JP2005238243A - Method for manufacturing main metallic body for spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a main metallic body for a spark plug, which method hardly produces defects. <P>SOLUTION: In the first process, a second workpiece W2 composed of a small diameter portion and a large diameter portion is formed by extruding a cylindrical first workpiece W1 in the axial direction. In the second process, a third workpiece W3 composed of a small diameter cylindrical portion having a second stem bore and a large diameter cylindrical portion having a first stem bore is formed by extruding the second workpiece W2 in the axial direction. Next, in the third process, a polygonal portion 37c having a polygonal shape in the cross section perpendicular to the axis is formed on the large diameter cylindrical portion 37 on the opposite side of the small diameter cylindrical portion 36, and a flange portion 37d is formed by bulging the small diameter cylindrical portion 36 side of the large diameter cylindrical portion 37 in the radial direction, by extruding the third workpiece W3 in the axial direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a spark plug metal shell.

  A general spark plug 100 includes a cylindrical metal shell 90 as shown in FIG. As shown in FIG. 7, a cylindrical insulator 91 extending in the axial direction of the metal shell 90 and having both ends protruding from both ends of the metal shell 90 is fixed in the metal shell 90. A center electrode 92 extends in the axial direction of the metal shell 90, the tip of the center electrode 92 protrudes from the tip of the insulator 91, and the rear end of the center electrode 92 is electrically connected to the terminal 94 in the insulator 91. And a terminal 94 protrudes from the rear end of the insulator 91. On the other hand, one end of the ground electrode 93 is fixed to the metal shell 90, and a discharge gap is formed between the other end of the ground electrode 93 and the center electrode 92.

  The metal shell 90 constituting this type of spark plug is manufactured as follows, as described in Patent Document 1. First, in the first step, a cylindrical first workpiece is prepared, and the first workpiece is extruded in the axial direction. Thereby, the 2nd workpiece | work consisting of a small diameter part and the large diameter part which is coaxial and united with this small diameter part is formed. In the second step, the second workpiece is further extruded in the axial direction. As a result, the first shaft hole is formed in the large diameter portion from the side opposite to the small diameter portion, and the angle perpendicular to the axial direction forms a polygon in a part of the large diameter portion opposite to the small diameter portion. A third work having a portion is formed. Next, in the third step, the third workpiece is further extruded in the axial direction. As a result, the first shaft hole is further formed on the smaller diameter side than the corner portion of the large diameter portion, and the small diameter portion side of the large diameter portion is bulged in the radial direction so as to have the flange portion. Form. At this time, in the manufacturing method disclosed in Patent Document 1, the third step is performed in three stages while the second shaft hole is formed in the small diameter portion and the small diameter portion is formed into a cylindrical small diameter cylindrical portion. The first shaft hole and the second shaft hole are communicated with each other.

  As shown in FIG. 7, the obtained fourth workpiece is subjected to cutting on the outer peripheral surface of the corner portion 81 of the large-diameter portion 80 on the side opposite to the small-diameter cylindrical portion 85 and on the flange portion 82 side. Thin portions 83 and 84 are formed in the portion, and the remaining corner portion 81 is left as a portion that can be sandwiched by a spanner or the like. A male screw 86 is formed on the outer peripheral surface of the small diameter cylindrical portion 85 of the fourth workpiece. In the metal shell 90 obtained in this way, an insulator 91 in which a center electrode 92 and the like are assembled is inserted into the first shaft hole 89 and the second shaft hole 88 that communicate with each other, and the thin portion 83 is caulked to the shaft side. Is integrated with the insulator 91 and the like. Further, the outer electrode 93 is fixed to the tip of the small diameter cylindrical portion 85 of the metal shell 90 by welding or the like. Thus, the spark plug 100 is obtained.

JP-A-4-329287

  However, in recent years, there has been a demand for miniaturization of spark plugs due to demands for miniaturization of parts. Under these requirements, the inventors have attempted to manufacture such a small metal shell for a spark plug by the conventional manufacturing method. However, depending on the manufacturing method, the metal shell can be efficiently manufactured. It was difficult. That is, when such a metal shell is manufactured by the manufacturing method, the metal shell is easily cracked. In addition, the service life of the processing mold is shortened.

