General Design Principles for DuPont Engineering Polymers - Module

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1—General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Defining the End-Use Requirements . . . . . . . . . . .1 Prototyping the Design . . . . . . . . . . . . . . . . . . . . . .3 Machining from Rod or Slab Stock . . . . . . . . . .3 Die Casting Tool . . . . . . . . . . . . . . . . . . . . . . . . . .3 Prototype Tool . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Preproduction Tool . . . . . . . . . . . . . . . . . . . . . . .3 Testing the Design . . . . . . . . . . . . . . . . . . . . . . . . . .4 Writing Meaningful Specifications . . . . . . . . . . . .4 2—Injection Molding . . . . . . . . . . . . . . . . . . . . . .5 The Process and Equipment . . . . . . . . . . . . . . . . . .5 The Molding Machine . . . . . . . . . . . . . . . . . . . . . . .5 The Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 3—Molding Considerations . . . . . . . . . . . . . . . .6 Uniform Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Draft and Knock-Out Pins . . . . . . . . . . . . . . . . . . . .7 Fillets and Radii . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Bosses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 Ribbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 Holes and Coring . . . . . . . . . . . . . . . . . . . . . . . . . . .8 Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 External Threads . . . . . . . . . . . . . . . . . . . . . . . .10 Internal Threads . . . . . . . . . . . . . . . . . . . . . . . . .10 Stripped Threads . . . . . . . . . . . . . . . . . . . . . . . .10 Thread Profile . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Threads—Effect of Creep . . . . . . . . . . . . . . . . .12 Undercuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 Molded-in Inserts . . . . . . . . . . . . . . . . . . . . . . . . .13 Part Design for Insert Molding . . . . . . . . . . . . . . .14 4—Structural Design . . . . . . . . . . . . . . . . . . . . .15 Short Term Loads . . . . . . . . . . . . . . . . . . . . . . . . .15 Tensile Stress—Short Term . . . . . . . . . . . . . . . . .15 Bending Stress . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Beams in Torsion . . . . . . . . . . . . . . . . . . . . . . . . . .15 Table of Contents i Tubing and Pressure Vessels . . . . . . . . . . . . . . . .15 Buckling of Columns, Rings and Arches . . . . . . .15 Flat Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 Other Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 Fatigue Resistance . . . . . . . . . . . . . . . . . . . . . . .22 Impact Resistance . . . . . . . . . . . . . . . . . . . . . . .22 Thermal Expansion and Stress . . . . . . . . . . . . .22 Long Term Loads . . . . . . . . . . . . . . . . . . . . . . . . . .22 Tensile Loads . . . . . . . . . . . . . . . . . . . . . . . . . . .24 Bending Load . . . . . . . . . . . . . . . . . . . . . . . . . . .25 Rib Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 Cross-Ribbing . . . . . . . . . . . . . . . . . . . . . . . . . . .26 Unidirectional Ribbing . . . . . . . . . . . . . . . . . . .28 5—Design Examples . . . . . . . . . . . . . . . . . . . . .32 Redesigning the Wheel . . . . . . . . . . . . . . . . . . . . .32 Web and Spoke Design . . . . . . . . . . . . . . . . . . .32 Rim Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 Finite Element Analysis in Wheel Design . . . .33 Cost Effective Design vs. Raw Material Cost . . . . . . . . . . . . . . . . . . . . . . . . .34 Chair Seats Reevaluated . . . . . . . . . . . . . . . . . . . .34 6—Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Cantilever Springs . . . . . . . . . . . . . . . . . . . . . . . . .37 7—Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39 Shaft Hardness and Finish . . . . . . . . . . . . . . . . . .39 Bearing Surface . . . . . . . . . . . . . . . . . . . . . . . . . . .39 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 Bearing Clearance . . . . . . . . . . . . . . . . . . . . . . . . .41 Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41 Protection against Dirt Penetration . . . . . . . . . . .42 Calculation of Bearings . . . . . . . . . . . . . . . . . . . . .42 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 Design Examples . . . . . . . . . . . . . . . . . . . . . . . . . .44 Gear Bearings . . . . . . . . . . . . . . . . . . . . . . . . . .44 Self-Aligning Bearings . . . . . . . . . . . . . . . . . . .44 Testing Guidelines . . . . . . . . . . . . . . . . . . . . . . .46 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
