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©1992-2015. Paul A. Tres. All rights reserved.
AUTOMOTIVE DESIGN Avoiding Plastic Design Pitfalls
Paul A. Tres ETS, Inc.
Bloomfield Hills, MI
Excerpts from the 7th English edition of DESIGNING PLASTIC PARTS FOR ASSEMBLY by Paul A. Tres,
© Carl Hanser Verlag, Münich 2014
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©1992-2015. Paul A. Tres. All rights reserved.
Fixing Honda Pitfall
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©1992-2015. Paul A. Tres. All rights reserved.
Lower Back Comfort Zone
FORE & AFT ADJUSTMENT Provides 2” (50 mm) of infinitely adjustable fore and aft displacement
VERTICAL ADJUSTMENT Five positions allow 2” (50 mm) of vertical adjustment in 0.5” increments
Lumbar Comfort
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©1992-2015. Paul A. Tres. All rights reserved.
Aftermarket Lumbar Support
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©1992-2015. Paul A. Tres. All rights reserved.
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©1992-2015. Paul A. Tres. All rights reserved.
Lumbar Gear Drive
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©1992-2015. Paul A. Tres. All rights reserved.
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©1992-2015. Paul A. Tres. All rights reserved.
• Number of gear teeth = 14 • Metric module = 1.00 • Pressure angle = 20o
• Tooth arc thickness = 1.83 mm • HOB addendum = 1.33 mm • HOB tip radius = 0.43 mm • Roll angle for loading = 42.556o
• Tooth face width = 4.5 mm • Gear input torque = 953.5 N·mm • Root diameter = 12.052 mm • Y –Lewis form factor = 0.37039 • Load tangent to base circle = 144.956 N • Load normal to tooth center line = 119.872 N • Parabola height = 1.72 • Parabola base = 1.995 • Bending moment arm = 1.422 N·mm • Load radius at center of tooth = 7.954 N
Satellite Gear Calculations
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©1992-2015. Paul A. Tres. All rights reserved.
Satellite-Sun Gears FEA
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©1992-2015. Paul A. Tres. All rights reserved.
Satellite Gear MSA
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©1992-2015. Paul A. Tres. All rights reserved.
0 10 20 30 40 50 60 Strain, %
Stre
ss, M
Pa
Stress, kpsi
16
14
12
10
8
6
4
2
0
120
100
80
60
40
20
0
-40oC
0oC
23oC
80oC
100oC 120oC
70
Tensile Stress/Strain Curves Delrin® 111P NC010 Lot VLD5M37, ISO 11403
Polymer Used: Delrin® 111P NC010
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©1992-2015. Paul A. Tres. All rights reserved.
0.04” (1 mm)
Solution
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©1992-2015. Paul A. Tres. All rights reserved.
Fixing Mercedes Pitfall
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©1992-2015. Paul A. Tres. All rights reserved.
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©1992-2015. Paul A. Tres. All rights reserved.
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©1992-2015. Paul A. Tres. All rights reserved.
Washer Fluid Bottle
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©1992-2015. Paul A. Tres. All rights reserved.
PP Grade PD-626 Units
Yield Stress 4,400 psi
Yield Strain 13 %
Flexural Modulus @ 1% secant 170,000 psi
Rockwell Hardness N/A R Scale
Heat Deflection Temperature @ 66 psi 190 oF
Notched Izod Impact @ 73oF 0.5 ft∙lb/in
Water Absorption after 24 hour N/A %
Density 0.9 g/cm3
Melt Flow Rate 12 dg/min
Polypropylene Properties
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©1992-2015. Paul A. Tres. All rights reserved.
Hot Plate Welding Process
Press
Press
Press
Press
Fusing area
Fixtures
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©1992-2015. Paul A. Tres. All rights reserved.
Weld Joint Design
1.3t = 0.105” (2.6 mm) 0.08” (2 mm)
0.27” (6.8 mm)
0.16” (4 mm)
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©1992-2015. Paul A. Tres. All rights reserved.
Bottle Volume Increased - 7.6l
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©1992-2015. Paul A. Tres. All rights reserved.
Weld Joint Desired
0.16” (4 mm)
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©1992-2015. Paul A. Tres. All rights reserved.
Weld Joint Achieved
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©1992-2015. Paul A. Tres. All rights reserved.
Deep Draw Warpage
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©1992-2015. Paul A. Tres. All rights reserved.
Blow Molding for Redesign
• 9” deep draw induces large warpage
• Increasing 5l initial volume to 7.6l compounded the problem
• Welding tried to compensate for warpage
• Creates pre-stress condition in the weld joint
Solution
Blow molding process
eliminates the design pitfall
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©1992-2015. Paul A. Tres. All rights reserved.
Thank you! Questions??