JP6725566B2 - Hollow material manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a hollow material having a hollow inside, and more particularly to a method for manufacturing a hollow material in which a male screw is formed by rolling.

When a rolling die is pressed against the workpiece to form a chevron, if there is a cavity inside the part where the rolling die is pressed, the workpiece will elastically deform due to the pressure of the rolling die (rolling force). In some cases, the desired mountain shape cannot be formed because the reaction force corresponding to the rolling force cannot be obtained. In order to prevent this, in Patent Document 1, after a steel ball group consisting of a plurality of steel balls is housed in a cavity of a workpiece, a jig is inserted into the cavity to press the steel ball group. A technique for rolling and taking out a steel ball group after processing is disclosed. According to this technique, the steel ball group can prevent the work piece from being crushed due to the rolling force and obtain a reaction force commensurate with the rolling force, so that a desired chevron can be formed.

JP, 2014-54644, A

However, in the above-mentioned conventional technique, in addition to the rolling process, a step of accommodating the steel ball group in the cavity of the workpiece, a step of pressurizing the steel ball group with a jig inserted in the cavity, and a rolling process This is complicated because it requires a step of taking out the steel ball group later.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a hollow member capable of forming a desired screw while simplifying a complicated process.

In order to achieve this object, the present invention is a method for manufacturing a hollow member having a hollow inside and at least a part of the external thread being formed on the outer peripheral surface corresponding to the hollow. A preparatory step of preparing a hollow work piece having at least two portions having different rigidity in the axial direction, a second portion having a cavity inside and a first portion having a rigidity higher than that of the second portion; And a rolling step of pressing the screw portion of the rolling die against the outer peripheral surface of the workpiece to form a screw. In the rolling step, the thread portion of the rolling die is sequentially pressed against the outer peripheral surface of the workpiece from the side of the first portion in the direction away from the first portion to form the screw in the second portion.

According to the method for manufacturing a hollow material according to claim 1, in the rolling step in which the thread portion of the rolling die is pressed against the outer peripheral surface of the workpiece to form the screw, the hollow portion is more than A screw is formed in the second part by sequentially pressing the threaded part of the rolling die from the side of the first part having high rigidity toward the outer peripheral surface of the workpiece in the direction away from the first part. By doing so, the rolling force generated when the threaded portion of the rolling die is pressed against the second portion is dispersed to the side of the first portion having higher rigidity than the second portion. Therefore, it is possible to prevent the second portion from being excessively crushed by the rolling force. As a result, a reaction force commensurate with the rolling force can be obtained also in the second part, so that a desired screw can be easily formed in the second part. Furthermore, since the step of accommodating the steel ball group inside the cavity is not required, the step can be simplified.
Further, after the workpiece and the rolling die are arranged such that the distance from the outer peripheral surface on the first portion side to the threaded portion is shorter than the distance from the outer peripheral surface on the second portion to the threaded portion, The rolling die is translated toward the workpiece until the screw is pressed against the outer peripheral surface of the second part. Thereby, a desired screw can be formed by a simple process.

According to the method for manufacturing a hollow member according to claim 2, the first part is connected to one end side in the axial direction of the second part, and by the rolling process, the first part is connected to the first part before the second part. A male screw is formed. Therefore, in addition to the effect of claim 1, a desired screw can be formed from the first portion to the second portion.

According to the hollow material manufacturing method of the third aspect, the workpiece has a portion having a different moment of inertia in the axial direction. Therefore, in addition to the effect of claim 1 or 2, a desired screw can be formed on a workpiece having a cross-sectional shape different in the axial direction.

According to the method for manufacturing a hollow member of the fourth aspect, the workpiece has a portion where the second moment of area is different in the axial direction in the portion where the male screw is formed. Therefore, in addition to the effect of the third aspect, a desired screw can be formed in a portion having a different cross-sectional shape in the axial direction.

According to the hollow material manufacturing method of the fifth aspect , the rolling die is a round die whose outer shape is a columnar shape. Since the shaft of the round die is arranged non-parallel to the axis of the workpiece, pressing the round die from the side of the first part causes the second part to move in the direction away from the first part. Can form threads. Therefore, in addition to the effect according to any one of claims 1 to 4 , the hollow material can be manufactured with simple equipment.

According to the method for manufacturing a hollow member according to claim 6 , since the rolling die is a circular die whose outer shape is a conical taper shape, a direction in which the rolling die is separated from the first portion by pressing from the first portion side. A thread can be formed on the second part towards. Therefore, in addition to the effect of any one of claims 1 to 4 , the hollow material can be manufactured with simple equipment.

According to the manufacturing method of hollow members according to claim 7, wherein the hollow member is a metal shell of the spark plug. Since the metallic shell of the spark plug has a portion having different rigidity in the axial direction, the application of the present invention is effective.

