JP2003223968A - Manufacturing method of spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a spark plug and the spark plug wherein at the jointing part between an earth electrode and a main body metal fitting, a fused protrusion part caused by the jointing can be removed precisely, and further wherein a spark plug with high quality can be manufactured effectively. <P>SOLUTION: In the manufacturing of the spark plug, the process of removing the protruded part to remove the fused protrusion part generated in the junction process is carried out against the junction part 101 between the main body metal fitting 5 and the earth electrode 4' joined by means of the joining process. In this process of removing the protruded part, against the fused protrusion part formed at least at either side of the inner side or the outer side of the junction part 101, by carrying out removing work by means of a shearing work or cutting work for a plurality of times against the same part, at least one part of this fused protrusion part is removed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a spark plug.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of spark plugs,
Joining of the ground electrode and the metal shell is performed by welding or the like.In the vicinity of the welded portion of the ground electrode and the metal shell, the welded portion is partially projected due to the welding, or the weld sag is formed. May occur and a fused protrusion may be formed. Then, since such a fused protrusion may interfere with normal surface formation and may contribute to the deterioration of the quality of the product, a removal process for removing such a fused protrusion is performed after the welding process. Often.

[0003]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to precisely remove a molten protrusion caused by welding in a welded portion of a ground electrode and a metal shell, and to provide a high quality spark plug. It is to provide a method of a spark plug that can be effectively manufactured.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to an insulator having a central through hole extending in the axial direction, a center electrode arranged on the tip side of the central through hole, and a diameter of the insulator. The metal shell is arranged so as to surround the outside in the direction, and one end is welded to the front end surface of the metal shell, and the other end is a ground electrode arranged so as to form a spark discharge gap with the center electrode. According to a method for manufacturing a spark plug, in order to solve the above problems, one end surface of a rod-shaped electrode member to be a ground electrode is welded to a tip surface of a metal shell, thereby joining the metal shell and the ground electrode. A welding step of forming a body, and a protruding portion removing step of removing a molten protruding portion generated in the welded portion between the metal shell and the ground electrode in a form protruding from the peripheral side surface of the ground electrode, The removal process At least one of the inner peripheral surface side and the outer peripheral surface side of the metal shell is characterized in that the fusion protrusion is removed by performing a plurality of removal processes by shearing and / or cutting on the fusion protrusion. And

In the case of removing the molten protrusions caused by the welding process as described above, for example, by shearing, if it is attempted to remove by a single shearing process, a long stroke of the tool required for the removal must be secured. I have to. That is, such a stroke is set in consideration of the material and thickness of the portion to be removed. However, the greater the thickness of the portion to be removed, the more shearing force is required. It is necessary to secure a stroke.

FIGS. 10 and 11 show an example of processing the welded portion 101 in the joined body W _p of the ground electrode 4 ′ and the metallic shell 5. FIG. 10 shows a processing example on the inner peripheral surface side of the metal shell 5, and FIG. 11 shows a processing example on the outer peripheral surface side. 10 (b) and 11 (b), the press blade (the inner shearing tool 203 (FIG. 10 (b)) reciprocating in the axial direction of the metal shell 5 and the outer shearing tool 201 (FIG. 11 (b)) shows an example of the shearing process, in which the stroke of the tool is long in one shearing process and the base end side of the fusion protrusion 101 is processed, so that as shown in the figure, There is a high possibility that the cutting edge will collide with the inner peripheral surface or the outer peripheral surface of the metal shell 5, and as a result, for example, a scratch 305 in FIG. Due to the presence of the metal shell, the metal shell after thread rolling may be hindered.
As shown in (b), the metal fitting side engaging portion 7 formed to project radially inward from the inner peripheral surface to support the insulator.
There is a possibility that the blade edge of the tool may collide with and the metal fitting side engaging portion 7 may be damaged. It is more difficult to remove the melted protrusion by such a single shearing process for a product having a smaller allowable stroke in the tool.

On the other hand, FIG. 10 (a) and FIG. 11 (a) show cutting using a rotary blade (inner cutting tool 204 (FIG. 10 (a)), outer cutting tool 202 (FIG. 11 (a)). If the molten protrusions are removed at once by the processing, as shown in FIG. 11 (a), the cutting scraps are rolled up from the molten protrusions during the processing, and the residue 303 is partially generated. Alternatively, as shown in FIG.
May contact the metal fitting side engaging portion 7 of the metal shell 5 and damage the metal fitting side engaging portion 7. Although the cutting dust is wound up depending on the material, it is more likely to occur when there is more cutting margin to be removed at one time in the cutting process.

