JP5535097B2 - Manufacturing method of spark plug metal shell and manufacturing method of spark plug - Google Patents

Description

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

  A spark plug used for ignition of an internal combustion engine such as a gasoline engine is generally attached to a center electrode, an insulator provided outside the center electrode, a metal fitting provided outside the insulator, and a metal fitting. And a ground electrode (also referred to as an “outer electrode”) that forms a spark discharge gap with the center electrode.

  The metal shell as a component of the spark plug has a cylindrical screw part with a screw formed on the outer peripheral surface, a cylindrical tip cylindrical part adjacent to the screw part and having a smaller diameter than the screw part, and a tip with respect to the screw part. It has a tool engaging part located on the opposite side to the cylindrical part, and has a through hole along the axial direction for accommodating the insulator. When attaching the spark plug to the engine head, the tool is fitted into the tool engaging portion of the metal shell and the spark plug is rotated so that the screw formed on the screw portion of the metal shell is inserted into the screw hole of the engine head. Screw together.

  When manufacturing the metal shell, the metal shell intermediate to be the metal shell is formed by multiple forgings using a metal mold for the starting material, and thread rolling is performed on the formed metal shell intermediate. Etc. are performed to manufacture the metal shell (see, for example, Patent Document 1).

JP 2009-95854 A

  When manufacturing the metal shell, if the tip cylindrical part (or the part that should become the tip cylindrical part, the same shall apply hereinafter) is formed by forging, cutting is performed compared to the case where the tip cylindrical part is formed by cutting. This is preferable because the amount can be reduced and the surface hardness of the tip cylindrical portion is improved.

  However, when the tip cylindrical portion is formed by forging, the tip surface of the tip cylindrical portion may not be flat. If the distal end surface of the distal end cylindrical portion does not have a flat shape, it may not be possible to secure sufficient bonding strength when bonding the ground electrode to the distal end surface, which is not preferable.

  The present invention has been made to solve the above-described problems, and aims to improve the flatness of the tip surface of the tip cylindrical portion formed by forging in the manufacture of the spark plug metal shell. To do.

  In order to solve at least a part of the above problems, the present invention can be realized as the following forms or application examples.

Application Example 1 A cylindrical screw portion having a screw formed on the outer peripheral surface and a cylindrical tip cylindrical portion having a smaller diameter than the screw portion adjacent to the screw portion and a through hole in the axial direction A method of manufacturing a spark plug metal shell,
A forging step of forming an m-th metal shell intermediate to be a metal shell by forging a metal starting material m times (m is a natural number of 2 or more);
The forging step includes an n-th metal shell intermediate forming step for obtaining an n-th metal shell intermediate by n-th (n ≦ m−1, n is a natural number) forging of the m times of forging, a tip surface forming step of forming the tip surface of the tip cylindrical portion or the tip surface of the portion to be the tip cylindrical portion by the (n + 1) -th forging process of m times of forging,
When the tip end side of the n-th metal shell intermediate body is the front end side in the axial direction of the n-th metal shell intermediate body, the inner peripheral side portion of the tip portion of the n-th metal shell intermediate body is the n-th metal shell intermediate body. A method for producing a metal shell for a spark plug, characterized in that the metal shell projects from the outer peripheral side portion of the tip of the metal fitting intermediate to the tip in the axial direction.

  In this method, since the inner peripheral side portion of the tip of the n-th metal shell intermediate formed by the n-th forging process protrudes from the outer peripheral side to the axial front end side, the (n + 1) -th forging process When forming the tip surface of the tip cylindrical part (or the tip surface of the part to be the tip cylindrical part), the outer peripheral side part of the tip part of the n-th metal shell intermediate is drawn inward, The shape becomes nearly flat as the molding proceeds, and finally a flat tip surface is molded. Therefore, in this method, the flatness of the tip surface of the tip cylindrical portion formed by forging can be improved.

[Application Example 2] A method of manufacturing a spark plug metal shell according to Application Example 1,
The n-th metal shell intermediate forming step includes an end portion for receiving a tip of a (n-1) metal shell intermediate (the 0th metal shell intermediate when n = 1 indicates the starting material). In addition, a receiving member that is movable along the axial direction is used to take out the n-th metal shell intermediate after the n-th metal shell intermediate molding step,
The method of manufacturing a spark plug metal shell, wherein an end portion of the receiving member has a shape corresponding to the outer peripheral side portion and the inner peripheral side portion at a distal end portion of the nth metal shell intermediate body.

