JP2019185868A - Manufacturing method for spark plug - Google Patents

Abstract

To provide a manufacturing method for a spark plug capable of reducing variations in an axial distance from a flange part to a male thread.SOLUTION: In a movement process, while maintaining a relationship between a reference position in a circumferential direction of a workpiece including a cylindrical part and a flange part and a reference position of a die, while bringing an end face of the die connected to a screw part into contact with a workpiece reference surface, the die is moved until the screw part of the die is pressed against the cylindrical part. The end face of the die includes at least a first part adjacent to the screw part and a second part adjacent to the first part. An angle θ1 formed by a reference plane perpendicular to the axis of the cylindrical part and the first part is larger than an angle θ2 formed by the reference plane and the second part. The angle θ2 is equal to or smaller than an angle θ3 formed by the reference plane and a workpiece reference plane.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing a spark plug, and more particularly to a method for manufacturing a spark plug in which a male thread is formed by rolling.

  The metal shell that insulates and holds the center electrode of the spark plug has a screw formed in a cylindrical portion provided with a flange portion. The spark plug is attached to the engine by engaging a male screw of a cylindrical portion with a screw hole of the engine. The buttocks regulate the amount of screwing into the engine. The spark plug creates a flame kernel in a spark gap between the ground electrode and the center electrode joined to the cylindrical portion. In order to grow the flame kernel, the spark plug is preferably attached to the engine so that the ground electrode does not inhibit the airflow in the combustion chamber generated in the compression stroke, which is the stage before ignition.

  By the way, when the metal shell is screwed into the engine, the cylindrical portion advances in the axial direction while rotating around the shaft along the screw winding until it is regulated by the flange portion. The position of the ground electrode in the circumferential direction of the cylindrical portion is determined when the flange portion restricts the movement of the male screw in the axial direction. Therefore, the position of the ground electrode in the circumferential direction of the tube portion depends on the circumferential distance between the helical winding of the male screw and the ground electrode, and the axial distance from the flange portion to the screw thread of the male screw.

  In Patent Document 1, in a technique of rolling a screw using a die to a cylindrical portion of a workpiece to which a ground electrode is bonded, a positioning member is interposed between an end surface of the die and a flange portion of the workpiece, A technique is disclosed in which rolling is performed after a positioning member is brought into contact with the end face of the die in a state where the rotation angle of the die is fixed, and the axial relative position between the die and the workpiece is set.

JP 2010-129520 A

  However, in the technique disclosed in Patent Document 1, if a foreign matter such as cutting powder is caught between the positioning member and the collar portion, the thread is displaced in the axial direction by the size of the foreign matter. The variation in the axial distance from the flange of the metal fitting to the thread is increased.

  The present invention has been made to solve this problem, and an object of the present invention is to provide a spark plug manufacturing method capable of reducing variations in the axial distance from the flange portion of the metal shell to the thread.

  In order to achieve this object, the present invention is a main body comprising a cylindrical tube portion extending from the front end side to the rear end side, and a hook portion projecting in a hook shape from the rear end side of the tube portion to the outside in the radial direction. A spark plug manufacturing method comprising: a metal fitting; a ground electrode connected to the tip of a cylindrical portion; and a center electrode insulated and held inside the metal shell and opposed to the ground electrode via a spark gap. In the moving step, the die is moved until the screw portion of the die is pressed against the cylindrical portion while maintaining the relationship between the reference position in the circumferential direction of the workpiece including the cylindrical portion and the flange portion and the reference position of the die. In the moving process, the die is moved while bringing the end surface of the die communicating with the screw portion into contact with the workpiece reference surface on the tip side of the flange portion of the workpiece. In the rolling process, the screw is rolled onto the cylinder portion by a die that presses the screw portion against the cylinder portion. The end face of the die includes at least a first part adjacent to the screw part and a second part adjacent to the first part, and an angle θ1 formed by a reference plane perpendicular to the axis of the cylinder part and the first part is The angle θ2 is larger than the angle θ2 formed by the reference plane and the second part, and the angle θ2 is less than or equal to the angle θ3 formed by the reference plane and the workpiece reference plane.

