangle onthiscomponentis more complex thanthose lookedatpreviously,thisisdue tothe angularnature of the front surface. Thisis highlightedthroughthe use of the arrow headinfigure 32. Thiseffectivelyaddsanother angulardimensiontothe design. Minimise section thickness;cooling time is proportionalto thesquareof the thickness. Reduce cost by reducing the cooling time. 0.065’’≤t≤0.5’’ – The minimisationof wall thicknesswithinthistype of productmust be a keyconsiderationduringthe designstage. Thisisa keyarea whichcan addto the weightof the product,and alsodetermine if the productcanultimatelywithstandthe forceswhich occur duringgeneral use. Therefore minimisingthe wall thicknesswhilstmaintainingperformance of the productis an importantelementtoconsider. Thispicture showsa complex componentused withinthe assemblyof the Deskjetprinter. From the initial appearance of thisproductitlooksas thoughthe wall thicknessof thiscomponentis consistentlyvaryingacrossthe component. Upon furtherinspectionof thiscomponentthe thoughtaboutwall thicknesswithinthe design becomesclearer. Whenlookingatthisproduct inmore detail itbecomesapparentthatsnapfits have beenusedtojointwoseparate polymer componentstocreate a sub-assemblyforuse in the printer. These are highlightedby the red circlesinthe picture. Whenthese twoseparate componentswere lookedat,itbecame evidentthatthe wall thicknessthroughouteachof these componentswasuniform. Ibelieve the twocomponentswere joinedtogetherinordertoadd strengthto thiscomponentwithinthe printerassemblyandalsotoenable thisparticularcomponent Figure 32 Figure 33
to withstandagreaterforce as this componentishingedandtherefore canbe openedandclosedby the userof the product andhas the potential tobe mis-used. Thisis acase where,whatfirst appearsto be bad designwithinthe productresultsinthe identificationof acleverdesigntechnique usedbythe HP companyinorderto improve the designof theirproduct. The picturesabove showthe complex polymercomponentwhichwasdiscussedabove inmore detail. These picturesshowthe twoseparate componentswithmore clarity,whilstalsoillustrating howthe wall thicknessof these componentsremainsconstantthroughoutthe componentdesign, despite initial appearances. Figure 36 showsthe size of the wall thickness usedthroughoutdesignof everycomponent withinthe product. The wall thicknessis representedbythe redlineswithinthispicture. Thisshowsgood,consistentdesign. Every componentwill consistentlyhave the same coolingtime due tothe use of the same wall thicknessall over,italsoprovidesabetter appearance whenfinished. The wall thickness usedwithinthisproductis3mm.This iswithin the 0.065 – 0.5 inchlimitandalsogivesa correspondingcoolingtimeof 9 minutes. This provedtobe a suitable wall thicknessforthis productas there were nosignsof voidsorsinking,asa resultof the coolingof the material,when the componentswere inspected. Keep rib thickness60% of thepart thicknessin orderto preventvoidsand sinks – Ribsare usedwidely withinthisproducttoprovide addedstrengthandsupporttokeyareas,such as large flatsurfaces and these are showninthe picturesbelow. Figure 34 Figure 35 Figure 36
Thisfigure showssome of the mainribsusedto supportthe structure of the mainpolymerbase used withinthisassembly. The picture showsthe wall thicknessmeasurementof the ribto be 1mm. The previousmeasurementof the wall thicknessof the maincomponentwas3mm. The rib thicknesshas therefore beenlimitedto30%of the part thickness inorder to preventthe formingof voidsandsinks withinthe design. Figure 38 showsanexample of badribdesignwithin the same product. The ribs highlightedhere were measuredtobe 3mm, the same thicknessasthe componentpart. This doesnot follow the design guideline whichstatesthatthe ribthicknessshould be limitedto60% of the part thickness. Withthis rule inmindthe maximumsize of the ribthickness shouldhave been2mm. Althoughthisisanexample of baddesign,isdoesnotseemtohave resultedin the appearance of any voidsor sinkingonthe componentsurfaces. Althoughvoidsandsinkinghasnotoccurred I believe thatthisbaddesign feature shouldbe addressedasitmay have causedflawswithinotherbatchesof the productionof thiscomponent. Avoid sharp corners,they producehigh stressesand obstruct material flow – Everypolymercomponentusedwithinthis productappearedto avoidthe use of sharp corners. As a resultthere were manyexamplesof gooddesignprocedure throughoutthe product. Thisdesignguidelinestatesthatthe radiusof the corner shouldbe equal to3/8 of the part thicknessandmustbe more than 0.06 inchesinmeasurement. The example includedinfigure 39,showsthe use of verylarge rounded cornerswithinthe mainbase of the product. It isclear to see that thisexample obeysthe guidelinesetout and inthe case of thisproductalsoadds to the aestheticappeal of the finishedproduct. Asan approximationthe radiususedwithinthisexample designisaround10mm, thiswas the largestexample of designtoavoidthe use of sharp cornerswithinthe product. Figure 37 Figure 38 Figure 40 Figure 39
Figure 40 showshowthisdesignguideline forplasticscanalsobe appliedtothe ribswhichare includedwithinthe designof the printer. Thisexampleshowshow HPhave incorporatedaradiuson the cornerswhichjoineveryribinthiscomponent,thisishighlightedbythe redarrow headsinthe picture. Due to the size of these radii itwas impossible toaccuratelymeasure the dimensionsused for thisguideline withinthisspecificcomponentandthereforeIam unable tosayif these radii adhere tothe dimensional rule,radius=3/8 part thicknessandgreaterthan0.06 inches. Figure 41 illustratesthe use of radii onthe corner of a structurallysupportiverib. Thisishighlightedbythe red circle withinthe picture. Due tothe positioningof this radii it wasdifficulttoaccuratelymeasure the size of the radii used,howeverwhenproportionallycomparingthe size of thisradii to that of the part thicknessanestimated radii wouldbe around1.5mm or greater. This radii therefore alsofollowsthe guidelinesforthe designfor plasticsinregardsto avoidingsharpcorners. Providesmoothtransitions,avoid changesin thicknesswhen possible – Whenit isnot possible touse constantwall thicknessthroughoutthe designof acomponentthenitisadvisedthata gradual transitionbetweenthe differentthicknessesisachieved. A few exampleswerefoundinthis product. Figure 41 Figure 42 Figure 43 Figure 44 Figure 45
The sequence of photographsabove showshoe the wall thicknesswithinasingularcomponentis mainlyconstantthroughout,however,insome instanceswithinthiscomponentthere isa fluctuationinthe partthickness,these have beenhighlightedinred. The hinge designwithinthiscomponentshowsasuccessfuldesignwhichprovidesasmooth transitionbetweenthe twopartthicknessesinvolved. The use of curveddesignwithinthisfeature allowsthe change in thicknesstobe introducedintothe part gradually,avoidingthe tendencyforasharpchange inpart thicknesstocause the feature tobecome brittle andsnap. There is one pointof weakness withinthisfeature wherethe curve takesasharp change in directionwhichmaycause problemswith the robustnessanddurabilityof thisdesign. This weakpointhasbeenidentifiedwiththe redarrow headinthe photographs. In contrastwiththe hinge designonthiscomponent, there isan illustrationof baddesignwhen concerningtransitionsbetweendifferingpartthicknesses. Thisisshownwiththe large,sloping,step change whichhas beenhighlightedinfigure 45. Whencomparingthese twohighlightedfeatures there isa clear distinctionbetweenhowthe partthicknesschangesoverthe gradientof the feature designwithinthe component. Inthe hinge the change isgradual andin the slopingfeature the change is suddenanddrastic. Thisarea of designforplasticsisone whichIfeel needstobe further developedbythe company. Keep section thicknessesuniform around bosses –There are manybosseswhichare usedwithinthe componentdesignof thisproduct. Due tothe forcesexperiencedduringnormal operating conditionswithinthe product,the mostsecure wayof ensuringthe forcesdonot disturbthe placing of the componentsthroughvibrationistosecure eachcomponentandsub-assemblywithscrews. Thisensuresa large numberof bossesmustbe includedinthe designof thisproduct. Figure 46 showsanexample of the bossdesignwithinthisproduct. Thisdesignshowsgood uniformityregardingwall thicknessaroundthe bossandalsoaroundthe ribswhichhave beenused to supportand strengthenthe material aroundthe boss. There are manyotherexamplesof this bossdesignbeingusedthroughoutmanycomponentswhichmake-upthisprinterassembly. Thisis illustratedinfigures 47,48 and 49. Figure 46
These picturesall helptoillustrate the pointthatregardlessof where the bossisplacedinrelationto the components’surfaces,facesandedges,the sectionthicknessremainsconstant. Frommypoint of viewthishelpsmaintainconsistencyintermsof the force loadingwhichthe material will experience fromthe mechanical fasteningsusedandalsomaintainsaconstantlookacross the product. It also ensuresthatthe same size of fasteningscanbe used,reducingthe numberof differentmechanical fasteningswithinthe producttothe minimumpossible. In contrastto the majorityof the bossesusedfor fasteningwithinthe productIdiscoveredthe boss withinthiscomponentwhichhasbeenhighlighted inred. It isveryclear thatthe wall thickness surroundingthisbossisnon-uniform. Thisboss almostgivesthe impressionthatduringthe manufacturingof the mouldusedforthe injection mouldingprocess,ahole wasdrilledwhichwasnot concentricwithanothercircularcomponent. The arrow headinfigure 50 isshowingthatone side of thisbossclearlyhasa muchgreaterthicknesswhen comparedto the otherside. Thisisthe worst example whichIfoundtodemonstrate the non-uniformthicknesssurroundingaboss. This means that HP have providedagooddesignoutcome ensuringthatmostbosseshave gooduniform thickness,however,thereisroomforimprovement. Ina competitive marketplace there isaneed to pursue perfectionandtherefore the aimistohave all bossesdesignedwith uniformthickness. Casesof bad design,like thatshowninfigure 50add additional costtothe costto produce the product. Figure 47 Figure 48 Figure 49 Figure 50
Usestandard generaltolerances;do nottolerance – Tolerancesallow forsome movementbetween twojoinedcomponents. The presence of these tolerancescanpreventextrastrainbeingplacedon the material aroundthe joinandresultinginthe crackingor snappingof the material,butitalso makesthe assemblyprocesseasier. The table below showsalistof standardgeneral tolerances. (Youssefi,K.,unknownyear) Dimension Tolerance Dimension Tolerance 0 ≤ d ≤ 25 ± 0.5 mm 0 ≤ d ≤ 1.0 ± 0.02 inch 25 ≤ d ≤ 125 ± 0.8 mm 1 ≤ d ≤ 5.0 ± 0.03 inch 125 ≤ d ≤ 300 ± 1.0 mm 5 ≤ d ≤ 12.0 ± 0.04 inch 300 ± 1.5 mm 12.0 ± 0.05 inch Usingthis table there were acouple of identifiedfeatureswithinthe productwhere these general tolerancesmaybe used. Figure 52 showsthe placingof some plasticcomponents withinthe base of the printer. There are some tolerancesbeingusedtohelpplace thesecomponents. The arrow headsare highlightingthe small gapswhich are evidentbetweenthe placedcomponentandthe guide whichisa feature onthe base component. The dimensionof the smallercomponentswhichhave been placedintothe base componentfall intothe 0 – 25mm categoryoutlinedinthe general tolerance table. This meansa tolerance of ±0.5mm shouldbe used. The approximate size of the tolerance gaphighlightedin thispicture isbetween0.5mmand0.75mm. Thiswas a veryrough measurementwhichwastaken so assumptionshave beenmade thatthe tolerance beingusedhere isthe general tolerance of 0.5mm. This picture therefore illustratesthe use of general tolerancingbeingutilizedwithinthe designforplasticcomponentswithinthisproduct. Figure 53 showsa componentof the assemblywhich usesone of the bossfeatureswithinthe productasits securingmechanism. Fromthispicture youcansee that the hole inthe componentisoff-setfromthe topof the boss. Thisultimatelymeanswhenascrewisinsertedduringthe assemblyprocess,the screwwillnotfitandthe component will be unable tobe secured. Thiserrormay be due to tolerancingissueswithinthe design. Toovercome this designflaw,the hole shouldhave agreatertolerance, resultingaslightlylargerdiameterholetoensure the topof the boss isnot obscuredinanyway. Figure 51 Figure 52 Figure 53
Minimumthicknessrecommended;0.025in or 0.65mm, up to 0.125mm for large parts – The thicknessof a componentwill directlyreflectthe strengthandrobustnesswhichthatpart contains, as a resultthere mustbe a minimumthicknesswhichisacceptablewithinanyproduct. The followingphotographsshow the wall thicknessinuse inthe Deskjetprinter. Thispicture showsthe measurementof the wall thicknessof the largestcomponentwithinthe printerassembly,the plasticbase component. Thispicture showsthat the wall thicknesshere is approximatelybetween3– 4mm. Thisis much greaterthan the minimumrecommended thicknessandproportionallylookscorrectforthe size of the componentpart. When analysingthe componentthere were nocrackswithinthe material surface oraround anyof the main cornersor other keyfeaturessuggestingthe presence of goodstrengthwithinthe component, thisisprimarilybecause of gooddesignandthe use of correct componentthickness. Round interior and exteriorcornersto 0.01 – 0.015 in radius(minimum),to preventand edgefrom chipping – Thisparticulardesignguideline isdisplayedwell withinthisproduct. Figure 55 showssome of the structural ribs withinthe product. Thispicture illustratesthe presence of roundedcornersonall surfacesof the ribs. These are keyfeaturesinproviding additional structural supportandstrengthand may be prone to chippinganddamage from othercomponentsduringthe assemblyprocess so itis importanttoround the cornersof these featurestotry and preventthisfrom happening. Thisisa goodexample of thisin actionas a small radii hasbeenplacedonevery edge,cornerandintersectionwithinthis component. Figure 56 showsa componentwhichhashighuser interaction,howeverafteryearsof use duringthe product’slife-spanthe componentstill looks relativelynew. Ibelievethisisdue tothe attentionduringthe designstage torounding cornersin orderto ensure the chippingof edges were minimalized. Asthe picture showsthere are manyinternal cornerswhichall have small radii placedonthem. I am assumingthese are all Figure 54 Figure 55 Figure 56
withinthe limitsof the designguideline asitistoo difficulttogeta measurementfortheiractual dimensional size. Thisfigure showsanexample of cornerradii onan external corner. The radii usedinthissituation appearsto be the same as the radii appliedto internal cornerswithinthisproduct. Aswiththe internal corners,the radii preventsthe chippingof edgesbutit alsoprovidesthe productwitha professionalsurface finish whichwill appeal tothe user. It alsopreventsthe userfrominjurydue to the use of sharpexternal corners. Thisisgood designasone designfeature hasthe abilityto addressmanyimportantissueswhicharise during the researchand testingstagesof the design process. Be careful of interactionswith othermaterialswhich may causedegradation of theplastic – Interactionswithothermaterialsusedwithinthe productcouldcause some degradationthe polymermaterial usedinthe product. Inthe case of thisprinterthe othermaterial whichneedsto be consideredcarefullyduringdesignisthe type of inkusedduringprintingandconsiderationof potential reactionsneedstooccurduringthe material selectionprocess. Figure 57 Figure 58 Figure 59 Figure 60 Figure 61
The photographsabove showthe extentandtype of interactionwhichoccursbetweenthe chosen polymermaterial,ABS Plastic,andthe printinginkwhichisusedwithinthisproduct. The interaction betweenthe twomaterialsiscontainedtoone areaof the mainbase of the product. The photographsshowthatthe extentof the reactionextendstodiscolouringof the ABS andaluminium componentsinthissmall,specificareaof the product. If the wrongplasticmaterial hadbeenchosen for use withinthisproductthenthe reactionbetweenthesematerialsmayhave ledtobubblingand meltingof the plasticmaterial. Thisisnotoccurringwithinthisproducttherefore thisisasuccessful design. Useof transfersinstead of embossing symbolsonto thepolymercomponentsso thatpartsare transferrablebetween productranges –I believe thatsome plasticcomponentswithinthisproduct have usedtransferrable stickersinsteadof embossedsymbolssothatthe informationappearingon some componentsmayeasilybe changed,perhapssothata particularcomponentmaybe used withinanotherproductrange producedbythe company,muchin the way the automotive industryproducesmanyrangesof different cars but has standardisedcomponentswhich are usedwithinmanyof the differentproduct ranges. Thisfigure showsanexample of thisbeingused withinthe product. The tranferusedat the bottomof the componentiscleardue to itsuse of colourwithinthe text,thisisnotachieveable whenebossedtexthasbeenused. Thisalso appearson whatI wouldclassas a standrad componentwithinaprinter, the hingeddoor whichallowsaccesstothe print-headforthe changingof inkcartridge etc. My thoughtswere that thistranferscouldbe removed,adifferenttransfercouldbe placedonthe componentandthenthis componentcouldbe easilyplacedintothe assemblyof adifferentrange of printersproducedbyHP. There are otherexamplesof componentswhere thisisnotthe case and the informationhasbeen emboassedonthe plasticcomponent. Figure 62 Figure 63 Figure 64
