JP7506360B2 - Electric resistance welding electrodes - Google Patents

Description

The present invention relates to an electrode for electric resistance welding in which a stopper member incorporating a magnet is housed within an electrode body, and the stopper member is cooled by cooling air.

WO2004/009280 describes that a magnet is housed in a stopper member that is composed of a large diameter portion and a small diameter portion, and that the magnet is cooled by a water cooling system.

Japanese Patent Application Laid-Open No. 2011-183414 describes that a magnet is housed in a stopper member composed of a large diameter portion and a small diameter portion, and that the stopper member housed in the electrode body is pressed by the tension of a compression coil spring or air pressure. This publication does not mention anything about a cooling method for the stopper member.

Japanese Patent Application Laid-Open No. 2017-006982 describes a synthetic resin sliding portion integrated with a guide pin that has a movable end surface and a stationary inner end surface formed thereon to interrupt the flow of cooling air.

Publication No. WO2004/009280 JP 2011-183414 A JP 2017-006982 A

The stopper member in Patent Document 1 is housed in a guide tube made of synthetic resin, and is cooled by flowing cooling water through a cooling water passage provided on the outer periphery of the guide tube. This type of cooling method has the problem that it is difficult to improve cooling performance because the cooling water flow does not directly contact the stopper member. In addition, bringing the cooling water into direct contact with the stopper member makes it difficult to establish a seal structure for the cooling water passage.

The stopper member in Patent Document 2 is built into the electrode, and there is no concept of removing the welding heat of the stopper member with a cooling fluid such as cooling water or cooling air. Patent Document 2 describes applying compressed air to the upper surface of the stopper member instead of a coil spring, but this is only related to the pressurizing means and does not suggest air cooling.

FIG. 4 of Patent Document 2 is reproduced in the drawings of this application. It is FIG. 5. In this figure, the electric wire connected to the terminal plate 27 in the cup member 26 is shown by a solid line, and a cylindrical base that receives this electric wire is shown, but this is a member that is not related to the inflow of cooling air. Also, paragraph 0033 of Patent Document 2 states that "Instead of the coil spring 28, compressed air may be used as an air spring on the upper surface of the stopper member 21." This means an air spring, and is not a concept in which an O-ring is also incorporated to move the cooling air. Note that the numbers of the members in FIG. 5 are unrelated to the numbers of the drawings of the embodiment of the present invention.

The cooling in Patent Document 3 is mainly air cooling of the sliding portion made of synthetic resin, and is not cooling of the stopper member as in the present invention.

As described above, the techniques disclosed in each of the patent documents do not directly bring cooling air into contact with the stopper member incorporating the magnet to prevent the magnet from overheating. Patent document 1 describes a structure in which the stopper member is indirectly water-cooled, making it difficult to improve cooling performance. Patent document 2 does not apply any cooling fluid to the stopper member. Patent document 3 does not disclose the stopper member itself incorporating a magnet.

The present invention has been provided to solve the above problems, and aims to provide effective cooling by bringing cooling air into direct contact with the stopper member containing a magnet, while also simplifying the intermittent structure for the cooling air.

The invention described in claim 1 is
An end cap having an insertion hole for a shaft-shaped part is attached to a cylindrical copper alloy electrode body,
A guide tube made of a heat insulating material is inserted into the electrode body,
The guide hole provided in the guide tube is composed of a large diameter hole and a small diameter hole communicating with the insertion hole,
a stopper member is provided, the stopper member having a large diameter portion having a circular cross section and inserted into the large diameter hole in a state capable of advancing and retracting, and a small diameter portion having a circular cross section and inserted into the small diameter hole in a state capable of advancing and retracting,
a thickness of the guide tube as viewed in a diameter direction of the electrode body is set to a value that allows the large diameter hole and the small diameter hole to be formed;
The small diameter portion is made of iron having good magnetic permeability,
a tip end surface of the small diameter portion of the stopper member serves as a stopper surface that receives a shaft-shaped part inserted into the small diameter hole,
a magnet is accommodated in the stopper member to attract the shaft-shaped part to the stopper surface via the small diameter portion,
an air passage is formed between the large diameter portion of the stopper member and the guide hole;
an air passage is formed between the small diameter portion of the stopper member and the guide hole;
a movable end surface formed at the boundary between the large diameter portion and the small diameter portion of the stopper member comes into contact with or separates from a stationary inner end surface formed at the boundary between the large diameter hole and the small diameter hole of the guide hole, thereby connecting and disconnecting the flow of cooling air so that the cooling air flows while directly contacting a surface of the stopper member;
a flow passage area of an air passage formed between the large diameter portion of the stopper member and the guide hole, a flow passage area of an air passage formed between the small diameter portion of the stopper member and the guide hole, and a flow passage area of a gap interval formed by the separation of the movable end face from the stationary inner end face are configured to be approximately equal to each other,
The electrode body is provided with a vent hole for supplying cooling air to the large diameter hole.

