JP2001043955A - Manufacture of spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a spark plug capable of restraining the occurrence and growth of a crack due to the difference of a heat contraction rate by dispersing and relaxing the discontinuity of a constituent distribution and thermal stress in the vicinity of a boundary between a wear-resistant tip or an electrode base material and an overall circumferential welded part. SOLUTION: After an overall circumferential welded part B straddling a wear-resistant tip 33 and a tip fixing surface formation part 32c is formed along the circumferential surface of the tip, an annealing process is applied to an overlap assembly A wherein the wear-resistant tip 33 is overlaid on a tip fixing surface 32d. That is, by applying the annealing process for the purpose of constituent dispersion and stress elimination, the discontinuity of a constituent distribution and thermal stress in the vicinity of a boundary between the wear- resistant tip 33 or an electrode base material 32 and the overall circumferential welded part B is dispersed and relaxed, so that the occurrence and growth of a crack due to the difference of a heat contraction rate can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a spark plug.

[0002]

2. Description of the Related Art In recent years, spark plugs used for ignition of an internal combustion engine have been developed to improve spark wear resistance.
A type in which a noble metal firing portion is formed by welding a noble metal tip mainly composed of Pt, Ir, or the like to the tip of the electrode is used. For example, when joining the noble metal tip to the tip surface of the center electrode, as a manufacturing method, a disk-shaped or columnar noble metal tip is overlapped on the tip of the center electrode, and along the outer periphery of the overlapping surface while rotating the center electrode. A method of forming a laser welded portion by irradiating a laser beam has been proposed (for example, JP-A-6-45050 and JP-A-10-112374).

FIG. 9 shows an example of a conventional manufacturing method when a noble metal tip is joined to the front end face of a center electrode. The core 3 at the center is made of a heat-resistant alloy containing Ni or Fe as a main component.
A disc-shaped or column-shaped noble metal tip 33 'mainly composed of Pt, Ir, or the like is superimposed on a tip end surface of an electrode base material 32' formed so as to cover 1 '. And the electrode base material 3
A laser beam LB is emitted from the laser light source L toward a boundary position between the noble metal tip 33 'and the electrode base material 32' while rotating the 2 'and the noble metal tip 33'. As a result, the noble metal tip 33 'and the electrode base material 32' melt and
Solidification is performed, and a laser welded portion B 'is formed straddling both of them to obtain a center electrode 3' having a noble metal firing portion 33a '. When the noble metal tip 33 'and the electrode base material 32' are uniformly melted, the physical properties such as the coefficient of thermal expansion in the laser welded portion B 'show an intermediate property between the two.

[0004]

By the way, when a weld is formed by laser welding, the components of the laser weld are alloyed by mixing the noble metal tip 33 'and the electrode base material 32'. In the vicinity of the boundary between the noble metal tip 33 'or the electrode base material 32' and the laser welded part B ', the component distribution changes sharply and becomes discontinuous. In general, the coefficient of thermal expansion is such that the noble metal tip 33 '> laser welded part B'> electrode base material 32 ', and especially near the above-mentioned boundary, the coefficient of thermal expansion sharply changes in accordance with the component distribution. Thermal stress also becomes discontinuous. In such a situation, when repeatedly exposed to a cooling and heating cycle as in an internal combustion engine, a crack K 'may be generated at the boundary due to a difference in thermal shrinkage. When the crack K 'grows, the noble metal tip 33' may fall off from the electrode base material 32 '.

[0005] For example, when the laser welded portion B 'is the electrode base material 3
When it reaches the center of 2 'and melts all the noble metal tip 33' and does not leave an unwelded area at the center in the radial direction, the bead width and depth of the laser weld B 'becomes large, so strong welding is performed. Power is gained. On the other hand, in this configuration, since the heat input from the welding heat source is large, the electrode base material 32 ′ and the core body 31 ′, which are more susceptible to thermal change than the noble metal tip 33 ′, do.
However, there is a problem that blowholes and cracks are easily generated due to excessive heat absorption. Therefore, while suppressing the amount of heat required for welding and taking care not to adversely affect the electrode base material 32 ′ and the core body 31 ′, as shown in FIG. 9, an unwelded region is formed at least in the radial center of the electrode base material 32 ′. Leave, noble metal tip 3
3 ′ may be welded such that a portion remains after welding. However, in this case, in the unwelded area, the electrode base material 32 and the noble metal tip 33 ′ are not yet joined, or are only temporarily fixed by resistance welding at most, so that the noble metal tip 33 ′ or the electrode When the crack generated at the boundary between the base material 32 'and the laser welded portion B' reaches the unwelded region, there is a problem that the chip is very likely to fall off.

