JP5519451B2 - Resistance welding method and system - Google Patents

Description

  The present invention relates to a resistance welding method and system for performing resistance welding on a laminate formed by laminating a plurality of workpieces.

  As a technique for joining a plurality of metal plates, these metal plates are laminated to form a laminate, and the laminate is sandwiched and pressed by a set of welding electrodes, and then the set of welding electrodes. 2. Description of the Related Art Resistance welding is conventionally known in which a current is applied between them to melt a portion in the vicinity of a contact surface of the metal plate. The melted portion becomes a solid phase called a nugget by solidification. In some cases, three or more metal plates may be joined together by resistance welding.

  Here, the metal plates do not always have the same thickness, but rather differ from each other in most cases. That is, the plurality of metal plates include a workpiece having the smallest thickness (hereinafter also referred to as the thinnest workpiece).

  When such thinnest workpiece is placed on the outermost part of the laminate and resistance welding is performed, the nugget between this thinnest workpiece and another workpiece adjacent to the thinnest workpiece must not grow sufficiently. There is. This is presumably because sufficient joule heat is not generated because the specific resistance is minimized because the thickness of the thinnest workpiece is minimal.

  It is recalled that the Joule heat of the thinnest workpiece is increased by increasing the current value in order to grow the nugget near the thinnest workpiece greatly. However, in this case, a large current flows through the workpiece having a large thickness, and this causes a problem that the workpiece is easily melted and scattered, so-called spatter is easily caused.

  Apart from this, it may be possible to lengthen the energization time. However, even in this case, it is not easy to generate sufficient Joule heat for the thinnest workpiece. Moreover, since the welding process time becomes long, the malfunction that welding efficiency falls will be caused.

  From this viewpoint, in Patent Document 1, when resistance welding is performed on a laminated body in which three or more metal plates are laminated and the thinnest workpiece is arranged on the outermost side, the pressure applied to the laminated body is reduced and a large current is applied. The first stage for energizing the battery for a short time, and the pressure force is set larger than the first stage, and the current value and the energization time are set to be longer than the current value of the first stage for energization. It has been proposed to have two stages, two stages.

  According to the description of Patent Document 1, it becomes possible to easily produce a spot welded joint having a nugget of a necessary size without adding an extra step and without generating spatter. That is.

JP 2005-262259 A

  It is still desired to further improve the bonding strength while further simplifying the control as compared with the conventional technique described in Patent Document 1.

  The present invention has been made in order to solve the above-described problems, and can sufficiently grow nuggets in the vicinity of the contact surface between the workpieces in the laminate, and can eliminate the concern that spatter is generated. It is an object to provide a resistance welding method and system.

In order to achieve the above object, the present invention is a resistance welding method for performing resistance welding on a laminate formed by laminating a plurality of workpieces,
The laminate is sandwiched between the first welding tip and the second welding tip, and is opposite to the first welding tip with respect to a workpiece that is located at the outermost part of the laminate and is in contact with the first welding tip. Contacting the auxiliary electrode with polarity; and
While conducting resistance welding with respect to the said laminated body by energizing between said 1st welding tip and 2nd welding tip, from the branch current which goes to said auxiliary electrode from said 1st welding tip, or from said auxiliary electrode Flowing a branch current toward the first welding tip;
Elapsed time after the start of energization is energizing time at the outermost of the work created by current test was performed in advance - if they match to the elapsed time when the slope changes from large to small in the graph of temperature, said first Electrically insulating one welding tip and the auxiliary electrode to stop the branch current;
It is characterized by having.

  That is, in the present invention, not only the laminated body is sandwiched between the first welding tip and the second welding tip, but also the auxiliary electrode is brought into contact with the work located at the outermost part of the laminated body for energization. Since the first welding tip that is in contact with the outermost workpiece together with the auxiliary electrode has a polarity opposite to that of the auxiliary electrode, a current flowing from the first welding tip to the auxiliary electrode or a current flowing in the opposite direction is obtained. Either one of them branches off. When this branch current flows inside the outermost workpiece, the contact surface between the outermost workpiece and the workpiece adjacent to the outermost workpiece is sufficiently heated.

  As a result of the heating by the branch current, a sufficiently large nugget grows on the contact surface. Thereby, the junction part excellent in joining strength is obtained.

  In addition, in this case, the value of the current flowing through the contact surfaces between the workpieces is smaller than that of normal resistance welding in which the laminate is sandwiched between only the first welding tip and the second welding tip and energized. For this reason, the concern that spatter occurs while the nugget formed on the contact surface grows to a sufficient size is eliminated.