The photographsabove showthe use of embossedinformationonplasticcomponentswithinthe printer. I donot necessarilythinkthisisbaddesignasthe componentsonwhichthisinformation appearson are also standardcomponentswhichcanbe interchangeablewithotherproductranges producedbyHP. The maindifference betweenthesecomponentsandthe componentdiscussed previouslyisthe type of informationincludedonthe surface of the component. The name onthe previouscomponentwhichusedatransferwasa particularname associatedwiththisproduct range. The informationcontainedonthe componentsshownaboveismaterial,safetyand informationregardingthe directionsof use. Ifeel embossingthisinformationisagood design decisionasthistype of informationiscommontoeveryproductrange therefore incurringnocostly remanufacture of componentstochange the embossedinformationforspecificproductranges. Re-entrantsorundercutsshould beavoided – Uponinspectionof the plasticcomponentswithinthis productthere were nore-entrantsorundercutsevidencedwithinthe designof anyof the components. Thisisa verygood,economicdesigndecisionfromHPasre-entrantsandundercuts can be a costlyadditional expense duringmanufacturingif these featuresare required. Figure 65 Figure 66 Figure 67
Large flatsurfacesshould beavoided asthey tend to warp – Large flatsurfacestendto warpdue to no strengtheningelementssupportingthe surface duringthe coolingprocess. The imagesbelow identifythe size of flatsurfacesusedwithinthe componentdesignof the printer. The surface highlightedinfigure68is a relatively large flatsurface withlittle supportfromribs whichare placedonthe inside face of the component. Frominspectingthiscomponent there isno clearevidence tosuggestthatany warpingof thissurface has takenplace,however, I still feel thatplacingafew more substantial supportribscouldreduce the probabilityof this occurringduringmultiple cyclesof the production processfor thiscomponent,thiswillavoidthe needforany remanufacture tooccur. Thisfigure showssuitable use of ribsinorderto strengthenandsupportthe bottomsurface of the plasticbase componentusedwithinthisproduct. Thisfigure showsgooddesignwhere supportis giveninmultipledirectionsdue tothe strategic placingof horizontal,vertical andsome diagonal ribs. The primaryrole of these ribsisto prevent the bottomof the base from warping. Thisisthe largestflatsurface usedwithinthe productand havinga true flatsurface is keyto producinga productwhichsitswell on an office desk,whichis the intendedpurpose forthisproduct. Howdo thesedesign guidelines relate to theoverall guidelines on DFMA? I believethe designguidelinesdiscussedinthissectionhelptoachieve thesemainpointsset-outby the Design forManufacture and Assemblyguidelines; - Minimize partcount - Make parts multi-functional - Eliminate interfaces - Designforpart inter-changeability The above pointsall helptoreduce the part count alsoreducesthe overall costof the product. It standsto reasonthat if the designissimplerandeasiertoassemblythenthe productiontime decreasesandthe productbecomescheapertoproduce as itis spendinglesstimeonthe production line before beingsold. - Designtolerancestomeetprocesscapability - Designpartswithself-locatingfeatures Figure 68 Figure 69
- Minimize numberof surfaces The pointsabove helpachieve increasedreliabilitywithinthe product. If parts are designedwith self-locatingfeaturesinmind,thenthe assemblyprocedure becomesmore consistentandtherefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandlessopportunity for errorsarises. By achievingthese DFMA pointsthe qualityof the productwill alsoincrease. If the productis composedof smallersub-assembliesthentheycanbe assembledwithmore attentiontodetail,if all componentswere insertedintoone mainassembly,the processwouldbecome rushedandleadto errorsloweringthe qualityof the output. Italsoencouragesthe designertoconstantly tryto review the designandmake it lighterandmore compact,resultinginahigherqualityoutputforthe user. DesignforFasteningandOther JoiningMethods Designconsiderationsformechanical fasteningandotherjoiningmethodsare widelydiscussedin the publicationentitledManufacturingEngineeringandTechnology, Kalpakjian,S.,andSchmid,S.R., 2009. Some the designguidelinessuggestedinthispublicationwhichwereevidencedwithinthe printerassemblywere;  Wheneverpossible,throughholesratherthanblindholesshouldbe specified  Interruptedinternalsurfaces –suchas internal splinesorradial holesthatgo throughthe thicknessof the part – shouldbe avoided  Designsshouldallow holestobe placedonflatsurfaces  Hole bottomsshouldmatch,if possible,standarddrill-pointangles;flatbottomsorodd shapesshouldbe avoided  Jointsshouldbe placedsothatthere iseasy accessfor a solderingironnozzle  There shouldbe goodfit-upof solderedjoints  Considerationof the type of loadingbeingplacedonthe material shouldbe consideredin the type of mechanical fasteningused  Compatibilityof the fasteningmaterialwiththatof the componentshouldbe considered  It isgenerallylesscostlytouse fewer,butlarger,fastenersthantouse a large numberof smallerones  The fit betweenpartstobe joinedshouldbe asloose aspossibletoreduce costsandto facilitate the assemblyprocess  Fastenersof standardsize shouldbe usedwheneverpossible  Holesshouldnotbe too close toedges or corners,to avoidthe possibilityof tearingthe material whenitissubjectedtoexternal forces Many of these were cleartosee ineverycomponentusedwithinthe designof the Deskjetprinter.
DesignConsiderationsforBoring Wheneverpossible,through holesratherthan blind holes should bespecified – Screwsare the main fixture usedwithinthe assembly. Thisinvolveshavingthe correcthole throughwhichthe screw can be placed. (Kalpakjian,S.,andSchmid,S.R., 2009, pg 642) Figure 70 and71 showthe use of a blindhole withinabossfeature situatedonthe under-side of one of the trimpiecesusedwithinthe designof thisproduct. Itisclear to see thatthisshowsthe use of a blindhole,whichdirectlyignoresthe designguideline given. Althoughthisappearstooppose the guideline,thisparticularhole needstobe a blindhole. The nature of thiscomponentrequiresan uninterruptedsurface finishonthe outersurface of the product. This isusedas a trim piece for providingthe final presentationlookof the finishedproduct,thisiswhatthe customerwill see when theyare consideringbuyingandusingthe product,if the aestheticof the producthadbeenspoilt withthe use of a throughhole,thiswouldmake the finishof the productlookunprofessionaland unattractive tothe customer. Thistherefore showsgooddesignandself-judgementonwhenthe correct time to obeyoroppose a specificguideline is needed. Figure 72 highlightsthe use of athroughhole within the designof thisproduct. This componentisan internal polymercomponentwhichdoesnothave any effectonthe outerappearance of the product. Due to the nature of the placementanduse of this componentitistherefore negligible if the topof end of the screw fixture canbe seenfromany particular surface of the component. AgainIthinkthisshows goodjudgementonthe part of the designas tothe requirementsof the componentandthe expenditure on the designfeature withinthe manufacturingprocess. Figure 70 Figure 71 Figure 72
Figures73, 74 and 75 showvariousotherinstancesof the use of blindandthroughholesthroughout the designof the printer. AgainIthinkeach of these exampleshasshownthatthe designerhashad to seriouslyconsiderthe aestheticsof the finishedproduct,the use requirementsof the component and alsothe placementof the componentwithinthe assembly. Sometimesthisresultsinthe designerdecidingtoignore the designguideline whenappropriate. Interrupted internalsurfaces – such as internalsplines or radialholes thatgo through thethickness of the part– should be avoided – Interruptedinternal surfacescancause difficultyinthe placingof componentsduringassemblyandeffectthe overall positioningof componentsandtherefore needs to be consideredwithin the designstage. Figure 76 showsa heavilyinterruptedinternal surface. Thisribsshownin thispicture are necessaryinprovidingextrastrengthforthe producthowever,itaffectsthe positioningof othercomponents. The presence of thiskindof internal surface interference ultimatelymeansthat the positioningof othercomponentsmustcome Figure 73 Figure 74 Figure 75 Figure 76
aboutas a resultof thisdesign. If thisinterruptedsurface wasnothere,thenitmayultimatelymean that HP couldproduce a more compact, lightweightprinter. The figuresabove showattemptswithinthe designtoavoidthe use of radial holeswhichprotrude throughthe thicknessof the component. The bossesshowninthese photographsare the design solutiontoavoidingthe use of a radial,through-thicknesshole. DesignConsiderationsforDrilling Designsshould allowholes to be placed on flat surfaces – It isimportantthat holes,orinthe case of the printerbosses,are placedonflatsurfacesas thispreventsthe introductionof loadforce atthe base of the bossfeature resultinginashearingof the feature. Italsopreventsabad joinbetween componentswithbadfit-upandbadlyfittingscrewsbeinglesslikelytooccur. (Kalpakjian,S.,and Schmid,S.R., 2009, pg.651) Thispicture of the mountedcircuitboardfromthe printerillustrateshow thisdesignforfastening guideline appliestothe designof the circuitboard as well asthe individual plasticandmetal componentswhichalsomake-upthe printer assembly. Ashighlightedinthispicture,the holes requiredforthe secure fixturingof the component are all placedona flatsurface andare placedso as not to cause concernabout interference withany of the electroniccomponentsincludedonthe circuitboard. Figure 80 illustratesbaddesignconcerningthe placementof a bosson the internal surface of the polymerbase. Itisclearto see fromthe photographthatthisbossis situatedonthe edge of a verylarge radius. Thiscan cause a great force loadingtooccur aroundthe bottomof the base where the bossfeature joinsthe Figure 77 Figure 78 Figure 79 Figure 80
surface of the polymerbase. Thismayincrease the probabilityof shearingoccurringaroundthis point. Hole bottomsshould match,if possible,standard drill-pointangles;flatbottomsorodd shapes should beavoided – The inclusionof standardiseddrill-pointangleswill eliminate the needfor customisingthe bottomof the screwwhichwill ultimatelybe insertedintothe pre-drilledhole. The drill-pointanglesare manufacturedtocorrespondwiththe screw-tipanglesavailable within standardspecificationscrews. Figure 81 and82 illustrate the use of flat-bottomedbosseswhichconsequentlymeanthe use of flat- bottomscrews. These screwsuponcloseranalysis have clearlybeenthroughamanual operationto file awaythe pointedtipof the screwthread,thiswasapparentdue to the markingsandfinish qualitywhichcouldbe seenonthe screw tip. The screw has onlyhadto undergoextraoperations due to the hole designwithinthisboss,if the tipof the screw andthe angle whichthisinvolveshad not beenremovedthenthe screwwouldhave beentoolongtofitcorrectlyinthe bossand would have causeddamage to the exteriorof the polymermaterial. Thisshows baddesignandthe consequenceswhichbaddesignmayhave onthe finishof the productand alsothe productiontime takento assemble the product. DesignConsiderationsforSoldering Jointsshould beplaced so that there is easy access fora soldering iron nozzle – Thisdirectlyrelates to the solderingof componentstoacircuitboard. Thisdesignconsiderationisshownonvarious componentsonthe mountedcircuitboardwithinthe printer. (Kalpakjian,S.,andSchmid,S.R.,2009, Figure 81 Figure 82 Figure 83 Figure 84
pg. 931) Figures83 and 84 showthe placingof manyelectroniccomponentsonthe circuitboard. The spacingbetweenthesecomponentsislarge allowingforthe size of the solderingironnozzle whichis neededtocomplete the solderingprocess. These photographsalsohighlightthe presence of two verydistinctive typesof soldering,one highlightedinredandthe otherinblue. The soldering techniqueshighlightedinblue isanautomatedsolderingtechniqueandsoallowsforthe positioning of componentstobe more denselycompactcomparedtothose whichare solderedusingamanual process. Thisshowsdesignconsiderationforhow the solderingprocesswill be undertakenandhow the use of automatedtechniquescanhelpimprove the outcome. Providea good fit-up of soldered joints – Providingagoodfit-upof the surfacestobe joinedis necessaryinorderto create a strong,stable solderedjointwhichcannotdegrade andbecome detachedthroughexcessive movementwithinthe joint. The photographsabove helptoillustrate whatismeantbythe goodfit-upof a solderedjoint. The photographsshowhoweachelectroniccomponentssitstightlyonthe surface of the circuitboard, thistightinteractionwiththe circuitboardisthe good ‘fit-up’talkedaboutinthisdesignguideline. Thistightfitprovidesamuch strongersolderedjoint. If there wasa space betweenthe surface of the circuitboard and the componentmovementwouldbe apparentwithinthe joint leadingtothe eventual failure due tostresseswithinthatjoint. DesignforMechanical Fastening Consideration of thetypeof loading being placed on the material should beconsidered in the typeof mechanicalfastening used – The loadingwhichisplacedona plasticcomponentthroughany mechanical fasteningcanbe large and can provide one of the maincausesof failure. (Kalpakjian,S.,andSchmid,S.R., 2009, pg. 942) The possible effectsof mechanical fastening loadinghasbeenconsideredwellwithinthis design,youcansee the wall thicknessusedinthe boassdesignandalsothe numberof ribswhich Figure 85 Figure 86 Figure 87
helpsupportandstrengthenthe design. Thiswill help disperse the loadingof the mechanical fastneing throughoutthe designof the bossfeature. The type of screwusedwithinthisdesignhasalsobeen well consideredwithregardstoloadingfroma mechanical fastening. Whendesigningaproductthe temptationistouse a countersinkscrewsothat the screwface finishesflushwiththe surface of the componenttoprovide aneat finish,however,thisshould generallybe avoidedwhenfasteningplastic components. The use of a countersinkscrew requires additional drillingoperations,these operationsreduce the part thicknessaroundthe hole. The large forces exertedtrhoughthe fixturethencause the plastictocrack aroundthe weakenedhole design, leadingtoa failure of the part. Inthisdesignthe screw whichhasbeenusedhasa flattop,thiswill avoidthe failure of the material aroundthe hole designedforthe screw andwill distibute the load fromthe fasteningmore evenly. Thisisa goodexample of designforfasteningwithinthisproduct. Compatibilityof the fastnenermaterialwith thatof the componentmaterial –The designof a componentneedstoconsideranydegradationwhichmayoccur due to the incompatabilityof the componentmaterial andthatof the fastnerwhichisjoiningtwocomponents. Inthe case of the HP Deskjetrpinterthe componentmaterial isABSplasticandthe fastenrrmaterial isanaluminium screw. The example of the degradationcausedbythisfastenerwithinone areaof thisproductis shownbelow. Whendis-assemblingthe printertoanalyse the componentsitwasclearin one case withinthe base componentof the assemblythatthe fastenerhadcausedsome damage tothe componentmaterial. Damage suchasthiswas not apparentinany othercomponent,orinany otherarea inthe base component,howeverthis illustratesthe importance of ensuringthe compatabilityof the twomaterialsbefore using themfor the productassembly. Iwouldn’t suggestthatthisshowsa greatdeal of bad designdue tomaterial selection,Ithinkother designfactorswere alsotoblame forthe damge seeninthispicture. It is generally less costly to use fewer,butlarger,fastenersthan to use a large numberof smaller ones– The mainfastenerusedthroughoutthisassemblyisasmall torsionscrew. The photograph belowillustratesthe numberof fastneingsusedwithinthe wholeassembly. Figure 88 Figure 89