8—Gears . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47 Combined Functions—Design Examples . . . . . .47 9—Gear Design . . . . . . . . . . . . . . . . . . . . . . . . . .49 Allowable Tooth Bending Stress . . . . . . . . . . . . .49 Diametral Pitch—Tooth Size . . . . . . . . . . . . . . . . .51 Lewis Equation . . . . . . . . . . . . . . . . . . . . . . . . . . .53 Selection of Tooth Form . . . . . . . . . . . . . . . . . . . .53 Designing for Stall Torque . . . . . . . . . . . . . . . . . .54 Gear Proportions . . . . . . . . . . . . . . . . . . . . . . . . . .54 Accuracy and Tolerance Limits . . . . . . . . . . . . . .56 Backlash and Center Distances . . . . . . . . . . . . . .57 Mating Material . . . . . . . . . . . . . . . . . . . . . . . . . . .58 Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58 Testing Machined Prototypes . . . . . . . . . . . . . . . .58 Prototype Testing . . . . . . . . . . . . . . . . . . . . . . . . .58 Helical Gear Design . . . . . . . . . . . . . . . . . . . . . . . .60 Worm Gear Design . . . . . . . . . . . . . . . . . . . . . . . .60 Mating Material . . . . . . . . . . . . . . . . . . . . . . . . . . .62 Bevel Gear Design . . . . . . . . . . . . . . . . . . . . . . . . .63 Fillet Radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63 Methods of Fastening . . . . . . . . . . . . . . . . . . . . . .63 When to Use Delrin ® Acetal Resin or Zytel ® Nylon Resin . . . . . . . . . . . . . . . . . . . . . . . .64 Zytel ® Nylon Resin . . . . . . . . . . . . . . . . . . . . . . .64 Delrin ® Acetal Resin . . . . . . . . . . . . . . . . . . . . . .64 10—Assembly Techniques . . . . . . . . . . . . . . . .65 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65 Mechanical Fasteners . . . . . . . . . . . . . . . . . . . . . .65 Self-Tapping Screws . . . . . . . . . . . . . . . . . . . . .65 Press Fitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68 Interference Limits . . . . . . . . . . . . . . . . . . . . . . .71 Effects of Time on Joint Strength . . . . . . . . . . .72 Snap-Fits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 Undercut Snap-Fits . . . . . . . . . . . . . . . . . . . . . .73 Cantilever Lug Snap-Fits . . . . . . . . . . . . . . . . . .75 ii 11—Assembly Techniques, Category II Welding, Adhesive Bonding . . . . . . . . . . . . . .77 Spin Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . .77 Basic Principles . . . . . . . . . . . . . . . . . . . . . . . . .77 Practical Methods . . . . . . . . . . . . . . . . . . . . . . .77 Pivot Welding . . . . . . . . . . . . . . . . . . . . . . . . . . .77 Inertia Welding . . . . . . . . . . . . . . . . . . . . . . . . . .81 Machines for Inertia Welding . . . . . . . . . . . . . .83 Jigs (Holding Devices) . . . . . . . . . . . . . . . . . . . .85 Couplings with Interlocking Teeth . . . . . . . . . .86 Joint Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . .87 Calculations for Inertia Welding Tools and Machines . . . . . . . . . . . . . . . . . . . . . . . . .89 Graphical Determination of Welding Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . .89 Quality Control of Welded Parts . . . . . . . . . . . .90 Welding Double Joints . . . . . . . . . . . . . . . . . . .93 Welding Reinforced and Dissimilar Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93 Spin Welding Soft Plastics and Elastomers . . . . . . . . . . . . . . . . . . . . . . . . . . .94 Ultrasonic Welding . . . . . . . . . . . . . . . . . . . . . . . .95 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . .95 Ultrasonic Welding Process . . . . . . . . . . . . . . .95 Welding Equipment . . . . . . . . . . . . . . . . . . . . . .97 Part Design Considerations . . . . . . . . . . . . . .100 Ultrasonic Welding Variables . . . . . . . . . . . . .103 Guide to Equipment Operation . . . . . . . . . . .104 Welding Performance . . . . . . . . . . . . . . . . . . .106 Other Ultrasonic Joining Techniques . . . . . . .108 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110 Vibration Welding . . . . . . . . . . . . . . . . . . . . . . . .110 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .110 Basic Principles . . . . . . . . . . . . . . . . . . . . . . . .111 Definition of Motion Center . . . . . . . . . . . . . .111 Typical Arrangements for Producing Vibrations . . . . . . . . . . . . . . . . . . . . . . . . . . .112 Welding Conditions . . . . . . . . . . . . . . . . . . . . .113 Joint Design . . . . . . . . . . . . . . . . . . . . . . . . . . .114 Test Results on Angular Welded Butt Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115 Joint Strength versus Welded Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115 Joint Strength versus Specific Weld Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . .116
Page 1: dDuPont Engineering Polymers Genera
Page 5 and 6: 1—General Introduction This secti
Page 7 and 8: Prototyping the Design In order to
