JP2011194464A - Method and device for spot welding - Google Patents

Abstract

The present invention provides a spot welding method and a spot welding apparatus capable of easily obtaining a uniform and stable welding quality when spot welding three stacked members to be welded, and a thin plate and a first thick plate. When spot welding the welded member 50 on which the second thick plate 53 is overlapped, the lower welding electrode 22 and the upper welding electrode 25 that contact the second thick plate 53 are opposed to each other and are in contact with the second thick plate 53. The welding member 50 is sandwiched and pressurized, and in this pressurized state, the thin plate 51 and the first thick plate 52 are spot-welded by energizing between the upper welding electrode 25 and the earth function electrode 28 in contact with the thin plate 51, and the upper welding electrode 25. The first thick plate 52 and the second thick plate 53 are spot welded by energizing between the upper welding electrode 25 and the lower welding electrode 22 in a non-energized state between the first thick plate 52 and the ground function electrode 28.
[Selection] Figure 1

Description

  The present invention relates to a spot welding method and a spot welding apparatus for spot welding a member to be welded in which a thin plate is superposed on one of two superposed thick plates.

  In general, for joining plate materials such as stacked steel plates, a large current is passed between the upper and lower welding electrodes for a certain period of time while applying pressure between a pair of upper and lower welding electrodes, and the joint is raised to almost the melting temperature. Spot welding to join is widely performed.

  A weld lump called a nugget is formed at the joint between the spot-welded plates. Since the joining strength depends on the nugget diameter, it is important to secure a nugget having a predetermined diameter or more when a high joining strength is required, for example, for automobile members.

  In general, when the applied pressure and energization time are constant, the nugget diameter gradually increases as the current increases. However, if the current value is excessive, the amount of heat generation increases, causing the scattering of molten metal between the plates. It becomes. In other words, the scattering is a molten metal explosion phenomenon due to overheating of the joint, and the molten metal is discharged from the joint, resulting in voids and cracks in the nugget, and discontinuities in the nugget shape and metal structure. As a result, the strength of the joint decreases significantly as the thickness of the joint decreases. On the other hand, when the current is too small, the nugget becomes small and sufficient bonding strength cannot be obtained.

  Further, when the applied pressure is small, the contact area between the plate materials is reduced, the contact resistance is increased, and it becomes a cause of scattering due to overheating. On the other hand, if the applied pressure is too large, the contact resistance decreases, the heat generation amount decreases, the nugget is small, and the welding strength decreases.

  Further, in a vehicle body structure of an automobile, for example, a center pillar, there is a structure in which a phosphorus hose is interposed between an outer panel and an inner panel. In this structure, it is required to spot weld a plate assembly in which three or more plate materials are overlapped.

  In particular, a reduction in the weight of the vehicle body is required along with a demand for improving the collision safety of the vehicle body. Along with this, a thick plate with high rigidity is arranged on the inner inner panel and phosphorus hose, a light thin plate is arranged on the outer outer panel, and three thick inner panels and phosphorus hose and thin outer panel are stacked. Members may be spot welded.

  When spot welding is performed with constant pressure and current applied to a member to be welded with a thin plate superimposed on one of these two thick plates, a nugget is generally formed between the thick plate and the thick plate at the joint. Then, it gradually grows, and eventually the thick plate and the thin plate are welded.

  For example, as shown in FIG. 7A, spot welding is performed on a three-layered member 150 in which a thin plate 151 having low rigidity and thick plates 152 and 153 having a thickness higher than that of the thin plate 151 are stacked in order from the top. In the state where the thin plate 151 and the thick plate 152 and the thick plate 152 and the thick plate 153 are in close contact with each other with no gap, the power supply 103 sandwiches the member to be welded 150 between the upper welding electrode 101 and the lower welding electrode 102. When energized, the current density in the energization path X between the upper welding electrode 101 and the lower welding electrode 102 is substantially uniform, and a good nugget is formed from the thin plate 151 to the thick plate 153, thereby obtaining the necessary welding strength. it can.

  However, actually, when the member to be welded 150 is sandwiched and pressed by the upper welding electrode 101 and the lower welding electrode 102, the thin plate 151 and the thick plate 152 having low rigidity are bent upward, and the thin plate 151 and the thick plate 150 are thick. A gap is generated between the plates 152 and between the thick plate 152 and the thick plate 153. In this case, the contact area between the upper welding electrode 101 and the thin plate 151 is increased by the bending of the thin plate 151, whereas the contact area between the thin plate 151 and the thick plate 152 and between the thick plate 152 and the thick plate 153 is small due to the gap. Become.

