REAL-TIME CONTROL OF NUGGET FORMATION IN SPOT WELDS.

In the mass production of resistance spot welds for commercial use, several uncontrollable variables tend to produce welds of varying quality. A microprocessing technique is described which is used with an infrared thermal sensing method to ensure weld uniformity. An optical fiber bundle ″pipes″ infrared radiation from a heated zone near the weld. A detection system provides a thermal signature of this zone, which reflects the progress of the heating inside the weld. A ″standard″ weld is made by trial and error, its thermal signature to serve as a model for all later welds of the same type. By controlling the welding-machine power in real time, the microprocessor ensures that all such welds will have the same thermal signature and, the same quality.