  In this method, the end portion of the receiving member used in the n-th metal shell intermediate forming step has a shape corresponding to the outer peripheral side portion and the inner peripheral side portion at the distal end portion of the n-th metal shell intermediate body. Therefore, the front end surface of the front end cylindrical portion formed by forging can be formed in a shape in which the front end portion of the nth metal shell intermediate body protrudes from the outer peripheral side portion to the front end side in the axial direction. The flatness of the film can be improved.

[Application Example 3] A method of manufacturing a spark plug metal shell according to Application Example 2,
The method of manufacturing a spark plug metal shell, wherein the receiving member is disposed on an outer periphery of a punch that molds at least a hole opening at the tip end side in the axial direction at a tip portion of the n-th metal shell intermediate body.

  In this method, the front end portion of the n-th metal shell intermediate is formed by using a receiving member disposed on the outer periphery of the punch for forming a hole opening at least on the front end side in the axial direction on the front-end portion of the n-th metal shell intermediate. Can be formed into a shape in which the inner peripheral side portion protrudes from the outer peripheral side portion toward the distal end side in the axial direction, and the flatness of the tip surface of the tip cylindrical portion formed by forging can be improved.

  In addition, this invention can be implement | achieved in various aspects, for example, can be implement | achieved with forms, such as the manufacturing method and manufacturing apparatus of a metal fitting, the manufacturing method and manufacturing apparatus of a spark plug.

It is explanatory drawing which shows the structure of the spark plug 100 in the Example of this invention. It is a flowchart which shows the manufacturing method of the metal shell 50 in a present Example. It is explanatory drawing which shows the manufacturing method of the metal shell 50 in a present Example. It is explanatory drawing which shows the manufacturing method of the metal shell 50 in a present Example. It is explanatory drawing which shows the manufacturing method of the metal shell 50 in a present Example. It is explanatory drawing which shows the manufacturing method of the metal shell 50 in a present Example. It is explanatory drawing which shows the manufacturing method of the metal shell 50 in a present Example. It is explanatory drawing which shows the manufacturing method of the metal shell 50 in a comparative example.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Example:
A-1. Spark plug configuration:
A-2. Manufacturing method of metal shell:
B. Variations:

A. Example:
A-1. Spark plug configuration:
FIG. 1 is an explanatory diagram showing the configuration of a spark plug 100 in an embodiment of the present invention. In FIG. 1, the side surface configuration of the spark plug 100 is shown on the right side of the axis OL that is the central axis of the spark plug 100, and the cross-sectional configuration of the spark plug 100 is shown on the left side of the axis OL. In the following, the upper side (the side on which the ground electrode 30 is disposed) along the axis OL in FIG. 1 is referred to as the distal end side of the spark plug 100, and the lower side (the side on which the terminal fitting 40 is disposed) is the rear. It shall be called the end side.

  As shown in FIG. 1, the spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode (outer electrode) 30, a terminal fitting 40, and a metal shell 50. The center electrode 20 is held by the insulator 10, and the insulator 10 is held by the metal shell 50. The ground electrode 30 is attached to the front end side of the metal shell 50, and the terminal metal fitting 40 is attached to the rear end side of the insulator 10.

  The insulator 10 is a cylindrical insulator having a shaft hole 12 that accommodates the center electrode 20 and the terminal fitting 40 at the center, and is formed by firing a ceramic material such as alumina. In the vicinity of the center of the insulator 10 along the axial direction, a central body portion 19 having a larger outer diameter than other portions is formed. A rear end side body portion 18 that insulates between the terminal metal fitting 40 and the metal shell 50 is formed on the rear end side of the central body portion 19. A front end body portion 17 is formed on the front end side of the central body portion 19, and a leg length portion 13 having an outer diameter smaller than that of the front end side body portion 17 is formed further on the front end side of the front end side body portion 17. .

