JP2007080640A - Method of manufacturing spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a spark plug in which a ground electrode can be prevented from being damaged when removing a welding projection formed at a jointportion between the main metal fittings and the ground electrode. <P>SOLUTION: A removing punch 320 in which a cutting blade 322 has been formed by notching a part of the tip part 325 worked in a tapered shape is fixed to a slide mechanism 330 in a state that its cutting edge is turned downward, and descended toward the main metal fittings 50 to which the ground electrode 30 is joined. By being guided to a slope 321 of the removing punch 320 contacted with the inner peripheral edge on the side opposite to the side on which a welding projecting part 80 of the tip face 57 has been formed, the cutting edge of the cutting blade 322 is positioned to the welding projecting part 80. Since even against a metal fittings assembly 200 of which the tip part 31 of the ground electrode 30 is inclined to the inner peripheral side of the main metal fittings 50, the cutting edge is positioned at the welding projecting part 80 so as to evade the tip part 31, the welding projecting part 80 can be cut without damaging the ground electrode 30. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark plug manufacturing method capable of reducing the damage of a ground electrode welded to a front end surface of a metal shell in one step of manufacturing the spark plug.

  Conventionally, spark plugs for ignition are used in internal combustion engines. In this spark plug, generally, a ground electrode is joined to the tip of the metal shell holding the insulator in which the center electrode is inserted, on the combustion chamber side, and the other end of the ground electrode is connected to the tip of the center electrode. A main spark discharge gap is formed so as to face the front end surface of the portion. The spark plug is attached to the internal combustion engine, the center electrode and the ground electrode are exposed to the air-fuel mixture in the combustion chamber, and spark discharge is performed between the two electrodes, so that the air-fuel mixture is ignited and combustion is performed.

  In one process of manufacturing such a spark plug, the base end portion of the ground electrode and the distal end surface of the metallic shell are joined by resistance welding or the like with the distal end surface of the metallic shell facing upward. At this time, a joint portion between the metal shell and the ground electrode may partially protrude or welding sag may occur at the joint portion, so-called welding protrusions may be formed. If the spark plug is assembled with these weld protrusions formed, the appearance of the product will be impaired, or the clearance between the inner peripheral surface of the metal shell and the outer peripheral surface of the insulator will be narrowed, causing side fire. There is a fear.

Therefore, after the metal shell and the ground electrode are welded, a process of removing the welding protrusion by cutting or shearing is performed. In particular, when cutting and removing the welding protrusion formed on the outer peripheral surface side of the metal shell, in general, the cutting is performed with the front end surface of the metal shell facing upward and descending along the axial direction of the metal shell from above. The blade tip of the blade is brought into contact with the welding projection, and the welding projection is removed by cutting (see, for example, Patent Document 1).
JP 2003-223968 A

  However, when the cutting blade is lowered from above the metallic shell, if the ground electrode is inclined toward the inner peripheral side or the outer peripheral side of the metallic shell with respect to the axis of the metallic shell, the cutting edge of the cutting blade will be the tip of the ground electrode. There was a possibility of causing scratches on contact with. In order to prevent this, when performing resistance welding between the ground electrode and the metal shell, the extension direction of the ground electrode is aligned with the axial direction of the metal shell, and resistance welding is performed accurately so that the ground electrode does not tilt. In addition, since it is necessary to correct the inclination of the ground electrode after welding, there is a problem that the manufacturing cost increases.

  The present invention has been made to solve the above-mentioned problems, and prevents the ground electrode from being damaged when removing the welding protrusion formed at the joint portion between the metal shell and the ground electrode. An object of the present invention is to provide a method for manufacturing a spark plug.

