JP4064114B2 - Manufacturing method of spark plug - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a spark plug.
[0002]
[Prior art]
Conventionally, in the manufacture of spark plugs, the ground electrode and the metal shell are joined by welding or the like, and in the vicinity of the welded portion of these ground electrode and metal shell, these welds partially protrude by the welding. Or a weld sag is formed to form a melt projection. And since such a fusion | melting protrusion part may inhibit normal surface formation and may contribute to the quality reduction of a product, the removal process which removes such a fusion | melting protrusion part after a welding process is performed. There are many cases.
[0003]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to provide a spark plug capable of accurately removing a molten projection caused by welding in a welded portion between a ground electrode and a metal shell, and thus effectively producing a high-quality spark plug. It is to provide a method.
[0004]
[Means for solving the problems and actions / effects]
The present invention includes an insulator having a central through hole extending in the axial direction, a center electrode disposed on the tip side in the central through hole, and a metal shell disposed so as to surround the radially outer side of the insulator; The present invention relates to a method of manufacturing a spark plug having one end welded to a front end surface of a metal shell and a ground electrode disposed so that a spark discharge gap is formed between the other end side and a center electrode. for,
Welding one end face of the rod-shaped electrode member to be the ground electrode to the front end face of the metal shell, thereby forming a joined body of the metal shell and the ground electrode;
In the welded portion of the metal shell and the ground electrode, including a protrusion removal step for removing the melt protrusion generated in a form protruding from the peripheral side surface of the ground electrode,
The protrusion removal step is performed by performing a removal process by shearing and / or cutting a plurality of times on the molten protrusion on at least one of the inner peripheral surface side and the outer peripheral surface side of the metal shell. The portion is removed.
[0005]
For example, when removing the molten protrusion generated by the welding process as described above by a shearing process, a long tool stroke necessary for the removal must be ensured when the removal is performed by a single shearing process. That is, such a stroke is set in consideration of the material and thickness of the part to be removed, but the greater the thickness of the part to be removed, the more shear force is required. It is necessary to secure the stroke.
[0006]
10 and 11 show the joined body W of the ground electrode 4 'and the metal shell 5. _p The example of a process with respect to the welding part 101 in is shown. FIG. 10 shows an example of processing on the inner peripheral surface side of the metal shell 5, and FIG. 11 shows an example of processing on the outer peripheral surface side. Further, in FIGS. 10B and 11B, a press blade (inner shearing tool 203 (FIG. 10B)) and outer shearing tool 201 (see FIG. 10) reciprocating in the axial direction of the metal shell 5 are shown. 11 (b)), in which the tool stroke is long in one shearing process and the base end side of the melt projection 101 is processed, so that the tool as shown in FIG. The cutting edge is likely to 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. 11B is formed on the outer peripheral surface. The presence may affect the metal shell after thread rolling, and the inner peripheral surface of the metal shell 5 supports the insulator as shown in FIG. Projecting radially inward from the inner peripheral surface There is a possibility that the cutting edge of the tool collides with the metal fitting side engaging portion 7 and damages the metal fitting side engaging portion 7. Such removal of the molten protrusion by one-time shearing is allowed in the tool. Products with smaller strokes are more difficult.
[0007]
On the other hand, FIG. 10 (a) and FIG. 11 (a) are obtained by cutting using a rotary cutter (inner cutting tool 204 (FIG. 10 (a)) and outer cutting tool 202 (FIG. 11 (a)). If removal of the melted protrusion is performed at one time, as shown in FIG. 11 (a), the cutting waste from the melted protrusion is rolled up during processing, and a residue 303 is partially generated, or 10A, the removed object 307 may come into contact with the metal fitting side engaging portion 7 of the metal shell 5 to damage the metal fitting side engaging portion 7. Although it depends on the material, the more the cutting margin is removed at a time in the cutting process, the more easily it is generated.