  The metal shell 50 has a through hole 59 along the axial direction, and is a substantially cylindrical metal fitting that accommodates a portion extending from a part of the rear end side body portion 18 of the insulator 10 to the leg long portion 13 in the through hole 59. For example, it is made of metal such as low carbon steel. The metal shell 50 includes a substantially cylindrical screw portion 52, a substantially cylindrical distal cylindrical portion 53 that is adjacent to the distal end side of the screw portion 52 and has a smaller diameter than the screw portion 52, and the distal cylindrical portion 53 with respect to the screw portion 52. Has a tool engaging portion 51 located on the opposite side. Note that the fact that the tip cylindrical portion 53 is smaller in diameter than the screw portion 52 means that the diameter of the tip cylindrical portion 53 is smaller than the diameter of the screw valley portion of the screw portion 52. The distal end surface 57 that is the end surface on the distal end side of the distal end cylindrical portion 53 has a hollow circular shape, and the distal end of the leg long portion 13 of the insulator 10 protrudes from the hollow portion of the distal end surface 57. A screw thread is formed on the side surface of the screw portion 52 to be screwed into a screw hole of the engine head when the spark plug 100 is attached to the engine head. The tool engaging portion 51 has, for example, a hexagonal cross-sectional shape, and the tool is fitted when the spark plug 100 is attached to the engine head. The metal shell 50 also has a seal portion 54 formed in a hook shape between the screw portion 52 and the tool engagement portion 51. An annular gasket 5 formed by bending a plate is fitted between the seal portion 54 and the engine head.

  The center electrode 20 is a substantially rod-shaped electrode in which a core material 25 having better thermal conductivity than the covering material 21 is embedded in a covering material 21 formed in a bottomed cylindrical shape. In this embodiment, the covering material 21 is made of a nickel alloy containing nickel as a main component, and the core member 25 is made of copper or an alloy containing copper as a main component. The center electrode 20 is accommodated in the shaft hole 12 of the insulator 10 with the front end side of the covering material 21 protruding from the shaft hole 12 of the leg long portion 13 of the insulator 10, and the center electrode 20 is interposed through the ceramic resistor 3 and the seal body 4. In addition, the insulator 10 is electrically connected to the terminal fitting 40 provided at the rear end.

  The ground electrode 30 is a bent substantially rod-shaped electrode. In the present embodiment, the ground electrode 30 is also formed of a coating material formed of a nickel alloy containing nickel as a main component, and a core material formed of copper or an alloy containing copper as a main component, like the center electrode 20; It consists of two layers. One end of the ground electrode 30 is joined to the front end surface 57 of the metal shell 50 by resistance welding, and the other end is bent so as to face the front end of the center electrode 20. A spark gap is formed between the free end of the ground electrode 30 and the tip of the center electrode 20.

A-2. Manufacturing method of metal shell:
FIG. 2 is a flowchart showing a method for manufacturing the metal shell 50 in the present embodiment. 3-7 is explanatory drawing which shows the manufacturing method of the metal shell 50 in a present Example.

  When manufacturing the metal shell 50, first, the starting material M is prepared (step S110 in FIG. 2). 3A shows a side configuration of the starting material M, and FIG. 3B shows a planar configuration of the starting material M. The starting material M is a substantially cylindrical metal material centered on the central axis Am. This starting material M is obtained, for example, by shearing a metal wire to a predetermined length.

  Next, a plurality of (multistage) forging processes using a mold for the starting material M are executed (step S120 in FIG. 2). In this embodiment, the number of forging processes (corresponding to m in the present invention) is four. 4 (a) to 4 (d) show the outline of each forging process. 4 (a) to 4 (d), the right side of the central axis Ad shows the state before each forging process, and the left side of the central axis Ad shows the state after each forging process. ing. In addition, in the hole of each die used for forging, the side into which the molding object is inserted is called the near side along the axial direction, and the side in the direction in which the molding object is pushed out is called the back side along the axial direction. . 5A to 5E show the configuration of the molded body 102 formed by each forging process. 5A to 5E, the cross-sectional configuration of each molded body 102 is shown on the right side of the central axis Ad, and the side configuration of each molded body 102 is shown on the left side of the central axis Ad. ing. In the starting material M and each molded body 102, the side that becomes the front end surface 57 of the metal shell 50 is referred to as the front end side along the axial direction, and the opposite side is referred to as the rear end side along the axial direction.