When the shaft-shaped part is inserted into the insertion hole of the end cap, the magnetic attraction force acting on the stopper surface through the small diameter part of the stopper member attracts the shaft-shaped part firmly to the small diameter part, and the shaft-shaped part is in a stable stationary state. When the opposing electrode advances and presses down the shaft-shaped part, the movable end face of the stopper member separates from the stationary inner end face of the guide hole, and cooling air flows through the air passages arranged in the large diameter part and the small diameter part. During this cooling air circulation, a welding current is passed through, and heat is generated from the molten part. The molten heat is transferred from the steel plate part to the shaft part, and then from the shaft part to the stopper member. In addition, the heat is transferred from the electrode body to the stopper member through the guide tube. The cooling air flow directly cools the outer peripheral surface of the stopper member, suppressing the welding heat being transferred to the magnet.

In other words, the cooling air flows while in direct contact with the surface of the stopper member, providing excellent protection for the magnet through a high air-cooling effect. In other words, if the magnet reaches an abnormally high temperature, it will enter a temperature demagnetization region, and in the worst case scenario, it will reach irreversible demagnetization, compromising the attraction stability of the shaft-shaped part. By having the cooling air flow while in direct contact with the surface of the stopper member, abnormal heating of the magnet is prevented.

In the case of a water-cooled system, a structure is required to separate the space for accommodating the stopper member from the space through which the cooling water flows, such as a watertight partition plate, which makes the structure complicated. However, in the case of an air-cooled system, even if cooling air is blown directly onto the stopper member, there is no adverse effect on the surrounding components, which simplifies the structure and avoids problems due to air leaks.

Even a small leak of the cooling water that cools the stopper member will have a negative effect on neighboring parts, requiring immediate action and the need to stop the production line immediately.However, with an air-cooled system, a small air leak will have a minimal negative effect on neighboring parts, so the line will not have to stop suddenly and operation can continue, making it possible to minimize economic losses by stopping the line at a convenient point.

A movable end face is formed at the boundary between the large diameter portion and the small diameter portion of the stopper member, and a stationary inner end face is formed at the boundary between the large diameter hole and the small diameter hole of the guide hole, so that part of the cooling air intermittent structure is formed in the stopper member itself, which is advantageous for simplifying the structure.

If spatter flies off during melting, it may be attracted to the magnet inside the stopper member and contaminate the inside of the electrode, but the exhaust action of the cooling air flow can prevent the spatter from entering. Since the welding current is passed after the cooling air starts to flow, spatter that tries to fly off toward the stopper member is forcibly pushed back by the headwind, which is also effective in dealing with spatter.

1A and 1B are cross-sectional views of an entire electrode and a cross-sectional view of a portion thereof. 2A-2A cross-sectional view and 2B-2B cross-sectional view of FIG. 1. FIG. 11 is a cross-sectional view showing a modified example of the air passage. FIG. This is a cross-sectional view reproduced from FIG. 4 of Patent Document 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an electric resistance welding electrode according to the present invention will now be described.

1 to 4 show an embodiment of the present invention.

First, the shaft-shaped part will be described.

There are various types of shaft-shaped parts, such as projection bolts and the rotating shafts of rotating parts, but here, the projection bolts are the object of welding. In this way, there are various types of parts to be welded. In the following explanation, the projection bolt may be simply referred to as a bolt.

