JPH08213150A - Manufacture of composite electrode for spark plug - Google Patents

Abstract

PURPOSE: To restrain the increase of manufacturing cost by forming the small diameter section of the composite center electrode of a multipolar spark plug without a cutting process and preventing the occurrence of a nonconforming product, with a formation time reduced for the small diameter section. CONSTITUTION: A copper core is tightly coupled to the inside of a nickel alloy billet to form the first composite material 18, and this material 18 is forward extruded, thereby preparing the second composite material 25 having an axial section 22 of d1 outer diameter. Then, the composite material 25 is forward extruded to form the third and stepped composite material 28 forward of the section 22 in such a state as having a small diameter section 29 of d3 outer diameter. Furthermore, the material 28 is extrusion molded to form the fourth composite material 32 having a medium diameter section 33 of d2 outer diameter between the axial section 22 and the small diameter section 29, thereby forming a composite center electrode. As a result, the small diameter section 29 of the composite center electrode can be formed without any cutting process, and various types of nonconformities due to a cutting process can be avoided.

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 composite electrode for a spark plug which is attached to a cylinder of an internal combustion engine and spark discharge is generated between the electrode and a counter electrode. The present invention relates to a method of manufacturing a composite center electrode or a composite lateral electrode for a spark plug whose outer diameter is gradually reduced toward the outside.

[0002]

2. Description of the Related Art Conventionally, a composite center electrode has the following first
-It manufactures by the manufacturing method (henceforth a conventional manufacturing method) which performs a 5th process. First, the first metal having excellent heat resistance and corrosion resistance is subjected to plastic working to form a cup having an axial hole having only a rear end opened. further,
By subjecting the second metal having excellent thermal conductivity to plastic working, a core material having a cylindrical portion that can be inserted into the axial hole is formed. Next, as shown in FIG. 12 (c), the shaft core (FIG. 12 (a)) is placed in the axial hole of the cup {see FIG. 12 (b)}.
The first step of forming the first composite material 101 is performed by inserting the cylindrical portion of the reference.

Next, by subjecting the first composite material 101 to front extrusion molding, as shown in FIG. 12 (d), the shaft-shaped portion 102 (outer diameter = φd1) and the front extrusion molding are formed on the tip side. A round rod-shaped extruded body 104 having a remaining portion 103 which is not applied is formed. Then, as shown in FIG. 12E, the second step of forming the round bar-shaped second composite material 106 by cutting the portion 105 including the remaining portion 103 of the extrusion molded body 104 is performed.

Next, the distal end side of the shaft-like portion 102 of the second composite material 106 is press-molded to form a diameter middle portion 107 (outer diameter = φd2) on the distal end side as shown in FIG.
), And the third step of forming the stepped third composite material 109 having the flange 108 on the rear end side.

Next, by cutting the outer periphery of the tip of the diameter middle portion 107 of the shaft-like portion 102 of the third composite material 109, as shown in FIG. 12 (g), the small diameter portion 110 (outer diameter) The fourth step of forming the stepped fourth composite material 111 having = φd3) is performed. The shaft-like portion 10 of the fourth composite material 111
2. The middle diameter portion 107 and the collar portion 108 are not cut.

As a characteristic of the conventional manufacturing method, as shown in FIG. 12 (f), in the third step, the second composite material 1 is used.
The front end side of 06 was subjected to press molding to reduce the diameter, and the rear end side was formed into a brim. The reason for this is that, because it is a composite material, the shaft-shaped portion 102 of φd1 is replaced with the middle diameter portion 107 of φd2.
From the experience, the limit of the cross-section reduction rate (calculation formula is the following mathematical formula 1) ε1,2 in the case of press forming into 21 was 21%. On the other hand, since the small diameter portion 110 having a smaller diameter of φd3 cannot be press-molded, a portion of φd2 was cut to φd3 by cutting a portion of φd2 in the fourth step. Here, the forward extrusion molding means that the molded body is constrained and extruded inside the mold (die), and the push-through molding is that the molded body is extruded without being constrained inside the mold (partially protruding). Say that.

