General Design Principles for DuPont Engineering Polymers - Module

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Design Examples . . . . . . . . . . . . . . . . . . . . . . .116 Comparison with other Welding Techniques . . . . . . . . . . . . . . . . . . . . . . . . . .117 Design Considerations for Vibration Welded 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 . . . . . . . . . . . . . . . . .122 12—Machining, Cutting and Finishing . . . .124 Safety Precautions . . . . . . . . . . . . . . . . . . . . . . .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 . . . . . . . . . . . . . . . . . . . . . .127 iii Annealing 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 . . . . . . . . . . . . . . . . . .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 . . . . . . . . . . . . . . . . . .131
1—General Introduction This section is to be used in conjunction with the product data for specific DuPont Engineering thermoplastic resins—Delrin ® acetal resins, Zytel ® nylon resins including glass reinforced, Minlon ® engineering thermoplastic resins and Crastin ® PBT and Rynite ® PET thermoplastic polyester resins and Hytrel ® polyester elastomers. Designers new to plastics design must consider carefully the aspects of plastic properties which differ from those of metals: specifically, the effect of environment on properties, and the effect of long term loading. Property data for plastics are obtained from physical tests run under laboratory conditions, and are presented in a similar manner as for metals. Test samples are molded in a highly polished mold cavity under optimum molding conditions. Tests are run under ASTM conditions at prescribed tensile rates, moisture levels, temperatures, etc. The values shown are representative, and, it should be recognized that the plastic part being designed will not be molded or stressed exactly as the test samples: • Part thickness and shape • Rate and duration of load • Direction of fiber orientation • Weld lines • Surface defects • Molding parameters All affect the strength and toughness of a plastic part. The designer must also have information regarding the effect of heat, moisture, sunlight, chemicals and stress. In plastic design, therefore, it is important to understand the application thoroughly, use reference information which most closely parallels the application, prototype the part and test it in the end-use application. The high cost of a poor initial design in terms of time, money, and market share is well known. It is the purpose of this design module to provide the designer with the information necessary to properly allow for environmental process, design and end-use effects, so that an efficient, functional part design is achieved in the shortest possible time. Delrin ® , Zytel ® , Minlon ® , Crastin ® , Rynite ® , and Hytrel ® are registered trademarks of E.I. du Pont de Nemours and Company. 1 Defining the End-Use Requirements The most important first step in designing a plastic part is to define properly and completely the environment in which the part will operate. Properties of plastic materials are substantially altered by temperature changes, chemicals and applied stress. These environmental effects must be defined on the basis of both short and long term, depending of course on the application. Time under stress and environment is allimportant in determining the extent to which properties, and thus the performance of the part will be affected. If a part is to be subject to temperature changes in the end-use, it is not enough to define the maximum temperature to which the part will be exposed. The total time the part will be at that temperature during the design life of the device must also be calculated. The same applies to stress resulting from the applied load. If the stress is applied intermittently, the time it is applied and the frequency of occurrence is very important. Plastic materials are subject to creep under applied stress and the creep rate is accelerated with increasing temperature. If loading is intermittent, the plastic part will recover to some extent, depending upon the stress level, the duration of time the stress is applied, the length of time the stress is removed or reduced, and the temperature during each time period. The effect of chemicals, lubricants, etc., is likewise time and stress dependent. Some materials may not be affected in the unstressed state, but will stress crack when stressed and exposed to the same reagent over a period of time. Delrin ® acetal resins, Zytel ® nylon resins, Minlon ® engineering thermoplastic resins, Rynite ® PET thermoplastic polyester resins and Hytrel ® polyester elastomers are particularly resistant to this phenomena. The following checklist can be used as a guide.
Page 1 and 2: dDuPont Engineering Polymers Genera
Page 3: 8—Gears . . . . . . . . . . . . .
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
Page 59 and 60:
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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