  In the first forging process shown in FIG. 4 (a), a substantially cylindrical sleeve 221k that receives the leading end side of the starting material M, and a sleeve 221k that is inserted into the hollow of the sleeve 221k along the leading end side of the starting material M along the axial direction. In a state where a substantially cylindrical pin (also referred to as “punch”, hereinafter the same) 221b for forming the hole is installed on the back side of the hole of the first forging die DIa, the die DIa The starting material M inserted into the holes is extruded by a substantially cylindrical pin 221a, and a molded body 102a shown in FIG. 5A is manufactured. After the extrusion molding, the sleeve 221k is moved to the front side of the hole of the mold DIa, and the manufactured molded body 102a is taken out from the hole of the mold DIa. In the first forging process, a substantially cylindrical material diameter portion MR having an outer diameter smaller than the outer diameter of the starting material M is mainly formed. The material diameter portion MR is a portion where the screw portion 52 and the tip cylindrical portion 53 are formed later. Further, the pin 221b forms a small-diameter hole SH on the distal end side of the molded body 102a. The inner diameter of the small diameter hole SH is a diameter corresponding to the outer diameter of the pin 221b. The pin (punch) 221b being inserted into the hollow of the sleeve 221k can also be expressed as the sleeve 221k being disposed on the outer periphery of the pin 221b.

  In the second forging process shown in FIG. 4B, similarly, the first forging process is performed in a state where the sleeve 222k and the pin 222b are installed at the back side of the hole of the die DIb for the second forging process. The molded body 102a manufactured by the above method is inserted into the hole of the mold DIb and extruded by the pins 222a, whereby the molded body 102b shown in FIG. 5B is manufactured. After the extrusion molding, the sleeve 222k is moved to the front side of the hole of the mold DIb, and the manufactured molded body 102b is taken out from the hole of the mold DIb. In the second forging process, the seal portion 54 is mainly formed. Further, the pin 222a forms a large-diameter hole LH on the rear end side of the molded body 102b. The inner diameter of the large-diameter hole LH is a diameter corresponding to the outer diameter of the pin 222a. In the present embodiment, the diameter of the large diameter hole LH is larger than the diameter of the small diameter hole SH. The second forging process in the present example corresponds to the (n-1) metal shell intermediate forming step in the present invention, and the molded body 102b formed by the second forging process is the first in the present invention. (N-1) It corresponds to a metal shell intermediate.

  Similarly, in the third forging process shown in FIG. 4C, the second forging process is performed in a state where the sleeve 223k and the pin 223b are installed on the back side of the hole of the die DIc for the third forging process. The molded body 102b manufactured by the above method is inserted into the hole of the mold DIc and extruded by the pins 223a, whereby the molded body 102c shown in FIG. 5C is manufactured. After the extrusion molding, the sleeve 223k is moved to the front side of the hole of the mold DIc, and the manufactured molded body 102c is taken out from the hole of the mold DIc. In the third forging process, the medium diameter hole MH located between the small diameter hole SH and the large diameter hole LH is mainly formed by the pin 223a. The inner diameter of the medium diameter hole MH is a diameter corresponding to the outer diameter of the tip of the pin 223a. In the present embodiment, the diameter of the medium diameter hole MH is smaller than the diameter of the large diameter hole LH and larger than the diameter of the small diameter hole SH. Note that the third forging process in this example corresponds to the n-th metal shell intermediate forming step in the present invention, and the molded body 102c formed in the third forging process is the n-th metal shell intermediate in the present invention. Corresponds to the body.

  FIG. 6 shows an enlarged view of the vicinity of the tip portion (X1 portion) of the molded body 102 in the third forging process shown in FIG. 4C. As shown in FIG. 6, in the end portion of the sleeve 223k used for the third forging process that receives the molded body 102c, the outer peripheral side portion OS protrudes from the inner peripheral side portion IS toward the rear end side in the axial direction. Therefore, the front end portion of the molded body 102c formed by the third forging process has a shape in which the inner peripheral side portion IP protrudes from the outer peripheral side portion OP toward the axial front end side. More specifically, the inner peripheral side portion IP of the tip portion of the molded body 102c has a planar shape substantially orthogonal to the axial direction, and the outer peripheral side portion OP is axially rearward from the boundary with the inner peripheral side portion IP. It has a tapered shape inclined toward the end side. The sleeve 223k used in the third forging process in the present embodiment corresponds to the receiving member in the present invention.