  That is, downsizing of the metal shell accompanying downsizing of the spark plug is accompanied by a reduction in the outer diameter of the corner portion, while the outer diameter of the flange portion is reduced for suitable sealing with the engine cylinder block. It is still required to have a certain size. That is, the difference between the outer diameter of the corner portion and the outer diameter of the flange portion becomes larger. Therefore, as in the conventional manufacturing method described above, in order to form a flange portion by bulging the small-diameter portion side of the large-diameter portion from the corner portion in the radial direction at a stroke only in the third step (to expand radially by a punch). Because the amount of displacement of the material of the metal shell is large), the metal shell is likely to crack. Further, since the deformation amount of the material of the metal shell is large, there is a possibility that the working mold may fail, and the life of the working mold is shortened.

  The present invention has been made in view of the above-described conventional situation, and an object to be solved is to provide a manufacturing method of a spark plug metal shell that is less likely to cause defective products.

The spark plug metal shell manufacturing method according to the present invention includes a second portion comprising a small diameter portion and a large diameter portion coaxially and integrally formed with the small diameter portion by extruding a cylindrical first workpiece in the axial direction. A first step of forming a workpiece;
By extruding the second workpiece in the axial direction, a shaft hole is formed in the large diameter portion from the side opposite to the small diameter portion, and a portion of the large diameter portion opposite to the small diameter portion is formed. A second step of forming a third workpiece having a cylindrical large-diameter cylindrical portion;
By extruding the third workpiece in the axial direction, the large-diameter cylindrical portion is squeezed, and a corner perpendicular to the axial direction forms a polygon on the opposite side of the small-diameter portion of the large-diameter cylindrical portion. And a third step of forming a fourth workpiece having a flange portion in which the third workpiece is radially expanded between the corner portion and the small diameter portion.

  In the method for manufacturing a metal shell for a spark plug according to the present invention, in the third step, the large-diameter cylindrical portion is squeezed, and the cross section perpendicular to the axial direction is polygonal at least on the side opposite to the small-diameter portion of the large-diameter cylindrical portion. At the same time as forming the corner portion to be formed, a flange portion is formed by bulging the third workpiece in the radial direction between the corner portion and the small diameter portion. For this reason, when the corner portion is formed in the large-diameter cylindrical portion, the material of the metal shell pressed by the small-diameter cylindrical portion and the material of the metal shell bulged radially in the small-diameter cylindrical portion side of the large-diameter cylindrical portion A flange part will be formed. In other words, since the flange portion is also formed by the material of the metal shell pushed to the small diameter cylindrical portion side when forming the corner portion (displacement of the material of the metal shell bulged in the radial direction of the large diameter cylindrical portion) Because the amount can be kept relatively small), it is difficult for the metal shell to crack. In addition, the deformation amount of the material of the metal shell can be suppressed to a relatively small amount, and the life of the processing mold is extended.

  Therefore, according to the manufacturing method of the present invention, it is possible to manufacture a spark plug metal shell that hardly generates defective products.

  In the manufacturing method of the present invention, the outer diameter of the large-diameter cylindrical portion of the third workpiece is larger than the maximum diameter of the corner portion of the fourth workpiece and smaller than the outer diameter of the flange portion of the fourth workpiece. Thereby, even when the difference between the outer diameter of the corner portion and the outer diameter of the flange portion due to the downsizing of the metal shell for spark plug is increased, the corner portion of the fourth workpiece from the large-diameter cylindrical portion of the third workpiece and Since the processing dimension for forming the flange portion is reduced, the metal shell is less likely to crack. Further, the amount of change in the material of the metal shell can be suppressed to a relatively small amount, and the service life of the processing mold is further extended.

  Hereinafter, an embodiment in which a method for manufacturing a metal shell for a spark plug according to the present invention is embodied will be described with reference to the drawings.

  In the present embodiment, first, in the first step, a columnar first workpiece W1 shown in FIG. 1 is prepared. Here, Fig.1 (a), (b) represents the front view and bottom view of the 1st workpiece | work W1. The first workpiece W1 is carbon steel (S25C, S35C).

  And the 1st workpiece | work W1 is inserted in the cavity C1 of the extrusion die P1 shown to Fig.2 (a). In the extrusion die P1, a cavity C1 extending in the axial direction is formed in the die 1. The cavity C1 has a smaller diameter on the front end side (lower side in FIG. 2A) than the rear end side, and a tapered step portion is formed between the front end side and the rear end side. The die 1 is provided with a punch 2 on the rear side of the cavity C1 so that the punch 2 can be raised and lowered, and a pin 3 and a sleeve 4 are provided on the tip side of the cavity C1. In this extrusion die P1, after the first work W1 is inserted into the cavity C1 from the rear end side of the extrusion die P1 with the punch 2 raised, the punch 2 is lowered. Thus, the first workpiece W1 is extruded forward in the axial direction. Thereby, the 2nd workpiece | work W2 which consists of the small diameter part 6 and the large diameter part 7 which is coaxial and united with this small diameter part 6 is formed. At this time, centering holes 6a and 7a are formed on the shaft cores of both end faces of the second workpiece W2. Here, FIGS. 2B and 2C show a plan view and a bottom view of the second workpiece W2.

