DFMA report

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.
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
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.
- Minimize partcount
- 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.
- Encourage modularassembly
The two pointsabove bothhelpachieve increasedreliabilitywithinthe product. If partsare
designedwithmodularassemblyinmind,thenthe assemblyprocedure becomesmore consistent
and therefore more reliable. Alsoif standardpartsare usedthe processbecomessimplifiedandless
opportunityforerrorsarises.
errorsloweringthe qualityof the output. Italsoencouragesthe designertoconstantlytryto review
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.
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.
- 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.
errorsloweringthe qualityof the output. Italsoencouragesthe designertoconstantlytryto review
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
UnknownAuthor,unknown year,Universityof Wisconsin;DetailedDesignforAssemblyGuidelines,
[ONLINE],Availableat; http://homepages.cae.wisc.edu/~me349/lecture_notes/detailed_dfa.pdf
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
Kalpakjian,S.,andSchmid,S.R.,2009, ManufacturingEngineeringandTechnology,6th
Edition,pg
642, 651, 931, 942 and428

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