  Therefore, the current density in the energization path X between the upper welding electrode 101 and the lower welding electrode 102 is higher on the thick plate 153 side than on the thin plate 151 side, and the thick plate 152 and the thick plate are larger than between the thin plate 151 and the thick plate 152. Between 153, the amount of heat generation increases locally. As a result, a nugget 155 is first formed at the junction between the thick plate 152 and the thick plate 153 as shown in FIG. 7A, and the nugget 155 gradually increases until the nugget 155 becomes thicker as shown in FIG. 7B. The plates 152 are welded together. However, the amount of penetration between the thin plate 151 and the thick plate 152 is small, the welding strength is unstable, the thin plate 151 may be peeled off from the thick plate 152, and the welding quality varies. This problem is particularly noticeable as the thick plates 152 and 153 are thicker and the nugget 155 is less likely to reach between the thick plate 152 and the thin plate 151.

  Similarly, the reason why the welding strength becomes unstable due to the small amount of penetration between the thin plate 151 and the thick plate 152 is that the thin plate 151 is thin, so that heat is taken away by the upper welding electrode 101 due to contact with the upper welding electrode 101, The temperature on the thin plate 151 side does not rise, and the nugget 155 may not be formed easily.

  As a countermeasure, for example, there is a spot welding method disclosed in Patent Document 1. In this spot welding method, as shown in FIG. 8, when spot-welding a three-layered member to be welded 150 in which a thin plate 151 and thick plates 152 and 153 are overlapped, the upper welding electrode 105 that abuts on the thin plate 151 side. Is made smaller than the tip diameter of the lower welding electrode 106 in contact with the thick plate 153 side, thereby reducing the contact area between the thin plate 151 and the upper welding electrode 105 with the thick plate 153 and the lower welding electrode 106. It is made to become smaller than the contact area. Accordingly, the current density in the energization path between the upper welding electrode 105 and the lower welding electrode 106 gradually decreases from the upper welding electrode 105 side toward the lower welding electrode 106. As a result, the amount of heat generated at the joint between the thin plate 151 and the thick plate 152 is increased, and the welding strength by the nugget formed between the thin plate 151 and the thick plate 152 is improved.

  Further, as shown in FIG. 9, the spot welding method disclosed in Patent Document 2 is a thick plate when spot welding a three-layered member 150 to be welded on which a thin plate 151 and thick plates 152 and 153 are superimposed. The thin plate 151 and the thick plates 152 and 153 are fixed by the clamp 110 so that a gap c is formed between the thick plate 152 and the thick plate 153 in advance. Further, the fixed welding electrode 111 is brought into contact with the thick plate 153, the movable welding electrode 112 is moved, and the member to be welded 150 is sandwiched between the fixed welding electrode 111 and the movable welding electrode 112. First, in the first welding process, a low pressure is applied. A nugget is formed between the thin plate 151 and the thick plate 152 by energizing for a short time. Thereafter, in the second welding step, the pressure applied by the movable welding electrode 112 is increased to eliminate the gap c between the thick plate 152 and the thick plate 153, thereby forming a nugget between the thick plate 152 and the thick plate 153, and the thin plate 151 and the thick plate 152. A nugget is formed between the thick plate 152 and the thick plate 153.

JP 2003-251468 A JP 2008-290099 A

  According to Patent Document 1, the upper welding electrode 101 and the lower welding electrode are made smaller by making the tip diameter of the upper welding electrode 101 in contact with the thin plate 151 smaller than the tip diameter of the lower welding electrode 102 in contact with the thick plate 153. The current density in the energization path between 102 gradually decreases from the upper welding electrode 101 toward the lower welding electrode 102, and the welding strength between the thin plate 151 and the thick plate 152 is improved.

