JP2012011398A - Resistance welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance welding method capable of forming a suitable welding part by preventing occurrence of welding defects irrespective of types of sheet assemblies.SOLUTION: When forming a welding part 70 by allowing a plurality of electrodes to contact with a plurality of mutually overlapped metal sheets (for example two sheets) 50, 60 and energizing them, a welding electrode 20 supplying electric current enough to form the welding part 70 at the metal sheet 50 by contacting with the one metal sheet 50 and a first energization electrode 30 and a second energization electrode 40 for achieving energization between themselves and the welding electrode 20 by contacting with the respective different metal sheets 50, 60 are used as the plurality of the electrodes. Both the energization electrodes 30, 40 are energized between themselves and the welding electrode 20, so that the electric current supplied from the welding electrode 20 to the one metal sheet 50 is divided to the first energization electrode 30 to the second energization electrode 40.

Description

  The present invention relates to a resistance welding method.

  In recent years, in the welding process of automobile parts, series welding and indirect welding tend to be used instead of direct welding for the purpose of improving productivity and versatility.

  Here, as an example of series welding, for example, as shown in FIG. 7, the stacked steel plates 150 and 160 are pressed from one direction with a pair of electrodes 110 and 120 arranged on one steel plate 150 side. There is one that energizes and obtains a spot-like weld (for example, see Patent Document 1 below). This type of welding method can be welded at multiple points simultaneously using a large number of electrodes, and the speed of welding can be increased. Therefore, this type of welding method is being suitably used for welding body panels of automobiles.

  Indirect welding, as shown in FIG. 8, the welding electrode 110 is pressed against the overlapping portion of the steel plates 150 and 160, and the current collecting electrode 130 is placed at the position away from the overlapping portion on the other side. By energizing the steel plate 160 in contact with the steel plate 160, a spot-like welded portion is formed in the overlapped portion (see, for example, Patent Document 2 below). Therefore, it tends to be preferably used when it is not desired to leave an indentation on the surface of the other steel plate 160 or when a pair of electrodes cannot be disposed so as to sandwich the overlapping portion of the steel plates 150 and 160.

Japanese Patent Laid-Open No. 11-333569 JP 2007-14968 A

  By the way, in the above series welding, the resistance heat generated at the contact point between one steel plate 150 and the electrodes 110 and 120 is transmitted to the contact portion between the steel plates 150 and 160, so that the welded portion is melt-formed at the contact portion. Therefore, usually, a predetermined temperature gradient is generated along the thickness direction of one of the steel plates 150 on the electrode 110, 120 side. In this case, in order to obtain a sufficiently large welded portion (so-called nugget) at the contact portion between the steel plates 150 and 160, a corresponding energization amount is necessary. Since the resistance heat generation at the contact points 110 and 120 becomes excessive, there is a problem in that one of the steel plates 150 is liable to generate a plate breakage due to overheating or a melting damage called dust.

  For example, in Patent Document 1, in order to solve this type of problem, the applied current at the initial stage of welding is applied to 1.5 times or more of the subsequent steady current, and one steel plate 150 of the electrodes 110 and 120 at the initial stage of welding. Measures are taken such that the pressure applied to is 1.1 times or more of the subsequent steady pressure. However, this type of countermeasure is effective only in the case of a limited board assembly, and this type of countermeasure is not sufficient in today's diversified board assembly. In other words, in plate assemblies used for recent welding, for the purpose of achieving both functional and cost aspects, diversification of such plate assemblies, such as plate assemblies with different plate thicknesses and plates made of different materials, has progressed. There is a real situation. Therefore, for example, if the steel plate (one steel plate 150) on which the pair of electrodes 110 and 120 is disposed is relatively thin or formed of a material that is highly sensitive to melting damage, the above countermeasure is taken. Even if it is taken, there is a risk of poor welding.

  On the other hand, as described above, indirect welding energizes between the welding electrode 110 installed on one steel plate 150 side and the current collecting electrode 130 (earth electrode) installed on the other steel plate 160 side. Thus, a welded portion is formed at a position corresponding to a position directly below the welding electrode 110 in the overlapped portion of the steel plates 150, 160. Depending on the state of the plate assembly, a gap may be formed between the overlapped portions of the steel plates 150, 160. (Plate gap) may be generated, and there may be a case where the energization path between the welding electrode 110 and the current collecting electrode 130 cannot be secured. In this case, since a sufficient current does not flow directly under the welding electrode 110, an effective welded portion may not be formed.

