Electrical resistance welding electrodes and methods for maintaining a tight seal.

Abstract

According to the present invention, a guide hole 6 is configured from a large-diameter hole 7, a medium-diameter hole 8, and a small-diameter hole 9. A sliding part 13 that is fitted into the guide hole 6 is configured from a synthetic resin material. A large-diameter part 24 of the sliding part 13 is slidably fitted into the large-diameter hole 7, and a medium-diameter part 25 is slidably fitted into the medium-diameter hole 8. A mobile end surface 33 of the sliding part 13 is arranged against a stationary inside end surface 32 of the guide hole 6. As a result of the width W1 of the mobile end surface being less than half the thickness W3 of the large-diameter part 24, the pressurizing force of the mobile end surface 33 is increased, fine metal pieces 34 are pressed into the parent material of the sliding part 13 from the mobile end surface 33, and the medium-diameter part 25 is thicker.

Description

Electrode for Electric Resistance Welding and Airtight Maintenance Method

[0001] This invention relates to an electrode for electric resistance welding and an airtight maintenance method in which the end face of a sliding part made of a synthetic resin material adheres to and separates from the inner end face formed in the electrode body to block and allow the passage of cooling air.

[0002] The electrodes for electric resistance welding described in JP-A-2002-248578, JP-A-2017-006982, JP-A-2017-047469, and JP-A-2017-136639 have a guide hole formed in the electrode body, which consists of a large-diameter hole, a medium-diameter hole, and a small-diameter hole. A sliding part made of a synthetic resin material with a guide pin is fitted into the guide hole. The end face formed on the sliding part adheres to the inner end face formed in a part of the guide hole to block the flow of cooling air, and the end face separates from the inner end face to allow the flow of cooling air.

[0003] JP-A-2002-248578, JP-A-2017-006982, JP-A-2017-047469, JP-A-2017-136639

[0004] In the technology described in the above patent documents, no consideration has been given to the contact area of the end face formed on the sliding part made of a synthetic resin material, such as the size of the area and the treatment of minute metal pieces that have entered the contact part. Also, no consideration has been given to minimizing the core deviation and inclination of the guide pin depending on the sliding state of the sliding part. Due to these matters, in the electrodes described in the above patent documents, the service life during which the airtightness of the cooling air can be reliably maintained is short.

[0005] The present invention has been provided to solve the above problems, and aims to increase the surface pressure of the movable end face formed on the sliding part made of a synthetic resin material to eliminate the adverse effects caused by the intrusion of minute metal pieces, and to select the sliding state of the sliding part to substantially eliminate the core deviation and inclination of the guide pin.

[0006] The invention described in claim 1 is characterized in that the electrode body, having a circular cross-section, is made of a metal material such as a copper alloy, a guide pin, having a circular cross-section, protrudes from the end face of the electrode body on which a steel plate component is placed and penetrates a pilot hole in the steel plate component, and is made of a heat-resistant hard material such as a metal or ceramic material, a sliding part, having a circular cross-section, is fitted into a guide hole formed in the electrode body so as to be slidable, and the central part into which the guide pin is inserted is made of a synthetic resin material, the guide hole is composed of a large diameter hole, a medium diameter hole and a small diameter hole, the large diameter part formed in the sliding part is fitted into the large diameter hole so as to be slidable with substantially no gap, the medium diameter part formed in the sliding part is fitted into the medium diameter hole so as to be slidable with substantially no gap, and a ventilation gap is formed between the small diameter hole and the guide pin, through which the guide pin penetrates, allowing cooling air to pass when the guide pin is pushed down. The movable end face formed at the boundary between the medium-diameter and large-diameter sections of the sliding section is configured to be in close contact with the stationary inner end face formed at the boundary between the medium-diameter and large-diameter sections of the guide hole, and the stationary inner end face and the movable end face are positioned on a virtual plane where the central axes of the electrode body intersect perpendicularly, the length in the direction of the central axis of the electrode body in which the medium-diameter section fits into the medium-diameter section is set to be shorter than the length by which the guide pin retracts during welding, a pressing means for pressing the movable end face against the stationary inner end face is placed in the guide hole, and the width dimension of the movable end face when viewed in the diametrical direction of the electrode body is set to be less than half the thickness dimension of the large-diameter section where the guide pin is inserted, thereby reducing the area of ​​the movable end face and increasing the pressure applied by the movable end face to the stationary inner end face, so that minute metal pieces that enter the contact area between the movable end face and the stationary inner end face are pushed from the movable end face into the base material of the sliding section. This is an electric resistance welding electrode characterized in that the width dimension of the movable end face of the electrode body, viewed in the diametrical direction, is set to less than half the thickness dimension of the large-diameter section where the guide pin is inserted, thereby allowing the thickness dimension of the medium-diameter section to be set larger, and thus configured to withstand the external force acting on the guide pin in the diametrical direction of the electrode body.

[0007] The width of the movable end face of the electrode body, viewed in the diametrical direction, is less than half the thickness of the large-diameter section where the guide pin is inserted. Therefore, by reducing the area of ​​the movable end face and increasing the pressure applied to the movable end face against the stationary inner end face, tiny metal fragments that enter the contact area between the movable end face and the stationary inner end face are pushed from the movable end face into the base material of the sliding part.

[0008] As the contact area between the movable end face and the stationary inner end face becomes smaller, the pressure per unit area, i.e., the surface pressure, increases. Therefore, the tiny metal piece that reaches the contact point is sandwiched between the metal surface of the stationary inner end face and the synthetic resin surface of the movable end face, and the metal piece becomes embedded in the soft base material of the sliding part, preventing the formation of a gap between the stationary inner end face and the movable end face.

