JP2000195646A - Manufacture of spark plug, and spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method giving high joint strength and being less liable to cause defects in a boundary face of joint, in the case of a spark plug with a main metallic part made up by joining a body part to an end part, different in material from each other. SOLUTION: An end part 1B, with which a ground electrode 4 is unified, of a main metallic part 1 is formed of a heat-resisting second structure 51 while the second structure 51 is joined by friction grip joint to a first structure 50 of a ferrous metal. In comparison with the conventional resistance welding method, troubles such as defects are less liable to occur. and the manufacturing yield can be enhanced. In comparison with the resistance welding method, the joint strength of a body part 1A to the end part 1B is enhanced, and such a trouble that the body part 1A comes off the end part 1B from a defective part, is less liable to occur, if a thread part 7 is formed by rolling, etc., on an outer circumferential surface of the main metallic part 1 in extending relation from the body part 1A to the end part 1B, or if some shock is exerted thereon when a spark plug is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug used for an internal combustion engine.

[0002]

BACKGROUND OF THE INVENTION Spark plugs for internal combustion engines are generally
An insulator is arranged around the center electrode, and a cylindrical metal shell is further arranged outside the metal shell.The base end of the ground electrode is joined to the end face of the metal shell by welding or the like, and the tip side is used as the center electrode. It has a structure that faces each other. However, when using spark plugs under particularly severe conditions such as for racing, severe impacts are repeatedly applied at high temperatures,
In some cases, the ground electrode welded may be broken at the base end. Therefore, instead of joining a separate ground electrode to the metal shell, some of the automotive spark plugs supposed to be used in this environment have the metal shell tip and the ground electrode formed by cutting from the same material. Are integrally formed. According to this structure, since no welded portion is formed on the base end side of the ground electrode, the breakage resistance of the ground electrode can be significantly improved.

By the way, the ground electrode of the spark plug is
Since it is exposed to a high temperature in the cylinder head, it must be made of a heat-resistant alloy such as a Ni alloy. If such a ground electrode is to be integrally formed with the metal shell as described above, the metal shell must of course be made of a heat-resistant alloy.
However, forming the entire metal shell from an expensive heat-resistant alloy causes a significant increase in manufacturing cost. Therefore, usually, only the tip of the metal shell to which the ground electrode is integrated is formed from a heat-resistant alloy, and the remaining metal is used. A method is adopted in which the main body is made of an inexpensive iron-based material such as carbon steel, and the two are joined. Conventionally, resistance welding is employed as this joining method.

[0004]

However, in the case of the resistance welding method, welding defects such as defects are apt to occur, and there is a disadvantage that the yield is easily reduced. The cause is
If there is uneven contact or oxide film due to local irregularities on the surface to be joined between the main body and the tip, the uniformity of energization will be impaired and the welding state will be difficult to stabilize, resulting in uneven heat generation. It is conceivable that welding defects easily occur. When a welding defect occurs at the joint interface, for example, when the mounting screw portion is formed by rolling or the like on the outer peripheral surface of the metal shell so as to straddle the main body portion and the front end portion, the main body portion and the front end portion are defective. Troubles such as peeling off from parts may occur.

[0005] Even if a weld having few defects is formed, the resistance welding mainly involves a diffusion bonding mechanism associated with heat generation by energization. However, there is a disadvantage that the diffusion bonding layer is not formed, and the bonding strength tends to be insufficient.

An object of the present invention is to provide a spark plug in which a metal shell is formed by joining a main body portion and a tip portion made of different materials to each other, so that the joining strength is high, a defect is not generated at the joining interface, and the production yield is good. It is an object of the present invention to provide a method for manufacturing a spark plug and a spark plug that can be manufactured thereby.

[0007]

The present invention provides a center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and the metal shell. According to a method for manufacturing a spark plug having a base end side integrated with a ground electrode whose front end side is opposed to a center electrode, in order to solve the above-described problems, the metal shell is bisected in the axial direction, and the ground electrode is A first structure made of an iron-based metal to be a main body, and a second structure to be a front end, the first structure being a main body, with a side to be integrated being a front end and a remaining part being a main body. And a second structural body made of a metal material having better heat resistance than the ferrous metal.

