General Design Principles for DuPont Engineering Polymers

1 General Design Principles forDuPont Engineering PolymersCopyright 2000 du Pont de Nemours and Company. All rights Engineering PolymersdStartwithDuPontDesign Guide Module I1 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 .. 42 Injection Molding .. 5 The Process and Equipment .. 5 The Molding Machine .. 5 The Mold .. 53 Molding Considerations .. 6 Uniform Walls .. 6 Configurations .. 6 Draft and Knock-Out Pins .. 7 Fillets and Radii .. 7 Bosses .. 8 Ribbing.

2 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 .. 144 Structural Design .. 15 Short Term Loads .. 15 Tensile Stress Short Term .. 15 Bending Stress .. 15 Beams .. 15 Beams in Torsion .. 15 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.

3 26 Unidirectional Ribbing .. 285 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. RawMaterial Cost .. 34 Chair Seats Reevaluated .. 346 Springs .. 36 Cantilever Springs .. 377 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 Table of Contentsi8 Gears .. 47 Introduction.

4 47 Combined Functions Design Examples .. 479 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 .. 6410 Assembly Techniques.

5 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 .. 7511 Assembly Techniques, Category IIWelding, 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 Toolsand Machines .. 89 Graphical Determination of WeldingParameters .. 89 Quality Control of Welded Parts.

6 90 Welding Double Joints .. 93 Welding Reinforced and DissimilarPlastics .. 93 Spin Welding Soft Plastics andElastomers .. 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 ProducingVibrations .. 112 Welding Conditions .. 113 Joint Design .. 114 Test Results on Angular Welded ButtJoints.

7 115 Joint Strength versus WeldedSurface .. 115 Joint Strength versus Specific WeldPressure .. 116iiDesign Examples .. 116 Comparison with other WeldingTechniques .. 117 Design Considerations for VibrationWelded Parts .. 118 Hot Plate Welding .. 119 Introduction .. 119 Welding Cycle .. 119 Joint Design .. 119 Part Design for Hot Plate Welding .. 120 Limitations of Hot Plate Welding .. 120 Practical Examples .. 120 Hot Plate Welding of Zytel .. 121 Riveting .. 121 Riveting Equipment .. 121 Riveting Operations .. 122 Relaxation of Shaft and Head .. 122 Caution .. 122 Practical Examples .. 122 Design for Disassembly .. 12212 machining , Cutting and Finishing .. 124 Safety Precautions.

8 124 machining Hytrel .. 124 General .. 124 Turning .. 124 Milling .. 124 Drilling .. 124 Tapping or Threading .. 125 Band Sawing .. 125 machining and Cutting of Delrin .. 125 Sawing .. 126 Drilling .. 126 Turning .. 126 Milling .. 126 Shaping .. 126 Reaming .. 126 Threading and Tapping .. 126 Blanking and Punching .. 126 Finishing of Delrin .. 127 Burr Removal .. 127 Filing and Grinding .. 127 Sanding and Buffing .. 127 Safety Precautions .. 127iiiAnnealing of Delrin .. 127 Air Annealing .. 127 Oil Annealing .. 127 Cooling Procedure .. 128 machining and Cutting of Zytel .. 128 Tool Design .. 128 Sawing .. 128 Drilling .. 128 Reaming .. 129 Threading and Tapping.

9 129 Turning .. 129 Milling .. 130 Blanking and Punching .. 130 Finishing of Zytel .. 130 Burr Removal .. 130 Filing and Grinding .. 130 Sanding and Buffing .. 130 Annealing of Zytel .. 131 Moisture-Conditioning .. 13111 GeneralIntroductionThis section is to be used in conjunction with theproduct data for specific DuPont Engineeringthermoplastic resins Delrin acetal resins, Zytel nylon resins including glass reinforced, Minlon Engineering thermoplastic resins and Crastin PBTand Rynite PET thermoplastic polyester resins andHytrel polyester elastomers. Designers new toplastics Design must consider carefully the aspects ofplastic properties which differ from those of metals:specifically, the effect of environment on properties,and the effect of long term data for plastics are obtained from physicaltests run under laboratory conditions, and are pre-sented in a similar manner as for metals.

10 Test samplesare molded in a highly polished mold cavity underoptimum molding conditions. Tests are run underASTM conditions at prescribed tensile rates, moisturelevels, temperatures, etc. The values shown arerepresentative, and, it should be recognized that theplastic part being designed will not be molded orstressed exactly as the test samples: Part thickness and shape Rate and duration of load Direction of fiber orientation Weld lines Surface defects Molding parametersAll affect the strength and toughness of a plastic designer must also have information regarding theeffect of heat, moisture, sunlight, chemicals and plastic Design , therefore, it is important to under-stand the application thoroughly, use referenceinformation which most closely parallels the applica-tion, prototype the part and test it in the high cost of a poor initial Design in terms of time,money, and market share is well known.