Method of build up welding to thin-walled portion

A method of build up welding to a thin-walled portion of a workpiece, comprising:

• a jig-mounting step (A) for installing a jig to the thin-walled portion of the workpiece to form a recess, wherein the jig is manufactured from a material with a higher melting temperature than the melting temperature of the molten metal and a heat capacity sufficient to reduce a cooling rate of the thin-walled portion after build-up welding, wherein the jig comprises a plurality of closely fitting segments shaped to make close contact with the thin-walled portion of the workpiece, and an outer-frame segment that encloses and holds the plurality of the closely fitting segments in an integrated manner, and wherein the recess is to store the molten metal in a surfaced portion in the vicinity of the thin-walled portion of the workpiece;
• a preheating step (B) for preheating the workpiece and the jig to a predetermined temperature under the condition with the jig installed to the thin-walled portion of the workpiece;
• a build up welding step (C) for continually build up welding to the thin-walled portion of the workpiece and forming weld beads on a surfaced portion;
• and
• a jig-removing step (D) for removing the jig after the weld beads solidify completely.