JPH07275992A - Manufacture of main tool for spark plug - Google Patents

Abstract

PURPOSE:To provide a manufacturing method, by which the development of flaw on an intermediate product successively charged is prevented and the following working at the end surface part is unnecessary, by forming the cutting waste punched out in a punching process of a cold forging to a columnar shape having a fixed shape and size. CONSTITUTION:A fourth forged product is formed to a large diameter hole at the upper end side and to middle diameter hole at the lower end side of the large diameter hole. On the other hand, the fourth forged product is formed to a small diameter hole 244 with step composed of an end surface hole at the lower end side and a guide hole for guiding a punch, having smaller diameter than the end surface hole at the upper end surface of the end surface hole. The step part 246 of the small diameter hole 244 with step has about 0.2-0.7mm or more diameter and roundness. A wall part 247 having 1-3mm thickness is formed between the guide hole and the middle diameter hole. Successively, the wall part 247 of the fourth forged product is punched out with the punch 46 at a fifth station to obtain a fifth forged product. At this time, stress developed at the wall part 247 is concentrated in the punching out diameter with the action of the roundness at the step part 246. Therefore, the center part of the wall part 247 punched out is formed to the columnar shaped cutting waste 49.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a metal shell for a spark plug which is mounted on an internal combustion engine mounted on an automobile or the like.

[0002]

2. Description of the Related Art Conventionally, a metal shell for a spark plug is a cold forging process for giving a shape to a cylindrical metal material, and a cutting process for adjusting the shape obtained by the cold forging process to a nearly final shape. Are mainly molded and mass-produced by. In the cold forging process, as shown in FIG. 10, first, a large-diameter head portion 291 and a small-diameter pipe portion (292) having different outer diameters and lengths are formed on the side surface of the metal material in the steps of upsetting and extrusion forming. And axial recesses 2 on both end faces.
93 and 294 are formed. Next, the through holes in the axial direction are punched out by penetrating the recesses at both ends of this intermediate molded product.

The punching process is performed by a punching station 300 shown in FIG. A punch 303 is attached to the movable die 301 of the punching station, which penetrates the intermediate molded product in the axial direction and has an air hole 302 through which air blown out from the tip is sent if necessary. . Further, a die 305 for holding an intermediate molded product is attached to the fixed die 304 of the punching station. Further, the die 305 is a kick that allows the chips 306 generated by the penetration of the through hole after the punching process to pass through the punch 303 to be separated from the punch 303 and eject the punched molded product 307 upward. The out sleeve 308 is assembled.

Punch 30 of kickout sleeve 308
On the 3 side, the diameter is 0.05-0.1m than the punch 303.
A passage hole 309 through which the punch 303 passes by a distance of m is opened. Intermediate molding is punching station 3
It is housed in a die 305 of 00, and the punch 303 penetrates through the recesses on both end surfaces of the intermediate molded product, and then the chip 3
06 is passed through the passage hole 309 of the kick-out sleeve 308 while being attached.

After that, the punch 303 returns to the position before the start of punching again. At this time, air is sent to the tip of the punch 303 through the air hole 302, and the chips 306 receive the air pressure for separating from the tip of the punch 303. The size of the chips 306 increases due to springback. As a result, even if the chips 306 are not separated from the tip of the punch 303 by air pressure, when the chips 306 reach the passage hole 309 of the kickout sleeve 308, the chips 306 contact the lower periphery of the passage hole 309 and receive a reaction force, and thus are separated from the tip of the punch 303. .

[0006]

However, in the conventional intermediate molded product, since the bottom of the recess 294 is formed by the single-step cylindrical tip of the punch, the punch 3 is punched.
When 03 penetrates the recess, the stress τ dispersed in the wall portion 310 at the boundary of the recess is generated as shown in FIG. For this reason, the wall portion 310 punched by the punch 303 has a punch 3
The other side of the tip of 03 expands and becomes a truncated cone chip 306.
And the chips 306 become the kickout sleeve 30.
When passing through the passage hole 309 of No. 8, the small piece 311 hits the periphery of the passage hole 309 and separates from the chips 306.

The small piece 311 separated from the chips 306 is
Even after the molded product 307 obtained by punching the kick-out sleeve 308 is discharged upward, the kick-out sleeve 3
The end surface 312 contacting the upper surface of the kick-out sleeve 308 of the intermediate molded product that is left on the upper surface of the die 08 and is then housed in the die 305 is damaged. For this reason, post-processing such as cutting for smoothing the damaged end surface 312 of the intermediate molded product and providing the required accuracy is required, resulting in an increase in manufacturing cost.