  According to the spark plug manufacturing method of the first aspect, in the moving step, the die is moved until the screw portion of the die is pressed against the cylinder portion of the workpiece while the end surface of the die is in contact with the workpiece reference surface. The end face of the die has an angle θ1 formed by the first part adjacent to the screw part and the reference plane larger than an angle θ2 formed by the second part adjacent to the first part and the reference plane, and the angle θ2 is set between the reference plane and the workpiece. The angle formed with the reference plane is equal to or smaller than θ3. As a result, even if foreign matter adheres to the end surface of the die or the workpiece reference surface, the foreign material is pushed away by the second portion while preventing the interference between the first portion and the workpiece reference surface in the moving process, and the end surface of the die is used as the workpiece reference. It can be easily adhered to the surface. Therefore, variation in the axial distance from the buttocks to the thread can be reduced.

  According to the spark plug manufacturing method of the second aspect, in the moving step, after the first part of the die is brought into contact with the first corner, the second part of the die is brought into contact with the workpiece reference surface. Since the workpiece is rounded at the first corner where the side surface of the flange portion intersects the workpiece reference surface, in addition to the effect of claim 1, the first corner of the workpiece damages the first portion of the die in the moving process. It can be difficult.

  According to the spark plug manufacturing method of the third aspect, since the angle θ2 is equal to the angle θ3, the contact area between the workpiece reference surface and the second part can be increased. Therefore, in addition to the effect of Claim 1 or 2, the posture of the workpiece in the rolling process can be stabilized.

  According to the spark plug manufacturing method of claim 4, since the second corner where the first part and the second part intersect is rounded, in addition to the effect of any one of claims 1 to 3, the movement In the process, the second corner of the die can hardly damage the workpiece reference surface.

It is a half sectional view of a spark plug. It is a side view of the workpiece moved between dies. (A) is a cross-sectional view of the work and dice in the initial stage of the moving process, (b) is a cross-sectional view of the work and dice in the middle stage of the moving process, and (c) is a cross-sectional view of the work and dice in the final stage of the moving process. It is sectional drawing of dice | dies.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a sectional side view of a spark plug 10 with an axis O as a boundary. In FIG. 1, the lower side of the drawing is referred to as the front end side of the spark plug 10, and the upper side of the drawing is referred to as the rear end side of the spark plug 10.

  As shown in FIG. 1, the spark plug 10 includes an insulator 11, a center electrode 13, a metal shell 15, and a ground electrode 22. The insulator 11 is a substantially cylindrical member formed of alumina or the like that is excellent in insulation at high temperatures and mechanical properties. The insulator 11 passes through the shaft hole 12 along the axis O.

  The center electrode 13 is a rod-shaped electrode that is inserted into the shaft hole 12 and held by the insulator 11 along the axis O. The center electrode 13 is disposed in the shaft hole 12 so as to protrude from the tip of the insulator 11. The center electrode 13 has a core material excellent in thermal conductivity embedded in the electrode base material. The electrode base material is made of an alloy mainly composed of Ni or a metal material made of Ni, and the core material is made of copper or an alloy mainly composed of copper.

  The terminal fitting 14 is a rod-like member to which a high voltage cable (not shown) is connected, and the distal end side is disposed in the insulator 11. The terminal fitting 14 is electrically connected to the center electrode 13 in the shaft hole 12. A metal shell 15 is fixed to the distal end side of the outer periphery of the insulator 11 with a space in the direction of the axis O from the terminal metal fixture 14.

  The metal shell 15 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel). The metal shell 15 includes a cylindrical portion 16 that is formed in a cylindrical shape, a flange portion 18 that projects in a hook shape in a direction perpendicular to the axis perpendicular to the axial direction of the cylindrical portion 16, and a shaft of the cylindrical portion 16 that sandwiches the flange portion 18. And a rear end portion 19 connected to the opposite side of the direction. The rear end portion 19 includes a thin portion 20 that is thinner than the flange portion 18, and a tool engagement portion 21 that protrudes radially outward from the thin portion 20.

  The cylinder part 16 is a part surrounding the portion on the tip side of the insulator 11, and a screw 17 is formed on the outer periphery. The male screw 17 engages with the screw hole 25 of the engine 24 to fix the metal shell 15 to the engine 24. The flange portion 18 is a portion for restricting the screwing amount of the male screw 17 into the engine 24 and closing the gap between the male screw 17 and the screw hole 25. In the present embodiment, a gasket 23 is attached between the flange portion 18 and the cylindrical portion 16. A gasket 23 sandwiched between the flange 18 and the engine 24 seals the gap between the male screw 17 and the screw hole 25.