[0008]
On the other hand, as in the present invention, when performing the removal process of the melted protrusion in the welded portion, it is possible to cope with the above-mentioned problems by performing the removal process at a plurality of times instead of removing at once. Therefore, the removal can be performed with high accuracy. That is, if the molten protrusion is gradually removed by a plurality of removal processes, for example, when performing a shearing process, the tool stroke per removal process can be reduced, In the case of performing the cutting process, the entire target portion is not removed at a time, so that the occurrence of winding can be effectively reduced.
[0009]
Specifically, in the removing step, the melt projection can be first sheared, and the remaining portion of the melt projection after the shearing can be further cut. Prior to the cutting process, by performing a preliminary process by a shearing process, it is possible to effectively suppress the hoisting of the cutting waste during the cutting process.
[0010]
Specifically, the following two methods are conceivable. First, shearing is performed so as to cut off the tip side portion in the protruding direction of the molten projection, and the remaining portion after the shearing of the molten projection is removed by cutting. If it does in this way, since the volume of the fusion | melting projection part which should be removed by cutting reduces, the margin for removal by one cutting will reduce, and it will become difficult to produce the winding-up of cutting waste. In the second method, a notch that is cut in the axial direction of the metal shell is formed by shearing on the melt projection, and the melt projection having the notch is cut. If it does in this way, since the cutting thickness which should be removed by cutting reduces, it will become difficult to produce the rolling-up of cutting waste similarly. As the cutting process, in addition to a narrow-cutting process using a blade, a grinding wheel grinding process is also included in the concept of the cutting process in the present invention. In particular, processing using a rotary cutter (milling with an end mill or the like) can be suitably employed. In this case, since the main part of the metal shell is formed in a cylindrical shape, it can be said that it is particularly advantageous to perform the cutting process with 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 cutting blade such as a press blade can be suitably employed.
[0011]
In addition, the inner melt projection formed on the inner peripheral surface side of the metal shell and the outer melt projection formed on the outer peripheral surface side in the welded portion may be removed independently. If both of them are subjected to shearing at the same time, the processing time can be shortened, thereby contributing to efficient product production.
[0012]
In the general spark plug manufacturing process, when the spark discharge gap is formed, a bending process is performed in which the ground electrode is bent in a direction in which the tip portion approaches the tip portion of the center electrode. In this case, in order to avoid interference between the cutting tool for shearing or the cutting tool and the ground electrode, at least the bending process of removing the inner molten protrusion formed on the inner peripheral surface side of the metal shell is included in the bending process. It is desirable to do this in advance. 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.
[0013]
In recent years, spark plugs in which a noble metal tip mainly composed of Pt, Ir, or the like is joined on an electrode surface facing a spark discharge gap in order to improve durability of the electrodes against spark discharge consumption. When the noble metal part such as the noble metal tip is joined 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 projection part is removed. Even in such a case, the tool may interfere with the noble metal portion, thereby hindering the execution of the removal process. From this point of view, it is desirable that the peripheral side surface of the ground electrode be an electrode base material surface to which the noble metal portion is not joined in the process of removing the inner molten protrusion prior to the above-described bending process of the ground electrode. Such a configuration is possible in a spark plug in which a spark discharge gap is formed by the ground electrode facing the peripheral side surface of the center electrode at the front end surface thereof. However, in the spark plug (so-called parallel electrode type spark plug) in which the ground electrode is opposed to the tip surface of the center electrode on the peripheral side surface, a noble metal tip is not bonded to the ground electrode side. Anything is acceptable. On the other hand, in the parallel electrode plug, even if the noble metal tip is of the type that is joined to the ground electrode side, if the recess or notch for avoiding interference with the noble metal tip is provided on the tool side, the above Removal processing can be performed.
