JP2017033812A - Method for manufacturing spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of successively welding a noble metal chip to a ground electrode while keeping the appearance quality of a spark plug.SOLUTION: A method for manufacturing a spark plug comprises the steps of: (A) bringing a ground electrode into contact with a noble metal chip and applying first load to the ground electrode and the noble metal chip; (B) decreasing the load applied to the ground electrode and the noble metal chip to lower than the first load after the step (A); and (C) performing resistance welding by passing current through the ground electrode and the noble metal chip while applying lighter load than the first load to the ground electrode and the noble metal chip in the midst of or during the step (B).SELECTED DRAWING: Figure 3

Description

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

  Conventionally, some spark plugs have a noble metal tip welded to a ground electrode. For example, in the technique described in Patent Document 1, while applying a predetermined pressure to the noble metal tip and the ground electrode, an electric current is passed through the noble metal tip and the ground electrode to perform resistance welding.

JP 2004-186152 A

  When pressure is applied to the noble metal tip and the ground electrode during resistance welding, a large pressure is mainly applied to the contact portion between the peripheral edge of the noble metal tip and the ground electrode. Then, current may flow locally at the contact portion between the peripheral edge where the large pressure is applied and the ground electrode, and welding may be performed unevenly. If welding is performed unevenly, the possibility of spattering during welding increases, and the appearance quality of the spark plug may be reduced. Therefore, there is a demand for a technique that can favorably weld the noble metal tip to the ground electrode while maintaining the appearance quality of the spark plug.

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

(1) According to an aspect of the present invention, there is provided a method for manufacturing a spark plug including a ground electrode to which a noble metal tip is bonded. The manufacturing method includes: (A) contacting a ground electrode and a noble metal tip and applying a first load to the ground electrode and the noble metal tip; and (B) after the step (A), the ground electrode. And a step of lowering the load applied to the noble metal tip than the first load; (C) during the step (B) or after the step (B), the ground electrode, the noble metal tip, And applying resistance welding to the ground electrode and the noble metal tip while applying a load smaller than the first load. In the spark plug manufacturing method of this type, the contact between the ground electrode and the noble metal tip is applied in advance before the resistance welding, since a load (first load) larger than the load applied during the resistance welding is applied. The state becomes stable and welding can be performed in a uniform state. As a result, the occurrence of spatter is suppressed, so that the noble metal tip can be favorably welded to the ground electrode while maintaining the appearance quality of the spark plug.

(2) In the spark plug of the above aspect, the amount that the noble metal tip is buried in the ground electrode by the step (C) is more than the amount that the noble metal tip is buried in the ground electrode by the step (A). There may be many. With such a form of spark plug, the amount of melting increases during resistance welding, and the welding strength can be improved.

  The present invention can be implemented in various forms other than the above-described form as a spark plug manufacturing method, such as a ground electrode manufacturing method and a spark plug.

It is a fragmentary sectional view of a spark plug. It is process drawing which shows the manufacturing method of a spark plug. It is process drawing which shows the method of welding a noble metal tip to a ground electrode. It is a schematic diagram which shows the method of welding a noble metal tip to a ground electrode. It is a graph which shows the change of the load added to a ground electrode and a noble metal tip.

A. Embodiment:
FIG. 1 is a partial cross-sectional view of a spark plug 100 manufactured by a spark plug manufacturing method according to an embodiment of the present invention. The spark plug 100 has an elongated shape along the axis O. In FIG. 1, the right side of the axis O indicated by a dashed line shows an external front view, and the left side of the axis O shows a cross-sectional view passing through the axis O. In the following description, the lower side in FIG. 1 is referred to as the front end side of the spark plug 100, and the upper side in FIG. 1 is referred to as the rear end side.

  The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, and a metal shell 50. The insulator 10 has at least a part of its outer periphery held by a cylindrical metal shell 50 and has a shaft hole 12 along the axis O. A center electrode 20 is provided in the shaft hole 12. The ground electrode 30 is fixed to the front end surface 57 of the metal shell 50 and forms a discharge gap with the center electrode 20. A noble metal tip 31 is bonded to the ground electrode 30.