On the other hand, as in the present invention, when the molten protrusions in the welded portion are removed, if they are not removed at once but are divided into a plurality of times, the above-mentioned problems occur. Can be dealt with and can be removed accurately. That is, if the molten protrusions are gradually removed by a plurality of removal processes, for example, when performing a shearing process, the tool stroke per removal process can be made small, and When cutting is performed, it is not necessary to remove all the target portions at once, so that the occurrence of winding can be effectively reduced.

Specifically, in the removing step, the melting protrusion may be subjected to shearing first, and the remaining portion of the melting protrusion after the shearing may be further cut. By carrying out preliminary processing by shearing prior to cutting, it is possible to effectively prevent the cutting chips from rolling up during cutting.

Specifically, the following two methods can be considered. First, shearing is performed so as to cut off the tip side portion in the projecting direction of the fusion protrusion, and the portion of the fusion protrusion remaining after the shearing is removed by cutting. In this case, the volume of the melted protrusions to be removed by cutting is reduced, the removal margin by one cutting is reduced, and cutting chips are less likely to be rolled up. In the second method, a cut portion that cuts in the axial direction of the metal shell is formed in the molten protrusion by shearing, and the molten protrusion having the notch is cut. In this way, the cutting thickness to be removed by the cutting process is reduced, and thus cutting chips are less likely to be rolled up. In addition, as the cutting process, in addition to the cutting process in a narrow sense using a cutting tool, a grindstone grinding process is included in the concept of the cutting process in the present invention. In particular, processing using a rotary blade (milling with an end mill or the like) can be preferably adopted. In this case, since the main part of the metal shell is formed into a cylindrical shape, it can be said that it is particularly convenient to perform the cutting work by a rotary blade that rotates around an axis parallel to the central axis of the metal shell. On the other hand, as the shearing process, a process using a shearing blade such as a press blade can be preferably adopted.

In addition, the inner molten protrusion portion formed on the inner peripheral surface side of the metal shell and the outer molten protrusion portion similarly formed on the outer peripheral surface side of the welded portion should be independently removed. However, if shearing is performed on both of them at the same time, the processing time can be shortened, which in turn contributes to efficient product manufacturing.

In a general spark plug manufacturing process, when forming a spark discharge gap, a bending process is performed in which the ground electrode is bent back so that its tip approaches the tip of the center electrode. In this case, in order to avoid interference between the shearing blade or the cutting tool and the ground electrode,
It is desirable to perform at least the step of removing the inner molten protrusion formed on the inner peripheral surface side of the metal shell prior to the bending step. This is because if the ground electrode is in a state before bending, the tool can be taken in and out of the metal shell from the side where the ground electrode is formed without any trouble.

In recent years, in order to improve durability of the electrode against exhaustion of spark discharge, a spark plug in which a noble metal tip mainly composed of Pt, Ir, or the like is joined on the surface of the electrode facing the spark discharge gap is becoming popular. When the noble metal part such as the noble metal tip is bonded to the peripheral side surface of the ground electrode in a protruding form, the ground electrode is in a state before the bending process for forming the spark discharge gap when the inner molten protrusion is removed. However, there is a possibility that the tool may interfere with the noble metal portion and hinder the removal process. From this point of view, it is desirable that the peripheral side surface of the ground electrode is an electrode base material surface to which the noble metal portion is not joined, in the step of removing the inner molten protrusion portion that is performed prior to the above-described bending step of the ground electrode. Such a configuration is possible with the spark plug in which the ground electrode faces the peripheral side surface of the center electrode at its tip end surface to form a spark discharge gap. However, even in the case of a spark plug (so-called parallel electrode type spark plug) in which the ground electrode forms a spark discharge gap by facing the tip surface of the center electrode on the peripheral side surface, a noble metal tip of a type that is not bonded to the ground electrode side is used. Anything will do. On the other hand, even if the parallel electrode plug is of a type in which the noble metal tip is joined to the ground electrode side, if a recess or notch or the like is provided on the tool side to avoid interference with the noble metal tip, Removal processing can be performed.