[0009] When the guide pin is pushed down and the movable end face separates from the stationary inner end face, creating a gap between the two ends, cooling air flows vigorously, and minute metal fragments and carbides are dispersed from the molten area to outside the electrode by the airflow. Normally, this is the dispersion, but during metal melting, minute metal fragments that are forcefully ejected from the molten area due to rapid air expansion may collide with the outer surface of the guide pin, bounce off, and move against the airflow to reach the movable end face. This phenomenon is thought to occur because, when the metal fragments are small, the dynamic pressure of the airflow acting on them is low, making it possible for them to move against the airflow. If such metal fragments adhere to the surface of the movable end face, when the guide pin returns to its standby position, a gap is formed between the stationary inner end face and the movable end face, making it impossible to seal the flow of cooling air. The abnormal behavior of metal fragments described above does not normally occur if the flow of cooling air is maintained properly, but it can occur with a low probability due to some cause as described above.

[0010] However, in the present invention, as described above, the metal piece is embedded in the soft base material of the sliding part, and no gap is formed between the stationary inner end face and the movable end face. Therefore, complete airtightness can be ensured, and economic losses due to air leakage can be avoided. Furthermore, if air leakage continues, noise is generated due to the air ejection, which deteriorates the working environment for workers. However, the environment is improved by maintaining airtightness as described above.

[0011] In other words, by reducing the surface area of ​​the movable end face made of synthetic resin material to increase the surface pressure, and by strongly pressing a minute metal piece against the movable end face, the metal piece is embedded from the movable end face into the base material of the sliding part.

[0012] The width of the movable end face of the electrode body, viewed in the diametrical direction, is set to less than half the thickness of the large-diameter section where the guide pin is inserted. Therefore, the thickness of the medium-diameter section is set to be larger to withstand the external force acting on the guide pin in the diametrical direction of the electrode body.

[0013] The sliding portion has two points, a large-diameter section and a medium-diameter section, that slide against the large-diameter and medium-diameter holes, so the sliding portion, into which the guide pin is integrated, is supported at two points. Therefore, even if an external force acts on the guide pin protruding from the end face of the electrode body in the diametrical direction of the electrode body due to collision with a steel plate component, the amount of tilt displacement of the guide pin or the sliding portion is not substantially problematic. Consequently, the contact between the stationary inner end face and the movable end face is not impaired, and reliable airtightness can be ensured.

[0014] Furthermore, the diameter of the middle section approaches the diameter of the large section, thereby allowing for a larger diameter in the middle section. Simultaneously, the wall thickness of the middle section can also be made as large as possible. Consequently, since the diametrical external force is received by the middle section, which has both increased diameter and wall thickness, elastic deformation in the middle section can be reduced, bringing the tilt displacement of the guide pin and sliding part to a level that is practically negligible. In particular, the reduction in elastic deformation due to the increased diameter is effective. This increase in wall thickness and diameter of the middle section is achieved in correlation with a reduction in the width dimension of the movable end face. In other words, the increase in wall thickness and diameter of the middle section and the increase in surface pressure of the movable end face are achieved simultaneously.

[0015] Although fine irregularities remain on the surface of the movable end face due to machining or injection molding, the increased surface pressure described above causes the protrusions of the irregularities pressed against the stationary inner end face to be flattened, thereby ensuring improved adhesion between the synthetic resin end face and the metal end face.

[0016] The invention described in claim 2 is an electric resistance welding electrode according to claim 1, wherein the ratio of the width dimension of the movable end face to the thickness dimension of the large diameter portion at the location where the guide pin is inserted is less than 0.5 to 0.3 or more.

[0017] If the width dimension of the movable end face is more than half the thickness dimension of the large diameter portion where the guide pin is inserted, i.e., if the above ratio is 0.5 or more, the contact area of ​​the annular movable end face becomes excessive, and the increase in surface pressure and the pressing of the metal piece as described above cannot be satisfactorily achieved. On the upper limit side, less than 0.5 is good. On the other hand, if the above ratio falls below 0.3, the contact area of ​​the movable end face becomes insufficient, the sealing area for the cooling air is insufficient, the sealing action becomes slow, and it is undesirable in terms of maintaining airtightness. On the lower limit side, 0.3 or more is good.

[0018] The invention described in claim 3 is characterized in that the electrode body, having a circular cross-section, is made of a metal material such as a copper alloy, a guide pin, having a circular cross-section, protrudes from the end face of the electrode body on which a steel plate component is placed and penetrates a pilot hole in the steel plate component, and is made of a heat-resistant hard material such as a metal or ceramic material, a sliding part, having a circular cross-section, is fitted into a guide hole formed in the electrode body so as to be slidable, and the sliding part, with the guide pin inserted into its center, is made of a synthetic resin material, the guide hole is composed of a large diameter hole, a medium diameter hole, and a small diameter hole, the large diameter part formed in the sliding part is fitted into the large diameter hole so as to be slidable with substantially no gap, the medium diameter part formed in the sliding part is fitted into the medium diameter hole so as to be slidable with substantially no gap, and a ventilation gap is formed between the small diameter hole and the guide pin, through which the guide pin penetrates, allowing cooling air to pass when the guide pin is pushed down. The movable end face, formed at the boundary between the medium-diameter and large-diameter sections of the sliding part, is configured to be in close contact with the stationary inner end face formed at the boundary between the medium-diameter and large-diameter sections of the guide hole. The stationary inner end face and the movable end face are positioned on a virtual plane where the central axes of the electrode body intersect perpendicularly. The length of the electrode body in the direction of the central axis where the medium-diameter section fits into the medium-diameter section is set to be shorter than the length the guide pin retracts during welding. A pressurizing means for pressing the movable end face against the stationary inner end face is placed inside the guide hole. The width dimension of the movable end face as seen in the diametrical direction of the electrode body is set to be less than half the thickness dimension of the large-diameter section where the guide pin is inserted. By reducing the area of ​​the movable end face and increasing the pressure applied to the stationary inner end face, minute metal fragments that have entered the contact area between the movable end face and the stationary inner end face are pushed from the movable end face into the base material of the sliding part. This method for maintaining airtightness in an electric resistance welding electrode is characterized by setting the width dimension of the movable end face of the electrode body, viewed in the diametrical direction, to less than half the thickness dimension of the large-diameter portion where the guide pin is inserted, thereby increasing the thickness dimension of the medium-diameter portion and allowing the external force acting on the guide pin in the diametrical direction of the electrode body to be received at the medium-diameter portion.