It is one side sectional drawing of the spark plug which used the hollow material in 1st Embodiment. It is a schematic diagram which forms a screw in a to-be-processed object. (A) is sectional drawing of the hollow material containing an axis line, (b) is sectional drawing of the hollow material in a comparative example. It is one side sectional drawing of the spark plug which used the hollow material in 2nd Embodiment. It is a schematic diagram which forms a screw in a to-be-processed object.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-sided sectional view taken along the axis O of a spark plug 10 using a hollow material according to a first embodiment of the present invention. In FIG. 1, the illustration of the threads of the male screw 36 is simplified. The lower side of the paper of FIG. 1 is referred to as the front end side of the spark plug 10, and the upper side of the paper is referred to as the rear end side of the spark plug 10 (same in FIG. 4). As shown in FIG. 1, in the spark plug 10, a metal shell 30 which is a hollow material holds the insulator 11.

The insulator 11 is a substantially cylindrical member formed of alumina or the like, which has excellent insulating properties and mechanical properties at high temperatures. A shaft hole 12 penetrates the insulator 11 along the axis O. A rear end facing surface 13 having a diameter reduced toward the front end side is formed on the front end side of the inner peripheral surface of the insulator 11 formed by the shaft hole 12. The insulator 11 has a large diameter portion 14 formed at the center in the direction of the axis O. The large-diameter portion 14 is a portion of the insulator 11 having the largest outer diameter. A small-diameter portion 15 having an outer diameter smaller than that of the large-diameter portion 14 is connected to the tip side of the large-diameter portion 14. The outer diameter of the small diameter portion 15 is substantially the same over the entire length of the small diameter portion 15 in the direction of the axis O. A tip portion 16 having an outer diameter smaller than that of the small diameter portion 15 is connected to the tip end side of the small diameter portion 15. A locking portion 17 is formed on the outer peripheral surface of the boundary between the tip portion 16 and the small diameter portion 15 so as to reduce its diameter toward the tip side.

The center electrode 20 is a rod-shaped member in which the head portion 21 is locked to the rear end facing surface 13, and a portion other than the head portion 21 is arranged in the shaft hole 12 closer to the front end than the rear end facing surface 13. There is. In the center electrode 20, a core material having excellent thermal conductivity is embedded in the electrode base material. The electrode base material is formed of an alloy containing Ni as a main component or a metal material containing Ni, and the core member is formed of copper or an alloy containing copper as a main component. It is possible to omit the core material. The center electrode 20 is electrically connected to the terminal fitting 22 in the shaft hole 12.

The terminal fitting 22 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is made of a conductive metal material (for example, low carbon steel). The terminal fitting 22 is fixed to the rear end of the insulator 11 with the front end inserted into the shaft hole 12.

The metal shell 30 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel or the like). The metal shell 30 is connected to the body portion 31 surrounding the tip portion 16 and the small diameter portion 15 of the insulator 11, a seat portion 32 connected to the rear end side of the body portion 31, and a rear end side of the seat portion 32. The connecting portion 33, the tool engaging portion 34 connected to the rear end side of the connecting portion 33, and the rear end portion 35 connected to the rear end side of the tool engaging portion 34 are provided.

The body portion 31 has an external thread 36 formed on the outer peripheral surface that is screwed into a screw hole of an internal combustion engine (not shown), and a shelf portion 37 that projects inward in the radial direction is provided on the inner peripheral surface. ing. The rear end surface 38 of the shelf portion 37 is reduced in diameter toward the front end side. The rear end surface 38 of the shelf portion 37 locks the locking portion 17 of the insulator 11 from the front end side. The inner diameter of the portion of the body portion 31 on the rear end side of the shelf portion 37 is substantially the same from the shelf portion 37 to the rear end of the body portion 31. The inner diameter of the portion of the body portion 31 on the tip side of the shelf portion 37 is smaller than the inner diameter of the portion of the body portion 31 on the rear end side of the shelf portion 37. A packing 39 is interposed between the shelf portion 37 and the locking portion 17. The packing 39 is an annular plate member formed of a metal material such as a mild steel plate that is softer than the metal material forming the metal shell 30.

The seat portion 32 is a portion for closing the gap between the screw hole of the internal combustion engine (not shown) and the male screw 36, and has an outer diameter larger than the outer diameter of the body portion 31. The seat portion 32 surrounds the boundary portion between the small diameter portion 15 and the large diameter portion 14. Since the inner peripheral surface of the seat portion 32 expands toward the rear end side, the thickness of the seat portion 32 in the radial direction gradually decreases toward the rear end side.

