JPH0645050A - Manufacture of spark plug - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a spark plug in which a noble metal chip is firmly bonded to a nickel electrode base material, without buckling deformation. CONSTITUTION:A method for manufacturing a spark plug in which a noble metal chip 2 excellent in spark consumption resistance is fused to the discharge side end part of the base material 11 of a cylindrical central electrode 1 comprises the steps of forming a minor diameter straight bar part 1A and a conical part 1B on the discharge side end part of the electrode base material 11 in such a manner as to be mutually continued; placing the noble metal chip 2 to cover the top end surface 13 of the minor diameter straight bar part of the electrode base material 11; and emitting a laser beam LB to the boundary surface between the noble metal chip 2 and the minor diameter straight bar part of the electrode base material 11 from the horizontal direction of the boundary surface while pressing the noble metal chip 2 in the long axial direction of the electrode base material 11 and forming a fused coagulated alloy part over the whole circumference of the boundary surface to mutually bond both electrodes.

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 spark plug in which an electrode member made of a noble metal and having an excellent spark wear resistance is joined to the tip of a center electrode.

[0002]

2. Description of the Related Art For a center electrode of a spark plug, a composite material in which a core of a good heat conductive metal such as copper (Cu) is embedded in a base material made of corrosion resistant and heat resistant metal mainly composed of nickel (Ni), A noble metal electrode member is welded to the tip for the purpose of reducing spark consumption and further improving durability. As its manufacturing method, there is a method of manufacturing a spark plug in which a noble metal electrode member is welded to the tip of the base material of the center electrode by resistance welding applying heat and pressure, and then the base material tip is cut to a small diameter. It has been proposed (Japanese Patent Publication No. 59-2152).

[0003]

However, when the noble metal electrode member is resistance-welded to the center electrode, the noble metal is buried in the Ni base material while being deformed so that the edge portion is rounded due to heating and pressure during resistance welding. It If the tip portion is then cut for the purpose of reducing the discharge voltage and improving the ignitability, the precious metal may be cut, and the expensive precious metal cannot be effectively used. Further, since the edge portion of the buried noble metal was rounded, when the Ni base material was consumed, the rounded portion was exposed in a short usage time or running time, and the discharge voltage was remarkably increased. The problem to be solved by the present invention is to provide a method for manufacturing a spark plug having a regular shape without buckling deformation of a noble metal tip by welding a noble metal electrode member to the tip of a center electrode by laser.

[0004]

According to the method of manufacturing a spark plug of the present invention, the center electrode made of a nickel alloy has a small diameter portion having a diameter smaller than that of the body portion at the discharge side end portion. In a method for manufacturing a spark plug, in which a disc-shaped electrode member having excellent spark wear resistance is joined, a small diameter straight rod portion having a diameter smaller than that of the body of the center electrode, the small diameter straight rod portion and the body portion A step of forming a conical portion that connects with each other, a step of placing the disk-shaped electrode member so as to cover the tip end surface of the small diameter straight rod portion, and the disk-shaped electrode member of the center electrode. While pressing in the longitudinal axis direction, the boundary surface between the disk-shaped electrode member and the small-diameter straight rod portion is irradiated with a laser from the horizontal direction of the boundary surface, and almost the entire circumference of the boundary surface, or the entire circumference of the boundary surface. The present invention is characterized in that a transition melting and solidifying alloy portion is formed and both electrodes are joined.

In the disk-shaped electrode member according to the second aspect, when the diameter is D, the thickness is T, the diameter of the small diameter straight rod portion is d, and the length of the small diameter straight rod portion is L. , 0.5mm ≦ D ≦ 1.5m
m, 0.3 mm ≦ T ≦ 0.6 mm, 0 ≦ (d−D) / 2
It is characterized in that ≦ 0.2 mm and 0.2 mm ≦ L ≦ 0.5 mm.

The disk-shaped electrode member according to a third aspect is characterized by being made of a noble metal.

[0007]

In the method for manufacturing a spark plug according to the present invention, the disc-shaped electrode member is prevented from being deformed by laser welding the disc-shaped electrode member to the tip of the small diameter straight rod portion of the center electrode. A spark plug with a stable shape can be obtained. Further, it is not necessary to perform cutting work after joining.

In the method for manufacturing the spark plug according to the second aspect, the shape of the disk-shaped electrode member, the small diameter straight rod portion of the center electrode, and the shape of the welded portion with the disk-shaped electrode member are defined. Therefore, the electrode base material and the disk-shaped electrode member are firmly bonded to each other, and the deformation of the electrode tip can be prevented.

