Dirk Noordegraaf - Sabic

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Dirk Noordegraaf - Sabic

  1. 1. Mechanical Assembly of Plastic ComponentsDirk NoordegraafThemadag Mikrocentrum Verbinden van Kunststoffen24 April 2012
  2. 2. Assembly MethodsMechanical Adhesives WeldingScrews Cyanoacrylates hot plateBolt and nuts 2K, UV Acrylates ultrasonicNails hot melt vibrationSnapfits 1K, 2K epoxy laserInserts 1K, 2K Polyurethane electromagneticRivets 1K, 2K SiliconeHeat/sonic inserts   No. 1
  3. 3. Mechanical Fixing = Managing Stress and Stress relaxationInserts, Screws, Snapfits all introduce local permanent stress and/or elongation Deformation = Constant Time No. 2
  4. 4. Relaxation modulus rRelaxations modulus E  = 5% Time No. 3
  5. 5. Maximum allowable elongation ε4 ε3 ε2 ε1 Time t (log) No. 4
  6. 6. Maximum allowable elongation Short term longtermProduct Polymer unreinforced reinforced unreinforced reinforcedLexan* resin PC 4 1 - 4 1) 0,8 0,4 - 0,5Noryl* resin PPO/PS 3 - 4 2) 1 - 2 1) 0,6 - 0,7 0,4Cycolac* resin ABS 2 1 - 2 1) 0,5 0,4Cycoloy* resin PC/ABS 3 0,6Ultem* resin PEI 5 0,5 - 3 1) 1 0,5Valox* resin PBT + PET 3 1 - 3 1) 2 1Xenoy* resin PC/PBT 4 1 - 3 1) 2 1Noryl GTX* resin PPE/PA 3 2 - 3 1) 2 11) Depending nature and loading of the filler.2) Depending ratio PPE/PS No. 5
  7. 7. Maximum allowable stress Elongation [ % ] σ1 σ2 σ3 σ 1> σ 2> σ 3 Stress [ h ] No. 6
  8. 8. Maximum allowable stressMaterial 23 °C 50 °C 70 °C 100 °C 120 °C 175 °CCycolac * resin 12 2 - - - -Cycoloy * resin 13 - -Noryl * resinUnreinforced 2) 8-14 5-10 3-7 0-3 - -Reinforced 1) 28 24 21 12 5 -Lexan* resinunreinforced 14 11 7 3,5 - -Reinforced 1) 35 28 21 14 7 -Valox* resinunreinforced 10 3,5Reinforced 1) 21 13 8Ultem* resinunreinforced 26 13 7Reinforced 1) 43 30 201) Depending nature and loading of the filler.2) Depending ratio PPE/PS No. 7
  9. 9. Managing stressSurface area Wall thickness No peak stresses (circular bosses, trilobal screws) Radii everywhere No. 8
  10. 10. Mechanical Assembly of Plastic ComponentsScrews
  11. 11. Screw JointsMolded in ThreadThreadforming ScrewsThreadcutting ScrewsMetal InsertsBolt and Nut No. 10
  12. 12. Screw Assemblyadvantages/disadvantagesSeparable Extra production stepVibration proof Extra partSelf regulating Local stress concentration No. 11
  13. 13. Screw AssemblyBasic rulesBeware of sinkmark when boss is located on the backside of A surfacekeep wallthickness/rib ratioNo automatic X / Y positioning by the screw.Centric boss needed. No. 12
  14. 14. Screw AssemblyIn molded thread
  15. 15. Screw AssemblyIn molded threadNote• use maximal radii both for external as well as internal thread• do not use tapered thread No. 14
  16. 16. Threaded pipe connection Max. torque for ¾ thread Ultem* 2400 resin 135 Nm Noryl* GFN1740V resin 100 Nm Noryl* GTX830 resin 90 NmTensile strengthUltem* 2400 resin 180 MPaNoryl* GFN1740V resin 165 MPa Maximum Torque correlated withNoryl* GTX830 resin 110 MPa Tensile Strenght No. 15
  17. 17. Screw AssemblyInserts
  18. 18. Screw AssemblyInsertsHeat insert US insert Expansion insert Threadcutting insertFully reversible assemblyExternal profile determine torque and pull out forceAvoid sharp edges No. 17