  However, depending on the pressure applied by the upper welding electrode 101 and the lower welding electrode 102, the thickness of the thin plate 151, the thick plates 152 and 153, and the shape and location of the member 150 to be welded, the distance between the upper welding electrode 101 and the lower welding electrode 102 is increased. The current density in the current path changes variously, resulting in variations in welding quality, and it is difficult to ensure uniform welding quality. In addition, it is extremely possible to switch to various upper welding electrodes 101 and lower welding electrodes 102 having different tip diameters depending on the thickness of the thin plate 151 and the thick plates 152 and 153 and the shape and location of the member 150 to be welded. It is awkward and concerns about a significant drop in productivity, which is not realistic. Moreover, a lot of management costs are required to prepare and manage various upper welding electrodes 101 and lower welding electrodes 102 having different tip diameters.

  On the other hand, in Patent Document 2, a nugget is formed between the thin plate 151 and the thick plate 152 in advance by energizing for a short time with a low pressure in the first welding process, and then a high pressure is applied in the second welding process. By eliminating the gap c between the thick plate 152 and the thick plate 153 and forming a nugget between the thick plate 152 and the thick plate 153, the welding strength between the thin plate 151 and the thick plate 152 is improved.

  However, since it is necessary to form a gap c between the thick plate 152 and the thick plate 153 in the first welding process, the shape of the member to be welded 150 is greatly limited and inferior in versatility, and is movable with the fixed welding electrode 111. It is extremely troublesome and difficult to control various pressures applied by the welding electrode 112, resulting in variations in welding quality and it is difficult to ensure uniform welding quality.

  Accordingly, an object of the present invention made in view of such a point is to easily and uniformly stabilize the case where a three-layered member to be welded in which a thin plate is superimposed on one of two stacked thick plates is spot-welded. An object of the present invention is to provide a spot welding method and a spot welding apparatus that can achieve the weld quality.

  The spot welding method according to the first aspect of the present invention that achieves the above object is a spot welding method in which spot welding is performed on a member to be welded in which a thin plate, a first thick plate having a thickness larger than the thin plate, and a second thick plate are sequentially stacked. In the method, the member to be welded is sandwiched and pressed between a first welding electrode which is disposed opposite to each other and abuts on the second thick plate and a second welding electrode which abuts on the thin plate, and the second welding electrode is pressed in the pressurized state. A first welding step of spot-welding the thin plate and the first thick plate by energizing between the thin plate and the earth functional electrode in contact with the thin plate, and a non-energized state between the second welding electrode and the ground functional electrode And a second welding step of spot welding the first thick plate and the second thick plate by energizing between the second welding electrode and the first welding electrode.

  According to this, in the first welding process, the second welding is performed in a state in which the member to be welded is sandwiched and pressed by the first welding electrode that is disposed to face each other and that contacts the second thick plate and the second welding electrode that contacts the thin plate. The thin plate and the first thick plate are spot-welded by energizing between the electrode and the earth function electrode in contact with the thin plate, and the second welding is performed with the second process electrode in a non-energized state between the second welding electrode and the earth function electrode. Since the first thick plate and the second thick plate are spot-welded by energizing between the electrode and the first welding electrode, the second welding is performed under optimum welding conditions for the thin plate and the first thick plate in the first welding step. The thin plate and the first thick plate can be spot-welded by energizing between the electrode and the earth function electrode, and sufficient welding strength between the thin plate and the first thick plate can be obtained. On the other hand, in the second welding step, the first thick plate and the second thick plate are spot-welded by energizing between the second welding electrode and the first welding electrode under optimum welding conditions for the first thick plate and the second thick plate. Thus, sufficient welding strength between the first thick plate and the second thick plate can be obtained. As a result, uniform and stable welding quality can be obtained in the three-layer member to be welded in which the thin plate, the first thick plate, and the second thick plate are stacked.

  The spot welding method according to claim 2 is a spot welding method in which spot welding is performed on a member to be welded in which a thin plate, a first thick plate having a thickness larger than the thin plate, and a second thick plate are sequentially stacked. The member to be welded is sandwiched and pressed by a first welding electrode that is disposed and abutted against the second thick plate and a second welding electrode that abuts on the thin plate, and the second welding electrode and the thin plate are sandwiched and pressurized in the sandwiched and pressurized state. A first welding step in which the thin plate and the first thick plate are spot-welded by energizing between the grounding function electrode and the second welding electrode and the second welding electrode in a non-contact state with the member to be welded. It has the 2nd welding process of energizing between the 1st welding electrodes and carrying out spot welding of the 1st thick plate and the 2nd thick plate.

