JP2020027680A - Manufacturing method of spark plug - Google Patents

Abstract

To provide a manufacturing method of a spark plug capable of suppressing positional displacement of printing of a mark.SOLUTION: A manufacturing method of a spark plug includes a printing step of forming a mark with an ink on a front end face of an elastic member and printing the mark by pressing the front end face to a bottom face of a rear end portion of a terminal fitting. A projection enclosing a perimeter of the bottom face of the rear end portion has a diameter reduced part where the inner diameter is reduced toward the bottom face, at least in a portion adjacent to the bottom face. A diameter of the front end face of the elastic member or a diameter of a circumscribed circle of the front end face is larger than a diameter of the bottom face of the terminal fitting. In the printing step, the front end face of the elastic member is inserted into the projection, and the front end face is made closer to the bottom face while abutting an outer edge of the front end face to an inner peripheral surface of the diameter reduced part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing a spark plug, and more particularly to a method for manufacturing a spark plug in which a terminal fitting is marked.

  There is known a spark plug in which an identification mark is printed on the bottom surface of a terminal fitting in order to prevent the spark plug from being erroneously assembled to an engine (Patent Document 1).

JP 2012-128948 A

  In this type of spark plug, there is a need for a technique for suppressing the displacement of the mark printing position.

  The present invention has been made in order to meet this demand, and has as its object to provide a method of manufacturing a spark plug which can suppress displacement of printing of a mark.

  In order to achieve this object, the present invention provides an insulator having a shaft hole extending along the axis from the front end side to the rear end side; At the end, a terminal fitting having a circular bottom surface facing the rear end side, and a cylindrical projection protruding toward the rear end side while surrounding the entire bottom surface, a mark on the bottom surface This is a method for manufacturing a spark plug to be attached. A printing step is provided in which a mark is formed on the tip surface of the elastic member with ink, and the mark is printed by pressing the tip surface against the bottom surface. The protrusion of the terminal fitting has a reduced diameter portion whose inner diameter decreases toward the bottom surface at least in a portion adjacent to the bottom surface, and the diameter of the distal end surface of the elastic member or the diameter of the circumscribed circle of the distal end surface is equal to the diameter of the terminal fitting. Larger than the diameter of the bottom. In the printing process, the distal end surface is inserted into the protrusion, and the distal end surface is brought close to the bottom surface while the outer edge of the distal end surface is brought into contact with the inner peripheral surface of the reduced diameter portion.

  According to the method for manufacturing a spark plug according to the first aspect, when the distal end surface is brought close to the bottom surface while the outer edge of the distal end surface of the elastic member inserted into the projection of the terminal fitting is brought into contact with the inner peripheral surface of the reduced diameter portion. The member is deformed according to the inner peripheral surface of the reduced diameter portion. Thereby, the front end surface of the elastic member can be brought closer to the center of the bottom surface of the terminal fitting. Therefore, it is possible to suppress the displacement of the mark printing.

  According to the spark plug manufacturing method of the second aspect, in the printing step, the front end surface is brought close to the bottom surface while the entire outer periphery of the front end surface of the elastic member is brought into contact with the inner peripheral surface of the reduced diameter portion. Since the distal end surface of the elastic member is deformed over the entire circumference, in addition to the effect of the first aspect, it is possible to further suppress the positional deviation of the mark printing.

  According to the method for manufacturing a spark plug according to the third aspect, the reduced diameter portion is a curved surface whose inner peripheral surface expands outward. The projection further has a straight portion that is adjacent to the rear end side of the reduced diameter portion and whose inner peripheral surface forms a straight line in a cross section including the axis. The diameter of the distal end surface of the elastic member or the diameter of the circumscribed circle of the distal end surface is equal to or less than the inner diameter of the rear end of the reduced diameter portion. . This makes it easier to bring the tip end surface of the elastic member closer to the center of the bottom surface of the terminal fitting. In addition to the effects of the first and second aspects, it is possible to further suppress the displacement of the mark printing.

