JP2021109216A - Resistance welder - Google Patents

Abstract

To provide a resistance welder capable of detecting not only the existence of a bolt but also the bolt of a longer size or a shorter size than a normal one in a neck-under length.SOLUTION: A lower electrode 4 comprises a bolt protective electrode 27 and a lower holder 29 having an air chamber 28, and an air pouring port 31 and a ventilation hole 32 communicating with outside are provided in the air chamber 28, and a detection body is housed in the air chamber 28. The detection body has a sensor rod 37, an outer cylinder 35 and an inner cylinder 40. An upper end surface 41 of the sensor rod 37 abuts on a distal end of a bolt, and a lower end surface 42 abuts on an upper end surface 43 of the inner cylinder. The outer cylinder 35 has a ventilation hole 46 communicating with the outside, and houses the inner cylinder 40 inside the outer cylinder 35. A clearance is formed between the upper inner periphery of the outer cylinder 35 and the upper outer periphery of the inner cylinder 40, and a portion between the lower inner periphery of the outer cylinder 35 and the lower outer periphery of the inner cylinder 40 cannot flow air. When pushed downward more than a regulation quantity by the sensor rod 37, a clearance is formed between the lower inner periphery of the outer cylinder 35 and the outer periphery of the inner cylinder 40.SELECTED DRAWING: Figure 2

Description

The present invention relates to a resistance welder that welds bolts to a base metal.

There is known a member detection device for a welding machine that can confirm the presence or absence of a supplied bolt when welding a bolt to a base material (Patent Document 1). The detection device of this welding machine is configured to include an upper electrode and a lower electrode, an air passage is formed in the upper electrode, and a pressure sensor is connected to the upper electrode. In addition, the lower electrode includes the electrode body, the replacement electrode, and the guide pin, and the upper opening of the electrode body and the large diameter hole of the replacement electrode are integrated to form an air chamber, and the air supply device is connected to the air chamber. Will be done. Further, the guide pin is configured to include a body portion and a bottom portion, and the air passage is formed so as to substantially coincide with the air passage of the upper electrode from the body portion upward. Then, when the bolt is supplied, the air in the air chamber is not supplied to the air passage, and when the bolt is not supplied, the air is supplied to the air passage to operate the pressure sensor. This makes it possible to detect the presence or absence of supplied bolts.

However, even if the presence or absence of the supplied bolt can be detected, it cannot be determined even if the supplied bolt is supplied with a long bolt having a length below the neck (l) longer than a regular bolt or a short bolt having a shorter length. It was a thing.

Japanese Unexamined Patent Publication No. 10-58155

Therefore, the present invention not only can detect the presence or absence of bolts by using compressed air, but also can detect long bolts and short short bolts whose neck length is longer than the normal one. The purpose is to provide a welding machine.

In order to solve the above problem, the resistance welding machine according to claim 1 includes an upper electrode and a lower electrode arranged to face the upper electrode, and supplies compressed air to an air chamber provided on the lower electrode side. A pressure sensor for connecting the device and measuring the air pressure in the air chamber is provided, and the lower electrode is a bolt protection electrode having a base material placed on the upper end surface and a bolt insertion hole in the axial center, and a bolt protection electrode below the bolt protection electrode. The lower holder is provided with a lower holder having an air chamber at the center of the shaft, and the air chamber of the lower holder is provided with an air inlet and a ventilation hole communicating with the outside, and the detector is housed in the air chamber. It has a sensor rod, an outer cylinder, and an inner cylinder. The upper end surface of the sensor rod abuts on the tip of the bolt and the lower end surface abuts on the upper end surface of the inner cylinder. Has a ventilation hole that communicates with the outside in the upper and lower middle parts, accommodates the inner cylinder inside, and air flows between the upper inner circumference of the outer cylinder and the upper outer circumference of the inner cylinder. A gap is formed to prevent air from flowing between the lower inner circumference of the outer cylinder and the lower outer circumference of the inner cylinder, and a groove is formed in the outer peripheral wall of the inner cylinder in the circumferential direction. It is characterized in that a gap through which air flows is formed between the lower inner circumference of the outer cylinder and the outer circumference of the inner cylinder when pushed downward a lot.
According to the second aspect of the present invention, a cooling electrode provided with a flow path for flowing a cooling liquid is interposed between the bolt protection electrode and the lower holder.
According to the third aspect of the present invention, an intermediate extension holder corresponding to the length under the neck of the bolt is interposed between the cooling electrode and the lower holder.
According to the fourth aspect of the present invention, the upper end surface of the sensor rod has a shape corresponding to the shape of the tip end portion of the bolt.