According to the present invention, the chips punched out in the punching step of the cold forging process are formed into a cylindrical shape having a constant outer diameter, so that the intermediate molded article to be inserted next is not scratched. It is an object of the present invention to provide a method for manufacturing a metal shell for a spark plug that prevents the above and does not require post-processing of the end face portion.

[0009]

According to the present invention, a cylindrical metal material is formed in a manufacturing method for manufacturing a metal shell having a circumferential ridge portion to which a step of an insulator is locked by cold forging. By doing so, a large diameter hole is formed on one end face side of the head, a circular large diameter head with an outer diameter larger than the head is formed on the head, and the large diameter head is formed on the other end face side. A forming step of forming a circular small-diameter leg portion with a smaller outer diameter and forming a small-diameter hole on the end surface of the small-diameter leg portion, and a smaller medium-diameter hole at the bottom of the large-diameter hole of the molded product of the forming step. Molding, and at the same time, an additional forming step of forming a stepped small diameter hole having a guide hole smaller than the small diameter hole in the small diameter hole, and punching out a molded product of the additional forming step to form the medium diameter hole and the step. It forms a through hole by communicating with a small diameter hole with it, and also functions as a step seat for the insulator. Employing the method of manufacturing a spark plug for the metal shell and a punching step of forming the inner peripheral ridge least as technical means.

According to the present invention, in the additional forming step, a step punch is inserted to maintain the shape of the large diameter hole of the molded product of the forming step, while the medium diameter hole smaller than the large diameter hole is made larger. The stepped punch is formed at the bottom of the diameter hole to form the stepped small diameter hole having a guide hole smaller than the small diameter hole, and the small diameter tube portion obtained by extending the small diameter leg is extruded. The method of manufacturing a metal shell for a spark plug is adopted as the first embodiment of the technical means.

The present invention is directed to a method of manufacturing a metal shell for a spark plug, characterized in that a non-circular fastening portion having a diameter smaller than that of the large diameter head is formed on an end face side of the large diameter head. Adopted as the second embodiment of the technical means. The present invention provides a method for manufacturing a metal shell for a spark plug, characterized in that a non-circular fastening portion having a diameter larger than that of the large-diameter head is formed on an end face side of the large-diameter head. Third
Is adopted as an embodiment of. The present invention provides a method for manufacturing a metal shell for a spark plug, characterized in that a circular caulking portion having an outer diameter smaller than that of the large-diameter head is formed on an end surface of the large-diameter head. Is adopted as the fourth embodiment of.

[0012]

When the punch for punching communicates the medium-diameter hole and the stepped small-diameter hole in the above-mentioned punching step, the stress generated in the central portion of the wall portion separating the medium-diameter hole and the stepped small-diameter hole is Concentrates in the punching direction due to the rounded effect of the stepped portion of the stepped small diameter hole. For this reason, the center portion of the punched wall portion becomes columnar chips. Since the cylindrical chips have high reproducibility in changes in shape and size, even if the punching is repeated, the chips pass smoothly through the passage holes of the kick-out sleeve, and no small chips are generated. As a result, the end surface of the molded product in the punching process that comes into contact with the kick-out sleeve is not damaged, and post-processing such as cutting is unnecessary.

[0013]

【Example】

[Structure of Embodiment] A method of manufacturing a metal shell for a spark plug according to the present invention will be described based on a first embodiment shown in FIGS. 1 to 7. Fig. 1 shows the shape of the finished metal shell, Fig. 2
[Fig. 4] is a view showing a spark plug in which the metal shell is assembled. The spark plug 1 includes a cylindrical insulator 2, a center electrode 3 held by the insulator 2, a ground electrode 4 that forms a spark gap G between the center electrode 3 and the tip surface of the center electrode 3,
And a tubular metal shell 5 for holding the ground electrode 4 and the like.