It is a one side sectional view of the spark plug in a 1st embodiment. (A) is a sectional view of the terminal fitting and the elastic member in the first half of the printing process, and (b) is a sectional view of the terminal fitting and the elastic member in the second half of the printing process. (A) is a sectional view of the terminal fitting and the elastic member in the first half of the printing process of the spark plug according to the second embodiment, and (b) is a sectional view of the terminal fitting and the elastic member in the second half of the printing process. (A) is sectional drawing of the terminal fitting and elastic member in the first half of the printing process of the spark plug in 3rd Embodiment, (b) is sectional drawing of the terminal fitting and elastic member in the latter half of a printing process. (A) is a top view of a terminal fitting showing a relation between an elastic member and a terminal fitting in the fourth embodiment, and (b) is a terminal fitting showing a relation between the elastic member and the terminal fitting in the fifth embodiment. FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-side cross-sectional view of the spark plug 10 according to the first embodiment, which is taken along an axis O. In FIG. 1, the lower side of the paper is referred to as the front end of the spark plug 10, and the upper side of the paper is referred to as the rear end of the spark plug 10. The spark plug 10 ignites an air-fuel mixture in an internal combustion engine (not shown), and includes an insulator 11 and a terminal fitting 20.

  The insulator 11 is a cylindrical member formed of alumina or the like having excellent mechanical properties and high-temperature insulation, and has a shaft hole 12 penetrating along the axis O. A center electrode 14 is arranged on the tip side of the shaft hole 12.

  The center electrode 14 is a rod-shaped member extending along the axis O, and copper or a core material containing copper as a main component is covered with nickel or a nickel-based alloy. It is possible to omit the core material. The center electrode 14 is held by the insulator 11, and the front end side protrudes from the front end of the insulator 11.

  The terminal fitting 20 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and is formed of a conductive metal material (for example, low carbon steel or the like). In the terminal fitting 20, a shaft 21 inserted into the shaft hole 12 and a rear end 22 disposed at the rear end 13 of the insulator 11 are connected. The shaft portion 21 is electrically connected to the center electrode 14 in the shaft hole 12 of the insulator 11. The rear end portion 22 includes a circular bottom surface 23 facing the rear end side, and a cylindrical projection 24 projecting toward the rear end side while surrounding the bottom surface 23 all around. In the present embodiment, the bottom surface 23 is circular with the axis O as the center.

  The terminal fitting 20 has a mark 25 on the bottom surface 23 of the rear end 22. The information represented by the mark 25 is appropriately set as necessary, such as identification of an engine (not shown) to which the spark plug 10 is attached, history information unique to the spark plug 10, the terminal fitting 20, and the like. The mark 25 is formed on the terminal fitting 20 by printing. Since the bottom surface 23 on which the mark 25 is provided is surrounded by the protrusion 24 over the entire circumference, it is possible to prevent the mark 25 from being scratched or rubbed.

  The metal shell 30 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel or the like). The metal shell 30 is caulked and fixed to the distal end side of the outer periphery of the insulator 11. A ground electrode 31 is joined to the metal shell 30. The ground electrode 31 is a rod-shaped metal member (eg, a nickel-based alloy) having conductivity. The ground electrode 31 forms a spark gap with the center electrode 14.

  The spark plug 10 is manufactured by, for example, the following method. First, the center electrode 14 is inserted into the shaft hole 12 of the insulator 11, and the center electrode 14 is arranged such that the tip of the center electrode 14 protrudes from the tip of the insulator 11. After the shaft portion 21 of the terminal fitting 20 is inserted into the shaft hole 12 and the conduction between the terminal fitting 20 and the center electrode 14 is secured, the metal shell 30 to which the ground electrode 31 has been joined in advance is assembled on the outer periphery of the insulator 11. Next, the ground electrode 31 is bent so as to face the center electrode 14 to obtain the spark plug 10. After that, the mark 25 is printed on the terminal fitting 20 of the spark plug 10. It is naturally possible to print the mark 25 on the terminal fitting 20 at a different timing.

  A method of printing the mark 25 on the terminal fitting 20 will be described with reference to FIG. FIG. 2A is a cross-sectional view including the axis O (see FIG. 1) of the terminal fitting 20 and the elastic member 40 in the first half of the printing step of printing the mark 25 on the terminal fitting 20. FIG. 2B is a cross-sectional view including the axis O of the terminal fitting 20 and the elastic member 40 in the latter half of the printing process. 2 (a) and 2 (b), the terminal fitting 20 is not shown except for the rear end portion 22, and the elastic member 40 is not shown except for the vicinity of the front end surface 41 (see FIG. 2). 3 (a) to FIG. 4 (b).)

