Patent ID: 8388395

Claim:
A method of manufacturing an ignition plug having an insulator with an axial hole, a center electrode provided in the axial hole, a substantially cylindrical metal shell and a plate-shaped ground electrode having a through hole formed in a center thereof, the method comprising: preparing an insulator having a cavity formed at a leading end portion thereof, said cavity formed by disposing a leading end of the center electrode in the axial hole of the insulator such that the leading end of the center electrode is recessed from a leading end of the insulator; assembling the insulator in an interior of the metal shell wherein the position of the insulator is fixed relative to the metal shell by crimping the metal shell to the insulator; sensing an image of the cavity of the insulator from a leading end side of the ignition plug and detecting a center of the cavity of the insulator based on the image so sensed; disposing the ground electrode at a leading end portion of the metal shell; axially aligning the center of the through hole of the ground electrode and the center of the cavity of the insulator based on said image; and welding the ground electrode and the metal shell together after the position of the insulator is fixed relative to the metal shell and after axially aligning the center of the through hole of the ground electrode and the center of the cavity of the insulator.