SUMMARY OF THE INVENTION It is an object of the present invention to disperse and alleviate discontinuity of component distribution and thermal stress near a boundary between a wear-resistant tip or an electrode base material and a welded portion, thereby reducing a difference in thermal shrinkage. It is an object of the present invention to provide a method of manufacturing a spark plug which can suppress the generation and growth of cracks caused by cracks.

[0007]

Means for Solving the Problems and Functions / Effects In order to solve the above problems, a first method of manufacturing a spark plug according to the present invention is as follows. And a ground electrode arranged to form a spark discharge gap. Ir, Rh, Pt, Pd, and Pd are applied to at least one of the center electrode and the ground electrode at a position corresponding to the spark discharge gap. Ru, R
e, W, Os, Mo, Au, and a spark-dissipating metal tip (hereinafter, referred to as a depletion-resistant chip) mainly composed of at least one of the following: a laser-welded metal sparking portion. A method for manufacturing a spark plug, comprising: forming a welded portion of a wear-resistant tip of an electrode base material from a heat-resistant alloy; and forming a welded portion extending between the wear-resistant tip and the welded portion on an outer peripheral surface of the tip. Is formed by fixing the wear-resistant chip to the portion to be welded and then performing an annealing process.

[0008] In the above method, after forming a welded portion over the wear-resistant tip and the portion to be welded along the outer peripheral surface of the tip,
Annealing is performed for the purpose of component diffusion and stress removal. As a result, the discontinuity of the component distribution and the thermal stress near the boundary between the wear-resistant tip or electrode base material and the welded portion is diffused and relaxed, and the generation and growth of cracks due to the difference in the thermal shrinkage rate are performed. Can be suppressed.

A second aspect of the method for manufacturing a spark plug of the present invention is to form a center electrode and a ground electrode opposed to the center electrode so that a spark discharge gap is formed between the center electrode and the center electrode. At least one of the center electrode and the ground electrode at a position corresponding to the spark discharge gap is provided with Ir, Rh, Pt, Pd, Ru, Re, W, Os,
A method for manufacturing a spark plug in which a spark consumable metal firing portion is formed by joining a spark consumable metal adhered member mainly containing any of Mo and Au by laser welding, wherein a ground electrode is The tip surface is arranged so as to face the side surface of the center electrode.
It is formed on the outer periphery of the center electrode corresponding to the position opposite to the tip end surface of the ground electrode. A spark-absorptive metal-fixed member is arranged on the outer periphery of the center electrode, and the spark-absorptive metal After the metal adhered member is melted by laser welding to form a spark consumable metal ignition portion, an annealing process is performed.

[0010] In the above method, the spark consumable metal adhered member disposed on the outer periphery of the center electrode is melted by laser welding, and the ignition portion is formed on the outer periphery by so-called overlay welding of the spark consumable metal. are doing. In other words, the bead of the overlay welding itself forms an ignition portion made of a spark consumable metal. Also in this case, the component distribution and the thermal stress are likely to be discontinuous in the vicinity of the boundary between the ignition portion made of a spark consumable metal and the electrode base material, but the component diffusion is promoted by performing an annealing treatment on this, The occurrence and growth of cracks due to the discontinuity of the thermal stress and the difference in the thermal shrinkage can be suppressed.

In the electrode base material, at least a portion to be welded can be made of a heat-resistant metal mainly composed of Fe or Ni. In the present specification, “main component” means a component having the highest weight content, and does not necessarily mean “a component occupying 50% by weight or more”.

The annealing treatment of the present invention is performed at 800 to 1100 ° C.
Temperature. Thereby, generation of a diffusion layer and removal of thermal stress at the boundary between the wear-resistant tip or the electrode base material and the welded portion can be smoothly performed.