  According to this, in the first welding step, the second welding electrode is held in a state in which the member to be welded is sandwiched and pressed by the first welding electrode that is disposed opposite to each other and contacts the second thick plate and the second welding electrode that contacts the thin plate. The thin plate and the first thick plate are spot-welded by energizing between the thin plate and the earth functional electrode in contact with the thin plate, and the ground functional electrode is not in contact with the thin plate in the second welding step, that is, the first welding electrode and the ground functional electrode. In the first welding step, the thin plate and the first plate are spot-welded by energizing between the second welding electrode and the first welding electrode in a non-energized state. It is possible to spot weld the thin plate and the first thick plate by energizing between the second welding electrode and the earth function electrode under the optimum welding conditions for the thick plate, and sufficient welding strength between the thin plate and the first thick plate. Is obtained. On the other hand, in the second welding step, the first thick plate and the second thick plate are spot-welded by energizing between the second welding electrode and the first welding electrode under optimum welding conditions for the first thick plate and the second thick plate. It is possible to obtain sufficient welding strength between the first thick plate and the second thick plate, and uniform in the three-layered member to be welded in which the thin plate, the first thick plate, and the second thick plate are stacked. Stable welding quality can be obtained.

  The spot welding apparatus according to claim 3, which achieves the above object, comprises spot welding a thin plate, a first thick plate having a thickness greater than the thin plate, and a member to be welded in which the second thick plates are sequentially stacked. In the apparatus, a first welding electrode facing the second thick plate of the member to be welded, and a first welding electrode facing the thin plate of the member to be welded while facing the first welding electrode coaxially. A second welding electrode that is clamped and pressed in cooperation with the electrode; an earth function electrode that contacts and separates a thin plate of a member to be welded that is clamped and pressed by the first welding electrode and the second welding electrode; and the first welding electrode And the second welding electrode and the ground function electrode in contact with the thin plate in a state where the member to be welded is sandwiched and pressurized by the second welding electrode, and the ground function electrode is separated from the thin plate. In contact with the second welding electrode Characterized in that a welding operation circuit for energizing between the serial first welding electrode.

  According to this, the grounding member that contacts the second welding electrode and the thin plate in a state in which the member to be welded is sandwiched and pressed by the first welding electrode that is disposed to face the second thick plate and the second welding electrode that contacts the thin plate. The thin plate and the first thick plate are spot-welded by energizing between the functional electrodes, and the second functional electrode is energized between the second welding electrode and the first welding electrode in a non-contact state where the ground functional electrode is separated from the thin plate. Since the 1 thick plate and the 2nd thick plate are spot welded, the thin plate and the 1st thick plate are spot welded by energizing between the upper welding electrode and the earth function electrode under the optimum welding conditions for the thin plate and the 1st thick plate. Thus, sufficient welding strength between the thin plate and the first thick plate can be obtained. Furthermore, it becomes possible to spot weld the first thick plate and the second thick plate by energizing between the second weld electrode and the first weld electrode under the optimum welding conditions for the first thick plate and the second thick plate. Sufficient welding strength between the first thick plate and the second thick plate can be obtained, and uniform and stable welding quality can be obtained in the member to be welded in which the thin plate, the first thick plate, and the second thick plate are stacked.

  A first welding electrode and a second welding electrode arranged opposite to each other; an earth function electrode that contacts and separates a thin plate of a member to be welded and pressed by the first welding electrode and the second welding electrode; And the second welding electrode in a state where the member to be welded is sandwiched and pressurized, the second welding electrode and the earth function electrode contacting the thin plate are energized, and the earth function electrode is separated from the thin plate in the non-contact state. The spot welding apparatus can be configured with a simple configuration using a welding energization circuit that energizes between the welding electrode and the first welding electrode.

  According to a fourth aspect of the present invention, in the spot welding apparatus of the third aspect, the second welding electrode is coaxially connected to the first welding electrode and close to the first welding electrode so that the member to be welded is the first welding electrode. The pressurizing actuator that reciprocates between a pressurizing position that cooperates to sandwich and pressurize and a retracted position that separates from the thin plate, and the earth function electrode is sandwiched and pressed by the first welding electrode and the second welding electrode. An earth function electrode actuator that is reciprocally moved between a contact position that contacts the thin plate of the member to be welded and a retracted position that is separated from the thin plate is provided.

