JPH08236263A - Manufacture of spark plug - Google Patents

Abstract

PURPOSE: To provide a spark plug with improved heat resistance by carrying out plating after an earthing electrode welded to main metal fittings is temporarily curved into almost the same shape as the final shape. CONSTITUTION: An earthing electrode 11 is joined to a tip end face of a cylindrical part of main metal fittings 4 by resistance welding. The earthing electrode 11 is bent into an L-shape which is almost the same shape as that in the final state to be assembled. Then, after the metal fittings 4 are pickled to remove oxides and powders due to cutting, corrosion resistant at high temperature and hardly processible surface treatment is carried out for the inner circumference and the outer circumference of the metal fittings 4 and the earthing electrode 11 by plating. Next, an insulator built in a middle axis 2 is assembled with the metal fittings 4 and a spark gap 12 is formed between the earthing electrode 11 and the middle axis 2. After that, if necessary, a gap gauge 13 is inserted in the spark gap 12 and the spark gap 12 is finely adjusted by lightly hitting the earthing electrode 11 from the outside. Troubles such as cracking and peeling of the plating scarcely occur in the obtained spark plug 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a spark plug in which a single or a plurality of ground electrodes are joined to the end surface of a tubular metal shell.

[0002]

2. Description of the Related Art Conventionally, in the case of performing easy-to-machine surface treatment, a method for manufacturing a spark plug having one or a plurality of ground electrodes as shown in FIG. 12 (hereinafter referred to as a conventional easy-machine surface treatment manufacturing method). ) Is known (FIG. 12 shows the case of a single ground electrode). In this conventional easy-to-machine surface treatment manufacturing method, first, as shown in FIG. 12A, a hexagonal portion 102 and a cylindrical portion 103 are provided on the outer circumference of a tubular metal shell 101.
After cold working, as shown in FIG. 12B, the upper end 1021 and the lower end 1022 of the hexagonal part 102, the upper part 1031 and the lower part 1032 of the cylindrical part 103 have predetermined axial and radial dimensions. A cutting process for cutting the outer periphery of the metal shell 101 is performed so that

Then, as shown in FIG. 12 (c), after welding one or a plurality of ground electrodes 104 to the tip surface 107 of the cylindrical metal shell 101, the tip portion of the ground electrode 104 is cut off, and as shown in FIG. As shown in d), after rolling the threaded portion 105 on the outer peripheral surface of the cylindrical portion 103 of the metal shell 101,
As shown in FIG. 12 (e), the metal shell 101 and the single or plural ground electrodes 104 are subjected to easy-to-machine surface treatment, and the insulator 106 with the inner shaft is assembled as shown in FIG. 12 (f). As shown in FIG. 12G, the spark plug 1 forming the spark gap 107 by performing a bending step of bending a single or a plurality of ground electrodes 104 from the middle toward the axis of the metal shell 101 into an L shape. Was being manufactured. In this case, the easily-processed surface treatment was mainly zinc plating, zinc plating chromate treatment or the like.

Further, when the difficult-to-process surface treatment is performed, a method for manufacturing a spark plug having a single or a plurality of ground electrodes as shown in FIG. 13 (hereinafter referred to as a conventional first difficult-to-process surface treatment manufacturing method). ) Is known (FIG. 13 shows the case of having a single ground electrode). In the conventional difficult-to-process surface treatment manufacturing method, first, as shown in FIG. 13A, a hexagonal portion 202 and a cylindrical portion 20 are provided on the outer periphery of a tubular metallic shell 201.
After cold working No. 3, as shown in FIG.
The upper end portion 2021 and the lower end portion 2022 of the hexagonal portion 202, and the upper portion 2031 and the lower portion 2032 of the cylindrical portion 203 are cut so as to cut the outer periphery of the metal shell so as to have predetermined axial and radial dimensions.

Then, as shown in FIG. 13C, after welding one or a plurality of ground electrodes 204 to the tip surface 207 of the cylindrical metallic shell 201, the tip portion of the ground electrode 204 is cut, and then the After the threaded portion 205 is rolled on the outer peripheral surface of the cylindrical portion 203 of the metal shell 201 as shown in d), the ground electrode 204 is masked with a heat shrinkable tube 208 or the like as shown in FIG. After that, the metal shell 201, the single or plural ground electrodes 204, and the welded portion 209 of the metal shell 201 are subjected to a difficult-to-process surface treatment.
After removing the masking as shown in (f) and assembling the insulator 206 with the center rod, as shown in FIG.
The spark plug 1 that forms the spark gap 207 is manufactured by performing a bending step of bending in an L-shape toward the axis of No. 1.

