EFFECT OF FIT-UP CONDITIONS WHEN USING CONSTANT CURRENT CONTROL SYSTEMS FOR RESISTANCE SPOT WELDING 930451

Resistance welding control systems utilizing secondary current feedback receive widespread utilization both in Europe and Japan. However, these types of control systems are only beginning to be used in any extended basis in this country. Currently, two variants of these systems are available; so called “self-teaching” systems, and “learning curve” systems. Either system has been shown to be capable of providing a stable secondary resistance welding current within two cycles. Recent work has indicated, however, that the self-teaching type control systems may be adversely affected by non-optimum set-up conditions, particularly poor fit-up and the introduction of organics (sealers or adhesives) at the faying surface. This work examines the performance of learning curve type constant current control systems under these adverse set-up conditions. Six conditions were selected for study; three degrees of progressively poorer fit-up, with and without an organic sealer. For each condition, current range curves were generated, and process measurements taken. For all sets of conditions, the learning curve control system performed well. Current range results indicated no premature expulsions associated with controller function, and in fact current range curves for all conditions were quite similar. Process results indicated that in all cases the current waveforms were quite stable. Current, voltage and dynamic resistance waveforms were quite similar for all trials. For the trials without adhesive, the firing angle results indicate that the controller functioned by compensating for variations in dynamic resistance throughout the process. A similar relationship between firing angle and dynamic resistance was not noted for the welds made with sealer.