| 摘要 |
A method of manufacturing a spark plug which includes an insulator, a center electrode, a metallic shell, a ground electrode, and a noble metal tip provided on the ground electrode and having a discharge surface forming a spark discharge gap in cooperation with the center electrode includes a fusion-zone formation step of forming a fusion zone through radiation of a high-energy beam to the boundary between the ground electrode and the noble metal tip. The fusion-zone formation step forms the fusion zone such that when the fusion zone is projected in a direction perpendicular to the discharge surface, 80% or more of the area of an overlap between the ground electrode and the noble metal tip overlaps the projected fusion zone and such that the shape of the fusion zone as viewed from a direction perpendicular to the discharge surface is substantially symmetrical with respect to a centerline perpendicular to the width direction of the ground electrode and passing through the center of the noble metal tip.
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