[0014]
In the case of a multipolar spark plug in which a plurality of ground electrodes are arranged around the center electrode, the removal processing of the present invention may be performed simultaneously on a plurality of ground electrodes (for example, all ground electrodes). The 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 projections may be performed simultaneously or independently. In either case, the processing efficiency can be increased in the former case.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to 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-surface discharge type spark plug, and has a cylindrical metal shell 5 and an insulator 3 fitted into the metal shell 5 so that the tip portion protrudes. The base end side is coupled to the center electrode 2 and the metal shell 5 provided inside the insulator 3 so that the peripheral side surface and the tip end side of the center electrode 2 face each other with the tip end portion of the insulator 3 interposed therebetween. A ground electrode 4 and the like are provided.
[0016]
The insulator 3 is made of a ceramic sintered body such as alumina or aluminum nitride, and has a hole (center through hole) 3d for fitting the center electrode 2 along its own axial direction. ing. Further, the metal shell 5 is formed in a cylindrical shape by a metal such as low carbon steel 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 is formed for attachment to the cylinder head that is not to be used.
[0017]
Two ground electrodes 4 are provided, one on each side of the center electrode 2, each having an end surface (ignition surface) 4 a and a side peripheral surface 2 b (ignition surface) on the front end side of the cylindrical center electrode 2. The other end is fixed and integrated with the metal shell 5 by welding while being curved so as to face each other substantially in parallel. In this embodiment, a semi-creeping type multipolar spark plug is described as an example. However, this is not a side facing type, but a so-called parallel structure in which the tip surface of the center electrode and the ground electrode face each other. The opposite type may be the target of application, and the type formed by combining these may be the target. In any case, it is first described that the spark plug can be applied to various types as long as the ground electrode is welded to the metal shell.
[0018]
The insulator 3 is disposed in such a positional relationship that the tip 3 a enters between the side peripheral surface 2 b of the center electrode 2 and the ignition surface 4 a of the ground electrode 4. In the axial direction of the center electrode 2, the front end surface 2 e side of the center electrode 2 is the front side, and the opposite side is the rear side, and the front end surface 3 e of the insulator 3 is on the rear side of the front end surface 4 a of the ground electrode 4. It is located in front of the edge 4f. On the other hand, the front end surface 2 e of the center electrode 2 is disposed so as to protrude from the front end surface 3 e of the insulator 3 by a predetermined height.
[0019]
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 similarly inserted and fixed on the other end side. A resistor 15 is disposed between the terminal fitting 13 and the center electrode 2 in the hole 3d. Both end portions of the resistor 15 are electrically connected to the center electrode 2 and the terminal fitting 13 through the conductive glass seal layers 16 and 17, respectively. The terminal fitting 13 is made of low carbon steel or the like, and a Ni plating layer (layer thickness: for example, 5 μm) for corrosion prevention is formed on the surface. The resistor 15 is composed of glass powder, ceramic powder, metal powder (for example, one or more of Zn, Sb, Sn, Ag and Ni), non-metallic conductive material powder (for example, amorphous carbon or Graphite), an organic binder, and the like are blended in predetermined amounts and sintered by a known technique such as hot pressing.
[0020]
In the center electrode 2, the electrode base material constituting the surface layer portion of the electrode is made of Ni or a Ni alloy, and if necessary, a core material made of Cu or a Cu alloy at the center for improving heat pulling. Inserted. On the other hand, the electrode base material of the ground electrode 4 is made of Ni or Ni alloy. Further, in this ground electrode 4 as well, a core material made of Cu or Cu alloy may be inserted in the center portion for improving heat pulling, and for the same purpose, pure Ni is surrounded by Cu or Cu in the center portion. A layered structure covered with an alloy may be inserted. In both the center electrode 2 and the ground electrode 4, the electrode base material can use a high heat-resistant Ni alloy, such as a Ni-base superalloy (for example, Inconel 600 (trade name) or Inconel 601 (trade name)). .
[0021]
Next, the manufacturing method of the spark plug of this invention is demonstrated.
