General Design Principles for DuPont Engineering Polymers - Module

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Vibration welding is not a competitor to pure spinwelding. For all circular parts which do not require a determined position to each other, spinwelding is still the cheapest and fastest assembly technique. Design Considerations for Vibration Welded Parts Parts which are intended to be assembled by vibration welding must be designed correctly to avoid rejects and failures. Perfect fitting of the joint area is essential. The first step is to choose an adequate joint giving the required strength and tightness. It should be decided at this stage of development whether flash traps or means to cover or conceal the joint are necessary. It is essential to support the joint flange all around the part in order to maintain equal pressure over the whole weld area. If, as shown in Figure 11.85, the jig cannot fulfill this requirement due to an interruption, weak spots or leakage can be expected. Thin ribs, however, are permissible, provided their thickness does not exceed appr. 80% of the wall section (see Figure 11.86). Special care must be taken to make sure vibrations are transmitted from the jig to the part with as little power loss as possible. Such loss may occur from too much clearance in the jig or because the part is held too far away from the joint. Circular parts without protruding features allowing a tight grip must be provided with ribs as shown in Figure 11.75A. With parts having relatively thin walls or which are molded in soft materials, vibrations should be transmitted to the part as near to the joint area as possible. For non-circular parts this is often only possible with a design similar to that shown in Figure 11.76B, regardless of whether it is a linear or angular weld. Some materials which have a high coefficient of friction, as for instance elastomers, require an initial surface lubrification before they can be satisfactorily vibrated and welded. The amount of melt produced during the vibration cycle is in direct relation to the surface flatness. Stiff parts, especially in glass filled resins, may not be flattened out completely by the weld pressure and so require longer vibration cycles to achieve good joints. When designing and molding such parts, it should therefore be kept in mind that the total assembly time depends partially on joint levelness which in turn can often be improved with appropriate design. 118 Figure 11.85 Bad joint design Figure 11.86 Ribs in vibration welded parts L = 0.8 T Figure 11.87 Vibration welding machines A) Commercial linear and angular welding machine. Manufacturer: Branson Sonic Power Company, Eagle Road, Danbury, Connecticut 06810, USA. Technical centers around the world.
B) Commercial linear and angular welding machine. Manufacturer: Mecasonic SA, Zone industrielle, Rue de Foran, Ville-la-Grand, Case postale 218, 74104 Annemasse Cédex, France. C) Commercial linear welding machine. Manufacturers: Hydroacoustics Inc., 999 Lehigh Station Road, P.O. Box 23447, Rochester, New York, 14692, USA. Europe: Bielomatic, Leuze GmbH & Co., Postfach 49, D-7442 Neuffen, Germany. 119 Hot Plate Welding Introduction Hot plate welding is a technique used for joining thermoplastic parts. Non symmetric parts with fragile internal components which can not accept vibration or ultrasonic welding are suitable for this technique. The joining of thermoplastic materials is obtained by fusion of the parts surfaces through bringing them into contact with a Teflon ® PTFE coated electrically heated plate. The parts are then pressed together. Alternatively heat can be radiated onto the welding surface using specially designed equipment. Welding Cycle Figure 11.88 shows step by step (I to VI) the typical hot plate welding cycle using an electrically heated, Teflon ® PTFE coated plate to melt the welding surfaces. Figure 11.88 Hot plate welding cycle 1 2 3 I II III IV V VI Joint Design The joint width W should be at least 2.5 times the wall thickness for engineering materials (see Figure 11.89a). Figure 11.89b–c show possible ways of incorporating flash traps. Gap a must be adjusted to obtain a complete closure of the outer lips after welding. This design reduces the effective weld surface and may need wider joints to obtain the same strength as a conventional joint. Thin walled parts may require a guiding jig, e.g., a shown in Figure 11.89d, to ensure adequate contact along the whole surface of the joint.
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dDuPont Engineering Polymers Genera
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8—Gears . . . . . . . . . . . . .
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1—General Introduction This secti
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Prototyping the Design In order to
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2—Injection Molding The Process a
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As a general rule, use the minimum
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Figure 3.11 Cored holes Figure 3.12
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Figure 3.19 Mold-ejection of rounde
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• Zytel ® nylon resin—Parts of
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4—Structural Design Short Term Lo
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Form of section Area A d d R R 1 1
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Table 4.03. Formulas for Stresses a
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Form of bar; manner of loading and
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Figure 4.01 Creep Stress (S), MPa (
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Figure 4.05 Creep in flexure of Zyt
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Example 1 It there are no restricti
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Determine the moment of inertia and
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Figure 4.11 Stress curves The compu
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Rim Design Rim design requirements
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Figure 5.08 Chair Seat Zytel ® 71
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Cantilever Springs Tests were condu
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7—Bearings Bearings and bushings
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debris is moved around continuously
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Table 7.01 Coefficient of Friction*
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Figure 7.15: Connecting rod spheric
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8—Gears Introduction Delrin ® ac
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9—Gear Design Allowable Tooth Ben
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Delrin ® 500. See the section on D
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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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Page 73 and 74: Table 10.01 Self-Threading Screw Pe
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Page 77 and 78: Undercut Snap-Fits In order to obta
Page 79 and 80: Cantilever Lug Snap-Fits The second
Page 81 and 82: 11—Assembly Techniques, Category
Page 83 and 84: Figure 11.03 Drill spindle position
Page 85 and 86: Inertia Welding By far the simplest
Page 87 and 88: Machines for Inertia Welding The pr
Page 89 and 90: This is not always easy, because ap
Page 91 and 92: The holder a, will have equal and o
Page 93 and 94: Calculations for Inertia Welding To
Page 95 and 96: If, for example, the angles of the
Page 97 and 98: Welding Double Joints The simultane
Page 99 and 100: Figure 11.37 Commercial bench-type
Page 101 and 102: Heat is generated throughout the pa
Page 103 and 104: Figure 11.45 Tapered or stepped hor
Page 105 and 106: Weld strength is therefore determin
Page 107 and 108: ) General Part Design The influence
Page 109 and 110: eticule in the eye piece is suitabl
Page 111 and 112: For this reason, if the strength of
Page 113 and 114: Figure 11.64A shows a variation whi
Page 115 and 116: 3. Vibrations, generated either by
Page 117 and 118: If one part is only vibrated at twi
Page 119 and 120: Another joint design, with flash tr
Page 121: Figure 11.82. A linear welded motor
Page 125 and 126: Hot Plate Welding of Zytel ® One o
Page 127 and 128: Figure 11.94 Applications of riveti
Page 129 and 130: Tolerances may be difficult to hold
Page 131 and 132: are used in either hand- or power-o
Page 133 and 134: ather than scrape, these drills wil
Page 135 and 136: The polishing operation is performe
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