[0019] The effect of the invention for maintaining airtightness is the same as the effect of the electrode for electric resistance welding described above.

[0020] This is a longitudinal cross-sectional view of the entire electrode. This is a cross-sectional view taken along line B-B in Figure 1A. This is a cross-sectional view taken along line C-C in Figure 1A. This is a cross-sectional view taken along line B-B in Figure 1A showing the dimensional relationship between W1 and W3. This is a local longitudinal cross-sectional view showing the dimensional relationship between W1 and W3. This is a cross-sectional view showing the pressed state of the metal piece. This is a partial plan view of the movable end face showing the presence of the metal piece. This is a cross-sectional view showing the state before the metal piece is pressed in. This is a cross-sectional view in the case of a projection bolt.

[0021] Next, embodiments for implementing the electrode for electric resistance welding and the method for maintaining airtightness according to the present invention will be described.

[0022] Figures 1A to 4 show embodiments of the present invention.

[0023] First, let me explain the electrode itself.

[0024] The electrode body 1, made of a conductive metal material such as chromium copper, is cylindrical in shape with a circular cross-section. A fixing part 2, which is inserted into a stationary member 11, and a cap part 4 on which a steel plate component 3 is placed are joined at a threaded part 5 to form the electrode body 1 with a circular cross-section. Guide holes 6 with a circular cross-section are formed in the electrode body 1. These guide holes 6 consist of a large diameter hole 7 formed in the fixing part 2, a medium diameter hole 8 formed in the cap part 4 with a smaller diameter than the large diameter hole 7, and a small diameter hole 9 with a smaller diameter than the medium diameter hole 8. The large diameter hole 7, medium diameter hole 8, and small diameter hole 9 are arranged coaxially aligned on the central axis O-O of the electrode body 1. A small diameter hole 9, which is even smaller in diameter than the medium diameter hole 8, is provided on the central axis O-O.

[0025] A guide pin 12, which has a circular cross-section, protrudes from the end face of the electrode body 1 on which the steel plate component 3 is placed and penetrates the pilot hole 10 of the steel plate component 3. This guide pin is made of a heat-resistant hard material such as stainless steel or ceramic.

[0026] Furthermore, as described later, the sliding portion 13, which has a circular cross-section and moves back and forth in a sliding state relative to the guide hole 6, is made of a heat-resistant insulating synthetic resin material, such as polytetrafluoroethylene [trade name = Teflon (registered trademark)]. Alternatively, a resin with excellent heat resistance and wear resistance can be used from among polyamide resins.

[0027] Next, I will explain the integrated component of the guide pin and the sliding part.

[0028] A guide pin 12 is inserted into the center of the sliding part 13 to integrate the guide pin 12 and the sliding part 13. Various structures can be used to integrate the guide pin 12 with the sliding part 13, such as molding the guide pin 12 together with the sliding part 13 during injection molding, or providing a connecting bolt structure on the guide pin 12.

[0029] This is the latter type of connecting bolt structure.

[0030] Specifically, a bolt 14 is integrally formed with the lower end of the guide pin 12, the bolt 14 passes through the bottom member 15 of the sliding part 13, a washer 16 is assembled, and it is tightened with a lock nut 17. The sliding part 13 performs an insulating function so that when the movable electrode 18, which is paired with the electrode body 1, operates and welding current is supplied, the current flows only from the welding projection 20 of the nut 19 to the steel plate part 3.

[0031] The nut 19 is for projection welding, and has a screw hole 28 formed in the center of its square body, with welding protrusions 20 at the four corners. The open end of the screw hole 28 engages with the tapered portion 21 of the guide pin 12. Because the nut 19 is floating above the steel plate part 3 in this way, a length L1 is left for the guide pin 12 to retract when the movable electrode 18 advances during welding.

[0032] The compression coil spring 22 is fitted between the washer 16 and the inner bottom surface of the guide hole 6, and its tension acts on the sliding part 13. Reference numeral 23 indicates an insulating sheet fitted to the inner bottom surface of the guide hole 6. The tension of the compression coil spring 22 enables the pressurized contact of the movable end surface with the stationary inner end surface, which will be described later. The compression coil spring 22 is a pressurizing means, but it is also possible to use the pressure of compressed air instead.

[0033] Next, we will explain the fitting relationships between each part of the sliding section and each part of the guide hole.