As another conventional second difficult-to-machine surface treatment manufacturing method, as shown in FIG. 14 (a), after the threaded portion 305 is rolled on the outer peripheral surface of the cylindrical portion 303 of the metal shell 301, While holding the ground electrode 304 with the chuck 307 or the like so as not to be immersed in the surface treatment layer 310, the metal shell 3
01 and one or more ground electrodes 304 and metal shell 30
After the surface treatment is applied to the welded portion 308 of No. 1 and the insulator 306 with a center rod is assembled as shown in FIG.
As shown in (c), the spark gap 307 is formed by performing a bending step of bending one or more ground electrodes 304 from the middle toward the axis of the metal shell 301 into an L shape.
Was produced. In this case, nickel plating was mainly used as the difficult-to-process surface treatment.

[0007]

However, it has become difficult to deal with the conventional easy-to-machine surface treatment due to the necessity of improving the heat resistance of the spark plug metal shell with the improvement of the output of the internal combustion engine or the reduction of the engine room space. .

That is, when continuously operated at a high speed, radiant heat received from the exhaust pipe of the engine causes the temperature of the entire spark plug to exceed the heat resistance of the conventional easily processed surface treatment layer. After continuous operation at such a high speed, the entire surface of the easily processed surface treatment layer applied to the metal shell and the ground electrode was discolored and peeled off, causing rust on the surface of the metal shell.
There is a danger of problems such as difficulty in removing the spark plug from the engine.

Therefore, if only the surface treatment step in the conventional easy-to-machine surface treatment manufacturing step is replaced with the difficult-to-machine surface treatment, the ground electrode is difficult to be generated by the conventional easily-machined surface treatment due to the subsequent bending step. There is a risk that cracks and peeling of the processed surface treatment layer may occur, and the difficult-to-process surface treatment layer separated between the spark gaps may be short-circuited in a bridge state to cause no electric spark.

In order to avoid this inconvenience, a method of providing a step of peeling off the difficult-to-process surface treatment layer once applied may be considered. As this method, acid treatment is generally performed, but in the case of a surface treatment layer that can be easily processed, it can be easily peeled off with hydrochloric acid, and the base material of the ground electrode is less likely to be damaged. Then, a strong acid such as hydrofluoric acid or aqua regia must be used, and there is a problem that the base material of the ground electrode is also corroded.

Although the stress applied to the surface treatment layer can be reduced by reducing the thickness of the surface treatment layer which is difficult to process, the thinness of the surface treatment layer results in poor corrosion resistance.

On the other hand, in the conventional difficult-to-process surface treatment manufacturing method, it takes a lot of man-hours such as masking so as not to perform surface treatment on the ground electrode or preventing it from immersing in the surface treatment layer. It was a bad thing. An object of the present invention is to provide a method for manufacturing a spark plug having a difficult-to-process surface treatment layer having excellent heat resistance.

[0013]

According to a first aspect of the present invention, a single or a plurality of ground electrodes connected to the front end surface of a tubular metal shell whose outer peripheral surface is threaded are temporarily put into a state substantially equivalent to the final shape. A first step of bending, a second step of finishing the first step with a difficult-to-process surface treatment with high-temperature corrosion resistance on the metallic shell, and an end of the metallic shell with an insulator with a center rod after the second step. And a third step of forming a spark gap between the ground electrode and the center pole by assembling.

According to a second aspect of the present invention, a first step of temporarily bending a plurality of ground electrodes connected to the front end surface of a tubular metal shell having an outer peripheral surface with a screw into a final shape, and the first step is completed. Later, a second step of subjecting the metal shell to a high-temperature corrosion-resistant difficult-to-process surface treatment, a third step of cutting the ground electrode to form a discharge end face after the second step, and a third step after the third step. A manufacturing method including a fourth step in which a spark gap is formed between the discharge end surface and the tip side surface portion of the center shaft by assembling the insulator with the center shaft to the metal shell is adopted.