The annealing treatment of the present invention is preferably performed for 0.5 to 3 hours. Thereby, the generation of the diffusion layer and the removal of the thermal stress at the boundary between the wear-resistant tip or the electrode base material and the welded portion can be sufficiently performed.

[0014] Further, the annealing treatment of the present invention is preferably performed by 10 ^-5 To
It is performed in a vacuum of rr or less. By performing the annealing treatment in a vacuum furnace, oxidation of the surface can be prevented.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. A spark plug 100 as an example of the present invention shown in FIG. 1 has a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a tip 21 protrudes, and a fire-resistant spark formed at the tip. One end is connected to the center electrode 3 provided inside the insulator 2 and the metal shell 1 by welding or the like with a noble metal firing portion (hereinafter simply referred to as a firing portion) 33a as a consumable metal firing portion protruding. And a ground electrode 4 and the like, the other end of which is bent back to the side and the side surface of which is arranged to face the tip of the center electrode 3. In addition, the ground electrode 4 has the above-described firing portion 33a.
A noble metal firing portion (hereinafter, also simply referred to as a firing portion) 43a as a spark-resistant consumable metal firing portion is formed, and a gap between the firing portion 33a and the facing firing portion 43a forms a spark. The discharge gap is g.

The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a hole 6 for fitting the center electrode 3 along its own axial direction. . The metal shell 1 is formed of a metal such as low carbon steel in a cylindrical shape, and forms a housing of the spark plug 100. A screw portion 7 for attaching the plug 100 to an engine block (not shown) is formed on the outer peripheral surface.

The firing portion 33a and the facing firing portion 4
A configuration in which one of 3a is omitted may be adopted. In this case, a spark is generated between the ignition portion 33a and the side surface of the ground electrode 4 having no ignition portion, or between the opposing ignition portion 43a and the tip end surface of the center electrode 3 having no ignition portion. The discharge gap g is formed. Hereinafter, an embodiment in which the ignition portion 33a according to the present invention is provided on the center electrode 3 will be described. However, the same can be applied to a case where the ignition portion 43a according to the present invention is provided on the ground electrode 4.

As shown in FIG. 2A, a small-diameter portion 32c of the electrode member 32 is used as a portion to be welded between the center electrode 3 and the ground electrode 4, and in this embodiment, at least a tip surface 32d as a surface portion thereof.
Are made of a heat-resistant alloy containing Ni or Fe as a main component. The following can be used as the heat-resistant alloy containing Ni or Fe as a main component. Ni-base heat-resistant alloy: In this specification, Ni is contained in an amount of 40 to 85% by weight, and the remainder is mainly composed of Cr, Co, Mo, W, Nb, Al, and Ti.
And a heat-resistant alloy composed of one or more of Fe. Specifically, the following can be used (all are trade names; the alloy composition is described in the literature (Revised 3rd Edition Metal Data Book (Maruzen); p. 138); Not performed): ASTROLOY, CABOT 21
4, D-979, HASTELLOY C22, HASTELLOY C276, HASTELLOY
G30, HASTELLOY S, HASTELLOY X, HAYNES 230, INCONE
L 587, INCONEL 597, INCONEL 600, INCONEL 601, INCO
NEL 617, INCONEL 625, INCONEL 706, INCONEL 718, IN
CONEL X750, KSN, M-252, NIMONIC 75, NIMONIC 80A, N
IMONIC 90, NIMONIC 105, NIMONIC 115, NIMONIC 263,
NIMONIC 942, NIMONIC PE11, NIMONIC PE16, NIMONIC P
K33, PYROMET 860, RENE 41, RENE 95, SSS 113MA, UDI
MET 400, UDIMET 500, UDIMET 520, UDIMET 630, UDIME
T 700, UDIMET 710, UDIMET 720, UNITEP AF2-1 DA6, W
ASPALOY.

Fe-based heat-resistant alloy: In this specification, Fe is contained in an amount of 20 to 60% by weight, and the balance is mainly composed of Cr, Co,
A heat-resistant alloy comprising one or more of Mo, W, Nb, Al, Ti and Ni is generically referred to. Specifically, the following can be used (all are trade names; the alloy composition is described in the literature (Revised 3rd Edition Metal Data Book (Maruzen), p. 138); A-286, ALLOY 901, DISCALOY, HAYNES 55
6, INCOLOY 800, INCOLOY 801, INCOLOY 802, INCOLOY
807, INCOLOY 825, INCOLOY 903, INCOLOY 907, INCOLO
Y 909, N-155, PYROMET CTX-1, PYROMET CTX-3, S-59
0, V-57, PYROMET CTX-1, 16-25-6, 17-14CuMo, 19-9D
L, 20-Cb3.