[0034] The sliding portion 13 has a large diameter portion 24 and a medium diameter portion 25, and a guide pin 12 smaller in diameter than the medium diameter portion 25 is integrated into it. The large diameter portion 24 is fitted into the large diameter hole 7 in a state where it can slide with substantially no gap between it and the inner surface of the large diameter hole 7, and the medium diameter portion 25 is fitted into the large diameter hole 8 in a state where it can slide with substantially no gap between it and the inner surface of the medium diameter hole 8. This "state where it can slide with substantially no gap" means that even when a force in the diametrical direction of the electrode body 1 is applied to the sliding portion 13, there is no rattling or loose feeling that would give the impression of a gap, and it is possible to slide in the direction of the central axis O-O. The guide pin 12 protrudes from the end face of the electrode body 1 through the small diameter hole 9, and a ventilation gap 26 is formed between the small diameter hole 9 and the guide pin 12, through which cooling air can pass when the guide pin 12 is pushed down.

[0035] The length of the electrode body in the direction of the central axis O-O, where the medium diameter portion 25 is fitted into the medium diameter hole 8, is set to be shorter than the length by which the guide pin 12 retracts during welding. In this embodiment, a tapered portion 27 is formed on the upper part of the medium diameter portion 25, and the length of the electrode body in the direction of the central axis O-O, where the medium diameter portion 25 is fitted into the medium diameter hole 8, is the length L2 excluding the tapered portion 27. Therefore, the length L2 of the electrode body in the direction of the central axis O-O, where the medium diameter portion 25 is fitted into the medium diameter hole 8, is set to be shorter than the length L1 by which the guide pin 12 retracts during welding. When the guide pin 12 is pushed down, a ventilation gap is first formed between the tapered portion 27 and the medium diameter hole 8.

[0036] Next, we will explain the intermittent structure of the cooling air.

[0037] A vent 29 is formed to guide cooling air into the guide hole 6. To secure an air passage at the sliding point between the large diameter portion 24 and the large diameter hole 7, a groove in the direction of the central axis O-O can be formed on the outer circumferential surface of the large diameter portion 24. However, as shown in Figure 1B, a flat portion 30 in the direction of the central axis O-O is formed on the outer circumferential surface of the large diameter portion 24, and an air passage 31 is formed by the flat portion 30 and the arc-shaped inner surface of the large diameter hole 7. Such flat portions 30 are formed at 90-degree intervals, providing air passages in four locations.

[0038] An annular stationary inner end face 32 is formed at the boundary between the medium-diameter hole 8 and the large-diameter hole 7 of the guide hole 6. In addition, an annular movable end face 33 is formed at the boundary between the medium-diameter portion 25 and the large-diameter portion 24 of the sliding portion 13. The stationary inner end face 32 and the movable end face 33 are arranged on a virtual plane where the central axes O-O of the electrode body 1 intersect perpendicularly, and the movable end face 33 is in close contact with the stationary inner end face 32 in an annular shape due to the tension of the compression coil spring 22, and this close contact seals the cooling air.

[0039] As shown in Figure 2B, the width of the stationary inner end face 32 of the electrode body 1, viewed in the diametrical direction, is large, but the width of the area where the movable end face 33 is in close contact is narrow, and the contact area of ​​the movable end face 33 is small. This contact width is W1, which will be described later.

[0040] Next, we will explain the width dimension of the movable end face.

[0041] The width dimension W1 of the movable end face 33 of the electrode body 1, as viewed in the diametrical direction, is the value obtained by subtracting the thickness dimension W2 of the medium diameter portion 25 from the thickness dimension W3 of the large diameter portion 24, as can be seen in Figure 2A. The thickness dimension W3 is the thickness dimension of the large diameter portion 24 where the guide pin 12 is inserted. The thickness dimension W2 is the thickness dimension of the medium diameter portion 25 where the guide pin 12 is inserted. Since the sliding portion 13 is fitted into the large diameter hole 7 and the medium diameter hole 8, the thickness of the sliding portion 13 is divided into the thickness dimension W3 of the large diameter portion 24 where the guide pin 12 is inserted and the thickness dimension W2 of the medium diameter portion 25 as viewed in the diametrical direction of the electrode body 1.

[0042] Incidentally, as is clear from FIG. 2A and the like, the contact area of the movable end face 33 is reduced by the cross-sectional area of the air passage 31. The reduction in the width dimension W1 of the movable end face 33 caused by the formation of the air passage 31 is determined so as not to impair the sealing of the cooling air. Further, in FIG. 2A, for the sake of clarity, the hatching of the metal cross-section and the texture of the synthetic resin part are not shown.

[0043] Next, the dimensions of each part will be described.

[0044] The dimensions of each part vary depending on the size scale of the electrode. Here, a square projection nut 19 with a length and width of 12 mm each and a thickness of 7.2 mm is electrically resistance welded to a steel plate part 3 with a thickness of 0.7 mm.

[0045] An example of the dimensions of each part of the electrode for welding such a projection nut 19 is as follows: - Diameter dimension of the guide pin 12 = 9.4 mm - Outer dimension of the large diameter part 24 = 17.8 mm - Thickness dimension W3 of the large diameter part at the guide pin insertion position = 4.2 mm - Outer dimension of the middle diameter part 25 = 14.3 mm - Width dimension W1 of the movable end face as seen in the diameter direction of the electrode body = 1.8 mm - Ratio of the width dimension W1 of the movable end face to the thickness dimension W3 of the large diameter part = 0.43 - Length L2 where the middle diameter part 25 fits into the middle diameter hole 8 = 2.4 mm - Length L1 by which the guide pin retreats during welding = 4.4 mm

[0046] The width dimension W1 of the movable end face 33 as seen in the diameter direction of the electrode body 1 is less than half of the thickness dimension W3 of the large diameter part 24 where the guide pin 12 is inserted. Here, the ratio of W1 to W3 is 0.43.

[0047] Next, the behavior of minute metal pieces will be described.