Figure 90 showsthe numberof fastenersusedwithin the assembly. There are at least24 fastenersshown inthisphotograph. Thisis a large numberwhen consideringalarge numberof the sub-assembliesdid not use screws,exceptforsecuringthemtothe base componentwithinthe mainassembly. There was alsotwo differentsizesof screw used,bothwere small insize. The twodifferentsizesof screw are highlightedinthe photograph. Ibelieve the number of fastenersusedwithinthe assemblyof thisproduct couldhave beenreducedwithareview of the design and the size of the screwsused. In otherinstancesthroughoutthe assemblyof thisproductthere were manyexamplesof how snap fitshave alsobeenusedasa methodof fasteningwithinthe product. Anexample of the type of snap fitsisshowninfigure 91. I believe the designof thisproductcouldbe improvedif the designwasto include more snapfitsto reduce the numberof requiredmechanical fasteners. Thiswill resultinareductioninthe net weightof the productand alsomake assembly timesquicker. The fit between partsto be joined should beasloose aspossible to reduce costsand to facilitate the assembly process – Thisdesignguidelineisaimedatreducingthe time takentoassemble the product. I founddue to the nature of the use of the product thatjointswere tightwithlittle orno room formovementbetweenthe twocomponents. Figure 92 showsanassemblywhichincludes bearingsusedforthe paperfeedingmechanism withinthe printer. The areashighlightedwithin thispicture showsthe tighttoleranceswhichexist inthe assemblybetweentwocomponentparts. Duringthe analysisof thiscomponentItriedto testthe ‘play’withinthe assemblytosee how loose ortight the assemblywas. Components withinthisassemblydidnotmove inanydirection, or in anyrotationor orientationincomparisonto the surroundingcomponents. Thiscouldbe classed as bad designaccordingtothisdesignguideline Figure 90 Figure 91 Figure 92
however,withoutthe tighttoleranceswhichare evidentinthissub-assemblythe workingof the productwouldnotbe of the performance requiredbythe customer. Fastenersof standard sizeshould beused wheneverpossible – The diametricsize of the fasteners usedwithinthisproductwere astandardM3 size,howeverthe lengthof screw usedwere not standard. Whenanalysedthe endof the screw thread appearedtohave manuallycutto size due to the markingsand roughappearance of the edgesonthe screw thread. Thisis showninfigures 93 and 94 below. Figure 93 showsthe twolengthsof screw used andthe flatbottomof the screw threadcan alsobe seeninthisphotograph. The endof the screw threadwhichappearsto have beencutto size is showninmore detail infigure 94. Holes should not be too close to edgesor corners,to avoid thepossibility of tearing the material when it is subjected to externalforces – The part thicknesssurroundingholesandbosseshave been examinedpreviouslyinthisreport,howeverthe positionof the hole relative tothe edgesand cornersof the producthave not yetbeenexamined. Figure 95 showsthe positioningof holesalong the outeredge of a sheetmetal component whichhousesaxlesandbearingswhichwas placeddirectlyinthe centre of the assembly. It iseasyto see that the positionof eachof these holeshasbeenconsideredcarefully. The smallestdistance of anyof these holestothe nearestedge isaround4-5mm. Thisis especially importantwithinthiscomponentdue tothe low strengthof the material andthe part thicknessof the sheetmetal whichhasbeenused. Figure 93 Figure 94 Figure 95
Figure 96 againlooksat the placementof holeswithin a componentrelative toedgesandcorners. The designshownhere haspositiveandnegative pointsto it,the hole doesnotappearto be too close toouter edge of the featuredsurface,itdoeshoweverappear to be veryclose to the inneredge where the heightof the surface suddenlytakesastep change to become higherthanthe surface on whichthe hole isplaced. Thisdoesnot presentaproblemwithregardsto forcesexertedonthe hole andthe possible cracking of the material,itmayhoweverprove tobe awkward whentryingtoinserta fasteningorcomponentinto thishole. Howdo thesedesign guidelines relate to theoverall guidelines on DFMA? I believethe designguidelinesdiscussedinthissectionhelptoachieve thesemainpointsset-outby the DesignforManufacture and Assemblyguidelines; - Minimize partcount - Make parts multi-functional - Reduce the numberof screwsand screw types The above pointsall helptoreduce the part count alsoreducesthe overall costof the product. It standsto reasonthat if the designissimplerandeasier toassemblythenthe productiontime decreasesandthe productbecomescheapertoproduce as itis spendinglesstimeonthe production line before beingsold. - Use standardparts and hardware - Encourage modularassembly The two pointsabove bothhelpachieve increasedreliabilitywithinthe product. If partsare designedwithmodularassemblyinmind,thenthe assemblyprocedure becomesmore consistent and therefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandless opportunityforerrorsarises. By achievingthese DFMA pointsthe qualityof the productwill alsoincrease. If the productis composedof smallersub-assembliesthentheycanbe assembledwithmore attentiontodetail,if all componentswere insertedintoone mainassembly,the processwouldbecome rushedandleadto errorsloweringthe qualityof the output. Italsoencouragesthe designertoconstantlytryto review the designandmake it lighterandmore compact,resultinginahigherqualityoutputforthe user. Figure 96
DesignforSheetMetal and Presswork Designforsheetmetal andpressworkisalsodiscussedwithinthe ManufacturingEngineeringand Technology(2009) publication. Some of the maindesignguidelinesoutlinedforsheetmetal and pressworkin thispublicationare; (Kalpakjian,S.,andSchmid,S.R.,2009, pg. 428)  The designof the sheetmetal partshouldreduce scrapto a minimum  To avoidmaterial fracture,wrinkling,orthe inabilitytoforma bend,arelief notchshouldbe incorporatedinto the componentdesignof apart for bending  A crescentor ear shouldbe usedforhole designoccurringnearabend  Scoringor embossingshouldbe usedtoobtainasharp innerradiusinbending  Designforease of blanking  Shearand formoperationsshould have aminimumheight(h) of 2 ½ the blankthickness Many of these designfeatures,goodandbad,are showninthe followingfigures. The design of the sheet metalpart should reducescrap to a minimum – The reductionof scrap during the productionprocessof any sheetmetal part directlyrelatestosavingsinthe costof production for that component. Figures97 and 98 showthe mainsourcesof scrap material fromthe designof thiscomponent. Figure 97 showsthe blankingoperationswhichare requiredwithinthiscomponentdesign. Figure 98 howevershowsthatnotall of the area whichappearstohave beenblankedinfigure 97is reducedtoscrap. Some of the blankedmaterial isusedtoforma surface on whichsome gearscan be placedas showninthe picture. Thisshowssome cleverdesignandprovidesinsightintohow the waste fromblankingoperationscanbe reduced. Figure 97 Figure 98
In contrastto the designshownabove,figure 99showspart of the designof thiscomponentwhich createswaste material duringthe productionprocedure. The endsof the sheetmetal component are shownwithinthisphotograph. Itisclear to see the non- symmetrical nature of the endsof thiscomponent. This meansthat whenproducedona large sheetof aluminiumin a batch product whenmanyof these componentsare cut fromthe same sheet,thenthere isgoingtobe waste material generatedfromcuttingmaterialfromthe perimeterof eachof these components. Having symmetrical endsmayreduce the amountof scrap material beingremovedduringthe productionprocess. To avoid material fracture,wrinkling,orthe inability to forma bend,a relief notch should beincorporated into the componentdesign of a partfor bending – To illustrate whatismeantbythe term‘relief notch’Ihave includedthe diagramshowninfigure 100. (efunda.com) The cut insetcuthighlightedinthe figure above showsarelief notch. Thissimple cutinthe material allowsabendto be formedwithoutthe material nexttothe bendrippingandtearingwhichis unwantedandcausesstressesandstrainswithinthe material. The photographsbelowshow some bendswithinthe sheet metal componentin Figure 99 Figure 100 Figure 102Figure 101
the printer. Figures101, 102 and 103, showinstanceswhere relief notcheshave beenusedthroughthe sheet metal component. Itisclearto see that there are no tears appearingthe material due tothe bend whichhas beenformed. Thisisagood example of relief notchdesign. A crescent orear should be used forhole design occurring near a bend – Introducingahole close to a bendmayresultinthe distortionof the hole duringandafterthe bendingoperation. The will therefore leavethe hole unusable due tothe distortedshapewhichwill be apparentinthe design. Figure 104 illustrateshow considerationhasbeen giventothe positioningof ahole neara bendin the sheetmetal component. The hole hasbeen placedwithsufficientspace fromthe edge and the bendwithinthe feature of the sheetmetal component. Thisissuccessful partdesignwhere failure throughcracking,tearingandsnappingdue to an ill placedhole hasbeeneliminatedfromthis component. Scoring or embossing should beused to obtain a sharp innerradiusin bending – Much inthe waya prototype ismade,byscoringa line incard before a subsequentbendingaction, bendswithinsheet metal componentsare alsoproducedinthisway. Hisgivesa more controlledoutputwithsharp innercornerson the internal face of the component. Figure 103 Figure 104
Figure 105 showsthe use of bothembossing and scoringinthe creation of the bendinthis sheetmetal component. The circle inthe picture highlightsthe embossedsectionwhich runs alongthe bottomface of the component. The arrow headis beingusedtopoint-outthe scoringwhichhas beenusedtomark the positionof the bendbefore the bending operationwasundertaken. Itisjust visibleasa dark line alone the lengthof the interior surface of the bend. Thisshowsa good combinationof techniquesinordertoachieve a successful andhighlyprofessional outcome. Design foreaseof blanking – There are manyblankedfeatureswithinthe designof thiscomponent. These will be highlightedinturnhoweverthere are some keydimensional andgeometricfeatures whichneedtobe definedbeforeanalysingthe designof the featureswithinthe printercomponent. (engr) Figure 105 Figure 106
The diagram above wastakenfroman online resource providedbySanJose State University,this outlinesthe importantdimensional restrictionswhenproducing blankedparts. These featureshave beenidentifiedwithinthe sheetmetal componentfromthe printerandare showninthe figure. The feature outlinedinredinthisfigure correspondstoW inthe previousdiagram. The constraint for thisfeature was the minimumwidththicknessof the cutwhichwas statedas 0.04 inches minimumformaterialswhichare thinnerthan0.047 inches,if possible thisshouldbe wider. The feature inthe componentpartfromthe printermeetsthiscriteriawithease. The widthof this feature liesbetween2-3mmandthe thicknessof the material isbetween1-2mm. The second feature highlightedbythe thickgreenline isthe lengthof the cut withinthisdesignedblanked feature. The lengthof thiscut isapproximately5mm. The maximumdimensionrecommendedwas 5W. W was previouslyestablishedasmeasuringbetween2-3mm, thistherefore meansthatthe designforblankingwithinthispiece fallswell withinthe limitsof the givenguidelines,meaningthe weaknessinthe strengthof the thinmaterial iskepttoa minimumwhere possible. Shearand foroperationsshould havea minimumheight(h) of 2 ½ the blankthickness – This isthe lastfeature to be consideredaspartof the designconsiderationfollowedwhen producingthe sheet metal component. Fromthe previous figure,the blankthicknesswas previouslyestablishedasbeing approximately1mm. The minimum heightforthe shearin thiscomponent shouldtherefore be 2½ mm. Figure 108 showsone of the shearfeatures presentinthiscomponent. Whenthe Figure 107 Figure 108
heightof the shearfeature wasmeasured,the dimensional valuewasfoundtobe approximately 3mm. This feature thenfulfilsthe dimensional restrictionsidentifiedbythe designguideline. This will helpto preventthe possibilityof failure occurringdue toinappropriatedesignwithinaverythin sheetmetal component. Thisagain,isanothersuccessful designfeatureincludedinthe designfor the HP Deskjetprinter. Howdo thesedesign guidelines relate to theoverall guidelines on DFMA? I believethe designguidelinesdiscussedinthissectionhelptoachieve thesemainpointsset-outby the DesignforManufacture and Assemblyguidelines; - Make parts multi-functional Thispointhelpstoreduce the part count alsoreducesthe overall costof the product. Itstands to reasonthat if the designissimplerandeasiertoassemblythenthe productiontime decreasesand the product becomescheapertoproduce asit isspendinglesstime onthe productionlinebefore beingsold. - Use standardparts and hardware - Designpartswithself-locatingfeatures - Minimize numberof surfaces - Simplifyandoptimize the manufacturingprocess - Designtolerancestomeetprocesscapability The pointsabove bothhelpachieve increasedreliabilitywithinthe product. If partsare designed withmodularself-locatingfeaturesinmind,thenthe assemblyprocedure becomesmore consistent and therefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandless opportunityforerrorsarises. By achievingthese DFMA pointsthe qualityof the productwill alsoincrease. If the productis composedof smallersub-assembliesthentheycanbe assembledwithmore attentiontodetail,if all componentswere insertedintoone mainassembly,the processwouldbecome rushedandleadto errorsloweringthe qualityof the output. Italsoencouragesthe designertoconstantlytryto review the designandmake it lighterandmore compact,resultinginahigherqualityoutputforthe user. Conclusion I believethisreporthasshownasuccessful designforamass producedproductfromthe HP company. There have beenmanyexamplesof gooddesignfeatures,suchasdesigningthe circuit board to alloweasyaccessforthe nozzle of the solderingiron. The have alsobeensome examples of baddesignwithinthisproduct,forexample the use of screwswithinthisproductwasnotgood, too manywere usedandtheywere notof a standardsize as theyappearto have beencut to length to fitthe boss designof acomponentpart. As a resultIthinkmy conclusionisthatthe product showcasessome goodDesignforManufacture and Assemblyfeatures,howeverthere isroomforimprovement. The designcouldbe made less expensive toproduce,more reliableandof betterqualityif afew of the bad designexamples highlightedinthisreportwere re-worked.
References Argos,2012, [ONLINE],Available at; http://www.argos.co.uk/static/Product/partNumber/9371424.htm#pdpFullProductInformation accessedNovember3rd 2012 Burman,M., Gershwin,S.B.,and Suyematsu,C,1998, Hewlett-PackardUsesOperationsResearchto Improve the Designof a PrinterProductionLine,[ONLINE],Available at; http://interfaces.journal.informs.org.proxy.lib.strath.ac.uk/content/28/1/24.full.pdf+html accessed November3rd 2012 Chan,V.,and Salustri,F.A.,2005, DesignforAssembly,[ONLINE],Available at; http://deed.ryerson.ca/~fil/t/dfmdfa.html accessedNovember3rd2012 Cook,C and Youssefi,K,unknownyear,Universityof Berkley;DFMA Guidelines,[ONLINE],Available at; https://mail.esdnl.ca/~craig_cook/df2202/dfma/DesignForManufacturingAndAssembly.pdf accessedNovember3rd2012 eFunda,2012, SheetMetal;Forming,[ONLINE] Availableat; http://www.efunda.com/processes/metal_processing/stamping_forming.cfm accessedNovember 3rd 2012 Hamidi,Mand Farahmand,K,2008, NorthDakota State University;DevelopingaDesignfor ManufacturingHandbook,[ONLINE],Availableat; http://www.ijme.us/cd_08/PDF/220%20IT%20302.pdf accessedNovember3rd 2012 Unknownauthor,[ONLINE] Available at; http://dora.eeap.cwru.edu/gcc/dissertation/chap_4.pdf accessedNovember3rd 2012 Unknownauthor,unknownyear,[ONLINE],Availableat; http://smaplab.ri.uah.edu/ipd/2_1.pdf accessedNovember3rd2012 UnknownAuthor,unknown year,Universityof Wisconsin;DetailedDesignforAssemblyGuidelines, [ONLINE],Availableat; http://homepages.cae.wisc.edu/~me349/lecture_notes/detailed_dfa.pdf accessedNovember3rd2012 Youssefi,K.,unknownyear,SanJose State University;DesignforManufacture andAssemblyII: DesignGuidelines,[ONLINE],Availableat; http://www.engr.sjsu.edu/minicurric/images/lecture_powerpoints/DFMA_II_Design_Guidelines.pdf accessedNovember3rd2012 Kalpakjian,S.,andSchmid,S.R.,2009, ManufacturingEngineeringandTechnology,6th Edition,pg 642, 651, 931, 942 and428

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DFMA report

  • 1.
    DFMA Report The Designfor Manufacturing and Assembly Features of a Deskjet Printer Kerrie Noble, 4th Year PDE, 200948192 11/5/2012 I declare that this submission is entirely my own original work. This is the final version of my submission. I declare that, except where fully referenced direct quotations have been included, no aspect of this submission has been copied from any other source. I declare that all other works cited in this submission have been appropriately referenced. I understand that any act of Academic Dishonesty such as plagiarism or collusion may result in the non- award of my degree. Signed …………………….…………………...Date 05/11/2012
  • 2.