When a plurality of ground electrodes are provided around the center electrode and the multi-pole type spark plug is targeted, the removal processing of the present invention is performed simultaneously on a plurality of ground electrodes (for example, all ground electrodes). Alternatively, removal processing may be performed on each ground electrode. Further, even when the removal processing of the plurality of ground electrodes is performed at the same time, both the inner and outer melting protrusions may be performed at the same time, or may be performed independently. In either case, the processing efficiency can be increased in the former case.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described with reference to the examples shown in the drawings. A spark plug 1 as an example of the present invention shown in FIG. 1 is configured as a so-called semi-creeping discharge type spark plug, and has a tubular metal shell 5 and an insulator 3 fitted into the metal shell 5 so that a tip portion thereof protrudes. The base end side is coupled to the center electrode 2 and the metal shell 5 provided inside the insulator 3, and the tip side of the center electrode 2 is opposed to the peripheral side surface of the center electrode 2 with the tip end of the insulator 3 interposed therebetween. It is provided with the arranged ground electrode 4 and the like.

The insulator 3 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a hole portion (center through hole) 3d into which the center electrode 2 is fitted along its own axial direction. have. Further, the metal shell 5 is formed of a metal such as low carbon steel into a cylindrical shape and constitutes a housing of the spark plug 1, and the spark plug 1 is illustrated on the outer peripheral surface thereof as shown in FIG. A threaded portion 6 for attaching to the cylinder head is formed.

Two ground electrodes 4 are provided, one on each side of the center electrode 2, and each of them has an end face (ignition face) 4a.
Is curved and formed so as to face the side circumferential surface 2b (firing surface) on the tip side of the cylindrical center electrode 2 substantially in parallel, while the other end side is fixed to the metal shell 5 by welding. It is integrated. In the present embodiment, a semi-creeping type multipolar spark plug has been described as an example, but a so-called parallel type in which the tip end face of the center electrode and the ground electrode face each other is not a side facing type. The facing type may be applied, or the type in which these are combined may be targeted. In any case, it should be mentioned above that the spark plug of the form in which the ground electrode is welded to the metal shell can be applied to various types.

The insulator 3 is arranged such that the tip portion 3a thereof is inserted between the side peripheral surface 2b of the center electrode 2 and the ignition surface 4a of the ground electrode 4. In the axial direction of the center electrode 2, the front end surface 2e side of the center electrode 2 is the front side and the opposite side is the rear side, and the front end surface 3e of the insulator 3 is the rear side of the front end surface 4a of the ground electrode 4. It is located in front of the edge 4f. On the other hand, the tip end surface 2e of the center electrode 2 is arranged so as to protrude from the tip end surface 3e of the insulator 3 by a predetermined height.

In the hole 3d of the insulator 3, the terminal fitting 13 is inserted and fixed on one end side, and the center electrode 2 is also inserted and fixed on the other end side. A resistor 15 is arranged between the terminal fitting 13 and the center electrode 2 in the hole 3d. Both ends of this resistor 15 are
It is electrically connected to the center electrode 2 and the terminal fitting 13 via the conductive glass seal layers 16 and 17, respectively. Further, the terminal fitting 13 is made of low carbon steel or the like, and a Ni plating layer (layer thickness: 5 μm, for example) for corrosion protection is formed on the surface. The resistor 15 is made of glass powder, ceramic powder, metal powder (for example, Zn, Sb, Sn, Ag and N).
i, which is mainly composed of one or more of i), and non-metallic conductive material powder (for example, amorphous carbon or graphite)
And an organic binder and the like in a predetermined amount and sintered by a known method such as hot pressing.

In the center electrode 2, the electrode base material constituting the surface layer of the electrode is made of Ni or Ni alloy, and if necessary, Cu or Cu alloy is formed in the center portion for improving heat transfer. The core material is inserted. On the other hand, the ground electrode 4
Also, the electrode base material is made of Ni or a Ni alloy. Further, also in this ground electrode 4, a core material made of Cu or Cu alloy may be inserted in the center portion for improving heat transfer,
For the same purpose, pure Ni is surrounded by Cu or C in the center.
A layered structure covered with a u alloy may be inserted. In both the center electrode 2 and the ground electrode 4, a highly heat-resistant Ni alloy, for example, a Ni-base superalloy can be used as the electrode base material (for example, Inconel 600 (trademark) or Inconel 601 (trademark)). .