According to a third aspect of the present invention, a first step of temporarily bending a plurality of ground electrodes connected to the front end surface of a tubular metallic shell having an outer peripheral surface with a screw into a final shape, and the first step After finishing, the ground electrode is cut to form a discharge end face.
And a third step of subjecting the metal shell to a high-temperature corrosion-resistant difficult-to-process surface treatment after the second step, and after the third step is completed, by assembling the insulator with a center rod into the electric discharge. A manufacturing method including a fourth step in which a spark gap is formed between the end face and the tip side face portion of the center rod is adopted.

A fourth aspect of the present invention is characterized in that, in the first to third aspects of the invention, the high-temperature corrosion-resistant difficult-to-process surface treatment is chromium plating, nickel plating, nickel plating chromate treatment, nickel chromium plating, or zinc nickel plating. At least one manufacturing method was adopted.

[0017]

According to the present invention, since the ground electrode welded to the metal shell is temporarily bent into a state substantially equivalent to the final shape and then plated, plating cracking occurs even in difficult-to-process surface treatment such as nickel plating. , Peeling can be prevented. As a result, the plating thickness can be increased to improve heat resistance and avoid the problem of discoloration of the plating, peeling off, rust, etc., which prevents it from being removed from the engine during use in the engine. it can.

Also, masking the ground electrode,
Since it is not necessary to keep only the ground electrode immersed in the surface treatment layer, the man-hours are reduced and the economic effect is large.
Since there is no need for strong acid treatment, the spark plug performance is stable.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A spark plug manufacturing method according to the present invention will be described with reference to the embodiments shown in FIGS. [First Embodiment] FIGS. 1 to 5 show a first embodiment of the present invention. FIG. 1 is a view showing a parallel electrode spark plug having a single ground electrode. The parallel electrode spark plug 1 includes a center electrode 2 to which a high voltage is applied, a tubular insulator 3 that holds the center electrode 2, and a tubular metal shell 4 that holds the insulator 3. There is.

The structure of the metal shell 4 will be described in detail with reference to FIGS. 2 and 3. A bolt-shaped hexagonal portion 5 that engages with a tool (not shown) is formed on the outer periphery of the metal shell 4 at one end side from the center portion. A threaded portion 6 for screwing into an engine block (not shown) of an internal combustion engine is formed on the outer periphery of the metal shell 4 from the center to the other end. An annular collar-shaped part (body) 7 is formed in the center of the metal shell 4. A shaft hole 8 for inserting the insulator 3 is formed inside the metal shell 4. A taper-shaped locking portion 9 that locks the insulator 3 projects inward from the shaft hole 8.

Further, the front end surface 10 of the metal shell 4 has a structure shown in FIG.
As shown in, the ground electrode 11 bent in the L shape toward the axis of the metal shell 4 is joined by means such as resistance welding. Inside the tips of the ground electrodes 11, a discharge surface 13 is formed between the tip of the center electrode 2 and a spark gap 12 having a predetermined gap length as shown in FIG. The ground electrode 11 is shown in FIG.
As shown in FIG. 3, the electrodes are formed to have a predetermined electrode height h.

[Manufacturing Method of First Embodiment] Next, a manufacturing method of this embodiment will be described with reference to FIGS. 4 and 5. Here, FIG. 4 is a process drawing showing the manufacturing method of this embodiment. (First step) By cold extrusion molding, a cross-sectional shape having a diameter larger than the diameter of the central portion 21 on one side of the central portion 21 of a metal material made of low carbon steel or the like in which iron contains carbon of several percent or less is formed. A hexagonal tubular portion 22 is formed, and a tubular portion 23 having a diameter smaller than the diameter of the central portion 21 and a cylindrical cross section is provided on the other side of the central portion 21 of the metal material, and further, by cold extrusion. The metal shell 4 is obtained by axially penetrating the metal material and forming the shaft hole 8 having the shelf portion 24 (see FIG. 4A).

Next, the hexagonal cylindrical portion 22 of the metal shell 4
By cutting the outer circumference of the above, the upper end portion 5a and the lower end portion 5b of the cylindrical shape are formed on the upper side to form the hexagonal portion 5 having a predetermined axial dimension, and the outer circumference of the cylindrical portion 23 of the cylindrical shape is formed. The metal shell 4 is obtained by forming the tubular portion 25 having the upper portion 25a on the upper side and the lower portion 25b on the lower side by performing the cutting process and forming the collar portion 7 on the central portion 21 (FIG. 4). (See (b)). Note that the metal shell 4 may be formed by cutting a cylindrical or hexagonal bar material without cold extrusion.