The connecting portion 33 is a portion for plastically deforming (bending) and caulking and fixing when the metal shell 30 is assembled to the insulator 11. The connecting portion 33 surrounds the distal end side of the large diameter portion 14. The tool engagement portion 34 is a portion that engages a tool such as a wrench when tightening the screw 36 in a screw hole of an internal combustion engine (not shown). The tool engaging portion 34 surrounds the portion of the insulator 11 on the rear end side of the large diameter portion 14 and the rear end side of the large diameter portion 14. The rear end portion 35 is bent inward in the radial direction and is located on the rear end side of the large diameter portion 14.

A filler 40 such as talc is arranged inside the tool engaging portion 34 and the rear end portion 35 in the radial direction, on the front end side of the rear end portion 35 and on the rear end side of the large diameter portion 14. A portion of the metal shell 30 from the rear end portion 35 to the shelf portion 37 applies a load for pressing the insulator 11 in the direction of the axis O to the large diameter portion 14 and the small diameter portion 15 via the packing 39 and the filling material 40. .. As a result, the metal shell 30 is fixed to the outer peripheral surface of the insulator 11. Since the packing 39 and the filling material 40 are compressed in the axial direction, airtightness can be secured.

The ground electrode 41 is a rod-shaped metal (for example, nickel-based alloy) member connected to the metal shell 30. The tip of the ground electrode 41 faces the center electrode 20 via a gap (spark gap). In the present embodiment, the ground electrode 41 is bent.

The spark plug 10 is manufactured, for example, by the following method. First, the center electrode 20 is inserted into the shaft hole 12 of the insulator 11 and arranged so that the tip of the center electrode 20 is exposed to the outside from the shaft hole 12. Next, the terminal fitting 22 is fixed to the rear end of the insulator 11 while ensuring the continuity between the terminal fitting 22 and the center electrode 20. Next, the insulator 11 is inserted into the metal shell 30 to which the screw 36 is formed on the outer peripheral surface and the ground electrode 41 is pre-bonded, and the connecting portion 33 and the rear end portion 35 are bent to attach the metal shell 30 to the insulator 11. Attach to. Next, the ground electrode 41 is bent so that the tip of the ground electrode 41 faces the center electrode 20, and the spark plug 10 is obtained.

FIG. 2 is a schematic view of forming a screw 36 (see FIG. 1) on the workpiece 50. FIG. 2 shows a sectional view of the workpiece 50 including the axis O. In FIG. 2, the threads of the thread portion 61 of the rolling die 60 are not shown, and the illustration of one side of the rolling die 60 with the axis 62 as a boundary is omitted. In FIG. 2, the inclination of the shaft 62 of the rolling die 60 with respect to the axis O of the workpiece 50 is exaggeratedly illustrated. In the present embodiment, the rolling die 60 is a round die in which the outer shape of the screw portion 61 is columnar.

The workpiece 50 is a material of the metal shell 30, and is integrally made by forging or cutting a single material (for example, low carbon steel or the like). The work piece 50 is a member before the connection portion 33 and the rear end portion 35 are bent and before the screw 36 (see FIG. 1) is formed on the body portion 31, and the cavity 54 is formed inside. ing.

In the workpiece 50, the outer diameter of the body portion 31 in which the screw 36 is formed on the outer peripheral surface 55 is the same over the entire length of the body portion 31 in the axis O direction. The body portion 31 is adjacent to the first portion 51 from which the shelf portion 37 projects from the inner peripheral surface of the body portion 31, the second portion 52 adjacent to the rear end side of the first portion 51, and the tip end side of the first portion 51. It is divided into the third part 53. The inner diameter of the first portion 51 is smaller than the inner diameter of the third portion 53, and the inner diameter of the third portion 53 is smaller than the inner diameter of the second portion 52. Therefore, the geometrical moment of inertia of the first portion 51 is larger than the geometrical moment of inertia of the third portion 53, and the geometrical moment of inertia of the third portion 53 is greater than the geometrical moment of inertia of the second portion 52. In the present embodiment, the total length of the first portion 51 and the third portion 53 in the axis O direction is shorter than the length of the second portion 52 in the axis O direction.

The workpiece 50 has the seat portion 32 adjacent to the rear end side of the second portion 52. In the vicinity of the second portion 52, the outer diameter of the seat portion 32 is larger than the outer diameter of the second portion 52, and the inner diameter of the seat portion 32 is substantially equal to the inner diameter of the second portion 52. The moment of inertia of area of the seat portion 32 is larger than the moment of inertia of area of the second portion 52.

Since the first portion 51 has a larger second moment of area than the second portion 52, it has higher rigidity than the second portion 52. Therefore, the first portion 51 is less likely to be crushed than the second portion 52 even when the rolling force described later acts. The second portion 52 has the same second moment of area over the entire length in the axial direction, but the first portion 51 connected to the second portion 52 has relatively high rigidity. The side closer to the portion 51 is less likely to be crushed.

