JP2822450B2 - Method for manufacturing electrode for spark plug - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an electrode used as a center electrode or a ground electrode of a spark plug for an internal combustion engine. More specifically, the present invention relates to a method for manufacturing an electrode having a structure in which a core material made of a metal having good thermal conductivity such as copper or a copper alloy is enclosed in a coating material made of a corrosion-resistant metal such as nickel, nickel, or a chromium alloy. Things.

[Prior Art] Conventionally, as a method of manufacturing an electrode for a spark plug, a cylindrical coating material having a concave cross section and a cylindrical core material having a convex cross section are used, and the core material is placed in the coating material. A method is known in which the two members are inserted and fitted together, and if necessary, brazed, joined by welding, heat diffusion, press fit caulking, or the like, then inserted into an extrusion mold, pressurized, and cold extruded into a rod shape ( For example, JP
No. -132628).

The extruded tip of the electrode manufactured by this method is completely covered with the coating material, but the core is exposed at the rear end of the pressure side. However, when the electrode is to be joined to another member at the rear end, there is a problem that sufficient joining strength cannot be obtained because copper (copper alloy) constituting the core material has low joining property.

Therefore, in such an application, it is desirable to seal the core material in the coating material. As a method for sealing the core material, after extruding, the coating material edge is extended by cold working, and then the core material is sealed. Is known, or a method of coating with another member made of corrosion-resistant metal is known (for example, Japanese Patent Publication No. 63-49356).

[Problems to be Solved by the Invention] However, the conventional manufacturing method has some disadvantages as described below.

One of them is adhesion between the covering material and the core material. That is, when the covering material and the core material are brazed and joined by welding or the like, it is difficult to join the entire outer peripheral surface of the core material, or a large amount of brazing material is required and the cost is high. Only the tip is joined. Therefore, although the front end portion is secured in close contact, it is inevitable that a gap behind the intermediate portion is formed due to the difference between the initial inner diameter of the covering material and the initial fitting of the core material. Then, there is a possibility that the voids remain until the subsequent process and sufficient adhesiveness cannot be obtained, resulting in a decrease in thermal conductivity. In particular, this tendency appears more remarkably when the electrode length is long.

Even when the rear end surface of the core material is sealed, a gap is easily generated between the core material and the coating material or another member for sealing, and the coating of the core material may be incomplete. Also, when the rear edge of the coating material is extended in the cold process, it becomes too thin, and when joining with other parts in the post-processing process, nests (a kind of cavity) may be formed,
There have been disadvantages that processing is difficult due to breakage, defects occur during use, and thermal conductivity is reduced.

Thus, the present invention solves the above-mentioned problems in the conventional method, has good adhesion, has excellent thermal conductivity, has a sufficient coating thickness, does not cause nests or tears, and has a simple and inexpensive process. It is intended to manufacture.

[Means for Solving the Problems] In order to solve the problems in the conventional method, the present invention provides a spark plug having a structure in which a core material made of a thermally conductive metal is enclosed in a coating material made of a corrosion-resistant metal. Insert the core material into the coating material, one end of which is open and the inner diameter of the opening side is larger than that of the closed side, and insert the leading end portion with a void around the rear end portion of the core material. Closely fixing to the closed end surface of the covering material, reducing the diameter of at least the opening side of the covering material so that the entire inner peripheral surface of the covering material is in close contact with the outer peripheral surface of the core material, and the opening edge of the covering material is sufficiently higher than the core material After molding, the opening edge of the coating material is bent inward and caulked to seal the open end, and then inserted into an extrusion mold so that the sealed end is on the tip side, and extruded into a rod shape It is manufactured by doing.

[Operation] In the above method, the initial shape of the coating material is such that the inner peripheral diameter on the opening side is large, and in a state where the core material is inserted into the coating material, the tip of the core material has It is tightly fixed to the coating material and has a void around the rear end.

Then, by reducing the diameter of at least the opening side of the coating material, when the entire inner peripheral surface of the coating material is brought into close contact with the outer peripheral surface of the core material,
The void at the rear end of the core material disappears, and the adhesion at the rear end is ensured.

The opening of the coating material is sealed by bending and caulking the edge sufficiently higher than the core material, and further extruded so that the sealed end is on the tip side, the gap disappears due to pressure from the surroundings, The adhesion at the sealing end becomes stronger.

Example Hereinafter, a method for manufacturing a center electrode of a spark plug according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a to-be-coated material 1 made of nickel or a nickel alloy. The coating material 1 has a dish-like shape having a circular bottom portion 11 as a closed end surface and a peripheral edge portion 12, and the peripheral edge portion 12 has a tapered shape whose diameter increases upward.

FIG. 2 is a sectional view of the initial core material 2 made of copper or a copper alloy, and the core material 2 is formed in a columnar shape.

In the present invention, first, the core 2 is attached to the bottom 11 of the covering 1.
Placed on top (Fig. 3) and assembled concentrically by brazing or resistance welding. In the case of resistance welding, work is easy if the core material 2 is in a state of protruding from the upper end edge 13 which is the opening edge of the coating material 1.