The insulator 2 is formed of a ceramic sintered body such as AlN or Al ₂ O ₃ . Inside the insulator 2, a shaft hole 6 that is open at the front end surface and the rear end surface is formed. Shaft hole 6 on the tip side of this insulator 2
The center electrode 3 is fitted in the shaft, and a part of the terminal electrode 7 and the resistor 8 are heat-sealed by the conductive glass powder 9 in the shaft hole 6 on the rear end side. Further, the stepped seat 10 at the center of the insulator 2 is locked to the inner peripheral ridge portion 26 of the metal shell 5 via the packing 11, and the maximum diameter portion 12 at the center of the insulator 2 is filled with the ring 13 and ceramics. It is fixed by caulking the caulking portion 15 of the metal shell 5 with the powder 14 in between.

The ground electrode 4 is made of a heat-resistant and corrosion-resistant nickel alloy such as nickel-chromium-iron alloy or nickel-manganese-silicon alloy. This ground electrode 4 is
After being welded to the front end surface of the metal shell 5, the end portion is bent into a substantially L shape so as to face the front end surface of the center electrode 3.

The metal shell 5 is made of low carbon steel (S10C, S1).
7C) or other metal material that is easily plastically worked, is cold forged by a cold forging machine, and then partially cut by a cutting machine to form the shape shown in FIG. A circular large-diameter cylindrical portion 17 that forms a sealing surface with a cylinder head (not shown) of the internal combustion engine is formed in a substantially central portion of the metal shell 5. A small-diameter pipe portion 16 having an outer diameter smaller than that of the large-diameter cylindrical portion 17 is formed on the tip side of the large-diameter cylindrical portion 17, and a threaded portion 18 is formed on the outer periphery thereof. This thread 18
Is for attachment to the cylinder head of an internal combustion engine.

A non-circular, for example, hexagonal fastening portion 19 having an outer diameter smaller than that of the large diameter tubular portion 17 is formed on the outer periphery of the metal shell 5 on the rear end side of the large diameter tubular portion 17. The fastening portion 19 is for applying a tool such as a wrench for fastening. Further, between the large-diameter cylindrical portion 17 and the fastening portion 19,
A thin-walled tubular portion 20 that is thinned by cutting is formed. A through hole 21 is formed inside the metallic shell 5 on the front end side so as to penetrate in the axial direction. This through hole 2
As shown in FIG. 1, 1 has a small-diameter hole 22 on the front end side, a large-diameter hole 23 having an inner diameter larger than that of the small-diameter hole 22 on the rear end side, and a minimum hole 24 and a medium-diameter hole 25 in the central portion. .

An inner peripheral protruding portion 26 is formed on the inner periphery of the small-diameter pipe portion 16 for locking the stepped seat 10 at the central portion of the insulator 2 via the packing 11. The position of the inner circumferential protruding portion 26 from the tip surface differs depending on the heat value of the plug, and the lower the heat value, the longer the length from the tip surface.

FIG. 3 is a view showing the third station of the cold forging machine. The movable die 28 of the third station 27 includes a punch 29 forming an inner diameter die and preforming the large diameter hole 231, a punch sleeve 30 holding the punch 29 in the axial direction, and an outer diameter die. A punch holder 31 for preforming the formed and crimped portion is assembled. The fixed die 32 of the third station 27 is a die for the outer diameter, and has a large-diameter cylindrical portion 234 and a small-diameter leg portion (screw portion) 2.
A die 33 for preforming 37, a lower punch 34 for preforming the small diameter hole 232 forming a die for inner diameter, and a kickout for discharging the third forged product d upward after the third step of the cold forging process is completed. The sleeve 35 and the like are assembled.

FIG. 4 is a view showing the fourth station of the cold forging machine. In the movable die 37 of the fourth station 36, a step punch 38 for additionally forming the medium diameter hole 241 is attached to the bottom of the large diameter hole 231 preformed in the third station. In addition, the fixed die 39 of the fourth station 36 has a large-diameter tubular portion 234 and a small-diameter tubular portion 245 preformed in the third station.
And a die 40 for additionally molding, and a small diameter portion 411 for leading the punch 46 with a tip for additionally molding the guide hole 243 in the small diameter hole 232 preformed in the third station.
A stepped punch 41 connected by a rounded step portion, a kick-out sleeve 42 for discharging the fourth forged product e upward after the fourth step of the cold forging process, and the like are assembled.

FIG. 5 is a view showing the fifth station of the cold forging machine. The movable die 44 of the fifth station 43 is provided with an air hole 45 penetrating the medium diameter hole 241 and the guide hole 243 additionally formed in the fourth station, and the air hole 45 penetrating the air blown from the tip. 46 is assembled.