  Here, for example, in Patent Document 2 above, as shown in FIGS. 9A and 9B, the pair of preliminary electrodes 140 and 140 are first energized in the vicinity of the planned welding position. After making the contact state between the steel plates 150 and 160 good, a technique is described in which a welding electrode 110 serving as a main electrode is brought into contact with a planned welding position and a welding current (current that can be welded) is supplied to the position. Has been. Therefore, if this method is used, it seems that proper welding can be performed in a state in which the gap is filled by the preliminary energization performed first. However, in this type of welding method, even if the welding method utilizing the pre-energization is employed, if the heat input sufficient to form a welded portion between the steel plates 150 and 160 is attempted, However, depending on the type of plate assembly, the above-mentioned plate breakage, melting damage, etc. may occur in the other steel plate 160.

  In view of the above circumstances, the technical problem to be solved by the present invention is to provide a resistance welding method capable of preventing the occurrence of welding failure and forming an appropriate welded portion regardless of the type of plate assembly. Let it be an issue.

  The solution to the above problem is achieved by the resistance welding method according to the present invention. That is, this welding method is a resistance welding method in which a plurality of electrodes are brought into contact with each other and a plurality of electrodes are brought into contact with each other and energized to form a welded portion. Among the plates, a welding electrode to be brought into contact with the outermost metal plate, a first current-carrying electrode to be in contact with the welding electrode in contact with the outermost metal plate, and a plurality of sheets Among the metal plates, a second current-carrying electrode for contacting the welding electrode with the metal plate on the backmost side is used, and both the current-carrying electrodes are connected to the welding electrode. It is characterized in that the current supplied from the welding electrode to the outermost metal plate is shunted to the first energizing electrode and the second energizing electrode. In addition, the metal plate on the outermost surface side and the outermost surface side is a metal plate located at both ends in the thickness direction among the plurality of metal plates, and is intended to limit the usage mode of the welded metal plate. Absent.

  As described above, the present invention provides a novel and original welding method that actively utilizes the shunted state of welding current that has been avoided in the past for the formation of an appropriate welded portion. That is, in the conventional welding process, energization between the electrodes is performed on the premise that all of the current supplied from the welding electrode to the metal plate is used without loss for resistance heating for forming the welded portion. On the other hand, the present invention has a technical feature that a current shunting state is positively generated in a plurality of metal plates by using two energizing electrodes. Therefore, according to this method, among the currents supplied from the welding electrode to the outermost metal plate, the current related to one shunt flows directly through the outermost metal plate toward the first energizing electrode. At the same time, the current related to the other shunt flows through the contact portion between the metal plates and is supplied to the metal plate on the backmost side. In this case, the current flowing from the welding electrode to the first energizing electrode is mainly used for resistance heating between the welding electrode and the outermost metal plate, and the current flowing to the second energizing electrode. Is mainly used for resistance heat generation at the contact portion between the metal plates located directly under the welding electrode. Therefore, the amount of current used for resistance heating between the metal plates is prevented as much as possible by preventing the occurrence of current loss due to unexpected (undesired) shunting, etc. by actively carrying out the shunt current. Can be adjusted. As a result, the temperature distribution in the thickness direction in the metal plate generated by the resistance heating at the two locations can be controlled to some extent, and for example, it is possible to energize so that the temperature at the contact portion between the metal plates is maximized. Become. Therefore, it is possible to bring about effective resistance heat generation at the contact portion between the metal plates while avoiding as much as possible the occurrence of welding failure such as melting damage on each metal plate, and thereby the contact portion or An appropriate welded portion can be efficiently formed in the vicinity thereof.

  In this case, a diversion ratio control means for controlling the ratio of the amount of current flowing to each energization electrode during diversion energization may be used. Specifically, the method etc. which electrically connect a variable resistance part to one or both of the electrode for 1st and 2nd electricity supply can be illustrated. In this way, by adjusting the resistance of the energization path including at least one of the energization electrodes, the ratio of the amount of current flowing to each energization electrode, that is, the shunt ratio is relatively changed. By appropriately adjusting the thickness, the diversion ratio can be controlled. Therefore, it is possible to control the temperature distribution in the plate thickness direction within the metal plate by controlling the diversion ratio according to the type of plate assembly, and to form a weld at or near the contact portion between the metal plates. Become.

