36 and back into secondary winding 54 of the first transformer successively the shape area applied pressure and the like of the second wheel electrodes controls reduction of the weld thickness tempering the weld joint in the heat treatment region 64 or both more specifically as the weld wheel electrodes bear down on the overlapped workpieces the pressure affects electrical resistance and current flow the electrical resistance and current generate heat for welding the overlapped edges of the workpieces are mashed down heated fused and seamlessly welded together residual heat remains in the weld region after welding as the second wheel electrode bear down on the weld joint the force of the second pair of electrodes and the completed weld are selected to reduce electrical resistance hence lesser heating an appropriate electrical resistance and lesser heating may also be achieved by careful determination of the size of the second wheel electrodes and the electromechanical properties thereof the current flow and electric resistance between the second wheel electrodes generate heat to perform a heat treating process such as hot planishing hot reducing tempering or the like hot planishing reduces the weld thickness with less force and produces less residual stress in the weld joint than cold planishing the residual heat also provides a temper heat which is advantageous when welding hardenable materials and high carbon materials finally the weld joint passes to the planish wheels where it is cold planished when desired to further reduce the weld joint or to improve the appearance of the finish on the workpieces it will be appreciated that the operation of cold planishing may be removed from the preferred embodiment of the present invention if the desired properties of the workpieces are achieved through the.