  According to this, the second welding electrode is coaxially connected to the first welding electrode, approaches the first welding electrode, and the member to be welded cooperates with the first welding electrode to hold and pressurize, and the retraction is separated from the thin plate. A pressure actuator that reciprocates between the position and a ground function electrode actuator that reciprocates between the contact position where the ground function electrode contacts the thin plate of the member to be welded and the retracted position away from the thin plate. The member to be welded can be clamped and pressed in cooperation with the first welding electrode by moving the second welding electrode to the pressing position by the pressurizing actuator, and the earth function electrode is moved to the contact position and the retracted position. By moving, the earth function electrode can be brought into and out of contact with the thin plate.

  According to a fifth aspect of the present invention, in the spot welding apparatus of the fourth aspect, the welding apparatus main body supported by the welding robot and a yoke extending to the welding apparatus main body are provided, and the first welding electrode is provided at the tip of the yoke. And the pressure actuator and the earth function electrode actuator are arranged in the welding apparatus main body.

  According to this, the first welding electrode is arranged on the welding apparatus main body arranged in the welding robot via the yoke, and the pressurizing actuator and the earth function electrode actuator are arranged on the welding apparatus main body, so that the spot welding apparatus becomes the welding robot. Can be installed.

  According to the present invention, the grounding member that contacts the first welding electrode and the thin plate in a state in which the member to be welded is sandwiched and pressed by the first welding electrode that is disposed to face the second thick plate and the second welding electrode that contacts the thin plate. The thin plate and the first thick plate are spot-welded by energizing between the mechanical electrodes and energized between the second welding electrode and the first welding electrode in a non-energized state between the first welding electrode and the earth function electrode. Since the first thick plate and the second thick plate are spot-welded, the second thick plate can be spot-welded to the thin plate, the first thick plate, and the first thick plate under optimum welding conditions. In addition, sufficient welding strength between the thin plate and the first thick plate, the first thick plate and the second thick plate can be obtained, and uniform and stable welding quality can be obtained in the three-layer member to be welded.

It is a schematic block diagram of the spot welding apparatus which concerns on one embodiment of this invention. It is explanatory drawing of the welding energization circuit of the spot welding apparatus in FIG. It is a spot welding apparatus operation | movement process drawing. It is spot welding apparatus operation | movement explanatory drawing, (a) shows the operation state of a spot welding apparatus, (b) is principal part operation | movement explanatory drawing. It is spot welding apparatus operation | movement explanatory drawing, (a) shows the operation state of a spot welding apparatus, (b) is principal part operation | movement explanatory drawing. It is spot welding apparatus operation | movement explanatory drawing, (a) shows the operation state of a spot welding apparatus, (b) is principal part operation | movement explanatory drawing. It is explanatory drawing of the conventional spot welding method. It is explanatory drawing of the conventional spot welding method. It is explanatory drawing of the conventional spot welding method.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 is a configuration diagram of a spot welding apparatus, FIG. 2 is an explanatory diagram of a welding energization circuit of the spot apparatus in FIG. 1, and FIGS. 4 to 6 are operation explanatory diagrams of the spot welding apparatus.

  In FIG. 1, 1 is a welding robot, 10 is a spot welding apparatus supported by the welding robot, and 50 is a member to be welded that is spot welded.

  Prior to the description of the welding robot 1 and the spot welding apparatus 10, the welded member 50 will be described. The member to be welded 50 is obtained by superposing a thin plate on one of two superposed thick plates, for example, a thin plate 51 having a lower rigidity in order from the top, a first thick plate 52 having a thickness higher than that of the thin plate 51, and a second thick plate. It is constituted by a three-layered board set in which 53 are overlapped.

  The welding robot 1 includes a base portion 2 installed to be rotatable around an operating axis S with respect to a floor surface, and a first arm 3 arranged to be rotatable around a horizontal axis U with respect to the base portion 2. The second arm 4 is disposed to be rotatable around the horizontal axis V with respect to the tip of the first arm 3, and is rotatable about the horizontal axis W with respect to the tip of the second arm 4. The spot welding apparatus 10 is connected and fixed to the tip of the third arm 5. Then, by the operation control of a robot control device (not shown), the base unit 2 is swiveled around the operation axis S, and the first arm 3, the second arm 4 and the third arm 5 are respectively rotated on the axes U, V and W. The spot welding apparatus 10 is configured to be movable in a three-dimensional direction by rotating around. Then, the welding robot 1 performs spot welding on the welded member 50 by sequentially moving the spot welding device 10 to each spot position of the welded member 50, that is, a welded portion.