  Next, in the second step, the second workpiece W2 is inserted into the cavity C2 of the extrusion die P2 shown in FIG. In this extrusion mold P2, a cavity C2 extending in the axial direction is formed in the die 11. The cavity C2 has a smaller diameter on the front end side (lower side in FIG. 3A) than on the rear end side, and a step is formed between the front end side and the rear end side. The die 11 is provided with a punch 12 on the rear side of the cavity C2 so that the punch 12 can be raised and lowered, and a pin 13 and a sleeve 14 are provided below the cavity C2. In the extrusion die P2, the second work W2 is inserted into the cavity C2 from the rear end side of the extrusion die P2 with the punch 12 raised, and then the punch 12 is lowered. Thus, the second workpiece W2 is extruded backward in the axial direction. As a result, the first shaft hole 17 a is formed in the large-diameter portion 7, and the intermediate work W <b> 2 ′ that becomes the large-diameter cylindrical portion 17 is formed. Here, FIGS. 3B and 3C show a plan view and a bottom view of the intermediate workpiece W2 '.

  Then, the intermediate workpiece W2 'is inserted into the cavity C3 of the extrusion die P3 shown in FIG. In the extrusion die P3, a cavity C3 extending in the axial direction is formed in the die 21. The cavity C3 has a smaller diameter than the rear end side on the front end side (the lower side of FIG. 4A), and a step portion is formed between the front end side and the rear end side. A punch 22 is provided on the rear side of C3 so as to be able to move up and down, and a pin 23 and a sleeve 24 are provided on the tip side of the cavity C3. In this extrusion mold P3, the punch 22 is raised. After inserting the intermediate work W2 ′ into the cavity C3 from the rear end side of the push fitting P3, the punch 22 is lowered, and the intermediate work W2 ′ is extruded backward in the axial direction, whereby the second shaft hole 26a. And a third work W3 having a small diameter cylindrical portion 26 is formed, where FIGS.4 (b) and 4 (c) show a plan view and a bottom view of the third work W3.

  Next, in the third step, the third cake W3 is inserted into the cavity C4 of the extrusion die P4 shown in FIG. In the extrusion die P4, a cavity C4 extending in the axial direction is formed by the die 31 and the punch outer sleeve 35. Of the cavities C4, the cavity C4 of the die 31 has the same diameter. On the other hand, the cavity C4 of the punch outer sleeve 35 has a larger diameter on the front end side (lower side in FIG. 5A) than the rear end side, and there is a tapered step portion between the front end side and the rear end side. It is formed. The punch outer sleeve 35 is provided with a punch 32 on the rear side of the cavity C4 so that the punch 32 can be raised and lowered, and the die 31 is provided with a pin 33 and a sleeve 34 on the tip side of the cavity C4. In this extrusion mold P4, the third work W3 was inserted into the cavity C4 with the die 31 and the punch outer sleeve 35 separated (specifically, the tip side of the third work W3 was placed in the 31st cavity 4). After that, the punch 32 is lowered. Then, the punch outer sleeve 35 is lowered while the punch 32 is engaged with the first shaft hole 27a of the third workpiece W3. Thus, the third work W3 is extruded backward in the axial direction. Accordingly, the large-diameter cylindrical portion 37 has a corner portion 37c having a polygonal cross section perpendicular to the axial direction on the opposite side of the small-diameter cylindrical portion 36, and a flange portion between the corner portion 37c and the small-diameter cylindrical portion 36. 37d is formed. At this time, the material of the metal shell of the large-diameter cylindrical portion 47 pushed to the small-diameter cylindrical portion 36 side by the punch outer sleeve 35 and the small-diameter cylindrical portion 36 side of the large-diameter cylindrical portion 47 are radially expanded by the punch 42. The flange portion 37d is formed by the material of the metal shell. Here, FIGS. 5B and 5C show a plan view and a bottom view of the fourth workpiece W4.

  Finally, the fourth workpiece W4 is taken out from the extrusion die P5, the second shaft hole 46a and the first shaft hole 47a are passed through with a drill, and a male screw is cut on the outer peripheral surface of the small diameter cylindrical portion 46. Further, as in the conventional case, cutting is applied to the outer peripheral surface of the rear end side of the corner portion 47c and the flange 47d side. Thus, the spark plug main body having the flange portion 47d having an outer diameter of a certain size and the corner portion 47c having an outer diameter smaller than that of the flange portion 47d for suitable sealing performance with the cylinder block of the engine. The bracket is completed. Note that the spark plug using this metallic shell exhibits a favorable sealing property with the cylinder block of the engine by the flange portion 47d.