  After the third forging process, the wall body 124c between the small diameter hole SH and the medium diameter hole MH in the molded body 102c is punched by a punching pin (not shown). FIG. 5D shows a molded body 102 c ′ in which the small diameter hole SH and the medium diameter hole MH are communicated by punching.

  In the fourth forging process shown in FIG. 4D, similarly, the molded body 102c ′ is placed in a state where the sleeve 224k and the pin 224b are installed on the back side of the hole of the die DId for the fourth forging process. The molded body 102d shown in FIG. 5 (e) is manufactured by being inserted into the hole of the mold DId and extruded by the pins 224a and the outer mold 224c. After the extrusion molding, the sleeve 224k is moved to the front side of the hole of the mold DId, and the manufactured molded body 102d is taken out from the hole of the mold DId. In the fourth forging process, the tool engaging portion 51 is mainly formed. Further, in the fourth forging process, a step portion CP2 having a small inner diameter is provided at a position on the back side of the hole of the die DId to be used, and therefore, the tip end portion of the molded body 102c ′ becomes the step portion CP2. The tip cylindrical portion 53 and the tip surface 57 are formed by being deformed so that the diameter is reduced by being pushed. As shown in FIG. 5 (e), a portion of the material diameter portion MR excluding the tip cylindrical portion 53 becomes a screw portion 52. Note that the fourth forging process corresponds to the tip surface forming step in the present invention.

  FIG. 7 shows an enlarged view of the vicinity of the tip portion (X2 portion) of the molded body 102 in the fourth forging process shown in FIG. 4 (d). FIG. 7A shows a state where the tip of the molded body 102 has not yet reached the position of the stepped portion CP2. As described above, at this time point, the distal end portion of the molded body 102 has a shape in which the inner peripheral side portion IP protrudes from the outer peripheral side portion OP toward the axial front end side. FIG. 7B shows a state in which the tip portion of the molded body 102 has passed the position of the step portion CP2. When the tip cylindrical portion 53 and the tip surface 57 are molded by the stepped portion CP2, the outer peripheral side portion OP of the tip portion of the molded body 102 is drawn inward, as shown in FIG. 7B. The tip positions of the outer peripheral part OP and the inner peripheral part IP are aligned with the molding, and the shape of the tip part of the molded body 102 becomes nearly flat. FIG. 7C shows a state in which the tip of the molded body 102 has reached the end of the sleeve 224k. A flat front end surface 57 is formed at the front end of the molded body 102 by the flat end of the sleeve 224k.

  When the forging process is completed a plurality of times, a cutting process is performed on the formed body 102d (see FIG. 5E) manufactured by the forging process (step S130 in FIG. 2). In the cutting process, the peripheral portion of the tool engaging portion 51 is cut. Next, the process (rolling process) which forms a screw in the outer peripheral surface in the screw part 52 of the molded body 102d is executed (step S140). The manufacture of the metal shell 50 is completed through the above steps. Thereafter, the manufactured metal shell 50 and other components are assembled to manufacture the spark plug 100 (FIG. 1).

  Here, as described above, in the manufacturing method of the metal shell 50 of the present embodiment, the distal end cylindrical portion 53 and the distal end surface 57 are formed by forging, and therefore the distal end cylindrical portion 53 and the distal end surface 57 are formed by cutting. Compared to the case of molding, the amount of cutting in the cutting process (step S130 in FIG. 2) can be reduced, and the surface hardness of the tip cylindrical portion 53 and the tip surface 57 can be improved. Therefore, in the manufacturing method of the metal shell 50 according to the present embodiment, the manufacturing time of the metal shell 50 can be shortened and the manufacturing cost can be reduced, and the tip cylindrical portion 53 and the tip surface 57 are made strong against the dent. be able to.

  Furthermore, in the manufacturing method of the metallic shell 50 of the present embodiment, the flatness of the distal end surface 57 of the distal cylindrical portion 53 can be improved as compared with the manufacturing method of the metallic shell 50 of the comparative example described below.

