In some spark plugs, noble metal tips made of noble metal and having superior wearing resistance are provided at a center electrode and an outer electrode opposing each other so as to enhance ignitability and durability.
The use of laser welding to join a noble metal tip to a center electrode or an outer electrode is proposed (see, for example, Patent Document 1).
Patent Document 1: JP-A-6-36856
In a spark plug described in Patent Document 1, an entire circumference of a boundary between a noble metal tip and a center electrode is welded by a laser, and the noble metal tip is joined to the center electrode by way of a wedged, fused, solidified metal alloy. Laser welding is described as making it possible to weld a noble metal tip to a leading-end face of a center electrode without deforming the noble metal tip, so that there can be provided a spark plug that prevents removal of a noble metal tip caused by repeated exertion of heat stress.