Next, the ground electrode 11 made of nickel alloy mainly composed of nickel is joined to the tip surface 10 of the tubular portion 25 of the metal shell 4 by resistance welding or the like (see FIG. 4 (c)). . The ground electrode 11 is made of nickel and C.
Inconel (N
i-Cr-Fe), and a noble metal material such as platinum, iridium, or an alloy thereof may be used for the discharge surface of these materials, and a nickel alloy filled with copper, pure nickel, or the like may be used. Good.

At this time, the ground electrode is cut into a prescribed length after welding. The prescribed length is determined in advance from the bent shape of the ground electrode and the position of the center rod when the insulator with the center rod is combined with the metal shell, which is performed in the subsequent steps. Then, the cylindrical portion 25 of the metal shell 4 is thread-rolled. That is, the metal shell 4 can be obtained by forming the screw portion 6 using a round die or a flat die having a thread shape of the screw portion (neither is shown) (see FIG. 4 (d)).

The length of the screw portion 6 is determined by the thickness of the cylinder head of the internal combustion engine. Here, the order of welding the ground electrode and thread rolling may be reversed. Next, the ground electrode is bent. In this bending step, the ground electrode is bent into an L-shape in the same manner as in the final assembled state (Fig. 4).
(E)).

(Second Step) Next, the metal shell 4 is pickled. That is, the metal shell 4 is immersed in hydrochloric acid having a capacity of 10 to 20% to remove rust, oxides, cutting chips generated by cutting, and after washing with water, the inner and outer circumferences of the metal shell 4 are removed. And the ground electrode 11 is plated with nickel (see FIG. 4).
(See (f)).

(Third step) Next, by assembling the insulator 9 in which the center shaft is incorporated in advance to the metal shell 4,
A spark gap is formed between the ground electrode 11 and the center pole. Thereafter, if necessary, a gap gauge 13 is inserted into the spark gap 12 and the ground electrode is tapped from the outside so that the gap length conforming to the standard can be obtained as shown in FIG. I do. Since the work of hitting the ground electrode is extremely light, there is almost no problem such as plating cracking or peeling.

[Modification] In the present embodiment, the present invention is used for the parallel electrode spark plug 1, but the present invention may be used for a multipolar spark plug having two or more poles. Further, in the present embodiment, the metal shell 4 has been described as having a shape in which the hexagonal portion 5 is larger than the collar-shaped portion 7. However, it is also applicable to a metal shell having a hexagonal portion 5 smaller than the collar-shaped portion 7. Needless to say.

As described above, in this embodiment, the plating process is performed after the resistance welding, the thread rolling, and the bending process of the ground electrode are performed. Therefore, the conventional plating process of the bending process of the ground electrode 11 is performed. Can be prevented from cracking and peeling, and the plating thickness can be increased.

In the conventional process, the plating thickness at the limit of cracking and peeling of the plating was about 8 μm, but according to this process, the thickness can be increased to about 12 μm, and the plating thickness can be increased by 50%. The performance and reliability of the spark plug can be further improved.

[Second Embodiment] FIG. 6 shows a second embodiment of the present invention and shows a method for manufacturing a bipolar spark plug having two ground electrodes. In the present embodiment, only the method of cutting the ground electrode after welding the ground electrode to the metallic shell and the method of forming the spark gap are different from those of the first embodiment, and therefore the differences will be mainly described.

(First Step) In the same step as the first embodiment, the metal shell 4 is obtained by cold extrusion molding or the like (see FIG. 6 (a)).

Next, the flange portions 7 are formed by cutting the outer circumferences of the tubular portions 22 and 23 of the metal shell 4.
The metallic shell 4 is obtained (see FIG. 6B).

Next, two ground electrodes 11 made of nickel and mainly made of nickel are joined to the opposite positions on the tip surface of the tubular portion 25 of the metal shell 4 by electric welding such as resistance welding. (See FIG. 6 (c)). At this time, the ground electrode is cut with a length having a margin larger than the specified length after welding.

Then, the cylindrical portion 25 of the metal shell 4 is thread-rolled (see FIG. 6 (d)). The steps of welding the ground electrode and thread rolling may be reversed.