Page 9 and 10: 2—Injection Molding The Process a
Page 11 and 12: As a general rule, use the minimum
Page 13 and 14: Figure 3.11 Cored holes Figure 3.12
Page 15 and 16: Figure 3.19 Mold-ejection of rounde
Page 17 and 18: • Zytel ® nylon resin—Parts of
Page 19 and 20: 4—Structural Design Short Term Lo
Page 21 and 22: Form of section Area A d d R R 1 1
Page 23 and 24: Table 4.03. Formulas for Stresses a
Page 25 and 26: Form of bar; manner of loading and
Page 27 and 28: Figure 4.01 Creep Stress (S), MPa (
Page 29 and 30: Figure 4.05 Creep in flexure of Zyt
Page 31 and 32: Example 1 It there are no restricti
Page 33 and 34: Determine the moment of inertia and
Page 35 and 36: Figure 4.11 Stress curves The compu
Page 37 and 38: Rim Design Rim design requirements
Page 39 and 40: Figure 5.08 Chair Seat Zytel ® 71
Page 41 and 42: Cantilever Springs Tests were condu
Page 43 and 44: 7—Bearings Bearings and bushings
Page 45 and 46: debris is moved around continuously
Page 47 and 48: Table 7.01 Coefficient of Friction*
Page 49 and 50: Figure 7.15: Connecting rod spheric
Page 51 and 52: 8—Gears Introduction Delrin ® ac
Page 53 and 54:
9—Gear Design Allowable Tooth Ben
Page 55 and 56:
Delrin ® 500. See the section on D
Page 57 and 58:
Figure 9.06 Sizes of gear teeth of
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The following additional examples i
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In practice, the most commonly used
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Driving Gear Meshing Gear Table 9.0
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A full-throated worm gear is shown
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Worm Material Gear Material Possibl
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10—Assembly Techniques Introducti
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For these materials, the finer thre
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Table 10.01 Self-Threading Screw Pe
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Figures 10.07 and 10.08 show calcul
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Undercut Snap-Fits In order to obta
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Cantilever Lug Snap-Fits The second
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11—Assembly Techniques, Category
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Figure 11.03 Drill spindle position
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Inertia Welding By far the simplest
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Machines for Inertia Welding The pr
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This is not always easy, because ap
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The holder a, will have equal and o
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Calculations for Inertia Welding To
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If, for example, the angles of the
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Welding Double Joints The simultane
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Figure 11.37 Commercial bench-type
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Heat is generated throughout the pa
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Figure 11.45 Tapered or stepped hor
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Weld strength is therefore determin
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) General Part Design The influence
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eticule in the eye piece is suitabl
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For this reason, if the strength of
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Figure 11.64A shows a variation whi
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3. Vibrations, generated either by
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If one part is only vibrated at twi
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Another joint design, with flash tr
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Figure 11.82. A linear welded motor
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B) Commercial linear and angular we
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Hot Plate Welding of Zytel ® One o
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Figure 11.94 Applications of riveti
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Tolerances may be difficult to hold
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are used in either hand- or power-o
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ather than scrape, these drills wil
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The polishing operation is performe
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