  As described above, according to the present invention, it is possible to sufficiently grow the nugget between the outermost workpiece in the stacked body and the workpiece adjacent to the outermost workpiece. In addition, the concern of spattering can be eliminated.

  Here, if the branch current is allowed to flow for an excessively long time, the nugget formed between the outermost workpiece and the workpiece adjacent thereto may be reduced. Therefore, in the present invention, when the slope in the energization time-temperature graph of the outermost workpiece changes from large to small, in other words, when the temperature increase rate of the outermost workpiece that has been large until then decreases. The branch current is stopped. For this reason, the nugget formed between the outermost workpiece and the workpiece adjacent to it can be greatly grown.

  In order to stop only the branch current, only the auxiliary electrode is separated from the outermost work, or only the electric path between the auxiliary electrode and the power source is cut, and then the first welding tip and the second welding are performed. What is necessary is just to continue the electricity supply between chip | tips. In order to disconnect the electrical path between the auxiliary electrode and the power source, a switch is interposed between the auxiliary electrode and the power source, and this switch may be turned off (disconnected).

The present invention is a resistance welding system for performing resistance welding on a laminate formed by laminating a plurality of workpieces,
A first welding tip and a second welding tip for sandwiching the laminate,
Auxiliary electrodes that are in contact with the outermost workpiece of the laminate together with the first welding tip and have a polarity opposite to that of the first welding tip;
A branch current from the first welding tip to the auxiliary electrode or the auxiliary electrode when conducting resistance welding by energizing between the first welding tip and the second welding tip sandwiching the laminate. A control circuit for controlling a time during which a branch current flows from the first welding tip to the first welding tip;
With
In the control circuit, the elapsed time after the start of energization coincided with the elapsed time when the slope in the energization time-temperature graph of the outermost work created in the energization test performed in advance changed from large to small . Sometimes , the first welding tip and the auxiliary electrode are electrically insulated to stop the branch current.

  By adopting such a configuration, as described above, it is possible to avoid the occurrence of spatter, and obtain a nugget formed between the outermost workpiece and a workpiece adjacent thereto as a sufficiently grown one. be able to.

  In order to stop the branch current, the electrical path between the first welding tip and the auxiliary electrode may be interrupted. For this purpose, for example, a switch may be provided between the auxiliary electrode and the power source for connecting or blocking the electrical path only between the auxiliary electrode and the power source. By switching this switch from the ON (connected) state to the OFF (disconnected) state or vice versa, the electrical path between the first welding tip and the auxiliary electrode can be connected or interrupted.

  Alternatively, a displacement mechanism for displacing the auxiliary electrode may be provided, and the auxiliary electrode may be brought into contact with or separated from the outermost workpiece under the action of the displacement mechanism. Naturally, while the auxiliary electrode is in contact with the outermost workpiece, the electrical path between the first welding tip and the auxiliary electrode is connected, while the auxiliary electrode is separated from the outermost workpiece. In the meantime, the electrical path between the first welding tip and the auxiliary electrode is interrupted.

  The auxiliary electrode may be moved toward or away from (displaced from) the outermost workpiece integrally with the first welding tip by a displacement mechanism for displacing the first welding tip. It is preferable to provide a separate displacement mechanism for displacement.

  Furthermore, it is preferable that the auxiliary electrode has an annular shape surrounding the first welding tip. In this case, branch currents flow uniformly and radially in the outermost workpiece. Accordingly, the contact surface between the outermost workpiece and the workpiece adjacent to the outermost workpiece is heated without unevenness, so that the nugget can be easily formed and the nugget can be sufficiently grown.

  According to the present invention, in addition to the first welding tip and the second welding tip that sandwich the laminated body, the auxiliary electrode that contacts the workpiece arranged at the outermost part of the laminated body is used to perform this auxiliary welding. A branch current passing through the outermost workpiece is caused to flow between the electrode and the first welding tip that is in contact with the outermost workpiece together with the auxiliary electrode. This branch current generates Joule heat that can sufficiently heat the contact surface between the outermost workpiece and the workpiece adjacent thereto. Therefore, a sufficiently large nugget can be grown on this contact surface, and as a result, sufficient bonding strength can be ensured.

  In addition, in the present invention, the branch current is stopped when the contact surface sufficiently generates heat. For this reason, it can be avoided that the nugget is reduced due to the branch current flowing for an excessively long time.