[Equation 1]

[0007]

However, in the conventional manufacturing method, even when a part of φd2 is cut in the fourth step, since the small diameter portion 110 of φd3 is considerably thin,
In order to obtain an appropriate cutting speed, it is necessary to increase the rotation speed of the spindle of the automatic cutting machine. However, like the automatic cutting machine, when the operation cycle of stop → acceleration → cutting → deceleration → stop is repeated, The fourth composite material 11 is obtained by cutting the third composite material 109 for a predetermined cutting time (for example, 4 seconds).
There is also a trade-off of the piece time for molding No. 1, and there is a limit to increasing the rotation speed of the spindle of the automatic cutting machine.

That is, in order to increase or decrease the rotational speed of the spindle, as shown in the time chart of FIG. 13, the required time ta from time t1 to time t2, time t3 to time t3 →
A large amount of time tb is required at time t4, resulting in a long peace time. Therefore, the optimum cutting speed cannot be obtained, the surface roughness of the surface to be cut is poor, chipping of the cutting tool occurs, and the number of defective products increases, resulting in an increase in manufacturing cost. Also, the dimensional accuracy is poor,
There are also problems caused by cutting burrs.

According to the present invention, the manufacturing cost is prevented from increasing by forming the small diameter portion without cutting, thereby shortening the molding time of the small diameter portion and preventing defective products. An object of the present invention is to provide a method of manufacturing a composite electrode for a spark plug that can be manufactured.

[0010]

According to a first aspect of the present invention, there is provided a first composite material having a second metal material having excellent heat conductivity in a cup made of a first metal material having excellent heat resistance and corrosion resistance. After forming a first step of forming and a front extrusion molding of the first composite material to form a shaft-shaped portion having a reduced diameter on the front end side of the first composite material and a remaining portion not subjected to extrusion molding, A second step of forming a second composite material from which the remaining portion is removed, and a forward extrusion molding of the second composite material to form a shaft-shaped portion in which the tip of the shaft-shaped portion of the second composite material has a reduced diameter. A third step of forming a third composite material having a small diameter portion,
By subjecting the third composite material to press-through molding, the diameter of the shaft-like portion of the third composite material closer to the small diameter portion is reduced to form a middle diameter portion thicker than the small diameter portion, and And a fourth step of forming a fourth composite material having a collar portion at the rear end portion of the shaft-shaped portion.

According to a second aspect of the present invention, a first composite material having a second metal material having excellent thermal conductivity is formed in a cup made of a first metal material having excellent heat resistance and corrosion resistance.
And a step of performing forward extrusion molding on the first composite material to form a shaft-shaped portion having a reduced diameter on the front end side of the first composite material and a remaining portion not subjected to extrusion molding, and then removing the remaining portion. A second step of forming a second composite material, and a forward extruding molding of the second composite material to form a shaft-shaped small-diameter portion in which the tip of the shaft-shaped portion of the second composite material is thinned. A fourth composite material having two parallel surfaces on the outer periphery of the shaft-like portion of the third composite material by performing a third step of forming the third composite material and a forging process on the third composite material. And a fourth step of forming a spark plug composite electrode.

According to a third aspect of the present invention, a first composite material having a second metal material having excellent heat conductivity is formed in a cup made of a first metal material having excellent heat resistance and corrosion resistance.
And a step of performing forward extrusion molding on the first composite material to form a shaft-shaped portion having a reduced diameter on the front end side of the first composite material and a remaining portion not subjected to extrusion molding, and then removing the remaining portion. A second step of forming a second composite material, and a forward extruding molding of the second composite material to form a shaft-shaped small-diameter portion in which the tip of the shaft-shaped portion of the second composite material is thinned. A third step of forming a third composite material having the same, and the third composite material is subjected to press molding to further reduce the diameter of the tip of the small diameter portion of the third composite material to form the smallest diameter small portion. And a fourth step of forming a fourth composite material having a collar portion at the rear end portion of the shaft-shaped portion, and a manufacturing method of a composite electrode for a spark plug.

[0013]

According to the first aspect of the invention, the first composite material is obtained by inserting the second metal material having excellent heat conductivity into the first metal material having excellent heat resistance and corrosion resistance. Is formed. Next, the first composite material is subjected to forward extrusion molding to form a second composite material. At this time, in the second composite material, a shaft-shaped portion having a reduced diameter on the front end side of the first composite material and a remaining portion not subjected to extrusion molding are formed, and then the remaining portion is removed.