According to the above-mentioned manufacturing method, the tip of the metal shell on the side where the ground electrode is integrated is formed of the heat-resistant second structure, and the second structure is formed of the first metal of the ferrous metal. By joining to the structure by friction joining, defects such as defects are less likely to occur as compared with the conventional resistance welding method, and the production yield can be improved. In addition, compared to the resistance welding method, the joining strength between the main body portion of the metal shell based on the first structure and the tip portion also based on the second structure is improved, and, for example, a shape extending over the main body portion and the tip portion. Even if the mounting screw is formed on the outer peripheral surface of the metal shell by rolling, etc., or if a slight impact is applied when using a spark plug, there is a problem that the main body and the tip will peel off from the defective part. It is extremely unlikely to occur.

[0009] The factors that reduce the defects at the joints and improve the joint strength by the above manufacturing method are presumed as follows. In the friction welding method, objects to be welded are relatively moved while being in contact with each other at a welding interface, and welding is performed using heat generated by the friction. Since objects to be bonded violently move across the interface, contact unevenness due to local unevenness is unlikely to occur, and uniform heat generation can be expected over the entire interface. In addition, in the case of resistance heating, electrical conduction failure due to the presence of an oxide film or the like has a large effect on an energized current value and, consequently, a calorific value. Almost independent of the conduction state, a uniform heat generation state is formed without being so sensitively affected by the cleanliness of the bonding interface before processing. As a result, it is considered that a defect based on uneven heat generation hardly occurs.

[0010] Further, the following important differences exist between the friction welding method and the resistance welding method. That is,
In the resistance welding method, the objects to be joined (the first structure and the second structure) do not move relative to each other at all during the joining process, and therefore, the joining mechanism is exclusively based on the diffusion of components through the contact interface between the objects to be joined. Be the subject. Therefore, as described above, the formation of a diffusion layer having a sufficient thickness may not be expected by short-time heating. Further, the mutual diffusion rates of the main component elements of the first structure and the second structure are not always the same, and in some cases, there is a large difference between the two. As a result, a large number of voids may be formed at the bonding interface due to the so-called Kirkendale effect. All of these can lead to a decrease in the reliability of the joint.

On the other hand, in the friction joining method, in addition to the diffusion joining effect due to frictional heating, the first structure and the second structure move vigorously relative to each other across the interface. Intense mechanical mixing forces will be applied. As a result, as shown in FIG. 4B, the interface between the first structure and the second structure has a complicated and complicated structure due to the mixing effect, and further proceeds to FIG. 4C. As shown in FIG. 5, a thermal alloying treatment can produce a mechanical alloying layer of a considerable thickness, which is not desired. Further, even if there is a difference in the mutual diffusion coefficient between the first structure and the second structure as described above, a uniform alloy state can be obtained by applying a mechanical mixing force. Is also reduced. Diffusion layers may be formed on both sides of the mechanical alloying layer, however, unlike in the case of energization and heating, frictional heat is locally generated near the contact interface between both structures, and from the interface. Since the cooling effect accompanying the movement of the structure (for example, high-speed rotation) is added to the distant portion, the thickness is smaller than that of the resistance welding method. Therefore, the occurrence of voids and the like due to the difference between the mutual diffusion coefficients can be suppressed. As described above, according to the present invention, it is possible to increase the reliability of joining between the main body and the distal end of the metal shell.

In the method for manufacturing a spark plug according to the present invention, before or after performing the friction joining, the second structure is subjected to a removing process including at least one of cutting, cutting, and polishing to ground. By removing portions other than the electrode and the portion intended for the tip portion, a processing step of forming a ground electrode portion on the second structure can be performed.
By forming the ground electrode by removing unnecessary parts from the second structure, which is originally one in the material state, no joint is formed between the ground electrode and the metal shell, and the ground electrode has a breakage resistance. Can be greatly improved.

In the friction joining step, the first structure and the second structure are brought into contact with each other at the joint surface and pressurized in the axial direction, and are relatively rotated around the axis to frictionally join them. It can be implemented in the form. As a result, a mechanical relative kinetic force can be efficiently applied to the joint surface of the two structures,
As a result, a good bonding state can be easily formed.