  Whether or not the contact surface has generated sufficient heat is plotted by plotting the temperature change against the energization time of the outermost work, creating an energization time-temperature graph, in other words, whether the inclination has changed from large to small. For example, the determination can be made based on whether or not the heating rate of the outermost workpiece that has been large until then has decreased.

It is a principal part expansion partial cross-sectional perspective view of the resistance welding system which concerns on this Embodiment. It is a longitudinal cross-sectional schematic diagram which shows the state which clamped the laminated body which is a welding object with all the 1st welding tips, the 2nd welding tips, and an auxiliary electrode. It is a longitudinal cross-sectional schematic diagram which shows the state which started electricity supply and sent the electric current which goes to a 2nd welding tip from a 1st welding tip, and the branch current which goes to an auxiliary electrode from a 1st welding tip. It is a longitudinal cross-sectional schematic diagram which shows the state which continued electricity supply from FIG. It is a graph which shows the relationship between the ratio of the time which sent the branch current which goes to an auxiliary electrode from a 1st welding tip, and the diameter of a nugget. It is a graph which shows the relationship between the time which sent the branch current which goes to an auxiliary electrode from a 1st welding tip, and the temperature of the thinnest workpiece | work arrange | positioned at the outermost part of a laminated body. It is a graph which shows the relationship between the temperature and specific resistance in various steel materials. FIG. 5 is a schematic current path diagram illustrating a path through which a current and a branch current flow in the equivalent circuit of FIG. 4. It is a longitudinal cross-sectional schematic diagram which shows the state which set the ON / OFF switch to the OFF state, and continued the electricity supply from the 1st welding tip to the 2nd welding tip. FIG. 10 is a schematic current path diagram showing a path through which a current and a branch current flow in the equivalent circuit of FIG. 9. It is a longitudinal cross-sectional schematic diagram which shows the state which complete | finished electricity supply (resistance welding). Contrary to FIG. 4, it is a longitudinal cross-sectional schematic diagram which shows the state which sent the electric current which goes to a 1st welding tip from a 2nd welding tip and a current branch electrode. It is a longitudinal cross-sectional schematic diagram which shows the state through which the electric current which goes to the auxiliary electrode from a 1st welding tip flows into the thinnest workpiece | work located in the uppermost part of a laminated body, and the workpiece | work just under it. It is a longitudinal cross-sectional schematic diagram which shows the state which clamped the laminated body different from FIG. 3 with all the 1st welding tips, the 2nd welding tips, and the auxiliary electrode, and started electricity supply. FIG. 15 is a schematic longitudinal sectional view showing a state in which the ON / OFF switch is turned off and the energization from the first welding tip to the second welding tip is continued following FIG. 14. FIG. 16 is a schematic longitudinal sectional view showing a state in which energization from the first welding tip to the second welding tip is further continued following FIG. 15.

  Hereinafter, a preferred embodiment of the resistance welding method according to the present invention will be described in detail in relation to a resistance welding system for carrying out the method, with reference to the accompanying drawings.

  FIG. 1 is an enlarged partial cross-sectional perspective view of a main part of the resistance welding system according to the present embodiment. This resistance welding system includes a welding gun (not shown) including a first welding tip 10, a second welding tip 12, and an auxiliary electrode 14, and the welding gun is, for example, an arm portion of an articulated robot such as a six-axis robot. Arranged at the tip. A configuration in which a welding gun is disposed on an arm of an articulated robot is known, and therefore a detailed description of this configuration is omitted.

  The laminated body 16 to be welded will be described briefly. In this case, the laminated body 16 is constituted by laminating three metal plates 18, 20, and 22 in this order from below. The thickness of the metal plates 18 and 20 is set to D1 (for example, about 1 mm to about 2 mm), and the thickness of the metal plate 22 is smaller than D1 (for example, about 0.5 mm to about 0). .7 mm). That is, the metal plates 18 and 20 have the same thickness, and the metal plate 22 is thinner than the metal plates 18 and 20. Hereinafter, the metal plate 22 may be referred to as the thinnest workpiece.

  The metal plates 18 and 20 are made of, for example, so-called high-tensile steel JAC590, JAC780 or JAC980 (all of which are high-performance high-tensile steel plates stipulated by the Japan Iron and Steel Federation standard), and the thinnest workpiece 22 is made of so-called mild steel, for example. It consists of a certain JAC270 (steel plate for high-performance drawing as defined in the Japan Iron and Steel Federation standard). The metal plates 18 and 20 may be the same metal species or different metal species.