[0048] When the guide pin is pushed down and the movable end face is separated from the stationary inner end face to form a gap between the two end faces, cooling air flows vigorously, and minute metal pieces, carbides, etc. are dissipated from the melting part to the outside of the electrode by the air flow. Usually, such dissipation occurs. However, during metal melting, minute metal pieces that have scattered vigorously from the melting part due to rapid air expansion may collide with the outer peripheral surface of the guide pin, bounce back, move against the air flow, and reach the movable end face. It is considered that such a phenomenon can occur because the dynamic pressure of the air flow acting on the minute metal pieces becomes low due to their small size, enabling them to move against the air flow. When such metal pieces adhere to the surface of the movable end face, when the guide pin returns to the standby position, a gap is formed between the stationary inner end face and the movable end face, and the flow of cooling air cannot be sealed. The abnormal behavior of the metal pieces as described above usually does not occur if the flow of cooling air is maintained soundly, but may occur with a low probability due to some cause as described above.

[0049] The minute metal pieces 34 scattered from the melting part are usually granular with rounded or angular parts having a diameter of about 0.1 to 0.2 mm. When such metal pieces 34 reach the movable end face 33 due to some cause as described above, they stop in a state of adhering to the surface of the movable end face 33. Even when the air flow of the cooling air continues at the time of this stop, it is considered that the metal pieces 34 stop on the surface of the movable end face 33 because, as shown in FIG. 3C, the metal pieces 34 are partially buried or pierced and protrude into the movable end face 33 made of a synthetic resin material.

[0050] When the sliding part 13 is pushed up in the state of FIG. 3C as described above, the movable end face 33 is pressed against the stationary inner end face 32 having a metal surface, and the metal pieces 34 protruding from the movable end face 33 are pushed into the base material of the movable end face 33. That is, since the movable end face 33 side is made of synthetic resin, the metal pieces 34 are relatively buried in the base material of the sliding part 13. Such a buried state is shown in FIG. 3D.

[0051] The seating area of ​​the movable end face 33 is the contact area with the stationary inner end face 32. This area is such that the width dimension of the movable end face 33, viewed in the diametrical direction of the electrode body 1, is less than half the thickness dimension of the large diameter portion 24 where the guide pin 12 is inserted. In this embodiment, the specific value is W1 / W3 = 0.43. By setting it to 0.43, the width dimension of the movable end face 33 is reduced, and the total contact area of ​​the movable end face 33 is set to be small. Consequently, the applied pressure per unit area, i.e., the surface pressure, increases, and the minute metal piece 34 that reaches the contact point is sandwiched between the metal surface of the stationary inner end face 32 and the synthetic resin surface of the movable end face 33. The metal piece 34 becomes embedded in the base material of the soft sliding portion 13, and no gap is formed between the stationary inner end face 32 and the movable end face 33, ensuring reliable airtightness and preventing cooling air leakage.

[0052] When W1 / W3 was set to 0.43, a test was conducted in which nuts were welded to steel plate part 3. As a result, no air leakage occurred even after 100,000 welds, i.e., welding 100,000 nuts. Therefore, it is judged that it can withstand use in automobile body assembly processes, etc. Similar test results were obtained when W1 / W3 was set to 0.45 and 0.48.

[0053] When W1 / W3 exceeds 0.5, the contact area of ​​the movable end face 33 becomes excessive, and the resulting decrease in surface pressure causes insufficient force to push the metal piece 34 from the surface of the movable end face 33 into the base material of the sliding part 13. When such a deficiency occurs, a gap is formed between the movable end face 33 and the stationary inner end face 32 when the guide pin 12 is protruding, causing air leakage. Therefore, it is appropriate to set W1 / W3 to less than 0.5.

[0054] Conversely, by setting W1 / W3 to 0.26 as the lower limit value, the width dimension of the movable end face 33 is significantly reduced, and the total contact area of ​​the movable end face 33 is set to be considerably smaller. Consequently, the pressure applied per unit area, i.e., the surface pressure, increases, and the minute metal piece 34 that reaches the contact point is sandwiched between the stationary inner end face 32, which is a metal surface, and the movable end face 33, which is a synthetic resin material surface, and the metal piece 34 becomes embedded in the base material of the soft sliding part 13.

[0055] However, as the widthwise dimension of the movable end face 33 becomes shorter, the contact width W1 of the movable end face 33 becomes too short, making it difficult to ensure sufficient sealing. Furthermore, when the widthwise dimension of the movable end face 33 becomes shorter, when a large metal piece 34 adheres to the movable end face 33 while traversing its width W1, it was observed that the metal piece 34 was not completely embedded in the surface of the movable end face 33. Even when embedded, it was observed that groove-shaped voids were formed in the widthwise direction of the movable end face 33 due to the deformation of the synthetic resin material during embedding. Due to these phenomena, it was found that even when the movable end face 33 was in close contact with the stationary inner end face 32, air leakage occurred and airtightness could not be maintained.

[0056] When W1 / W3 was set to 0.26 and the nut welding test was performed as described above, air leakage occurred after approximately 25,000 welds. This is thought to be due to the excessive shortening of W1 as described above. Furthermore, unfavorable test results were also obtained when W1 / W3 was set to 0.28.

[0057] On the other hand, when W1 / W3 is 0.3 or greater, the contact area of ​​the movable end face 33 becomes appropriately small, and the resulting increase in surface pressure is judged to provide a sufficient force to push the metal piece 34 from the surface of the movable end face 33 into the base material of the sliding part 13. In addition, the air leakage associated with the excessive shortening of W1 described above was avoided. Therefore, it is appropriate to set W1 / W3 to 0.3 or greater.

[0058] Next, we will explain the cushioning function of the middle diameter section.