Further, the fixed die 47 of the fifth station 43
A die 48 that holds the large-diameter cylinder portion and the screw portion that are additionally formed in the fourth station 36 is attached to the. Further, after the fifth step of the cold forging process is completed, the die 48 passes through the punch 46 to separate the chips 49 generated by the penetration of the medium diameter hole 241 and the guide hole 243, and separates from the punch 46. A kick-out sleeve 50 that discharges f upward is assembled. On the punch 46 side of the kick-out sleeve 50, a small-diameter hole 51 for guiding the punch 46 having a diameter of 0.05 to 0.1 mm larger than the punch 46 is opened.

[Manufacturing Method of Embodiment] Next, a manufacturing method of the metal shell 5 of this embodiment will be described with reference to FIGS. First, as shown in FIG. 7A, a cylindrical metal material a having a diameter φ14.8 made of, for example, low carbon steel is cut into a predetermined length.

(First Step of Cold Forging) Next, the columnar metal material a is inserted into the first station (not shown) of the cold forging machine and swage-formed to form a columnar shape. A circular bullet-shaped first forged product b having an outer diameter larger than the metal material a (for example, φ15.1) is obtained. Note that FIG. 7B
As shown in, the small hole 211 is formed on the lower end surface of the first forged product b.
Is formed, and an arc-shaped corner 212 is formed on the outer peripheral edge of the lower end surface.

(Second Step of Cold Forging) Next, the first forged product b is inserted into the second station (not shown) of the cold forging machine and extruded to form the second forging. Obtain the product c. As shown in FIG. 7C, a large hole 221 is formed on the upper end surface of the second forged product c, and a small hole 222 is formed on the lower end surface thereof. Further, the second forged product c has an outer diameter larger than the first forged product b on the upper end side (for example, φ15.4).
In 8), a circular head portion 223 and a circular leg portion 224 having an outer diameter smaller than that of the head portion 223 are formed on the lower end side. And
A step 225 is formed between the head 223 and the leg 224.

(Third Step of Cold Forging) Next, as shown in FIG. 3, the second forged product c is processed by the third step of the cold forging machine.
The third forged product d is obtained by inserting it into the station 27 and performing upset molding (upset molding) and extrusion molding using the punch 29, punch holder 31, die 33 and lower punch 34. As shown in FIG. 7D, the inner diameter of the large diameter hole 231 is preformed on the upper end surface of the third forged product d, and the inner diameter of the small diameter hole 232 is preformed on the lower end surface thereof. Further, on the head 233 side of the third forged product d, a circular large-diameter head 234 having an outer diameter larger than the head 223 of the second forged product c (for example, φ18.9) (for example, axial dimension 10. 1 mm), that is, the outer diameter of the large diameter cylindrical portion 17 is preformed.

Then, on the upper end surface side of the head 233 of the third forged product d, an outer diameter smaller than the large diameter head 234 (for example, φ1
In 5.56), the circular small-diameter cylindrical portion 235 (for example, the axial dimension of 2.7 mm), that is, the outer diameter of the swaged portion 15 is preformed. Further, a circular small-diameter leg portion 237 having an outer diameter smaller than that of the large-diameter head portion 234 is preformed on the leg portion 236 side of the third forged product d.

(Fourth Step of Cold Forging) Next, as shown in FIG. 4, the third forged product d is inserted into the fourth station 36 of the cold forging machine and extrusion molded. Thus, a fourth forged product e is obtained. As shown in FIG. 7E, a step punch 38 is inserted on the upper end side of the fourth forged product e to maintain the shape of the large-diameter hole 231 of the third forged product d while maintaining the large-diameter hole 231. A medium diameter hole 241 smaller than 231 is formed at the bottom of the fourth forged product e of the large diameter hole 231. On the other hand, the lower end surface of the fourth forged product e has a stepped punch 4 having a small diameter portion 411 at the tip.
1 is inserted to extend the small diameter hole 232 of the third forged product d and a guide hole 243 for guiding the step punch 41 with a smaller diameter than the end face hole 242 of the end face hole 242 and the upper end side end face hole 242 of the fourth forged product e. A stepped small-diameter hole 244 is formed. The step portion (inner peripheral ridge portion) 246 of the stepped small diameter hole 244 is 0.2
Rounded with a radius of 0.7 mm or more.