  Alternatively, a combination in which all of the metal plates 18, 20, and 22 are mild steel may be used, or a combination in which only the metal plate 18 is high-tensile steel and the metal plates 20 and 22 are mild steel may be used.

  Of course, the material of the metal plates 18, 20, and 22 is not particularly limited to the steel material described above, and any material may be used as long as resistance welding is possible.

  The first welding tip 10 and the second welding tip 12 formed in the shape of a long bar sandwich the laminate 16 to be welded between the first welding tip 10 and the second welding tip 12, and the laminate 16 is energized. In the present embodiment, it is assumed that a current flows from the first welding tip 10 toward the second welding tip 12.

  When the welding gun is of the so-called X type, the first welding tip 10 is provided on one chuck claw constituting an openable / closable chuck pair, and the second welding tip 12 is the remaining chuck of the chuck pair. Provided on the nails. That is, as the chuck pair is opened or closed, the first welding tip 10 and the second welding tip 12 are separated from or approach each other.

  The welding gun may be a so-called C type. In this case, the second welding tip 12 is arranged at the tip of the fixed arm, while the first welding tip 10 is connected to, for example, a ball screw. As the ball screw is urged to rotate, the first welding tip 10 approaches or separates from the second welding tip 12.

  In this case, the auxiliary electrode 14 is formed in an annular shape and surrounds the first welding tip 10. The welding gun that supports the first welding tip 10 is provided with a displacement mechanism such as a ball screw or a cylinder for moving the auxiliary electrode 14 toward or away from the laminated body 16. By this displacement mechanism, the auxiliary electrode 14 can approach or separate from the stacked body 16 separately from the first welding tip 10.

  In the present embodiment, the first welding tip 10 is electrically connected to the positive electrode of the power source 24, and the second welding tip 12 and the auxiliary electrode 14 are electrically connected to the negative electrode of the power source 24. The As can be understood from this, the first welding tip 10 and the auxiliary electrode 14 both come into contact with the thinnest workpiece 22 constituting the laminated body 16, but their polarities are opposite to each other.

  In the above configuration, when the separation distance Z between the first welding tip 10 and the auxiliary electrode 14 is excessively large, the resistance between the first welding tip 10 and the auxiliary electrode 14 increases, and a branch current i2 (described later) 3) becomes difficult to flow. Therefore, the separation distance Z is set to a distance at which the resistance between the first welding tip 10 and the auxiliary electrode 14 can flow the branch current i2 at an appropriate current value.

  An ON / OFF switch 26 is interposed between the negative electrode of the power supply 24 and the auxiliary electrode 14. That is, the negative electrode of the power supply 24 and the auxiliary electrode 14 are electrically connected when the ON / OFF switch 26 is in the ON state, and are insulated when in the OFF state.

  The resistance welding system further includes an RB (robot) controller (not shown) as a control circuit for controlling the operation of the welding gun and the articulated robot, and the ON / OFF switch 26 is controlled under the control action of the RB controller. The ON / OFF state is switched.

  The main part of the resistance welding system according to the present embodiment is basically configured as described above. Next, regarding its operation and effect, in relation to the resistance welding method according to the present embodiment. explain.

  In order to perform the resistance welding method according to the present embodiment, first, an energization test is performed using a test piece.

  Specifically, under the action of the RB controller, the articulated robot moves the welding gun so that the laminate 16 is disposed between the first welding tip 10 and the second welding tip 12. Thereafter, the chuck claws are closed or the displacement mechanism is urged, so that the first welding tip 10 and the second welding tip 12 are relatively close to each other, and as a result, the laminated body is between them. 16 is pinched. The auxiliary electrode 14 comes into contact with the thinnest workpiece 22 simultaneously with this clamping.

  Next, energization is started. As described above, since each of the first welding tip 10 and the second welding tip 12 is connected to the positive electrode and the negative electrode of the power source 24, the first welding tip 10 to the second welding tip 12 are shown in FIG. A current i1 toward The Joule heat based on the current i1 heats between the metal plates 18 and 20 and between the metal plates 20 and 22, respectively. Note that reference numerals 30 and 32 in FIG. 3 indicate heating regions.

  Here, the auxiliary electrode 14 is also in contact with the thinnest workpiece 22, and the polarity of the auxiliary electrode 14 is negative. Accordingly, the first welding tip 10 starts with the branch current i2 toward the auxiliary electrode 14 simultaneously with the above-described current i1. Since the auxiliary electrode 14 has an annular shape, the branch current i2 flows radially.