  In addition, when forming a welded portion at a plurality of points on a plurality of metal plates, the first energizing electrode is made a welding electrode rather than the welded portion closest to the welding electrode among the already formed welded portions. The metal plate on the outermost surface side may be brought into contact with the close position, and diversion energization may be performed at this contact position. For example, as shown in FIG. 6, when the welded portion 70 has already been formed in the vicinity of the position where the welded portion is to be formed (the planned welding position 70 ′), the upper and lower metal plates (steel plates 50, 60). Even if the current-carrying electrodes 30 and 40 are respectively installed in the above-mentioned currents, the first current-carrying electrode 30 is formed first depending on the location of the first current-carrying electrode 30 (for example, the position indicated by the one-dot chain line in FIG. The welded portion 70 may cause an unexpected diversion, which may lead to a situation in which the welding current cannot be supplied to a position where welding should be performed (the planned welding position 70 ′). On the other hand, as described above, if the first energizing electrode 30 is installed at a position closer to the welding electrode 20 than the existing welding portion 70 (position indicated by a solid line in FIG. 6), the current flows. A predetermined amount of current can flow toward the first and second energization electrodes without causing loss of quantity or disturbance of the diversion ratio. Therefore, even when the resistance welding is performed at a plurality of points, the welding operation can always be performed under a certain condition, and it is possible to form a stable quality welded portion.

  In this case, the first energizing electrode may be brought into contact with the outermost metal plate around the welding electrode. For example, as shown in FIG. 6, when the first energizing electrode 30 is arranged side by side on the welding electrode 20 and the outermost metal plate (one metal plate 50) side, the direction indicated by the alternate long and short dash line in FIG. Since a current flow occurs in one metal plate 50, there is a problem that the heat generation region of the welding electrode 20 is inevitably biased toward the first energizing electrode 30. In contrast, if the first energizing electrode is arranged around the welding electrode as described above, the current density between the welding electrode and the first energizing electrode can be evenly distributed in the circumferential direction. Yes (see FIG. 2 below). In this case, since the heat generation amount at the contact portion between the welding electrode and the metal plate is not so large, the temperature distribution at the contact portion can be made uniform in the circumferential direction. Therefore, even when welding a metal plate that requires a relatively high welding temperature, it is possible to form an appropriate welded portion without causing welding defects such as cracks in the outermost metal plate. It becomes.

  In addition, the resistance welding method according to the present invention allows a current to flow between these electrodes in a state in which the welding electrode and the first current-carrying electrode are pressed against the outermost metal plate as a pre-process of shunting current. Thus, the method may include a step of closing gaps between the plurality of metal plates. By providing such a pre-process, a good contact state is formed between the metal plates at the site to be welded, and at the same time, the energization between the second energization electrode and the welding electrode, and thus the diversion energization is automatically and Started continuously. Therefore, it is possible to reduce the cycle time required for a series of welding operations by reducing the trouble of changing the movement operation and energization operation of these electrodes in the middle, and to reduce the power consumption at that time and improve the productivity. it can.

  As described above, according to the resistance welding method according to the present invention, it is possible to provide a resistance welding method capable of preventing the occurrence of welding failure and forming an appropriate welded portion regardless of the type of plate assembly. Can do.

It is principal part sectional drawing for demonstrating the whole structure of the resistance welding method which concerns on one Embodiment of this invention. It is principal part sectional drawing for demonstrating the preliminary | backup energization process used as the pre-process of a shunt energization process. It is principal part sectional drawing for demonstrating a shunt electric current supply process. It is a principal part expanded sectional view for demonstrating the resistance heating state at the time of shunt energization. It is the graph which represented typically the temperature distribution in the plate | board thickness direction inside a metal plate shown in FIG. It is principal part sectional drawing for demonstrating the energization state in the case of forming a welding part in two or more points with respect to two metal plates with the resistance welding method which concerns on this invention. It is principal part sectional drawing for demonstrating the series welding method which is the conventional resistance welding method. It is principal part sectional drawing for demonstrating one indirect welding method which is the conventional resistance welding method. It is principal part sectional drawing for demonstrating the other indirect welding method which is the conventional resistance welding method, Comprising: (a) is principal part sectional drawing at the time of electricity supply by a preliminary electrode, (b) is at the time of electricity supply by a main electrode FIG.

  Hereinafter, an embodiment of a resistance welding method according to the present invention will be described with reference to the drawings. In this embodiment, a case where two steel plates to be a body panel of an automobile are to be welded will be described as an example. In the following description, the vertical direction is simply referred to as the vertical direction unless otherwise specified.