Next, the second composite material is subjected to front extrusion molding to form a third composite material. At this time,
In the third composite material, a shaft-shaped small-diameter portion is formed by thinning the tip of the shaft-shaped portion of the second composite material. Next, the fourth composite material is formed by subjecting the third composite material to press molding. At this time, the fourth composite material is formed with a diameter middle portion in which the diameter of the shaft-like portion of the third composite material is reduced, and a flange portion is formed at the rear end of the shaft-like portion. Further, the diameter middle part is formed thinner than the shaft-like part and thicker than the small diameter part. Therefore, in the third step, since the small diameter portion of the composite electrode can be formed without cutting, it is possible to prevent defective products while shortening the forming time of the small diameter portion. This can suppress an increase in the manufacturing cost of the composite electrode (center electrode).

According to the second aspect of the present invention, the first composite material is formed by inserting the second metal material having excellent heat conductivity into the first metal material having excellent heat resistance and corrosion resistance. . Next, the first composite material is subjected to forward extrusion molding to form a second composite material. At this time, the second composite material is formed with a shaft-shaped portion having a reduced diameter on the front end side of the first composite material and a remaining portion not subjected to extrusion molding, and the remaining portion is removed.

Next, the second composite material is subjected to forward extrusion molding to form a third composite material. At this time,
In the third composite material, a shaft-shaped small-diameter portion is formed by thinning the tip of the shaft-shaped portion of the second composite material. Next, the fourth composite material is formed by subjecting the third composite material to forging.
At this time, in the fourth composite material, two parallel surfaces are formed on the outer periphery of the shaft-shaped portion of the third composite material. Therefore, in the third step, since the small diameter portion of the composite electrode can be formed without cutting, it is possible to prevent defective products while shortening the forming time of the small diameter portion. This can suppress an increase in the manufacturing cost of the composite electrode (side electrode).

According to the invention of claim 3, claim 1
In the same third step as that of the invention described in 1), after forming the third composite material, the third composite material is subjected to press molding to further reduce the diameter of the tip of the small diameter portion and the rear end of the smallest diameter portion. A fourth composite material having a brim at its end is formed. Therefore,
This fourth composite material can be effectively molded without increasing the number of steps when the tip diameter of the composite electrode (for example, the center electrode) is made thinner than the small diameter portion described in claim 1.

[0018]

EXAMPLE A method of manufacturing a composite electrode for a spark plug according to the present invention will be described based on an example shown in the drawings.

[Manufacturing Method of First Embodiment] FIGS. 1 to 8
Shows a first embodiment of the present invention, and FIG. 1 is a process diagram showing a method for manufacturing a composite center electrode for a bipolar spark plug.

(First Manufacturing Step, Cup Molding Step) First, a columnar material is cut from a wire made of a first metal material such as nickel or nickel alloy having excellent heat resistance and corrosion resistance. Then, as shown in FIG.
Then, the billet 3 having a cylindrical cross section is formed by inserting the billet 3 into the round hole 1a of FIG.
At this time, an arcuate corner 4 is formed on the outer periphery of the tip of the billet 3, and a flat surface 5 is formed on the rear end surface of the billet 3. As the nickel alloy, for example, 8 wt% Fe, 16 wt% Cr, 0.2 wt% Cu,
Inconel 600 (trade name) consisting of 75.8 wt% Ni, Ni-Mn-Si alloy, Ni-Mn-Si-Cr
An alloy, a Ni-Mn-Si-Cr-Al alloy, or the like can be used. Here, 2a is a kick-out pin for ejecting the billet 3 after molding from the inside of the round hole 1a of the mold 1.

(Second manufacturing process, cup molding process) Next,
As shown in FIG. 3, the billet 3 is inserted into the round hole 6 of the mold 6.
The billet 8 having a cylindrical cross-section is formed by inserting the billet 8 into a and punching it with the punch 7. At this time, a substantially circular pilot hole 9 is formed on the rear end surface of the billet 8. Here, 7a is a kick-out pin for protruding the billet 8 after molding from the inside of the round hole 6a of the die 6.

(Third manufacturing process, cup forming process) Next,
As shown in FIG. 4, the billet 8 is inserted into the round hole 10a of the die 10 and the pilot hole 9 is further punched by the punch 11 so that the cross-sectional shape becomes as shown in FIG. 1 (b). The cup 12 having a cylindrical shape is formed. At this time, cup 12
An axial hole (recess) 13 having a closed front end and an open rear end is formed inside the. Here, 11a is a kick-out pin for protruding the molded cup 12 from the inside of the round hole 10a of the mold 10.