  The insulator 10 is an insulator formed by firing a ceramic material such as alumina. The insulator 10 is a cylindrical member in which a part of the center electrode 20 is accommodated at the front end side and the shaft hole 12 that accommodates a part of the terminal fitting 40 is formed at the rear end side. At the center in the axial direction of the insulator 10, a central body 19 having a larger outer diameter is formed. On the rear end side of the central body portion 19, a rear end side body portion 18 that insulates between the terminal fitting 40 and the metal shell 50 is formed. 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 of the central body portion 19. Further on the distal end side of the distal end side body portion 17, a leg length portion 13 is formed which has an outer diameter smaller than that of the distal end side body portion 17 and decreases toward the center electrode 20 side.

  The metal shell 50 is a cylindrical metal fitting that surrounds and holds a portion extending from a part of the rear end body portion 18 of the insulator 10 to the long leg portion 13. The metal shell 50 is made of, for example, low carbon steel, and is subjected to a plating process such as nickel plating or zinc plating. The metal shell 50 includes a tool engaging portion 51, a seal portion 54, and a mounting screw portion 52 in order from the rear end side. A tool for attaching the spark plug 100 to the engine head is fitted into the tool engaging portion 51. The attachment screw portion 52 has a thread that is screwed into the attachment screw hole of the engine head. The seal portion 54 is formed in a hook shape at the base of the mounting screw portion 52. An annular gasket 5 formed by bending a plate is fitted between the seal portion 54 and the engine head. The front end surface 57 of the metal shell 50 has a hollow circular shape, and the front end portion of the long leg portion 13 of the insulator 10 and the front end portion of the center electrode 20 protrude from the center thereof.

  A thin caulking portion 53 is provided on the rear end side of the metal shell 50 from the tool engaging portion 51. Further, between the seal portion 54 and the tool engaging portion 51, a compression deformation portion 58 having a small thickness is provided in the same manner as the caulking portion 53. Between the inner peripheral surface of the metal shell 50 from the tool engaging portion 51 to the crimping portion 53 and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, annular ring members 6 and 7 are interposed. Further, talc (talc) 9 powder is filled between the ring members 6 and 7. When the spark plug 100 is manufactured, the compression deformable portion 58 is compressed and deformed by pressing the caulking portion 53 inward so as to be bent inward, and the compression deformation of the compression deformable portion 58 causes the ring members 6, 7 and The insulator 10 is pressed toward the front end side in the metal shell 50 through the talc 9. By this pressing, the talc 9 is compressed in the direction of the axis O, and the airtightness in the metal shell 50 is enhanced.

  On the inner periphery of the metal shell 50, an insulator step located at the base end of the leg long portion 13 of the insulator 10 via the annular plate packing 8 is connected to the metal inner step portion 56 formed on the inner periphery of the mounting screw portion 52. The part 15 is pressed. The plate packing 8 is a member that maintains airtightness between the metal shell 50 and the insulator 10, and prevents the combustion gas from flowing out.

  The ground electrode 30 is formed of a nickel alloy mainly composed of nickel, such as Inconel (trade name) 600 or Inconel 601. The proximal end of the ground electrode 30 is welded to the distal end surface 57 of the metal shell 50. In the present embodiment, the ground electrode 30 is bent at an intermediate portion so that one side surface of the tip portion of the ground electrode 30 faces the center electrode 20. In the present embodiment, a noble metal tip 31 is joined to the tip of the ground electrode 30 at a position facing the center electrode 20. The noble metal tip 31 is made of a platinum alloy such as a platinum-nickel alloy or a platinum-iridium alloy.

  The center electrode 20 is a rod-like member in which a core material 22 having better thermal conductivity than the electrode base material 21 is embedded in the electrode base material 21. The electrode base material 21 is made of a nickel alloy containing nickel as a main component, and the core member 22 is made of copper or an alloy containing copper as a main component.

  In the vicinity of the rear end portion of the center electrode 20, a flange portion 23 protruding to the outer peripheral side is formed. The flange 23 contacts the shaft hole inner step 14 formed in the shaft hole 12 from the rear end side, and positions the center electrode 20 in the insulator 10. The rear end portion of the center electrode 20 is electrically connected to the terminal fitting 40 via the ceramic resistor 3 and the seal body 4.