When manufacturing the multipolar plug as described above, first, as shown in FIG. 2 (a), one end face of each of the two rod-shaped (for example, square bar-shaped) ground electrodes 4 ′ to be the ground electrodes, Attached to the front end surface 5a of the metal shell 5 by electric resistance welding, _P (Welding process). And this joined body W _P On the other hand, a bending process as shown in FIG. 2B is performed. Prior to such a bending process, the welded portion 101 between the metal shell 5 and the ground electrode 4 ′ welded by the welding process is welded. The molten protrusion caused by the above is removed (protrusion removal step). Specifically, at least one of the inner peripheral surface side and the outer peripheral surface side of the metal shell 5 with respect to the molten protrusion (more specifically, both on the inner peripheral surface side and the outer peripheral surface side of the metal shell 5), shearing At least a part of the molten protrusion is removed by performing removal processing by machining or cutting multiple times on the same location.
[0022]
As shown in the inner surface processing example of FIG. 8, as the multiple times of removal processing, the shearing processing is performed as shown in FIG. 8A prior to the cutting processing, and the sheared portion is processed. Thus, cutting can be performed as shown in FIG. FIG. 3A shows an enlarged view of a portion A in FIG. 8A, and FIG. 3B shows an enlarged view of a portion B in FIG. 8B. As shown in FIG. 3, in the welded portion 101 between the ground electrode 4 ′ and the metal shell 5, the joint W _p The center axis of the cylinder (almost the same as the center axis of the final spark plug) O ₅ An outer melt projection (hereinafter also referred to simply as an outer projection) 101a that protrudes outward in the radial direction and an inner melt projection (hereinafter also referred to as an inner projection) 101b that projects inward are formed. Yes.
[0023]
FIG. 3 shows an example in which a notch that is cut in the axial direction of the metal shell 5 is formed by shearing in the inner protrusion in the shearing process, and the inner protrusion in which the notch is formed is removed by cutting. ing. As shown in FIG. 3, the melted protrusions 101 a and 101 b are formed so as to protrude from the peripheral side surface of the ground electrode 4.
[0024]
First, in FIG. 3A, as shown in FIG. ₅ Using a shear tool for inner side 203 such as a press blade reciprocating in the direction of, a notch 101c is formed at a predetermined position on the base end side of the inner melting projection 101b to the middle position of the inner melting projection 101b. Yes. In manufacturing the spark plug, since the two ground electrodes 4 ′ are welded to the metal shell 5, the cutout portion 101 c is separately formed on the other inner melt projection portion 101 b. In the case where the two inner melting projections 101b are generated, the inner shearing tool 203 is attached to the joined body W to perform shearing on one projection. _p Center axis O ₅ So that the movement of the tool 203 is not hindered by the interference of the other protrusion and the tool 203 in the axial direction. A relief groove 205 is provided along. Then, as shown in FIG. 3 (b), the inner melting projection 101b in which the notch 101c is formed is cut by the inner cutting tool 204. In the production of the spark plug, the two inner melting projections 101b formed with the two notches 101c are simultaneously cut by the inner cutting tool 204. The inner cutting tool 204 has a central axis O as shown in FIG. ₅ (In this embodiment, the central electrode O rotates). ₅ It is configured as a rotary cutter such as an end mill that rotates around a coaxial rotation axis.
[0025]
Thus, the inner side fusion | melting protrusion part 101b in which the notch part 101c was formed is easily removed from the welding part 101 by cutting. Further, by forming the notch 101c, the scrap of the melted protrusion to be removed can be easily peeled off without damaging the surroundings. This is because the cut thickness decreases due to the formation of the notch 101c, and the cutting progresses promptly by the cutting and the fall is promoted. For example, when the notch 101c is not present, the tool moves at high speed while the uncut portion is connected to the welded portion for a long time when the molten protrusion is cut at a stretch. Supports the insulator 3 (refer to FIG. 1) formed on the inner surface of the metal shell 5 by scraping the electrode and the like as it is scraped up and damaging the electrodes, or by pushing the scraped material in the feed direction of the tool. This leads to a problem that the metal fitting engagement portion 5a side is damaged and damaged. Further, since the melted protrusion is removed so as to be forcibly removed, burrs or the like may remain in the welded part 101 in the form of protrusions.