According to the invention of claim 1, when a bolt having a regular length under the neck is supplied, the tip of the bolt pushes the sensor rod downward by a specified amount, and the lower end surface of the sensor rod is the inner cylinder of the detector. It abuts on the upper end surface. At this time, the compressed air that has flowed into the air chamber from the air inlet is blocked, and the pressure sensor becomes a predetermined pressure, which is normal.
On the other hand, when the bolt is not supplied, the sensor rod is not pushed downward, and a gap is created between the lower end surface of the sensor rod and the upper end surface of the inner cylinder. The compressed air that has flowed into the air chamber from the air inlet passes through this gap and flows out to the outside through the ventilation holes of the outer cylinder and the ventilation holes of the lower holder. Therefore, the pressure of the pressure sensor becomes lower than the specified value, resulting in an abnormality.
When a short bolt whose neck length is shorter than the specified value is supplied, the sensor rod is not pushed downward by the specified amount, and the lower end surface of the sensor rod and the inner cylinder are the same as when the bolt is not supplied. A gap is created between the upper end surface and the upper end surface. The compressed air that has flowed into the air chamber from the air inlet passes through this gap and flows out to the outside through the ventilation holes of the outer cylinder and the ventilation holes of the lower holder. Therefore, the pressure of the pressure sensor becomes lower than the specified value, resulting in an abnormality.
Further, when a long bolt having a length under the neck of the bolt longer than the specified value is supplied, the sensor rod is pushed downward by a larger amount than the specified amount. Then, the inner cylinder is pushed downward by a specified amount, a gap is created between the outer cylinder and the inner cylinder in the circumferential groove formed in the inner cylinder, and the compressed air flowing into the air chamber passes through the gap. It flows out through the ventilation holes of the outer cylinder and the ventilation holes of the lower holder. Therefore, the pressure of the pressure sensor becomes lower than the specified value, resulting in an abnormality.
In this way, not only the presence or absence of the supplied bolt but also the case where the length under the neck of the bolt is longer or shorter than the specified value can be identified, and an abnormality can be detected.
According to the invention of claim 2, since the cooling electrode provided with the flow path for flowing the cooling liquid is interposed between the bolt protection electrode and the lower holder, the bolt protection electrode having the highest heat during welding is provided. It can be cooled from directly underneath, and the cooling efficiency is high.
According to the invention of claim 3, since the intermediate extension holder corresponding to the length under the neck of the bolt is interposed between the cooling electrode and the lower holder, even a bolt having a long length under the neck of the bolt can be cooled. This can be done simply by interposing an intermediate extension holder between the electrode and the lower holder.
According to the invention of claim 4, the upper end surface of the sensor rod is shaped to correspond to the shape of the tip of the bolt. Therefore, if the shape of the tip of the bolt is different from the specified shape, the sensor bolt The pressing amount will be different from the specified value, and an abnormality can be detected.

It is sectional drawing of the main part which shows the Example of this invention. It is an enlarged end view of the main part which shows the operating state of the lower electrode part with respect to a regular bolt. It is an enlarged end view of the main part which shows the operating state of the lower electrode part with respect to the state without a bolt. It is an enlarged end view of the main part which shows the operating state of the lower electrode part with respect to a short bolt. It is an enlarged end view of the main part which shows the operating state of the lower electrode part with respect to a long bolt. In the enlarged end view of the main part of the detector, (a) shows the disassembled state and (b) shows the assembled state. It is an enlarged end view of the main part which shows the operating state of the lower electrode with respect to a regular bolt when an extension holder is attached. It is an enlarged end view of the main part which shows the operating state of the lower electrode with respect to a short bolt when an extension holder is attached. It is an enlarged end view which shows the shape of the sensor rod corresponding to the shape of the bolt tip portion. It is an enlarged end view which shows the shape of the sensor rod corresponding to the diameter of a bolt.

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In FIG. 1, reference numeral 1 denotes a resistance welder (spot welder), which includes an upper electrode 3 fixed to the lower end of the upper electrode holder 2 and a lower electrode 4 arranged to face the upper electrode 3.