On the other hand, the ignition section 33a and the opposing ignition section 43a are formed of Ir, Rh, Pt, Pd, Ru, Re,
Spark consumable metal containing at least one of W, Os, Mo, and Au as a main component, in this embodiment, Ir or P
It is mainly composed of a noble metal containing any one of t as a main component. By using these noble metals, the wear resistance of the ignition portion can be improved even in an environment where the temperature of the center electrode is likely to increase. Further, the weldability to the above-mentioned heat-resistant alloy is also good. For example, when a precious metal based on Pt is used, Pt alone or Pt
-Ni alloy (for example, Pt-1 to 30% by weight Ni alloy),
Pt-Ir alloys, Pt-Ir-Ni alloys and the like can be suitably used. In addition, Ir mainly composed of Ir
-Pt alloy, Ir-Rh alloy, etc. can be used.

When an Ir-based noble metal material is used, an oxide (composite oxide) of a metal element belonging to Group 3A (so-called rare earth element) and Group 4A (Ti, Zr, Hf) of the periodic table of elements is used. ) In the range of 0.1 to 15% by weight. This makes it possible to effectively suppress the consumption of Ir component due to oxidation and volatilization. As the oxide, Y ₂ O ₃ is preferably used, and in addition, La ₂ O ₃ , ThO ₂ , ZrO _{2 and the} like can be preferably used. In this case, the metal component is Ir alloy,
Ir alone may be used.

FIG. 2 shows a manufacturing process of the spark portion on the center electrode side of the spark plug according to the present invention. In FIG. 2A, a center electrode 3 includes a columnar electrode base material 32 made of a heat-resistant alloy containing Ni or Fe as a main component and an electrode base material 3
2 embedded in a central portion of the core 2 and made of a good heat conductive metal containing Cu or Ag as a main component. The electrode base material 32 is continuously provided from the large-diameter portion 32a to the small-diameter portion 32c on the distal end side via the reduced-diameter portion 32b, and is formed by cutting or plastic working. Tip surface 3 of small diameter portion 32c
A noble metal tip 33 as a wear-resistant tip is placed on 2d, and the noble metal tip 33 is welded to the small diameter portion 32c to form a noble metal firing part 33a as a spark consumable metal firing part.

Next, the steps up to the formation of the noble metal firing portion 33a will be described. In FIG. 2B, a disc-shaped or column-shaped noble metal chip (consumable chip) 33 is superimposed on a tip surface (chip-fixed surface) 32d to form a superposition assembly A. In addition, the noble metal tip 33 is made of an alloy composition constituting the ignition portion 33a. In addition, the small diameter portion 32
When the c and the noble metal tip 33 are overlapped, the tip surface 32
A concave portion may be provided in d, and the lower surface of the noble metal tip 33 may be placed in this concave portion.

As shown in FIG. 2C, a YAG beam emitted from a laser light source L
(Yttrium, aluminum, garnet) The laser beam LB is intermittently applied in a substantially horizontal direction toward a boundary position between the noble metal tip 33 and the small diameter portion 32c. At this time, the center electrode 3 is rotated in a predetermined direction, and irradiation is performed over the entire circumference at intervals where the irradiation surfaces overlap each other. As a result, the noble metal tip 3 constituting the superposition assembly A
3 and a small-diameter portion 32c, a full-circle laser weld (full-circle weld) B is formed along the outer peripheral surface, and the noble metal tip 33 is formed.
Is fixed to the tip surface 32d. At this time, the components of the electrode base material 32 and the noble metal tip 33 are in a state of being melted and solidified in the entire circumference laser welded portion B.

For the laser beam LB, other means such as an electron beam may be employed.
2 and the shape of the noble metal tip 33, FIG.
(C) It may be set so as to go from obliquely upward to obliquely downward. In addition to or instead of rotation of the center electrode 3, the laser light source L can be rotated in a direction opposite to that of the center electrode 3. Further, a plurality of laser light sources L may be provided.

