초록 ▼

There is provided a method of manufacturing a metal shell formed body by cold forging for a metal shell of a spark plug. In the manufacturing method, a semi-finished formed body is first provided with a second inner step without the formation of an annular front end portion. After the semi-finished

There is provided a method of manufacturing a metal shell formed body by cold forging for a metal shell of a spark plug. In the manufacturing method, a semi-finished formed body is first provided with a second inner step without the formation of an annular front end portion. After the semi-finished formed body is inserted from its front end side into a die, a punch is pushed into the semi-finished formed body from its rear end side. By pushing the punch, an annular front-facing surface of the punch is pushed onto the second inner step so as to press a front end portion of the formed body against an annular front end portion forming part of the die. By such a forming step, the metal shell formed body is obtained in which the annular front end portion is formed by extrusion.

대표청구항 ▼

1. A method of manufacturing a metal shell formed body for a spark plug, the metal shell formed body comprising: a body part having formed therein an axial hole for insertion of an insulator and having formed thereon a radially outwardly protruding flanged portion; a cylindrical intermediate portion

1. A method of manufacturing a metal shell formed body for a spark plug, the metal shell formed body comprising: a body part having formed therein an axial hole for insertion of an insulator and having formed thereon a radially outwardly protruding flanged portion; a cylindrical intermediate portion located in front of the body part; and an annular front end portion located in front of the cylindrical intermediate portion and made smaller in outer diameter than the cylindrical intermediate portion,the manufacturing method comprising the steps of:a semi-finished formed body producing step for cold forging a metal material, to produce a semi-finished formed body with the flanged portion and the cylindrical intermediate portion, the flanged portion having a front facing surface, the semi-finished formed body having an axial hole faulted therein along a center axis thereof such that the axial hole includes, in order of mention from the rear to the front, a large-diameter hole region, a first middle-diameter hole region smaller in diameter than the large-diameter hole region, a small-diameter hole region smaller in diameter than the first middle-diameter hole region and a second middle-diameter hole region larger in diameter than the small-diameter hole region; andan annular front end portion forming step for, after the semi-finished formed body producing step, forming the annular front end portion by pushing a punch into the semi-finished formed body and thereby pressing a front end portion of the semi-finished formed body against a die while maintaining said front-facing surface of the flanged portion spaced from contact with the die. 2. The manufacturing method of the metal shell formed body for the spark plug according to claim 1, wherein the semi-finished formed body producing step includes forming a first inner step between the large-diameter hole region and the first middle-diameter hole region and forming a second inner step between the first middle-diameter hole region and the small-diameter hole region; andwherein the die is fittable around the semi-finished formed body by clearance fitting and having an inner circumferential cylindrical surface shaped to mate with the cylindrical intermediate portion, a reduced-diameter inner cylindrical surface smaller in inner diameter than the inner circumferential cylindrical surface and a tapered inner circumferential surface between the inner circumferential cylindrical surface and the reduced-diameter inner cylindrical surface;wherein the punch has an annular front-facing surface shaped to push at least one of the first and second inner steps;wherein the annular front end portion forming step includes:inserting and placing the semi-finished formed body from a front end side thereof into the die; andpushing the punch into the semi-finished formed body from a rear end side thereof so as to, by pushing of the annular front-facing surface onto at least one of the first and second inner steps, force the semi-finished formed body toward the front, press a front end portion of the semi-finished formed body against the reduced-diameter inner cylindrical surface and the tapered inner circumferential surface of the die and thereby form the annular front end portion by cold forging. 3. The manufacturing method of the metal shell formed body for the spark plug according to claim 2, wherein the punch is shaped to push both of the first and second inner steps and force the semi-finished formed body toward the front. 4. The manufacturing method of the metal shell formed body for the spark plug according to claim 3, wherein an axial dimension of the small-diameter hole region of the semi-finished formed body is larger than a design dimension of a small-diameter hole region of the metal shell formed body; andwherein an axial dimension from the first inner step to the second inner step of the semi-finished formed body is smaller than a design dimension between first and second inner steps of the metal shell formed body. 5. The manufacturing method of the metal shell formed body for the spark plug according to claim 1, wherein the semi-finished formed body producing step includes forming a first inner step between the large-diameter hole region and the first middle-diameter hold region; andwherein the manufacturing methods further comprises, after the semi-finished formed body producing step and before or in parallel with the annular front end portion forming step, a step for forming a second inner step between the first middle-diameter hole region and the small-diameter hole region. 6. The manufacturing method of the metal shell formed body for the spark plug according to claim 5, wherein the semi-finished formed body producing step includes forming a temporary tapered portion between the first middle-diameter hole region and the small-diameter hole region; andwherein the die is fittable around the semi-finished formed body by clearance fitting and having an inner circumferential cylindrical surface shaped to mate with the cylindrical intermediate portion, a reduced-diameter inner cylindrical surface smaller in inner diameter than the inner circumferential cylindrical surface and a tapered inner circumferential surface between the inner circumferential cylindrical surface and the reduced-diameter inner cylindrical surface;wherein the punch has an annular front-facing surface shaped to push the first inner step and a small-diameter hold region forming surface shaped to push the temporary tapered portion; wherein the annular front end portion forming step includes:inserting and placing the semi-finished formed body from a front end side thereof into the die; andpushing the punch into the semi-finished formed body from a rear end side thereof so as to, by at least one of pushing of the annular front-facing surface onto the first inner step and pushing of the small-diameter hole region forming surface onto the temporary tapered portion, force the semi-finished formed body toward the front, press a front end portion of the semi-finished formed body against the reduced-diameter inner cylindrical surface and the tapered inner circumferential surface of the die and thereby form the annular front end portion by cold forging and, at the same time, press the small-diameter hole region forming surface of the punch against the temporary tapered portion of the semi-finished formed body and thereby form the second inner step by cold forging. 7. The manufacturing method of the metal shell formed body for the spark plug according to claim 5, wherein an axial dimension of the small-diameter hole region of the semi-finished formed body is larger than a design dimension of a small-diameter hole region of the metal shell formed body; andwherein an axial dimension from the first inner step to the second inner step of the semi-finished formed body is smaller than a design dimension between first and second inner steps of the metal shell formed body. 8. A manufacturing method of a metal shell for a spark plug, further comprising: manufacturing the metal shell formed body by the manufacturing method according to claim 1; andforming a thread on at least a part of the cylindrical intermediate portion of the metal shell formed body. 9. A manufacturing method of a spark plug, comprising: manufacturing a metal shell by the manufacturing method according to claim 8; andplacing an insulator in the metal shell formed body.