The iron projection bolt 1 is composed of a shaft 2 with a male thread, a disk-shaped flange 3 that is integrated with the shaft 2, and fusion projections 4 provided on the surface of the flange 3 on the shaft 2 side. The fusion projections 4 are arranged near the outer periphery of the flange 3, and three of them are provided at 120 degree intervals.

Next, the electrode body will be described.

The electrode body 5 is cylindrical and made of a copper alloy such as chromium copper. An end cap 6 made of a copper alloy such as beryllium copper is connected to the end of the electrode body 5 via a threaded portion 7. The end cap 6 is provided with an insertion hole 8 into which the shaft portion 2 of the bolt 1 is inserted, and an insulating tube 9 made of an insulating material is provided in a part of the insertion hole 8. A fixing portion 11 is connected to the other end side of the electrode body 5 via a threaded portion 10. The fixing portion 11 is connected to a stationary member 24 by taper fitting or the like.

The insulating materials used for the insulating tube 9, the guide tube 13, and the insulating sheet 29 described below are polytetrafluoroethylene (product name: Teflon, registered trademark), polyamide resin, or the like.

Next, the guide tube will be described.

The guide tube 13, which has a circular cross section, is inserted into the electrode body 5 by a method such as press-fitting. The guide hole 14 formed in the guide tube 13 is composed of a large diameter hole 15 and a small diameter hole 16 which communicates with the insulating tube 9 and the insertion hole 8. A fixing pin 23 made of synthetic resin is driven into the guide tube 13 to prevent the guide tube 13 from shifting out of position. As is clear from Figures 1 and 2, the thickness of the guide tube 13 as viewed in the diameter direction of the electrode body 5 is set to a value that allows the large diameter hole 15 and the small diameter hole 16 to be formed.

Next, the stopper member will be described.

In terms of its external appearance, the stopper member 17 is composed of a large diameter portion 18 which has a circular cross-section and is inserted into the large diameter hole 15 in a state where it can advance and retreat, and a small diameter portion 19 which also has a circular cross-section and is inserted into the small diameter hole 16 in a state where it can advance and retreat.

As shown in FIG. 1B, the large diameter portion 18 of the stopper member 17 is made of a non-magnetic material such as stainless steel and has a cup-like shape. A magnet 20 is accommodated therein. The magnet 20 is a permanent magnet. The small diameter portion 19 is made of iron with good magnetic permeability, and its tip surface is a stopper surface 21 that receives the shaft portion 2. The small diameter portion 19 and the large diameter portion 18 are preferably integrated by welding. The blackened areas are welded portions 22, and the surfaces are smoothed after welding. The container-like large diameter portion 18 is sealed by the small diameter portion 19, and the magnet 20 is in close contact with the lower surface of the small diameter portion 19. The magnet 20 may be embedded vertically as shown by the two-dot chain line in FIG. 1B.

When the shaft portion 2 is inserted into the insertion hole 8 and the tip of the shaft portion 2 is received by the stopper surface 21 , the attractive force of the magnet 20 acts on the shaft portion 2 , and the shaft portion 2 is firmly attracted to the stopper surface 21 .

Next, the air passage will be described.

An air passage 25 is formed between the large diameter portion 18 of the stopper member 17 and the guide hole 14, i.e., between the large diameter hole 15, and an air passage 26 is formed between the small diameter portion 19 of the stopper member 17 and the guide hole 14, i.e., between the small diameter hole 16. The air passages 25 and 26 are annular gaps as shown in Fig. 2. Note that, for ease of viewing, the matte pattern and hatching showing the cross section have been omitted in Fig. 1(C).

A movable end surface 27 formed at the boundary between the large diameter portion 18 and the small diameter portion 19 of the stopper member 17 is configured to connect and disconnect the flow of cooling air by coming into contact with and separating from a stationary inner end surface 28 formed at the boundary between the large diameter hole 15 and the small diameter hole 16 of the guide hole 14. The movable end surface 27 and the stationary inner end surface 28 exist on an imaginary plane perpendicularly intersecting the central axis O-O of the electrode.