  In order to achieve the above object, a spark plug manufacturing method according to the first aspect of the present invention provides a ground electrode joint in which a ground electrode is welded to the metal shell while a welding projection is formed on the inner peripheral side of the metal shell. A spark plug manufacturing method comprising: a holding step of holding the metal shell having the ground electrode welded to a front end surface thereof with the front end surface facing upward; and a state in which the cutting edge faces downward A lowering step of lowering the cutting blade of the metal shell from above the tip surface of the metal shell toward the welding projection, and a cutting step of cutting the welding projection after the lowering step. The cutting blade is provided with a slope inclined in a direction approaching the welding projection from the base side to the tip side of the cutting blade on the side opposite to the welding projection side of the cutting blade when cutting the welding projection. In the process, The inclined surface is brought into contact with the inner peripheral edge of the front end surface of the metal shell opposite to the side on which the weld protrusion is formed, and is guided by the inclined surface so that the cutting edge of the cutting blade is the weld protrusion. It is positioned with respect to the part.

  The spark plug manufacturing method of the invention according to claim 2 is characterized in that, in addition to the configuration of the invention of claim 1, the cutting blade has a cutting edge formed above the slope. To do.

  Further, in the spark plug manufacturing method of the invention according to claim 3, in addition to the configuration of the invention of claim 1 or 2, the cutting blade and the inclined surface are formed at one end of a round bar-shaped cutting member. The outer diameter of the cutting member is the same as the minimum inner diameter within the allowable manufacturing tolerance range of the inner diameter of the metal shell.

  Further, in the spark plug manufacturing method of the invention according to claim 4, in addition to the configuration of the invention of claim 3, the cutting member is held by a slide mechanism supported so as to be movable up and down. The cutting blade is guided by the slope, and the movement in the displacement direction different from the downward direction is performed by the slide mechanism.

  In the spark plug manufacturing method according to the first aspect of the present invention, in the descending step, the cutting edge of the cutting blade to be lowered toward the welding projection can be guided to the slope and positioned with respect to the welding projection. In other words, since the cutting blade can be moved in a displacement direction different from the downward direction by the inclined surface, even when the ground electrode is inclined and welded to the inside of the metal shell, contact between the cutting blade and the ground electrode is avoided. It is possible to position the cutting edge of the cutting blade with respect to the welding projection portion. Thereby, in the ground electrode joining step of welding the ground electrode and the metal shell, it is not necessary to manage the ground electrode so as not to be inclined, and labor during manufacturing can be reduced.

  Further, in the above descending process, while the inclined surface is in contact with the inner peripheral edge of the front end surface of the metal shell, the cutting blade moves in a displacement direction different from the downward direction, but the inner peripheral edge and the inclined surface are in contact with each other When is finished, the cutting edge is positioned with respect to the welding projection, and the moving direction of the cutting blade is only the downward direction. Since the welding projection is formed in the vicinity of the boundary between the ground electrode and the metal shell, as in the invention according to claim 2, if the cutting edge of the cutting blade is positioned above the slope, the inner peripheral edge of the tip surface In the state where the contact with the inclined surface is finished, the blade edge is located above the welding projection. In other words, the cutting edge of the cutting blade does not cut obliquely from the upper side but cuts from the upper side to the lower side of the welding projection, so that the remaining projection protrudes toward the inner peripheral side of the metal shell after cutting the welding projection. The amount can be reduced.

  Further, as in the invention according to claim 3, if the welding protrusion is cut with the round bar-shaped cutting member formed with the cutting blade and the inclined surface, even if the remaining portion protrudes to the inner peripheral side of the metal shell, It is possible to secure the minimum inner diameter of the manufacturing tolerance that can be allowed by the inner diameter at the time of manufacturing the metal shell, including the protruding tip. Thereby, it is not necessary to inspect whether the minimum inner diameter is ensured after the cutting stroke, and the labor during manufacturing can be reduced. Further, when the spark plug is manufactured without ensuring the minimum inner diameter, a side fire may occur, but this can be prevented in advance.

  Further, the cutting member is moved in a displacement direction different from the descending direction by the inclined surface. However, as in the invention according to claim 4, if the previous cutting member is held by the slide mechanism, the cutting member is moved in the displacement direction. Can be moved smoothly. That is, since the resistance from the inclined surface that presses the inner peripheral edge of the front end surface of the metallic shell is reduced, it is possible to prevent the metallic shell from being damaged due to the contact between the inner circumferential edge and the inclined surface.

