Plastics joining staking

Reduction of the number of product components, usually achieved by combining functions. Typical examples include box and cover assemblies joined with live hinges, the use of self-tapping screws to eliminate nuts, and staking of molded plastic bosses instead of metal rivets or screws. 

In addition, experimental tests are recommended with materials to be welded or staked, etc., to determine the suitability of ultrasonic assembly, especially where dissimilar plastic resin systems are being joined. 

Figure 8.11 Ultrasonic joining operating, (a) Swaging the plastic ridge is melted and reshaped (left) by ultrasonic vibrations to lock another part into place, (b) Staking ultrasonic vibrations melt and reform a plastic stud (left) to lock a dissimilar component into place (right), (c) Insertion a metal insert (left) is embedded in a preformed hole in a plastic part by ultrasonic vibration (right), (d) Spot welding two plastic components (left) are joined at localized points (right).

When two pieces of plastic must be joined together in service but must also be suited to simple disassembly, threaded joints are possible. Such joints may be plastic to plastic, as in toothpaste tubes and caps, where male and female threads are molded. If metal screws are to be used, female threads can be molded in a plastic part to accept the metal screw. If such a threaded application does not have to withstand much tension in the screw, a selftapping screw may be turned into a molded hole of appropriate diameter. Self-tapping screws designed for plastics applications are better suited than those for metal appUca-tions. Metal female-threaded inserts may be molded into plastic parts to accept metal screws in a subsequent assembly operation. Metal female-threaded inserts may also be staked into a molded hole of appropriate size, sometimes mechanically, often with heat ( heat staking ) to soften the thermoplastics at the interface so as to achieve more positive bonding (Figs. 9.16 and Fig. 9.17). 

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