Here, in the preparation step of manufacturing the metal shell 30 (hollow material), the workpiece 50 that is the material of the metal shell 30 is prepared. The axis 62 of the rolling die 60 is arranged non-parallel to the axis O of the workpiece 50 while being included in a virtual plane including the axis O of the workpiece 50. Specifically, the distance D1 from the outer peripheral surface 55 of the third portion 53 on the first portion 51 side of the workpiece 50 supported by the support blade (not shown) to the screw portion 61 of the rolling die 60 is The rolling die 60 is arranged so as to be shorter than the distance D2 from the outer peripheral surface 55 of the second portion 52 to the screw portion 61 of the rolling die 60.

In the rolling step, the rolling die 60 is moved so that the screw portion 61 of the rolling die 60 is pressed against the third portion 53 of the workpiece 50, and then the rolling die 60 is rolled to the second portion 52 of the workpiece 50. The rolling die 60 is moved in parallel until the screw portion 61 of the forming die 60 is pressed. That is, the screw portion 61 of the rolling die 60 is sequentially pressed against the third portion 53, the first portion 51, and the second portion 52 in this order. As a result, the rolling dies 60, 60 apply a rolling force to the workpiece 50 in accordance with the rotational movement, and form the screw 36 on the outer peripheral surface 55 of the first portion 51, the second portion 52, and the third portion 53. To do.

In this rolling process, a rolling force is applied from the third portion 53, which has higher rigidity than the second portion 52, to the first portion 51 at the initial stage of rising of the thread of the male screw 36. The rolling force at this time is adjusted to such an extent that elastic deformation from the third portion 53 to the first portion 51 is suppressed and a reaction force commensurate with the rolling force is obtained. As described above, the rolling die 60 applies the rolling force from the third portion 53, which has higher rigidity than the second portion 52, to the first portion 51, so that the work piece 50 is elastically deformed at the initial stage of the thread ridge rising. Crushing can be suppressed.

Then, the screw portion 61 of the rolling die 60 is sequentially pressed against the outer peripheral surface 55 of the workpiece 50 in the direction away from the first portion 51, so that the second portion 52 is formed with a screw. By doing so, the rolling force generated when the threaded portion 61 of the rolling die 60 is pressed against the second portion 52 is dispersed to the first portion 51 having higher rigidity than the second portion 52. Therefore, it is possible to prevent the second portion 52 from being excessively crushed by the rolling force. As a result, the reaction force commensurate with even rolling force second part 52 smell is obtained, can be rolling the desired male thread 36 deficiency less to the workpiece 50.

As in the first embodiment, when the male screw 36 is formed in a portion where the second moment of area is different in the axial direction in the portion where the male screw 36 is formed, the portion where the male screw 36 is formed has the highest rigidity. It corresponds to the first part of the claims. Of the portion having lower rigidity than the first portion, the portion where the male screw 36 is mainly formed corresponds to the second portion described in the claims. Therefore, the first part 51 and the second part 52 of the first embodiment correspond to the first part and the second part described in the claims, respectively.

FIG. 3A is a cross-sectional view including the axis O of the hollow material (metal shell 30) in which the male screw 36 is formed by the above method, and FIG. 3B is a cross-sectional view of the hollow material 63 in the comparative example. Is. In FIGS. 3A and 3B, the illustration of the graphic on one side of the axis O as a boundary is omitted. The scale of the partially enlarged views shown in FIGS. 3A and 3B is larger than the actual scale. In the hollow material 63 in the comparative example, the shaft 62 of the rolling die 60 is arranged in parallel with the axis O of the workpiece 50, and then the rolling die 60 is translated so that the first portion 51 of the workpiece 50 can be moved. The thread portion 61 of the rolling die 60 was pressed against the second portion 52 and the third portion 53 at the same time to perform the rolling process.

As shown in FIG. 3B, the hollow member 63 in the comparative example in which the screws 36 are simultaneously formed on the first portion 51, the second portion 52, and the third portion 53 is the first portion 51 and the third portion 53. There was a defect 65 at the top of the mountain 64 of the second portion 52, which has a lower rigidity. It is presumed that this was because the second portion 52 having low rigidity was excessively elastically deformed so as to be crushed, and a reaction force commensurate with the rolling force was not obtained, so that the material flow due to the protrusion of the mountain 64 was insufficient. It The loss 65 of the crest 64 causes damage to the crest of the screw hole of the internal combustion engine (not shown).

On the other hand, as shown in FIG. 3A, a hollow member (metal shell 30) in which a male screw 36 is formed from the first part 51 and the third part 53 having higher rigidity than the second part 52 to the second part 52. Had a complete chevron not only in the first part 51 and the third part 53 but also in the second part 52.