FIG. 7 is a view showing the step of bending the ground electrode, which is performed next. The bending machine 27 that performs this bending process includes a molding surface 28 having a shape corresponding to the predetermined bending shape of the ground electrode 11.
And a guide 30 for guiding the metal shell 4 to the side of the metal mold 4, and a bending punch 31 that moves from the inside of the metal shell 4 toward the outside (in the direction of the arrow in the drawing).

The bending punch 31 penetrates the shaft hole 8 of the metal shell 4 and presses the two ground electrodes 11 against the upper surface of the bending die 29 for plastic deformation. The bending punch 31
Is a shoulder portion 3 that abuts a locking portion 9 in the shaft hole 8 of the metal shell 4.
2, the length of the leg portion 33 extending downward from the shoulder portion 32 determines the electrode height of the two ground electrodes 11.

Next, the metal shell 4 is attached to the molding surface 2 of the bending die 29.
After being inserted into the guide 30 so as to be in contact with 8, the ground electrode 11 is bent in an L shape toward the axial center of the metal shell 4 from the middle by the tip surface of the leg portion 33 of the bending punch 31 (FIG. 6 (e )reference).

By this bending step, the two ground electrodes 11 are
2 and the two ground electrodes 11 are formed to have a predetermined electrode height h.

(Second Step) Nickel plating is performed as in the first embodiment (see FIG. 6 (f)).

(Third Step) FIG. 8 is a diagram showing a punching step of the ground electrode. The punching molding machine 34 which performs this punching step guides the punching die 36 and the metal shell 4 to the punching die 36 side, which has a discharge hole 35 for discharging a cut piece (not shown) cut from the tip of the ground electrode 11. The guide 37 and the punching punch 38 that moves from the inside to the outside (in the direction of the arrow in the drawing) of the metal shell 4 and the like. The punching punch 38 is formed by the metal shell 4
The tip ends of the two ground electrodes 11 are punched out from the shaft hole 8.

Next, the ground electrode 11 of the metal shell 4 is inserted into the guide 37 so as to come into contact with the upper surface of the punching die 36, and then the tip portions 39 of the punching punch 38 punch out the tip portions of the two ground electrodes 11. As a result, as shown in FIG. 9, the discharge end face 13 having the punching diameter φ is formed at the tips of the two ground electrodes 11 (see FIG. 6G).
The order of the punching process of the ground electrode and the plating process may be reversed. The metal shell 4 is manufactured by performing the above first to third steps.

(Fourth Step) Next, the spark gap 12 is formed between the ground electrode 11 and the center rod by assembling the insulator in which the center rod is incorporated into the metal shell 4 (FIG. 6 ( See h)).

When the punching step is performed after the plating step, the ground electrode 11 may be deformed due to the collision of the metal shells 4 when the metal shells are taken in and out, when the metal plate 4 is punched with high precision in the punching step. Is prevented. As a result, the ground electrode 1 after assembling the insulator with the center shaft
The accuracy of the gap length of the spark gap 12 (see FIG. 1) formed between the first discharge end surface 13 and the tip of the center electrode 2 and the accuracy of the position of the spark gap 12 can be dramatically improved. .

Since the number of non-standard metal shells 4 can be significantly reduced, the dimensions between the discharge end faces 13 of the plurality of ground electrodes 11 are set so that the gap length of the spark gap 12 conforming to the standard can be obtained. Adjustment work for expanding and narrowing can be eliminated. Therefore, mass productivity can be improved, and the manufacturing cost of the spark plug 1 can be significantly reduced.

[Third Embodiment] FIG. 10 shows a third embodiment of the present invention and is a view showing a step of bending a ground electrode. The bending machine 41 of this embodiment includes a cored bar 42 which is fitted into the shaft hole 8 of the metal shell 4 to hold the metal shell 4, and a bending die 43 which moves toward the two ground electrodes 11 from above in the drawing. Etc. The cored bar 42 has a shoulder portion 44 that comes into contact with the locking portion 9 in the shaft hole 8 of the metal shell 4, and has a length of a head portion 45 that extends upward from the shoulder portion 44 and is an electrode of the two ground electrodes 11. Height is decided. Also, the bending die 43
Has a molding surface 46 on the lower surface, and sandwiches the two ground electrodes 11 with the upper portion of the head portion 45 of the cored bar 42, and from the middle of the two ground electrodes 11 to the axial center of the metal shell 4. The two ground electrodes are bent toward the L shape. As in this example,
In the bending process of the two ground electrodes 11, the bending die 43 may move with respect to the metal shell 4 and force may be applied from the outside of the metal shell 4.