  The thin portion 20 is a portion for plastic deformation and caulking and fixing when the metal shell 15 is assembled to the insulator 11. The tool engaging portion 21 is a portion that engages a tool such as a wrench when the screw 17 is screwed into the screw hole 25 of the engine 24.

  The ground electrode 22 is a rod-shaped metal member (for example, a nickel-base alloy) that is joined to the cylindrical portion 16 of the metal shell 15. A spark gap is formed between the ground electrode 22 and the center electrode 13. In the present embodiment, the ground electrode 22 is bent.

  The spark plug 10 is manufactured by the following method, for example. First, the metal shell 15 is obtained by processing the workpiece 30 (see FIG. 2). The workpiece 30 has a ground electrode 22 (a straight bar before bending) joined to a cylindrical portion 16 formed by cold forging, cutting, or the like. After the screw 17 is rolled on the cylindrical portion 16 of the work 30 by the die 41 (see FIG. 2), plating or the like is performed to obtain the metal shell 15.

  Separately, the center electrode 13 is inserted into the shaft hole 12 of the insulator 11, and the tip of the center electrode 13 is disposed so as to be exposed to the outside from the shaft hole 12. Next, the terminal fitting 14 is inserted into the shaft hole 12 of the insulator 11, and conduction between the terminal fitting 14 and the center electrode 13 is ensured. Next, the insulator 11 is inserted into the metal shell 15, the rear end of the metal shell 15 is bent, and the metal shell 15 is assembled to the insulator 11. The spark plug 10 is obtained by bending the ground electrode 22 and attaching the gasket 23.

  When the metal shell 15 of the obtained spark plug 10 is screwed into the screw hole 25 of the engine 24, the metal shell 15 is disposed along the screw winding until the gasket 23 disposed in the cylinder portion 16 is in close contact with the engine 24. 15 advances in the axial direction while rotating about the axis O. The position of the ground electrode 22 in the circumferential direction of the metal shell 15 attached to the engine 24 is determined when the flange portion 18 and the gasket 23 restrict the movement of the male screw 17 in the axial direction.

  When a high voltage is applied to the terminal fitting 14, the spark plug 10 attached to the engine 24 generates a spark discharge between the ground electrode 22 and the center electrode 13 to create a flame kernel. In order to grow the flame kernel and make it easy to ignite the air-fuel mixture, it is preferable that the ground electrode 22 does not inhibit the airflow generated in the compression stroke, which is the stage before ignition.

  If the variation in the thickness of the gasket 23 is sufficiently small, the position of the ground electrode 22 in the circumferential direction with respect to the center electrode 13 (axis O) when the spark plug 10 is attached to the engine 24 is It depends on the axial and circumferential positions of the helical winding of the external thread 17 with respect to the workpiece reference plane 31 (see FIG. 2). If the position of the helical winding in the axial direction of the cylindrical portion 16 varies, the circumferential position of the ground electrode 22 with respect to the center electrode 13 varies. For example, when the pitch of the male screw 17 is 1.00 mm and the helical winding of the male screw 17 is displaced by about 28 μm in the axial direction, the position of the ground electrode 22 is the axis O when the tightening torque of the male screw 17 is constant. 10 ° off around

  Therefore, in order to improve the accuracy of the position of the ground electrode 22 (angle around the axis O) with respect to the center electrode 13 of the spark plug 10 attached to the engine 24 and to improve the stability of ignition of the air-fuel mixture, It is necessary to determine the position accuracy in the axial direction after determining the position in the circumferential direction of the helical winding of the screw 17.

  With reference to FIG.2 and FIG.3, the method to roll the screw | thread 17 to the workpiece | work 30 using the die | dye 41 is demonstrated. FIG. 2 is a side view of the workpiece 30 moved between the dies 41. In the present embodiment, the die 41 is a round die, and three dice 41 are arranged. In FIG. 2, a part of two dies 41 facing the work 30 (a part of the dies 41) out of the three dies 41 in total is schematically illustrated.