On the lower end side of the fourth forged product e, a small diameter pipe portion 245 obtained by extending the small diameter leg portion 237 of the third forged product d is formed. A wall portion 247 having a thickness of 1 to 3 mm is formed between the guide hole 243 and the medium diameter hole 241.

(Fifth Step of Cold Forging) Next, the fourth forged product e is inserted into the fifth station 43 of the cold forging machine as shown in FIG. e wall 24
The fifth forged product f is obtained by punching 7 with the punch 46. As shown in FIG. 7 (f), the fifth forged product f
The intermediate hole 241 and the stepped small hole 244 are communicated with each other by a cylindrical opening having the inner surface of the guide hole 243 as the side surface of the punch 46, and a through hole 253 that penetrates the inside in the axial direction is formed. A small diameter tube portion 254 is formed.

At this time, as shown in FIG. 6, the stress σ generated in the central portion of the wall portion 247 is the step portion 246 of the stepped small diameter hole 244.
Concentrate in the punching direction due to the roundness effect of. Therefore, the central portion of the wall portion 247 punched out by the tip of the punch 46 becomes a columnar chip 49. Then, the punch 46 keeps the chips 49 attached to the tip of the punch 46.
Pass through the small hole 51 of 0. At this time, cylindrical chips 4
Since the diameter of 9 is smaller than the diameter of the small diameter hole 51, it passes smoothly through the small diameter hole 51, and it is prevented that small pieces are separated from the chips 49 and remain around the upper side of the small diameter hole 51.

After that, the punch 46 has its air blown to the tip by the air hole 45 and is pulled back upward.
By this time, the chips 49 receive the pressure of the air sent to the tip portion of the punch 46, and if the pressure is larger than the adhesive force with the tip portion of the punch 46, they are separated from the tip of the punch 46.

If the chips 49 are not separated only by the pressure of the air sent to the tip of the punch 46, they reach the lower part of the small diameter hole 51. At this time, the chips 49 have returned to the diameter in the state where no stress is applied by the spring back, so they hit the periphery of the lower side of the small diameter hole 51, receive a reaction force from the periphery of the lower side of the small diameter hole 51, and from the tip of the punch 46. To separate. Further, the kickout sleeve 50 discharges the fifth forged product f,
The upper end surface of the kick-out sleeve 50 is in a state capable of supporting the fourth forged product e to be inserted next without any foreign matter.

(Sixth Step of Cold Forging) Fifth Forged Product f
Is inserted into the sixth station (not shown) of the cold forging machine and extrusion molded to obtain a sixth forged product g. As shown in FIG. 7 (g), the small diameter cylindrical portion 264 of the head 261 of the sixth forged product g (for example, the outer diameter dimension φ15.
56, a non-circular hexagonal fastening portion 265 (for example, axial dimension 9 mm) having an outer diameter smaller than the large-diameter cylindrical portion 263 (for example, φ18.97) is formed on the side of 56, axial dimension 2.7 mm.

(Cutting) As shown in FIG. 1, the sixth forged product g formed by cold forging has a large-diameter cylindrical portion 17
The metal shell 5 is manufactured by thread-rolling the threaded portion 18 on the outer circumference of the small-diameter pipe portion 16 having a smaller outer diameter, and cutting the outer diameter of the caulking portion 15, the large-diameter tubular portion 17, the thin-walled tubular portion 20, and the like. To be done. Then, the rod-shaped ground electrode 4 is joined to the tip end surface of the metal shell 5 by welding to obtain the finished product shape shown in FIG.

(Assembling Step) After the surface of the metal shell 5 manufactured by the cold forging and cutting as described above is plated, the inside of the metal shell 5 as shown in FIG. Then, the insulator 2 including the center electrode 3 is inserted. And the stepped seat 10 at the center of the insulator 2 is the packing 1.
1 is engaged with the inner peripheral protruding portion 26 of the metal shell 5 and the maximum diameter portion 12 of the central portion of the insulator 2 is joined to the caulking portion 15 of the metal shell 5 via the ring 13 and the ceramic filling powder 14. It is crimped and fixed by. As a result, the spark plug 1 is manufactured by assembling the insulator 2 and the like inside the metal shell 5.

[Effect of Embodiment] The metal shell 5 of this embodiment
In the manufacturing method of, since the stepped small-diameter hole 244 having the guide hole 243 for guiding the punch 46 is formed at the fourth station 36, the small-diameter pipe portion is formed after the punch forming at the fifth station 43 of the cold forging process. No post-processing is required to smooth the end surface of 254 and achieve the required accuracy,
The manufacturing cost can be reduced accordingly.