    Contents Introduction to Designfor Manufacture and Assembly ...................................................................3 My ChosenProduct ...................................................................................................................... 3 Design for Automation and Assembly ............................................................................................ 5 Design for Plastics....................................................................................................................... 17 Design for Fastening and Other Joining Methods.......................................................................... 31 Design Considerations for Boring............................................................................................. 32 Design Considerations for Drilling............................................................................................ 34 Design Considerations for Soldering......................................................................................... 35 Design for Mechanical Fastening.............................................................................................. 36 Design for Sheet Metal and Presswork......................................................................................... 41 Conclusion ................................................................................................................................. 46 References................................................................................................................................. 47
  • 4.
    Introductionto DesignforManufactureandAssembly In manyinstancesthefailure of acomponentorproduct can be traced back to the designof parts and assembly proceduresbeingused. DesignforManufacture andAssembly,more commonly abbreviatedtoDFMA,isthe processbywhichdesigns,assemblysequencesandproceduresare analysedandalteredinordertoincrease the effectivenessof automatedassembly. (unknown author,dora.eeap) The term‘increasingeffectiveness’,isdefinedasminimisingthe costof productionand/ortime tomarketfor a product,while maintaininganappropriate levelof quality. (Cook,C.,and Youssefi,K,) Thiscanbe expandedfurther,tothe pointwhere DFMA can alsobe definedasthe processof proactivelydesigningproductstooptimizeall the manufacturingfunctions: fabrication,assembly,test,procurement,shipping,delivery,service,andrepairwhile alsoassuring the bestcost, quality,reliability,regulatorycompliance,safety,time-to-market,andcustomer satisfaction. (Hamidi,M.,andFarahmand,K, 2008) To achieve the objectivesof DFMA,whichwere outlinedabove,there are some keyguidelinesto followduringthe design stage of anymassproducedproduct;  Minimize partcount  Make parts multi-functional  Reduce the numberof screwsand screw types  Facilitate partshandling  Use standardparts and hardware  Encourage modularassembly  Use stack assemblies/Don’tfightgravity  Designpartswithself-locatingfeatures  Minimize numberof surfaces  Assemble inthe open  Simplifyandoptimize the manufacturingprocess  Eliminate interfaces  Designforpart inter-changeability  Designtolerancestomeetprocesscapability These keyguidelinesleadtothe abilitytoidentifymanyfeatureswithinatypical massproduced product. (unknownauthor,smaplab) Toshow how DFMA is appliedinanindustrial settingIhave chosento lookat a mass producedproductwhere manyDFMA featurescan be highlighted. MyChosenProduct The product whichI have chosentoanalyse forthisstudyon DFMA is the HP DeskjetF4200 All-In- One seriesprinter. The Desk-topprinterwasfirstdevelopedin2007 and has since beenproducedin Chinafor the Hewlett-PackardDevelopmentCompany. Thisisamass producedproductwithinthe printerandcopierbusinesssector,andissoldworld-wide.
  • 5.
    Ink-jetprintersare amulti-billiondollarindustryworldwide,andsince theintroductionof the deskjetproductseriesinthe 80’s,the marketand competitionwithinithasgrownsignificantly. In the 90’s HP facedthe followingconflictionswhendesigningthe latestdesk-jetproducts;  Upholdingthe HPreputationforqualityandservice  Meetingthe increasingdemandforprintingproductsandincreasingthe company’smarket share  Achievingthe targetsforprofitandrevenue growth  Andalsosustainingthe ‘HPWay’ of management HP seta targetof producing300,000 printerspermonthfromthe productionline inVancouverwith the aid of an automatedmanufacturingsystem. The operationsreportproducedin2008, as a joint venture withthe Hewlett-Packardcompanyandthe MassachusettsInstitute of Technology,outlined the newsystemdesign forthe productionof the Deskjetproductandhighlightedthe successthe companywere havingwiththisatthat particulartime withinthe company’shistory. (Burman,M., Gershwin,S.B.,and Suyematsu,C,1998) ThisreporthighlightedthatDesignforManufacture andAssemblywasalarge considerationforthis company,as far back as 1998. Throughthe use of systemdesignthe companyappearedtohave re- assessedthe designforproductionneedswithinthe product,andhada large successwiththis. Asa resultIwas interestedinfindingoutif DFMA wasstill consideredindepthbythe companythrough the analysingof the designof one of theirmore recentDeskjetprintermodels. WithDFMA there are nine maindesignareaswhichshouldbe considered;  Designformachining  Designforcasting  Designforforging  Designforsheetmetal andpresswork  Designforwelding  Designforfasteningandotherjoiningmethods  Designforplastics  Designforassemblyandautomation  Faulttree analysis The four areaswhichhave beenhighlightedabove,designforsheetmetal andpresswork,designfor fasteningandotherjoiningmethods,designforplastics,anddesignforassemblyandautomation,
  • 6.
    are the fourDFMAdesignareaswhichI will explore throughoutthe reportasI feltthese were key areas fordesignconsiderationwhichmainlyaffectedthe designoutcome of aDeskjetprinter. DesignforAutomationandAssembly The main aimof DesignforAssemblyistosimplifythe productsothatthe cost of manufacture is reduced. Thisincludesbothpartdesignandthe designof the whole productwithananalytical approach inorderto identifyanyassemblyproblemsearlywithinthe designprocess. (Chan,V.,and Salustri,F.A.,2005) There are a fewrecommendedguidelinesforthissmall areaof DesignforManufacture and Assembly;  Use pyramidassembly,avoidthe needtorepositionthe partiallycompletedassemblyinthe fixture  Designpartsthat have end-to-endsymmetryandrotational symmetryaroundthe axisof insertion  Designpartsthat, inthose instancesinwhichthe partcannot be made symmetric,are obviouslyasymmetric  Provide featuresthatwillavoidjammingof parts  Avoidfeaturesthatwill allowtanglingof parts  Avoidpartsthat are stickyor slippery  Reduce the numberof differentpartstoa minimum  Considerareductioninthe numberof separate parts  Introduce guidesandchamferstohelpwiththe placementof parts  Showconsiderationwithinthe designof difficultyof assemblyindirectionsother thanabove  Create a large base on whichthe assemblycanbe built. Featuresthatmake itsuitable for quickand accurate locationonthe workcarrier These are the mainDesignforAutomationandAssemblyguidelinesasgiveninareportby Wisconsin UniversityconcerningDesignforAssemblyguidelines. These are the featureswhichIwill analyse withinthe HPDeskjetprinter. Usepyramid assembly,avoid theneed to reposition thepartially completed assembly in thefixture – Figure 1 showsa planview of the hinge system whichisuse to attach the scanner/copiertopcover. The areas highlightedwithinthe picture clearly illustrate the ‘open-nature’of the hingesonthe outersurface of the product. Thismeansthat there are no sidesortop to the hinge allowingthe connectionfromthe coverto slotintothe correct place fromdirectlyabove,the maindirectionof insertionwhenusingapyramidal assembly. Within the red triangularsectionwhichIhave highlighted withinthe picture,the screw type usedfor assemblingthisproductcanbe clearlyidentified. AsFigure 1
  • 7.
    thisscrewappearson the topsurface of the printer,thisalsohelpstosuggestapyramidal assembly as the top of the screwappearsto be in the same plane asthe otherfeaturesidentifiedinthe product. If the screwtop had appearedtohave beenona differentplane tothe hinge systemwhich had beenpreviouslyidentified,thenIwouldnothave suggestedthe use of pyramidal assembly withinthisproduct. Thiswouldbe because of the needforseparate assemblyactionstooccur in manydifferentdirectionsduringthe entire assemblyprocess. However,asthispicture illustrates, separate componentshave beenlocatedintotheircorrectpositionandthensecuredinplace ina stackedassemblystyle,the maincharacteristicof pyramidal assembly. Thisisfurtherevidencedin figure 2 below. The colour coordinatedspotsinfigure 3highlightthe manydifferentcomponentlevelswithinthe printerbase,withgreenbeingthe highestplacedcomponentandreddenotingthe lowestplaced component. Thishelpstoshowthe obviousstructure withwhichthe printerwasassembled. The structure inthe centre of the picture illustratesthe blackplasticcasing,whichisusedforhousingthe inkcartridges,whichislocatedonslide railswhichare attachedtosheetmetal component. The only waythe assemblyforthese particularcomponentscanbe successful istoinsertthe componentsin the correct orderin a sequential fashion,where the nextcomponentisstackedontopof the other. I believethisshowsagoodexample of pyramidalassemblyasitclearlyillustratesthe stackingof the componentsandthe orderof componentinsertionhasalsohadto be consideredindetail. Figure 2 Figure 3 Figure 4 Figure 5
  • 8.
    Thisfigure showsa closerviewofhowthe componentswithinthe printerare stacked. This illustratesthe pyramidal assemblywhichwashighlightedinfigure 3. Figure 5 showshowthe stackingof componentscontinuestolowerlevelsthanthose whichwere highlightedinthe previousfigure. The arrow headin thisfigure ishighlightingthe rollerbarwhich existsbelow the ink-headassemblywhichwasdiscussedinthe previousfigure. Thisfurther highlightsthe extentof pyramidal assemblywhichisinuse withinthisproduct. Design partsthathaveend-to-end symmetry and rotationalsymmetry around theaxisof insertion – The Deskjetprinterhasmanycomponentswhichneedtobe insertedduringanyassembly procedure. Thistherefore meansthatthe inclusionof componentswithfeaturesthatallow forquick and easyassemblylocationare necessary. One suchfeature whichallowsforquickandeasy assemblylocationisthe use of componentswithcharacteristicsymmetryinmanydirections,to avoidconfusionoverthe orientationof the componentpriortolocatingthe componentwithinthe assembly. The componentinFigure 6, showsa bad example of partsymmetrywithinthis product. The dashedline depictsthe axisof insertionforthisparticularcomponent. Therefore there are manyfeatureswithinthe componentdesignwhichpreventthis componentfrombeingsymmetrical,ina rotational sense,aroundthe axisof insertion. There are manyfeatureshighlightedinthis figure whichall contribute tomakingthis componentnon-symmetrical. The firstof these featuresare the recessesonthe topedge of the component,these are large incomparison to the size of the componentandare all individuallysized. These recessesare alsonotreplicatedon the bottomedge of the component. The inclusionof rollerbearings onone side of thiscomponent alsocreatesa non-symmetrical partaroundthe axisof insertion. The bottomedge of this componentincludesridgeswhichhave been incorporatedintothe designinorderto increase the strengthdue tothe thinwall thickness of the part. The top edge of the componenthasa much largerwall thickness and therefore doesnotneedtheseridgesto provide supportorincrease strength,these featurestherefore alsoaddtothe non- symmetrical nature of the component. Thisis a particularlybadexample of end-to-endand rotational symmetrywithinpartdesign, however,there are alsogoodexamplesof Figure 6 Figure 7
  • 9.
    part symmetrywithinthisproduct. The axleand rotatingbearings,infigure 7,are part of a largersub-assemblywithinthe product. The axisof rotationis againshownbythe dashedline whichhasbeenimposedonthe picture. Inthis instance itisclear to see thatthe bearingsandaxle are all cylindrical shapeswithnoaddedfeatures, thismeansthat the componenthasrotational symmetryaroundthe axisof insertion. Thisclearly demonstratesthisspecificguideline fordesigningforautomationandassembly. Inadditionthis componentalsohasend-to-endsymmetry,the blue dashedlinedenotesthe axisof symmetry aroundthe centre of the component. Thisfigure therefore clearlydemonstratesthe advantagesof componentdesignwithend-to-endandrotational symmetry. The benefitsof thistype of componentdesignwhenconsideringassemblyproceduresisnow clear,itiseasyto assume that, withthistype of component,assemblywillbe muchmore efficientdue toreductionof time needed to correctlyorientthe componentduringthe assemblyprocess. Withthistype of componentdesign the orientationisremovedasafactor of concern as the componentwill operate regardlessof its orientation. Design partsthat,in thoseinstancesin which the partcannotbe madesymmetric,areobviously asymmetric– Upon furtheranalysisof the Deskjetprinteritbecame evidentthatthe majorityof componentswithinthe productwere designedwiththisguideline asakeylimitingfactor. Some examplesfromthe productare shownbelow; In the example showninFigure 8,the mainoutline of thiscomponentis symmetrical aboutthe centre-lineaxis, shownhere inred. There are however, some small butsignificantfeatures incorporatedwithinthe designwhich make thiscomponentdeliberately asymmetrictoassistwithassembly operations. Some of the asymmetric featuresinclude the use of rounded cornerswithininsetswhichhave beencut intothe surface of the design,these featuresare highlightedinblue. A second asymmetricfeature incorporatedinthis designisthe use of an additional feature addedontothe face of the topsurface of the component,thisfeature isusedasa catch feature inorderto keepa hinged componentinplace whenthe printerisnot inuse. This feature ishighlightedinthe figure ingreen. These featureshelpto make the componentasymmetricinnature to ensure the componentcanonlybe insertedinthe correctorientationduring Figure 8 Figure 9
  • 10.
    assembly. Similarfeatureshave alsobeenidentifiedinasecondcomponentwithintheproduct, showninfigure 9. In thisfigure itiseasiertoidentifyanasymmetricfeatureandtovisualise how thishashelpedplace the componentduringassembly. The sheetmetal componenthighlightedinthe picture hasa side panel ononlyone edge of the component. Due to the positioningof othercomponentsrelativeto thispiece of sheetmetal,andthe inclusionof the side panel,ittherefore meansthatthisparticular componentcanonlybe fittedinone orientationduringassembly, thisisonlypossiblethroughthe use of thissimple asymmetricfeature. Providefeaturesthatwill avoid jamming of parts – Forquickand efficientassembly,itisimportant that any part doesnotjam while instorage before beingmovedontothe productionline. Thisis alsoan importantconsiderationatanearly stage of the designprocessforanycomponentof the Deskjetprinter. The figuresincludedabove show anumberof features,incorporatedwithin variouscomponentsof the Deskjetprinter,whichavoidthe jammingof partsbefore andduringthe assemblyprocedure. In Figure 10 the use of ribs has beenhighlighted. Aswithmostproducts,itisobviousthatfeatures such as ribsare primarilythere toaddstrengthandsupportto large,flatpolymersurfaces,however these featuressecondaryrole istopreventcomponentsfromjammingwhile containedinstorage Figure 10 Figure 11 Figure 12 Figure 13
  • 11.
    before beingmovedtothe assemblyline.The inclusionof these featurespreventsidentical componentpartsbeingstacked andconsequentlybecomingjammedwhile beingstoredin respective batches. There are manyotherexamplesof manytypesof featuresaimedatavoidingthe jammingof parts duringstorage. In figure 11 you can see twoverydifferentfeatureswhichIbelieve alsohelppreventjamminginone of the variouscomponentswithinthe Deskjetprinter. The componentshownhere isthe coverused for the scanningcomponentof the printer. The twokeyfeatureshere are the use andshape of the hingesandalsothe differinglevelheightswhichhave beendesignedintothe component. The differentheightlevelspreventthe internal stackingof these components,forexample,plasticcups may be able to stack internallydue tothe conal shape of the product. Withthe componentshown here,thiscannothappendue to the lackof indentedsurface featuresandthe differingsurface heights. Alsobyplacingthe hingesonthe outeredge of the product,witha relativelylarge height, preventstwoof these componentsinstorage becomingjammed. The featuresinfigure 12 workin a similarwayto that of the ribs infigure 10. These three- dimensional featuresdirectlypreventthe stackingof componentswithinastorage situation. Finally, figure 13 showsan itemof trim usedforaestheticappeal withinthe Deskjetprinter. The design featuresoutlinedinthispicture are the outeredgeswhichhave suitablyroundedcornersandthe top-surface indentation. Fromexperience,componentstendtobecome jammedwhenflatsurfaces and sharpcorners are usedwithinthe designof the product. Thiscomponentdeliberately differentiatesthe topandbottomsurfacesbyincludingthe surface indent,ashighlighted,toprevent stacking. The roundedcornersalso helptolessenthe probability of componentsbecomingjammed or damagedduringstorage. Figure 14 Figure 15
  • 12.