  As shown in FIG. 2, the workpiece 30 is connected to the cylindrical portion 16, the flange portion 18, and the rear end portion 19 along the axis O from the front end side toward the rear end side. The thin portion 20 and the ground electrode 22 of the workpiece 30 are in a straight state before bending. A ground electrode 22 is joined to the tip of the cylindrical portion 16. The ground electrode 22 is disposed on a straight line passing through an alignment mark (not shown) such as a punch mark attached to the cylindrical portion 16 and parallel to the axis O.

  The workpiece 30 is rounded at a first corner 33 where a workpiece reference surface 31 facing the distal end side of the flange portion 18 and a side surface 32 of the flange portion 18 intersect. In the present embodiment, a part of the side surface 32 is tapered (a part of the side surface 32 is formed in a conical shape), but is not necessarily limited thereto. Of course, the entire side surface 32 of the flange 18 can be a cylindrical side surface. Note that the outer diameter of the connecting portion 34 that connects the workpiece reference surface 31 and the cylindrical portion 16 is smaller than the outer diameter of the cylindrical portion 16. The gasket 23 (see FIG. 1) is disposed on the workpiece reference surface 31.

  The work holder 40 is a member that holds the work 30, and includes a collet chuck, a mandrel type stopper, and the like on the tip side. The work holder 40 is inserted along the axis O from the front end side of the work holder 40 toward the front end side of the work 30 from the rear end side of the work 30. The work holder 40 allows rotation of the held work 30 around the axis O and movement of the work 30 to the rear end side (upper side in FIG. 2). The work holder 40 reciprocates between a work supply device (not shown) such as a parts feeder and the die 41 by an actuator (not shown).

  The work holder 40 is provided with a spring (not shown). When a force to the rear end side of the axis line O is applied to the work 30 with the work holder 40 holding the work 30, the spring has its own elastic force on the work piece 30 on the front end side of the axis O (lower side in FIG. 2). The position of the workpiece 30 in the axial direction is restored.

  In the die 41, the central axis (not shown) of the die 41 and the screw portion 42 are arranged along the axis O of the workpiece 30 held by the workpiece holder 40. The end surface 43 of the die 41 faces the rear end side in the axial direction of the workpiece 30. The die 41 is reciprocated in a direction perpendicular to the axis O of the workpiece 30 by an actuator (not shown), and further rotates around the central axis of the die 41. The control device (not shown) stores the rotation angle of an arbitrary reference point on the die 41 and operates the actuator so that the arbitrary reference point on the die 41 is positioned at a predetermined rotation angle (hereinafter, “ It can be set to “the reference position of the die”.

  The end face 43 of the die 41 includes a first part 44 adjacent to the screw part 42 and a second part 45 adjacent to the first part 44. The first part 44 and the second part 45 are annular surfaces. The second corner 46 where the first part 44 and the second part 45 intersect is rounded. An angle θ1 (acute angle side) formed by the reference plane 47 perpendicular to the axis O and the first portion 44 is larger than an angle θ2 (acute angle side) formed by the reference plane 47 and the second portion 45. Further, the angle θ2 is equal to or smaller than the angle θ3 (acute angle side) formed by the reference plane 47 and the workpiece reference plane 31. In this embodiment, θ2 = θ3.

  The length in the radial direction of the first portion 44 in the direction perpendicular to the axis O (the distance from the screw portion 42 to the second corner 46) is the length in the radial direction of the workpiece reference surface 31 in the direction perpendicular to the axis O. Shorter than that. The radial length (creeping distance) of the second part 45 is shorter than the radial length (creeping distance) of the workpiece reference surface 31. The length in the radial direction from the first portion 44 to the second portion 45 in the direction perpendicular to the axis O is equal to or greater than the length in the radial direction of the workpiece reference surface 31 in the direction perpendicular to the axis O. This is because the workpiece reference surface 31 and the second portion 45 are overlapped in the moving process in which the die 41 approaches the workpiece 30 for rolling.

  3A is a cross-sectional view of the work 30 and the die 41 in the initial stage of the moving process in which the die 41 approaches the work 30 for rolling, and FIG. 3B is a cross-sectional view of the work 30 and the medium 30 in the middle stage of the moving process. FIG. 3C is a cross-sectional view of the die 41, and FIG. 3C is a cross-sectional view of the work 30 and the die 41 at the final stage of the moving process. In FIG. 3B and FIG. 3C, the illustration of the nozzle 48 is omitted.