Next, the diameter of the peripheral portion 12 of the coating material 1 is reduced through the process shown in FIG. The lower die 31 has an inner diameter of the lower half slightly smaller than the outer diameter of the coating material 1, and a composite material having the core material 2 assembled therein is arranged in the lower die 31 so that the opening side faces upward. At 32, apply force from above. As a result, the inner peripheral surface of the coating material 1 comes into close contact with the outer peripheral surface of the core material 2 and, at the same time, the peripheral portion of the coating material 1
12 is extended, and the upper edge 13 becomes higher than the rear end face 21 of the core material 2 (FIG. 5).

At this time, the height of the upper end edge 13 from the rear end face 21 of the core 2 may be such that the rear end face 21 can be sufficiently covered by bending and caulking. This is further bent and caulked using a mold shown in FIG. The molding die includes a lower die 41 having an inner diameter substantially equal to the outer diameter of the coating material 1 and a pressing die 42. The coating material 1 is arranged such that the open end of the coating material 1 faces downward and pressed. Is bent inward to seal the open end (FIG. 7).

In the next step, extrusion molding is performed using an extrusion die shown in FIG. The extrusion die is a lower die 51 having a small diameter part 53 in the middle part.
The upper die 52 is extruded into a rod having a predetermined diameter, as shown in FIG. At this time, the covering material 1 needs to be disposed in the lower mold 51 so that the sealing end 22 faces downward. The force acts and the joint becomes stronger. Further, even if a gap remains between the bent and crimped portion and the core material 2 in the previous step, the gap disappears in this step and complete adhesion can be achieved.

In this step, since the brim-shaped portion 14 remains at the rear end, the brim-shaped portion 14 is punched out by a punching die 62 after being arranged in the lower mold 61 shown in FIG. To complete.

12 to 22 show a second embodiment of the present invention. In the present embodiment, as shown in FIG. 12, the coating material 1 is formed into a cylindrical shape having one end opening, and the inner peripheral diameter of the rear end portion 15 on the opening side is made larger than the inner peripheral diameter of the front end portion 16. is there.

As shown in FIG. 13, the core material 2 is a rod having a large-diameter portion 23 at the rear end. The leading end 24 of the core 2 is formed so as to be aligned with the inner peripheral surface of the leading end 16 of the covering 1, and the large diameter section 23 is formed slightly smaller than the inner diameter of the trailing end 15 of the covering 1. I have.

After inserting the core material 2 into the covering material 1 and tightly fixing the front end thereof (FIG. 14), the rear end 15 of the covering material 1 is reduced in diameter in the same manner as in the above embodiment (FIG. 15). , At the same time stretch the trailing edge
13 is formed so as to be higher than the core material 2 (FIG. 16).

The subsequent steps (FIGS. 17 to 22) are the same as in the first embodiment (FIGS. 6 to 11). The initial shape of the coating material 1 only needs to have a large inner peripheral diameter on the opening side as described above.
Similarly, the adhesion between the core material 2 and the coating material 1 can be improved.

Further, in the above embodiment, the method of manufacturing the center electrode of the spark plug has been described, but it may be used for manufacturing the ground electrode. Accordingly, the present invention can be suitably applied to a case where another member is joined to the rear end or both ends of the electrode, the joining property is improved, and a highly reliable electrode can be manufactured.

[Effects of the Invention] As described above, the electrode manufactured by the method of the present invention has good adhesion, excellent heat conductivity, and has a sufficient coating thickness because the core material is sealed before extrusion. There is no risk of breakage or tearing. Moreover, compared to the conventional method of fitting and fixing the covering material and the core material, the initial molding accuracy of the covering material and the core material is not required, and the electrode can be manufactured in a simple process at low cost.

[Brief description of the drawings]

1 to 11 show an embodiment of the present invention. FIG. 1 is an overall sectional view of a covering material, FIG. 2 is an overall sectional view of a core material, FIG.
The figure shows a state in which the core material is assembled to the covering material, FIGS.
FIG. 11 is a view showing a step of sealing and extruding the coating material with the core material assembled, and FIGS. 12 to 22 show another embodiment of the present invention, and FIG. Section 13 of the overall material
Fig. 14 is a cross-sectional view of the entire core material, Fig. 14 shows a state where the core material is assembled to the coating material, and Figs. 15 to 22 show steps of sealing and extruding the coating material with the core material assembled. FIG. DESCRIPTION OF SYMBOLS 1 ... Coating material 11 ... Bottom part (closed end face) 13 ... Rear edge (opening edge) 2 ... Core material 22 ... Sealed end

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01T 13/00 H01T 21/02 B21D 53/00 B21C 23/22

Claims (1)

(57) [Claims] 1. A method for manufacturing a spark plug electrode having a structure in which a core material made of a thermally conductive metal is sealed in a coating material made of a corrosion-resistant metal, wherein one end is opened and the inner diameter on the opening side is closed. The core material is inserted into the coating material having a larger diameter than the side, and the front end portion is tightly fixed to the closed end surface of the coating material in a state where there is a gap around the core material rear end, and at least the opening side of the coating material After reducing the diameter of the coating material so that the entire inner peripheral surface of the coating material is in close contact with the outer peripheral surface of the core material and the opening edge of the coating material is sufficiently higher than the core material, the opening edge of the coating material is moved inward. A method for manufacturing an electrode for a spark plug, characterized in that the opening end is sealed by bending and caulking, and further inserted into an extrusion mold so that the sealed end is on the tip side and extruded into a rod shape.