To supply cooling air to the air passage 25, an air vent 32 is provided in the electrode body 5, and an air supply pipe 37 extending from an air pump (not shown) is connected to the air vent 32.

An insulating sheet 29 is fitted on the inner bottom surface of the electrode body 5, and a current-carrying plate 30 is fixed on top of the insulating sheet 29. A compression coil spring 31 is fitted between the lower surface of the stopper member 17 and the current-carrying plate 30, and the tension of the spring presses the movable end surface 27 against the stationary inner end surface 28. This pressing prevents the flow of cooling air.

1C, the gap of the air passage 25 is indicated by the reference character L1, and the gap of the air passage 26 is indicated by the reference character L2. The gap when the movable end face 27 is separated from the stationary inner end face 28 (so-called open valve gap) is indicated by the reference character L3. The flow passage area of the air passage 25, the flow passage area of the air passage 26, and the flow passage area due to the gap length L3 are set to be approximately equal. This allows the cooling air to flow smoothly, and a cooling air flow with less turbulence and less bending of the air passage is obtained.

As is clear from FIG. 2, the diameter of the air passage 25 is larger than the diameter of the air passage 26. Therefore, if the flow passage areas of both air passages 25, 26 are made substantially the same, the gap distance L1 will be larger than the gap distance L2.

The gap distance of the air passage is L1>L2, but in order to further reduce the curvature of the air passage, it is set to L3>L1>L2. By doing so, the degree of bending of the air flow is reduced and turbulence is also reduced, and the flow rate of the cooling air is increased, thereby further improving the cooling effect.

When some kind of inclined force acts on the stopper member 17, by making the gap distance L2<L1, the gap distance L2 is small and the outer peripheral surface of the large diameter portion 18 contacts the inner peripheral surface of the large diameter hole 15 at an early stage, so that the inclination angle of the stopper member 17 can be kept small, and misalignment of the shaft portion 2 with respect to the central axis O-O can be reduced, preventing a deterioration in welding quality.

1(A), in a state in which the lower end of the shank 2 of the bolt 1 is attracted to the stopper surface 21, a distance L4 is provided between the fusion bonding projection 4 and the steel plate part 12, and by widening this distance L4, the gap distance L3 between the movable end face 27 and the stationary inner end face 28 also becomes wider. A pilot hole is drilled in the steel plate part 12, and the shank 2 is inserted into the pilot hole and the insertion hole 8. The steel plate part 12 is placed on the end cover 6, and the position of the steel plate part 12 is determined by a robot device or the like so that the pilot hole is coaxial with the insertion hole 8.

Next, a modified example of the air passage will be described.

3 is a cross-sectional view corresponding to the cross section taken along line 2A-2A in FIG. The air passages 25 and 26 described above are annular spaces, but in this modified example, they are formed by processing the small diameter portion 19 of the stopper member 17. The small diameter portion 19 is inserted into the small diameter hole 16 in a state where it can slide substantially without any gap. A flat surface 39 is formed on the outer surface of the small diameter portion 19 in the direction of the central axis O-O, and an air passage 40 is formed between this flat surface 39 and the arc-shaped inner surface of the small diameter hole 16. The flat surfaces 39 are provided at 90 degree intervals, and there are four air passages 40.

Although not shown, an air passage structure similar to that shown in FIG. 3 is also adopted on the large diameter portion 18 side.

The above-mentioned "state in which there is substantially no gap and the electrode body 5 can slide" means that even when a force is applied to the guide tube 13 in the diameter direction of the electrode body 5, there is no rattling sensation that gives the feeling of a gap, and the electrode body 5 can slide in the direction of the central axis O-O.

Next, the energizing circuit will be described.

In this embodiment, it is possible to check whether the bolt 1 is inserted into the insertion hole 8. A signal wire 33 joined to the conductive plate 30 and a signal wire 34 joined to the electrode body 5 are provided, and both signal wires 33, 34 are connected to a detection device 35. When the bolt 1 is properly inserted into the insertion hole 8, a detection current flows from the detection device 35 through the signal wire 34 to the electrode body 5. The detection current flows into the detection device 35 through the end cover 6, the steel plate part 12, the shaft portion 2, the stopper member 17, the compression coil spring 31, the conductive plate 30, and the signal wire 33. The detection device 35 detects the detection current and uses it as a trigger signal to advance the movable electrode 36.