[0026]
FIG. 4 shows an example in which the two outer protrusions 101a are removed by the same method as in FIG. 3, and the same effect as in FIG. 3 can be achieved. 4A shows an enlarged view of a portion C in FIG. 9A, and FIG. 4B shows an enlarged view of a portion D in FIG. 9C. As shown in FIG. 4A, in the outer melt projection 101a, the outer shearing tool 201 (the central axis O as shown in FIG. 9A). ₅ The outer molten projection 101a is sheared to an intermediate position to form a notch 101d. In manufacturing the spark plug, since the two ground electrodes 4 ′ are welded to the metal shell 5, the cutout portion 101 d is separately formed on the other outer melt projection portion 101 a. . Next, as shown in FIG. 4B, the outer melt projection 101a in which the notch 101d is formed is removed by an outer cutting tool 202 (for example, a rotary blade such as an end mill). In the production of the spark plug, the outer melt projection 101a in which the two notches 101d are formed is simultaneously cut by the outer cutting tool 202. As shown in the side views of FIGS. 9B and 9C, the outer cutting tool 202 has a central axis O. ₅ Axis of rotation O parallel to ₂ It is comprised as a rotary cutter which has.
[0027]
In addition, it is possible to shorten the processing time by performing shearing simultaneously on both the inner melt projection 101b formed on the inner side and the outer melt projection 101a formed on the outer side in the welded portion 101. It is effective. That is, it is preferable to perform the process of FIG. 3A and the process of FIG.
[0028]
Further, as shown in FIGS. 5 and 6, the tip end portion in the protruding direction of the melt projection portion may be cut off instead of the formation of the notch in the shearing process. In this case, the volume of the melted protrusion to be removed by the cutting process is reduced, and the removed object 300 becomes a small amount. As a result, a large roll-up that damages the surroundings occurs, or the product (specifically, metal Side engagement portion (stepped portion) 5a and the like), and the occurrence of scratches and the like can be effectively suppressed.
[0029]
In FIG. 5 (a), the shearing process is performed so that the front end portion of the inner melting projection 101b is cut off by the inner shearing tool 203 similar to that in FIGS. Further, in FIG. 5 (b), the inner melting projection 101b whose tip is cut off is cut by the inner cutting tool 204 similar to FIG. Further, in FIG. 6A, the tip of the outer melt projection 101a is cut off by the outer shearing tool 201 as in FIGS. 4 and 9, and the remaining part is cut by the outer cutting tool 202. ·Remove. In this way, defects such as scratches can be effectively suppressed as in the case of FIG.
[0030]
In addition, as shown to Fig.3 (a), as the metal shell 5, the center axis line O of an internal peripheral surface ₅ From the side close to the tip surface 5b, the central axis O ₅ And a reduced diameter portion (metal-side engagement portion) 5a that continues to the straight portion 5f and inclines in the reduced diameter direction toward the rear side, and is further formed in this order. And the axial distance H between the front end edge 5c of the reduced diameter portion 5a ₁ Is more effective when the object of the present invention is set to be less than 1.5 mm (this axial distance H ₁ Is better applied to those having a thickness of 1.1 mm or less). That is, when the distance between the front end surface 5b and the front end edge 5c is small as described above, the removal process is difficult, and a tool or a removal object acts on the reduced diameter portion (stepped portion) or the tool stroke is insufficient. Therefore, there is a high possibility that the removed substance remains, and there is a high possibility that a defect such as a scratch or a residue will occur in the product. However, the application of the present invention can effectively eliminate such problems.
