Patent ID: 8523624

Claim:
A method of manufacturing a spark plug for an internal combustion engine comprising the steps of: preparing a tubular metal shell, an assembly of an insulator and a cylindrical center electrode, and at least one ground electrode base material, said center electrode being secured in said insulator and having a protruding portion that protrudes from an end of said insulator, said ground electrode base material being rod-shaped and having a first and a second end that are opposite to each other in a lengthwise direction of said ground electrode base material; joining the first end of said ground electrode base material to an end of said metal shell such that the lengthwise direction of said ground electrode base material is substantially parallel to an axial direction of said metal shell; bending said ground electrode base material to move the second end thereof outward in a radial direction of said metal shell, thereby forming a bend between the first and second ends of said ground electrode base material; joining a noble metal chip by laser welding to an inner side surface of a portion of said ground electrode base material between the bend and the second end; fitting the assembly of said insulator and said center electrode in said metal shell such that the end of said insulator protrudes from the end of said metal shell and the axial direction of said metal shell substantially coincides with an axial direction of said center electrode; and bending said ground electrode base material at the first end thereof to make the portion thereof between the bend and the second end being substantially parallel to the axial direction of said center electrode and closer to the center electrode in a radial direction of said center electrode than the first end, thereby forming a ground electrode, said ground electrode having an inclined portion, a straight portion, and a bend between the inclined and straight portions which corresponds to the bend of said ground electrode base material, the inclined portion extending obliquely with respect to the axial direction of said center electrode from a base end of said ground electrode, which corresponds to the first end of said ground electrode base material, to the bend, the straight portion extending substantially parallel to the axial direction of said center electrode from the bend to a tip end of said ground electrode which corresponds to the second end of said ground electrode base material, the straight portion having an inner side surface to which is joined said noble metal chip that faces a side surface of the protruding portion of said center electrode through a spark gap in the radial direction of said center electrode.