As described above, according to the embodiment, a desired screw can be formed in the second portion 52 corresponding to the cavity 54 of the workpiece 50 having the cavity 54. Further, since the step of accommodating the steel ball group inside the cavity 54 of the workpiece 50 is not required, the step can be simplified.

In the workpiece 50, the first portion 51 is connected to one end side of the second portion 52 in the direction of the axis O, and the thread 36 is attached to the first portion 51 before the second portion 52 by the rolling process. Since it is formed, the desired screw 36 can be formed from the first portion 51 to the second portion 52. Further, the workpiece 50 has the first portion 51, the second portion 52 and the third portion 53 having different moments of inertia in the direction of the axis O, and the screw 36 is formed on the outer peripheral surface 55 thereof. The desired screw 36 can be formed on the workpiece 50 having different cross-sectional shapes in the direction of the axis O.

The rolling die 60 is a round die having a cylindrical outer shape, and since the shaft 62 of the round die is arranged non-parallel to the axis O of the workpiece 50, the rolling die is placed on the side of the first portion 51. By pressing from above to the workpiece 50, the screw 36 can be formed on the second portion 52 in the direction away from the first portion 51. Therefore, the hollow material (metal shell 30) can be manufactured with simple equipment. Since the metal shell 30 of the spark plug 10 has a portion having different rigidity in the direction of the axis O, the above method is suitable.

Next, a second embodiment will be described with reference to FIGS. 4 and 5. In the first embodiment, a case has been described in which the hollow material (metal shell 30) has different sectional moments of inertia in the portion where the male screw 36 is formed (body 31) in the direction of the axis O. On the other hand, in the second embodiment, a hollow material (metal shell 80) in which the second moment of area of the portion (body 81) where the male screw 85 is formed is the same in the direction of the axis O will be described. The same parts as those in the first embodiment are designated by the same reference numerals, and the following description will be omitted.

FIG. 4 is a one-sided cross-sectional view of the spark plug 70 using the hollow material (metal shell 80) according to the second embodiment with the axis O as a boundary. As shown in FIG. 4, in the spark plug 70, a metal shell 80 made of a hollow material holds an insulator 71.

The insulator 71 is a substantially cylindrical member made of alumina or the like, which has excellent insulating properties and mechanical properties at high temperatures. The insulator 71 has a small-diameter portion 72 having an outer diameter smaller than that of the large-diameter portion 14 connected to the front end side of the large-diameter portion 14. The outer diameter of the small diameter portion 72 is substantially the same over the entire length of the small diameter portion 72 in the axis O direction. A tip portion 73 having an outer diameter smaller than that of the small diameter portion 72 is connected to the tip end side of the small diameter portion 72. The outer diameter of the tip portion 73 is reduced toward the tip side.

A ring-shaped heat dissipation member 74 is fixed to the outer peripheral surface of the small diameter portion 72 on the tip side of the boundary between the tip portion 73 and the small diameter portion 72. In the present embodiment, the heat dissipation member 74 is made of metal such as stainless steel and is joined to the small diameter portion 72 by brazing. The means for fixing the heat dissipation member 74 to the insulator 71 is not limited to brazing. A groove or a protrusion may be provided in the insulator 71, and the groove or the protrusion may be used to restrict the movement of the heat dissipation member 74 with respect to the insulator 71 in the direction of the axis O.

The metal shell 80 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel or the like). The metal shell 80 is connected to a body portion 81 surrounding the tip portion 73 and the small diameter portion 72 of the insulator 71, a seat portion 82 connected to the rear end side of the body portion 81, and a rear end side of the seat portion 82. The tool engaging portion 83 and the rear end portion 84 connected to the rear end side of the tool engaging portion 83 are provided.

On the outer peripheral surface of the body portion 81, a male screw 85 to be screwed into a screw hole of an internal combustion engine (not shown) is formed. The inner diameter of the body 81 is the same over the entire length in the direction of the axis O. Since the inner diameter of the body 81 is slightly smaller than the outer diameter of the heat dissipation member 74, the outer peripheral surface of the heat dissipation member 74 joined to the insulator 71 contacts the inner peripheral surface of the body 81.

The seat portion 82 is a portion for closing the gap between the screw hole of the internal combustion engine (not shown) and the male screw 85, and has an outer diameter larger than the outer diameter of the body portion 81. The seat portion 82 surrounds the boundary portion between the small diameter portion 72 and the large diameter portion 14. Since the inner peripheral surface of the seat portion 82 expands toward the rear end side, the thickness of the seat portion 82 in the radial direction gradually decreases toward the rear end side.