The effects of the embodiment described above are as follows.

When the bolt 1 is inserted into the insertion hole 8 of the end cover 6, the bolt 1 is firmly attracted to the small diameter portion 19 of the stopper member 17 by the magnetic attraction force acting on the stopper surface 21 through the small diameter portion 19 of the stopper member 17, and is in a stable stationary state. When the opposing electrode 36 advances and pushes down the bolt 1, the movable end surface 27 of the stopper member 17 moves away from the stationary inner end surface 28 of the guide hole 14, and cooling air flows through the air passages 25, 26 arranged in the large diameter portion 18 and the small diameter portion 19, respectively. During this cooling air circulation, a welding current is applied, and heat is generated from the molten part. The molten heat is transferred from the steel plate part 12 to the shaft portion 2, and further from the shaft portion 2 to the stopper member 17. In addition, the heat is transferred from the electrode body 5 to the stopper member 17 through the guide tube 13. The outer peripheral surface of the stopper member 17 is directly cooled by the cooling air flow, and the welding heat transferred to the magnet 20 is suppressed.

That is, the cooling air flows while in direct contact with the surface of the stopper member 17, providing excellent protection for the magnet due to the high air-cooling effect. In other words, if the magnet 20 reaches an abnormally high temperature, it will enter a temperature demagnetization region, and in the worst case scenario, it will reach irreversible demagnetization, compromising the attraction stability of the bolt 1. By having the cooling air flow while in direct contact with the surface of the stopper member 17, abnormal heating of the magnet 20 is prevented.

Immediately after welding a normal number of bolts, for example, four bolts per minute, to the steel plate part 12, the bolt 1 was manually pulled out of the insertion hole 8 together with the steel plate part 12. At that time, the bolt 1 was not pulled out easily, but had to be pulled slightly. Therefore, it was confirmed that the attractive force attracting the bolt 1 to the stopper surface 21 was sufficient. In reality, it is structurally impossible to measure the magnet temperature immediately after welding, so the pull-out test method was used to confirm the change in attractive force. If the magnet 20 were heated to an abnormally high temperature, it would reach a range of irreversible demagnetization or the attractive magnetic force would decrease, but since no such decrease in attractive force was observed, it was determined that the cooling effect of the cooling air was achieved properly.

In the case of a water-cooled system, a structure for separating the space for accommodating the stopper member 17 from the space through which the cooling water flows, such as a watertight partition plate, is required, which makes the structure complicated. However, in the case of an air-cooled system, even if cooling air is blown directly onto the stopper member 17, there is no adverse effect on the surrounding components, which simplifies the structure and avoids problems due to air leaks.

Even a small leak of the cooling water that cools the stopper member 17 will have a detrimental effect on neighboring parts, requiring immediate action and the need to stop the production line immediately. However, with an air-cooled system, a small air leak will have a smaller detrimental effect on neighboring parts, so the line will not have to stop suddenly and operation can continue, making it possible to minimize economic losses by stopping the line at a convenient point.

A movable end face 27 is formed at the boundary between the large diameter portion 18 and the small diameter portion 19 of the stopper member 17, and a stationary inner end face 28 is formed at the boundary between the large diameter hole 15 and the small diameter hole 16 of the guide hole 14, so that part of the intermittent structure for cooling air is formed in the stopper member 17 itself, which is advantageous for simplifying the structure.

If spatter scatters during melting, it may be attracted by the magnet 20 in the stopper member 17 and contaminate the inside of the electrode, but the exhaust action of the cooling air flow can prevent the intrusion of spatter. As the welding current is passed after the cooling air starts to flow, spatter that tries to scatter toward the stopper member 17 is forcibly pushed back by the headwind, which is also effective in dealing with spatter.