  19. 19. Boss Design D+0.5 mm 0.5-1.5° Draft angle 0.05 –0.2 mm D 2*D 2 mm for flash W Reduce mass R=0.25WD ~ 0.5W for reduced sink markBoss outer diameter at least twice insert outer diameterHole ø = insert outer ø - 0.5 mmInserts should stand slightly above the surface of the plastic so that thebolt rests on the top surface of the insert and not on the plastic part. No. 18
  20. 20. Screw AssemblyScrews
  21. 21. Screw Assembly 45°±5°Threadcutting ScrewsUse only for rigid plastics Thread formingto avoid high stresses Generally used for plastics No. 20
  22. 22. Screw Assembly Boss design Diameter screw is determined by the outer d maximum stress at stripping 1.7-2.5*d detail A d+0.2mm Unreinforced resins R dhole = 0,8 x dscrew d Reinforced resins0.3-0.5d dhole = 0,88 x dscrew A Thread Lead-in counterbore to reduce radial edge Engagement Hole d stresses 1.7-2.2*d R s Wallthickness No. 21
  23. 23. Screw AssemblyScrew Design Fax FFlank angle Frad = 0.26F • 30° for low radial stresses Fax = 0.97F FradThread pitch • max. 8° for vibration resistance 30°Core diameter • small to enable material flow • enough space for displaced materialTolerances • only + tool to reduce thread stripping No. 22
  24. 24. Screw AssemblyScrew installation processPositioning and fixationAlignmentInstallation • torque • speed No. 23
  25. 25. Screw Assembly torque  Stripping torque   Clamp force Installation torque Screw head in contact with thread head in contact bossforming without clamp load Thread friction (installation torque Ti) destruction of threadforming the joint (stripping torque Ts) Thread engagement No. 24
  26. 26. Torque versus hole diameterMaterial Lexan* resin 161 Torque versus hole diameterScrew PT K40 2Depth 6 mmSpeed 400 RPM 1.5 torque Nm installation torque 1 strip torque 0.5 0 3 3.2 3.4 3.6 3.8 diameter mm Largest difference between installation and strip torque is at 3.4 mm No. 25
  27. 27. Torque versus installation speedCycolac* resin4.0 mm hole optimal driver speed 35.0 mm screw8.0 mm depth stripping torque 2 torque (Nm)heat generation weakens and melts boss at 1 high speed installation torquetorque and flank stress decrease 0 0 500 1000 1500 2000 2500 driver speed (rpm) No. 26
  28. 28. Screw AssemblySnapfits
  29. 29. Strain in constant width and thickness beam  max Nonlinear FE analysis f h l 3*f*h l = 10 mm max = 93,2 MPa (103,5) h = 2 mm  max = 3,7 % (4,5) max = x 100% 2* l2 f = 1,5 mm F = 20,1 N (20,7) b = 3 mm f*E*b*h3 E = 2.300 N/mm2 (manualFbending = calculation) 4*l3 3 *E* f * hmax = 2 * l2 Length is a dominant factor in the snapfit No. 28
  30. 30. Conical Snapfits 2,2 f 2,1hs 2,0 1,9 h0 1,8 3 *f * hs 1,7 = max 100 % Ks 1,6 2* l2 * Ks 1,5 1,4Ks = Geometry factor 1,3 1,2 1,1 l = 10 mm 1,0 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 h1 = 2 mm R = h o/ hs h2 = 1 (0.8) mm f = 1,5 mm max = 58,7 MPa max = 52,4 MPa b = 3 mm  max = 2,3 %  max = 2,0 % E = 2.300 N/mm2 F = 12,3 N F = 10,8 N No. 29
  31. 31. Insertion and Pull-out Forces F f F2 2 1 F1 h l c F : deflection force F1 : insertion force F2 : pull-out force 1 : insertion angle : pull out angle f : deflection http://www.sabic-ip.com/webtools/redirect?tool=snapfit No. 30
  32. 32. Screw AssemblyPressfits