    The figuresabove areagainhighlightingmore featureswhichIbelieve couldleadtothe jammingof parts,however,withthese featuresIbelieve the jammingismore likelytooccurduringthe assembly processratherthan duringstorage before beingusedforassembly. Figure 14showsthe mountedcircuitboardwithinthe assembly. Inthisfigure the wirescomingfrom the circuitboard have beenhighlighted. Thiscomponentdesignhasagood elementinthatthe wiresall leave the circuitboardinthe same directionsothat theycan be containedinone cornerof the assembly. Ido believe thatthisdesigncouldalsobe improved. Ibelieveitcouldbe possibleto include atrack withinthe designof the printerbase where the wirescanbe fedthroughduring assembly,thiswouldpreventthe wiresbecomingtangledwithothercomponentswhichare added to the assemblyafterthe circuitboardhas beensecured. Thiswouldhowever,needtobe consideredasthe time takentofeedwiresthroughanenclosedtrackwithinthe base would adverselyaffectthe total time takentoassemble the product. Figure 15 and16 showthe electronictape connectingthe print-headtothe circuitboard,thisis effectivelythe intelligence withinthe product. Infigure 15featureswhichhave beenspecifically designedforthistype of productto ensure the tape issecuredinplace andalsoto preventjamming whenthe printerisinuse and the preventionof tanglingwithothercomponentsduringassembly. I thinkthisissuccessful designasthe operationof the productisnotlimitedinanywaybut considerationhasalsoclearlybeengiventothe manufacturingprocess. Figure 16 howevershows howcloselythe tape issecuredtoothercomponentsconcernedwiththe movementof the print- headand the highpotential tanglingof these componentsdue tocompactand difficult circumstancessurroundingassembly. The electronictape issecuredinplace,howeverthe toothed beltwhichdrivesthe movementof the print-headhastobe insertedmanuallyalongside the tape. The space betweenthese twocomponentsisminimalandthereforethe riskof tangling andthe difficultyof assemblymustbe high. Figure 16
  • 13.
    Avoid partsthatare stickyor slippery – Before disassemblingthe printertodiscoverthe designof the componentsbeingusedwithinthisparticularmodel Iassumedthatthisspecificdesignguideline may be hard to achieve withinthisproductdue tothe needformovingpartswhichare primarilyof metallicstructure. Thiswasprovedwhenthe componentswere analysedinmore detail. In figure 17 the arrow headis highlightingthe use of ametallicaxle, believedtobe steel,whichisusedto mountand secure the inkcartridge headwithinthe assembly. The ink cartridge headisthe principle moving componentwithinthe printerandit movesina horizontal motionalong thisaxle. Therefore,thiscomponent withinthe printerwill have toendure the highestlevelof force andfriction duringconstantuse of a sustained periodof time. Due to these requirementsitisimperativethatthe axle islubricatedtoovercome the frictioncausedbythe motionof the print-head. Thislubrication causesthe surface of the axle tobecome veryslipperyandtherefore makesthe assemblyof this componentdifficult. Thisisan unavoidableuse of astickyand slipperysurface becausetothe operational requirementsof the product,however,Ibelieve the axle placedinasub-assembly before beingplacedandfixedwithinthe mainbodyof the printer. Thisisdue to the nature of the othercomponentssurroundingthe axle,the fixturesbeingusedandalsothe experience Ihadwhen tryingto disassemble the componenttoanalyse the design. If thiscomponenthasbeenplacedin the mainassemblyaspart of a smallersub-assemblythenIbelievethisshowsthoughtwithinthe designprocessof howa difficultcomponentcanbe insertedintothe mainassemblywithmore ease. Thisis anotherexample of the use of a slippery/stickycomponentwithinthe printer. Aswiththe previouscomponent, the axle,thiscomponentisanecessitydue to the operational requirementsof the product. The difference betweenthis componentandthe axle isthe way in whichthisproducthas beenplacedinto the mainassemblyof the printer. The axle whichhas beendiscussedabove hasbeen placedwithinasub-assemblybefore being includedinthe mainassemblyprocedure. In thisfigure,itisclearto see that the component isnot part of a sub-assemblyandhassimplybeen placedintothe requiredpositionwithinthe component. Fromthispicture itisclearto see the amountof liquidincludedwithinthe texture of thiscomponent. Ibelieve thiscouldhave causedthe Figure 17 Figure 18
  • 14.
    speedof the productionandassemblyofthisproducttoslow however,overcomingthisthrough designmaybe difficult. Ibelievethe onlypossiblesolutiontothisproblemwouldbe tolookintothe use of differentmaterialswhichsatisfythe criteriaof use duringthe product’slife-span. Reducethe numberof differentpartsto a minimum – As the Deskjetprinterisacomplex product, the numberof differentcomponentsinvolvedwill be higherthanmostothermassproduced products. Figure 19 showssome of the screwsusedto assemble the product. It is clearto see fromthe picture that all of the screwsare the same diameterandlength. Theyare alsothe same type of screw,all were removedfromthe product usingthe same,standardsizedAllen-key. Thisisa prime example of designingtominimizethe numberof different parts usedwithinthe assemblyof aproduct. Figure 20 illustratesthe all the componentswhichare partof the HP Deskjetprinterassembly. Aspart of thisassemblyIcountedapproximately 53 differentcomponentswithinthis product. Althoughthisisa complex productinvolvingthe use of many mechanismsandfixtures,itisalsoa small andcompact product soI believe thisisa large numberof different componentsforsucha small product. I believethisnumberof components adds tothe overall weightof the product. When comparingthe physical specificationsof thisproductwithanothersimilarmodel fromarival company,itiseasyto see howdesignandthe numberof differentcomponentswithinthe assemblymaymatter. Physical Specificationfor HP DeskjetF4200 All-in-One Series Height– 161.5mm Width– 437.5mm Depth– 290.4mm Weight– 4.9kg Figure 19 Figure 20
  • 15.
    Physical Specificationsfor EpsonStylusSX130 Printer,Scanner, Copier(argos, 2012) Height– 150mm Width– 436mm Depth– 365mm Weight– 3.9kg It isclear to see fromthiscomparisonthatthe two productsare verysimilarinsize butthe Epson printeris1kg lighterthanthe HP Deskjetbeinganalysedinthisreport. Ibelieveone of the main factors inthismustbe the numberof differentcomponentsbeingusedwithinthe design. Ibelieve that the numberof differentpartsbeingusedinaproductproportionallyaffectsthe weightof the product. However,toprove thisI wouldalsoneedtoanalyse the EpsonStylusSX130. Considera reduction in the numberof separateparts – It became clearduringthe disassemblyof this productthat sub-assemblieshadbeenused throughoutthe assemblyprocedure forthis product. Whenfirstlookingatthe product the overall impressionitcreatesisone of complexity, large numberof parts and time consuming assemblyprocedures. Thisiswhatisshown infigure 21. However,uponfurtheranalysis it became clearthatthe complex appearance of the productsoonbecame splitintomore manageable sub-assemblies. These are showninfigure 22 and 23. These are twoof the mainsub-assemblieswithinthe mainbase assemblyof the product. Whenthese sub- assemblieswere removedfromthe product there were fewcomponentsleftwithinthe mainbase of the printer. Those componentswhichwere leftwere small,lightcomponentswhichwere directlyfixedtothe plasticbase of the product. Figure 21 Figure 22 Figure 23
  • 16.
    Introducechamfersand guidesto helpwith the placementof parts – Chamfersandguidesare essential forease of assembly,whichhelpstoreduce the time takentoproduce the product. There were manyexampleswithinthisproductof the use of chamfersandguides. In figure 24, the use of guidescanbe clearlyseen. The guideshere are situatedonthe side of the mainpolymerbase forprintertoaid the placementof the manysub-assemblieswhichare inserted duringthe mainassemblyprocedure. Uponinspectionof the sub-assemblieswhenIwasdis- assemblingthe productitwasevidentthatthese guideswere extremelyimportantinthe placingof the sub-assemblies. The guidespin-pointedthe exactpositionof eachsub-assembly,Ialsonoticed that itwas impossibletoplace anysub-assemblyintothe wrongpositiondue tothe designof these guidesandalsodue to the shape and size of the componentswhichwere beingusedthroughoutthe product. In figure 25, the simplicityof the designof the guidesusedforassemblyisshown. The designisa simple t-intersectionwiththe wall of the polymerbase. Althoughsimplisticthisdesignisaneasy and effective wayof placingcomponentswithinaproductand I feel itisusedwidely andsuccessfully withinthisproduct. Relativelylarge forcescanbe presentdue tothe movementof components withinaprinterbutthese guidessuccessfullysecure the componentsinplace withnoproblems occurringduringthe use of the product. Showconsideration within thedesign of difficulty of assembly in directions otherthan above – The figure usedabove alsodemonstratedthiskeydesignguideline,itiseasytosee fromthe ‘t’ designof the guide thatcomponentscan be insertedbyslidingthemintoplace fromdirectlyabovethe product. There were manyotherdesigncasesthroughoutthe productwhichalsoconsideredthis designforassemblyfeature. Figure 26 highlightsone of the bossesusedfor securingcomponents. Thisbossispositionedina vertical directionfromthe horizontalplane. This indicatesthatduringassemblyall componentsmustbe insertedfromabove tocoincide withthisdesignfeature, as thisindicatesthatscrewsare insertedina downward directionfromdirectlyabove the base of the product. Figure 24 Figure 25 Figure 26
  • 17.
    Thiswas evidencedwithineverycomponentandsub-assemblywithinthe productandIthinkHP have fulfilledthisdesignguideline withgreatsuccess. There washoweveroninstance wherethe screw had beeninsertedinaverticallyupwarddirectionfromthe bottomsurface onthe under-side of the base. Thisis showninfigure 28 where the base of the product has beenturnedupside down. It isthenclear to see thata specificcomponenthasbeeninsertedinthe opposite directionfrom everyothercomponentwithinthe product. ThiswouldsuggestbaddesignandIthinkthe company needtoreviewthe designof the base of the printeranddecide if a separatelyattachedcomponent on thissurface isnecessary. In figure 27 there isanotherclearexample of designconsiderationforassemblyfromabove. The highlightedhinge componentispartof the frontpapertray whichcan be raisedandloweredduring the operationof the printer. Thishinge feature hasthree sides,one side hasbeenremovedtoallow tolerancingsothe tray can be closedwithoutinterference andcollisionswiththe othercomponent part. Thismeansthat the onlypossible directionof insertionduringthe assemblyprocedure isfrom directlyabove,asimple designsolutionwhichaidsthe assemblyprocess. Createa large baseon which the assembly can be built – This isthe final designguideline fordesign for automationandassembly. Thisparticulardesignguideline,Ifeel,isshowcasedwell withinthis product. Figure 29 showsthe bottomsurface of the polymerbase usedforthe Deskjetprinter. Whenthe base size was comparedtoother similarproducts(see page 11/12) itwas establishedthatthissize of base wasaverage for thistype of product,in termsof assembly it isa good size toavoidtryingto insert componentsintotightlypact,small spaces. Thispicture alsohighlightssome other featureswhichare importantforautomation duringassembly. The featureshighlightedare locatingfeaturesusedtosecure the product Figure 27 Figure 28 Figure 29
  • 18.
    to the productionlinesothe productdoesnothave to be moved,ordoesnotslipduringthe assemblyprocedure. These featureswill thereforeallow forself-locationwhichisidealforuse withinanautomated assemblyline. (homepages,Wisconsin) Howdo thesedesign guidelines relate to theoverall guidelines on DFMA? I believethe designguidelinesdiscussedinthissectionhelptoachieve thesemainpointsset-outby the DesignforManufacture and Assemblyguidelines; - Minimise partcount – reducingpartcount alsoreducesthe overall costof the product. It standsto reasonthat if the designissimplerandeasiertoassemblythenthe production time decreasesandthe productbecomescheapertoproduce asit isspendinglesstime on the productionline before beingsold. - Facilitate partshandling - Use standardparts and hardware The two pointsabove bothhelpachieve increasedreliabilitywithinthe product. If partsare designedwithhandlinginmind,eithermanual orautomated,thenthe assemblyprocedure becomesmore consistentandtherefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandlessopportunitiesforerrorsarise. - Encourage modularassembly - Use stack assemblies/Don’tfightgravity - Designpartswithself-locatingfeatures - Assemble inthe open By achievingthese DFMA pointsthe productwill alsobecomelessexpensive toproduce, howeveritwill alsoincreasethe qualityof the product. If the productiscomposedof smaller sub-assembliesthentheycanbe assembledwithmore attentiontodetail,if all components were insertedintoone mainassembly,the processwouldbecomerushedandleadtoerrors loweringthe qualityof the output. Italsoencouragesthe designertoconstantlytryto review the designandmake it lighterandmore compact,resultinginahigherqualityoutputforthe user. DesignforPlastics Due to the large quantitiesinwhichthisproductisproducedIbelieve thisproductwasproduced usinginjectionmoulding. Thiswasevidentwhenanalysingthe polymercomponentsused throughoutthe designof the productas some ejectionmarkswere evidentonthe surface of particularcomponents. Thisthereforemeansthatcertaindesignguidelinesforinjectionmoulding and plasticsmustbe consideredwithinthe productanditscomponentsfromanearlystage inthe designprocess. Accordingto a resource fromSan Jose State University the maindesignforplastics guidelinesare;(Youssefi,K.,unknownyear)  Provide adequate draftangle foreasierpartremoval fromthe mould(2˚minimum)  Minimize sectionthickness;coolingtimeisproportionaltothe square of the thickness. Reduce costby reducingcoolingtime. 0.065’’≤t≤0.5’’
  • 19.
     Keepribthickness60%of thepart thicknessinordertopreventvoidsandsinks  Avoidsharpcorners,theyproduce highstressandobstructmaterial flow  Provide smoothtransitions,avoidchangesinthicknesswhenpossible  Keepsectionthicknessuniformaroundbosses  Use standardgeneral tolerances;donottolerance  Minimumthicknessrecommended;0.25inor0.65mm, up to 0.125mm for large parts  Roundinteriorandexteriorcornersto0.1 – 0.015 inradius(min.) topreventanedge from chipping  Be careful of interactionswithothermaterialswhichmaycause degradationof the plastic  Use transfersinsteadof embossingsothatparts are interchangeablebetweenproduct ranges  Re-entrantsorundercutsshouldavoided  Large flatsurfacesshouldbe avoidedastheytendtowarp Many of these are evidencedwithinthe designof the printerandare discussedbelow. Provideadequatedraftangleforeasierpart removalfromthemould (2˚ minimum) – This productis composedof manyinjectionmouldedpolymerparts,there wastherefore manyexamplesof the inclusionof draftangleswithinthe designof eachcomponent. The figuresbelowhighlightsome of these. Figure 30 showsone of the polymercomponentsusedforhousingrollerbearingswhichmovesthe paperthroughthe printingoperation. Thisisone of the more complex polymercomponentsused withinthe designof thisproduct, howeveritisstill viabletosee adraft angle withinthiscomponent design. The solidredlineswithinthispicture highlightthe angularnature of eachof the outeredges of the component,the dottedredlineshave beenaddedtorepresentthe angle of these edgesto the normal vertical line. Fromthese redlinesitistherefore easytosee the angularnature of the edgesusedwithinthiscomponentdesign,itisalsocleartosee that the draft angle ismore than the 2˚ minimumrequiredtohelpthe removal of the componentfromthe mouldduringthe manufacturingprocess. Figure 30 Figure 31
  • 20.