[0031]
Further, as shown in FIG. 4A, as the metal shell 5, the central axis O of the outer peripheral surface is provided. ₅ From the side close to the tip surface 5b, the central axis O ₅ And a diameter-enlarged portion (stepped portion) 5e that continues to the linear portion 5g and inclines in the diameter-enlarging direction toward the rear side, and is further formed in this order. Axial direction distance H from front edge 5d of portion 5e ₂ Is less than 1.5 mm, and the object of the present invention is preferably (this axial distance H ₂ Is better applied to those having a thickness of 1.1 mm or less). Similarly to the removal on the inner surface, if the distance between the front end surface 5b and the front end edge 5c is close, there is a high possibility that defects such as scratches and residues will occur in the product. However, the application of the present invention can effectively eliminate such problems.
[0032]
Then, after the protrusion removing process as described above is completed, a bending process is performed as shown in FIG. In the bending step, the ground electrode 4 ′ (all ground electrodes if 2 or more) is bent by being pressed against the molding recess 120 of the punching die K. In this bending process, the joined body W obtained by the welding process. _P , The front end surface of the welded ground electrode 4 ′ is the central axis O of the metal shell 5. ₅ The ground electrode 4 'is bent so as to be in a positional relationship facing the surface, and the bent member becomes the ground electrode 4 in the final product. In the present invention, the electrode member before bending is the ground electrode 4 ′, and the electrode member after bending is the ground electrode 4.
[0033]
After the bending process, the center electrode 2 mounted on the insulator 3 is inserted into the metal shell 5 as shown in FIG. 2C, and a gap g is formed between the bent ground electrode 4. When a cylindrical surface along the insulator 3 or the center electrode 2 is formed on the tip surface of the ground electrode 4 after bending, a punching process is performed with a cylindrical punch before assembling the center electrode or the like. Become.
[0034]
FIG. 7 shows an enlarged view of the vicinity of the welded portion of the spark plug obtained by the method shown in FIGS. 3 and 4 described above, in the spark plug manufacturing method of the present invention. 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. The removal surface includes a first processed scratch region 110a in which a processing scratch formed by the removal processing is oriented mainly in a predetermined first direction, and a second oriented mainly in a second direction different from the first direction. It is formed in a shape having a processing flaw region 110b.
[0035]
The first processing flaw region 110a and the second processing flaw 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 axial direction. On the other hand, the direction is substantially orthogonal. And the processing flaw of the 1st processing flaw area | region 110a is made by the tool for shearing processing (refer FIG. 8 (a) and FIG. 9 (a)) which can be reciprocated in parallel with the center axis direction of a spark plug (main metal fitting). The formed flaws in the shearing process, and the flaws in the second flawed damage area 110b are cutting tools having a rotation axis parallel to the central axis direction of the spark plug (metal fitting) (FIGS. 8B and 9B). ))). Thus, if a shearing scratch is formed on the front side and a cutting scratch is formed on a portion near the step portion on the rear side, the vicinity of the step portion can be made into a precision surface by cutting, and the step portion The shape accuracy in the vicinity is high.
[0036]
Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and the present invention is not limited to the wording of each claim without departing from the scope described in each claim. To the extent that can be easily replaced by them, and improvements based on knowledge that a person skilled in the art normally has can be added as appropriate.
[0037]
For example, in the above-described embodiment, the outer melt projections 101b of the two ground electrodes 4 are cut at the same time, but the metal shell 5 (joint W _p ) Center axis O ₅ It is also possible to cut the outer melt projections 101a of both electrodes 4 separately using a rotary knife that rotates around a rotation axis that is parallel to and not coaxial.
[Brief description of the drawings]
FIG. 1 is an overall view of a spark plug showing an embodiment of the present invention.
FIG. 2 is an explanatory diagram partially explaining a method for manufacturing a spark plug.
FIG. 3 is an explanatory diagram for explaining a process of removing an inner melting protrusion.
FIG. 4 is an explanatory diagram for explaining a process of removing an outer melt projection.
FIG. 5 is an explanatory diagram for explaining a method different from that in FIG. 3;
6 is an explanatory diagram for explaining a method different from that in FIG. 4;
FIG. 7 is an explanatory view showing an enlarged vicinity of a welded portion.