[0059] To withstand the diametrical external force acting on the guide pin 12, it is advantageous to increase the diameter and wall thickness of the middle diameter portion 25 as much as possible. The increase in wall thickness and diameter of the middle diameter portion 25 is achieved by making the width dimension W1 of the movable end face 33 less than half the thickness dimension W3 of the large diameter portion 24.

[0060] If the worker's hand slips and the steel plate component 3 collides with the guide pin 12 from the diametrical direction of the electrode body 1, the guide pin 12 will attempt to tilt. However, since the width dimension W1 of the movable end face 33 is set so that the diameter of the middle diameter portion 25 is increased, the force per unit area acting on the cylindrical surface of the middle diameter portion 25 is reduced, and the tilt angle becomes negligible. Furthermore, the reduction in force also reduces the amount of compressive deformation of the middle diameter portion 25, which is effective in reducing the tilt angle.

[0061] Next, I will explain other examples.

[0062] The above example is for a projection nut, but the example shown in Figure 4 is for a projection bolt. The projection bolt 36 consists of a shaft portion 37 with a male thread formed thereon, a circular flange 38 integrated with the shaft portion 37, and a welding projection 39 provided on the lower surface of the flange 38. The guide pin 12 is tubular and hollow, and has a receiving hole 40 into which the shaft portion 37 is inserted. The other components, including parts not shown, are the same as in the previous example, and the same reference numerals are used for components with similar functions.

[0063] Next, the operation of the electrodes described above will be explained.

[0064] Figure 1A shows the state in which the movable end face 33 is in close contact with the stationary inner end face 32 due to the tension of the compression coil spring 22, thereby sealing off the flow of cooling air. If, at this time, a tiny piece of metal 34 is interposed between the movable end face 33 and the stationary inner end face 32, the airtight seal will be maintained by the pushing action described in Figure 3.

[0065] When the movable electrode 18 advances and the gap L1 disappears, the medium-diameter portion 25 that has entered the medium-diameter hole 8 exits the medium-diameter hole 8, forming a passage for cooling air. The cooling air passes through the vent 29, air passage 31, medium-diameter hole 8, and ventilation gap 26, and is released to the outside through the gap between the lower surface of the nut 19 and the steel plate component 3. This airflow removes impurities such as sputter in a direction away from the electrode. When the guide pin 12 is pushed down, an air passage is initially formed by the tapered portion 27. The inclination of the tapered portion 27 forms an air passage with a large flow area in the initial stage, which is suitable for reliable cooling air circulation. Also, when the guide pin 12 returns, the guide function of the tapered portion 27 allows the medium-diameter portion 25 to smoothly enter the medium-diameter hole 8. The same operation is observed in the case of the projection bolt 36 shown in Figure 4.

[0066] The effects and benefits of the embodiments described above are as follows:

[0067] The width dimension W1 of the movable end face 33 of the electrode body 1, as viewed in the diametrical direction, is less than half the thickness dimension W3 of the large diameter portion 24 where the guide pin 12 is inserted. Therefore, by reducing the area of ​​the movable end face 33 and increasing the pressure applied to the stationary inner end face 32, tiny metal fragments 34 that have entered the contact area between the movable end face 33 and the stationary inner end face 32 are pushed from the movable end face 33 into the base material of the sliding portion 13.

[0068] As the contact area of ​​the movable end surface 33 with the stationary inner end surface 32 decreases, the pressure per unit area, i.e., the surface pressure, increases. Therefore, the minute metal piece 34 that reaches the contact point is sandwiched between the metal surface of the stationary inner end surface 32 and the synthetic resin surface of the movable end surface 33, and the metal piece 34 becomes embedded in the soft base material of the sliding part 13, so that no gap is formed between the stationary inner end surface 32 and the movable end surface 33.

[0069] When the guide pin 12 is pushed down and the movable end face 33 separates from the stationary inner end face 32, creating a gap between the two end faces, cooling air flows vigorously, and minute metal fragments 34 and carbides are dispersed from the molten area to outside the electrode by the airflow. Normally, this is the dispersion, but during metal melting, minute metal fragments 34 that are rapidly scattered from the molten area due to the rapid expansion of air may collide with the outer surface of the guide pin 12, bounce off, and move against the airflow to reach the movable end face 33. This phenomenon is thought to occur because, when the metal fragments 34 are small, the dynamic pressure of the airflow acting on them is low, making it possible for them to move against the airflow. If such metal fragments 34 adhere to the surface of the movable end face 33, a gap is formed between the stationary inner end face 32 and the movable end face 33 when the guide pin 12 returns to the standby position, making it impossible to seal the flow of cooling air. The abnormal behavior of the metal piece 34 described above does not normally occur if the circulation of cooling air is maintained properly, but it may occur with a low probability due to some reason as described above.

[0070] However, in this embodiment, as described above, the metal piece 34 is embedded in the base material of the soft sliding part 13, and no gap is formed between the stationary inner end face 32 and the movable end face 33. Therefore, complete airtightness can be ensured, and economic losses due to air leakage can be avoided. Furthermore, if air leakage continues, noise is generated due to the air ejection, which deteriorates the working environment for workers. However, by maintaining airtightness as described above, the environment is improved.

[0071] In other words, by reducing the area of ​​the movable end face 33 made of synthetic resin material to increase the surface pressure, and by strongly pressing the minute metal piece 34 against the movable end face 33, the metal piece 34 is embedded from the movable end face 33 into the base material of the sliding part 13.