  The workpiece 30 is aligned in a state where the circumferential position of the ground electrode 22 with respect to the cylindrical portion 16 is aligned (hereinafter referred to as “the circumferential reference position of the workpiece”) by a workpiece feeder (not shown) such as a parts feeder. Is done. The workpiece holder 40 holds the workpiece 30, maintains the reference position in the circumferential direction of the workpiece 30 with respect to the die 41, and inserts the cylindrical portion 16 between the dies 41 as shown in FIG.

  At this time, the work holder 40 holds the work 30 so that the work reference surface 31 is positioned on the tip end side (lower side in FIG. 3A) in the axial direction with respect to the second portion 45 of the die 41. In other words, the first corner 33 of the workpiece 30 is located on the tip end side in the axial direction with respect to the second corner 46 of the die 41. The dice 41 at this time is set to a state where an arbitrary reference point on the die 41 is positioned at a predetermined rotation angle (a reference position of the dice 41) by a control device (not shown).

  In the moving process, the three dies 41 in the direction perpendicular to the axis O of the workpiece 30 are maintained in a state where the relationship between the reference position in the circumferential direction of the workpiece 30 and the reference position of the die 41 is maintained (without rotating the die 41). Moves and the die 41 approaches the workpiece 30. The nozzles 48 arranged toward the end face 43 of each die 41 discharge the formed oil. The rolling oil discharged from the nozzle 48 flows through the first portion 44 and the second portion 45 of the die 41 and then flows down to the screw portion 42.

  As shown in FIG. 3B, in the die 41 approaching the work 30, the first portion 44 first hits the first corner 33 of the work 30. Since the first corner 33 is rounded, the first corner 33 can hardly damage the first portion 44 of the die 41.

  Since the workpiece 30 and the die 41 have a relationship of θ2 ≦ θ3 (see FIG. 2) and θ2 <θ1, the first portion 44 does not interfere with the workpiece reference surface 31, and the die 41 has the first angle 33 of the workpiece 30. The first part 44 approaches the work 30 while rubbing. The workpiece 30 whose first corner 33 is pushed by the first portion 44 of the die 41 moves to the rear end side (upper side in FIG. 3B) of the axis O. The work holder 40 applies a force toward the tip side (lower side in FIG. 3B) to the work 30 by a restoring force of a spring (not shown), and the first corner 33 of the work 30 is moved to the first part of the die 41. 44.

  As shown in FIG. 3C, when the second corner 46 of the die 41 exceeds the first corner 33 of the workpiece 30 and approaches the workpiece 30, the second portion 45 of the die 41 is moved to the tip side of the workpiece reference surface 31 ( Enter the lower side of FIG. Since the second corner 46 where the first portion 44 and the second portion 45 intersect is rounded, the second corner 46 of the die 41 can hardly damage the workpiece reference surface 31.

  Since the workpiece 30 and the die 41 are in a relationship of θ2 ≦ θ3 (see FIG. 2), even if foreign matter such as chips adheres to the second portion 45 or the workpiece reference surface 31, the second portion 45 pushes away the foreign matter. Easy to do. The rolling oil flowing from the second part 45 to the first part 44 wets the foreign matter between the second part 45 and the workpiece reference surface 31 to make it easy to push away the foreign matter, and further wash away the foreign matter pushed away by the second part 45. , Preventing reattachment of foreign matter to the work 30.

  The die 41 moves until the screw portion 42 contacts (bits into) the cylindrical portion 16 while the second portion 45 enters the distal end side (the lower side in FIG. 3C) of the workpiece reference surface 31. The work holder 40 applies a force toward the tip side (the lower side in FIG. 3C) to the work 30 by a restoring force of a spring (not shown), so that foreign matter adheres to the second portion 45 and the work reference surface 31. Even if this is done, the foreign matter can be pushed away to make it difficult to bite the foreign matter between the second portion 45 and the workpiece reference surface 31. The axial force that the spring applies to the workpiece 30 can be adjusted by the elastic force of the spring.

  In the rolling process, the die 41 is rotated by a preset rotation angle so that the predetermined male screw 17 is formed in a state where the screw portion 42 of the die 41 is pressed against the cylindrical portion 16. The die 41 stops rotating and then moves in a direction perpendicular to the axis O so as to move away from the workpiece 30. As a result, the predetermined male screw 17 is formed on the workpiece 30.