Next, an annealing process is performed on the lap assembly A (center electrode 3) after the laser welding. FIG.
As shown in (d), the center electrode 3 after laser welding is placed in a vacuum heating furnace equipped with a heater 51 and a vacuum pump 52.
To accommodate. 950 ± in a vacuum of 10 ⁻⁵ Torr or less
After heating at 50 ° C. for 2 hours and then gradually cooling, the annealing treatment for the purpose of component diffusion (formation of a diffusion layer) and stress removal (relaxation of thermal stress) is completed. Noble metal tip 33 or small diameter part 32
By forming a diffusion layer near the boundary between c (electrode base material 32) and the entire circumference laser welded portion B, diffusion of components and relaxation of thermal stress are achieved, and generation of cracks due to differences in thermal shrinkage is suppressed. are doing.

The noble metal tip 33 is formed into a plate by hot rolling a molten alloy obtained by blending and melting each alloy component so as to have a predetermined composition, and the plate material is subjected to a predetermined process by hot stamping. The one formed by punching into a chip shape or the one formed by cutting an alloy into a linear or rod-shaped material by hot rolling or hot forging and then cutting it to a predetermined length in a length direction can be used. . Further, the noble metal tip 33 may be made of a material that is prepared by mixing and heating each metal powder so as to have a predetermined composition, sintering the powder particles, and densifying with volume shrinkage.

The noble metal tip 33 is fixed to the front end face 32d before welding. When the molten alloy is solidified, the noble metal tip 33 is liable to be displaced or eccentric, and the electrode is tilted (eccentric) or the irradiation position of the laser beam LB is displaced. Sex is impaired. Therefore, before laser welding, the noble metal tip 33 is connected to the tip surface 3 by resistance welding or the like.
At the time of temporary fixing to 2d, or at the time of laser welding, the tip surface of the noble metal tip 33 is pressed to hold and fix the noble metal tip 33 to the tip surface 32d, thereby preventing these.

FIG. 3 is a front view of the central electrode side ignition portion before welding. In the drawing, the dimensions of each part are as follows. When the outer diameter of the noble metal tip 33 is d1, the outer diameter of the small diameter portion 32c is d3, and the outer diameter of the large diameter portion 32a is D, d1 ≦ 1.5 [mm] d1 ≦ d3 ≦ d1 + 1.5 [mm] 1 0.5 ≦ D [mm].

The thickness of the noble metal tip 33 is 11 and the small diameter portion 3
When the thickness of 2c is l3, l1≥0.5 [mm] and 0≤l3≤0.4 [mm]. The included angle θ of the reduced diameter portion 32b is θ ≦ 110 °.

FIG. 4 is a longitudinal half sectional view of the ignition portion on the side of the center electrode, in which the noble metal tip 33 and the front end face 32d are superposed in a laminating manner. It is formed along the plane. When the depth of the bead of the laser welded portion B is t and the width is l2, t ≦ d1 / 2 l2 ≧ 0.4 [mm]

As is apparent from comparison with FIG.
The overlap assembly A of this embodiment has an unwelded region at least at the radial center thereof, and a part of the noble metal tip 33 and a small diameter portion 32c remain after welding. If the entire circumference laser weld B reaches the center of the lap assembly A and all the noble metal tips 33 are melted to leave no unwelded area at the center in the radial direction, the bead of the full circumference laser weld B is used. By increasing the width l2 and the depth t, a strong welding force can be obtained. However, on the other hand, the laser light source L requires a large amount of heat (energy), and the electrode base material 32 and the core body 31 that are more susceptible to a thermal change than the noble metal tip 33 absorb too much of this heat and blow holes. And cracks are likely to occur. Therefore, the unwelded area is left at least in the radial center of the superposition assembly A in consideration of not affecting the electrode base material 32 and the core 31 while suppressing the amount of heat required for welding. In the unwelded area of the lap assembly A, the noble metal tip 3
3 and the remaining portion of the small-diameter portion 32c (the electrode base material 32) are not or at least hardly affected by the welding, and it is considered that the component distribution before the welding and joining is maintained substantially as it is.