  FIG. 8 is an explanatory view showing a method of manufacturing the metal shell 50 in the comparative example. FIG. 8 is an enlarged view of the vicinity of the tip portion (X2 portion) of the molded body 102 in the fourth forging process shown in FIG. FIG. 8A shows a state where the tip of the molded body 102 has not yet reached the position of the stepped portion CP2. In the comparative example, the shape of the front end portion of the molded body 102c is a flat shape in which the positions of the inner peripheral portion IP and the outer peripheral portion OP are aligned. FIG. 8B shows a state where the tip of the molded body 102 has passed the position of the stepped portion CP2. When the tip cylindrical portion 53 and the tip surface 57 are molded by the stepped portion CP2, the outer peripheral side portion OP of the tip portion of the molded body 102 is drawn inward, as shown in FIG. 8B. With the molding, the outer peripheral side portion OP pops out due to the plastic flow of the metal, and the outer peripheral side portion OP has a shape protruding from the inner peripheral side portion IP to the tip side in the axial direction. FIG. 8C shows a state in which the tip of the molded body 102 has reached the end of the sleeve 224k. The distal end portion of the molded body 102 has a shape in which the outer peripheral side portion OP protrudes toward the distal end side in the axial direction from the inner peripheral side portion IP. Therefore, the outer peripheral side portion OP first contacts the end portion of the sleeve 224k and is flat. However, the material is insufficiently filled at the position of the inner peripheral portion IP. Therefore, the front end surface 57 of the front end cylindrical portion 53 in the molded body 102d does not have a flat shape but a shape in which the inner peripheral side portion IP side is recessed.

  On the other hand, in the manufacturing method of the metal shell 50 of the present embodiment, the forging process (that is, the third forging process) immediately before the forging process (that is, the fourth forging process) for forming the distal end cylindrical portion 53 and the distal end surface 57 is performed. The tip portion of the molded body 102c molded in the processing) has a shape in which the inner peripheral side portion IP protrudes from the outer peripheral side portion OP toward the axial front end side. Therefore, when the tip cylindrical portion 53 and the tip face 57 are formed. The outer peripheral side portion OP of the distal end portion of the molded body 102 is drawn inward, the shape of the distal end portion of the molded body 102 becomes nearly flat as the molding progresses, and finally a flat distal end surface 57 is molded. The Therefore, in the manufacturing method of the metal shell 50 of the present embodiment, the flatness of the distal end surface 57 of the distal end cylindrical portion 53 can be improved.

  In the manufacturing method of the metal shell 50 of the present embodiment, the distal end cylindrical portion 53 (and the distal end surface 57) is formed by the last forging process (fourth forging process) in a plurality of forging processes. The third forging die does not have a step portion for forming the tip cylindrical portion 53, and these molds are of a plurality of types with different distances between the tip cylindrical portion 53 and the seal portion 54. It can be used in common for manufacturing the metal shell 50. Further, as shown in FIG. 4B, in the second forging process, a step portion for forming the seal portion 54 is provided in the mold DIb, but a step for forming the tip cylindrical portion 53 is provided. Since the portion is not provided, the distance between the seal portion 54 and the tip surface of the molded body 102 can be finely adjusted freely by shifting the sleeve 222k along the axial direction. The same applies to the third forging process. Thus, in the manufacturing method of the metal shell 50 of the present embodiment, the number of cases where a common mold can be used for manufacturing different types of metal shells 50 can be increased. Versatility can be improved. Further, by shifting the sleeve along the axial direction, the manufacturing dimension along the axial direction of the metal shell 50 can be finely adjusted without changing the dimension of the mold.

B. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

  The configuration of the spark plug 100 and the metal shell 50 as its component in the above embodiment is merely an example, and can be variously modified.

  Moreover, the manufacturing method of the metal shell 50 in the above embodiment is merely an example, and various modifications can be made. For example, in the above embodiment, the forging process (step S120 in FIG. 2) is configured by four forging processes, but the number of forging processes (stages) performed in the forging process is m times (m Is a natural number of 2 or more). Moreover, in the said Example, although the front-end | tip cylindrical part 53 and the front end surface 57 are shape | molded in the last (fourth) forging process of four times of forging processes, it is nth (n <= m-1, n Is a natural number) to form a molded body 102 (n-th metal shell intermediate) in which the inner peripheral side portion IP of the tip protrudes from the outer peripheral side portion OP toward the front end in the axial direction. What is necessary is just to shape | mold the front end surface 57 of the front-end | tip cylindrical part 53 by the forging process of (n + 1) th time made into object.