  Hereinafter, an embodiment of a spark plug manufacturing method embodying the present invention will be described with reference to the drawings. First, the structure of a spark plug 100 as an example of a spark plug manufactured by the spark plug manufacturing method of the present embodiment will be described. FIG. 1 is a partial cross-sectional view of a spark plug 100. 1, the side where the center electrode 20 is provided will be referred to as the front end side of the spark plug 100, and the side where the connection terminal 40 is provided will be described as the rear end side.

  As shown in FIG. 1, the spark plug 100 generally includes an insulator 10, a metal shell 50 that holds the insulator 10, a center electrode 20 that is held in the shaft hole 12 of the insulator 10, and a metal shell. The ground electrode 30 is joined to the front end portion 31 of the center electrode 20 so as to be opposed to the front end portion 22 of the center electrode 20, and the connection terminal 40 is provided on the rear end side of the insulator 10.

  First, the insulator 10 constituting the insulator of the spark plug 100 will be described. As is well known, the insulator 10 is formed by firing alumina or the like, and is a cylindrical insulating member having an axial hole 12 in the axis O direction. A flange portion 19 having the largest outer diameter is formed substantially at the center in the direction of the axis O, and a rear end side body portion 18 is formed on the rear end side. A front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 is formed on the front end side from the flange portion 19, and the outer diameter of the front end side body portion 17 is further closer to the front end side than the front end side body portion 17. A small leg length portion 13 is formed. The long leg portion 13 is reduced in diameter toward the distal end side, and is exposed to the combustion chamber when the spark plug 100 is assembled to an internal combustion engine (not shown).

  Next, the center electrode 20 will be described. In the center electrode 20, a metal core 23 made of copper or a copper alloy for promoting heat dissipation is embedded in the center of an electrode base material made of a nickel-based alloy such as Inconel (trade name) 600 or 601. It is a rod-shaped electrode. The distal end portion 22 of the center electrode 20 protrudes from the distal end surface of the insulator 10 and is formed so as to become smaller in diameter toward the distal end side. A columnar electrode tip 90 is welded to the distal end surface of the distal end portion 22 so that the column axis is aligned with the axis of the center electrode 20. Further, a noble metal tip 91 made of a noble metal is joined to the tip of the electrode tip 90 in order to improve spark wear resistance. The center electrode 20 is electrically connected to the connection terminal 40 held on the rear end side of the shaft hole 12 via the sealing material 4 and the resistor 3 provided inside the shaft hole 12. The rear end 42 of the connection terminal 40 is exposed from the rear end of the insulator 10, and a high voltage cable (not shown) is connected to the rear end 42 via a plug cap (not shown). A high voltage is applied to 20.

  Next, the metal shell 50 will be described. The metal shell 50 is a cylindrical metal fitting for holding the insulator 10 and fixing the spark plug 100 to an internal combustion engine (not shown). The metal shell 50 holds the insulator 10 so as to surround the flange portion 19, the distal end side trunk portion 17, and the leg length portion 13 from the rear end side barrel portion 18 in the vicinity of the flange portion 19 of the insulator 10. The metal shell 50 is formed of a low carbon steel material, and includes a tool engaging portion 51 to which a spark plug wrench (not shown) is fitted, and a screw portion 52 to be screwed into an engine head provided on an internal combustion engine (not shown). ing. Further, the metal shell 50 has a caulking portion 53 on the rear end side of the tool engaging portion 51. By caulking the caulking portion 53, the step portion 15 formed between the front end side body portion 17 and the leg long portion 13 of the insulator 10 is attached to the plate packing 8 on the step portion 56 formed on the inner periphery of the metal shell 50. The metal shell 50 and the insulator 10 are integrated. In order to complete sealing by caulking, an annular shape is formed between the inner peripheral surface in the vicinity of the caulking portion 53 of the metal shell 50 and the outer peripheral surface of the rear end side body portion 18 in the vicinity of the flange portion 19 of the insulator 10. Ring members 6 and 7 are interposed, and talc (talc) 9 powder is filled between the ring members 6 and 7. Further, a flange 54 is formed at the center of the metal shell 50, and the gasket 5 is inserted into the vicinity of the rear end side (upper part in FIG. 1) of the screw 52, that is, the seat surface 55 of the flange 54. Yes.