The tool engagement portion 83 is a portion that engages a tool such as a wrench when tightening the screw 85 in a screw hole of an internal combustion engine (not shown). The tool engagement portion 83 surrounds the large diameter portion 14 of the insulator 71. The rear end portion 84 is bent inward in the radial direction and is located on the rear end side of the large diameter portion 14. The large-diameter portion 14 of the insulator 71 interferes with the rear end portion 84, and movement of the metal shell 80 toward the rear end of the insulator 71 is restricted. A packing 86 is interposed between the seat portion 82 and the large diameter portion 14. The packing 86 is an annular plate member formed of a metal material such as a mild steel plate that is softer than the metal material forming the metal shell 80.

Since the heat dissipation member 74 fixed to the insulator 71 contacts the inner peripheral surface of the body 81 of the metal shell 80, heat conduction from the insulator 71 to the metal shell 80 can be ensured via the heat dissipation member 74. Since the packing 86 is in close contact with the seat portion 82 and the large diameter portion 14, airtightness can be secured. Note that the packing 86 can be omitted. Even if the packing 86 is omitted, the heat radiation member 74 can ensure airtightness.

The spark plug 70 is manufactured by the following method, for example. First, the heat dissipation member 74 is fixed to the insulator 71. Next, the center electrode 20 is inserted into the shaft hole 12 of the insulator 71 and arranged so that the tip of the center electrode 20 is exposed to the outside from the shaft hole 12. Next, the terminal fitting 22 is fixed to the rear end of the insulator 71 while ensuring the electrical connection between the terminal fitting 22 and the center electrode 20. Next, the insulator 71 is inserted into the metal shell 80 to which the screw 85 is formed on the outer peripheral surface and the ground electrode 41 is previously joined, and the rear end portion 84 is bent to assemble the metal shell 80 to the insulator 71. Next, the ground electrode 41 is bent so that the tip of the ground electrode 41 faces the center electrode 20, and the spark plug 70 is obtained.

FIG. 5 is a schematic view of forming a screw 85 (see FIG. 4) on the outer peripheral surface 95 of the workpiece 90. FIG. 5 shows a cross-sectional view of the workpiece 90 including the axis O. In FIG. 5, the threads of the thread portion 101 of the rolling die 100 are not shown, and the illustration of one side of the rolling die 100 with the shaft 102 as a boundary is omitted. In FIG. 5, the external inclination of the thread portion 101 of the rolling die 100 with respect to the axis O of the workpiece 90 is exaggeratedly illustrated. In the present embodiment, the rolling die 100 is a round die in which the outer shape of the screw portion 101 is a conical taper shape.

The workpiece 90 is a material of the metallic shell 80, and is integrally made by forging or cutting a single material (for example, low carbon steel). The workpiece 90 is a member before the rear end 84 is bent and before the screw 85 (see FIG. 4) is formed on the body 81, and the cavity 94 is formed inside.

In the workpiece 90, the outer diameter and the inner diameter of the body portion 81 in which the screw 85 is formed on the outer peripheral surface 95 are the same over the entire length of the body portion 81 in the axis O direction. The portion of the workpiece 90 from the body portion 81 to the seat portion 82 of the metal shell 80 (see FIG. 4) includes a first portion 91 corresponding to the seat portion 82 and a second portion 92 corresponding to the body portion 81. Is divided into The first portion 91 is adjacent to the rear end side of the second portion 92. In the vicinity of the second portion 92, the outer diameter of the first portion 91 is larger than the outer diameter of the second portion 92, and the inner diameter of the first portion 91 is substantially equal to the inner diameter of the second portion 92. The moment of inertia of area of the first portion 91 in the vicinity is larger than the moment of inertia of area of the second portion 92.

Since the first portion 91 has a larger second moment of area than the second portion 92, it has higher rigidity than the second portion 92. The second portion 92 has the same second moment of area over the entire length in the axial direction, but the rigidity of the connecting first portion 91 is relatively high. Therefore, even if a rolling force, which will be described later, acts on the second portion 92. 92 is less likely to be crushed toward the first portion 91 side.

Here, in the preparation step of manufacturing the metal shell 80 (hollow material), a workpiece 90 that is a material of the metal shell 80 is prepared. In a cross section including the axis O of the workpiece 90, the outer shape of the screw portion 101 of the rolling die 100 is arranged non-parallel to the axis O of the workpiece 90. Specifically, the distance D1 from the outer peripheral surface 95 of the second portion 92 of the workpiece 90 supported by the supporting blade (not shown) on the side closer to the first portion 91 to the threaded portion 101 of the rolling die 100. However, the rolling die 100 is arranged so as to be shorter than the distance D2 from the outer peripheral surface 95 of the second portion 92 on the side far from the first portion 91 to the screw portion 101 of the rolling die 100.