FIG. 8 is an explanatory diagram for explaining a process of removing the inner melting protrusion.
FIG. 9 is an explanatory diagram for explaining a process 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]
1 Spark plug
2 Center electrode
3 Insulator
4, 4 'ground electrode
5 metal shell
5a Step part (reduced diameter part)
5e Stepped part (expanded part)
101 Welded part
101a Outer melt projection
101b Inner melting protrusion
101c, 101d Notch
201 External shearing tool
202 External cutting tool
203 Internal shearing tool
204 Internal cutting tool
W _p Zygote

Claims (10)

An insulator having a central through hole extending in the axial direction, a central electrode disposed on the tip side in the central through hole, a metal shell disposed so as to surround a radially outer side of the insulator, and the main body A spark plug manufacturing method having a ground electrode disposed so that one end is welded to a front end surface of a metal fitting and a spark discharge gap is formed between the other end side and the center electrode,
Welding one end surface of the rod-shaped electrode member to be the ground electrode to the front end surface of the metal shell, thereby forming a joined body of the metal shell and the ground electrode;
In the welded portion between the metal shell and the ground electrode, including a protrusion removal step of removing the melt protrusion generated in a form protruding from the peripheral side surface of the ground electrode,
The protrusion removal step includes performing a removal process by shearing and / or cutting a plurality of times on the molten protrusion on at least one of the inner peripheral surface side and the outer peripheral surface side of the metal shell, While removing the molten protrusion ,
The method for manufacturing a spark plug is characterized in that in the removing step, a shearing process is first performed on the molten projection part, and a remaining part of the molten projection part after the shearing process is further cut . The molten protrusion performs the shearing to cut off the distal end side portion in the protruding direction of the method for producing a spark plug according to claim 1 for removing by cutting a portion remaining after shearing of the molten protrusion. With respect to the melting protrusion, the shearing by forming a notch cut into the axial direction of the metallic shell, the spark plug according to claim 1 for the cutting to the melting protrusion formed in the notch Production method. The shearing process is simultaneously performed on both of the inner molten protrusion formed on the inner peripheral surface side of the metal shell and the outer molten protrusion formed on the outer peripheral surface side in the welded portion. a spark plug manufacturing method according to any one of 3. The spark plug manufacturing method according to any one of claims 1 to 4 , wherein the cutting is performed by a rotary blade that rotates about an axis parallel to a central axis of the metal shell. 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 an inner melt projection formed on the inner peripheral surface side of the metal shell The spark plug manufacturing method according to any one of claims 1 to 5 , wherein the removing step is performed at least prior to the bending step. The spark plug manufacturing method according to claim 6, wherein a peripheral side surface of the ground electrode is an electrode base material surface to which a noble metal portion is not bonded. The spark plug manufacturing method according to claim 7 , wherein the ground electrode forms the spark discharge gap by facing a peripheral side surface of the center electrode at a front end surface thereof. As the metal shell,
In a cross-sectional outline including the central axis of the inner peripheral surface, a linear portion parallel to the central axis from the side close to the tip surface, and a contraction that inclines in a reduced diameter direction toward the rear side following the linear portion. The diameter part is formed in this order,
Furthermore, the axial direction distance between the front end surface and the front end edge of the reduced diameter portion is less than 1.5 mm,
The method for manufacturing a spark plug according to any one of claims 1 to 8 , wherein the above-described one is used. As the metal shell,
In the cross-sectional outline including the central axis of the outer peripheral surface, from the side close to the tip surface, a linear portion parallel to the central axis, and a diameter increasing incline in a diameter increasing direction toward the rear side while continuing to the linear portion. Are formed in this order,
Furthermore, the axial direction distance between the front end surface and the front end edge of the enlarged diameter portion is less than 1.5 mm,
The method for manufacturing a spark plug according to any one of claims 1 to 9 , wherein the above-described one is used.

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