  Next, the ground electrode 30 will be described. The ground electrode 30 is made of a metal having high corrosion resistance. As an example, a nickel-based alloy such as Inconel (trade name) 600 or 601 is used. The ground electrode 30 has a substantially rectangular cross section perpendicular to the longitudinal direction of the ground electrode 30 and has a bent rectangular bar-like outer shape. And the square-bar-shaped base end part 32 is joined to the front end surface 57 of the metal shell 50 on the front end side in the axis O direction by resistance welding. A tapered surface 59 that is chamfered in a tapered shape is formed on the inner peripheral side of the distal end surface 57. On the other hand, the distal end portion 31 opposite to the proximal end portion 32 of the ground electrode 30 is bent so as to face the distal end portion 22 of the center electrode 20, and a spark discharge gap is formed therebetween.

  Next, in the process of manufacturing the spark plug 100 according to the present embodiment, the protrusion removal jig 300 used for removing the welding protrusion 80 (so-called welding sag) generated when the ground electrode 30 is welded to the metal shell 50 will be described. This will be described with reference to FIGS. FIG. 2 is a diagram illustrating a schematic configuration of the protrusion removing jig 300. FIG. 3 is a side view of the front end portion of the removal punch 320 as viewed from the front side in FIG. FIG. 4 is a side view of the front end portion of the removal punch 320 as viewed from the left side of FIG. In FIG. 2, the vertical direction is + Y, -Y direction, the horizontal direction is -X, + X direction, the front and back direction of the paper is -Z, + Z direction, and in the following drawings, the direction shown in FIG.

  The protrusion removal jig 300 shown in FIG. 2 is formed when the ground electrode 30 is resistance-welded to the front end surface 57 of the metal shell 50 in the ground electrode joining step, which is a process of manufacturing the spark plug 100. It is a jig | tool for removing the welding projection part 80 formed in the inner peripheral side. The protrusion removal jig 300 includes a removal punch 320 on which a cutting blade 322 for cutting the welding protrusion 80 is formed, a known lifting device 310 that moves the removal punch 320 in the vertical direction (Y-axis direction), and the like. The slide mechanism 330 uses a known linear guideway that moves in the left-right direction (X-axis direction), and includes a fixing member 360 that fixes the metal fitting assembly 200 in which the ground electrode 30 is welded to the metal shell 50.

  Immediately below the protrusion removing jig 300 is a metal fitting assembly 200 in which the metal shell 50 and the ground electrode 30 are integrally bonded in the ground electrode bonding step, with the front end surface 57 of the metal shell 50 facing upward (+ Y direction). In this state, it is mounted on the mounting table 370. In the unformed threaded portion 152 (threaded portion 52 after thread formation) of the metal shell 50 of the bracket assembly 200, the thread has not yet been rolled in the process before cutting the weld projection 80, The periphery of the forming screw portion 152 is held by a fixing member 360 such as a chuck and is held and fixed on the mounting table 370. The projection removing jig 300 and the mounting table 370 are positioned so that the axis O direction of the metal shell 50 projected onto the YZ plane matches the axis P direction of the removal punch 320 described later.

