In-Process Weld Quality Monitoring Techniques for Resistance-Spot Welds

Abstract

Dynamic resistance and thermal condition of the weld are the two process parameters which are monitored and related to weld quality of resistance-spot welds in mild steel. The investigation reported in Part I is concerned with measurement and application of dynamic or instantaneous resistance of spot welds. Thus, an electronic instrumentation system has been designed which computes dynamic resistance. The results of investigation show that the pattern of variation exhibited by the instantaneous resistance of a spot weld is indicative of the state of nugget growth and therefore can be used in monitoring weld quality. In Part II of the dissertation thermal condition of the weld is related to the state of nugget growth. The thermal condition of the weld, in this instance, is assessed from the monochromatic radiant emission from the weld surface, thermal radiation from the weld being collected through an aperture at the electrode tip. In addition, a mathematical equation has been developed for initial static resistance of the weldment; also, probable forms of equations relating dynamic resistance and time are suggested. It is also demonstrated that the classical w-6 theorem is a more reliable basis for deriving any relationship connecting weld voltage and weld temperature.