  In this spark plug metal shell manufacturing method, in the third step, the large-diameter cylindrical portion 27 is squeezed, and at least the opposite side of the large-diameter cylindrical portion 27 opposite to the small-diameter portion has a polygonal cross section perpendicular to the axial direction. At the same time as forming the corner portion 37c, a flange portion 37d is formed between the corner portion and the small-diameter portion, and the third workpiece is bulged in the radial direction. Therefore, the material of the metal shell pressed by the small-diameter cylindrical portion 36 when forming the corner portion in the large-diameter cylindrical portion, and the metal shell of the metal shell bulged in the radial direction on the small-diameter cylindrical portion 36 side of the large-diameter cylindrical portion 27. The flange portion 37d is formed by the material. That is, since the flange portion 37d is also formed by the material of the metal shell pushed to the small diameter cylindrical portion 36 side when forming the corner portion 37c (the metal shell bulged in the radial direction of the large diameter cylindrical portion 27). Since the amount of displacement of the material can be kept relatively small), the metal shell is hardly cracked. Further, the deformation amount of the material of the metal shell can be suppressed to a relatively small amount, and the life of the processing jig is extended.

  Therefore, according to the manufacturing method of the present embodiment, it is possible to manufacture a spark plug metal shell that is unlikely to generate defective products.

  Note that the present invention is not limited to the specific embodiments described above, and various modifications can be made within the scope of the present invention depending on the purpose and application. For example, in the manufacturing method of the spark plug metal shell of the embodiment, the second shaft hole 26a is provided in the intermediate work W2 ′ in the second process, but after the intermediate work W2 ′ is used in the third process, the fourth process is performed. As a process, you may perform the process which provides a 2nd axial hole.

  INDUSTRIAL APPLICABILITY The present invention can be used in a method for manufacturing a spark plug metal shell in which corners having a diameter smaller than that of a large-diameter cylindrical part are formed.

It is related with the manufacturing method of the metal shell for spark plugs of an embodiment, and is a front view and a bottom view of the 1st work. It is related with the manufacturing method of the metal shell for spark plugs of an embodiment, and is a sectional view of a forming machine in the 1st process, a top view of the 2nd work, and a bottom view. It is related with the manufacturing method of the metal shell for spark plugs of embodiment, It is sectional drawing of the molding machine in a 2nd process, the top view of a workpiece | work, and a bottom view. It is related with the manufacturing method of the metal shell for spark plugs of embodiment, It is sectional drawing of the molding machine in a 2nd process, the top view of a 3rd workpiece | work, and a bottom view. It is related with the manufacturing method of the metal shell for spark plugs of embodiment, and is a sectional view of a molding machine in the 3rd process, a top view of the 4th work, and a bottom view. It is a side view of a partial cross section of a spark plug according to a conventional manufacturing method of a metal shell for a spark plug. It is a side view of a partial cross section of a metal shell according to a conventional method for manufacturing a metal shell for a spark plug.

Explanation of symbols

W1 ... 1st work W2 ... 2nd work W3 ... 3rd work W4 ... 4th work 6, 16 ... Small diameter part 7, 17 ... Large diameter part 26, 46 ... Small diameter cylindrical part 26a, 46a ... 2nd shaft hole 27, 47 ... Large diameter cylindrical portion 17a, 27a, 47a ... First shaft hole 47c ... Corner portion 47d ... Flange portion

Claims (1)

A first step of forming a second workpiece comprising a small-diameter portion and a large-diameter portion coaxially and integrally with the small-diameter portion by extruding a cylindrical first workpiece in the axial direction;
By extruding the second workpiece in the axial direction, a shaft hole is formed in the large diameter portion from the side opposite to the small diameter portion, and a portion of the large diameter portion opposite to the small diameter portion is formed. A second step of forming a third workpiece having a cylindrical large-diameter cylindrical portion;
By extruding the third workpiece in the axial direction, the large-diameter cylindrical portion is squeezed, and a corner perpendicular to the axial direction forms a polygon on the opposite side of the small-diameter portion of the large-diameter cylindrical portion. And a third step of forming a fourth workpiece having a flange portion in which the third workpiece is radially expanded between the corner portion and the small diameter portion. A method of manufacturing a metal shell.

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