[0072] The width dimension W1 of the movable end face 33 of the electrode body 1, as viewed in the diametrical direction, is less than half the thickness dimension W3 of the large-diameter portion 24 where the guide pin 12 is inserted. Therefore, the thickness dimension of the medium-diameter portion 25 is set to be large so that it can withstand the external force acting on the guide pin 12 in the diametrical direction of the electrode body 1.

[0073] Since the sliding portion 13 has two points, the large-diameter portion 24 and the medium-diameter portion 25, that slide against the large-diameter hole 7 and the medium-diameter hole 8, the sliding portion 13, into which the guide pin 12 is integrated, is supported at two points. Therefore, even if an external force acts on the guide pin 12 protruding from the end face of the electrode body 1 in the diametrical direction of the electrode body 1 due to a collision with the steel plate component 3, the amount of tilt displacement of the guide pin 12 and the sliding portion 13 is not substantially problematic. Consequently, the contact between the stationary inner end face 32 and the movable end face 33 is not impaired, and reliable airtightness can be ensured.

[0074] Furthermore, the diameter of the middle diameter section 25 approaches the diameter of the large diameter section 24, thereby allowing the diameter of the middle diameter section 25 to be set larger. At the same time, the wall thickness of the middle diameter section 25 can also be made as large as possible. Therefore, since the diametrical external force is received by the middle diameter section 25, which has both increased diameter and wall thickness, the elastic deformation in the middle diameter section 25 can be reduced, and the tilt displacement of the guide pin 12 and sliding part 13 can be reduced to a level that is practically not a problem. In particular, the reduction in the amount of elastic deformation due to the increase in diameter is effective. This increase in wall thickness and diameter of the middle diameter section 25 is achieved in correlation with reducing the width dimension W1 of the movable end face 33. In other words, the increase in wall thickness and diameter of the middle diameter section 25 and the increase in surface pressure of the movable end face 33 are achieved simultaneously.

[0075] Although fine irregularities remain on the surface of the movable end face 33 due to machining or injection molding, the increased surface pressure described above causes the convex portions of the irregularities pressed against the stationary inner end face 32 to be crushed, thereby ensuring improved adhesion between the synthetic resin end face and the metal end face.

[0076] The ratio of the width dimension W1 of the movable end face 33 to the thickness dimension W3 of the large diameter portion 24 where the guide pin 12 is inserted is set to less than 0.5 and 0.3 or more.

[0077] If the width dimension W1 of the movable end face 33 is more than half the thickness dimension W3 of the large diameter portion 24 where the guide pin 12 is inserted, i.e., if the above ratio is 0.5 or more, the contact area of ​​the annular movable end face 33 becomes excessive, and the increase in surface pressure and the pressing of the metal piece 34 as described above cannot be satisfactorily achieved. On the upper limit side, less than 0.5 is good. On the other hand, if the above ratio falls below 0.3, the contact area of ​​the movable end face 33 becomes insufficient, the sealing area for the cooling air becomes insufficient, the sealing action becomes slow, and it is undesirable in terms of maintaining airtightness. On the lower limit side, 0.3 or more is good.

[0078] A method for maintaining airtightness of an electrode for electric resistance welding is as follows: The electrode body, which has a circular cross-section, is made of a metal material such as a copper alloy; a guide pin, which has a circular cross-section, protrudes from the end face of the electrode body on which a steel plate component is placed and penetrates a pilot hole in the steel plate component, and is made of a heat-resistant hard material such as a metal or ceramic material; the guide pin is fitted into a guide hole formed in the electrode body so as to be able to slide, and a sliding part, which has a circular cross-section and into which the guide pin is inserted, is made of a synthetic resin material; the guide hole is made of a large diameter hole, a medium diameter hole and a small diameter hole; the large diameter part formed in the sliding part is fitted into the large diameter hole so as to be able to slide with substantially no gap; the medium diameter part formed in the sliding part is fitted into the medium diameter hole so as to be able to slide with substantially no gap; and a ventilation gap is formed between the small diameter hole and the guide pin by the guide pin that penetrates the small diameter hole, allowing cooling air to pass through when the guide pin is pushed down. The movable end face, formed at the boundary between the medium-diameter and large-diameter sections of the sliding part, is configured to be in close contact with the stationary inner end face formed at the boundary between the medium-diameter and large-diameter sections of the guide hole. The stationary inner end face and the movable end face are positioned on a virtual plane where the central axes of the electrode body intersect perpendicularly. The length of the electrode body in the direction of the central axis where the medium-diameter section fits into the medium-diameter section is set to be shorter than the length the guide pin retracts during welding. A pressurizing means for pressing the movable end face against the stationary inner end face is placed inside the guide hole. The width dimension of the movable end face as seen in the diametrical direction of the electrode body is set to be less than half the thickness dimension of the large-diameter section where the guide pin is inserted. By reducing the area of ​​the movable end face and increasing the pressure applied to the stationary inner end face, minute metal fragments that have entered the contact area between the movable end face and the stationary inner end face are pushed from the movable end face into the base material of the sliding part. The width of the movable end face of the electrode body, viewed in the diametrical direction, is set to less than half the thickness of the large-diameter section where the guide pin is inserted. This allows the thickness of the medium-diameter section to be set larger, thereby absorbing the external force acting on the guide pin in the diametrical direction of the electrode body at the medium-diameter section.

[0079] The effect of the example of the airtightness maintenance method is the same as the effect of the electrode for electric resistance welding described above.