  The spot welding apparatus 10 includes a welding apparatus body 20 that is supported by a linear guide 12 fixed to a support bracket 11 attached to the third arm 5 so as to be slidable in the vertical direction. The welding apparatus main body 20 is attached with a C-shaped yoke 21 extending downward, and a lower welding electrode 22 as a first welding electrode is attached to a lower end of the C-shaped yoke 21.

  In addition, a pressure actuator 23 is mounted on the upper end of the welding apparatus main body 20 using a cylinder device or a servo motor as a drive source in the present embodiment. A rod 24 that moves up and down on the same axis as the lower welding electrode 22 through a ball screw mechanism (not shown) in the welding apparatus main body 20 by the pressurizing actuator 23 protrudes below the welding apparatus main body 20, and the lower end of the rod 24 is below the tip of the rod 24. An upper welding electrode 25, which is a second welding electrode facing the welding electrode 22 and movable coaxially with the lower welding electrode 22, is attached. As a result, the upper welding electrode 25 approaches the lower welding electrode 22 by moving the pressurizing actuator 23 away from the lower welding electrode 22, and the lower welding electrode 22. It clamps in cooperation, that is, clamps and moves toward and away from the lower welding electrode 22 between the pressing position of the lower moving end that applies a pressing force to the welded member 50.

  The welding apparatus body 20 is mounted with a ground function electrode actuator 26 adjacent to the pressurizing actuator 23 and using a servo motor as a drive source in the present embodiment, which is a servo motor. A rod 27 that moves up and down via a ball screw mechanism (not shown) in the welding apparatus main body 20 by the earth function electrode actuator 26 protrudes below the welding apparatus main body 20, and is parallel to the moving direction of the upper welding electrode 25 at the lower end of the rod 27. A movable earth function electrode 28 is attached. As a result, the earth function electrode 28 comes into contact with the retracted position of the ascending moving end by the operation of the earth function electrode actuator 26 and the member to be welded 50 held between the lower welding electrode 22 and the upper welding electrode 25 so as to be energized. In the portion, the thin plate 51 and the first thick plate 52 move between the contact positions of the lower moving ends that apply pressure so that they can be energized.

  The earth function electrode actuator 26, the rod 27, and the earth function electrode 28 can be formed by the same configuration as the pressurizing actuator 23, the rod 24, and the upper welding electrode 25.

  Further, a servo motor 15 is mounted on the upper end of the support bracket 11, and a ball screw 17 connected to the servo motor 15 is screwed into a nut 18 fixed to the welding apparatus main body 20 to constitute a screw mechanism. The welding apparatus main body 20 is moved up and down by the rotation of.

  FIG. 2 shows a welding energization circuit 30 of the spot welding apparatus 10. The welding energization circuit 30 has a welding power source 31, one end of the welding power source 31 is connected to the upper welding electrode 25 via an electric wire, the other end is connected to the earth function electrode 28 via a first switch 32, and It is connected to the lower welding electrode 22 via the second switch 33.

  2A, the first switch 32 is ON and the second switch 33 is OFF when the upper welding electrode 25 and the earth function electrode 28 are in contact with the thin plate 51 of the member 50 to be welded. The upper welding electrode 25 and the earth function electrode 28 are energized through the member to be welded 50, and the upper welding electrode is turned on when the first switch 32 is OFF and the second switch 33 is ON as shown in FIG. 25 and the lower welding electrode 22 are energized through the member to be welded 50.

  The operations of the pressure actuator 23, the earth function electrode actuator 26, the servo motor 15, and the first switch 32 and the second switch 33 of the welding energization circuit 30 are controlled by the welding apparatus controller 40, and spot welding is performed by position control of the welding robot 1. When the apparatus 10 moves to each spot position of the welded member 50, that is, the welded portion, the welding apparatus controller 40 operates the pressure actuator 23, the earth function electrode actuator 26, and the servo motor 15 to operate the lower welding electrode 22. And the welded member 50 are sandwiched between the upper welding electrode 25 and the earth function electrode 28, and a pressure is applied. Then, the welding apparatus controller 40 selectively activates the first switch 32 and the second switch 33 to energize between the upper welding electrode 25 and the earth function electrode 28 or between the upper welding electrode 25 and the lower welding electrode 22. The welding member 50 is spot welded.