The second structure can be made of a Ni-based heat-resistant alloy. Since the Ni-based heat-resistant alloy has excellent high-temperature strength and high affinity with Fe, which is a main component of the first structure, a high-strength bonded state can be formed.

By the manufacturing method of the present invention as described above, the spark plug of the present invention having the following specific structure is realized. In the spark plug, the metal shell is bisected in the axial direction, and the side where the ground electrode is integrated is the tip, and the remaining part is the main body. The main body is made of an iron-based metal. The grounded electrode is made of a metal material having better heat resistance than the iron-based metal constituting the main body, and between the main body and the distal end, each of the main body and the distal end is formed. A bonding layer in which the component metal elements are mixed at an intermediate composition ratio between the two parts is formed. Then, as schematically shown in FIG. 6, the weight concentration of Fe (hereinafter, referred to as main body main component) as a main metal element of the main body portion at an arbitrary position in the bonding layer is set to NA, The average weight concentration in the part is NAM, the average weight concentration in the tip part is NAT, and the weight concentration of the main component metal element at the tip part (hereinafter referred to as tip main component) at an arbitrary position in the bonding layer is NB. Assuming that the average weight concentration in the tip portion of the tip main component in the tip portion is NBT and the average weight concentration in the body portion is NBM, the relative concentration SA of the main component in the bonding layer is given by: SA = (NA−NAT) / ( NAM-NAT); When the relative concentration SB of the tip main component in the bonding layer is defined as: SB = (NB−NBM) / (NBT−NBM), 0.3 ≦ S
A region where B / (SA + SB) ≦ 0.7 is formed with a thickness of 3 μm or more.

By securing an area of 0.3 ≦ SB / (SA + SB) ≦ 0.7 with a thickness of 3 μm or more, the main body of the metal shell based on the first structure and the tip of the metal shell based on the second structure are also formed. A bonded state having few defects and excellent strength can be formed with the portion. For example, in the conventional resistance welding method, only thermal component diffusion occurs between the first structure and the second structure. Therefore, as shown in FIG. The concentration of the component changes almost continuously through the bonding interface, and the heat generation time is kept relatively short, so that the thickness of the concentration change region also becomes small. Therefore, 0.3 ≦ KB ≦ 0.7 (where KB
= SB / (SA + SB)) also has a thickness t of at most 2.
It is as small as μm or less. However, when the method of the present invention based on friction welding is employed, as shown in FIG. 7B, the respective materials of the first structure and the second structure are almost uniformly mixed due to the mechanical alloying effect described above. A layer (corresponding to the aforementioned mechanical alloying region) in which the rate of change of each concentration in the joining direction between the tip main component and the main body main component is suppressed to be smaller than the diffusion regions before and after is formed near the joining interface. It is formed with a considerable thickness. As a result, the thickness t of the region can be secured at a large value of 3 μm or more, which was impossible by the resistance welding method, and the reliability of the joining is improved. The thickness t is more desirably 5 μm or more.

[0017]

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 includes a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1, and a tip portion exposed from the insulator 2 with the tip end exposed. A center electrode 3 is provided and a ground electrode 4 whose base end is integrated with the metal shell 3 and whose front end faces the center electrode 3.

The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a central electrode 3 in a through hole 6 formed along its own axial edge direction.
Is inset.

The metal shell 1 is formed in a cylindrical shape as a whole, and forms a housing of the spark plug 1. The metal shell 1 is bisected in the axial direction, and the side where the ground electrode 4 is integrated is the tip 1B, and the remaining part is the main body 1A, and the main body 1A is made of an iron-based metal such as low carbon steel. The tip portion 1B and the ground electrode 4 integrated with the tip portion 1B are made of a metal material having better heat resistance than the iron-based metal constituting the main body portion 1A, for example, Inconel 600 (“Inconel” is a product of Inco UK). (Trade name) or the like. On the outer peripheral surface on the distal end side of the metal shell 1, a mounting screw portion 7 is formed so as to extend over the main body portion 1A and the distal end portion 1B. On the other hand, in the main body 1A, a gas seal portion 1c and a hexagonal portion 1e are formed adjacent to the base end side of the mounting screw portion 7. Also, 1
d is a caulking part for fixing the metal shell 1 to the insulator 2.