  FIG. 2 is a process diagram showing a method for manufacturing the spark plug 100. In the manufacturing method of the present embodiment, first, a metal shell 50 to which a non-bent rod-shaped ground electrode 30 is welded is prepared, and other members shown in FIG. 1 such as the center electrode 20 and the insulator 10 are also prepared. Are prepared and assembled as shown in FIG. 1 (step S100).

  Subsequently, the noble metal tip 31 is welded to the rod-shaped ground electrode 30 that is not bent (step S120). A method for welding the noble metal tip 31 will be described later. Finally, the ground electrode 30 to which the noble metal tip 31 is welded is bent and bent (step S130), and the spark plug 100 is completed.

  FIG. 3 is a process diagram showing a method for welding the noble metal tip 31 to the ground electrode 30. FIG. 4 is a schematic diagram showing a method of welding the noble metal tip 31 to the ground electrode 30. In this embodiment, first, as shown in FIG. 4, a ground electrode 30 (specifically, an unbent rod-like shape welded to the metal shell 50 is interposed between the upper electrode 91 and the lower electrode 92 of the resistance welder 90. The ground electrode 30) and the noble metal tip 31 are disposed. In the present embodiment, the noble metal tip 31 is disposed on the vertically lower side, and the ground electrode 30 is disposed on the vertically upper side so as to be in contact with the noble metal tip 31. Both the ground electrode 30 and the noble metal tip 31 have a flat surface to be joined.

  After the ground electrode 30 and the noble metal tip 31 are arranged as shown in FIG. 4, a force is applied vertically downward using the upper electrode 91 while the lower electrode 92 is fixed, so that the ground electrode 30 and the noble metal tip 31 are applied. The first load W1 is applied for a predetermined time (step S200 in FIG. 3). By applying the first load W <b> 1, the noble metal tip 31 is buried in a predetermined amount with respect to the ground electrode 30. In the present embodiment, applying the first load W1 before the second load W2 described later is referred to as “preload”.

  FIG. 5 is a graph showing changes in the load applied to the ground electrode 30 and the noble metal tip 31. After the first load W1 is applied to the ground electrode 30 and the noble metal tip 31, in this embodiment, as shown in FIG. 5, the force applied to the upper electrode 91 is reduced to reduce the ground electrode 30 and The load applied to the noble metal tip 31 is made lower than the first load W1. In the present embodiment, the load is reduced from the first load W1 to the second load W2 that is smaller than the first load W1 (step S210 in FIG. 3). At this time, the upper electrode 91 and the ground electrode 30, the ground electrode 30 and the noble metal tip 31, and the noble metal tip 31 and the lower electrode 92 are not separated from each other (that is, kept in contact with each other). And the noble metal tip 31 are gradually reduced from the first load W1 to the second load W2. The second load W2 is preferably 200N to 400N, for example, and the first load W1 is preferably 2 to 5 times the second load W2, for example.

  After the load applied to the ground electrode 30 and the noble metal tip 31 is reduced to the second load W2, the ground electrode 30 and the noble metal tip 31 between the upper electrode 91 and the lower electrode 92 are applied while the second load W2 is applied. A current of 800 to 1200 A is passed through the noble metal tip 31 to the ground electrode 30 by resistance welding (step S220). The load applied in this resistance welding only needs to have the second load W2 as an initial value, and may change in accordance with the precious metal tip 31 being buried in the ground electrode 30. That is, the load applied during resistance welding may not be a constant value during the period when resistance welding is performed. The resistance welding time, current value, and load are larger in the amount of precious metal tip 31 buried in ground electrode 30 in resistance welding in step S220 than the amount of precious metal tip 31 buried in ground electrode 30 due to the preload in step S200. It is set to be. The “amount of the noble metal tip 31 buried in the ground electrode 30” is the amount of change in the volume of the portion protruding from the ground electrode 30 of the noble metal tip 31 before and after preloading or before and after resistance welding.