As shown in FIG. 1, the upper electrode holder 2 has an upper through hole 5a formed through the axial center portion, a piping nut 6 is detachably screwed into the upper portion, and the upper electrode 3 is detachably connected to the lower portion. Will be done. An inflow pipe 7 for cooling water penetrating the central portion of the upper through hole 5a was hanging and fixed to the axial center portion of the pipe nut 6, and the upper end portion of the inflow pipe 7 was attached to a side portion of the pipe nut 6. It communicates with the inflow nipple 8 of the cooling water. A return water channel 9 having a diameter larger than that of the inflow pipe 7 and communicating with the upper through hole 5a of the holder 2 is formed in the lower axial center portion of the pipe nut 6, and the return water channel 9 is provided on the side portion of the pipe nut 6. It communicates with the attached cooling water outflow nipple 10.

A connecting nut 12 having an air flow passage 11 formed in a shaft center portion is detachably screwed onto the upper portion of the piping nut 6, and a central portion of the inflow pipe 7 is screwed to the lower shaft center portion of the connecting nut 12. The upper air ejection pipe 13 penetrating the above air ejection pipe 13 is suspended and fixed. The air supply pipe 14 is connected to the upper part of the connecting nut 12. The air supply pipe 14 connects the secondary supply pipe 14b to the primary supply pipe 14a connected to the air compressor (compressed air supply device) 15 via a pressure reducing solenoid valve 16, and connects the secondary supply pipe 14b. Connect to the connecting nut 12. The solenoid valve 16 reduces the pressure on the primary supply pipe 14a side to the detection range and supplies it to the secondary supply pipe 14b, and a pressure sensor 17 is attached to the secondary supply pipe 14b. ing. The secondary supply pipe 14b is branched into an upper air ejection pipe 13 and a lower air ejection passage 19 that supplies air to the lower electrode 4 via a branch pipe 18. The compressed air may be supplied to the lower electrode 4 by another route, and the pressure sensor may be provided separately.

As shown in FIG. 1, the above-mentioned upper electrode 3 has a socket 20 detachably tapered and fitted to the lower portion of the upper electrode holder 2, and a relay holder 21 detachably tapered to the lower portion of the socket 20. The electrode tip 22 is detachably screwed to the lower portion of the relay holder 21. The lower portion of the electrode tip 22 is cylindrical and has a recess 23 in the center of the lower surface.

A lower through hole 5b communicating with the upper through hole 5a of the piping nut 6 is formed in the axial center of the socket 20, and the lower end of the lower through hole 5b opens in the upper axial center of the relay holder 21. The inverted space portion 24 is formed.

The inflow pipe 7 described above passes through the upper and lower through holes 5a and 5b, and its lower end faces the inverted space portion 24. As a result, the cooling water that has flowed in from the inflow nipple 8 flows between the upper air ejection pipe 13 and the inflow pipe 7, is inverted upward in the reversing space 24, and passes through the through holes 5a and 5b on the outside of the inflow pipe 7. It circulates and flows from the outflow nipple 10 toward the external cooling water tank to cool the upper electrode 3.

The upper air ejection pipe 13 passes through the central portion of the inflow pipe 7 and the central portion of the electrode tip 22, and the lower end thereof is opened in the recess 23 of the electrode tip 22. As a result, the compressed air supplied from the secondary supply pipe 14b is ejected into the recess 23. In FIG. 1, W is a work welded to the base material 25, and is a bolt in this example.

In the bolt, a protrusion L for welding is projected downward from the seating surface of the bolt head. There are various types of bolt screws such as M5, M6, M8, M10, M12, etc., there are various tip shapes, and there are various under-neck lengths.

The lower electrode 4 has a bolt protection electrode 27 on which a plate-shaped base material 25 is placed on the upper end surface and has a bolt insertion hole 26 in the shaft center portion, and an air chamber 28 is arranged below the bolt protection electrode 27 and has an air chamber 28 in the shaft center portion. The lower holder 29 is provided. In the figure, a cooling electrode 30 is interposed between the bolt protection electrode 27 and the lower holder 29.

The lower holder 29 is provided with an air injection port 31 at the lower part of the air chamber 28 and a ventilation hole 32 communicating with the outside at the upper and lower intermediate portions. The air chamber 28 houses the detector 33, which will be described later. The air chamber 28 has a small diameter at the lower portion and a large diameter at the upper portion via a step portion 34, and a female screw is provided on the inner peripheral surface of the upper portion of the air chamber. A male threaded portion provided at the lower part of the cooling electrode 30 is screwed into the female threaded portion to detachably connect the lower holder 29 and the cooling electrode 30. The step portion 34 of the air chamber supports the large diameter step portion 36 of the outer cylinder 35 of the detection body to hold the detection body 33 in the air chamber 28.

