Resistance Welding Using Homopolar Generators as Power Supplies

The University of Texas Center for Electromechanics (CEM) was originally formed to address the pulsed power requirements in the nuclear fusion research areas. It was determined that inertial energy storage using homopolar conversion could effectively meet these requirements. Two homopolar generators have been built and tested by the CEM; one is under construction and several others are scheduled to begin construction in mid-1977. The machines have been so successful that the CEM is now investigating other areas requiring high energy pulses. Many of these applications have previously been limited by availability of peak power, either by reason of existing technology or economics. One such area is resistance welding where we feel the present generation of homopolar generators offers the potential to significantly extend the limits of cross-sectional areas that can be successfully and economically resistance welded. Since homopolar generators are used effectively as energy storage devices, storing energy (inertially) slowly and then discharging it very quickly, they are ideal sources for the high power inputs required for resistance welds. This energy storage capability can eliminate demand charges when used in-plant and makes on-site resistance welding possible without requiring excessively large prime movers. The CEM has done some welding feasibility experiments using the 5 MJ homopolar generator. Thus far, one-inch bars (both 1018 steel and 304 stainless) , four-inch Schedule 80 304 SS pipe and four-inch Schedule 40 steel pipe have been welded. The pipe welds were completed in under one second at peak currents of up to 170 kA using less than 30% of the available energy in the 5 MJ machine. The design and construction of larger homopolars that could supply sufficient power and energy to resistance weld cross sections on the order of 100 in2 on the same time scale is a straightforward extrapolation of the existing technology.