Next, a method for manufacturing the spark plug of the present invention will be described. In manufacturing the above-described multipolar plug, first, as shown in FIG. 2A, one end surface of each of the two rod-shaped (for example, rectangular rod-shaped) ground electrodes 4 ′ to be the ground electrodes is It is attached to the front end surface 5a of the metal shell 5 by electric resistance welding to form a joined body W _P (welding process). Then, 2 to the conjugate W _P
Although the bending step as shown in (b) is performed, the metal shell 5 welded by the welding step prior to the bending step.
With respect to the welded portion 101 between the ground electrode 4'and the ground electrode 4 ', the molten protrusion portion due to welding sag or the like is removed (projection portion removing step). Specifically, shearing is performed on at least one of the inner peripheral surface side and the outer peripheral surface side of the metal shell 5 with respect to the fusion protrusion (more specifically, both on the inner peripheral surface side and the outer peripheral surface side of the metal shell 5). At least a part of the fused protrusion is removed by performing the removal process by the process or the cutting process a plurality of times on the same location.

As shown in the example of inner surface processing of FIG. 8, as a plurality of times of removal processing, prior to cutting processing, FIG.
It is possible to perform shearing as shown in FIG. 8A and perform cutting as shown in FIG. 8B for the sheared portion to be processed. It should be noted that FIG. 3 (a) shows an enlarged view of a portion A in FIG. 8 (a).
FIG. 8B shows an enlarged view of part B of FIG. 8B. Figure 3
As shown in FIG. 5, in the welded portion 101 of the ground electrode 4 ′ and the metal shell 5, a radial direction with respect to the central axis O ₅ of the joined body W _p (which is almost the same as the central axis of the final product spark plug) O _5. An outer melting protrusion (hereinafter, also simply referred to as an outer protrusion) 101a that protrudes outward and an inner melting protrusion (hereinafter, also referred to as an inner protrusion) 101b that protrudes inward are formed.

FIG. 3 shows that, in the shearing process, a notch cut in the axial direction of the metal shell 5 is formed in the inner protrusion by shearing, and the inner protrusion having the notch is removed by cutting. An example is shown. As shown in FIG. 3, the fused protrusions 101 a and 101 b are formed so as to protrude from the peripheral side surface of the ground electrode 4.

First, in FIG. 3 (a), as shown in FIG. 8 (a), an inner shearing tool 203 such as a press blade reciprocating in the direction of the central axis O ₅ is used, and the inner melting protrusion 101b is used.
At a predetermined position on the base end side, a notch 101c is formed that cuts to the intermediate position of the inner melting protrusion 101b. In manufacturing the present spark plug, since the two ground electrodes 4'are welded to the metal shell 5, the notch 101c is also separately formed on the other inner melting protrusion 101b. This inner shearing tool 203 is
In the case where two inner melting protrusions 101b are formed, the tool 2 is used to perform shearing on one protrusion.
03 is moved along the central axis O ₅ of the joined body W _p , so that the interference between the other protrusion and the tool 203 does not hinder the movement of the tool 203, the other protrusion 2 at the position corresponding to
Have 05. Then, as shown in FIG. 3 (b), the inner melting protrusion 101 b having the cutout 101 c is cut by the inner cutting tool 204. In manufacturing the present spark plug, the two inner melting protrusions 101b having the two notches 101c are simultaneously cut by the inner cutting tool 204. As shown in FIG. 8B, the inner cutting tool 204 rotates about a rotation axis parallel to the central axis O ₅ (in this embodiment, it rotates about a rotation axis parallel to and coaxial with the center electrode O _5). It is configured as a rotary blade such as an end mill.

The inner molten protrusion 101b having the notch 101c formed in this way is welded by a cutting process.
Easily removed from. Further, by forming the cutout portion 101c, the scraps of the melted protruding portion to be removed can be easily peeled off without damaging the surroundings. This is because the cut thickness is reduced due to the formation of the cutout portion 101c, the cutting progresses promptly by the cutting, and the drop is promoted. For example, when there is no notch 101c, when trying to cut off the melted protrusion at a stretch, the tool moves at high speed while the uncut portion remains bonded to the welded portion for a long time, so the already cut portion has a spiral shape. Supports the insulator 3 (see Fig. 1) formed on the inner surface of the metal shell 5 by turning into scrap and damaging the electrode, etc. Therefore, the metal fitting side engaging portion 5a for doing so may sag and damage it. Further, since the molten protrusion is removed so as to be stripped off forcibly, burrs and the like may remain in the welded portion 101 in the form of a protrusion.