  As described above, even if foreign matter adheres to the second part 45 of the die 41 or the workpiece reference surface 31, the second part 45 of the die 41 pushes away the foreign matter when the die 41 approaches the work 30. The two portions 45 can be easily brought into close contact with the workpiece reference surface 31. As a result, the variation in the distance from the rear end of the screw portion 42 pressed against the cylindrical portion 16 to the workpiece reference surface 31 due to the biting of foreign matter between the second portion 45 and the workpiece reference surface 31 can be made difficult to occur. . Therefore, variation in the axial distance from the workpiece reference surface 31 to the thread of the external thread 17 can be reduced.

  When the die 41 approaches the workpiece 30, the second portion 45 of the die 41 pushes away the foreign matter and causes the screw portion 42 of the die 41 to bite into the workpiece 30 as it is, so that the time required for a series of a plurality of processes does not increase. it can. Therefore, the processing speed of the external thread 17 can be increased. Moreover, since the external thread 17 is rolled by three round dies (die 41), the deformation generated in the cylindrical portion 16 at the time of rolling is suppressed as compared with the case where the thread is rolled using two round dies. Easy to do.

  Since the workpiece 30 and the die 41 have a relationship of θ2 = θ3 (see FIG. 2), the contact area between the workpiece reference surface 31 and the second portion 45 can be increased, and the posture of the workpiece 30 in the rolling process can be stabilized. . As a result, variations in the shape of the thread of the external thread 17 can be made difficult to occur.

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

  In the embodiment, the case where the work holder 40 permits the rotation of the work 30 that rotates with the rotation of the die 41 has been described, but the present invention is not necessarily limited thereto. A mechanism for rotating the workpiece 30 held by the workpiece holder 40 is provided, and the screw 17 can be rolled by rotating the workpiece 30 in a direction opposite to the rotation direction of the die 41 in synchronization with the rotation of the die 41. It is.

  In the embodiment, the case where three round dies are used as the die 41 has been described. However, the present invention is not necessarily limited to this. The number of dies 41 can be set as appropriate.

DESCRIPTION OF SYMBOLS 10 Spark plug 13 Center electrode 15 Main metal fitting 16 Cylindrical part 17 Male thread 18 Girth part 22 Ground electrode 30 Work piece 31 Work reference plane 32 Side face of collar part 33 First angle 41 Die 42 Screw part 43 End face 44 First part 45 Second Part 46 Second angle 47 Reference plane O Axis θ1, θ2, θ3 angles

Claims (4)

A metal shell comprising: a cylindrical tube portion extending from the front end side to the rear end side; and a flange portion protruding in a hook shape from the rear end side of the tube portion to the outside in the radial direction;
A ground electrode connected to the tip of the cylindrical portion;
A spark plug manufacturing method comprising a central electrode insulated and held inside the metal shell and opposed to the ground electrode via a spark gap,
The die is moved until the threaded portion of the die is pressed against the cylindrical portion while maintaining the relationship between the reference position in the circumferential direction of the workpiece including the cylindrical portion and the flange portion and the reference position of the die. A moving step of moving the die while contacting an end surface of the die communicating with the threaded portion with a workpiece reference surface on the tip side of the flange portion of the workpiece;
A rolling step of rolling a screw on the cylindrical portion by the die that presses the threaded portion against the cylindrical portion,
The end surface of the die includes at least a first part adjacent to the screw part and a second part adjacent to the first part,
An angle θ1 formed between a reference plane perpendicular to the axis of the cylindrical portion and the first portion is larger than an angle θ2 formed between the reference plane and the second portion, and the angle θ2 is the reference plane and the workpiece reference. A method for manufacturing a spark plug having an angle θ3 or less with a surface. The workpiece is rounded at the first corner where the side surface of the collar and the workpiece reference plane intersect,
2. The spark plug manufacturing method according to claim 1, wherein, in the moving step, after the first part of the die is brought into contact with the first corner, the second part of the die is brought into contact with the workpiece reference surface.   The spark plug manufacturing method according to claim 1, wherein the angle θ2 is equal to the angle θ3.   The spark plug manufacturing method according to any one of claims 1 to 3, wherein a second corner where the first part and the second part intersect is rounded.

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