Patent ID: 6846214

Claim:
A method of manufacturing a spark plug for an internal combustion engine, the spark plug including an insulator having a through-hole formed therein, a center electrode made of a nickel-based alloy disposed at one end of the through-hole, a metal housing holding the insulator therein, and a ground electrode connected to the metal housing and disposed to face the center electrode, forming a spark gap therebetween, the manufacturing method comprising steps of: attaching a noble metal chip directly on a flat end surface of the center electrode, the noble metal chip being made of an iridium alloy containing iridium and a noble metal having a melting point in a range from 1,500 to 2,100° C. and a linear expansion coefficient in a range from 8×10 −6 to 11×10 −6 /° C., the iridium alloy having a melting point equal to or higher than 2,200° C., a surface area of the flat end surface of the center electrode, to which the noble metal chip is directly attached, being larger than a surface area of the noble area chip which is directly attached to the flat end surface of the center electrode; and radiating a laser beam on the noble metal chip in a direction substantially perpendicular to an axial direction of the center electrode, thereby forming a molten bond containing more than 1-weight-percent noble metal having a melting point in a range from 1,500 to 2,100° C. and a linear expansion coefficient in a range from 8×10 −6 to 11×10 −6 /° C. between the center electrode and the noble metal chip, wherein the laser is a Yag laser, and wherein the Yag laser energy is in a range of 5.0 J-10.0 J.