In FIG. 4, the same method as in FIG.
An example in which the two outer protrusions 101a are removed is shown, and the same effect as in the case of FIG. 3 can be achieved. Figure 4 (a)
9A shows an enlarged view of the C portion in FIG. 9A, and FIG. 4B shows an enlarged view of the D portion in FIG. 9C. Figure 4
As shown in (a), in the outer fusion protrusion 101a,
A shearing tool 201 for outer side (a shearing blade such as a press blade reciprocating in the direction of the central axis O ₅ as shown in FIG. 9A) shears the outer melting protrusion 101a to an intermediate position. The notch 101d is formed. When manufacturing this spark plug, two ground electrodes 4 '
Since the metal is welded to the metal shell 5, the notch 10
1d is separately formed on the other outer melting protrusion 101a. Next, as shown in FIG. 4B, the outer melting protrusion 101a having the notch 101d formed therein is removed by an outer cutting tool 202 (for example, a rotary blade such as an end mill). In manufacturing the present spark plug, the outer melting protrusion 101a having the two notches 101d is simultaneously cut by the outer cutting tool 202. This outside cutting tool 2
02 is configured as a rotary blade having a rotation axis O ₂ parallel to the central axis O ₅ , as shown in the side views of FIGS. 9B and 9C.

If the shearing process is performed simultaneously on both the inner melting protrusion 101b formed on the inner side and the outer melting protrusion 101a formed on the outer side of the welded portion 101, the processing time is shortened. It is possible and effective. That is, the process of FIG.
It is advisable to carry out the step (a) at the same time.

Further, as shown in FIGS. 5 and 6, instead of forming the notch in the shearing process, the tip of the fusion protrusion in the projecting direction may be cut off. In this case, the volume of the molten protrusion to be removed by cutting is reduced, and the amount of the removed material 300 is reduced, so that a large roll-up that damages the surroundings occurs, or the product (specifically, metal It can be prevented from being pressed against the side engaging portion (step portion) 5a), and the occurrence of scratches or the like can be effectively suppressed.

In FIG. 5A, the inner melting protrusion 101b is formed.
The tip portion of the inner shearing tool 2 is the same as that in FIGS. 3 and 8.
Shearing is performed so as to cut off with 03.
Further, in FIG. 5B, the inner molten protrusion 101b, the tip of which is cut off, is cut by the same inner cutting tool 204 as in FIG. Further, in FIG. 6A, the tip portion of the outer melting protrusion 101a is cut off by the outer shearing tool 201 as in FIGS. 4 and 9, and the remaining portion is cut by the outer cutting tool 202. ·Remove. By doing so, defects such as scratches can be effectively suppressed as in the case of FIG.

As shown in FIG. 3 (a), the metal shell ₅ has a cross-section contour line including the central axis O ₅ of the inner peripheral surface, which is parallel to the central axis O ₅ from the side closer to the tip surface 5b. A straight portion 5f, and a reduced diameter portion (metal side engagement portion) 5 that follows the straight portion 5f and inclines in the decreasing direction toward the rear side.
a is formed in this order, and the axial distance H ₁ between the tip surface 5b and the front end edge 5c of the reduced diameter portion 5a is 1.5 mm.
It is even more effective to make the object of the present invention the object of the present invention (it is even better to apply the object of which the axial distance H ₁ is 1.1 mm or less). That is, in this way, the tip surface 5
If the distance between b and the front end edge 5c is small, the removal process is difficult, and the tool or the removed material may act on the reduced diameter portion (stepped portion), or the removed tool may remain due to insufficient tool stroke. It is highly likely to cause defects such as scratches and residue on the product. However, by applying the present invention, such a problem can be effectively eliminated.

Further, as shown in FIG. 4 (a), the metal shell 5 is a straight line parallel to the central axis O ₅ from the side closer to the tip surface 5b in the cross-sectional outline including the central axis O ₅ of the outer peripheral surface. A portion 5g and a diameter-increasing portion (stepped portion) 5e that follows the straight portion 5g and inclines in the diameter-increasing direction toward the rear side are formed in this order, and further the tip surface 5b and the diameter-increasing portion 5e are formed.
Those axial distance of H ₂ and the front end edge 5d of is less than 1.5 mm, may be the subject of the present invention (Note that even better when this axial distance H ₂ is applicable to the 1.1mm or less ). Similar to the removal on the inner surface, the tip surface 5
If b and the front edge 5c are close to each other, there is a high possibility that defects such as scratches and residues will occur in the product. However, by applying the present invention, such a problem can be effectively eliminated.