According to the third aspect of the present invention, since the disc-shaped electrode member is made of a noble metal having high heat resistance and corrosion resistance, it is possible to suppress wear of the spark plug due to spark discharge over a long period of time, and You can get a lifespan spark plug.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a method for manufacturing a spark plug according to the present invention. The center electrode 1 of (a) is made of silicon (S
i), a Ni base alloy 11 containing manganese (Mn) and chromium (Cr), or a Ni base alloy 11 such as Inconel 600 containing chromium (Cr) and iron (Fe), and a base material 1.
1 and a core 12 of a good heat conductive metal mainly composed of Cu or silver (Ag). The center electrode 1 has a small diameter straight rod portion 1A (diameter of 0.8 mm) which is smaller than the diameter of the body portion 14.
5 mm × height 0.25 mm) is cut or plastically worked so that the conical portion 1B is continuous. 2 is 0.8m in diameter
It is a noble metal tip of a disk-shaped electrode member having m × 0.5 mm height.

As shown in (b), the center electrode 1 comprises a base material 11, a core 12, and a noble metal tip 2 mounted on the small diameter straight rod portion 1A at the tip, and the noble metal tip 2 is a thin circle. Plate-shaped, gold (Au), platinum (Pt), iridium (I
r), Ir to which rare earth oxide is added, or Pt
-Made of Ir alloy material. The noble metal tip 2 is mounted so as to cover the tip surface 13 of the base material 11.

As shown in (c), the welding of the noble metal tip 2 is performed by intermittently applying the YAG (yttrium, aluminum, garnet) laser beam LB having a heat amount of 2.0 J to the tip surface 13 of the base material 11. Irradiation is performed from the direction parallel to the boundary surface with the noble metal tip 2. At this time, the central electrode 1 is rotated and is irradiated a plurality of times at intervals where the irradiation surfaces L1 overlap each other over the entire circumference of the boundary surface. As a result, as shown in FIG. 2A, the melt-solidified alloy portion 3 in which the components of the base material 11 and the components of the noble metal tip 2 are melted is produced. The melt-solidified alloy parts 3 of both are formed over substantially the entire circumference or the entire circumference.

At the time of this laser welding, as shown in FIG. 2B, the tip surface 21 of the noble metal tip 2 has a small diameter straight rod portion 1.
The extension of A causes some deformation in the longitudinal direction, but for example, 1K
When the presser 4 of g is used, the deformation can be suppressed and the noble metal tip 2 can be fixed so as not to move during laser welding, as shown in FIG.

FIG. 3 is a graph showing the relationship between the pressing load and the deformation amount 1 of the noble metal tip 2 in the longitudinal direction. As can be seen from the graph, when the pressing load is 500 g or less, the deformation amount 1 is slightly recognized, but when the pressing load is 3000 g or more, the load is too large and the indentation of the presser 4 is the noble metal tip 2.
Will remain. Therefore, the amount is preferably 600 g to 2500 g.

The melt-solidified alloy part 3 produced by laser welding has physical properties intermediate between the two, such as the coefficient of linear expansion, because the components of the base material 11 and the components of the noble metal tip 2 are melted as described above. ing. Therefore, the spark plug having the melt-solidified alloy portion 3 is characterized in that high heat is applied to the tip portion of the center electrode 1 and peeling between the noble metal tip 2 and the base material 11 due to a difference in thermal expansion does not easily occur. To have.

As shown in FIG. 4A, the shape of the noble metal tip 2 before welding has a diameter D, a thickness T, a small diameter straight rod portion 1A having a diameter d, and a small diameter straight rod portion. When the length of 1A is L, 0.5 mm ≦ D ≦ 1.5 mm, 0.3 mm ≦ T ≦ 0.6
mm, 0 ≦ (d−D) /2≦0.2 mm, 0.2 mm ≦
L ≦ 0.5 mm.

FIG. 5 shows a change in the spark discharge gap increase amount when a durability test of a 2000 cc, 6-cylinder gasoline engine was performed at 5000 rpm for 300 hours for 300 hours.
As can be seen from this graph, the diameter D of the precious metal tip 2
Is less than 0.5 mm, the spark discharge is concentrated and the gap increase amount is rapidly increased. That is, the smaller the diameter D of the noble metal tip 2 is, the easier it is to fly and the discharge voltage is lowered, but on the other hand, the concentration of spark discharge becomes remarkable, and the electrode consumption is accelerated. Also, the diameter D is 1.5 m
When m is exceeded, the amount of increase in the gap hardly changes, but the spark discharge surface becomes large and the ignitability deteriorates. In addition, the amount of expensive precious metal used increases and the cost increases.

The reason why the thickness T of the noble metal tip 2 is set to 0.3 mm or more is that the thickness T is 0.3, as shown in FIG.
This is because if the thickness is less than mm, even the edge portion 22 of the front end surface 21 of the noble metal tip 2 is melted and rounded when the laser beam LB is irradiated, and the discharge voltage becomes high. Further, the thickness T of the noble metal tip 2 is set to 0.6 mm or less because the edge portion 22 does not change at the time of laser irradiation even if it is thicker than 0.6 mm, but the cost becomes high.