  The removal punch 320 is formed of a cylindrical metal member, and has an outer diameter B that is substantially the same with a slightly smaller diameter than the inner diameter A of the tip hole of the metal shell 50 of the metal fitting assembly 200. Specifically, the outer diameter B of the removal punch 320 is formed to be the same as the design value (minimum inner diameter) that the inner diameter A of the tip hole of the metal shell 50 should have. In this way, when removing the welding projection 80 by the removal punch 320, the removal punch 320 only passes through the tip hole of the metal shell 50, and a minimum inner diameter is secured as the tip hole inner diameter A of the metal shell 50. Can be confirmed. As shown in FIGS. 3 and 4, the tip portion disposed on the lower side (−Y direction side) when the axis P direction of the removal punch 320 is the vertical direction (Y axis direction) of the protrusion removal jig 300. 325 is formed in a tapered shape, and a tapered surface on the + X direction side of the tip end portion 325 is configured as an inclined surface 321. The removal punch 320 corresponds to the “cutting member” in the present invention.

  Further, the portion from the side surface on the −X direction side to the front end surface on the −Y direction side of the removal punch 320 is penetrated in the Z-axis direction by two planes, the YZ plane and a plane that intersects the YZ plane at an acute angle. A cutout portion 326 that is cut out in this manner is formed. By this cutout portion 326, a cutting blade 322 is formed in which the side surface on the −X direction side of the removal punch 320 is a blade surface and the blade edge 327 is directed downward (−Y direction side). In the direction of the axis P of the removal punch 320, the position C of the cutting edge 327 of the cutting blade 322 is above the inclined surface 321 (+ Y direction side), that is, the rear end side of the removal punch 320 from the start position D of the tapered portion. Is located.

  Since the removal punch 320 is configured in this way, the cutting blade 322 has a blade base 328 (the root portion of the cutting blade 322 formed in a protruding shape by cutting out the removal punch 320 as described above). The cutting edge 327 has a shape arranged downward (in the −Y direction). The inclined surface 321 has a shape that inclines in the −X direction from the cutting edge 328 side to the cutting edge 327 side of the cutting blade 322. The inclined surface 321 is moved in the −X direction by the drag received at the time when the removal punch 320 moving in the downward direction (−Y direction) contacts the metal shell 50 in the descending step described later. It is provided for.

  Next, as shown in FIG. 2, the removal punch 320 has a flange portion 329 at the rear end, and the flange portion 329 is sandwiched between the slider 333 and the pressing plate 334 of the slide mechanism 330. The holding plate 334 is fastened to the slider 333 with bolts 335, and thereby the removal punch 320 is fixed to the slider 333. The slider 333 is provided so as to be movable in the X-axis direction along the guide rail 332. A base 331 that supports the guide rail 332 is fixed to the lifting device 310, and the slide mechanism 330 that holds and holds the removal punch 320 can be moved in the Y-axis direction by the lifting device 310.

  Next, a manufacturing method of the spark plug 100 including a series of steps for removing the welding projection 80 generated when the metal shell 50 and the ground electrode 30 are resistance-welded will be described with reference to FIGS. I will explain. In addition, it demonstrates centering around the manufacturing method of the principal part of this Embodiment, and abbreviate | omits or simplifies description about a well-known part. 5-8 is a figure for demonstrating a series of operation | movement at the time of removing the welding projection part 80 of the metal fitting assembly 200 with the removal punch 320. FIG.

  First, the insulator 10 is formed by using alumina as a main raw material, performing grinding or the like so as to have a predetermined shape, and firing at a high temperature. On the other hand, the rod-shaped center electrode 20 and the ground electrode 30 are produced from the nickel-based alloy described above. Note that when the center electrode 20 is formed, the metal core 23 is inserted. The center electrode 20, the sealing material 4, the resistor 3, the connection terminal 40 previously produced by plastic working or the like are integrally formed on the formed insulator 10 by a glass sealing process. In this glass sealing step, a glaze layer may be formed on the surface of the insulator 10.

  The metal shell 50 is made by using a steel material and performing plastic working, cutting, or rolling to a predetermined shape. At this time, a tool engagement portion 51 having a predetermined shape, an unformed screw portion 152 (a thread is not formed), a flange portion 54, and the like are formed on the metal shell 50.

  Then, the base end portion 32 of the ground electrode 30 is joined by resistance welding to the distal end surface 57 of the cylindrical metal shell 50 before assembling the insulator 10 and the like, and the metal fitting assembly 200 (see FIG. 2) is formed. (Ground electrode joining process). The ground electrode 30 is in a rod-like state before being subjected to bending, and is joined in a state in which the distal end portion 31 is directed upward from the distal end surface 57 of the metal shell 50.

  Next, as shown in FIG. 2, the metal fitting assembly 200 with the axis O direction of the metal shell 50 set to the vertical direction and the front end surface 57 of the metal shell 50 facing upward is placed on the mounting table 370, and the fixing member 360 is placed. Thus, the metal fitting assembly 200 is held and fixed by holding the periphery of the unformed screw portion 152 (holding step). In this holding step, the holding position of the metal fitting assembly 200 is positioned so that the axis O direction of the metal shell 50 projected onto the YZ plane in FIG. 2 and the axis P direction of the removal punch 320 coincide. Further, the axis O direction of the metal shell 50 projected onto the XY plane and the axis P direction of the removal punch 320 are arranged such that the axis P direction is shifted to the + X direction side with respect to the axis O direction. At this time, the inclined surface 321 of the removal punch 320 is located in the + Y direction from the portion of the front end surface of the metal shell 50 opposite to the side where the welding projection 80 is formed.

  Then, the lifting device 310 is driven, and the removal punch 320 together with the slide mechanism 330 is vertically lowered toward the front end surface 57 of the metal shell 50 of the metal fitting assembly 200 held on the mounting table 370 (lowering step). . Then, as shown in FIG. 5, the inclined surface 321 of the distal end portion 325 of the removal punch 320 abuts on the distal end surface 57 of the metal shell 50 of the metal fitting assembly 200. At this time, the axis P of the removal punch 320 and the axis O of the metal shell 50 are aligned in the Z-axis direction. For this reason, more specifically, it is removed at the edge portion on the inner peripheral side of the portion of the front end surface 57 of the metal shell 50 opposite to the side on which the welding projection 80 is formed with the axis O interposed therebetween. The inclined surface 321 of the punch 320 comes into contact. As described above, in the present embodiment, the tapered surface 59 is provided on the inner peripheral side of the front end surface 57, and the inner peripheral edge of the front end surface 57 with which the inclined surface 321 of the removal punch 320 abuts is the same as that of the metal shell 50. The ridge angle portion formed by the inner peripheral surface and the tapered surface 59 is indicated. However, when the tip surface 57 is not provided with the tapered surface 59, the inclined surface 321 of the removal punch 320 comes into contact with the ridge angle portion formed by the tip surface 57 and the inner peripheral surface.

  When the removal punch 320 is further lowered, the slope 321 of the removal punch 320 receives a drag force from the inner peripheral edge of the front end surface 57 of the metal shell 50 (the inner peripheral edge of the tapered surface 59). The removal punch 320 is guided in the moving direction by the fixed slide mechanism 330 and moves in the −X direction. Then, as shown in FIG. 6, when the distal end portion 31 of the ground electrode 30 of the bracket assembly 200 is inclined toward the inner peripheral side of the metal shell 50 with respect to the base end portion 32, the distal end portion 31 of the ground electrode 30 is removed. It contacts the side surface of the punch 320 on the −X direction side.

  When the removal punch 320 is further lowered in this state, the tip 31 of the ground electrode 30 is pressed to the −X direction side by the side surface of the removal punch 320 on the −X direction side. Then, as shown in FIG. 7, the inner peripheral edge (the inner peripheral edge of the tapered surface 59) of the front end surface 57 of the metal shell 50 is at the rear end of the inclined surface 321 of the removal punch 320 (starting position D of the tapered portion shown in FIG. 3). When it reaches, the axis O of the metal shell 50 and the axis P of the removal punch 320 are almost overlapped. As described above, the outer diameter B of the removal punch 320 is substantially the same as the inner diameter A of the tip hole of the metal shell 50, and the cutting blade 322 of the removal punch 320 has the side surface on the −X direction side of the removal punch 320 as the blade surface. The cutting edge 327 is located above the rear end of the slope 321 of the removal punch 320. For this reason, the cutting edge 327 of the cutting blade 322 is moved and positioned from the upper side (+ Y direction side) along the side surface on the + X direction side of the ground electrode 30 so as to be in contact with the root portion of the welding projection 80. The

  Accordingly, when the removal punch 320 is further lowered, as shown in FIG. 8, the removal punch 320 is inserted into the metal shell 50, and the cutting blade 322 is slid straightly downward (−Y direction) accordingly. Therefore, the welding projection 80 is cut from the root (cutting process). For this reason, the protrusion amount of the remainder after cutting is small.

  Thus, when cutting the welding projection 80, the cutting edge 327 of the cutting blade 322 is positioned and positioned from the lateral direction (+ X direction side) above the welding projection 80 (+ Y direction). The tip 31 of the ground electrode 30 and the cutting blade 322 do not intersect. For this reason, when the distal end portion 31 of the ground electrode 30 is welded to the inner peripheral side of the metal shell 50 with respect to the base end portion 32, it is not necessary to correct the tilt.

  Next, using a known rolling die (not shown), the thread is rolled on the unformed screw portion 152 of the metal fitting assembly 200 to form the screw portion 52. In the subsequent process, the metal fitting assembly 200 is subjected to a plating process for improving corrosion resistance. After drying, the insulator 10 in which the center electrode 20 and the like are integrated is assembled to the metal fitting assembly 200. At this time, by using the plate packing 8, the ring members 6, 7, the talc 9, and the like described above to form the crimped portion 53, the metal fitting assembly 200 and the insulator 10 are integrated. Next, as shown in FIG. 1, a process of bending the ground electrode 30 is performed, and a spark discharge gap is formed between the tip portion 31 of the ground electrode 30 and the tip portion 22 of the center electrode 20, thereby completing the spark plug 100. .

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, the removal punch 320 of the present embodiment has an outer diameter B that is substantially the same as the inner diameter A of the tip hole of the metal shell 50, but is acceptable as the inner diameter of the metal shell 50 in the manufacturing process of the spark plug 100. It may be the same as the minimum inner diameter of the tolerance range. When the spark plug 100 is completed, it is sufficient that the distance between the inner peripheral surface of the metal shell 50 and the outer peripheral surface of the insulator 10 is a predetermined distance that can reduce the occurrence of side fire. . The inner diameter of the metal shell 50 may be reduced by a process of rolling a thread on the unformed screw portion 152 of the metal shell 50 or a process of plating performed after the cutting process. The minimum inner diameter that should be ensured as the inner diameter of the metal shell 50 after the cutting process may be set as the outer diameter of the removal punch 320 after the expected size is taken into account. If it does in this way, while cutting the welding projection part 80 by a cutting process, the minimum inside diameter of the manufacturing tolerance range allowable as an inside diameter of the metal shell 50 can be ensured.

  In the present embodiment, the slope 321 provided on the removal punch 320 is formed by processing the tip 325 of the removal punch 320 into a tapered shape, but from the side surface on the opposite side of the blade edge 327 across the axis P. A plate-like slope may be formed over the tip surface. At this time, the rear end position of the slope is positioned closer to the front end side of the removal punch 320 than the position of the cutting edge 327 of the cutting blade 322. Alternatively, a member having a slope may be assembled to the distal end portion 325 of the removal punch 320.

  In the present embodiment, the cutting edge 325 of the removal punch 320 is cut out to form the cutting blade 322. However, a separately prepared cutting blade may be assembled to the leading end 325. In this case, the cutting edge of the cutting blade is positioned on the rear end side of the removal punch 320 with respect to the slope, and the blade surface of the cutting blade is positioned on the −X direction side surface of the removal punch 320.

  Further, the removal punch 320 does not have to be cylindrical. At least the manufacturing tolerance in which the distance between the rear end position of the slope 321 and the position of the cutting edge 327 of the cutting blade 322 is acceptable as the inner diameter of the metal shell 50 in the left-right direction (X-axis direction) of the protrusion removing jig 300. It is only necessary to have the same distance as the minimum inner diameter of the range.

  Further, a biasing member may be provided in the slide mechanism 330 so that the slider 333 is always biased in the + X direction. In the slide mechanism 330, the slider 333 is guided by the guide rail 332 so that the inclined surface 321 of the removal punch 320 that is lowered in the lowering step is always in contact with the inner peripheral edge of the front end surface 57 of the metal shell 50 of the metal fitting assembly 200. It is preferable to perform marking or provide a stopper at a site to be positioned above.

  Further, a recess is provided on the side surface on the rear end side from the position C (see FIG. 3) of the blade edge 327 of the removal punch 320, and the tip 31 of the ground electrode 30 is attached to the removal punch 320 when the welding projection 80 is removed. You may make it not contact | abut on a side surface. By forming such a concave portion, it is possible to avoid the tip portion 31 of the ground electrode 30 from being rubbed by rubbing against the side surface of the removal punch 320, and to avoid the possibility of unintentional electric field concentration. be able to.

  The present invention can be applied to a method for manufacturing a spark plug used in an internal combustion engine.

1 is a partial cross-sectional view of a spark plug 100. FIG. 3 is a diagram showing a schematic configuration of a protrusion removing jig 300. FIG. FIG. 3 is a side view of a front end portion of a removal punch 320 as viewed from the front side in FIG. FIG. 3 is a side view of a front end portion of a removal punch 320 as viewed from the left side in FIG. FIG. 10 is a diagram for describing a series of operations when removing the welding projection 80 of the metal fitting assembly 200 by the removal punch 320. FIG. 10 is a diagram for describing a series of operations when removing the welding projection 80 of the metal fitting assembly 200 by the removal punch 320. FIG. 10 is a diagram for describing a series of operations when removing the welding projection 80 of the metal fitting assembly 200 by the removal punch 320. FIG. 10 is a diagram for describing a series of operations when removing the welding projection 80 of the metal fitting assembly 200 by the removal punch 320.

Explanation of symbols

DESCRIPTION OF SYMBOLS 30 Ground electrode 50 Main metal fitting 57 Front end surface 80 Welding protrusion 100 Spark plug 320 Removal punch 321 Slope 322 Cutting blade 327 Cutting edge 328 Cutting edge 330 Sliding mechanism

Claims (4)

A spark plug manufacturing method comprising a ground electrode joining step in which a ground electrode is welded to the metal shell in a state in which a welding projection is formed on the inner peripheral side of the metal shell,
Holding the metal shell with the ground electrode welded to the tip surface, with the tip surface facing upward;
A lowering step of lowering the cutting blade in a state in which the blade tip is directed downward from above the tip surface of the metal shell toward the welding projection,
A cutting step of cutting the weld projection after the descending step,
The cutting blade is inclined in a direction approaching the welding projection from the base side to the tip side of the cutting blade on the side opposite to the welding projection side of the cutting blade when the welding projection is cut. With a slope,
In the descending step, the inclined surface is brought into contact with the inner peripheral edge of the front end surface of the metal shell opposite to the side on which the weld projection is formed, and is guided by the inclined surface, A method for manufacturing a spark plug, characterized in that a cutting edge is positioned with respect to the weld projection.   2. The spark plug manufacturing method according to claim 1, wherein a cutting edge of the cutting blade is formed above the inclined surface. The cutting blade and the slope are formed at one end of a round bar-shaped cutting member,
3. The method for manufacturing a spark plug according to claim 1, wherein an outer diameter of the cutting member is the same as a minimum inner diameter within a manufacturing tolerance range allowable in an inner diameter at the time of manufacturing the metal shell. The cutting member is held by a slide mechanism supported to be movable up and down,
4. The spark plug according to claim 3, wherein in the lowering step, the cutting blade is guided by the inclined surface and the movement in a displacement direction different from the lowering direction is performed by the slide mechanism. 5. Production method.

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