  The rear end portion 22 of the terminal fitting 20 has a circular bottom surface 23 facing the rear end side, a reduced diameter portion 26 having its spherical inner peripheral surface adjacent to the outer periphery of the bottom surface 23, and an inner periphery of the reduced diameter portion 26. A straight portion 27 having its own conical inner peripheral surface adjacent to the rear end of the surface and having a straight inner peripheral surface in a cross section including the axis O is provided. The inner diameter of the reduced diameter portion 26 is reduced toward the bottom surface 23. In the present embodiment, the reduced diameter portion 26 is a curved surface whose inner peripheral surface bulges outward, and the inner peripheral surface of the linear portion 27 decreases in diameter toward the distal end side (the bottom surface 23 side). The inner peripheral surface of the linear portion 27 and the inner peripheral surface of the reduced diameter portion 26 are smoothly connected, and the inner peripheral surface of the reduced diameter portion 26 and the bottom surface 23 are smoothly connected.

  The elastic member 40 is a member having elasticity for printing the mark 25 formed on the front end surface 41 with ink on the bottom surface 23 of the rear end portion 22. The elastic member 40 is made of synthetic resin such as thermoplastic elastomer or rubber such as silicone rubber. In the present embodiment, the elastic member 40 is formed in a column shape having a circular tip surface 41. The elastic member 40 is attached to the tip of an arm (not shown) that reciprocates between a stage (not shown) on which the mark 25 is formed and the bottom surface 23 of the rear end 22.

  The ink for forming the mark 25 is appropriately selected from an ultraviolet curable type, an electron beam curable type, a thermosetting type, and the like. In the present embodiment, the mark 25 (ink) is attached to the flat distal end surface 41 of the elastic member 40 by transfer. The diameter D3 of the front end surface 41 of the elastic member 40 is larger than the diameter D1 of the bottom surface 23 of the rear end portion 22 and is equal to or smaller than the inner diameter D2 of the rear end of the reduced diameter portion 26 of the rear end portion 22 (D1 <D3 ≦ D2). ). The mark 25 is formed in a narrower area inside the end face 41 of the elastic member 40 than the area corresponding to the bottom surface 23 (diameter D1).

  In the printing process, after the distal end surface 41 of the elastic member 40 attracts the mark 25 formed on the stage (not shown), the distal end surface 41 of the elastic member 40 on which the mark 25 is attached is moved along the axis O (FIG. 1) and inserted inside the projection 24 of the rear end portion 22. Since the inner peripheral surface of the linear portion 27 of the rear end portion 22 is increased in diameter toward the rear end side, when the elastic member 40 is inserted into the projection 24, the outer edge 42 of the front end surface 41 and the linear portion 27 are inserted. And the outer edge 42 of the front end surface 41 can be made hard to contact with the inner peripheral surface of the linear portion 27.

  Since the rear end portion 22 and the elastic member 40 have a relationship of D1 <D3 ≦ D2, when the elastic member 40 is inserted into the projection 24, first, the outer edge 42 of the front end surface 41 hits the inner peripheral surface of the reduced diameter portion 26. (See FIG. 2B). When the distal end surface 41 is further brought close to the bottom surface 23 while the outer edge 42 of the distal end surface 41 is in contact with the inner peripheral surface of the reduced diameter portion 26, the vicinity of the outer edge 42 of the distal end surface 41 of the elastic member 40 is mainly reduced. Deforms according to the inner peripheral surface of. Since the elastic member 40 is deformed in a state where the outer edge 42 of the distal end surface 41 is restrained by the reduced diameter portion 26, the distal end surface 41 can be brought closer to the center of the bottom surface 23. When the tip surface 41 contacts the bottom surface 23, the mark 25 is transferred (printed) to the bottom surface 23. Therefore, when the tip surface 41 of the elastic member 40 is inserted into the projection 24, even if the center of the tip surface 41 is displaced from the center of the bottom surface 23, the printing of the mark 25 with respect to the center of the bottom surface 23 is performed. The displacement can be suppressed.

  Since the mark 25 is formed in a narrower area inside the end face 41 of the elastic member 40 than the area corresponding to the bottom surface 23 (diameter D1), the vicinity of the outer edge 42 of the end face 41 of the elastic member 40 is reduced in diameter. When deforming according to the inner peripheral surface of the portion 26, it is possible to make it difficult to deform the region of the distal end surface 41 where the mark 25 is attached. As a result, it is possible to prevent the mark 25 from being printed on the bottom surface 23 in a deformed state.

  In particular, the distal end surface 41 is brought closer to the bottom surface 23 while the entire periphery of the outer edge 42 of the distal end surface 41 of the elastic member 40 is brought into contact with the inner peripheral surface of the reduced diameter portion 26. The deformation of 41 is regulated over the entire circumference. Thereby, the tip surface 41 of the elastic member 40 can be more easily brought to the center of the bottom surface 23 as compared with the case where a part of the outer edge 42 of the tip surface 41 is deformed. Therefore, the displacement of the printing of the mark 25 can be further suppressed.