(Fourth Manufacturing Step, Axial Core Forming Step) On the other hand, as shown in FIG. 1A, the second metal material such as copper or copper alloy having excellent thermal conductivity is subjected to plastic working. The shaft core 14 having a columnar cross section is formed. The shaft core 14 has a shaft-shaped cylindrical portion 15 on the front end side, which has an axial dimension slightly longer than the depth of the axial hole 13 of the cup 12, and has an outer diameter substantially the same as the inner diameter of the axial hole 13, and a rear portion. Cylindrical part 1 on the end side
A disk portion 15a having an outer diameter larger than 5 is formed.

(Fifth Manufacturing Step, First Composite Material Forming Step) Next, as shown in FIG. 5, a fitting body in which the cylindrical portion 15 of the shaft core 14 is loosely fitted in the axial hole 13 of the cup 12 is formed. , Mold 17
1 (c), the first composite material 1 is inserted into the round hole 17a of
8 is formed. At this time, the shaft core 14 is tightly held in the cup 12 with the disk portion 15 a protruding from the rear end surface of the axial hole 13. The above corresponds to the first step of the invention described in claim 1. Here, 16a is a kick-out pin for protruding the first composite material 18 after molding from the inside of the round hole 17a of the mold 17.

(Sixth Manufacturing Step, First Extrusion Molding Step) Next, as shown in FIG. 6, the first composite material 18 is inserted into the round hole 19a of the mold 19 and pushed by the punch 20 to move forward. By extruding, the diameter of the front end side of the first composite material 18 is reduced to form a round bar-shaped extruded body 21 as shown in FIG. 1 (d). A round shaft-shaped portion (φd1: for example, φ2.6) 22 having an outer diameter smaller than that of the first composite material 18 is formed on the front end side of the extruded body 21, and front extrusion molding is performed on the rear end side. The remaining part 23 which is not formed is molded.

(Seventh Manufacturing Step, Cutting Step, Second Composite Material Forming Step) Next, by cutting the portion 24 including the remaining portion 23 on the rear end side of the extrusion molded body 21, as shown in FIG. 1 (e). As described above, the second composite material 25 having the shaft-shaped portion 22 is formed. The above corresponds to the second step of the invention described in claim 1.

(Eighth Manufacturing Step, Third Composite Material Forming Step, Second Extrusion Molding Step) Next, as shown in FIG. 7, the second composite material 25 is inserted into the round hole 26a of the die 26. Punch 2
By pushing in at 7 and extruding forward, the second
The tip side of the shaft-like portion 22 of the composite material 25 is further thinned,
As shown in FIG. 1F, the stepped third composite material 28 is formed. On the tip end side of the shaft-shaped portion 22 of the third composite material 28, a small diameter portion (φ) having a round shaft shape having an outer diameter smaller than that of the shaft-shaped portion 22 is formed.
d3: For example, φ2.0) 29 is molded. The above corresponds to the third step of the invention described in claim 1.

[Equation 2] The cross-section reduction ratios ε 1 and 3 at this time are 40.8% according to the equation of the above-mentioned equation 2, and the extrusion molding is possible although the small diameter portion 29 cannot be pushed through.

(Ninth Manufacturing Step, Fourth Composite Material Forming Step, Push Molding Step) Next, as shown in FIG. 8, the third composite material 28 is placed in the round hole 30a of the round-hole-shaped die 30. By inserting it into the mold and pushing it with the punch 31 to form the shaft, the tip side of the shaft-like portion 22 of the third composite material 28 is further thinned, and as shown in FIG. 4th composite material 3
Form 2 Between the shaft-shaped portion 22 and the small-diameter portion 29 of the fourth composite material 32, a round shaft-shaped portion having a smaller outer diameter than the shaft-shaped portion 22 and a larger outer diameter than the small-diameter portion 29 is formed. A middle diameter portion (φd2: φ2.5, for example) 33 is formed, and a flange portion 34 is formed on the rear end side of the fourth composite material 32. Fourth
The composite material 32 is used as the composite center electrode 41 (see FIG. 9). The above corresponds to the fourth step of the invention described in claim 1. Here, 31a is a kick-out pin for ejecting the molded fourth composite material 32 from the waiting hole 30a of the die 30.

