Method for securing a metal noble tip to an electrode of a spark plug using a resistance and laser welding process

Abstract

There is provided a method for producing a spark plug in which welding strength between a noble metal tip and an electrode joined by laser welding can be restrained from becoming weak. A noble metal tip () to be joined to a center electrode () or ground electrode of a spark plug to form a spark discharge gap is resistance-welded to each electrode containing no noble metal and then laser-welded. In the noble metal tip () exposed under a severe environment involving spark discharge, a molten portion () formed in such a manner that a portion of the noble metal tip () and a portion of the electrode are melted by laser welding and a non-molten portion () on the noble metal tip () side are apt to be peeled from each other in a boundary surface () between the molten portion () and the non-molten portion (). The noble metal content in the molten portion () however becomes higher because a flange portion is formed in a bottom portion by pressing force applied on the noble metal tip () at the time of resistance welding and then irradiated with a laser beam. Accordingly, peeling can be prevented from occurring in the boundary surface ().