| 摘要 |
PROBLEM TO BE SOLVED: To provide a producing method of a main body metal fitting for spark plug, by which a tapered part can be formed into a desired shape by a cold-forging, in the cylindrical main body metal fitting for spark plug having the tapered part for executing the seal on the outer peripheral surface. SOLUTION: The first member 20 to be worked, provided with a first tapered part 23 having the tapered angle A is formed in the first process. In the second process, the first tapered part 23 is deformed into a second tapered part 33 having the tapered angle B by using a second forming die 62 provided with a tapered seat surface 68 having the tapered angle B larger than the tapered angle A in a stepped inner hole 65. In the third process, the second tapered part 33 is deformed into a third tapered part 43 having the tapered angle C by using a third forming die 63 provided with a tapered seat surface 69 having the tapered angle C smaller than the tapered angle B in a stepped inner hole 66, and a third punch member 73 having the outer diameter at the front end part 73b smaller than the outer diameter of a small diameter leg part in a second member 30 to be worked.
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