In the rolling process, the threading die 101 of the rolling die 100 is pressed against the second portion 92 of the workpiece 90 on the side close to the first portion 91 (hereinafter referred to as "rear end side"). After moving 100, the rolling die until the screw portion 101 of the rolling die 100 is pressed against the second portion 92 of the workpiece 90 on the side farther from the first portion 91 (hereinafter referred to as the “tip side”). Translate 100. That is, the threaded portion 101 of the rolling die 100 is sequentially pressed against the second portion 92 from the first portion 91 side (rear end side) in the direction away from the first portion 91 (front end side). As a result, the rolling dies 100, 100 apply a rolling force to the workpiece 90 in accordance with the rotational movement, and the outer peripheral surface 95 of the body portion 81 is provided with the first portion 91 (the rear end side) from the first portion 91. The screw 85 is formed on the second portion 92 in the direction away from 91 (the tip side).

In this rolling process, a rolling force is applied to the rear end side of the second portion 92 adjacent to the first portion 91 having a rigidity higher than that of the second portion 92 in the initial stage of rising of the thread of the male screw 85. The rolling force at this time is adjusted to such an extent that elastic deformation on the rear end side of the second portion 92 is suppressed and a reaction force commensurate with the rolling force is obtained. As described above, the rolling die 100 first applies a rolling force to a portion adjacent to the first portion 91 having a rigidity higher than that of the second portion 92, so that the elastic deformation of the workpiece 90 in the initial stage of the thread ridge rises. It is possible to suppress crushing due to.

Next, the rolling die 100 sequentially presses the threaded portion 101 of the rolling die 100 against the outer peripheral surface 95 of the workpiece 90 in a direction away from the first portion 91, thereby forming a screw on the second portion 92. To be done. By doing so, the rolling force generated when the threaded portion 101 of the rolling die 100 is pressed against the second portion 92 is dispersed to the side of the first portion 91 having higher rigidity than the second portion 92. .. Therefore, it is possible to prevent the second portion 92 from being excessively crushed. As a result, a reaction force commensurate with the rolling force is obtained in the second portion 92 as well, so that the desired screw 85 with few defects can be rolled on the workpiece 90.

In the workpiece 90, the first portion 91 is connected to one end side (rear end side) of the second portion 92 in the axis O direction, and the first portion 91 having high rigidity is adjacent to the second portion 92 by the rolling process. Since the screw 85 is formed from the rear end side to the front end side of the portion 92, the desired screw 85 can be formed over the entire length of the second portion 92. Further, the workpiece 90 has the first portion 91 and the second portion 92 having different moments of inertia in the direction of the axis O, and the screw 85 is formed on the outer peripheral surface 95 of the second portion 92. The desired screw 85 can be formed on the workpiece 90 having a different cross-sectional shape in the O direction.

The rolling die 100 is a circular die whose outer shape is a conical taper shape, and since the outer shape of the thread portion 101 of the round die is arranged non-parallel to the axis O of the workpiece 90, the round die is By pressing the workpiece 90 from the rear end side of the second portion 92, the screw 85 can be formed on the second portion 92 in the direction away from the first portion 91. Therefore, the hollow material (metal shell 80) can be manufactured with simple equipment. Since the metal shell 80 of the spark plug 70 has a portion having different rigidity in the direction of the axis O, the above method is preferable.

When the second moment of area is the same over the entire length in the axial direction in the portion where the male screw 85 is formed as in the second embodiment, the portion where the male screw 85 is formed falls within the scope of the claims. It corresponds to Part 2 of the description. A portion that is arranged at the end of the second portion in the axial direction and has higher rigidity than the second portion corresponds to the first portion described in the claims. Therefore, the first portion 91 and the second portion 92 of the second embodiment correspond to the first portion and the second portion described in the claims, respectively.

In addition to the first portion 91 on the rear end side of the second portion 92 described in the second embodiment, a portion having higher rigidity than the second portion 92 on the tip end side of the second portion 92 (hereinafter referred to as “high rigidity portion”). , The first part 91 or the high-rigidity part can be the first part described in the claims. Which of the first portion 91 and the high-rigidity portion is the first portion described in the claims can be appropriately set. For example, considering the difficulty of collapsing against the rolling force at both ends of the second portion 92 in the axial direction, the side that is less likely to be collapsible may be the first portion.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and various improvements and modifications can be easily made without departing from the spirit of the present invention. Can be inferred.

In the embodiment, the case where the round dies are used as the rolling dies 60 and 100 has been described, but the rolling dies are not limited to this, and it is naturally possible to use other rolling dies. Examples of other rolling dies include a flat die, a rotary type rolling die in which a segment die and a roller die are combined, and a rack type rolling die.