FIG. 5 shows the state of the boundary region of the conventional all-around laser weld B. Noble metal tip 33 or electrode base material 3
In the vicinity of the boundary between No. 2 and the entire circumference laser welded portion B, the component distribution is discontinuous. In general, the coefficient of thermal expansion is as follows: noble metal tip 33> all-round laser weld B> electrode base material 32;
In the vicinity of this boundary, thermal stress is discontinuous.

FIG. 6 shows the situation of the boundary region of the laser welded portion B around the entire circumference according to the present invention. Due to the annealing treatment, a diffusion layer C is generated in a boundary region between the noble metal tip 33 or the electrode base material 32 and the entire circumference laser welded portion B, and the diffusion of the component distribution and the relaxation of the thermal stress are achieved.

Then, it was confirmed by a repeated durability test of a cooling / heating cycle that generation and growth of a crack K were suppressed when a diffusion layer C was formed in a boundary region of the laser welded portion B around the entire circumference. The ignition part 33 on the center electrode side of the spark plug of FIG.
a is heated to 950 ± 20 ° C. for 2 minutes and then slowly cooled for 1 minute. This cooling / heating cycle was repeated 1,000 times, and the rate of crack development was measured. The crack growth rate is
In FIG. 4, when the depth of the bead of the laser welding portion B around the circumference is t and the depth from the outer surface of the crack is t0, t0
/ T.

In FIG. 7, 100% when no annealing process is performed.
% When the annealing temperature is 800%.
In the range of １1100 ° C., there is a tendency for the temperature to decrease significantly when the temperature increases. In addition, when the annealing temperature is constant, the crack growth rate decreases as the annealing time increases. It is considered that the annealing treatment caused the diffusion layer C to be generated in the vicinity of the boundary between the noble metal tip 33 or the small diameter portion 32c (the electrode base material 32) and the entire circumference laser welded portion B, thereby suppressing the generation and growth of the crack K. .

It should be noted that the present invention provides a spark plug in which the tip end surface of the ground electrode faces the side surface of the center electrode, for example, FIG.
It can also be used for forming a high melting point metal ignition portion of a multipolar spark plug as shown in FIG. Also, as shown in FIG.
A spark plug of a semi-surface discharge type which is a modification of the multi-pole spark plug, that is, a spark plug 10 in which the tip of the insulator 2 enters the spark discharge gap g.
2 is similarly applicable. In this case, the firing unit 334
Are formed in a ring shape in the circumferential direction of the outer peripheral surface of the center electrode 330 corresponding to the position of the front end surface 4a of the ground electrode 4 facing the same. This can be easily formed using the spark consumable metal adhered member 64 as follows. In other words, as shown in FIG. 20, a linear spark consumable metal fixing member 340 as a fixing member is wound and arranged in a circumferential groove 331 formed on the outer peripheral surface of the center electrode 330, By dissolving the spark consumable metal adhered member in
The ignition portion 334 is formed by filling the inside of the circumferential groove 331 with the spark consumable metal.

Specifically, as shown in FIG. 10A, a peripheral groove (for example, having a trapezoidal cross section) 331 is formed at the tip of the center electrode base material 330, and the peripheral groove 331 is formed. -Consumable metal adhered member 3 formed in a ring shape
Insert 40 and swage. Then, as shown in FIG. 3B, the laser beam 337 is irradiated onto the spark-consumable metal-fixed member 340 while rotating the center electrode base material 330 at a predetermined speed. As a result, as shown in FIG. 8C, the spark consumable metal-fixed member 340 is melted, and the ignition portion 334 is formed in the peripheral groove 331 so as to be welded by overlaying. Here, part of the metal component of the electrode base material is
It may be alloyed with the ignition part 334. When the ignition portion 334 is formed at the edge of the front end surface of the center electrode 330 as in the semi-surface discharge type spark plug 102 of FIG. 22, as shown in FIG. The tip of the electrode base material 330 is removed by cutting, polishing, cutting, or the like so that the firing portion 334 is exposed.

FIG. 8 shows an example of dimensions of each part on the center electrode side. d1 ≦ DD D ≧ 1.5 [mm] l1 ≧ 1.0 [mm] t ≦ 0.4 [mm]

The present invention can be applied to the ground electrode 4 together with or instead of the center electrode 3. Note that the portion where the chip-fixed surface is formed is not limited to the small-diameter portion 32c. When the small-diameter portion 32c is not provided, the portion where the chip-fixed surface is formed is the reduced-diameter portion 32b, and the tip-fixed surface is the distal end surface of the reduced-diameter portion 32b.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a spark plug to which a manufacturing method of the present invention is first applied, and an enlarged view of a main part thereof.