  Moreover, in the said Example, the shape of the front-end | tip part of the molded object 102c shape | molded by the forging process of the 3rd time is a planar shape in which the inner peripheral side part IP is substantially orthogonal to an axial direction, and the outer peripheral side part OP is inner periphery. Although it is assumed that the tapered shape is inclined toward the rear end side in the axial direction toward the outside from the boundary with the side portion IP, the shape of the tip portion of the molded body 102c is such that the inner peripheral portion IP is more axial than the outer peripheral portion OP. Other shapes may be used as long as the shape protrudes toward the tip side.

  Moreover, in the said Example, in the forge process for shape | molding the molded object 102 in which the inner peripheral side part IP of the front-end | tip part protruded from the outer peripheral side part OP to the axial direction front end side, such inner peripheral side part IP and outer periphery The sleeve 223k having the end corresponding to the shape of the side portion OP is used. However, the sleeve 223k may be a member having the end corresponding to the shapes of the inner peripheral portion IP and the outer peripheral portion OP. For example, not only the sleeve 223k but also other parts may be used.

  Further, a portion to be the tip cylindrical portion 53 and / or the tool engaging portion 51 is formed by forging, and processing (for example, cutting) is performed on such a portion, so that the tip cylindrical portion 53 and / or the tool engagement is performed. A joint portion 51 may be formed.

  In addition, among the constituent elements of the present invention in the above-described embodiments, elements other than the elements described in the independent claims are additional elements, and can be omitted or combined as appropriate.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 10 ... Insulator 12 ... Shaft hole 13 ... Leg long part 17 ... Front end side trunk | drum 18 ... Rear end side trunk | drum 19 ... Center trunk | drum 20 ... Center electrode 21 ... Covering material 25 ... Core material 30 ... Ground electrode 40 ... Terminal fitting 50 ... Metal fitting 51 ... Tool engaging portion 52 ... Screw portion 53 ... Cylinder tip portion 54 ... Seal portion 57 ... Front end surface 59 ... Through hole 100 ... Spark plug 102 ... Molded body 302 ... Molded body

Claims (4)

A metal shell for a spark plug having a cylindrical screw portion having a screw formed on an outer peripheral surface, a cylindrical tip cylindrical portion having a smaller diameter than the screw portion adjacent to the screw portion, and having a through hole in the axial direction. A manufacturing method of
A forging step of forming an m-th metal shell intermediate to be a metal shell by forging a metal starting material m times (m is a natural number of 2 or more);
The forging step includes an n-th metal shell intermediate forming step for obtaining an n-th metal shell intermediate by n-th (n ≦ m−1, n is a natural number) forging of the m times of forging, a tip surface forming step of forming the tip surface of the tip cylindrical portion or the tip surface of the portion to be the tip cylindrical portion by the (n + 1) -th forging process of m times of forging,
When the tip end side of the n-th metal shell intermediate body is the front end side in the axial direction of the n-th metal shell intermediate body, the inner peripheral side portion of the tip portion of the n-th metal shell intermediate body is the n-th metal shell intermediate body. A method for producing a metal shell for a spark plug, characterized in that the metal shell projects from the outer peripheral side portion of the tip of the metal fitting intermediate to the tip in the axial direction. It is a manufacturing method of the metal shell for spark plugs according to claim 1,
The n-th metal shell intermediate forming step includes an end portion for receiving a tip of a (n-1) metal shell intermediate (the 0th metal shell intermediate when n = 1 indicates the starting material). In addition, a receiving member that is movable along the axial direction is used to take out the n-th metal shell intermediate after the n-th metal shell intermediate molding step,
The method of manufacturing a spark plug metal shell, wherein an end portion of the receiving member has a shape corresponding to the outer peripheral side portion and the inner peripheral side portion at a distal end portion of the nth metal shell intermediate body. It is a manufacturing method of the metal shell for spark plugs according to claim 2,
The method of manufacturing a spark plug metal shell, wherein the receiving member is disposed on an outer periphery of a punch that molds at least a hole opening at the tip end side in the axial direction at a tip portion of the n-th metal shell intermediate body.   A method for manufacturing a spark plug, comprising the step of manufacturing the metal shell using the method for manufacturing a metal shell for a spark plug according to claim 1.

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