  Since the distal end surface 41 of the elastic member 40 is gently deformed along the inner peripheral surface of the reduced diameter portion 26 formed of a curved surface, the distal end surface 41 can be continuously deformed. Accordingly, the center of the front end surface 41 can be continuously brought close to the center of the bottom surface 23 of the rear end portion 22, so that the front end surface 41 can be easily brought to the center of the bottom surface 23. Therefore, the displacement of the printing of the mark 25 can be further suppressed.

  The second embodiment will be described with reference to FIG. In the first embodiment, the case where the inner peripheral surface of the reduced diameter portion 26 of the rear end portion 22 is a spherical band-shaped curved surface bulging outward. On the other hand, in the second embodiment, a case will be described in which the inner peripheral surface of the reduced diameter portion 52 of the rear end portion 22 is a conical curved surface. The same parts as those described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 3A is a cross-sectional view including the axis O (see FIG. 1) of the terminal fitting 50 and the elastic member 60 in the first half of the spark plug printing process according to the second embodiment. FIG. 3B is a sectional view including the axis O of the terminal fitting 50 and the elastic member 60 in the latter half of the printing process.

  The rear end portion 22 of the terminal fitting 50 has a circular bottom surface 51 facing the rear end side, a reduced diameter portion 52 having its own conical inner peripheral surface adjacent to the outer periphery of the bottom surface 51, and an inner periphery of the reduced diameter portion 52. A straight portion 53 having a conical inner peripheral surface adjacent to the rear end of the surface. The inner diameter of the reduced diameter portion 52 and the straight portion 53 decreases toward the bottom surface 71. However, in the section including the axis O, the angle (the acute angle side) between the axis O and the reduced diameter portion 52 is larger than the angle (the acute angle side) between the axis O and the linear portion 53.

  The elastic member 60 is formed in a truncated cone shape whose outer peripheral surface increases in diameter from the circular front end surface 61 on which the mark 25 is attached to the rear end side. The diameter D3 of the front end surface 61 of the elastic member 60 is larger than the diameter D1 of the bottom surface 51 of the rear end portion 22 and is equal to or smaller than the inner diameter D2 of the rear end of the reduced diameter portion 52 of the rear end portion 22 (D1 <D3 ≦ D2). ).

  In the printing step, the tip surface 61 of the elastic member 60 with the mark 25 is inserted into the projection 24 of the rear end 22 along the axis O (see FIG. 1). Since the rear end portion 22 and the elastic member 60 have a relationship of D1 <D3 ≦ D2, when the front end surface 61 is brought closer to the bottom surface 51 while the outer edge 62 of the front end surface 61 is in contact with the inner peripheral surface of the reduced diameter portion 52, the elasticity is reduced. The member 60 is deformed according to the inner peripheral surface of the reduced diameter portion 52. Accordingly, when the distal end surface 61 of the elastic member 60 is inserted into the inside of the projection 24, the distal end surface 61 of the elastic member 60 is moved downward even if the center of the distal end surface 61 is shifted with respect to the center of the bottom surface 51. 51 can be centered. Therefore, it is possible to suppress displacement of the printing of the mark 25.

  Further, while the entire periphery of the outer edge 62 of the distal end surface 61 of the elastic member 60 is brought into contact with the inner peripheral surface of the reduced diameter portion 52, the distal end surface 61 is brought close to the bottom surface 51, so that the distal end surface 61 of the elastic member 60 extends over the entire periphery. And the tip surface 61 of the elastic member 60 can be further easily brought to the center of the bottom surface 51. Therefore, the displacement of the printing of the mark 25 can be further suppressed.

  The third embodiment will be described with reference to FIG. In the first and second embodiments, the case where the linear portions 27 and 53 are adjacent to the rear ends of the reduced diameter portions 26 and 52 of the rear ends 22 of the terminal fittings 20 and 50 has been described. On the other hand, in the third embodiment, a case where the straight portion on the rear end side of the reduced diameter portion 72 is omitted will be described. The same parts as those described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 4A is a cross-sectional view including the axis O (see FIG. 1) of the terminal fitting 70 and the elastic member 80 in the first half of the spark plug printing process according to the third embodiment, and FIG. 10 is a cross-sectional view including the axis O of the terminal fitting 70 and the elastic member 80 in the latter half of FIG.