By making the flow passage areas of the three passages, the air passage 25 on the large diameter portion 18 side, the air passage 26 on the small diameter portion 19 side, and the air passage formed by the distance between the stationary inner end face 28 and the movable end face 27, approximately the same, the flow condition of the cooling air can be made smooth, making it easier to increase the flow rate of the cooling air, which is preferable for improving the cooling effect. Also, by setting the distance by which the movable end face is separated from the stationary inner end face to be large, the bending of the cooling air flow is reduced, the pressure loss due to the bending of the flow passage is reduced, and the contact of the cooling air with the stopper member can be improved.

In the above embodiment, when an annular air passage 25 is provided between the outer peripheral surface of the large diameter portion 18 of the stopper member 17 and the inner peripheral surface of the large diameter hole 15 of the guide hole 14, and an annular air passage 26 is provided between the outer peripheral surface of the small diameter portion 19 of the stopper member 17 and the inner peripheral surface of the small diameter hole 16 of the guide hole 14, the air passage gap L1 on the small diameter hole 16 side can be set larger than the air passage gap L2 on the large diameter hole 15 side, so that the flow area of both air passages 25, 26 can be made substantially the same. At the same time, by selecting the distance L3 by which the movable end face 27 of the stopper member 17 is separated from the stationary inner end face 28 of the guide hole 14, the flow area of the cooling air at this separated portion can be made substantially the same as the flow area of the annular air passages 25, 26. Therefore, the cooling air flowing along the outer portion of the stopper member 17 becomes a smooth air flow with little turbulence, and the surface of the stopper member 17 is effectively cooled.

As described above, the electrode of the present invention provides effective cooling by bringing cooling air into direct contact with the stopper member incorporating a magnet, and simplifies the structure for interrupting the cooling air flow, making it applicable in a wide range of industrial fields, such as automobile body welding processes and sheet metal welding processes for home appliances.

1 Projection bolt, shaft-shaped part 2 Shaft part 3 Flange 4 Welding projection 5 Electrode body 6 End cover 8 Insertion hole 12 Steel plate part 13 Guide tube 14 Guide hole 15 Large diameter hole 16 Small diameter hole 17 Stopper member 18 Large diameter part 19 Small diameter part 20 Magnet 21 Stopper surface 25 Air passage 26 Air passage 27 Movable end surface 28 Stationary inner end surface 32 Vent 40 Air passage L1 Gap distance L2 Gap distance L3 Gap distance L4 Distance between fusion projection and steel plate part O-O Central axis

Claims (1)

An end cap having an insertion hole for a shaft-shaped part is attached to a cylindrical copper alloy electrode body,
A guide tube made of a heat insulating material is inserted into the electrode body,
The guide hole provided in the guide tube is composed of a large diameter hole and a small diameter hole communicating with the insertion hole,
a stopper member is provided, the stopper member having a large diameter portion having a circular cross section and inserted into the large diameter hole in a state capable of advancing and retracting, and a small diameter portion having a circular cross section and inserted into the small diameter hole in a state capable of advancing and retracting,
a thickness of the guide tube as viewed in a diameter direction of the electrode body is set to a value that allows the large diameter hole and the small diameter hole to be formed;
The small diameter portion is made of iron having good magnetic permeability,
a tip end surface of the small diameter portion of the stopper member serves as a stopper surface that receives a shaft-shaped part inserted into the small diameter hole,
a magnet is accommodated in the stopper member to attract the shaft-shaped part to the stopper surface via the small diameter portion,
an air passage is formed between the large diameter portion of the stopper member and the guide hole;
an air passage is formed between the small diameter portion of the stopper member and the guide hole;
a movable end surface formed at the boundary between the large diameter portion and the small diameter portion of the stopper member comes into contact with or separates from a stationary inner end surface formed at the boundary between the large diameter hole and the small diameter hole of the guide hole, thereby connecting and disconnecting the flow of cooling air so that the cooling air flows while directly contacting a surface of the stopper member;
a flow passage area of an air passage formed between the large diameter portion of the stopper member and the guide hole, a flow passage area of an air passage formed between the small diameter portion of the stopper member and the guide hole, and a flow passage area of a gap interval formed by the separation of the movable end face from the stationary inner end face are configured to be approximately equal to each other,
2. An electrode for electric resistance welding, comprising: a vent hole provided in said electrode body for supplying cooling air to said large diameter hole.

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