  FIG. 1 shows a resistance welding apparatus 10 for carrying out a resistance welding method according to an embodiment of the present invention. As shown in the figure, this resistance welding apparatus 10 includes a plurality of electrodes 20, 30, and 40, and a plurality of metal plates (two steel plates 50 and 60 in the illustrated example) overlapped with each other. This is an apparatus for forming a welded portion 70 (see FIG. 4 described later) between the steel plates 50 and 60 by bringing the plurality of electrodes 20, 30 and 40 into contact with each other and energizing them. Here, the plurality of electrodes 20, 30, 40 are brought into contact with the outermost metal plate (one steel plate 50 in the illustrated example) to supply a predetermined amount of current, and one steel plate 50. And the first electrode 30 for energization with the welding electrode 20 and the metal plate on the back side (the other steel plate 60 in the illustrated example) and the welding electrode 20. It consists of the electrode 40 for the 2nd electricity supply for energizing between.

  Among these, the front-end | tip part 21 of the electrode 20 for welding is exhibiting what is called a taper shape where an outer diameter becomes small gradually as it goes to the front end side (downward). In the illustrated example, the distal end portion 21 is composed of a flat surface formed at the top and a conical surface with an outer diameter gradually increasing from the flat surface toward the base end side (upward), as shown in FIG. Has been. In addition, the magnitude | size of the vertex angle of a conical surface is arbitrary, for example, is set in the range of 100 degree | times or more and 170 degrees or less.

  The first current-carrying electrode 30, together with the welding electrode 20, has its tip 31 directed toward the upper surface 51 of one steel plate 50, and the tip 31 is moved to the upper surface 51 by relative movement in the axial direction. It can be pressed. Further, in this embodiment, the first energizing electrode 30 has a cylindrical shape, and constitutes a so-called coaxial electrode together with the welding electrode 20 disposed on the inner periphery thereof. In this case, the distal end portion 31 of the first energizing electrode 30 has a shape that gradually decreases in thickness toward the distal end side (downward). In this illustrated example, as shown in FIG. It has an arc shape that bulges downward in the axial section. Further, as shown in FIGS. 1 and 2, the first energizing electrode 30 has a plurality of cutout portions 32 extending from the distal end portion 31 toward the proximal end side (upward) at equal intervals in the circumferential direction (see FIG. In the example shown, it is formed at 6 locations).

  Although not shown in the figure, the first energizing electrode 30 is provided with an axial direction moving means composed of, for example, a spring or a cylinder so that it can move in the axial direction independently of the welding electrode 20. It is configured. The welding electrode 20 is also provided with the same axial movement means, and can be moved in the axial direction independently of the first energization electrode 30. In this embodiment, in a state where no axial force is received (the state where the steel plate 50, 60 is not pressed), the tip 21 of the welding electrode 20 is disposed around the periphery as shown in FIG. The first energization electrode 30 is set so as to be one level lower than the tip 31 (position close to one steel plate 50).

  The second current-carrying electrode 40 is a so-called ground electrode and has a sufficiently large contact area so that the resistance heat generation at the contact portion with the other steel plate 60 does not cause a problem. . In this illustrated example, the contact surface 41 of the second energizing electrode 40 is overlapped with one steel plate 50 among the upper surface 61 of the other steel plate 60 (the surface facing the lower surface 52 of one steel plate 50). It is made to contact the area | region remove | deviated from the fitting part.

  The welding electrode 20 and the current-carrying electrodes 30 and 40 are electrically connected to each other. Specifically, the welding electrode 20 and the first energizing electrode 30 are connected to a power source 80. The second energizing electrode 40 is connected to the power source 80 via the first energizing electrode 30. Further, in this embodiment, a variable resistor 90 as a diversion ratio control means described later is disposed between the first energizing electrode 30 and the second energizing electrode 40.

  Hereinafter, an example of the resistance welding method according to the present invention using the resistance welding apparatus 10 having the above configuration will be described. In this embodiment, the steel plate in the central axis direction of the welding electrode 20 and the first energizing electrode 30 as coaxial electrodes and the contact portion between the tip portions 21 and 31 of the electrodes 20 and 30 and one steel plate 50 are used. Each electrode 20 and 30 shall be arrange | positioned and moved so that 50 normal line direction (thickness direction) may correspond.

