Thermoplastic coupling is a patented welding process that is used to join thermoplastic parts. At the drill press, during a connector design brainstorming session, an engineer at Lucent Technologies' Bell Laboratories inserted a plastic rod into a cavity that was slightly too small in its cross section. He hit it with a hammer once to make it fit, and found when he tried to strike it a second time, it wouldn't budge. The explanation was simple: a single stroke converts kinetic energy into thermal energy when a shaft is rammed into a cavity slightly smaller in diameter than the shaft. Trapped frictional heat causes the two to weld permanently together.

Thermoplastic coupling has been used since 1994 to weld more than 15 million handsets for telephones. This welding process has resulted in cost savings of five to eight cents per handset, because thermoplastic coupling eliminates the cost of two screws, and the labor to apply those screws.

Other benefits of thermoplastic coupling range from the sheer strength of the weld to ergonomic and environmental safety. Because there are no harsh solvents or glues used with this type of welding, it is environmentally friendly. Thermoplastic coupling also avoids repetitive-motion injuries, common to assembly workers, by eliminating the torque motion necessary to apply screws.

The thermoplastic weld is very strong, since plastic is literally fused with plastic. This opens the door to a myriad of uses for large-volume assembly of injection-molded products, such as toys, computer and other permanent electronic equipment housings, auto parts, and disposable medical products.

The technology is easy to transfer and to implement. Process steps can be eliminated on the assembly line, such as applying screws, glue, and a drying process, all typically used for a redundant assembly process. Thermoplastic coupling saves money and time, and is striking in its utter simplicity.

This work was done by Robert J. O'Connor and Jaime R. Arnett at Lucent Technologies' Bell Laboratories. This technology is available for licensing. Lucent has available an entire package, including a patent, press-weld machinery specifications, and other technical information necessary to implement the process. For more information, contact John Simon, District Manager, Lucent Technologies GRL Corp., Miami Lakes, FL; (305) 817-8143; fax (305) 817-8180; e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it..

Electronics Tech Briefs Magazine

This article first appeared in the February, 1999 issue of Electronics Tech Briefs Magazine.

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