[0080] As described above, the electrode and airtightness maintenance method of the present invention increase the surface pressure of the movable end face formed on the sliding part made of synthetic resin material, eliminating the problems caused by the intervention of minute metal fragments, and substantially eliminating misalignment and tilt of the guide pin by selecting the sliding state of the sliding part. Therefore, it can be used in a wide range of industrial fields, such as automobile body welding processes and sheet metal welding processes for household electrical appliances. Explanation of symbols

[0081] 1 Electrode body 6 Guide hole 7 Large diameter hole 8 Medium diameter hole 9 Small diameter hole 12 Guide pin 13 Sliding part 18 Movable electrode 19 Projection nut 24 Large diameter part 25 Medium diameter part 26 Ventilation gap 29 Ventilation opening 31 Air passage 32 Stationary inner end face 33 Movable end face 34 Metal piece 36 Projection bolt 40 Receiving hole W1 Width dimension of movable end face W2 Thickness dimension of medium diameter part W3 Thickness dimension of large diameter part L1 Retraction length of guide pin L2 Insertion length of medium diameter part

Claims

1. The electrical resistance welding electrode consists of: the main body of the electrode, which has a circular cross-section and is made of metallic material such as copper; a guide pin, which also has a circular cross-section, protruding from the end surface of the main body of the electrode, where the steel plate component is positioned, which is inserted through the guide hole of the steel plate component, and is made of a heat-resistant hard material such as metal or ceramic; and a sliding part, which has a circular cross-section, that fits snugly into the guide hole formed in the main body of the electrode in a sliding state, with a central area where the guide pin is inserted, and is made of synthetic resin material, where the guide holes are composed of large diameter, medium diameter, and small diameter holes.The large-diameter section formed in the slide fits snugly into the large-diameter hole in a significantly sliding condition with no gaps. The medium-diameter section formed in the slide fits snugly into the medium-diameter hole in a significantly sliding condition with no gaps. A ventilation gap through which cooling air passes is formed between the small-diameter hole and the guide pin. When the guide pin is pushed down by the guide pin, which then inserts through the small-diameter hole, the movable end surface formed at the boundary between the medium-diameter and large-diameter sections of the slide is shaped into close contact with the stationary inner end surface formed at the boundary between the medium-diameter and large-diameter holes of the guide hole.The stationary inner end surface and the movable end surface are positioned on a virtual plane where the center axis of the electrode's main body intersects perpendicularly. The length in the direction of the center axis of the electrode's main body where the medium-diameter section is fitted into the medium-diameter hole is set shorter than the length to which the guide pin moves backward during welding. The pressure unit that presses the movable end surface against the stationary inner end surface is positioned in the guide hole with the width of the movable end surface visible in the diameter direction of the electrode's main body less than half the thickness of the large-diameter section at the position where the guide pin is inserted. The area of ​​the movable end surface is shaped to be smaller to increase the pressure applied by the movable end surface against the stationary inner end surface.and a small metal piece which will pass into the close contact position of the movable end surface and the stationary inner end surface will be pushed from the movable end surface into the base material of the sliding part, and by the width of the movable end surface visible in the diameter direction of the main body of the electrode which is less than half the thickness of the large diameter section at the position where the guide pin is inserted, the thickness of the medium diameter section is shaped to be large enough to withstand the external force acting on the guide pin in the diameter direction of the main body of the electrode.

2. Electrical resistance welding electrodes according to claim 1, where the ratio of the width of the movable end surface to the thickness of the large diameter section at the position where the guide pin is inserted is less than 0.5 and greater than or equal to 0.3.

3. Methods for maintaining the hermetically sealed electrical resistance welding electrodes,The assembly method involves: forming the main body of the electrode, which has a circular cross-section, using a metallic material such as copper; forming the guide pin, which also has a circular cross-section, protruding from the end surface of the main body of the electrode, where the steel plate component is positioned, and which is inserted through the pilot hole of the steel plate component by a heat-resistant, hard material such as metal or ceramic; and forming the sliding section, which has a circular cross-section, to fit snugly into the guide hole formed in the main body of the electrode in a sliding state, with a central area where the guide pin is inserted, using a synthetic resin material, where the guide holes are formed from large-diameter holes and medium-diameter holes.The small-diameter hole and the large-diameter section formed in the sliding part are fitted snugly into the large-diameter hole in a state of significant sliding with no gaps. The medium-diameter section formed in the sliding part is fitted snugly into the medium-diameter hole in a state of significant sliding with no gaps. A ventilation gap through which cooling air passes is formed between the small-diameter hole and the guide pin. When the guide pin is pushed down by the guide pin, which will insert through the small-diameter hole, the movable end surface formed at the boundary between the medium-diameter and large-diameter sections of the sliding part is shaped to be in close contact with the stationary inner end surface formed at the boundary between the medium-diameter hole and the large-diameter hole of the guide hole.The stationary inner end surface and the movable end surface are positioned on a virtual plane where the center axes of the electrode's main body intersect perpendicularly. The length in the direction of the center axis of the electrode's main body where the medium-diameter section fits into the medium-diameter hole is set shorter than the length that the guide pin moves backward during welding. The pressure unit that presses the movable end surface against the stationary inner end surface is positioned in the guide hole. The visible width of the movable end surface in the diameter direction of the electrode's main body is less than half the thickness of the large-diameter section at the position where the guide pin is inserted. The area of ​​the movable end surface is shaped to be smaller to maximize the pressure applied by the movable end surface against the stationary inner end surface.And a small metal piece will pass into the close contact position of the movable end surface, and the stationary inner end surface will be pushed from the movable end surface into the base material of the sliding section, and by the width of the movable end surface visible in the diameter direction of the main body of the electrode being less than half the thickness of the large-diameter section at the position where the guide pin is inserted, the thickness of the medium-diameter section will be shaped to be large enough to withstand the external force that will be acted on the guide pin in the diameter direction of the main body of the electrode by the medium-diameter section;