In the cooling electrode 30, the sensor rod 37 of the detection body 33 slides up and down in the central hole. Inside the cooling electrode 30, a flow path 38 through which cooling water flows is formed. The cooling water flowing in from the inflow port 39 flows through the flow path 38 and flows out from the outflow port (not shown) to cool the cooling electrode 30. Since the cooling electrode 30 is interposed between the bolt protection electrode 27 and the lower holder 29, cooling can be performed from directly under the bolt protection electrode 27, which has the highest heat during welding, and the cooling efficiency is improved.

As shown in FIG. 6, the detector 33 has a sensor rod 37, an outer cylinder 35, and an inner cylinder 40. In the sensor rod 37, the upper end surface 41 abuts on the tip end portion of the bolt W, and the conical lower end surface 42 abuts on the upper end surface 43 of the inner cylinder 40. The lower portion of the sensor rod 37 is formed to have a diameter larger than that of the body portion, and is held by engaging with the holding lid 45 at the step portion 44.
The outer cylinder 35 has a vent hole 46 that allows the lower outer peripheral surface of the sensor rod 37 to slide up and down on the upper inner peripheral surface and communicates with the outside in the middle portion in the vertical direction, and the inner cylinder 40 is inside the outer cylinder. To accommodate. The upper inner diameter of the outer cylinder 35 is formed to be larger than the outer diameter of the inner cylinder 40, and a gap 47 through which air flows is formed between the upper inner circumference of the outer cylinder 35 and the upper outer circumference of the inner cylinder 40. A groove is provided in the circumferential direction on the inner peripheral surface of the lower part of the outer cylinder, and the O-ring 48 is fitted in the groove. The O-ring 48 closes the gap between the lower inner peripheral wall of the outer cylinder 35 and the lower outer peripheral wall of the inner cylinder 40 to prevent air from flowing in the vertical direction.
The inner cylinder 40 is formed with a groove 49 in the circumferential direction on the outer peripheral wall of the intermediate portion in the vertical direction, and when the sensor rod 37 pushes the inner cylinder downward more than a specified amount, the lower inner peripheral wall and the inner portion of the outer cylinder 35 are formed. A gap 50 through which air flows is formed between the cylinder 40 and the outer peripheral wall (FIG. 5).

A step portion 51 is provided on the lower inner peripheral surface of the outer cylinder 35, and the lower end of the first compression spring 52 is engaged with the step portion 51. A first compression spring 52 is interposed in the gap 47 between the inner peripheral surface of the outer cylinder 35 and the outer peripheral surface of the inner cylinder 40 to urge the lower end surface 42 of the sensor rod 37 upward.
A step portion 53 is provided on the inner peripheral surface of the inner cylinder 40, and a second compression spring 54 that engages with the step portion 53 and urges the inner cylinder 40 upward is interposed. A collar 55 is formed at the lower end of the inner cylinder, and the collar 55 abuts on the lower end of the outer cylinder 35 to regulate the inner cylinder 40 from moving upward any more. Reference numerals 56 and 57 are O-rings.

The sensor rod 37 has an insulating member 58 interposed in the upper and lower intermediate portions to ensure insulation between the upper portion and the lower portion. The holding lid 45 integrally holds the sensor rod 37, the outer cylinder 35, and the inner cylinder 40. Further, the code 59 is a bolt protection sleeve, and the code 60 is an insulating member.

Next, the operation will be described. The base material 25 is placed on the bolt protection electrode 27, the bolt W is supplied into the bolt insertion hole 26 by a parts feeder or the like, the upper electrode 3 is lowered, and the upper electrode 3 (electrode tip 22) and the lower electrode 4 are placed. (Bolt protection electrode 27) sandwiches the base material 25 and the bolt W. When a bolt W having a regular length under the neck is supplied, as shown in FIG. 2, the tip of the bolt W abuts on the upper end surface 41 of the sensor rod 37 and pushes the sensor rod 37 downward by a specified amount to make the sensor. The lower end surface 42 of the rod 37 comes into contact with the upper end surface 43 of the inner cylinder 40 of the detector. At this time, the compressed air that has flowed into the air chamber 28 from the air inlet 31 is blocked by the lower end surface 42 of the sensor rod 37 contacting the upper end surface 43 of the inner cylinder 40 of the detector, and the pressure sensor 17 has a predetermined pressure. And becomes normal. As a result, the welding work will be continued.