  The rear end portion 22 of the terminal fitting 70 includes a circular bottom surface 71 facing the rear end side, and a reduced-diameter portion 72 in which a conical inner peripheral surface of the bottom surface 71 is adjacent to the outer periphery of the bottom surface 71. The inner diameter of the reduced diameter portion 72 is reduced toward the bottom surface 71.

  The elastic member 80 is formed in a truncated cone shape whose outer peripheral surface is reduced in diameter from the circular front end surface 81 on which the mark 25 is attached to the rear end side. The diameter D3 of the front end surface 81 of the elastic member 80 is larger than the diameter D1 of the bottom surface 71 of the rear end portion 22 and is equal to or smaller than the inner diameter D2 of the rear end of the reduced diameter portion 72 of the rear end portion 22. Thereby, the same operation and effect as in the second embodiment can be realized.

  Fourth and fifth embodiments will be described with reference to FIG. In the first to third embodiments, the case where the distal end surfaces 41, 61, 81 of the elastic members 40, 60, 80 are circular has been described. On the other hand, in the fourth and fifth embodiments, the case where the distal end surfaces of the elastic members 90 and 100 have a shape other than a circle will be described. The same parts as those described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 5A is a plan view of the terminal fitting 20 showing a relation between the elastic member 90 and the terminal fitting 20 in the fourth embodiment, and FIG. 5B is a plan view of the elastic member 100 and the terminal in the fifth embodiment. FIG. 3 is a plan view of a terminal fitting 20 showing a relationship with the fitting 20.

  As shown in FIG. 5A, the elastic member 90 is a member having a hexagonal end surface on which the mark 25 is provided, and is formed in a hexagonal column shape as a whole. The outer shape of the elastic member 90 illustrated in FIG. 5A is equal to the shape of the outer edge of the distal end surface of the elastic member 90. The diameter D3 of the circumscribed circle 91 on the distal end surface of the elastic member 90 has a relationship of D1 <D3 ≦ D2. Accordingly, when the distal end surface is brought close to the bottom surface 23 while the outer edge of the distal end surface of the elastic member 90 is in contact with the inner peripheral surface of the reduced diameter portion 26, the elastic member 90 is deformed according to the inner peripheral surface of the reduced diameter portion 26, and the elastic member 90 is deformed. Can be brought closer to the center of the bottom surface 23. Thereby, the displacement of the printing of the mark 25 with respect to the bottom surface 23 can be suppressed.

  Further, since the diameter of the inscribed circle (not shown) of the distal end surface of the elastic member 90 is larger than the diameter D1 of the bottom surface 23, when the distal end surface of the elastic member 90 approaches the bottom surface 23, the distal end of the elastic member 90 is closed. The entire outer periphery of the surface can be pressed against the inner peripheral surface of the reduced diameter portion 26. As a result, the outer edge of the distal end surface of the elastic member 90 is constrained by the reduced diameter portion 26 over the entire circumference, so that the effect of suppressing the displacement of the printing of the mark 25 can be improved.

  As shown in FIG. 5B, the elastic member 100 has a distal end surface provided with arc-shaped protrusions at four locations on the outer periphery of a circular base. A mark 25 is formed on the circular portion (base). The outer shape of the elastic member 100 illustrated in FIG. 5B is equal to the shape of the outer edge of the distal end surface of the elastic member 100. The diameter D3 of the circumscribed circle 101 passing through the outer edges of the four protrusions on the distal end surface of the elastic member 100 has a relationship of D1 <D3 ≦ D2. Accordingly, when the distal end surface is brought close to the bottom surface 23 while the outer edge of the distal end surface of the elastic member 100 is in contact with the inner peripheral surface of the reduced diameter portion 26, the elastic member 100 is deformed according to the inner peripheral surface of the reduced diameter portion 26, and the elastic member 100 is deformed. Can be brought closer to the center of the bottom surface 23. Thereby, the displacement of the printing of the mark 25 with respect to the bottom surface 23 can be suppressed.

  As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily inferred.

  In the first and second embodiments, the inner peripheral surfaces of the linear portions 27 and 53 of the terminal fittings 20 and 50 increase in diameter as they move away from the reduced diameter portions 26 and 52 toward the rear end (the inner peripheral surfaces are conical). Is described, but the present invention is not necessarily limited to this. It is of course possible to make the inner peripheral surfaces of the straight portions 27 and 53 cylindrical.