    Figure 31 alsohighlightstheuse of draftangleswithinthe designof the mainbase designforthe printer. Thisisa side viewof the componentandagainthe solidredlineshighlightthe slope of the outeredges. Thisisanothergooddesignexample of the use of draftangleswithinthisproduct. Againitis easyto see thatthe draftanglesusedhere are greaterthan the minimumrequired. The final example of the use of draftangleswithinthe designof one of the componentsusedwithin thisproducthas beentakenfrom the front panel componentof the printer. This componentisthe maincomponentwhichcan be seenwhenthe printerisinuse,this componentalsohousesthe papertrayand allowsaccessto the print-headtoenable the changingof the inkcartridges. Thisisan example of the use of draftangleswithina componentwithaveryspecificandhigh surface finishspecification. Thisprovesthat regardlesstothe requiredtolerancingand finishingof the component,there isstillaneedfor draft angles. The draftangle onthiscomponentis more complex thanthose lookedatpreviously,thisisdue tothe angularnature of the front surface. Thisis highlightedthroughthe use of the arrow headinfigure 32. Thiseffectivelyaddsanother angulardimensiontothe design. Minimise section thickness;cooling time is proportionalto thesquareof the thickness. Reduce cost by reducing the cooling time. 0.065’’≤t≤0.5’’ – The minimisationof wall thicknesswithinthistype of productmust be a keyconsiderationduringthe designstage. Thisisa keyarea whichcan addto the weightof the product,and alsodetermine if the productcanultimatelywithstandthe forceswhich occur duringgeneral use. Therefore minimisingthe wall thicknesswhilstmaintainingperformance of the productis an importantelementtoconsider. Thispicture showsa complex componentused withinthe assemblyof the Deskjetprinter. From the initial appearance of thisproductitlooksas thoughthe wall thicknessof thiscomponentis consistentlyvaryingacrossthe component. Upon furtherinspectionof thiscomponentthe thoughtaboutwall thicknesswithinthe design becomesclearer. Whenlookingatthisproduct inmore detail itbecomesapparentthatsnapfits have beenusedtojointwoseparate polymer componentstocreate a sub-assemblyforuse in the printer. These are highlightedby the red circlesinthe picture. Whenthese twoseparate componentswere lookedat,itbecame evidentthatthe wall thicknessthroughouteachof these componentswasuniform. Ibelieve the twocomponentswere joinedtogetherinordertoadd strengthto thiscomponentwithinthe printerassemblyandalsotoenable thisparticularcomponent Figure 32 Figure 33
  • 21.
    to withstandagreaterforce asthis componentishingedandtherefore canbe openedandclosedby the userof the product andhas the potential tobe mis-used. Thisis acase where,whatfirst appearsto be bad designwithinthe productresultsinthe identificationof acleverdesigntechnique usedbythe HP companyinorderto improve the designof theirproduct. The picturesabove showthe complex polymercomponentwhichwasdiscussedabove inmore detail. These picturesshowthe twoseparate componentswithmore clarity,whilstalsoillustrating howthe wall thicknessof these componentsremainsconstantthroughoutthe componentdesign, despite initial appearances. Figure 36 showsthe size of the wall thickness usedthroughoutdesignof everycomponent withinthe product. The wall thicknessis representedbythe redlineswithinthispicture. Thisshowsgood,consistentdesign. Every componentwill consistentlyhave the same coolingtime due tothe use of the same wall thicknessall over,italsoprovidesabetter appearance whenfinished. The wall thickness usedwithinthisproductis3mm.This iswithin the 0.065 – 0.5 inchlimitandalsogivesa correspondingcoolingtimeof 9 minutes. This provedtobe a suitable wall thicknessforthis productas there were nosignsof voidsorsinking,asa resultof the coolingof the material,when the componentswere inspected. Keep rib thickness60% of thepart thicknessin orderto preventvoidsand sinks – Ribsare usedwidely withinthisproducttoprovide addedstrengthandsupporttokeyareas,such as large flatsurfaces and these are showninthe picturesbelow. Figure 34 Figure 35 Figure 36
  • 22.
    Thisfigure showssome ofthe mainribsusedto supportthe structure of the mainpolymerbase used withinthisassembly. The picture showsthe wall thicknessmeasurementof the ribto be 1mm. The previousmeasurementof the wall thicknessof the maincomponentwas3mm. The rib thicknesshas therefore beenlimitedto30%of the part thickness inorder to preventthe formingof voidsandsinks withinthe design. Figure 38 showsanexample of badribdesignwithin the same product. The ribs highlightedhere were measuredtobe 3mm, the same thicknessasthe componentpart. This doesnot follow the design guideline whichstatesthatthe ribthicknessshould be limitedto60% of the part thickness. Withthis rule inmindthe maximumsize of the ribthickness shouldhave been2mm. Althoughthisisanexample of baddesign,isdoesnotseemtohave resultedin the appearance of any voidsor sinkingonthe componentsurfaces. Althoughvoidsandsinkinghasnotoccurred I believe thatthisbaddesign feature shouldbe addressedasitmay have causedflawswithinotherbatchesof the productionof thiscomponent. Avoid sharp corners,they producehigh stressesand obstruct material flow – Everypolymercomponentusedwithinthis productappearedto avoidthe use of sharp corners. As a resultthere were manyexamplesof gooddesignprocedure throughoutthe product. Thisdesignguidelinestatesthatthe radiusof the corner shouldbe equal to3/8 of the part thicknessandmustbe more than 0.06 inchesinmeasurement. The example includedinfigure 39,showsthe use of verylarge rounded cornerswithinthe mainbase of the product. It isclear to see that thisexample obeysthe guidelinesetout and inthe case of thisproductalsoadds to the aestheticappeal of the finishedproduct. Asan approximationthe radiususedwithinthisexample designisaround10mm, thiswas the largestexample of designtoavoidthe use of sharp cornerswithinthe product. Figure 37 Figure 38 Figure 40 Figure 39
  • 23.
    Figure 40 showshowthisdesignguidelineforplasticscanalsobe appliedtothe ribswhichare includedwithinthe designof the printer. Thisexampleshowshow HPhave incorporatedaradiuson the cornerswhichjoineveryribinthiscomponent,thisishighlightedbythe redarrow headsinthe picture. Due to the size of these radii itwas impossible toaccuratelymeasure the dimensionsused for thisguideline withinthisspecificcomponentandthereforeIam unable tosayif these radii adhere tothe dimensional rule,radius=3/8 part thicknessandgreaterthan0.06 inches. Figure 41 illustratesthe use of radii onthe corner of a structurallysupportiverib. Thisishighlightedbythe red circle withinthe picture. Due tothe positioningof this radii it wasdifficulttoaccuratelymeasure the size of the radii used,howeverwhenproportionallycomparingthe size of thisradii to that of the part thicknessanestimated radii wouldbe around1.5mm or greater. This radii therefore alsofollowsthe guidelinesforthe designfor plasticsinregardsto avoidingsharpcorners. Providesmoothtransitions,avoid changesin thicknesswhen possible – Whenit isnot possible touse constantwall thicknessthroughoutthe designof acomponentthenitisadvisedthata gradual transitionbetweenthe differentthicknessesisachieved. A few exampleswerefoundinthis product. Figure 41 Figure 42 Figure 43 Figure 44 Figure 45
  • 24.
    The sequence ofphotographsabove showshoe the wall thicknesswithinasingularcomponentis mainlyconstantthroughout,however,insome instanceswithinthiscomponentthere isa fluctuationinthe partthickness,these have beenhighlightedinred. The hinge designwithinthiscomponentshowsasuccessfuldesignwhichprovidesasmooth transitionbetweenthe twopartthicknessesinvolved. The use of curveddesignwithinthisfeature allowsthe change in thicknesstobe introducedintothe part gradually,avoidingthe tendencyforasharpchange inpart thicknesstocause the feature tobecome brittle andsnap. There is one pointof weakness withinthisfeature wherethe curve takesasharp change in directionwhichmaycause problemswith the robustnessanddurabilityof thisdesign. This weakpointhasbeenidentifiedwiththe redarrow headinthe photographs. In contrastwiththe hinge designonthiscomponent, there isan illustrationof baddesignwhen concerningtransitionsbetweendifferingpartthicknesses. Thisisshownwiththe large,sloping,step change whichhas beenhighlightedinfigure 45. Whencomparingthese twohighlightedfeatures there isa clear distinctionbetweenhowthe partthicknesschangesoverthe gradientof the feature designwithinthe component. Inthe hinge the change isgradual andin the slopingfeature the change is suddenanddrastic. Thisarea of designforplasticsisone whichIfeel needstobe further developedbythe company. Keep section thicknessesuniform around bosses –There are manybosseswhichare usedwithinthe componentdesignof thisproduct. Due tothe forcesexperiencedduringnormal operating conditionswithinthe product,the mostsecure wayof ensuringthe forcesdonot disturbthe placing of the componentsthroughvibrationistosecure eachcomponentandsub-assemblywithscrews. Thisensuresa large numberof bossesmustbe includedinthe designof thisproduct. Figure 46 showsanexample of the bossdesignwithinthisproduct. Thisdesignshowsgood uniformityregardingwall thicknessaroundthe bossandalsoaroundthe ribswhichhave beenused to supportand strengthenthe material aroundthe boss. There are manyotherexamplesof this bossdesignbeingusedthroughoutmanycomponentswhichmake-upthisprinterassembly. Thisis illustratedinfigures 47,48 and 49. Figure 46
  • 25.
    These picturesall helptoillustratethe pointthatregardlessof where the bossisplacedinrelationto the components’surfaces,facesandedges,the sectionthicknessremainsconstant. Frommypoint of viewthishelpsmaintainconsistencyintermsof the force loadingwhichthe material will experience fromthe mechanical fasteningsusedandalsomaintainsaconstantlookacross the product. It also ensuresthatthe same size of fasteningscanbe used,reducingthe numberof differentmechanical fasteningswithinthe producttothe minimumpossible. In contrastto the majorityof the bossesusedfor fasteningwithinthe productIdiscoveredthe boss withinthiscomponentwhichhasbeenhighlighted inred. It isveryclear thatthe wall thickness surroundingthisbossisnon-uniform. Thisboss almostgivesthe impressionthatduringthe manufacturingof the mouldusedforthe injection mouldingprocess,ahole wasdrilledwhichwasnot concentricwithanothercircularcomponent. The arrow headinfigure 50 isshowingthatone side of thisbossclearlyhasa muchgreaterthicknesswhen comparedto the otherside. Thisisthe worst example whichIfoundtodemonstrate the non-uniformthicknesssurroundingaboss. This means that HP have providedagooddesignoutcome ensuringthatmostbosseshave gooduniform thickness,however,thereisroomforimprovement. Ina competitive marketplace there isaneed to pursue perfectionandtherefore the aimistohave all bossesdesignedwith uniformthickness. Casesof bad design,like thatshowninfigure 50add additional costtothe costto produce the product. Figure 47 Figure 48 Figure 49 Figure 50
  • 26.
    Usestandard generaltolerances;do nottolerance– Tolerancesallow forsome movementbetween twojoinedcomponents. The presence of these tolerancescanpreventextrastrainbeingplacedon the material aroundthe joinandresultinginthe crackingor snappingof the material,butitalso makesthe assemblyprocesseasier. The table below showsalistof standardgeneral tolerances. (Youssefi,K.,unknownyear) Dimension Tolerance Dimension Tolerance 0 ≤ d ≤ 25 ± 0.5 mm 0 ≤ d ≤ 1.0 ± 0.02 inch 25 ≤ d ≤ 125 ± 0.8 mm 1 ≤ d ≤ 5.0 ± 0.03 inch 125 ≤ d ≤ 300 ± 1.0 mm 5 ≤ d ≤ 12.0 ± 0.04 inch 300 ± 1.5 mm 12.0 ± 0.05 inch Usingthis table there were acouple of identifiedfeatureswithinthe productwhere these general tolerancesmaybe used. Figure 52 showsthe placingof some plasticcomponents withinthe base of the printer. There are some tolerancesbeingusedtohelpplace thesecomponents. The arrow headsare highlightingthe small gapswhich are evidentbetweenthe placedcomponentandthe guide whichisa feature onthe base component. The dimensionof the smallercomponentswhichhave been placedintothe base componentfall intothe 0 – 25mm categoryoutlinedinthe general tolerance table. This meansa tolerance of ±0.5mm shouldbe used. The approximate size of the tolerance gaphighlightedin thispicture isbetween0.5mmand0.75mm. Thiswas a veryrough measurementwhichwastaken so assumptionshave beenmade thatthe tolerance beingusedhere isthe general tolerance of 0.5mm. This picture therefore illustratesthe use of general tolerancingbeingutilizedwithinthe designforplasticcomponentswithinthisproduct. Figure 53 showsa componentof the assemblywhich usesone of the bossfeatureswithinthe productasits securingmechanism. Fromthispicture youcansee that the hole inthe componentisoff-setfromthe topof the boss. Thisultimatelymeanswhenascrewisinsertedduringthe assemblyprocess,the screwwillnotfitandthe component will be unable tobe secured. Thiserrormay be due to tolerancingissueswithinthe design. Toovercome this designflaw,the hole shouldhave agreatertolerance, resultingaslightlylargerdiameterholetoensure the topof the boss isnot obscuredinanyway. Figure 51 Figure 52 Figure 53
  • 27.
    Minimumthicknessrecommended;0.025in or 0.65mm,up to 0.125mm for large parts – The thicknessof a componentwill directlyreflectthe strengthandrobustnesswhichthatpart contains, as a resultthere mustbe a minimumthicknesswhichisacceptablewithinanyproduct. The followingphotographsshow the wall thicknessinuse inthe Deskjetprinter. Thispicture showsthe measurementof the wall thicknessof the largestcomponentwithinthe printerassembly,the plasticbase component. Thispicture showsthat the wall thicknesshere is approximatelybetween3– 4mm. Thisis much greaterthan the minimumrecommended thicknessandproportionallylookscorrectforthe size of the componentpart. When analysingthe componentthere were nocrackswithinthe material surface oraround anyof the main cornersor other keyfeaturessuggestingthe presence of goodstrengthwithinthe component, thisisprimarilybecause of gooddesignandthe use of correct componentthickness. Round interior and exteriorcornersto 0.01 – 0.015 in radius(minimum),to preventand edgefrom chipping – Thisparticulardesignguideline isdisplayedwell withinthisproduct. Figure 55 showssome of the structural ribs withinthe product. Thispicture illustratesthe presence of roundedcornersonall surfacesof the ribs. These are keyfeaturesinproviding additional structural supportandstrengthand may be prone to chippinganddamage from othercomponentsduringthe assemblyprocess so itis importanttoround the cornersof these featurestotry and preventthisfrom happening. Thisisa goodexample of thisin actionas a small radii hasbeenplacedonevery edge,cornerandintersectionwithinthis component. Figure 56 showsa componentwhichhashighuser interaction,howeverafteryearsof use duringthe product’slife-spanthe componentstill looks relativelynew. Ibelievethisisdue tothe attentionduringthe designstage torounding cornersin orderto ensure the chippingof edges were minimalized. Asthe picture showsthere are manyinternal cornerswhichall have small radii placedonthem. I am assumingthese are all Figure 54 Figure 55 Figure 56
  • 28.
    withinthe limitsof thedesignguideline asitistoo difficulttogeta measurementfortheiractual dimensional size. Thisfigure showsanexample of cornerradii onan external corner. The radii usedinthissituation appearsto be the same as the radii appliedto internal cornerswithinthisproduct. Aswiththe internal corners,the radii preventsthe chippingof edgesbutit alsoprovidesthe productwitha professionalsurface finish whichwill appeal tothe user. It alsopreventsthe userfrominjurydue to the use of sharpexternal corners. Thisisgood designasone designfeature hasthe abilityto addressmanyimportantissueswhicharise during the researchand testingstagesof the design process. Be careful of interactionswith othermaterialswhich may causedegradation of theplastic – Interactionswithothermaterialsusedwithinthe productcouldcause some degradationthe polymermaterial usedinthe product. Inthe case of thisprinterthe othermaterial whichneedsto be consideredcarefullyduringdesignisthe type of inkusedduringprintingandconsiderationof potential reactionsneedstooccurduringthe material selectionprocess. Figure 57 Figure 58 Figure 59 Figure 60 Figure 61
  • 29.
