Abstract: Surfaces of metal workpieces being welded are fused at a constant speed of feeding the workpieces towards each other, and the speed of feeding is, before the upsetting, increased to a final value thereof for a period of (1.0 to 4.0) (.DELTA.max/v.sub.1), where .DELTA..sub.max is the maximum gap between the workpiece surfaces being welded and v.sub.1 is the average speed of feeding the workpieces over the period of its increase. Empirical formulas are given to determine the maximum gap for workpieces of various thicknesses.

Abstract: Work pieces to be joined together by the flash butt welding method are brought together at a preset no-load voltage, the end faces of the work pieces are fused, and an upsetting is accomplished. The amount of the upsetting is determined within from 1.2 to 3.0 of the amount of the maximum gap between the end faces of the work pieces being welded together, which gap forms in the course of fusing the end faces of the work pieces. The maximum gap is determined from the following relation:.DELTA..sub.max =f(U.sub.o,.delta.),where:.DELTA..sub.max =maximum gap;U.sub.o =no-load voltage;.delta.=thickness of the work pieces being welded together.Empirical formulas to determine the maximum gap for work pieces of various thicknesses are presented.