  First, from the state shown in FIG. 1, the welding electrode 20 and the first energizing electrode 30 are lowered, and the respective tip portions 21 and 31 are pressed against the upper surface 51 of one steel plate 50 with a predetermined pressure. Then, the electrodes 20 and 30 are energized while the tip portions 21 and 31 are in contact with one steel plate 50. As a result, as shown in FIG. 2, the welding electrode 20, one steel plate 50, the first energizing electrode 30, and the power source 80 are electrically connected, and a first closed loop circuit having these electrical elements is formed. The By applying pressure and energizing in this way, resistance heat is generated in the contact portion of the one steel plate 50 with the welding electrode 20, and the contact portion and its peripheral region are softened by this resistance heat generation. Thereby, the softening part of one steel plate 50 begins to deform | transform toward the other steel plate 60 which opposes. At this stage, the amount of current to be passed between the welding electrode 20 and the first current-carrying electrode 30 is set to such a size that a welded portion 70 described later can be formed between the pair of steel plates 50 and 60. Alternatively, on the premise that the energization amount is increased in the energization process thereafter, the size may be suppressed to such a level that the welded portion 70 is not formed.

  And by continuing the said pressurization energization for a predetermined period, as shown in FIG. 3, the softened part is pushed toward the other steel plate 60 which opposes, and the upper surface of the other steel plate 60 is shown. 61 is contacted. Thereby, a gap (plate gap) between both the steel plates 50 and 60 is filled, and the both steel plates 50 and 60 are electrically connected. Therefore, in this stage, in addition to the first closed loop circuit described above, the welding electrode 20, one steel plate 50, the other steel plate 60, the second energizing electrode 40, the variable resistor 90, and the first energizing electrode 30 are provided. Are electrically connected to form a second closed loop circuit having these electrical elements. And by forming two closed loop circuits in this way, the welding current A supplied to the one steel plate 50 from the welding electrode 20 (current having a magnitude capable of forming the welded portion 70 between the steel plates 50, 60). Part flows toward the first energizing electrode 30 that is in contact with the periphery of the welding electrode 20 (a flow indicated by a one-dot chain line in FIG. 3), and the remaining part is in contact with one steel plate 50 and the other steel plate 60. It flows into the other steel plate 60 through the portion, and flows toward the second energizing electrode 40 in contact with the upper surface 61 of this steel plate 60 (a flow indicated by a two-dot chain line in FIG. 3).

FIG. 4 schematically shows the heat generation state (temperature distribution) inside the steel plates 50 and 60 when the shunt current is applied between the welding electrode 20 and the current-carrying electrodes 30 and 40 in this way. . In the figure, the darker portions (the hatched portions) have a greater amount of heat generation, that is, a higher temperature. Here, the current (first shunt) A ₁ flowing from the welding electrode 20 to the first energizing electrode 30 is mainly used for resistance heating between the welding electrode 20 and one of the steel plates 50, and the second The current (second shunt) A ₂ flowing to the energizing electrode 40 is mainly used for resistance heat generation at the contact portion between the steel plates 50 and 60 located immediately below the welding electrode 20, and is shown in FIG. Thus, the highest temperature distribution is shown in the contact part between both the steel plates 50 and 60. FIG. Of the contact portion between the welding electrode 20 and one of the steel plates 50, the periphery of the tip portion 21 that is close to the first energizing electrode 30 (in this embodiment, the conical surface of the tip portion 21 and the steel plate 50). Even the contact portion) shows a high temperature distribution.