  Accordingly, in this case, a heating region 34 different from the heating region 32 is formed inside the thinnest workpiece 22. Since the branch current i2 flows radially, the heating region 34 heats the contact surfaces of the metal plates 20 and 22 radially. The heating region 34 expands with time and is integrated with the heating region 32 as shown in FIG.

  As a result of heat being transferred from both the heating regions 32 and 34 integrated in this manner, the contact surface between the metal plates 20 and 22 sufficiently rises in temperature and starts to melt. As a result, a nugget 36 is formed between the metal plates 20 and 22. A nugget 38 is also formed between the metal plates 18 and 20 by the current i1.

  In order to grow the nugget 36 between the metal plates 20 and 22 greatly, it is considered that the auxiliary electrode 14 is brought into contact with the thinnest workpiece 22 for a long time so that the branch current i2 flows for a long time. However, as shown in FIG. 5, when the branch current i2 flows for an excessively long time, in other words, when the ratio of the energization time of the branch current i2 to the energization time of the current i1 is increased, the diameter of the nugget 36 is increased. May be smaller.

  Therefore, in the present embodiment, in the above energization test, the temperature of the thinnest workpiece 22 is measured while energizing the branch current i2, and the result is plotted. That is, a graph of energization time-temperature in the thinnest workpiece 22 is created. As the temperature measuring means, a known device such as a thermocouple or a radiation thermometer may be used.

  FIG. 6 shows an example. FIG. 6 shows a case where the temperature gradient of the thinnest workpiece 22 changes from the maximum to the minimum at the point B. In other words, in this case, the temperature of the thinnest workpiece 22 increases rapidly with the lapse of time until reaching the point B, but does not increase so much after reaching the point B.

  The reason why the temperature of the thinnest workpiece 22 changes in this way is that the material of the thinnest workpiece 22 undergoes transformation, and the specific resistance changes accordingly. That is, to explain steel materials as an example, as shown in FIG. 7, steel material A (plot of ◆) containing 0.23% of C (weight%, the same shall apply hereinafter) Mn 0.46%, and C of 0.32 %, Mn 0.69%, Cr 1.09%, Ni 0.07% steel B (Plot), C 0.34%, Mn 0.55%, Cr 0.78 %, Ni 3.5%, Mo 0.39% steel C (triangle plot), C 0.13% Mn 0.25% Cr 12.95% steel D (x In all of the plots), the rate of change in specific resistance is small at about 800 ° C. This is because an A3 transformation that changes from a body-centered cubic crystal to a face-centered cubic crystal occurs before and after this change rate becomes different.

  In other words, when the thinnest workpiece 22 made of any of the steel material A, the steel material B, the steel material C, or the steel material D is used, the specific resistance rises with a large slope until reaching the A3 transformation point of about 800 ° C. For this reason, the temperature of the thinnest workpiece 22 also rises with a large inclination. This is because the Joule heat generated due to the large specific resistance increases. When the temperature exceeds about 800 ° C., the slope of the specific resistance becomes small. As a result, the slope of the temperature rise of the thinnest workpiece 22 becomes small based on the fact that the generated Joule heat becomes small.

  In short, the temperature of the thinnest workpiece 22 can be efficiently increased up to about 800 ° C., which is the A3 transformation point, but the temperature rise of the thinnest workpiece 22 becomes smaller at temperatures exceeding that (see FIG. 6). .

  Each of point A to point D in FIG. 5 corresponds to each of point A to point D in FIG. That is, the elapsed time from the origin in FIG. 5 to each of the points A to D and the elapsed time from the origin in FIG. 6 to each of the points A to D are equal to each other.

  And the diameter of the nugget 36 between the metal plates 20 and 22 reaches the point B so as to be understood by comparing the points A to D in FIG. 5 and the points A to D in FIG. The maximum is obtained when the branch current i2 is stopped and only the current i1 is continued. If the branch current i2 continues to flow after the point B is exceeded, the diameter of the nugget 36 tends to decrease as indicated by the point D in FIG.

  After obtaining the above knowledge through an electrical test, this resistance welding is performed. In this resistance welding, the branch current i2 is stopped at the point B determined by the energization test, that is, when the temperature gradient of the thinnest workpiece 22 changes from the maximum to the minimum. For this purpose, for example, the branch current i2 starts to flow in the energization test, and the elapsed time until the temperature gradient of the thinnest workpiece 22 changes from the maximum to the minimum is input to the RB controller. What is necessary is just to perform the control which makes the ON / OFF switch 26 OFF when it is time.