Then, after the above-mentioned protrusion removing step is completed, a bending step is performed as shown in FIG. 2 (b).
In the bending step, the ground electrode 4 ′ (all ground electrodes if 2 or more) is bent by pressing against the molding recess 120 of the punching die K. In this bending step, in the joined body W _P obtained by the welding step, the ground electrode 4 ′ that has been welded is placed in such a positional relationship that the tip end surface faces the central axis O ₅ of the metal shell 5. 4 ′ is bent, and the bent member becomes the ground electrode 4 in the final product. In the present invention, the electrode member before bending is used as the ground electrode 4'and the electrode member after bending is used as the ground electrode 4.

After the bending, the center electrode 2 mounted on the insulator 3 is inserted into the metal shell 5 as shown in FIG. 2 (c), and a gap g is formed between the center electrode 2 and the ground electrode 4 which is bent. When forming a cylindrical surface along the insulator 3 or the center electrode 2 on the tip end surface of the ground electrode 4 after bending, a punching step with a cylindrical punch may be performed before assembling the center electrode or the like. Become.

FIG. 7 is an enlarged view showing the vicinity of the welded portion of the spark plug obtained by the method shown in FIGS. 3 and 4 in the spark plug manufacturing method of the present invention. However, a removal surface smoothed by the above-described removal processing is formed on at least one of the inner surface and the outer surface of the welded portion where the metal shell 5 and the ground electrode 4 are welded. Then, on the removal surface, the processing scratch formed by the removal processing has a first processing scratch region 110a oriented mainly in a predetermined first direction and a second processing scratch oriented second direction different from the first direction. It is formed in a shape having a processed scratch region 110b.

The first processed scratch region 110a and the second processed scratch region 110b are formed adjacent to each other in the front-rear direction. In this embodiment, the first direction is substantially the same as the axial direction of the center electrode, and the second direction is the same. The direction is substantially orthogonal to the axial direction. Then, the processing scratch in the first processing scratch region 110a is caused by a shearing tool (see FIGS. 8A and 9A) that can reciprocate parallel to the central axis direction of the spark plug (metal shell). The shearing scratches that have been formed, and the processing scratches in the second processing scratch region 110b are spark plugs (metal shells).
A cutting tool having a rotation axis parallel to the central axis direction of the
(B) and FIG. 9 (b)). In this way, by forming a shearing flaw on the front side and forming a cutting flaw on the rear side near the step portion, it is possible to form a precision surface by cutting in the vicinity of the step portion. The shape accuracy in the vicinity becomes high.

The embodiment of the present invention has been described above.
The present invention is not limited to this, and is not limited to the wording of each claim without departing from the scope described in each claim, and extends to a range easily replaced by those skilled in the art, and Further, improvements based on the knowledge that those skilled in the art usually have can be added as appropriate.

For example, in the above embodiment, the outer fused protrusions 101b of the two ground electrodes 4 were cut at the same time, but not parallel to the central axis O _{5 of the} metal shell 5 (the joined body W _p ) and coaxial. Using a rotary blade that rotates around the axis of rotation,
It is also possible to separately machine the outer fused protrusions 101a of both electrodes 4.

[Brief description of drawings]

FIG. 1 is an overall view of a spark plug showing an embodiment of the present invention.

FIG. 2 is an explanatory view partially explaining the method for manufacturing the spark plug.

FIG. 3 is an explanatory diagram illustrating a step of removing an inner melting protrusion.

FIG. 4 is an explanatory view illustrating a step of removing an outer melting protrusion.

FIG. 5 is an explanatory diagram explaining a method different from that in FIG.

FIG. 6 is an explanatory diagram illustrating a method different from that in FIG.

FIG. 7 is an explanatory view showing the vicinity of a welded portion in an enlarged manner.

FIG. 8 is an explanatory diagram illustrating a step of removing an inner molten protrusion.

FIG. 9 is an explanatory view illustrating a step of removing the outer melting protrusion.

FIG. 10 is a diagram illustrating a comparative example of the present invention.