(Structure of Spark Plug) FIG. 9 is a half sectional view showing a spark discharge portion of a two-pole spark plug (spark plug) 42 for an internal combustion engine having a composite center electrode 41 manufactured by the manufacturing method of this embodiment. Is.

This two-pole spark plug 42 for internal combustion engine
Is a cylindrical insulator 43 made of a sintered body such as alumina,
It is composed of a tubular metal shell 44 that holds the insulator 43, and a two-pole side electrode 45 welded to the front end surface of the metal shell 44. The composite center electrode 41
Is inserted into the shaft hole 46 in a state where at least the small diameter portion 29 projects from the tip end surface of the insulator 43. Also,
The tip surface of the two-pole side electrode 45 forms a spark gap with the side surface of the tip portion of the composite center electrode 41.

[Effects of First Embodiment] As described above, in this embodiment, as shown in FIG. 1, the small diameter portion 29 of the composite center electrode 41 can be formed by plastic working by forward extrusion, so No processing is required. This makes it possible to avoid various problems caused by cutting. For example, since shavings are eliminated, the material cost of expensive nickel (Ni) alloy material is reduced, deterioration of surface roughness of the cut surface of the composite material, occurrence of chipping of cutting bite can be prevented, and frequent occurrence of defective products is suppressed. be able to. In addition, dimensional accuracy does not deteriorate and cutting burrs do not occur. Furthermore, since it is possible to shorten the manufacturing time of one composite center electrode 41, it is possible to shorten the piece time. Therefore, the material cost can be reduced, the occurrence of defective products can be suppressed, the automatic cutting machine can be eliminated, and the piece time can be shortened, so that the manufacturing cost can be reduced.

[Second Embodiment] FIG. 10 shows a second embodiment of the present invention and is a process chart showing a method for manufacturing a composite lateral electrode.

In this embodiment, using the manufacturing method of the first embodiment, as shown in FIG. 10 (f), a cylindrical small diameter portion 29 having an outer diameter smaller than that of the shaft portion 22 is formed. After forming the third composite material 28, by forging the shaft-shaped portion 22 of the third composite material 28, two parallel surfaces 35 are formed on the outer periphery of the shaft-shaped portion 22 as shown in FIG. Having a fourth
The composite material 36 is formed. This fourth composite material 36 is used as a composite lateral electrode of a multipolar spark plug.

[Third Embodiment] FIG. 11 shows a third embodiment of the present invention and is a process diagram showing a method for manufacturing a composite center electrode.

In this embodiment, using the manufacturing method of the first embodiment, as shown in FIG. 11 (f), a cylindrical small-diameter portion 29 (for example, an outer portion) having an outer diameter smaller than that of the shaft-like portion 22 is used. Diameter d3 =
After forming the third composite material 28 having a thickness of 2.0 mm), the small diameter portion 2
The tip of 9 is molded so as to be the smallest diameter smallest portion 37 (for example, outer diameter d4 = 1.8 mm) having a smaller outer diameter, and the shaft-shaped portion 2
The collar portion 34 is formed at the rear end of the second composite material 38 to form the fourth composite material 38. The cross-section reduction rate of this fourth composite material 38 is 19%.
Therefore, the punching process is possible.

[Modification] In this embodiment, the present invention is applied to a composite center electrode 41 in which a first metal material and a second metal material are integrated.
Alternatively, the present invention was used in the method for manufacturing a composite lateral electrode.
Manufacture of a composite center electrode or a composite lateral electrode in which a first metal material and a second metal material are integrated and a third metal material such as pure nickel (Ni) having excellent thermal conductivity is enclosed in the second metal material. You may use for the method. As the second metal material (Cu, Cu alloy), use is made of a cylindrical rod body in which the disk portion 15a (see FIG. 1 (a)) is omitted and which is enclosed in the cup 12 of the first metal material. May be.

A noble metal electrode such as platinum may be attached to the firing surface of the composite center electrode 41 or the firing surface of the composite side electrode. In this embodiment, the composite center electrode 41 is assembled to the two-pole spark plug 42. However, the side electrode has one pole and the spark plug faces the front end surface of the composite center electrode, or the side electrode has three or more poles. The composite center electrode 41 may be attached to the spark plug. Also, molds 1, 6, 10, 17, 2
6, 30 may be composed of two or more parts.

