Method and apparatus for welding metal parts coated with a thermoplastic

摘要

A pair of thermoplastic coated, paramagnetic metal sheets (26 and 27) are moved from a position within a first bus loop half (28) to a position within a second loop half (29) while a pair of electrodes (31 and 32) are cyclically moved to engage and weld a line of spots along the sheets. Constant current pulses are cyclically applied to the welding electrode (32) and through the loop halves (28 and 29) to the welding electrode (31). The current divides in the loop halves in proportion to the positionment of the metal sheets in the respective loop halves so that eddy current and hysteresis losses are held to constant minimum values. Auxiliary heaters (43 and 44) act to heat the electrodes to melt and displace the thermoplastic coating along the line of engaged spots prior to the cyclic application of the weld pulses.