11 is a diagram illustrating a comparative example different from FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 spark plug 2 center electrode 3 insulator 4, 4'grounding electrode 5 metal shell 5a stepped portion (reduced diameter portion) 5e stepped portion (expanded portion) 101 welded portion 101a outer melting protrusion 101b inner melting protrusion 101c, 101d Notch 201 Outer shearing tool 202 Outer cutting tool 203 Inner shearing tool 204 Inner cutting tool W _p Joint

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuki Shimokawara             14-18 Takatsuji-cho, Mizuho-ku, Nagoya City, Aichi Prefecture             Inside this special ceramics company (72) Inventor Yoshio Hotta             14-18 Takatsuji-cho, Mizuho-ku, Nagoya City, Aichi Prefecture             Inside this special ceramics company F-term (reference) 5G059 CC03 CC09 GG05

Claims (11)

[Claims] 1. An insulator having a center through hole extending in the axial direction, a center electrode arranged on the tip side of the center through hole, and a main body arranged so as to surround a radially outer side of the insulator. A method of manufacturing a spark plug, comprising: a metal fitting; and a ground electrode, one end of which is welded to a front end surface of the metal shell, and the other end of which is arranged so as to form a spark discharge gap between the center electrode and the metal fitting. A welding step of forming a joined body of the metal shell and the ground electrode by welding one end surface of a rod-shaped electrode member to be the ground electrode to the tip surface of the metal shell, the metal shell and the A protrusion removing step for removing a molten protrusion that is formed in a welded portion with the ground electrode that protrudes from the peripheral side surface of the ground electrode, wherein the protrusion removing step includes an inner periphery of the metal shell. Face-to-face And at least one of the outer peripheral surface side, the melting protrusion is removed by performing the removing process by shearing and / or cutting a plurality of times on the melting protrusion, thereby manufacturing the spark plug. Method. 2. The spark plug according to claim 1, wherein in the removing step, the melting protrusion is first subjected to shearing, and the remaining portion of the melting protrusion after the shearing is further cut. Manufacturing method. 3. The spark according to claim 2, wherein the shearing process is performed so as to cut off a tip side portion in the projecting direction of the melting protrusion, and the portion of the melting protrusion remaining after the shearing is removed by cutting. Manufacturing method of plug. 4. The cutting process is performed on the melting protrusion by cutting the melting protrusion in the axial direction of the metal shell by the shearing process, and the cutting is performed on the melting protrusion having the notch. A method for manufacturing the described spark plug. 5. The shearing process is simultaneously performed on both the inner melting projection portion formed on the inner peripheral surface side of the metal shell and the outer melting projection portion similarly formed on the outer peripheral surface side of the welded portion. The method for manufacturing a spark plug according to claim 1, wherein 6. The method of manufacturing a spark plug according to claim 1, wherein the cutting process is performed by a rotary blade that rotates about an axis parallel to a central axis of the metal shell. 7. A bending step of forming the spark discharge gap by bending back the ground electrode in a direction in which a tip portion approaches the tip portion of the center electrode, and is formed on an inner peripheral surface side of the metal shell. 7. The step of removing the inner molten protrusion portion is performed at least prior to the bending step.
The method for manufacturing a spark plug according to any one of 1. 8. The method of manufacturing a spark plug according to claim 7, wherein the peripheral side surface of the ground electrode is an electrode base material surface to which the noble metal portion is not joined. 9. The method of manufacturing a spark plug according to claim 8, wherein the ground electrode forms the spark discharge gap by facing a peripheral side surface of the center electrode at a tip end surface thereof. 10. The metal shell, as a cross-sectional outline including a central axis of the inner peripheral surface, a straight portion parallel to the central axis from a side closer to the tip surface,
A diameter-reduced portion that follows the straight portion and inclines in the diameter-reduction direction toward the rear side is formed in this order, and the axial distance between the tip surface and the front end edge of the diameter-reduced portion is 1.5 mm. The method for manufacturing a spark plug according to claim 1, wherein a material that is less than or equal to is used. 11. The metal shell as a cross-section contour line including a central axis line of the outer peripheral surface, a straight portion parallel to the central axis line from a side closer to the distal end surface,
A diametrically enlarged portion is formed in this order following the straight portion and inclined in the diametrical expansion direction toward the rear side, and the axial distance between the tip surface and the front end edge of the diametrically enlarged portion is 1.5 mm. The method for manufacturing a spark plug according to claim 1, wherein a material that is said to be less than is used.