Here, the degree of contribution to the temperature distribution shown in FIG. 4 for each of the diversions A ₁ and A ₂ can be described using, for example, the graph shown in FIG. The vertical axis of the graph shows the plate thickness direction position (depth from the reference point) when the center contact portion between the welding electrode 20 and one steel plate 50 is used as the reference (zero point). In the graph, the broken line indicates the distribution of resistance heat generated by the shunt A ₁ , and the alternate long and short dash line indicates the distribution of resistance heat generated by the shunt A ₂ , and the solid lines indicate the steel plates 50 and 60 based on the distribution of resistance heat generated. The internal temperature gradient is shown. Thus, the diversion A ₁ to contribute resistance heating is mainly first current-carrying electrode 30 to the temperature rise of the steel sheet 50 and 60, when the majority in the shunt A ₂ to the second current-carrying electrodes 40 When considering, the temperature gradient inside the steel plates 50 and 60 can be considered as the sum of the resistance heat generation by the above-mentioned split flow A ₁ and the resistance heat generation by the split flow A ₂ . Therefore, by carrying out the diversion energization as described above, the resistance heat generated by the diversions A ₁ and A ₂ is dispersed in the central portion and the surface portion in the plate thickness direction. Further, the magnitudes (current amounts) of the shunts A ₁ and A ₂ at this time can be easily changed by adjusting the resistance in each closed loop circuit as described above. For example, by reducing the amount of current of the shunt A ₁ flowing through the first energization electrode 30, the resistance heat generation distribution of A ₁ shown in FIG. 5 is shifted in the direction of overall reduction (left side in FIG. 5). Accordingly, since the amount of current of the shunt A ₂ flowing through the second energizing electrode 40 is increased, the resistance heating distribution of A ₂ shown in FIG. Right). In this case, since the peak temperature position of the steel plates 50 and 60 moves from X ₁ to X ₂ , for example, when the contact portion between both the steel plates 50 and 60 is in the vicinity of the position X ₂ , as described above. By adjusting the diversion ratio, it is possible to bring the peak temperature to an appropriate depth position. Therefore, effective resistance heat generation is brought about at the contact portion between the steel plates 50 and 60 while avoiding as much as possible the occurrence of welding failure such as melting damage due to local overheating to the steel plates 50 and 60. Thus, it is possible to efficiently form the weld portion 70 having an appropriate size at or near the contact portion. In addition, as described above, the pressurization energization of the welding electrode 20 and the first energization electrode 30 automatically switches to the diversion energization using both the energization electrodes 30 and 40, so that a short work is required. A series of welding operations can be performed efficiently in time. Therefore, it is suitable also in terms of productivity.

In this embodiment, the first current-carrying electrode 30 having a cylindrical shape and gradually tapering as the distal end portion 31 moves toward the distal end side is used, and this is used for welding that has a substantially axial shape. Since it is disposed on the outer periphery of the electrode 20, the diversion A ₁ is uniformly generated from the welding electrode 20 toward the first energization electrode 30 over the entire periphery. As a result, the current density of the shunt A ₁ is evenly distributed in the circumferential direction, so that the resistance heat generation at the contact portion between the welding electrode 20 and one of the steel plates 50 and the temperature distribution can be made substantially uniform. Therefore, even when a metal plate of a type that requires a relatively high welding temperature is welded, it is not necessary to cause a welding failure such as a crack in one of the steel plates 50.

Regarding the adjustment of the diversion ratio, in this embodiment, the variable resistor 90 is installed between the first energization electrode 30 and the second energization electrode 40 as the diversion ratio control means. Thus, by appropriately adjusting the value of the variable resistor 90 included in the second closed loop circuit in accordance with the plate assembly of the steel plates 50 and 60, the ratio of the amount of current flowing through each closed loop circuit, that is, the shunt ratio Since A ₂ / A ₁ can be controlled, the welded portion 70 can always be formed at or near the contact portion between the steel plates 50 and 60 regardless of the type of plate assembly.

  As mentioned above, although one embodiment of the resistance welding method according to the present invention has been described, the resistance welding method and the resistance welding apparatus used in this method are not limited to the above-described embodiments, and are arbitrary within the scope of the present invention. It is possible to take the form.

  For example, regarding the shape of the first energizing electrode 30, the above embodiment has described the case of using a cylindrical shape as a whole and the tip portion 31 having a tapered shape. Of course, it has other shapes. It is also possible to use an electrode as the first energizing electrode 30. For example, like the second energizing electrode 40 in the above embodiment, an electrode having a shape with a sufficiently large contact area so that the resistance heat generation at the contact portion with the metal plate does not cause a problem. It can also be used as the first energizing electrode 30. FIG. 6 shows an example thereof. In this illustrated example, an electrode having the same shape as the second energizing electrode 40 is used as the first energizing electrode 30. Even in this case, the first energizing electrode 30 is brought into contact with one steel plate 50 to energize with the welding electrode 20, and the second energizing electrode 40 is brought into contact with the other steel plate 60. By energizing between the welding electrode 20, the current supplied from the welding electrode 20 to the one steel plate 50 can be divided into the first energizing electrode 30 and the second energizing electrode 40. . Therefore, while avoiding the occurrence of poor welding as much as possible, effective resistance heat is generated in the contact portion between the steel plates 50 and 60, and the contact portion or the vicinity thereof has an appropriate size. The welding part 70 can be formed efficiently.