  In the third embodiment, the case where the inner peripheral surface of the reduced diameter portion 72 of the terminal fitting 70 is formed in a conical shape is described, but the present invention is not necessarily limited to this. It is of course possible to make the inner peripheral surface of the reduced diameter portion 72 into a spherical band shape.

  In the fourth embodiment, the case where the distal end surface of the elastic member 90 is hexagonal has been described, but the present invention is not necessarily limited to this. Naturally, it is possible to make the distal end surface of the elastic member 90 an arbitrary polygon.

  In the fifth embodiment, the case where the distal end surface of the elastic member 100 is provided with arc-shaped protrusions at four locations on the outer circumference of the circle serving as the base has been described. However, the present invention is not necessarily limited to this. Of course, it is possible to change the shape of the base and the number and shape of the projections to different ones.

  In the embodiment, the case where the mark 25 (ink) is applied by transfer to the flat tip surfaces 41, 61, 81 of the elastic members 40, 60, 80 has been described, but the present invention is not necessarily limited to this. It is of course possible to form irregularities in the shape of the mark 25 on the front end surface of the elastic member and transfer the ink applied to the convex portion to the rear end of the terminal fitting. Similarly, it is of course possible to transfer the ink applied to the concave portion on the front end surface to the rear end portion of the terminal fitting.

  In the embodiment, the case has been described where the mark 25 (ink) attached to the distal end surfaces 41, 61, 81 of the elastic members 40, 60, 80 is transferred (printed) to the rear end of the terminal fitting. It is not limited. It is of course possible to make the elastic member a porous body from which ink permeates through the holes, press the front end surface of the elastic member against the rear end of the terminal fitting, and print the mark 25 with the ink permeating from the holes.

  In addition, each embodiment, by adding a part or a plurality of parts of the configuration of the other embodiment to the embodiment, or by replacing the part or a plurality of parts of the configuration of the embodiment, etc. The embodiment may be modified to be configured. For example, the elastic member 40 described in the first embodiment may be replaced with the elastic members 60 and 80 described in the second and third embodiments, or the elastic member 90 described in the fourth and fifth embodiments may be replaced. , 100 can be replaced with the elastic members 60, 80 described in the second and third embodiments.

DESCRIPTION OF SYMBOLS 10 Spark plug 11 Insulator 12 Shaft hole 20, 50, 70 Terminal 22 Back end 23, 51, 71 Bottom 24 Projection 25 Mark 26, 52, 72 Reduced diameter part 27 Linear part 40, 60, 80, 90, 100 Elastic members 41, 61, 81 Tip surface 42, 62, 82 Outer edge 91, 101 Circumscribed circle D1 Diameter of bottom surface D2 Inner diameter at rear end of reduced diameter portion D3 Diameter of tip surface or diameter of circumscribed circle of tip surface O Axis

Claims (3)

An insulator formed with an axial hole extending along the axis from the front end side to the rear end side,
The insulator is disposed on the rear end side of the shaft hole, and has a circular bottom surface facing the rear end side at the rear end portion thereof, and projects toward the rear end side while surrounding the bottom surface over the entire circumference. A terminal fitting having a cylindrical projection, and
A method for manufacturing a spark plug, wherein a mark is attached to the bottom surface,
Forming a mark on the tip end surface of the elastic member with ink, and printing the mark by pressing the tip end surface against the bottom surface,
The protrusion of the terminal fitting, at least in a portion adjacent to the bottom surface, has a reduced diameter portion whose inner diameter is reduced toward the bottom surface,
The diameter of the distal end surface of the elastic member or the diameter of a circumscribed circle of the distal end surface is larger than the diameter of the bottom surface of the terminal fitting,
In the printing step, a spark plug that inserts the distal end face of the elastic member into the inside of the protrusion and brings the distal end face close to the bottom surface while applying an outer edge of the distal end face to an inner peripheral surface of the reduced diameter portion. Production method.   2. The method according to claim 1, wherein, in the printing step, the front end surface is brought closer to the bottom surface while an entire periphery of an outer edge of the front end surface of the elastic member is brought into contact with an inner peripheral surface of the reduced diameter portion. 3. The reduced diameter portion is a curved surface whose inner peripheral surface bulges outward,
The protrusion is further adjacent to the rear end side of the reduced diameter portion, the inner peripheral surface has a straight portion that is straight in a cross section including the axis,
The method according to claim 1, wherein a diameter of the distal end surface of the elastic member or a diameter of a circumscribed circle of the distal end surface is equal to or less than an inner diameter at a rear end of the reduced diameter portion.

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