Laser spot welding and real-time evaluation

The high-repetition-rate pulsed-YAG-laser welding of insulated copper wires to terminal posts and their real-time evaluation with stress-wave emission (SWE) are discussed. It is shown that to minimize damage to the wire from the incident radiation a shoulder terminal, wherein the shoulder covers the wire, is desirable. The experimental and the analytical results show that for the geometry a terminal made out of higher melting-point material than copper is desirable. SWE techniques have been used to predict the quality of a laser weld in real time. An experimental criterion has been established for such a prediction. This criterion has been verified by resistance measurement, visual observation, and, to a limited extent, mechanical-pull testing. It is shown that an almost linear relation exists between the threshold crossings of an SWE signal and the quality of the weld.