On the other hand, when the bolt is not supplied, as shown in FIG. 3, the sensor rod 37 is not pushed downward, and a gap 61 is created between the lower end surface 42 of the sensor rod and the upper end surface 43 of the inner cylinder. The compressed air that has flowed into the air chamber 28 from the air injection port 31 passes through the gap 61, and flows out to the outside through the ventilation holes 46 of the outer cylinder and the ventilation holes 32 of the lower holder. Therefore, the pressure of the pressure sensor 17 becomes lower than the specified value, resulting in an abnormality. As a result, the welding work will be stopped.

When a short bolt W1 whose neck length is shorter than the specified value is supplied, as shown in FIG. 4, the sensor rod 37 is not pushed downward by a specified amount, and the sensor rod 37 is not supplied as in the case where the bolt is not supplied. A gap 61 is created between the lower end surface 42 and the upper end surface 43 of the inner cylinder. The compressed air that has flowed into the air chamber 28 from the air injection port 31 passes through the gap 61, and flows out to the outside through the ventilation holes 46 of the outer cylinder and the ventilation holes 32 of the lower holder. Therefore, the pressure of the pressure sensor 17 becomes lower than the specified value, resulting in an abnormality. As a result, the welding work will be stopped.

Further, when a long bolt W2 having a length below the neck longer than the specified value is supplied, the sensor rod 37 is pushed downward by a larger amount than the specified amount, as shown in FIG. Along with this, the inner cylinder 40 that comes into contact with the lower end of the sensor rod 37 is also pushed downward by a specified amount more than the specified amount, and the gap 50 between the outer cylinder and the inner cylinder is formed by the circumferential groove 49 formed in the inner cylinder 40. The compressed air that has flowed into the air chamber 28 flows out to the outside through the gap 50, the ventilation hole 46 of the outer cylinder, and the ventilation hole 32 of the lower holder. Therefore, the pressure of the pressure sensor 17 becomes lower than the specified value, resulting in an abnormality. As a result, the welding work will be stopped.

As described above, according to the present invention, not only the presence or absence of the supplied bolt but also the case where the length under the neck of the bolt is longer or shorter than the specified amount can be identified, and an abnormality can be detected.

FIG. 7 shows a hollow cylindrical intermediate extension holder 62 interposed between the cooling electrode 30 and the lower holder 29. When the length under the neck of the bolt is long, it can be dealt with only by interposing an intermediate extension holder 62 corresponding to the length under the neck. As shown in FIG. 7, when a bolt W having a regular under-neck length is supplied, the tip of the bolt W abuts on the upper end surface 41 of the sensor rod 37 and pushes the sensor rod 37 downward by a specified amount to make the sensor. The lower end surface 42 of the rod 37 comes into contact with the upper end surface 43 of the inner cylinder of the detector. At this time, the compressed air flowing into the air chamber 28 from the air inlet 31 is blocked by the lower end surface 42 of the sensor rod abutting on the upper end surface 43 of the inner cylinder of the detector, and the pressure sensor 17 becomes a predetermined pressure. It becomes normal. As a result, the welding work will be continued.

FIG. 8 shows the case of a short bolt W3 having a shorter neck length than the normal one, the sensor rod 37 is not pushed downward by a specified amount, and the lower end surface 42 of the sensor rod 37 and the upper end surface of the inner cylinder are formed. A gap 61 is created between the rod and the 43. The compressed air that has flowed into the air chamber 28 from the air injection port 31 passes through the gap 61, and flows out to the outside through the ventilation holes 46 of the outer cylinder and the ventilation holes 32 of the lower holder. Therefore, the pressure of the pressure sensor 17 becomes lower than the specified value, resulting in an abnormality. As a result, the welding work will be stopped.

In the case of a bolt having a length under the neck longer than the normal one, the sensor rod 37 is pushed downward by a larger amount than the specified amount, as shown in FIG. 5, although not shown. Along with this, the inner cylinder 40 that abuts on the lower end of the sensor rod 37 is also pushed downward by a specified amount, and the circumferential groove 49 formed in the inner cylinder creates a gap 50 between the outer cylinder and the inner cylinder. The generated compressed air that has flowed into the air chamber 28 flows out through the gap 50, through the ventilation holes 46 of the outer cylinder, and through the ventilation holes 32 of the lower holder. Therefore, the pressure of the pressure sensor 17 becomes lower than the specified value, resulting in an abnormality. As a result, the welding work will be stopped.