  33. 33. Press fitsShaft/Hub Joint Bush/Housing Joint No. 32
  34. 34. Key parameters for a press fit Diametric Interference [ U ] Relative Diametric Interference [ U R ] Relaxationsmodulus [ E r (t) ] Coefficient of friction [µ 0 ]http://www.sabic-ip.com/webtools/redirect?tool=bosscalc No. 33
  35. 35. Key parameters for a press fitF p d = D 1+ U D1 D2 D 1 = Hub inner diameter (nominal) D 2 = Hub outer diameter U = Interference (d - D1) 2 p = Holding pressure [ MPa ] F = Assembly force Interference U is diameter difference between joining parts Interference UThe relative Interference is: x 100 % Nominal diameter D1 No. 34
  36. 36. Maximum interferences for unreinforced Lexan* resin and Noryl* resin 13 Plastic shaft/Plastic hubMaximum interference 12(μ m/mm of the shaft 11 10 9 Metal shaft/Plastic hub 8 Calculation exemple 7 0,2 0,3 0,4 0,5 0,6 0,7 Hub inner diameter / hub outerdiameter ( D1 / D2) No. 35
  37. 37. Calculation example L Maximum interference D1 / D2 = 8 / 12 = 0,66 p = 8 / 18 = 0,44d = D 1+ U D1 D2 Value 7,6 * 8 = 60,8 µ 8,4 * 8 = 67,2 µ The maximum allowable interference is D1 = 8 mm 0,06 mm D2 = 12 mm (18 mm) ( 0.067 mm) No. 36
  38. 38. Summary• Mechanical fastening particularly advantageous is the assembly needs be unassembled during life time• Managing long term lower level stresses in mechanical joint of key importance to prevent failure• Performance, peak stresses and maximum allowable stresses for most mechanical joints are very well predictable No. 37
  39. 39. SABIC-IP Global DisclaimerTHE MATERIALS, PRODUCTS AND SERVICES OF SABIC INNOVATIVE PLASTICSHOLDING BV, ITS SUBSIDIARIES AND AFFILIATES (“SELLER”), ARE SOLD SUBJECTTO SELLER’S STANDARD CONDITIONS OF SALE, WHICH CAN BE FOUND AThttp://www.sabic-ip.com AND ARE AVAILABLE UPON REQUEST. ALTHOUGH ANYINFORMATION OR RECOMMENDATION CONTAINED HEREIN IS GIVEN IN GOODFAITH, SELLER MAKES NO WARRANTY OR GUARANTEE, EXPRESS OR IMPLIED, (i)THAT THE RESULTS DESCRIBED HEREIN WILL BE OBTAINED UNDER END-USECONDITIONS, OR (ii) AS TO THE EFFECTIVENESS OR SAFETY OF ANY DESIGNINCORPORATING SELLER’S PRODUCTS, SERVICES OR RECOMMENDATIONS.EXCEPT AS PROVIDED IN SELLER’S STANDARD CONDITIONS OF SALE, SELLERSHALL NOT BE RESPONSIBLE FOR ANY LOSS RESULTING FROM ANY USE OF ITSPRODUCTS OR SERVICES DESCRIBED HEREIN. Each user is responsible for makingits own determination as to the suitability of Seller’s products, services or recommendationsfor the user’s particular use through appropriate end-use testing and analysis. Nothing inany document or oral statement shall be deemed to alter or waive any provision of Seller’sStandard Conditions of Sale or this Disclaimer, unless it is specifically agreed to in a writingsigned by Seller. No statement by Seller concerning a possible use of any product, serviceor design is intended, or should be construed, to grant any license under any patent orother intellectual property right of Seller or as a recommendation for the use of suchproduct, service or design in a manner that infringes any patent or other intellectual propertyright.SABIC Innovative Plastics is a trademark of Sabic Holding Europe BV* Trademark of SABIC Innovative Plastics IP BV No. 38

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