When the noble metal tip 2 is joined to the tip of the small diameter straight rod portion 1A of the center electrode 1, the distance between the outer edge of the small diameter straight rod portion 1A and the outer edge of the noble metal tip 2 (d-D) / 2 The reason why is 0 or more and 0.2 mm or less is shown below. As shown in FIG. 4B, the center electrode 1 and the noble metal tip 2 are laser-welded by being placed on the tip surface 13 of the small diameter straight rod portion 1A of the center electrode 1 so as to be covered with the noble metal tip 2. When the diameter d of the center electrode 1 and the diameter D of the noble metal tip 2 are the same, the laser focus position 23 is a curved surface without steps,
The heat of the laser beam LB is evenly absorbed by the base material 11 of the center electrode 1 and the noble metal tip 2. However, if there is a step greater than 0.2 mm at the laser focus position 23, the focus is deviated, the heat of the laser beam LB is dispersed, and the penetration depth cannot be sufficiently obtained or the penetration depth varies. Therefore, it is preferably 0.1 mm to 0.
15mm is good.

The length L of the small diameter straight rod portion 1A of the center electrode 1 is set to 0.2 mm or more when the small diameter straight rod portion 1A is short when the precious metal tip 2 and the base material 11 are welded. The heat at the time of laser welding is drawn from the base metal 11 through the core 12, resulting in insufficient melting of the noble metal tip 2, and the components of the base metal 11 and the noble metal tip 2 of the melt-solidified alloy part 3 are uniformly melted. Because you can't expect it.
Further, the length L of the small diameter straight rod portion 1A is set to 0.5 mm or less because when the length L is longer than 0.5 mm, the base material 11 that is more likely to be changed by heat than the noble metal tip 2 is the laser beam LB. This is because the heat is absorbed too much and blow holes and cracks are likely to occur.

The noble metal tip 2 of the present invention contains N
Au, Pt, Ir, etc. were used as the material excellent in spark consumption resistance than the base material 11 made of i alloy, but ruthenium (R
Alloys such as u), tungsten (W), and chromium (Cr) may be used.

[0022]

According to the method of manufacturing a spark plug of the present invention, since the electrode and the noble metal tip are joined only by laser welding, the center electrode of the spark plug having a regular shape without buckling deformation of the noble metal tip. Can be obtained.
Further, by using a laser beam for welding, it is possible to weld an electrode material having a higher melting point than platinum alloy and which is difficult to join by resistance welding.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for manufacturing a spark plug according to the present invention.

FIG. 2 is a sectional view of the tip of the spark plug electrode of the present invention and a sectional view of the tip of the electrode when the precious metal tip is welded without applying a pressing load.

FIG. 3 is a graph showing the relationship between the pressing load at the electrode tip and the amount of electrode deformation during laser welding.

FIG. 4 is a partial perspective view of an electrode tip according to the spark plug manufacturing method of the present invention.

FIG. 5 is a graph showing the relationship between the diameter of a noble metal tip and the spark discharge gap increase amount.

[Explanation of symbols]

 1 Center electrode 2 Noble metal tip (disk-shaped electrode member) 3 Melt-solidified alloy part 11 Base material 13 Tip surface 1A Small straight rod part 1B Cone part LB Laser beam

Claims (3)

[Claims] 1. A center electrode made of a nickel alloy has a small-diameter portion having a diameter smaller than that of a body portion at an end portion on a discharge side, and a disc-shaped electrode member excellent in spark wear resistance is joined to the small-diameter portion. In the method for manufacturing a spark plug comprising: a step of forming a small diameter straight rod portion having a smaller diameter than the body portion of the center electrode, and a conical portion connecting the small diameter straight rod portion and the body portion; A step of placing the tip end surface of the small diameter straight rod portion so as to cover the discoid electrode member, and the discoid electrode member while pressing the discoid electrode member in the longitudinal axis direction of the central electrode. A laser is irradiated to the boundary surface with the small diameter straight rod portion from the horizontal direction of the boundary surface, and a melt-solidified alloy portion is formed over substantially the entire circumference of the boundary surface or around the entire circumference to join both electrodes. A method for manufacturing a spark plug, comprising: 2. The disk-shaped electrode member according to claim 1, wherein the diameter is D, the thickness is T, the diameter of the small diameter straight rod portion is d, and the length of the small diameter straight rod portion is L. 0.5mm ≦ D ≦ 1.5
mm, 0.3 mm ≦ T ≦ 0.6 mm, 0 ≦ (d−D) /
A method for manufacturing a spark plug, wherein 2 ≦ 0.2 mm and 0.2 mm ≦ L ≦ 0.5 mm. 3. A method for manufacturing a spark plug, wherein the disk-shaped electrode member according to claim 1 or 2 is made of a noble metal.