[Brief description of drawings]

FIG. 1 is a process drawing showing each manufacturing process according to the first embodiment of the present invention.

FIG. 2 is a sectional view showing a first manufacturing process according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a second manufacturing step according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a third manufacturing process according to the first embodiment of the present invention.

FIG. 5 is a sectional view showing a fifth manufacturing process according to the first embodiment of the present invention.

FIG. 6 is a sectional view showing a sixth manufacturing process according to the first embodiment of the present invention.

FIG. 7 is a sectional view showing an eighth manufacturing process according to the first embodiment of the present invention.

FIG. 8 is a sectional view showing a ninth manufacturing process according to the first embodiment of the present invention.

FIG. 9 is a front view showing a judgment surface of a main part of the spark plug manufactured by using the first embodiment of the present invention.

FIG. 10 is a process drawing showing each manufacturing process according to the second embodiment of the present invention.

FIG. 11 is a process drawing showing each manufacturing process according to the third embodiment of the present invention.

FIG. 12 is a process drawing showing each manufacturing process according to a conventional manufacturing method.

FIG. 13 is a time chart showing changes in the rotation speed of the spindle.

[Explanation of symbols]

 18 1st composite material 22 Shaft-like part 23 Remaining part 25 2nd composite material 28 3rd composite material 29 Small diameter part 32 4th composite material (composite center electrode) 33 Diameter center part 34 Collar part 35 Parallel surface 36 4th composite material ( Composite outer electrode) 37 Smallest diameter part 38 Fourth composite material (composite center electrode) 41 Composite center electrode 42 Two-pole spark plug

Claims (3)

[Claims] 1. A first step of forming a first composite material having a second metal material having excellent thermal conductivity in a cup made of a first metal material having excellent heat resistance and corrosion resistance, and (b) By subjecting the first composite material to forward extrusion molding, a shaft-shaped portion having a reduced diameter on the tip side of the first composite material and a remaining portion not subjected to extrusion molding are formed, and then the remaining portion is removed to obtain a second composite material. A second step of forming a material, and (c) by subjecting the second composite material to forward extrusion molding, a shaft-shaped small-diameter portion in which the tip of the shaft-shaped portion of the second composite material is thinned. A third step of forming a third composite material having: (d) by subjecting the third composite material to press molding,
A fourth composite having a shaft portion having a collar portion formed at a rear end portion of the third composite material by reducing a diameter of a portion of the shaft portion near the small diameter portion to form a middle diameter portion thicker than the small diameter portion. Fourth forming composite
A method of manufacturing a composite electrode for a spark plug, comprising the steps of: 2. A first step of forming a first composite material having a second metal material having excellent thermal conductivity in a cup made of a first metal material having excellent heat resistance and corrosion resistance, and (b) By subjecting the first composite material to forward extrusion molding, a shaft-shaped portion having a reduced diameter on the tip side of the first composite material and a remaining portion not subjected to extrusion molding are formed, and then the remaining portion is removed to obtain a second composite material. A second step of forming a material, and (c) by subjecting the second composite material to forward extrusion molding, a shaft-shaped small-diameter portion in which the tip of the shaft-shaped portion of the second composite material is thinned. A third step of forming a third composite material having: (d) a third composite material having two parallel surfaces on the outer periphery of the shaft-like portion by forging. 4. A method of manufacturing a composite electrode for a spark plug, comprising the fourth step of forming a composite material. 3. A first step of forming a first composite material having a second metal material having excellent thermal conductivity in a cup made of a first metal material having excellent heat resistance and corrosion resistance, and (b) By subjecting the first composite material to forward extrusion molding, a shaft-shaped portion having a reduced diameter on the tip side of the first composite material and a remaining portion not subjected to extrusion molding are formed, and then the remaining portion is removed to obtain a second composite material. A second step of forming a material, and (c) by subjecting the second composite material to forward extrusion molding, a shaft-shaped small-diameter portion in which the tip of the shaft-shaped portion of the second composite material is thinned. A third step of forming a third composite material having: (d) by subjecting the third composite material to press molding,
A fourth step of forming a fourth composite material by further thinning the tip of the small diameter portion of the third composite material to form the smallest diameter portion and having a collar portion at the rear end portion of the shaft-like portion. A method for manufacturing a composite electrode for a spark plug, comprising: