JP6121342B2 - Manufacturing method of spark plug - Google Patents

Description

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

  In general, a spark plug has a center electrode and a ground electrode on the tip side. The center electrode protrudes from the tip of the insulator while being held in the shaft hole of the insulator. On the other hand, the ground electrode is joined to the tip of the metal shell.

  The metal shell is usually plated to prevent corrosion. In particular, barrel plating is used for simultaneously plating a large number of metal shells (Patent Document 1, etc.).

JP 2001-68250 A JP 2007-284755 A JP 2008-236263 A

  The barrel plating of the metallic shell is performed on a workpiece (hereinafter also referred to as “joined body”) in which a rod-like ground electrode member is joined to the tip of the metallic shell. In the barrel plating process, the plating process proceeds while a large number of workpieces rotate freely in a large barrel. The inventors have found that the leading end side of the metal shell to which the ground electrode member is joined may enter the hole at the rear end of the other metal shell, and the two metal shells may stick to each other and cannot be separated. I found it. When the plating process is performed in a state where the two metal shells are fixed as described above, there arises a problem that a plating defect occurs.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, a preparation step of preparing a joined body in which a rod-like ground electrode member is joined to a tip portion of a cylindrical metal shell having a screw portion at a tip portion; And a plating step of performing a plating process on the joined body using the spark plug. In this manufacturing method, the preparation step includes a step of inclining the ground electrode member of the joined body outward in the radial direction of the metal shell with respect to a direction parallel to a central axis of the metal shell, and the plating step The bonding body is plated in a state where the ground electrode member is inclined.
According to this manufacturing method, the barrel plating process is performed on the joined body in a state where the ground electrode member is inclined outward in the radial direction of the metal shell. It is possible to reduce the possibility of occurrence.

(2) In the above manufacturing method, the step of inclining the ground electrode member includes (i) joining the ground electrode member to the tip end portion of the metal shell so as to extend along a direction parallel to the central axis of the metal shell. And (ii) when the ground electrode member is joined to the tip end of the metal shell, the ground electrode member is tilted toward the outer side in the radial direction of the metal shell. It is good also as a thing which is any one of the process joined in the state inclined toward the radial direction outer side of the metal fitting.
According to this configuration, it is possible to obtain a joined body in which the ground electrode member is tilted outward in the radial direction of the metal shell.

(3) In the above manufacturing method, when the inner diameter of the rear end portion of the metal shell is B (mm) and the outer diameter of the screw portion is A (mm), −1.5 ≦ A−B <0. It is good also as a thing.
In general, since the inner diameter B of the rear end portion of the metal shell is larger than the outer diameter A of the screw portion, there is a possibility that a screw portion of a certain metal shell bites into a hole in the rear end portion of another metal shell. . According to the above configuration, even in such a case, by using the joined body in which the ground electrode member is inclined outward in the radial direction of the metal shell as the workpiece for the barrel plating process, It is possible to reduce the possibility that the metal shells are fixed to each other and plating failure occurs.

(4) In the above manufacturing method, the joined body to be processed in the plating step is formed on a virtual plane perpendicular to the central axis from the distal end side where the ground electrode member is disposed along the central axis of the metal shell. When viewed by projection, the shortest distance between the most radially outer point of the ground electrode member and the outer periphery of the threaded portion may be 0.3 mm or more.
According to this configuration, since the ground electrode member sufficiently protrudes radially outward from the metal shell, the possibility that the two metal shells adhere to each other during the barrel plating process to cause plating defects is further reduced. be able to.

  Note that the present invention can be realized in various modes. For example, it can be realized in the form of a spark plug manufacturing method, a spark plug metal shell manufacturing method, and the like.

The front view which shows the spark plug as one Embodiment. Explanatory drawing which shows the shape of the joined body of the main metal fitting and the ground electrode member in the process before and after the plating treatment. Explanatory drawing which shows an example of a barrel plating apparatus. Explanatory drawing which shows the state which two metal shells as a comparative example adhered. Explanatory drawing which shows the experimental result about the influence which the dimension of the joined body of a main metal fitting and a ground electrode member has on a plating process. Explanatory drawing which shows an example of the process before and behind the plating process in one Embodiment. Explanatory drawing which shows an example of the process before and behind the plating process in other embodiment. Explanatory drawing which shows an example of the process before and behind the plating process in other embodiment.

  FIG. 1 is a front view showing a spark plug 100 as an embodiment of the present invention. In FIG. 1, the lower side where the ignition part of the spark plug 100 exists is defined as the front end side of the spark plug 100, and the upper side is defined as the rear end side. The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50. The insulator 10 has an axial hole extending along the axis O. The axis O is also referred to as “center axis”. The center electrode 20 is a rod-shaped electrode extending along the axis O, and is held in a state of being inserted into the shaft hole of the insulator 10. The ground electrode 30 is an electrode having one end fixed to the distal end portion 52 of the metal shell 50 and the other end facing the center electrode 20. The terminal fitting 40 is a terminal for receiving power supply, and is electrically connected to the center electrode 20. The metal shell 50 is a cylindrical member that surrounds the outer periphery of the insulator 10, and fixes the insulator 10 inside. A screw portion 54 is formed on the outer periphery of the metal shell 50. The screw part 54 is a part where a screw thread is formed, and is screwed into a screw hole of the engine head when the spark plug 100 is attached to the engine head.

  FIG. 2 shows the shape of the joined body 200 of the metal shell and the ground electrode member in the steps before and after the plating treatment of the embodiment. FIG. 2A shows a process of preparing a joined body 200 as a workpiece for plating treatment. In this step, the rod-shaped ground electrode member 30p is joined to the tip 52 of the metal shell 50 in an inclined state. More specifically, the ground electrode member 30p is joined in a state of being inclined outward in the radial direction RD of the metal shell 50 with respect to a direction OD parallel to the central axis O of the metal shell 50. Here, the “radial direction RD of the metallic shell 50” means a direction from the central axis O of the metallic shell 50 toward the outside. The ground electrode member 30p is a member that becomes a curved ground electrode 30 as shown in FIG. 1 by being bent after the plating process. The length of the rod-shaped ground electrode member 30p before being bent is usually 5 to 20 mm. 2A is plated using a barrel plating apparatus (FIG. 2B).

  FIG. 3 is an explanatory view showing an example of a barrel plating apparatus. This barrel plating apparatus has a barrel BM BM and a plating tank PM. In the barrel plating process, a large number of joined bodies 200 are put into the barrel tank BM, and the whole barrel tank BM is immersed in the plating solution LZ in the plating tank PM. In the barrel tank BM, a conductor CC having a negative potential through a resin-coated lead wire L1 is disposed so as to contact the joined body 200. In the plating rod PM, a metal plate PZ (for example, a zinc plate) having a positive potential is further disposed at a position outside the barrel rod BM. In this state, when the barrel tank BM is rotated around the rotation axis AX1, a large number of joined bodies 200 are plated while being freely moved while being stirred according to the rotation of the barrel tank BM. As a result, a plating layer is uniformly formed on the outer surface of the joined body 200.

  As shown in FIG. 2A, the joined body 200 as a workpiece of the plating process is joined to the tip 52 of the metal shell 50 with the ground electrode member 30p tilted outward. This inclined ground electrode member 30p has a great effect in suppressing the problem described in the prior art (the problem that the two metal shells 50 are fixed to each other and cannot be separated during the barrel plating process).

  FIG. 4 is an explanatory view showing a state in which two metal shells 50a and 50b as a comparative example are fixed to each other. Here, the threaded portion 54b of the second metal shell 50b is fixed to each other in a state where the screw portion 54b of the second metal shell 50b enters the hole of the rear end portion 56a of the first metal shell 50a. In this example, the ground electrode member 30p faces a direction parallel to the central axis of the metal shell 50b. Further, particularly in this example, the threaded portion 54b of the second metal shell 50b is caught by the outlet of the rear end portion 56a of the first metal shell 50a, and is fixed without being easily separated.

  On the other hand, in this embodiment, as shown in FIGS. 2A and 2B, the ground electrode member 30p is inclined outward in the radial direction RD in the joined body 200 that is a workpiece for barrel plating. It is joined to the metal shell 50 in a state. By doing so, it is possible to prevent or suppress a state in which the ends of the two metal shells (that is, two joined bodies) bite into each other and are fixed as shown in FIG.

  After the barrel plating process, in FIG. 2C, a processing process for erecting the ground electrode member 30p is performed. Here, “upright” means a state of being oriented in a direction parallel to the central axis O of the metal shell 50. After FIG. 2C, a caulking process of the metal shell 50 and the insulator 10, a bending process of the ground electrode member 30p, and the like are performed as necessary.

  FIG. 5 is an explanatory diagram showing experimental results on the influence of the dimensions of the joined body 200 on the plating process. FIG. 5A is a front view of the joined body 200, and FIG. 5B is a plan view of the joined body 200 projected onto a virtual plane perpendicular to the central axis O along the central axis O of the metal shell 50. It shows the state as seen. However, in FIG. 5B, only the shapes of the threaded portion 54 and the ground electrode member 30p of the metal shell 50 are drawn for convenience of illustration.

The following three dimensions were considered as the dimensions of the joined body 200 related to the quality of the plating process.
(1) Outer diameter A (mm) of the threaded portion 54 of the metal shell 50
(2) Inner diameter B (mm) of the hole in the rear end portion 56 of the metal shell 50
(3) Radial protrusion amount L (mm) of the ground electrode member 30p
The radial protrusion amount L (mm) of the ground electrode member 30p is determined when the joined body 200 is projected onto a virtual plane perpendicular to the central axis O as shown in FIG. It is defined as the shortest distance between the most radially outer point of the member 30p and the outer periphery of the threaded portion 54 of the metal shell 50.

  When the outer diameter A (mm) of the threaded portion 54 of the metal shell 50 is smaller than the inner diameter B (mm) of the hole at the rear end of the metal shell 50, as described with reference to FIG. There is a high possibility that the threaded portion 54b of the 50b enters the hole of the rear end portion 56a of the other metal shell 50a and the two are fixed. In terms of preventing or suppressing such sticking, it is considered that the effect of tilting the ground electrode member 30p is great when the value of (A−B) is less than 0 (ie, minus).

  FIG. 5C shows the experimental results of the relationship between the value of (A-B) and the yield in the barrel plating process. Here, experimental results are shown for two cases where the radial protrusion amount L of the ground electrode member 30p is 0.3 mm and 0 mm. L = 0 mm is a comparative example in which the ground electrode member 30 p is not inclined with respect to the metal shell 50. In the example of L = 0.3 mm, the yield of the barrel plating process was 100% in any case where the value of (A−B) was in the range of −0.5 mm to −3.0 mm. Here, the “yield” is a case where the bonded body 200 having a portion where plating is insufficient by visual inspection after the plating process is rejected, and a case where the plated layer is uniformly formed over the entire bonded body 200 is passed. This is the value when

  In the comparative example in which the radial protrusion amount L of the ground electrode member 30p is 0 mm, the yield of the barrel plating process is 100% when the value of (AB) is in the range of -0.5 mm to -1.5 mm. Was less than. This is presumably because the sticking described with reference to FIG. 4 occurred and the plating layer was not uniformly formed in the sticking parts. On the other hand, also in the comparative example of L = 0 mm, when the value of (A−B) was −2.0 mm or more, the yield of the barrel plating process was 100%. The reason for this is that when the inner diameter B of the hole at the rear end portion 56 of the metal shell 50 is sufficiently larger than the outer diameter A of the threaded portion 54 of the metal shell 50, the sticking as shown in FIG. This is presumed to be because of this. However, even in the case of L = 0 mm, it is preferable that the ground electrode member 30p is inclined and joined in that the yield of the barrel plating process can be more reliably maintained.

  In consideration of the result of FIG. 5C described above, the effect of joining the ground electrode member 30p by tilting is particularly when the value of (A−B) is less than 0 and −1.5 mm or more (ie, This is conspicuous in the case of −1.5 ≦ A−B <0).

  FIG. 5D illustrates the effect of the radial protrusion amount L of the ground electrode member 30p. When the radial protrusion amount L was 0.3 mm or more, no rejected product was found after barrel plating. On the other hand, when the radial protrusion amount L is in the range of 0 mm to 0.2 mm, some rejected products were found. In the experiment of FIG. 5D, the value of (AB) was a constant value of −0.5 mm. Considering the result of FIG. 5D, the value of the radial protrusion amount L (mm) is preferably set to 0.3 mm or more.

  Drawing 6 is an explanatory view showing an example of a process before and behind plating processing in one embodiment. FIG. 6A shows the metal shell member 50p before rolling and before plating. In the step of FIG. 6B, the metal shell 50 is created by forming the threaded portion 54 in the metal shell member 50p by rolling. In the step of FIG. 6C, the joined body 200 is formed by welding the tip end portion 52 of the metal shell 50 with the ground electrode member 30p tilted. 6A to 6C correspond to a preparation process for preparing the joined body 200. Thereafter, a barrel plating process is performed (FIG. 6D), and a processing process for erecting the ground electrode member 30p is performed (FIG. 6E). 6C to 6E correspond to FIGS. 2A to 2C. In the process of FIG. 6, since the ground electrode member 30p is welded to the front end portion 52 of the metal shell 50 in a tilted state, there is an advantage that a step of tilting the ground electrode member 30p is unnecessary.

