UPSET WELDING CONNECTION METHOD

PROBLEM TO BE SOLVED: To attain, in an upset welding connection method for butt-welding two bars, stable and robust welding independently from the end surface shape or area of a welded part with an inexpensive welding facility while preventing contamination associated with welding and forming a bump-like diameter increased portion in which the outer diameter of the welded part is extended in a neat shape.SOLUTION: Two bars are butt-welded by holding the two bars at positions distant from the welded part thereof by a pair of opposed upset weld electrodes respectively, supplying power to the upset welding electrodes while pressurizing the upset weld electrodes in mutually approaching directions with a first welding pressure such that the two bars contact with each other at the welded part to heat the welded part, and then pressurizing the upset weld electrodes in the mutually approaching directions with a second welding pressure higher than the first welding pressure while supplying power to the upset weld electrodes.