| 摘要 |
PROBLEM TO BE SOLVED: To provide a manufacturing method giving high joint strength and being less liable to cause defects in a boundary face of joint, in the case of a spark plug with a main metallic part made up by joining a body part to an end part, different in material from each other. SOLUTION: An end part 1B, with which a ground electrode 4 is unified, of a main metallic part 1 is formed of a heat-resisting second structure 51 while the second structure 51 is joined by friction grip joint to a first structure 50 of a ferrous metal. In comparison with the conventional resistance welding method, troubles such as defects are less liable to occur. and the manufacturing yield can be enhanced. In comparison with the resistance welding method, the joint strength of a body part 1A to the end part 1B is enhanced, and such a trouble that the body part 1A comes off the end part 1B from a defective part, is less liable to occur, if a thread part 7 is formed by rolling, etc., on an outer circumferential surface of the main metallic part 1 in extending relation from the body part 1A to the end part 1B, or if some shock is exerted thereon when a spark plug is used.
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