  According to the method for manufacturing the spark plug 100 in the present embodiment described above, a large load (first load) is applied in advance to the ground electrode 30 and the noble metal tip 31 prior to resistance welding. And the noble metal tip 31 can be made uniform before welding. Therefore, during resistance welding, welding between the ground electrode 30 and the noble metal tip 31 is stably performed, and generation of spatter during welding can be suppressed. As a result, it is possible to suppress the appearance of the spark plug 100 from being damaged by sputtering. In addition, since the contact state between the ground electrode 30 and the noble metal tip 31 can be made uniform before welding, it is possible to suppress local current flow during resistance welding. As a result, the noble metal tip 31 can be favorably welded to the ground electrode 30. Therefore, according to the present embodiment, the noble metal tip 31 can be favorably welded to the ground electrode 30 while maintaining the appearance quality of the spark plug 100. When the noble metal tip 31 is enlarged, welding is performed with a large current in order to increase the welding strength, and thus the above-described effect of the present embodiment is particularly remarkable.

  Further, in this embodiment, the noble metal tip 31 is grounded by performing resistance welding while applying the second load W2 rather than the amount in which the noble metal tip 31 is buried in the ground electrode 30 by applying the first load W1. Since the amount buried in 30 is increased, the amount of melting during resistance welding can be increased. Therefore, the welding strength between the noble metal tip 31 and the ground electrode 30 can be improved.

B. Variations:
<First Modification>
In the above embodiment, the noble metal tip 31 is attached to the ground electrode 30 by performing resistance welding while applying the second load W2 rather than the amount in which the noble metal tip 31 is buried in the ground electrode 30 by applying the first load W1. The amount to be buried is increased. On the other hand, the noble metal tip 31 is applied to the ground electrode 30 by performing resistance welding while applying the second load W2 rather than the amount in which the noble metal tip 31 is buried in the ground electrode 30 by applying the first load W1. The amount to be buried may be reduced.

<Second Modification>
In the above embodiment, the noble metal tip 31 is disposed vertically downward and the ground electrode 30 is vertically upward between the lower electrode 92 and the upper electrode 91 of the resistance welder 90. However, the noble metal tip 31 is disposed vertically upward and the ground electrode 30 is disposed. It may be arranged vertically downward.

<Third Modification>
In the above embodiment, the lower electrode 92 is fixed and a load is applied vertically downward from the upper electrode 91 to the ground electrode 30 and the noble metal tip 31. The direction in which the load is applied is not limited to this, and the upper electrode 91 may be fixed and the load may be applied vertically upward from the lower electrode 92. Further, a load may be applied from both the upper electrode 91 and the lower electrode 92.

<Fourth Modification>
In the above embodiment, resistance welding is performed after the load applied to the ground electrode 30 and the noble metal tip 31 is reduced to the second load W2. In contrast, resistance welding may be performed while the load applied to the ground electrode 30 and the noble metal tip 31 is being reduced. Even in this case, resistance welding is performed while a load lower than the first load W1 is applied.

  The present invention is not limited to the above-described embodiments and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features of the embodiments and the modified examples corresponding to the technical features in the embodiments described in the summary section of the invention are intended to solve part or all of the above-described problems or to achieve the above-described effects. In order to achieve part or all of the above, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 12 ... Shaft hole 13 ... Leg long part 14 ... Shaft hole inner step part 15 ... Insulator step part 17 ... Tip side Body 18 ... Rear end side body 19 ... Central body 20 ... Center electrode 21 ... Electrode base material 22 ... Core material 23 ... Gutter 30 ... Ground electrode 31 ... Precious metal tip 40 ... Terminal metal fitting 50 ... Main metal fitting 51 ... Tool Engagement part 52 ... Mounting screw part 53 ... Clamping part 54 ... Seal part 56 ... Stage part 57 ... End face 58 ... Compression deformation part 90 ... Resistance welding machine 91 ... Upper electrode 92 ... Lower electrode 100 ... Spark plug

Claims (2)

A method of manufacturing a spark plug including a ground electrode to which a noble metal tip is bonded,
(A) contacting the ground electrode with the noble metal tip and applying a first load to the ground electrode and the noble metal tip;
(B) After the step (A), reducing the load applied to the ground electrode and the noble metal tip from the first load;
(C) While applying the load smaller than the first load to the ground electrode and the noble metal tip during the step (B) or after the step (B), the ground electrode, the noble metal tip, A process of performing resistance welding by passing an electric current through
A method of manufacturing a spark plug, comprising: It is a manufacturing method of the spark plug according to claim 1,
The amount of the noble metal tip buried in the ground electrode in the step (C) is larger than the amount of the noble metal tip buried in the ground electrode in the step (A). Production method.

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