The ground electrode 4 is integrated with the distal end surface of the metal shell 1 such that the base end 4a is inclined inward, while the distal end 4b is substantially parallel to the distal end surface of the center electrode 3. As opposed to this. Further, the base end 4a has a larger diameter than the tip 4b. Thereby, the breakage resistance of the ground electrode 4 when receiving an impact or the like is further enhanced. In this embodiment, both sides of the base end portion 4a are formed as tapered surfaces in a flared form to widen the width.

Next, the main body 1A of the metal shell 1 and the tip 1
As shown schematically in FIG. 4 (c), the main component metal element (Fe in this case) of the main body 1A and
A bonding layer is formed in which the tip portion 1B main component metal element (in this case, Ni) is mixed at an intermediate composition ratio between the two portions. As described above with reference to FIG.
Assuming that B = SB / (SA + SB), a region where 0.3 ≦ KB ≦ 0.7 is formed with a thickness of 3 μm or more, preferably 5 μm or more.

Such a spark plug 100 can be manufactured, for example, as follows. As shown in FIG. 2A, a first structure 50 to be the main body 1A of the metal shell 1
And a second structure 51 to be the tip 1B. In this embodiment, the first structure 50 is made of low carbon steel, and the gas seal portion 1c and the hexagonal portion 1e are already formed by forging. However, at this stage, the mounting screw portion 7 is not yet formed in the cylindrical portion 7a on the distal end side, and the distal end of the cylindrical portion 7a is closed in order to equalize the surface pressure of the friction welding. It is shaped. Further, a convex portion 7b is formed at the center of the closed front end surface in order to concentrate frictional pressure in the central portion of the surface at the initial stage of joining and to promote heat generation in the central portion and further softening of the material. On the other hand, the second structure 51 is formed of a Ni-based heat-resistant alloy into a solid columnar shape having substantially the same outer diameter as the cylindrical portion 7a. In this embodiment, the axial length of the cylindrical portion 7a of the first structure 50 is set to about 22.5 mm, and the axial length of the second structure 51 is set to about 7 mm.

The first structure 50 and the second structure 51
Are gripped by the chucks C1 and C2 in a substantially coaxial positional relationship such that the distal end surface of the cylindrical portion 7a and one end surface of the second structure 51 face each other. In this state, FIG.
As shown in FIG. 2B, for example, in a state where the second structure 51 is stationary and fixed, the first structure 50 is rotated around the axis together with the chuck C1 (the chuck is not shown in FIG. 2B and thereafter). Do).

In this state, the first structure 50 and the second structure 51 are relatively approached in the axial direction (for example, the second structure 51 is fixed and the first structure 50 is approached toward the first structure 50). As a result, as shown in FIG. 2 (c), the end surface of the cylindrical portion 7a is brought into contact with the end surface of the second structure 51, and the rotation of the first structure 50 is performed while pressing in the axial direction. continue. As a result, the cylindrical portion 7a and the second structure 51 generate frictional heat at the contact surface (joining surface) thereof, and are joined together while generating burrs B around them. At this time, both structures 50, 51
The second structure 51 may be rotated in the opposite direction to the first structure 51 in order to increase the relative rotation speed between them.

FIG. 4A schematically shows a state of the bonding interface immediately before the contact, and FIG. 4B schematically shows a state of the bonding interface estimated during the progress of the bonding. The interface between the first structure 50 and the second structure 51 is softened by heat generation, and the softened material is vigorously mixed by mechanical force due to rotational friction to form a complicated and complicated structure. Then, as shown in FIG. 3C, it is presumed that this mixed region eventually forms a mechanical alloying layer.
In addition, a slight diffusion layer may be formed on both sides of the mechanical alloying layer due to the friction heat generated subsequently.