Moreover, in the method for manufacturing the metallic shell 5 of this embodiment, upset molding and extrusion molding (molding of the small diameter leg portion 237) are used at the third station 27 of cold forging. Accordingly, the manufacturing method of the metal shell 5 of this embodiment is
The outer diameter of the circular large-diameter head portion 234 (large-diameter cylindrical portion 17) can be formed on the small-diameter leg portion 237 side of the head portion 233 of the third forged product d. At the same time, according to the method for manufacturing the metal shell 5 of this embodiment, the circular small-diameter cylindrical portion 235 (outer diameter smaller than the large-diameter head portion 234) (the caulking portion 15 of the metal shell 5) is provided on the end face side of the head portion 233. The outer diameter can be preformed.

As a result, according to the method of manufacturing the metallic shell 5 of this embodiment, the cutting allowance at the time of cutting the outer periphery of the caulking portion 15 can be reduced, so that the amount of cutting by the cutting machine can be reduced and the conventional method can be used. The amount of chips can be reduced more than that of one. Therefore, according to the method of manufacturing the metal shell 5 of this embodiment, the cutting size of the cylindrical metal material a can be shortened and the material cost can be reduced, so that the manufacturing cost and the product cost can be reduced. Furthermore, since the method for manufacturing the metal shell 5 of this embodiment can reduce the amount of chips during cutting, it is possible to improve the workability of the discharging work for discharging the chips from the cutting machine. The rate can be improved.

Further, the method of manufacturing the metal shell 5 of this embodiment can reduce the load on the cutting machine during cutting. Therefore, the method for manufacturing the metal shell 5 of this embodiment can shorten the piece time of the finished metal shell 5 (without the ground electrode 4 in FIG. 1) discharged from the cutting machine, and can reduce the cutting edge of the cutting machine. Long life can be achieved and accuracy of finished products can be improved.

[Manufacturing Method of Second Embodiment] A manufacturing method of the metal shell for a spark plug of the present invention will be described based on a second embodiment shown in FIGS. 8 and 9. The metal shell 5 is largely different from that of the first embodiment in that the metal shell 5 is a spark plug metal shell provided with a fastening portion (hexagonal cylinder portion) 59 having an outer diameter larger than that of the large-diameter cylindrical portion 17. As shown in FIG. 9, the metal shell 5 is manufactured through the steps of FIGS. 9 (i) to 9 (n). Figure 9
(H) to (j) are inner views of the manufacturing process of the first embodiment.
Manufactured in the same manner as in (c).

In FIG. 9 (k), the large diameter hole 231 is preformed by upset molding and extrusion molding, and a hexagonal fastening portion (hexagonal cylinder) having a diameter larger than the head 233 is formed on the head 233 side. Part) 265 is formed. Further, the caulking portion 15 of the circular small-diameter cylindrical portion 235 having an outer diameter smaller than that of the head portion 233 is preformed on the upper end surface side of the head portion 233.
Further, the circular small-diameter leg portion 2 has an outer diameter smaller than that of the head portion 233.
36 and small diameter hole 232 are preformed. Furthermore, FIG.
In (l), the large-diameter hole 231 in FIG. 9 (k) is dug down to form the large-diameter cylindrical portion 17 having a predetermined length s of the head 233, and the small-diameter hole 232 and the small-diameter leg portion 236 extend. The small diameter hole 232a and the small diameter leg portion 236a are preformed.

Next, FIGS. 9 (m) to 9 (n) are manufactured by the same method as the manufacturing process of FIGS. 7 (e) to 7 (f) of the first embodiment. That is, as shown in FIG. 9 (m), a medium-diameter hole 241 smaller than the large-diameter hole 231 is formed by extrusion molding, while a stepped punch is inserted at the lower end of the small-diameter hole 232a to extend the end face hole 242 and the punch. A stepped small-diameter hole 244 including a guide hole 243 for guiding is formed. Further, as shown in FIG. 9 (n), punching is performed using a punch to form a guide hole 243.
The side surface of the punch communicates with the inner surface of the punch to form the through hole 253 and the small tube portion 254 having the step 246 is manufactured.