    The photographsabove showtheextentandtype of interactionwhichoccursbetweenthe chosen polymermaterial,ABS Plastic,andthe printinginkwhichisusedwithinthisproduct. The interaction betweenthe twomaterialsiscontainedtoone areaof the mainbase of the product. The photographsshowthatthe extentof the reactionextendstodiscolouringof the ABS andaluminium componentsinthissmall,specificareaof the product. If the wrongplasticmaterial hadbeenchosen for use withinthisproductthenthe reactionbetweenthesematerialsmayhave ledtobubblingand meltingof the plasticmaterial. Thisisnotoccurringwithinthisproducttherefore thisisasuccessful design. Useof transfersinstead of embossing symbolsonto thepolymercomponentsso thatpartsare transferrablebetween productranges –I believe thatsome plasticcomponentswithinthisproduct have usedtransferrable stickersinsteadof embossedsymbolssothatthe informationappearingon some componentsmayeasilybe changed,perhapssothata particularcomponentmaybe used withinanotherproductrange producedbythe company,muchin the way the automotive industryproducesmanyrangesof different cars but has standardisedcomponentswhich are usedwithinmanyof the differentproduct ranges. Thisfigure showsanexample of thisbeingused withinthe product. The tranferusedat the bottomof the componentiscleardue to itsuse of colourwithinthe text,thisisnotachieveable whenebossedtexthasbeenused. Thisalso appearson whatI wouldclassas a standrad componentwithinaprinter, the hingeddoor whichallowsaccesstothe print-headforthe changingof inkcartridge etc. My thoughtswere that thistranferscouldbe removed,adifferenttransfercouldbe placedonthe componentandthenthis componentcouldbe easilyplacedintothe assemblyof adifferentrange of printersproducedbyHP. There are otherexamplesof componentswhere thisisnotthe case and the informationhasbeen emboassedonthe plasticcomponent. Figure 62 Figure 63 Figure 64
  • 30.
    The photographsabove showtheuse of embossedinformationonplasticcomponentswithinthe printer. I donot necessarilythinkthisisbaddesignasthe componentsonwhichthisinformation appearson are also standardcomponentswhichcanbe interchangeablewithotherproductranges producedbyHP. The maindifference betweenthesecomponentsandthe componentdiscussed previouslyisthe type of informationincludedonthe surface of the component. The name onthe previouscomponentwhichusedatransferwasa particularname associatedwiththisproduct range. The informationcontainedonthe componentsshownaboveismaterial,safetyand informationregardingthe directionsof use. Ifeel embossingthisinformationisagood design decisionasthistype of informationiscommontoeveryproductrange therefore incurringnocostly remanufacture of componentstochange the embossedinformationforspecificproductranges. Re-entrantsorundercutsshould beavoided – Uponinspectionof the plasticcomponentswithinthis productthere were nore-entrantsorundercutsevidencedwithinthe designof anyof the components. Thisisa verygood,economicdesigndecisionfromHPasre-entrantsandundercuts can be a costlyadditional expense duringmanufacturingif these featuresare required. Figure 65 Figure 66 Figure 67
  • 31.
    Large flatsurfacesshould beavoidedasthey tend to warp – Large flatsurfacestendto warpdue to no strengtheningelementssupportingthe surface duringthe coolingprocess. The imagesbelow identifythe size of flatsurfacesusedwithinthe componentdesignof the printer. The surface highlightedinfigure68is a relatively large flatsurface withlittle supportfromribs whichare placedonthe inside face of the component. Frominspectingthiscomponent there isno clearevidence tosuggestthatany warpingof thissurface has takenplace,however, I still feel thatplacingafew more substantial supportribscouldreduce the probabilityof this occurringduringmultiple cyclesof the production processfor thiscomponent,thiswillavoidthe needforany remanufacture tooccur. Thisfigure showssuitable use of ribsinorderto strengthenandsupportthe bottomsurface of the plasticbase componentusedwithinthisproduct. Thisfigure showsgooddesignwhere supportis giveninmultipledirectionsdue tothe strategic placingof horizontal,vertical andsome diagonal ribs. The primaryrole of these ribsisto prevent the bottomof the base from warping. Thisisthe largestflatsurface usedwithinthe productand havinga true flatsurface is keyto producinga productwhichsitswell on an office desk,whichis the intendedpurpose forthisproduct. Howdo thesedesign guidelines relate to theoverall guidelines on DFMA? I believethe designguidelinesdiscussedinthissectionhelptoachieve thesemainpointsset-outby the Design forManufacture and Assemblyguidelines; - Minimize partcount - Make parts multi-functional - Eliminate interfaces - Designforpart inter-changeability The above pointsall helptoreduce the part count alsoreducesthe overall costof the product. It standsto reasonthat if the designissimplerandeasiertoassemblythenthe productiontime decreasesandthe productbecomescheapertoproduce as itis spendinglesstimeonthe production line before beingsold. - Designtolerancestomeetprocesscapability - Designpartswithself-locatingfeatures Figure 68 Figure 69
  • 32.
    - Minimize numberofsurfaces The pointsabove helpachieve increasedreliabilitywithinthe product. If parts are designedwith self-locatingfeaturesinmind,thenthe assemblyprocedure becomesmore consistentandtherefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandlessopportunity for errorsarises. By achievingthese DFMA pointsthe qualityof the productwill alsoincrease. If the productis composedof smallersub-assembliesthentheycanbe assembledwithmore attentiontodetail,if all componentswere insertedintoone mainassembly,the processwouldbecome rushedandleadto errorsloweringthe qualityof the output. Italsoencouragesthe designertoconstantly tryto review the designandmake it lighterandmore compact,resultinginahigherqualityoutputforthe user. DesignforFasteningandOther JoiningMethods Designconsiderationsformechanical fasteningandotherjoiningmethodsare widelydiscussedin the publicationentitledManufacturingEngineeringandTechnology, Kalpakjian,S.,andSchmid,S.R., 2009. Some the designguidelinessuggestedinthispublicationwhichwereevidencedwithinthe printerassemblywere;  Wheneverpossible,throughholesratherthanblindholesshouldbe specified  Interruptedinternalsurfaces –suchas internal splinesorradial holesthatgo throughthe thicknessof the part – shouldbe avoided  Designsshouldallow holestobe placedonflatsurfaces  Hole bottomsshouldmatch,if possible,standarddrill-pointangles;flatbottomsorodd shapesshouldbe avoided  Jointsshouldbe placedsothatthere iseasy accessfor a solderingironnozzle  There shouldbe goodfit-upof solderedjoints  Considerationof the type of loadingbeingplacedonthe material shouldbe consideredin the type of mechanical fasteningused  Compatibilityof the fasteningmaterialwiththatof the componentshouldbe considered  It isgenerallylesscostlytouse fewer,butlarger,fastenersthantouse a large numberof smallerones  The fit betweenpartstobe joinedshouldbe asloose aspossibletoreduce costsandto facilitate the assemblyprocess  Fastenersof standardsize shouldbe usedwheneverpossible  Holesshouldnotbe too close toedges or corners,to avoidthe possibilityof tearingthe material whenitissubjectedtoexternal forces Many of these were cleartosee ineverycomponentusedwithinthe designof the Deskjetprinter.
  • 33.
    DesignConsiderationsforBoring Wheneverpossible,through holesratherthan blindholes should bespecified – Screwsare the main fixture usedwithinthe assembly. Thisinvolveshavingthe correcthole throughwhichthe screw can be placed. (Kalpakjian,S.,andSchmid,S.R., 2009, pg 642) Figure 70 and71 showthe use of a blindhole withinabossfeature situatedonthe under-side of one of the trimpiecesusedwithinthe designof thisproduct. Itisclear to see thatthisshowsthe use of a blindhole,whichdirectlyignoresthe designguideline given. Althoughthisappearstooppose the guideline,thisparticularhole needstobe a blindhole. The nature of thiscomponentrequiresan uninterruptedsurface finishonthe outersurface of the product. This isusedas a trim piece for providingthe final presentationlookof the finishedproduct,thisiswhatthe customerwill see when theyare consideringbuyingandusingthe product,if the aestheticof the producthadbeenspoilt withthe use of a throughhole,thiswouldmake the finishof the productlookunprofessionaland unattractive tothe customer. Thistherefore showsgooddesignandself-judgementonwhenthe correct time to obeyoroppose a specificguideline is needed. Figure 72 highlightsthe use of athroughhole within the designof thisproduct. This componentisan internal polymercomponentwhichdoesnothave any effectonthe outerappearance of the product. Due to the nature of the placementanduse of this componentitistherefore negligible if the topof end of the screw fixture canbe seenfromany particular surface of the component. AgainIthinkthisshows goodjudgementonthe part of the designas tothe requirementsof the componentandthe expenditure on the designfeature withinthe manufacturingprocess. Figure 70 Figure 71 Figure 72
  • 34.
    Figures73, 74 and75 showvariousotherinstancesof the use of blindandthroughholesthroughout the designof the printer. AgainIthinkeach of these exampleshasshownthatthe designerhashad to seriouslyconsiderthe aestheticsof the finishedproduct,the use requirementsof the component and alsothe placementof the componentwithinthe assembly. Sometimesthisresultsinthe designerdecidingtoignore the designguideline whenappropriate. Interrupted internalsurfaces – such as internalsplines or radialholes thatgo through thethickness of the part– should be avoided – Interruptedinternal surfacescancause difficultyinthe placingof componentsduringassemblyandeffectthe overall positioningof componentsandtherefore needs to be consideredwithin the designstage. Figure 76 showsa heavilyinterruptedinternal surface. Thisribsshownin thispicture are necessaryinprovidingextrastrengthforthe producthowever,itaffectsthe positioningof othercomponents. The presence of thiskindof internal surface interference ultimatelymeansthat the positioningof othercomponentsmustcome Figure 73 Figure 74 Figure 75 Figure 76
  • 35.
    aboutas a resultofthisdesign. If thisinterruptedsurface wasnothere,thenitmayultimatelymean that HP couldproduce a more compact, lightweightprinter. The figuresabove showattemptswithinthe designtoavoidthe use of radial holeswhichprotrude throughthe thicknessof the component. The bossesshowninthese photographsare the design solutiontoavoidingthe use of a radial,through-thicknesshole. DesignConsiderationsforDrilling Designsshould allowholes to be placed on flat surfaces – It isimportantthat holes,orinthe case of the printerbosses,are placedonflatsurfacesas thispreventsthe introductionof loadforce atthe base of the bossfeature resultinginashearingof the feature. Italsopreventsabad joinbetween componentswithbadfit-upandbadlyfittingscrewsbeinglesslikelytooccur. (Kalpakjian,S.,and Schmid,S.R., 2009, pg.651) Thispicture of the mountedcircuitboardfromthe printerillustrateshow thisdesignforfastening guideline appliestothe designof the circuitboard as well asthe individual plasticandmetal componentswhichalsomake-upthe printer assembly. Ashighlightedinthispicture,the holes requiredforthe secure fixturingof the component are all placedona flatsurface andare placedso as not to cause concernabout interference withany of the electroniccomponentsincludedonthe circuitboard. Figure 80 illustratesbaddesignconcerningthe placementof a bosson the internal surface of the polymerbase. Itisclearto see fromthe photographthatthisbossis situatedonthe edge of a verylarge radius. Thiscan cause a great force loadingtooccur aroundthe bottomof the base where the bossfeature joinsthe Figure 77 Figure 78 Figure 79 Figure 80
  • 36.
    surface of thepolymerbase. Thismayincrease the probabilityof shearingoccurringaroundthis point. Hole bottomsshould match,if possible,standard drill-pointangles;flatbottomsorodd shapes should beavoided – The inclusionof standardiseddrill-pointangleswill eliminate the needfor customisingthe bottomof the screwwhichwill ultimatelybe insertedintothe pre-drilledhole. The drill-pointanglesare manufacturedtocorrespondwiththe screw-tipanglesavailable within standardspecificationscrews. Figure 81 and82 illustrate the use of flat-bottomedbosseswhichconsequentlymeanthe use of flat- bottomscrews. These screwsuponcloseranalysis have clearlybeenthroughamanual operationto file awaythe pointedtipof the screwthread,thiswasapparentdue to the markingsandfinish qualitywhichcouldbe seenonthe screw tip. The screw has onlyhadto undergoextraoperations due to the hole designwithinthisboss,if the tipof the screw andthe angle whichthisinvolveshad not beenremovedthenthe screwwouldhave beentoolongtofitcorrectlyinthe bossand would have causeddamage to the exteriorof the polymermaterial. Thisshows baddesignandthe consequenceswhichbaddesignmayhave onthe finishof the productand alsothe productiontime takento assemble the product. DesignConsiderationsforSoldering Jointsshould beplaced so that there is easy access fora soldering iron nozzle – Thisdirectlyrelates to the solderingof componentstoacircuitboard. Thisdesignconsiderationisshownonvarious componentsonthe mountedcircuitboardwithinthe printer. (Kalpakjian,S.,andSchmid,S.R.,2009, Figure 81 Figure 82 Figure 83 Figure 84
  • 37.
    pg. 931) Figures83 and84 showthe placingof manyelectroniccomponentsonthe circuitboard. The spacingbetweenthesecomponentsislarge allowingforthe size of the solderingironnozzle whichis neededtocomplete the solderingprocess. These photographsalsohighlightthe presence of two verydistinctive typesof soldering,one highlightedinredandthe otherinblue. The soldering techniqueshighlightedinblue isanautomatedsolderingtechniqueandsoallowsforthe positioning of componentstobe more denselycompactcomparedtothose whichare solderedusingamanual process. Thisshowsdesignconsiderationforhow the solderingprocesswill be undertakenandhow the use of automatedtechniquescanhelpimprove the outcome. Providea good fit-up of soldered joints – Providingagoodfit-upof the surfacestobe joinedis necessaryinorderto create a strong,stable solderedjointwhichcannotdegrade andbecome detachedthroughexcessive movementwithinthe joint. The photographsabove helptoillustrate whatismeantbythe goodfit-upof a solderedjoint. The photographsshowhoweachelectroniccomponentssitstightlyonthe surface of the circuitboard, thistightinteractionwiththe circuitboardisthe good ‘fit-up’talkedaboutinthisdesignguideline. Thistightfitprovidesamuch strongersolderedjoint. If there wasa space betweenthe surface of the circuitboard and the componentmovementwouldbe apparentwithinthe joint leadingtothe eventual failure due tostresseswithinthatjoint. DesignforMechanical Fastening Consideration of thetypeof loading being placed on the material should beconsidered in the typeof mechanicalfastening used – The loadingwhichisplacedona plasticcomponentthroughany mechanical fasteningcanbe large and can provide one of the maincausesof failure. (Kalpakjian,S.,andSchmid,S.R., 2009, pg. 942) The possible effectsof mechanical fastening loadinghasbeenconsideredwellwithinthis design,youcansee the wall thicknessusedinthe boassdesignandalsothe numberof ribswhich Figure 85 Figure 86 Figure 87
  • 38.
    helpsupportandstrengthenthe design. Thiswillhelp disperse the loadingof the mechanical fastneing throughoutthe designof the bossfeature. The type of screwusedwithinthisdesignhasalsobeen well consideredwithregardstoloadingfroma mechanical fastening. Whendesigningaproductthe temptationistouse a countersinkscrewsothat the screwface finishesflushwiththe surface of the componenttoprovide aneat finish,however,thisshould generallybe avoidedwhenfasteningplastic components. The use of a countersinkscrew requires additional drillingoperations,these operationsreduce the part thicknessaroundthe hole. The large forces exertedtrhoughthe fixturethencause the plastictocrack aroundthe weakenedhole design, leadingtoa failure of the part. Inthisdesignthe screw whichhasbeenusedhasa flattop,thiswill avoidthe failure of the material aroundthe hole designedforthe screw andwill distibute the load fromthe fasteningmore evenly. Thisisa goodexample of designforfasteningwithinthisproduct. Compatibilityof the fastnenermaterialwith thatof the componentmaterial –The designof a componentneedstoconsideranydegradationwhichmayoccur due to the incompatabilityof the componentmaterial andthatof the fastnerwhichisjoiningtwocomponents. Inthe case of the HP Deskjetrpinterthe componentmaterial isABSplasticandthe fastenrrmaterial isanaluminium screw. The example of the degradationcausedbythisfastenerwithinone areaof thisproductis shownbelow. Whendis-assemblingthe printertoanalyse the componentsitwasclearin one case withinthe base componentof the assemblythatthe fastenerhadcausedsome damage tothe componentmaterial. Damage suchasthiswas not apparentinany othercomponent,orinany otherarea inthe base component,howeverthis illustratesthe importance of ensuringthe compatabilityof the twomaterialsbefore using themfor the productassembly. Iwouldn’t suggestthatthisshowsa greatdeal of bad designdue tomaterial selection,Ithinkother designfactorswere alsotoblame forthe damge seeninthispicture. It is generally less costly to use fewer,butlarger,fastenersthan to use a large numberof smaller ones– The mainfastenerusedthroughoutthisassemblyisasmall torsionscrew. The photograph belowillustratesthe numberof fastneingsusedwithinthe wholeassembly. Figure 88 Figure 89
  • 39.