  When the electrode having the shape as shown in the illustrated example is used for the first energizing electrode 30, it is not always necessary to dispose the first energizing electrode 30 around the welding electrode 20. For example, one point in FIG. When arranged at a position indicated by a chain line, the current flow from the welding electrode 20 to the first energizing electrode 30 through one steel plate 50 may be disturbed by the weld 70 that has already been formed. There is. Therefore, as shown in FIG. 6, when forming the welded portion 70 at a plurality of points on the two steel plates 50, 60, the first energizing electrode 30 is used for welding among the welded portions 70 that have already been formed. It is made to contact with one steel plate 50 at a position closer to the welding electrode 20 than the welding portion 70 closest to the electrode 20 (a position indicated by a solid line in FIG. 6), and shunt energization is performed at this contact position. It is good to do. By installing the first current-carrying electrode 30 in this way, a predetermined amount of current flows to the first and second current-carrying electrodes 30 and 40 without causing a loss of current amount or disturbance of the shunt ratio. be able to. Therefore, even when the resistance welding is performed at a plurality of points, the welding operation can always be performed under a certain condition, and a stable quality welded portion 70 can be continuously formed. .

  In the above embodiment, the case where the variable resistor 90 is used as the diversion ratio control means has been described. Of course, it is possible to configure the diversion ratio control means with other elements. For example, not only the variable resistor 90 but also a fixed resistor can be installed between the current-carrying electrodes 30 and 40. Further, by configuring each closed loop circuit in a form different from the above form (for example, by directly connecting the second energizing electrode 40 to the power source 80 without passing through the first energizing electrode 30). The various resistors may be installed between the first energizing electrode 30 and the power source 80.

  Moreover, although the said embodiment demonstrated taking the case where the resistance welding method which concerns on this invention was applied to the welding process of the two steel plates used as the body panel of a motor vehicle as an example, this invention is a part other than the above. Of course, it can also be applied to the welding process.

  Moreover, although the case where two metal plates are welded is shown in the above embodiment, the present invention is not limited to this, and the welding method according to the present invention may be applied when welding three or more metal plates. it can. Specifically, although not shown, the welding electrode and the first energizing electrode are brought into contact with the outermost metal plate, and the second energizing electrode is brought into contact with the outermost metal plate. In this case, a first shunt flowing from the welding electrode through the outermost metal plate to the first energizing electrode, and a second diverting from the welding electrode through the outermost metal plate to the second energizing electrode. By adjusting the size of the diversion, the welded portion can be formed at the optimum position in the thickness direction of the plurality of metal plates. As a result, adjacent metal plates can be reliably welded, and a situation in which the plate is cut or melted on the outermost metal plate or the outermost metal plate can be prevented.

  Of course, other specific forms can be adopted for matters other than the above as long as the technical significance of the present invention is not lost.

DESCRIPTION OF SYMBOLS 10 Resistance welding apparatus 20 Welding electrode 30 1st electricity supply electrode 40 2nd electricity supply electrode 50, 60 Steel plate 70 Welding part 70 'Welding planned position 80 Power supply 90 Variable resistance 110,120 Electrode (welding electrode)
130 Electrode for current collection 140 Spare electrode 150,160 Steel plate A Welding current A ₁ current split (electrode for first energization)
A ₂ split flow (second energizing electrode)

Claims (2)

In a resistance welding method for forming a welded portion by energizing a plurality of electrodes in contact with a plurality of metal plates stacked on each other,
As the plurality of electrodes, among the plurality of metal plates, a welding electrode to be brought into contact with the outermost metal plate and an electric current between the welding electrode to be brought into contact with the outermost metal plate A first current-carrying electrode and a second current-carrying electrode for contacting the welding electrode with the metal plate on the backmost side of the plurality of metal plates. use,
By energizing both the energizing electrodes with the welding electrode, the current supplied from the welding electrode to the outermost metal plate is changed to the first energizing electrode and the first energizing electrode. A resistance welding method characterized by diverting a current to an electrode for two energizations. When forming the welded portion at a plurality of points with respect to the plurality of metal plates,
The first energization electrode is brought into contact with the outermost metal plate at a position closer to the welding electrode than the welding portion closest to the welding electrode among the already formed welding portions; The resistance welding method according to claim 1, wherein the shunt energization is performed at a contact position.

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