  Alternatively, the temperature of the thinnest workpiece 22 is measured using the known temperature measuring means as described above, and the ON / OFF switch 26 is controlled to be turned off when the temperature at the point B in FIG. 6 is reached. You may do it.

  That is, first, in accordance with the current test, the current i1 flows from the first welding tip 10 sandwiching the laminate 16 toward the second welding tip 12, and the first welding tip 10 branches to the auxiliary electrode 14. A current i2 is supplied. As a result, the heating regions 30, 32, and 34 are formed as in FIGS. 3 and 4, the nugget 36 is formed between the metal plates 20 and 22, and the nugget 38 is formed between the metal plates 18 and 20. It is formed. FIG. 8 shows a current path in the equivalent circuit in this case.

  In this case, the current value of the current i1 flowing through the metal plates 18 and 20 is smaller than that of general resistance welding in which the branch current i2 is not passed. For this reason, it is avoided that the calorific value of the metal plates 18 and 20 becomes excessively large while the nugget 36 between the metal plates 20 and 22 is growing large. Accordingly, concerns that spatter will occur are eliminated.

  As the ratio of the branch current i2 is increased, the heating region 34 and thus the nugget 36 can be increased. However, when the ratio of the branch current i2 is excessively increased, the current value of the current i1 is decreased. 30 and 32 become smaller. For this reason, while the size of the nugget 36 is saturated, the nugget 38 tends to be small. Therefore, it is preferable that the ratio of the branch current i2 is set so that the current i1 flows so that the nugget 38 is sufficiently grown.

  The ratio between the current i1 and the branch current i2 can be adjusted, for example, by changing the separation distance Z (see FIGS. 1 and 2) between the first welding tip 10 and the auxiliary electrode 14 as described above. It is. Alternatively, a mechanism or a resistor for adjusting the amount of current may be provided between the current path of the branch current i2, for example, between the auxiliary electrode 14 and the power source 24, thereby adjusting the ratio of the branch current i2.

  As described above, when the branch current i2 continuously flows, the nugget 36 tends to be slightly smaller. Therefore, in the present embodiment, the branch current i2 is stopped when the diameter of the nugget 36 becomes maximum.

  For example, when the elapsed time from when the branch current i2 starts flowing in the energization test to when the temperature gradient of the thinnest workpiece 22 changes from the maximum to the minimum is input to the RB controller, the RB controller becomes this time. Sometimes, the ON / OFF switch 26 is turned off as shown in FIG. Further, when the information regarding the temperature of the thinnest workpiece 22 measured by the temperature measuring means is sent to the RB controller, the RB controller sets the ON / OFF switch 26 to the OFF state when the temperature reaches the point B in FIG. Control.

  Thereby, the power supply 24 and the auxiliary electrode 14 are electrically insulated. As a result, the branch current i2 stops. FIG. 10 shows a current path in the equivalent circuit at this time.

  When the branch current i2 is stopped as described above, only the current i1 from the first welding tip 10 to the second welding tip 12 flows through the thinnest workpiece 22. As a result, the heating region 34 (see FIG. 4) disappears.

  On the other hand, in the metal plates 18 and 20, the same state as that during normal resistance welding is formed. That is, in the metal plates 18 and 20 having a large thickness, the amount of heat generated by Joule heat increases, and as a result, the heating region 30 expands and the temperature further increases. The contact surfaces of the metal plates 18 and 20 are heated by the heating region 30 whose temperature has been increased, whereby the temperature in the vicinity of the contact surfaces is sufficiently increased (heat generation) and melted, and the growth of the nugget 38 is promoted. .

  Thereafter, energization may be continued until the nugget 38 is sufficiently grown, for example, until it is integrated with the nugget 36 as shown in FIG. The degree of growth of the nugget 38 relative to the energization duration may be confirmed in advance by a resistance welding test using a test piece or the like.

  Here, the contact surfaces of the metal plates 18 and 20 are preheated by the heating region 30 formed when the current i1 passes when the nugget 36 is grown between the metal plates 20 and 22. . For this reason, the familiarity between the metal plates 18 and 20 is improved before the nugget 38 grows. Therefore, it is difficult for spatter to occur.

  As described above, in the present embodiment, when the nugget 36 between the metal plates 20 and 22 is grown, spatter is generated both when the nugget 38 between the metal plates 18 and 20 is grown. It can be avoided.

  When a predetermined time (a time during which the nugget 38 can sufficiently grow) elapses in a welding timer included in the RB controller, energization is stopped and the first welding tip 10 is thinnest as shown in FIG. Separate from the workpiece 22. Alternatively, the first welding tip 10 and the second welding tip 12 may be electrically insulated by separating the first welding tip 10 from the thinnest workpiece 22, thereby stopping the welding.