FIG. 2 is an explanatory view of a manufacturing process of a center electrode side ignition portion of the spark plug of FIG. 1;

FIG. 3 is a front view of a center electrode side firing portion before welding connection.

FIG. 4 is a vertical half sectional view of a center electrode side firing portion.

FIG. 5 is a conceptual explanatory view showing a state of a boundary region of a conventional all-around laser weld.

FIG. 6 is a conceptual explanatory view showing a state of a boundary region of a laser welding portion at the entire circumference according to the present invention.

FIG. 7 is an explanatory diagram showing a change in a crack growth rate.

FIG. 8 is a longitudinal half sectional view showing a main part of a spark plug which is a second application target of the spark plug manufacturing method of the present invention.

FIG. 9 is an explanatory view showing a conventional manufacturing process of a center electrode side firing portion.

FIG. 10 is an explanatory diagram of a firing portion forming step in a second method of manufacturing a spark plug according to the present invention.

FIG. 11 is a longitudinal sectional view showing an example of a form of formation of a firing portion in a multipolar spark plug.

FIG. 12 is a longitudinal sectional view showing an example of a form of formation of a firing part in a semi-surface discharge type spark plug.

[Explanation of symbols]

3 Center electrode 31 Core body 32 Electrode base material 32a Large diameter portion 32b Reduced diameter portion 32c Small diameter portion (tip fixing surface forming portion) 32d Tip surface (tip fixing surface) 33 Noble metal tip (spark consumable metal tip; Consumable tip) 33a Noble metal ignition part (spark-resistant expendable metal ignition part; ignition part) 4 Ground electrode A Lamination assembly B All-around laser weld (All-around weld) C Diffusion layer L Laser light source LB Laser beam g Spark discharge gap

Claims (5)

[Claims] 1. A center electrode, comprising: a center electrode; and a ground electrode arranged such that a side surface of the center electrode faces a tip end surface of the center electrode so as to form a spark discharge gap, and a ground electrode is provided at a position corresponding to the spark discharge gap. At least one electrode base material of the center electrode and the ground electrode is provided with Ir, Rh, Pt, Pd,
Spark consumable metal tip (hereinafter, referred to as consumable chip), which is mainly composed of at least one of Ru, Re, W, Os, Mo, and Au (hereinafter referred to as consumable chip), is joined by laser welding. A method for manufacturing a spark plug having a firing portion, wherein a welded portion of a wear-resistant tip of the electrode base material is made of a heat-resistant alloy, and welding is performed over the wear-resistant tip and the welded portion. By forming the part along the chip outer peripheral surface,
A method for manufacturing a spark plug, comprising: performing an annealing treatment after fixing the wear-resistant tip to the welded portion. 2. A center electrode, and a ground electrode arranged opposite to the center electrode so that a spark discharge gap is formed between the center electrode and the center electrode at a position corresponding to the spark discharge gap. At least one of the electrode and the ground electrode includes Ir, Rh, Pt, Pd, Ru, Re,
A method for producing a spark plug in which a spark consumable metal ignition portion is formed by joining a spark consumable metal adhered member containing any of W, Os, Mo and Au as a main component by laser welding, The ground electrode is arranged such that a front end surface thereof faces a side surface of the center electrode, and the firing portion corresponds to a position where the front end surface of the ground electrode faces the outer periphery of the center electrode. The spark consumable metal-fixed member is disposed on the outer periphery of the center electrode, and in this state, the spark consumable metal-fixed member is melted by laser welding; A method for manufacturing a spark plug, comprising: performing an annealing treatment after forming a reactive metal ignition portion. 3. The method according to claim 1, wherein the annealing is performed at a temperature of 800 to 1100 ° C. 4. The method according to claim 1, wherein the annealing is performed for 0.5 to 3 hours. 5. The method for manufacturing a spark plug according to claim 1, wherein the annealing is performed in a vacuum of 10 ⁻⁵ Torr or less.