Patent ID: 7097525

Claim:
A method for manufacturing a spark plug provided with a housing, a substantially cylindrical center electrode held in an insulated manner in the housing, an earth electrode having first and second axial end portions, one of said axial end portions being joined to the housing, and a noble metal chip joined on a first end-side surface of the other axial end portion of the earth electrode, comprising: performing a provisional bending process wherein the spark plug is mounted to a holder and the earth electrode is bent from a condition in which the earth electrode is straight and in parallel with an axial line of the center electrode to a condition in which the other axial end portion of the earth electrode is located closer to a tip of the center electrode; locating a bending punch having a first pressing surface and a second pressing surface perpendicular to the first pressing surface in such a manner that the first pressing surface is fitted to a second end-side surface located diametrically opposite to the first end-side surface of the earth electrode and the second pressing surface is fitted to a tip surface of the earth electrode, the tip surface connecting the first and second end-side surfaces; first moving the bending punch so as to make the second pressing surface come into contact with the tip surface of the earth electrode; and second moving the bending punch, as a main bending process, so that the first pressing surface presses the second end-side surface downward toward the tip of the center electrode in the axial direction of the center electrode, the tip surface of the earth electrode being held by the second pressing surface during the second moving process, whereby the noble metal chip axially opposes the tip of the center electrode via a spark gap of a predetermined length.