    Figure 90 showsthenumberof fastenersusedwithin the assembly. There are at least24 fastenersshown inthisphotograph. Thisis a large numberwhen consideringalarge numberof the sub-assembliesdid not use screws,exceptforsecuringthemtothe base componentwithinthe mainassembly. There was alsotwo differentsizesof screw used,bothwere small insize. The twodifferentsizesof screw are highlightedinthe photograph. Ibelieve the number of fastenersusedwithinthe assemblyof thisproduct couldhave beenreducedwithareview of the design and the size of the screwsused. In otherinstancesthroughoutthe assemblyof thisproductthere were manyexamplesof how snap fitshave alsobeenusedasa methodof fasteningwithinthe product. Anexample of the type of snap fitsisshowninfigure 91. I believe the designof thisproductcouldbe improvedif the designwasto include more snapfitsto reduce the numberof requiredmechanical fasteners. Thiswill resultinareductioninthe net weightof the productand alsomake assembly timesquicker. The fit between partsto be joined should beasloose aspossible to reduce costsand to facilitate the assembly process – Thisdesignguidelineisaimedatreducingthe time takentoassemble the product. I founddue to the nature of the use of the product thatjointswere tightwithlittle orno room formovementbetweenthe twocomponents. Figure 92 showsanassemblywhichincludes bearingsusedforthe paperfeedingmechanism withinthe printer. The areashighlightedwithin thispicture showsthe tighttoleranceswhichexist inthe assemblybetweentwocomponentparts. Duringthe analysisof thiscomponentItriedto testthe ‘play’withinthe assemblytosee how loose ortight the assemblywas. Components withinthisassemblydidnotmove inanydirection, or in anyrotationor orientationincomparisonto the surroundingcomponents. Thiscouldbe classed as bad designaccordingtothisdesignguideline Figure 90 Figure 91 Figure 92
  • 40.
    however,withoutthe tighttoleranceswhichare evidentinthissub-assemblytheworkingof the productwouldnotbe of the performance requiredbythe customer. Fastenersof standard sizeshould beused wheneverpossible – The diametricsize of the fasteners usedwithinthisproductwere astandardM3 size,howeverthe lengthof screw usedwere not standard. Whenanalysedthe endof the screw thread appearedtohave manuallycutto size due to the markingsand roughappearance of the edgesonthe screw thread. Thisis showninfigures 93 and 94 below. Figure 93 showsthe twolengthsof screw used andthe flatbottomof the screw threadcan alsobe seeninthisphotograph. The endof the screw threadwhichappearsto have beencutto size is showninmore detail infigure 94. Holes should not be too close to edgesor corners,to avoid thepossibility of tearing the material when it is subjected to externalforces – The part thicknesssurroundingholesandbosseshave been examinedpreviouslyinthisreport,howeverthe positionof the hole relative tothe edgesand cornersof the producthave not yetbeenexamined. Figure 95 showsthe positioningof holesalong the outeredge of a sheetmetal component whichhousesaxlesandbearingswhichwas placeddirectlyinthe centre of the assembly. It iseasyto see that the positionof eachof these holeshasbeenconsideredcarefully. The smallestdistance of anyof these holestothe nearestedge isaround4-5mm. Thisis especially importantwithinthiscomponentdue tothe low strengthof the material andthe part thicknessof the sheetmetal whichhasbeenused. Figure 93 Figure 94 Figure 95
  • 41.
    Figure 96 againlooksatthe placementof holeswithin a componentrelative toedgesandcorners. The designshownhere haspositiveandnegative pointsto it,the hole doesnotappearto be too close toouter edge of the featuredsurface,itdoeshoweverappear to be veryclose to the inneredge where the heightof the surface suddenlytakesastep change to become higherthanthe surface on whichthe hole isplaced. Thisdoesnot presentaproblemwithregardsto forcesexertedonthe hole andthe possible cracking of the material,itmayhoweverprove tobe awkward whentryingtoinserta fasteningorcomponentinto thishole. Howdo thesedesign guidelines relate to theoverall guidelines on DFMA? I believethe designguidelinesdiscussedinthissectionhelptoachieve thesemainpointsset-outby the DesignforManufacture and Assemblyguidelines; - Minimize partcount - Make parts multi-functional - Reduce the numberof screwsand screw types The above pointsall helptoreduce the part count alsoreducesthe overall costof the product. It standsto reasonthat if the designissimplerandeasier toassemblythenthe productiontime decreasesandthe productbecomescheapertoproduce as itis spendinglesstimeonthe production line before beingsold. - Use standardparts and hardware - Encourage modularassembly The two pointsabove bothhelpachieve increasedreliabilitywithinthe product. If partsare designedwithmodularassemblyinmind,thenthe assemblyprocedure becomesmore consistent and therefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandless opportunityforerrorsarises. By achievingthese DFMA pointsthe qualityof the productwill alsoincrease. If the productis composedof smallersub-assembliesthentheycanbe assembledwithmore attentiontodetail,if all componentswere insertedintoone mainassembly,the processwouldbecome rushedandleadto errorsloweringthe qualityof the output. Italsoencouragesthe designertoconstantlytryto review the designandmake it lighterandmore compact,resultinginahigherqualityoutputforthe user. Figure 96
  • 42.
    DesignforSheetMetal and Presswork Designforsheetmetalandpressworkisalsodiscussedwithinthe ManufacturingEngineeringand Technology(2009) publication. Some of the maindesignguidelinesoutlinedforsheetmetal and pressworkin thispublicationare; (Kalpakjian,S.,andSchmid,S.R.,2009, pg. 428)  The designof the sheetmetal partshouldreduce scrapto a minimum  To avoidmaterial fracture,wrinkling,orthe inabilitytoforma bend,arelief notchshouldbe incorporatedinto the componentdesignof apart for bending  A crescentor ear shouldbe usedforhole designoccurringnearabend  Scoringor embossingshouldbe usedtoobtainasharp innerradiusinbending  Designforease of blanking  Shearand formoperationsshould have aminimumheight(h) of 2 ½ the blankthickness Many of these designfeatures,goodandbad,are showninthe followingfigures. The design of the sheet metalpart should reducescrap to a minimum – The reductionof scrap during the productionprocessof any sheetmetal part directlyrelatestosavingsinthe costof production for that component. Figures97 and 98 showthe mainsourcesof scrap material fromthe designof thiscomponent. Figure 97 showsthe blankingoperationswhichare requiredwithinthiscomponentdesign. Figure 98 howevershowsthatnotall of the area whichappearstohave beenblankedinfigure 97is reducedtoscrap. Some of the blankedmaterial isusedtoforma surface on whichsome gearscan be placedas showninthe picture. Thisshowssome cleverdesignandprovidesinsightintohow the waste fromblankingoperationscanbe reduced. Figure 97 Figure 98
  • 43.
    In contrastto thedesignshownabove,figure 99showspart of the designof thiscomponentwhich createswaste material duringthe productionprocedure. The endsof the sheetmetal component are shownwithinthisphotograph. Itisclear to see the non- symmetrical nature of the endsof thiscomponent. This meansthat whenproducedona large sheetof aluminiumin a batch product whenmanyof these componentsare cut fromthe same sheet,thenthere isgoingtobe waste material generatedfromcuttingmaterialfromthe perimeterof eachof these components. Having symmetrical endsmayreduce the amountof scrap material beingremovedduringthe productionprocess. To avoid material fracture,wrinkling,orthe inability to forma bend,a relief notch should beincorporated into the componentdesign of a partfor bending – To illustrate whatismeantbythe term‘relief notch’Ihave includedthe diagramshowninfigure 100. (efunda.com) The cut insetcuthighlightedinthe figure above showsarelief notch. Thissimple cutinthe material allowsabendto be formedwithoutthe material nexttothe bendrippingandtearingwhichis unwantedandcausesstressesandstrainswithinthe material. The photographsbelowshow some bendswithinthe sheet metal componentin Figure 99 Figure 100 Figure 102Figure 101
  • 44.
    the printer. Figures101, 102and 103, showinstanceswhere relief notcheshave beenusedthroughthe sheet metal component. Itisclearto see that there are no tears appearingthe material due tothe bend whichhas beenformed. Thisisagood example of relief notchdesign. A crescent orear should be used forhole design occurring near a bend – Introducingahole close to a bendmayresultinthe distortionof the hole duringandafterthe bendingoperation. The will therefore leavethe hole unusable due tothe distortedshapewhichwill be apparentinthe design. Figure 104 illustrateshow considerationhasbeen giventothe positioningof ahole neara bendin the sheetmetal component. The hole hasbeen placedwithsufficientspace fromthe edge and the bendwithinthe feature of the sheetmetal component. Thisissuccessful partdesignwhere failure throughcracking,tearingandsnappingdue to an ill placedhole hasbeeneliminatedfromthis component. Scoring or embossing should beused to obtain a sharp innerradiusin bending – Much inthe waya prototype ismade,byscoringa line incard before a subsequentbendingaction, bendswithinsheet metal componentsare alsoproducedinthisway. Hisgivesa more controlledoutputwithsharp innercornerson the internal face of the component. Figure 103 Figure 104
  • 45.
    Figure 105 showstheuse of bothembossing and scoringinthe creation of the bendinthis sheetmetal component. The circle inthe picture highlightsthe embossedsectionwhich runs alongthe bottomface of the component. The arrow headis beingusedtopoint-outthe scoringwhichhas beenusedtomark the positionof the bendbefore the bending operationwasundertaken. Itisjust visibleasa dark line alone the lengthof the interior surface of the bend. Thisshowsa good combinationof techniquesinordertoachieve a successful andhighlyprofessional outcome. Design foreaseof blanking – There are manyblankedfeatureswithinthe designof thiscomponent. These will be highlightedinturnhoweverthere are some keydimensional andgeometricfeatures whichneedtobe definedbeforeanalysingthe designof the featureswithinthe printercomponent. (engr) Figure 105 Figure 106
  • 46.
    The diagram abovewastakenfroman online resource providedbySanJose State University,this outlinesthe importantdimensional restrictionswhenproducing blankedparts. These featureshave beenidentifiedwithinthe sheetmetal componentfromthe printerandare showninthe figure. The feature outlinedinredinthisfigure correspondstoW inthe previousdiagram. The constraint for thisfeature was the minimumwidththicknessof the cutwhichwas statedas 0.04 inches minimumformaterialswhichare thinnerthan0.047 inches,if possible thisshouldbe wider. The feature inthe componentpartfromthe printermeetsthiscriteriawithease. The widthof this feature liesbetween2-3mmandthe thicknessof the material isbetween1-2mm. The second feature highlightedbythe thickgreenline isthe lengthof the cut withinthisdesignedblanked feature. The lengthof thiscut isapproximately5mm. The maximumdimensionrecommendedwas 5W. W was previouslyestablishedasmeasuringbetween2-3mm, thistherefore meansthatthe designforblankingwithinthispiece fallswell withinthe limitsof the givenguidelines,meaningthe weaknessinthe strengthof the thinmaterial iskepttoa minimumwhere possible. Shearand foroperationsshould havea minimumheight(h) of 2 ½ the blankthickness – This isthe lastfeature to be consideredaspartof the designconsiderationfollowedwhen producingthe sheet metal component. Fromthe previous figure,the blankthicknesswas previouslyestablishedasbeing approximately1mm. The minimum heightforthe shearin thiscomponent shouldtherefore be 2½ mm. Figure 108 showsone of the shearfeatures presentinthiscomponent. Whenthe Figure 107 Figure 108
  • 47.
    heightof the shearfeaturewasmeasured,the dimensional valuewasfoundtobe approximately 3mm. This feature thenfulfilsthe dimensional restrictionsidentifiedbythe designguideline. This will helpto preventthe possibilityof failure occurringdue toinappropriatedesignwithinaverythin sheetmetal component. Thisagain,isanothersuccessful designfeatureincludedinthe designfor the HP Deskjetprinter. Howdo thesedesign guidelines relate to theoverall guidelines on DFMA? I believethe designguidelinesdiscussedinthissectionhelptoachieve thesemainpointsset-outby the DesignforManufacture and Assemblyguidelines; - Make parts multi-functional Thispointhelpstoreduce the part count alsoreducesthe overall costof the product. Itstands to reasonthat if the designissimplerandeasiertoassemblythenthe productiontime decreasesand the product becomescheapertoproduce asit isspendinglesstime onthe productionlinebefore beingsold. - Use standardparts and hardware - Designpartswithself-locatingfeatures - Minimize numberof surfaces - Simplifyandoptimize the manufacturingprocess - Designtolerancestomeetprocesscapability The pointsabove bothhelpachieve increasedreliabilitywithinthe product. If partsare designed withmodularself-locatingfeaturesinmind,thenthe assemblyprocedure becomesmore consistent and therefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandless opportunityforerrorsarises. By achievingthese DFMA pointsthe qualityof the productwill alsoincrease. If the productis composedof smallersub-assembliesthentheycanbe assembledwithmore attentiontodetail,if all componentswere insertedintoone mainassembly,the processwouldbecome rushedandleadto errorsloweringthe qualityof the output. Italsoencouragesthe designertoconstantlytryto review the designandmake it lighterandmore compact,resultinginahigherqualityoutputforthe user. Conclusion I believethisreporthasshownasuccessful designforamass producedproductfromthe HP company. There have beenmanyexamplesof gooddesignfeatures,suchasdesigningthe circuit board to alloweasyaccessforthe nozzle of the solderingiron. The have alsobeensome examples of baddesignwithinthisproduct,forexample the use of screwswithinthisproductwasnotgood, too manywere usedandtheywere notof a standardsize as theyappearto have beencut to length to fitthe boss designof acomponentpart. As a resultIthinkmy conclusionisthatthe product showcasessome goodDesignforManufacture and Assemblyfeatures,howeverthere isroomforimprovement. The designcouldbe made less expensive toproduce,more reliableandof betterqualityif afew of the bad designexamples highlightedinthisreportwere re-worked.
  • 48.
    References Argos,2012, [ONLINE],Available at; http://www.argos.co.uk/static/Product/partNumber/9371424.htm#pdpFullProductInformation accessedNovember3rd 2012 Burman,M.,Gershwin,S.B.,and Suyematsu,C,1998, Hewlett-PackardUsesOperationsResearchto Improve the Designof a PrinterProductionLine,[ONLINE],Available at; http://interfaces.journal.informs.org.proxy.lib.strath.ac.uk/content/28/1/24.full.pdf+html accessed November3rd 2012 Chan,V.,and Salustri,F.A.,2005, DesignforAssembly,[ONLINE],Available at; http://deed.ryerson.ca/~fil/t/dfmdfa.html accessedNovember3rd2012 Cook,C and Youssefi,K,unknownyear,Universityof Berkley;DFMA Guidelines,[ONLINE],Available at; https://mail.esdnl.ca/~craig_cook/df2202/dfma/DesignForManufacturingAndAssembly.pdf accessedNovember3rd2012 eFunda,2012, SheetMetal;Forming,[ONLINE] Availableat; http://www.efunda.com/processes/metal_processing/stamping_forming.cfm accessedNovember 3rd 2012 Hamidi,Mand Farahmand,K,2008, NorthDakota State University;DevelopingaDesignfor ManufacturingHandbook,[ONLINE],Availableat; http://www.ijme.us/cd_08/PDF/220%20IT%20302.pdf accessedNovember3rd 2012 Unknownauthor,[ONLINE] Available at; http://dora.eeap.cwru.edu/gcc/dissertation/chap_4.pdf accessedNovember3rd 2012 Unknownauthor,unknownyear,[ONLINE],Availableat; http://smaplab.ri.uah.edu/ipd/2_1.pdf accessedNovember3rd2012 UnknownAuthor,unknown year,Universityof Wisconsin;DetailedDesignforAssemblyGuidelines, [ONLINE],Availableat; http://homepages.cae.wisc.edu/~me349/lecture_notes/detailed_dfa.pdf accessedNovember3rd2012 Youssefi,K.,unknownyear,SanJose State University;DesignforManufacture andAssemblyII: DesignGuidelines,[ONLINE],Availableat; http://www.engr.sjsu.edu/minicurric/images/lecture_powerpoints/DFMA_II_Design_Guidelines.pdf accessedNovember3rd2012 Kalpakjian,S.,andSchmid,S.R.,2009, ManufacturingEngineeringandTechnology,6th Edition,pg 642, 651, 931, 942 and428