FIG. 3 shows an example of a rotation control pattern of the first structure 50 and the second structure 51 from the start to the end of the friction welding. When the first structure 50 reaches the target rotation speed NS, the relative approach between the first structure 50 and the second structure 51 is started, and when they come into contact, the axial joining load starts to increase (for example, at time T1). ). First structure 50
When the heat generated by friction between the first structure 50 and the second structure 51 increases and the material softens, even if the first structure 50 and the second structure 51 continue to approach each other, the plastic flow of the material causes The increase in load becomes dull.

When the joining process is completed, the first structure 50
When the rotation of the first structure is suddenly stopped, a strong inertial force acts on the softened region and a trouble such as breakage may occur. Therefore, the second structure 51 is started to rotate in the same direction as the first structure 50 (time T2). When the speed becomes substantially the same as that of the first structure 50 (time T3), the rotation is continued for a while at a constant rotation speed.
As a result, the relative rotational speed at the joint interface between the second structure 51 and the first structure 50 becomes 0, and frictional heat generation stops. Then, the temperature of the softened region is lowered and hardened, and the bonding state is stabilized. In addition, since the rotation of the second structure 51 and the first structure 50 is continued, the cooling is promoted by the airflow generated in the surface layer portion. When the cooling is completed, the rotation of the second structure 51 and the first structure 50 is stopped (time T4, T5).

When cooling after the joining is completed, the rotation speed of the second structure 51 is increased while the rotation speed of the first structure 50 is reduced, and when the rotation speed becomes substantially the same, a constant rotation speed is reached. Alternatively, the rotation may be continued.

Returning to FIG. 2, when the friction welding is completed,
As shown in (d), the burr B is removed by cutting or the like, and further, as shown in (e), the tip side of the second structure 50 is externally cut to form the ground electrode 4, and the through hole 6 is formed. Of the second structure 51 and the first structure 50
On the outer surface of the above, a mounting screw portion 7 is formed by rolling in such a manner as to extend over both. Thereby, the metal shell 1 in which the main body 1A based on the first structure 50 and the tip 1B (in which the ground electrode 4 is integrated) based on the second structure 51 is frictionally joined is obtained. Since the joining layer between the first structure 50 and the second structure 51 has a small number of defects as described above due to the friction joining, problems such as interface peeling during thread rolling are extremely unlikely to occur.

As shown in FIG. 5, the ground electrode 4 may be formed on the second structure 51 in advance by cutting or the like, and this may be frictionally joined to the first structure 50.

When the insulator 2 and the center electrode 3 are assembled to the metal shell 1, the spark plug 100 shown in FIG. 1 is obtained. The spark plug 100 has its mounting screw 7
Is mounted on an engine block (particularly that of a racing car engine) and is used as a source of ignition for an air-fuel mixture supplied to a combustion chamber.

FIG. 8 shows Ni cross-sections of the cross-section near the bonding layer between the first structure 50 and the second structure 51 that have been friction-welded, using EPMA attached to the SEM.
((A)) and characteristic X-ray images of Fe ((b)) (magnification:
This shows an example of the result of line analysis of the intensity distribution of each characteristic X-ray on an analysis line (shown by → for each characteristic X-ray image) crossing the bonding interface (about 750 times) (characteristic X-ray). In the image, the brighter part has higher characteristic X-rays, which means that the element concentration is higher). FIGS. 9A to 9C show the results of the same analysis performed on the members joined by resistance welding. First, Ni of the resistance welded product (FIG. 9A)
And in the characteristic X-ray image of Fe (FIG. 9B), Ni
On the side of the second structure mainly composed of
It can be seen that the components have diffused to some extent, but that the Ni components have hardly diffused to the second structure side. According to the line analysis profile shown in FIG. 9C, the thickness t of the above-mentioned region where 0.3 ≦ KB ≦ 0.7 (the main component element at the tip is Ni) is about 2 μm. On the other hand, in the case where the friction welding is performed, the thickness t of the region where 0.3 ≦ KB ≦ 0.7 is about 10.7 μm. In addition, approximately at the center in the thickness direction of the bonding layer, a layer in which the rate of change of the concentration of Ni and Fe is suppressed to be smaller than that of the diffusion regions before and after is approximately 8%.
It is formed with a thickness of about μm. This is presumably because the respective materials of the first structure and the second structure were substantially uniformly mixed due to the mechanical alloying effect.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view and a plan view showing an example of a spark plug of the present invention.

