| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a principal hardware for a spark plug which can materialize the long life of a manufacturing device and is less liable to produce a defective article. SOLUTION: In the first step of the invented method, a first cylindrical workpiece W1 is extruded axially so as to form a second workpiece W2 comprising a small diameter portion 6 and a large diameter portion 7. In the second step, the second workpiece W2 is extruded axially so as to form a third workpiece comprising a small diameter cylindrical portion 26 and a large diameter cylindrical portion 27. In the next third step, the diameter of the large diameter cylindrical portion 27 is reduced so as to form a fourth workpiece W4 of which the large diameter cylindrical portion 37 has a thin-walled cylindrical part 37b. In the fourth step, the fourth workpiece W4 is extruded axially so as to form a fifth workpiece W5 of which the thin-walled cylindrical part 47b has a corner 47c. COPYRIGHT: (C)2005,JPO&NCIPI
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