  As the energization (welding) is stopped in this manner, the heat generation of the metal plates 18 and 20 is also terminated. As time passes, the nugget 38 is cooled and solidified, whereby the metal plates 18 and 20 are joined together.

  As described above, the metal plates 18 and 20 constituting the laminate 16 and the metal plates 20 and 22 are joined together, and eventually a joined product is obtained.

  In this bonded product, the bonding strength between the metal plates 20 and 22 is excellent as well as the bonding strength between the metal plates 18 and 20. This is because the nugget 36 between the metal plates 20 and 22 is sufficiently grown along with the branch current i2 flowing through the thinnest workpiece 22 as described above.

  Moreover, as understood from the above, when the resistance welding system according to the present embodiment is configured, the auxiliary electrode 14, a displacement mechanism for displacing the auxiliary electrode 14, and the branch current i2 toward the auxiliary electrode 14 are provided. It is sufficient to provide an ON / OFF switch 26 for generating and stopping generation. Therefore, the configuration of the resistance welding system does not become complicated with the provision of the auxiliary electrode 14.

  In addition, after obtaining the necessary information by conducting a single energization test, the resistance welding can be performed based on this information, so the energization time of the branch current i2 that maximizes the diameter of the nugget 36 can be reduced. It is not necessary to create as many test pieces as possible and to conduct a plurality of current tests. That is, according to the present embodiment, there is also an advantage that the conditions during the main resistance welding can be easily and easily set.

  In the above-described embodiment, the branch current i2 is stopped by turning the ON / OFF switch 26 to the OFF state, but instead, when a predetermined time set in the welding timer elapses. The auxiliary electrode 14 may be separated from the thinnest workpiece 22 and thereby the branch current i2 may be stopped. In this case, a displacement mechanism for displacing the auxiliary electrode 14 separately from the first welding tip 10 may be provided.

  In addition, as shown in FIG. 12, a current from the second welding tip 12 in contact with the metal plate 18 toward the first welding tip 10 in contact with the thinnest workpiece 22 may be allowed to flow. Also in this case, the polarity of the auxiliary electrode 14 in contact with the thinnest workpiece 22 is reversed from that of the first welding tip 10. That is, the second welding tip 12 and the auxiliary electrode 14 are electrically connected to the positive electrode of the power source 24, while the first welding tip 10 is electrically connected to the negative electrode of the power source 24. As a result, a current i1 from the second welding tip 12 toward the first welding tip 10 and a branch current i2 from the auxiliary electrode 14 toward the first welding tip 10 are generated.

  In any case, the auxiliary electrode is not particularly limited to the annular auxiliary electrode 14. For example, it may be a long bar like the first welding tip 10 and the second welding tip 12. In this case, one or a plurality of auxiliary electrodes may be used. When a plurality of auxiliary electrodes are used, the plurality of auxiliary electrodes are simultaneously brought into contact with or separated from the thinnest workpiece 22. Also good.

  Furthermore, in each aspect described above, as shown in FIG. 13, the branch current i <b> 2 is applied not only to the thinnest workpiece 22 in contact with the first welding tip 10 but also to the metal plate 20 positioned immediately below the thinnest workpiece 22. May also flow.

  In this case, resistance heat is generated between the thinnest workpiece 22 and the metal plate 20, and as a result, a nugget 36 is generated. On the other hand, even if a current from the first welding tip 10 toward the auxiliary electrode 14 does not flow between the metal plates 18 and 20, or even if it flows, the amount of current is very small. Therefore, the nugget 36 generated between the thinnest workpiece 22 and the metal plate 20 easily grows.

  Or you may make it comprise a laminated body with four or more metal plates, and as shown in FIG. 14, you may make it comprise the laminated body 16a only with two metal plates 18 and 20. As shown in FIG. Hereinafter, this case will be described.

  When resistance welding is performed on the laminated body 16a, the articulated robot, and thus the welding gun, moves under the action of the RB controller as described above to move between the first welding tip 10 and the second welding tip 12. The stacked body 16a is sandwiched. Further, the auxiliary electrode 14 contacts the metal plate 20. As a result, the state shown in FIG. 14 is formed.

  Thereafter, similarly to the above, under the control action of the RB controller, the current i1 flows between the first welding tip 10 and the second welding tip 12, and energization is started. At the same time, the branch current i2 from the first welding tip 10 toward the auxiliary electrode 14 flows radially.