In the embodiment, the workpieces 50 and 90 have different sectional shapes in the direction of the axis O, and the workpieces 50 and 90 are provided with the first portions 51 and 91 and the second portions 52 and 92 having different moments of inertia. The case was explained. However, it is not necessarily limited to this. Instead of making the workpieces 50 and 90 from a single material, it is naturally possible to manufacture a workpiece by joining a plurality of materials having different Young's moduli in the direction of the axis O. By making the part made of a material with a large Young's modulus the first part and the part made of a material with a smaller Young's modulus the second part, the rigidity of the first part is higher than that of the second part. However, the bending of the first portion when the rolling force is applied can be made smaller than the bending of the second portion.

In the embodiment, the metal shells 30 and 80 of the spark plugs 10 and 70 are given as an example of the hollow material, but the hollow material is not necessarily limited thereto. Examples of hollow materials other than the metal shell of the spark plug include hollow bolts having cavities, pipes formed with male threads, and the like.

In the embodiment, the case where the cavities 54 and 94 are opened at both ends of the workpieces 50 and 90 in the axis O direction has been described, but the present invention is not limited to this. When the blind hole that does not pass through opens in only one side of the workpiece in the direction of the axis O, the blind hole is a cavity. In this case as well, similar to the above embodiment, a desired screw can be formed on the outer peripheral surface of the workpiece corresponding to the cavity formed of the blind hole. Further, it is naturally possible to extend the screw to the outer peripheral surface of the workpiece corresponding to the portion other than the cavity.

Although the case where the filler 40 is interposed between the large diameter portion 14 of the insulator 11 and the rear end portion 35 of the metal shell 30 has been described in the first embodiment, the present invention is not limited to this. It is of course possible to omit the filler 40 and bring the rear end portion 35 of the metal shell 30 into contact with the large diameter portion 14 of the insulator 11. Similarly, in the second embodiment, it is naturally possible to interpose the filler 40 between the large diameter portion 14 of the insulator 11 and the rear end portion 84 of the metal shell 80.

In the first embodiment, a case has been described in which the first portion 51 and the third portion 53 having different moments of inertia are formed on the tip side of the second portion 52 of the workpiece 50, but the present invention is not limited to this. It is not something that can be done. For example, it is naturally possible to make the inner diameter of the third portion 53 the same as the inner diameter of the first portion 51, extend the first portion 51 to the tip of the workpiece 50, and omit the third portion 53.

In the first embodiment, a case has been described in which the geometrical moment of inertia of the third portion 53 of the workpiece 50 is made larger than the geometrical moment of inertia of the second portion 52, but the invention is not necessarily limited to this. For example, the geometrical moment of inertia of the third portion 53 may be the same as the geometrical moment of inertia of the second portion 52, or the geometrical moment of inertia of the third portion 53 may be smaller than the geometrical moment of inertia of the second portion 52. It is of course possible to do so.

10,70 Spark plug 30,80 Metal shell (hollow material)
36,85 Male thread 50,90 Work piece 51,91 First part 52,92 Second part 54,94 Cavity 55,95 Outer peripheral surface 60,100 Rolling die (round die)
61, 101 screw part 62, 102 axis D1, D2 distance O axis

Claims (7)

A method of manufacturing a hollow material having a hollow inside, wherein at least a part of the male screw is formed on an outer peripheral surface corresponding to the hollow,
Preparation for Preparing a Hollow Workpiece Having at least Two Different Stiffness Portions in the Axial Direction, a Second Part Having the Cavity Inside and a First Part Having a Rigidity Higher Than the Second Part Process,
A rolling step of pressing the threaded portion of the rolling die to the outer peripheral surface of the workpiece to form the male thread,
In the rolling step, the workpiece is processed such that the distance from the outer peripheral surface on the first portion side to the threaded portion is shorter than the distance from the outer peripheral surface on the second portion to the threaded portion. And the rolling die, the rolling die is moved in parallel toward the workpiece until the screw portion is pressed against the outer peripheral surface of the second portion, and the first portion is moved. by successively pressing the pre Symbol root Ji portion from the side to Kigai periphery Previous toward a direction away from the first part of the method of manufacturing a hollow member that forms the external thread on the second part. The first portion is connected to one end side of the second portion in the direction of the axis,
The method for manufacturing a hollow member according to claim 1, wherein the rolling step includes a step of forming a screw on the first portion before the second portion. The method for manufacturing a hollow member according to claim 1, wherein the workpiece has a portion having a different moment of inertia in the direction of the axis. The method for manufacturing a hollow member according to claim 3, wherein the workpiece has a portion having a second moment of area that differs in a direction of the axis in a portion where the male screw is formed. The rolling die is a round die whose outer shape is a cylindrical shape,
Manufacturing method of the round die of the shaft hollow member according to any one of the four claims 1, which is non-parallel disposed with respect to said axis. The rolling die method of producing a hollow member according to any one of claims 1 contour is round die forms a conical taper 4. It said hollow member is a manufacturing method of a hollow member according to claim 1 which is a metal shell of the spark plug 6.

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