METHOD FOR MANUFACTURING SPARK PLUG

摘要

[Problem] To provide a technique capable of readily determining the presence of cracks in an insulating body during a step for manufacturing a spark plug. [Solution] A method for manufacturing a spark plug is provided with a fitting step for inserting and fitting an insulating body from an opening on the rear-end side in the axial direction of a main metal fitting. The fitting step includes a displacement restriction step for restricting the displacement of the relative positions, in the radial direction intersecting with the axial direction, of the main metal fitting and the insulating body so that the amount of misalignment between the axis of the main metal fitting and the axis of the insulating body is equal to or less than a predetermined value while allowing displacement of the relative positions, in the axial direction, of the main bracket and the insulating body. In the fitting step, acoustic emission generated from the insulating body is detected, whereby the presence of cracks in the insulation body generated during the fitting step is determined.