  Drawing 7 is an explanatory view showing an example of the process before and behind the plating processing in other embodiments. The difference from FIG. 6 is that the steps of FIGS. 7C and 7D are performed instead of the step of FIG. 6C, and the other steps are the same as those of FIG. In the step of FIG. 7C, the ground electrode member 30p is welded to the front end portion 52 of the metal shell 50 in an upright state. The ground electrode member 30p is tilted using the pressing jig 300 in the step of FIG. The side surface 310 of the pressing jig 300 is a plane inclined at a predetermined angle with respect to the central axis of the metal shell 50. When the pressing jig 300 is moved from the front end side (upper side in the figure) of the metal shell 50 toward the rear end side (lower side in the figure), the ground electrode member is moved along the side surface 310 of the pressing jig 300. 30p tilts. By adjusting the inclination angle of the side surface 310 of the pressing jig 300 in advance, the inclination angle of the ground electrode member 30p and the radial protrusion amount L (FIG. 5B) can be adjusted.

  FIG. 8 is an explanatory diagram showing an example of steps before and after the plating process in still another embodiment. The difference from FIG. 7 is that the steps of FIGS. 8B and 8C are performed instead of the steps of FIGS. 7B and 7C, and the other steps are the same as those of FIG. . In the process of FIG. 8B, before forming the threaded portion 54 by rolling, the ground electrode member 30p is welded to the front end portion 52 of the metal shell member 50p in an upright state. In the process of FIG. 8C, the metal shell 50 is created by forming the threaded portion 54 in the metal shell member 50p by rolling. The subsequent steps are the same as those after FIG.

  As can be understood from FIGS. 6 to 8, various processes can be used as the process of inclining the ground electrode member 30 p outward in the radial direction of the metal shell 50. Moreover, you may use processes other than FIGS. 6-8.

  As described above, in the present embodiment, the ground electrode member 30p is tilted outward in the radial direction of the metal shell 50 with respect to the direction parallel to the central axis O of the metal shell 50. When the plating process is performed by the plating apparatus, it is possible to suppress a problem that the bonded bodies 200 are fixed to each other and plating becomes insufficient.

Modification Examples The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the scope of the invention.

・ Modification 1:
As the spark plug, spark plugs having various configurations other than those shown in FIG. 1 can be applied to the present invention. In particular, various modifications can be made to the specific shapes of the terminal fitting and the insulator. Further, in the various embodiments described above, the ground electrode member 30p is erected after the plating process. However, the ground electrode member 30p is not erected, and the subsequent processing (for making the shape of the final ground electrode 30) is performed. Bending may be performed. In the case where the ground electrode member 30p is not erected after the plating process, for example, (i) when the subsequent processing is performed without returning the tilted state of the ground electrode member 30p, or (ii) the ground electrode member 30p is tilted. In this case, there is a case where subsequent machining is performed after returning to a state in which the inclination is reduced, although it is not allowed to stand upright.

DESCRIPTION OF SYMBOLS 10 ... Insulator 20 ... Center electrode 30 ... Ground electrode 30p ... Ground electrode member 40 ... Terminal metal fittings 50, 50a, 50b ... Main metal fitting 50p ... Main metal fitting member 52 ... Tip part 54, 54b ... Screw part 56, 56a ... Rear end Part 100 ... Spark plug 200 ... Assembly 300 ... Pressing jig 310 ... Side surface

Claims (4)

A preparation step of preparing a joined body in which a rod-shaped ground electrode member is joined to the tip portion of a cylindrical metal shell having a threaded portion at the tip portion, and a plating step of performing plating treatment of the joined body using a barrel plating apparatus A spark plug manufacturing method comprising:
The preparation step includes a step of inclining the ground electrode member of the joined body outward in the radial direction of the metal shell with respect to a direction parallel to a central axis of the metal shell,
The method for producing a spark plug according to claim 1, wherein the plating step performs the plating process on the joined body in a state where the ground electrode member is inclined. It is a manufacturing method of the spark plug according to claim 1,
The step of tilting the ground electrode member includes:
(I) After joining the ground electrode member to the tip end portion of the metal shell so as to extend along a direction parallel to the central axis of the metal shell, the ground electrode member is directed radially outward of the metal shell. And tilting process,
(Ii) when joining the ground electrode member to the distal end portion of the metallic shell, joining the ground electrode member in a state inclined toward the radially outer side of the metallic shell;
A method for manufacturing a spark plug, which is any one of the above. It is a manufacturing method of the spark plug according to claim 1 or 2,
A spark plug characterized in that −1.5 ≦ A−B <0, where B (mm) is the inner diameter of the rear end of the metal shell and A (mm) is the outer diameter of the threaded portion. Manufacturing method. It is a manufacturing method of the spark plug according to claim 3,
When the joined body to be processed in the plating step is viewed from the front end side where the ground electrode member is disposed along the central axis of the metal shell, projected onto a virtual plane perpendicular to the central axis, A method for manufacturing a spark plug, characterized in that a shortest distance between a point on the outermost radial direction of the ground electrode member and an outer periphery of the threaded portion is 0.3 mm or more.

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