  As can be understood from FIG. 14, the metal plates 18 and 20 are softened by being heated by Joule heat based on the current i <b> 1, thereby forming the softened portion 50. On the other hand, the metal plate 20 through which the current i1 and the branch current i2 flow is heated and melted by Joule heat based on the current i1 and the branch current i2, thereby forming a melting portion 52.

  In the welding timer included in the RB controller, a time during which the softened portion 50 obtained as described above can be sufficiently softened is set in advance. Therefore, when this set time is reached, the ON / OFF switch 26 is turned off under the action of the RB controller (welding timer) as shown in FIG. Accordingly, the branch current i2 is stopped.

  When the branch current i2 is stopped as described above, only the current i1 from the first welding tip 10 to the second welding tip 12 flows through the metal plates 18 and 20. This current i1 is larger than the current i1 until the branch current i2 is stopped.

Therefore, the Joule heat at the contact surfaces of the metal plates 18 and 20 having a large resistance is larger than before the branch current i2 stops. As a result, as shown in FIG. 16, the melted portion 52 grows greatly toward the softened portion 50, and finally a nugget is formed from the melted portion 52.

  As described above, the softened portion 50 is formed in advance on the contact surfaces of the metal plates 18 and 20. For this reason, the space between the metal plates 18 and 20 is well sealed. Therefore, even when the branch current i2 is stopped and the current value of the current i1 becomes large, it is possible to avoid spattering from between the metal plates 18 and 20.

  As described above, even when resistance welding is performed on the two metal plates 18 and 20, a large nugget is grown on the contact surfaces of the metal plates 18 and 20 while avoiding the occurrence of spatter. Can do.

DESCRIPTION OF SYMBOLS 10, 12 ... Welding tip 14 ... Auxiliary electrode 16, 16a ... Laminate 18, 20 ... Metal plate 22 ... Thinnest work (metal plate) 24 ... Power source 30, 32, 34 ... Heating area 36, 38 ... Nugget 50 ... Softening Part 52 ... Melting part i1 ... Current i2 ... Branch current

Claims (6)

A resistance welding method for performing resistance welding on a laminated body formed by laminating a plurality of workpieces,
The laminate is sandwiched between the first welding tip and the second welding tip, and is opposite to the first welding tip with respect to a workpiece that is located at the outermost part of the laminate and is in contact with the first welding tip. Contacting the auxiliary electrode with polarity; and
While conducting resistance welding with respect to the said laminated body by energizing between said 1st welding tip and 2nd welding tip, from the branch current which goes to said auxiliary electrode from said 1st welding tip, or from said auxiliary electrode Flowing a branch current toward the first welding tip;
Elapsed time after the start of energization is energizing time at the outermost of the work created by current test was performed in advance - if they match to the elapsed time when the slope changes from large to small in the graph of temperature, said first Electrically insulating one welding tip and the auxiliary electrode to stop the branch current;
The resistance welding method characterized by having.   2. The resistance welding method according to claim 1, wherein only the auxiliary electrode is separated from the outermost workpiece, or the branch current is stopped by cutting only an electric path between the auxiliary electrode and a power source. The resistance welding method characterized by the above-mentioned. A resistance welding system for performing resistance welding on a laminate formed by laminating a plurality of workpieces,
A first welding tip and a second welding tip for sandwiching the laminate,
Auxiliary electrodes that are in contact with the outermost workpiece of the laminate together with the first welding tip and have a polarity opposite to that of the first welding tip;
A branch current from the first welding tip to the auxiliary electrode or the auxiliary electrode when conducting resistance welding by energizing between the first welding tip and the second welding tip sandwiching the laminate. A control circuit for controlling a time during which a branch current flows from the first welding tip to the first welding tip;
With
In the control circuit, the elapsed time after the start of energization coincided with the elapsed time when the slope in the energization time-temperature graph of the outermost work created in the energization test performed in advance changed from large to small . when the resistance welding system, characterized by stopping the branch current and the auxiliary electrode and the first welding tip electrically insulating.   4. The resistance welding system according to claim 3, wherein a switch for connecting or stopping only an electric path between the auxiliary electrode and the power source is provided between the auxiliary electrode and the power source. .   4. The resistance welding system according to claim 3, further comprising a displacement mechanism for moving only the auxiliary electrode toward or away from the outermost workpiece.   The resistance welding system according to any one of claims 3 to 5, wherein the auxiliary electrode has an annular shape surrounding the first welding tip.

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