FIG. 9 shows a shape in which the upper end surface 41 of the sensor rod 37 corresponds to the shape of the tip end portion of the bolt W. In the figure (a), the shape of the upper end surface 41 is formed in an inclined concave shape, (b) is a concave shape, and (c) is a flat shape. As a result, when the shape of the tip of the bolt W is different from the specified shape, the pressing amount of the sensor rod 37 is different from the specified value, and an abnormality can be detected.

Further, in FIG. 10, the diameter of the upper part of the sensor rod 37 is made to correspond to the screw diameter of the bolt W. For example, FIG. 6A corresponds to M8, FIG. 3B corresponds to M6, and FIG. 3C corresponds to M4.

1 Resistance welding machine (spot welding machine)
2 Upper electrode holder 3 Upper electrode 4 Lower electrode 5a Upper through hole 5b Lower through hole 6 Piping nut 7 Inflow pipe 8 Inflow nipple 9 Return water channel 10 Outflow nipple 11 Flow passage 12 Connecting nut 13 Upper air ejection pipe 14 Air supply pipe 14a Primary Supply pipe 14b Secondary supply pipe 15 Air compressor (compressed air supply device)
16 Electromagnetic valve 17 Pressure sensor 18 Branch pipe 19 Lower air ejection path 20 Socket 21 Relay holder 22 Electrode tip 23 Recessed 24 Inverted space 25 Base material 26 Bolt insertion hole 27 Bolt protection electrode 28 Air chamber 29 Lower holder 30 Cooling electrode 31 Air Injection port 32 Vent hole 33 Detector 34 Step 35 Outer cylinder 36 Large diameter step 37 Sensor rod 38 Flow path 39 Inflow port 40 Inner cylinder 41 Upper end surface 42 Lower end surface 43 Upper end surface 44 Step part 45 Holding lid 46 Vent hole 47 Gap 48 O-ring 49 Groove 50 Gap 51 Step 52 First compression spring 53 Step 54 Second compression spring 55 Collar 56, 57 O-ring 58 Insulation member 59 Bolt protection sleeve 60 Insulation member 61 Gap 62 Intermediate extension holder W work (Regular bolt)
W1 Short bolt W2 Long bolt W3 Short bolt L Protrusion

Claims (4)

It is provided with an upper electrode and a lower electrode arranged opposite to the upper electrode, and a pressure sensor for connecting a compressed air supply device for supplying compressed air to an air chamber provided on the lower electrode side and measuring the air pressure in the air chamber is provided. The lower electrode includes a bolt protection electrode on which a base material is placed on the upper end surface and has a bolt insertion hole in the axial center portion, and a lower holder arranged below the bolt protection electrode and having an air chamber in the axial center portion. The air chamber of the holder is provided with an air inlet and a ventilation hole that communicates with the outside, and the detector is housed in the air chamber. The detector has a sensor rod, an outer cylinder, and an inner cylinder, and the upper end surface of the sensor rod is The lower end surface abuts on the tip of the bolt and the lower end surface abuts on the upper end surface of the inner cylinder. It has pores, accommodates the inner cylinder inside, forms a gap for air to flow between the upper inner circumference of the outer cylinder and the upper outer circumference of the inner cylinder, and forms the lower inner circumference of the outer cylinder and the lower outer circumference of the inner cylinder. Air cannot flow between the two, and a groove is formed in the outer peripheral wall of the inner cylinder in the circumferential direction, and when the sensor rod pushes the inner cylinder downward more than the specified amount, the lower inner circumference of the outer cylinder and the inner cylinder are pressed. A resistance welding machine characterized in that a gap through which air flows is formed between the electrode and the outer periphery of the electrode. The resistance welding machine according to claim 1, wherein a cooling electrode having a flow path for flowing a cooling liquid inside is interposed between the bolt protection electrode and the lower holder. The resistance welding machine according to claim 2, wherein an intermediate extension holder corresponding to the length under the neck of the bolt is interposed between the cooling electrode and the lower holder. The resistance welding machine according to any one of claims 1 to 3, wherein the upper end surface of the sensor rod has a shape corresponding to the shape of the tip of the bolt.

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