Spark plug and its manufacturing method

摘要

A hole is formed on a central electrode. A chip has a leg portion. A distal end of the leg portion is entirely united with a bottom surface of the hole by resistance welding. A plurality of fused portions are formed at a boundary between the chip and the central electrode. The fused portions integrate the chip and the central electrode by fusing them together. Each fused portion extends in a radial direction of the chip. The entire periphery of a pointed end of each fused portion penetrates radially inside the outer cylindrical surface of the leg portion of the chip.