[Modification] In the manufacturing process of FIG. 7 of the first embodiment, the fastening portion (hexagonal cylinder portion) 265 is the sixth portion of FIG.
Although manufactured in the process, it may be manufactured in any process after the fourth forged product in FIG. 7D is formed. Further, although the hexagonal tubular portion 265 was formed without inverting the forged product as shown in FIG. 7G, it may be formed by inverting.

[Brief description of drawings]

FIG. 1 is a half sectional view showing a shape of a finished product of a metal shell according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a spark plug assembled with the metal shell of FIG.

FIG. 3 is a sectional view showing a main part of a third station of the cold forging machine.

FIG. 4 is a sectional view showing a main part of a fourth station of the cold forging machine.

FIG. 5 is a sectional view showing a main part of a fifth station of the cold forging machine.

FIG. 6 is an explanatory diagram of a stress distribution during punching at a fifth station.

FIG. 7 is a cross-sectional view showing cutting and shapes of first to sixth forged products.

FIG. 8 is a half sectional view showing a shape of a finished product of a metal shell of a second embodiment of the present invention.

FIG. 9 is a cross-sectional view showing the cutting and the shapes of the first to sixth forged products according to the second embodiment.

FIG. 10 is a sectional view showing a main part of a conventional punching station.

FIG. 11 is an explanatory diagram of stress distribution in a conventional punching process.

[Explanation of symbols]

 1 Spark Plug 2 Insulator 5 Main Metal Fitting 10 Step Seat 15 Caulking Part 17 Large Diameter Cylindrical Part 18 Screw Part 19 Fastening Part (Hexagonal Cylindrical Part) 21 Through Hole 22 Small Diameter Hole 23 Large Diameter Hole 24 Smallest Hole 25 Medium Diameter Hole 26 Inner peripheral protruding portion 41 Stepped punch 46 Punch 231 Large diameter hole 237 Small diameter leg 241 Medium diameter hole 242 End face hole 243 Guide hole 244 Stepped small diameter hole 245 Small diameter pipe portion 246 Stepped portion (inner peripheral protruding portion) 247 Wall Part 253 Through hole 263 Large-diameter cylinder part 264 Small-diameter cylinder part 265 Fastening part 411 Small-diameter part

Claims (5)

[Claims] Claim: What is claimed is: 1. In a manufacturing method for manufacturing a metal shell provided with a circumferential ridge portion with which a step of an insulator is locked by cold forging, (a) a cylindrical metal material is molded to obtain a head. A large-diameter hole is formed on one end surface side of the part, and a circular large-diameter head portion is formed on the head portion with an outer diameter larger than the head portion, and an outer diameter smaller than the large-diameter head portion on the other end surface side. A forming step of forming a circular small-diameter leg portion and forming a small-diameter hole in an end face of the small-diameter leg portion; and (b) forming a smaller medium-diameter hole in the bottom portion of the large-diameter hole of the molded product of the forming step. At the same time, an additional forming step of forming a stepped small diameter hole having a guide hole smaller than the small diameter hole in the small diameter hole, and (c) punching the molded product of the additional deformation step to form the medium diameter hole and the Inner peripheral protrusion that communicates with a small stepped hole to form a through hole and also functions as a stepped seat for the insulator A spark plug manufacturing method for the metal shell at least having a punching step of forming the part. 2. The method for manufacturing a metal shell for a spark plug according to claim 1, wherein in the additional molding step, a step punch is inserted to maintain the shape of the large diameter hole of the molded product of the molding step. While forming the medium diameter hole smaller than the large diameter hole at the bottom of the large diameter hole and inserting a step punch to form the stepped small diameter hole having a guide hole smaller than the small diameter hole,
A method for manufacturing a metal shell for a spark plug, characterized by extruding a small-diameter pipe portion obtained by extending the small-diameter leg portion. 3. The spark plug metal shell manufacturing method according to claim 1, wherein a non-circular fastening portion having a diameter smaller than the large diameter head is formed on an end face side of the large diameter head. And a method for manufacturing a metal shell for a spark plug. 4. The spark plug metal shell manufacturing method according to claim 1, wherein a non-circular fastening portion having a diameter larger than the large diameter head is formed on an end face side of the large diameter head. And a method for manufacturing a metal shell for a spark plug. 5. The spark plug metal shell manufacturing method according to claim 1, wherein a circular caulking portion having an outer diameter smaller than that of the large-diameter head is formed on an end surface of the large-diameter head. A method for producing a metallic shell for a spark plug, which is a feature.