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. We describe a microprocessing technique 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 ensure that all such welds will have the same thermal signature and, thus, the same quality.