FIG. 2 shows a method of manufacturing the metal shell.

FIG. 3 is a schematic diagram showing an example of a rotation control pattern during friction welding.

FIG. 4 is a schematic diagram estimating and showing a process of forming a frictional joint.

FIG. 5 is an explanatory view showing an example of a step of performing friction welding after forming a ground electrode in advance on a second structure.

FIG. 6 is a view schematically showing a distribution state of a main component element and a tip main component element in the vicinity of a bonding layer.

FIG. 7 is a view for explaining the distribution of the main component elements of the main body and the main component elements of the tip in comparison with the difference between the resistance welded product and the friction bonded product.

FIG. 8 shows N by EPMA near the joining interface of a friction-joined product.
Characteristic X-ray images of i and Fe and their line analysis profiles.

FIG. 9 shows N by EPMA near the joining interface of a resistance welded product.
Characteristic X-ray images of i and Fe and their line analysis profiles.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 metal shell 1A main body 1B tip 2 insulator 3 center electrode 4 ground electrode 50 first structure 51 second structure 100 spark plug

Claims (8)

[Claims] 1. A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a base end side integrated with the metal shell, and a tip end side having the center. A method for manufacturing a spark plug comprising an electrode and a ground electrode opposed to the spark plug, wherein the metal shell is bisected in the axial direction, a side where the ground electrode is integrated is a tip, and a remaining part is a main body. A first structure made of an iron-based metal to be the main body,
The second structure to be the tip portion, a second structure made of a metal material having better heat resistance than the iron-based metal constituting the first structure, and the second structure in the axial direction A method for manufacturing a spark plug, comprising a friction joining step of friction joining. 2. Before or after performing the friction welding, the second structure is subjected to a removing process including at least one of cutting, cutting, and polishing, and is scheduled on the ground electrode and the distal end portion. The method for manufacturing a spark plug according to claim 1, further comprising a processing step of forming the ground electrode portion on the second structure by removing portions other than the formed portion. 3. In the friction joining step, the first structure and the second structure are brought into contact with each other at a joint surface and pressurized in the axial direction, and are relatively rotated around the axis. The method for producing a spark plug according to claim 1, wherein the two are friction-welded by the method. 4. The method according to claim 1, wherein the second structure is made of a Ni-based heat-resistant alloy. 5. A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, a base end side integrated with the metal shell, and a tip side being the center. A spark plug including an electrode and a ground electrode facing the electrode, wherein the metal shell is bisected in the axial direction, the side where the ground electrode is integrated is a tip, and the remaining part is a body, the body being Is formed of an iron-based metal, the tip and the ground electrode integrated therewith are formed of a metal material having better heat resistance than the iron-based metal forming the main body, and the main body and Between the tip portion, a bonding layer in which the main component metal elements of the main body portion and the tip portion are mixed at an intermediate composition ratio of both portions is formed, and any of the bonding layers The main metal element of the main body at the position That Fe (hereinafter, body referred ingredient) the weight concentration of NA, NAM average weight concentration within the body portion of the body main component, also the average weight concentration within the tip portion N
AT, the weight concentration of the main component metal element (hereinafter referred to as the tip main component) at the tip portion at an arbitrary position in the bonding layer is NB, and the average weight concentration of the tip main component in the tip portion is NBT. , The average weight concentration in the body
The relative concentration SA of the main body main component in the bonding layer is: SA = (NA−NAT) / (NAM−NAT); The relative concentration SB of the tip main component in the bonding layer is: SB = (NB −NBM) / (NBT−NBM);
The region where ≦ SB / (SA + SB) ≦ 0.7 has a thickness of 3 μm.
A spark plug characterized by being formed with a length of at least m. 6. The spark plug according to claim 5, wherein said tip main component is Ni. 7. The spark plug according to claim 5, wherein a mounting screw portion is formed on an outer peripheral surface of the metal shell so as to extend over the main body portion and the distal end portion. 8. The spark according to claim 5, wherein a base end of the ground electrode integrated with the front end of the metal shell has a larger diameter than a front end. plug.