[Fourth Embodiment] FIG. 11 shows a fourth embodiment of the present invention and is a view showing a punching process of a ground electrode. In the punching molding machine 47 of this embodiment, a piece (not shown) cut from the tip of the ground electrode 11 is inserted inside the cored bar 48 which is fitted into the shaft hole 8 of the metal shell 4 and holds the metal shell 4. A discharge hole 50 for discharging the () is formed. Further, the punching punch 49 cuts the tips of the two ground electrodes 11 from the outside of the metal shell 4 toward the inside (in the direction of the arrow in the figure). As in this embodiment, a force may be applied from the outside of the metal shell 4 in the punching process of the ground electrode 11.

[Modification] In the second to fourth embodiments, the present invention is applied to the two-pole spark plug 1, but the present invention may be applied to a multi-pole spark plug having three or more poles. Although nickel plating is used in the first to fourth embodiments, nickel plating chromate treatment, chrome plating, nickel chrome plating, zinc nickel plating or the like may be used.

[Brief description of drawings]

FIG. 1 is a side view showing a parallel electrode type spark plug according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a metal shell according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a main part of FIG.

FIG. 4 is a process drawing showing the manufacturing method of the first embodiment of the present invention.

FIG. 5 is a side view showing a step of finely adjusting the spark gap according to the first embodiment of the present invention.

FIG. 6 is a process drawing showing the manufacturing method of the second exemplary embodiment of the present invention.

FIG. 7 is a sectional view showing a bending machine for bending a ground electrode according to a second embodiment of the present invention.

FIG. 8 is a cross-sectional view showing a punching machine for punching a ground electrode according to a second embodiment of the present invention.

FIG. 9 is a front view showing a main part according to a second embodiment of the present invention.

FIG. 10 is a sectional view showing a bending machine for bending a ground electrode according to a third embodiment of the present invention.

FIG. 11 is a sectional view showing a punching machine for punching a ground electrode according to a third embodiment of the present invention.

FIG. 12 is a process diagram of a conventional easy-to-process surface treatment manufacturing method.

FIG. 13 is a process drawing for performing the first conventional difficult-to-process surface treatment manufacturing method.

FIG. 14 is a process drawing of the second conventional difficult-to-process surface treatment manufacturing method.

[Explanation of symbols]

 1 parallel electrode type spark plug 2 center rod 4 metal shell 11 ground electrode 12 spark gap 13 discharge end face

Claims (4)

[Claims] 1. A first step of temporarily bending a single or a plurality of ground electrodes connected to a front end surface of a tubular metallic shell having an outer peripheral surface with a screw, into a state substantially equivalent to a final shape,
(B) A second step of subjecting the metal shell to a high-temperature corrosion-resistant difficult-to-process surface treatment, and (c) a spark gap is formed between the ground electrode and the center shaft by assembling the metal shell insulator with the metal shell. A method of manufacturing a spark plug, comprising: a third step. 2. A first step of: (a) temporarily bending a plurality of ground electrodes connected to the front end surface of a tubular metal shell having an outer peripheral surface with a screw into a final shape; and (b) the metal shell. A second step of applying a difficult-to-process surface treatment having high-temperature corrosion resistance, (c) a third step of cutting the ground electrode to form a discharge end surface, and (d)
A method of manufacturing a spark plug, comprising: a fourth step in which a spark gap is formed between the discharge end surface and a tip side surface portion of the center shaft by assembling an insulator with a center shaft into the metal shell. 3. A first step of: (a) temporarily bending a plurality of ground electrodes connected to the front end surface of a tubular metal shell having an outer peripheral surface with a screw into a final shape; and (b) the ground electrode. Disconnect,
A second step of forming a discharge end surface, (c) a third step of subjecting the metal shell to a high-temperature corrosion-resistant difficult-to-process surface treatment, and (d)
A method of manufacturing a spark plug, comprising: a fourth step in which a spark gap is formed between the discharge end surface and a tip side surface portion of the center shaft by assembling an insulator with a center shaft into the metal shell. 4. The high-temperature corrosion resistant difficult-to-process surface treatment according to claim 1, wherein the surface treatment is at least one of chromium plating, nickel plating, nickel plating chromate treatment, nickel chromium plating, and zinc nickel plating. Spark plug manufacturing method.