  Next, referring to the spot welding device operation process diagram shown in FIG. 3 and the spot welding device operation explanatory diagram of FIGS. 4 to 6, both the upper welding electrode 25 and the earth function electrode 28 for explaining the operation of the spot device 10 are retracted. The welding apparatus 10 is moved to the spot position of the welded member 50 by the position control of the welding robot 1 while the first switch 32 and the second switch 33 are both OFF, that is, welding of the welded member 50 is performed. 4 is positioned so that the portion is located between the lower welding electrode 22 and the upper welding electrode 25, and the welding apparatus main body 20 is further moved by the servo motor 15, so that the lower welding electrode 22 is moved as shown in FIG. The tip 22a is brought into contact with the second thick plate 53 to determine the relative position between the member to be welded 50 and the spot welding apparatus 10, so-called positioning is performed. In this positioned state, the tip 22a of the lower welding electrode 22 contacts the second thick plate 53 of the member to be welded 50, while the tip 25a of the upper welding electrode 25 and the earth function electrode as shown in FIG. The tip 28a of 28 is opposed to the thin plate 51 with a gap.

  Next, in the first welding step, the upper welding electrode is actuated by the operation of the pressure actuator 23 in a state where the lower welding electrode 22 is in contact with the second thick plate 53 of the member to be welded 50 as shown in FIG. 22 is moved from the retracted position toward the pressurizing position approaching the lower welding electrode 22 to be brought into pressure contact with the thin plate 51 to sandwich the member 50 to be welded between the lower welding electrode 22 and the upper welding electrode 25. Apply pressure. Similarly, by operating the earth function electrode actuator 26, the earth function electrode 28 is moved from the retracted position toward the contact position so as to come into contact with the thin plate 51 of the member 50 to be energized, and the thin plate 51 and the first thick plate at this portion. 52 is brought into close contact with electricity.

  The welded member 50 is sandwiched between the lower welding electrode 22 and the upper welding electrode 25 and pressed, and the ground function electrode 28 is in contact with the welded member 50 so as to be energized. Switch 32 is turned on. As a result, as shown in FIG. 5B, a current i is caused to flow from the upper welding electrode 22 to the earth function electrode 28 from the welding power source 31. Then, a part ia of the current i is applied to the thin plate 51 and the first thick plate 52 between the lower welding electrode 22 and the upper welding electrode 25, which is a welded portion sandwiched and pressed between the lower welding electrode 22 and the upper welding electrode 25. By flowing through the energization path formed from the thin plate 51 to the first thick plate 52 through the junction point a located at the contact portion, the junction point a is heated and melted, and the formation of the nugget 55 is started. The nugget 55 gradually increases as the energization progresses.

  Further, a part ib of the current i flowing between the upper welding electrode 22 and the earth function electrode 28 does not pass through the junction point a and flows through the energization path of the thin plate 51 on the upper welding electrode 22 and the earth function electrode 28 side. This shunt ib is an invalid shunt that hardly contributes to the heat generation at the junction point a.

  After energization for a preset time t, the nugget 55 becomes large, the thin plate 51 and the first thick plate 52 are welded, and then the first switch 32 is turned off, and the current from the upper welding electrode 22 to the earth function electrode 28 i is cut off and the formation of the nugget 55 is stopped.

  Here, if the calorific value at the junction point a between the thin plate 51 and the first thick plate 52 is too small, a sufficiently large nugget 55 cannot be obtained, resulting in insufficient welding strength, but if the calorific value is excessive, scattering occurs. Insufficient welding strength and melting of the thin plate 51 are concerned, so that an energization time t that can ensure the optimum welding quality at the junction point a between the thin plate 51 and the first thick plate 52 is previously set in experiments or simulations. It is preferable to set based on this.

  Next, the earth function electrode actuator 26 is operated to move the earth function electrode 28 from the contact position to the retracted position, and the earth function electrode 28 is pulled away from the thin plate 51 of the member 50 to be welded. A slight gap is formed between the thin plate 51 and the first thick plate 52 in the portion along with the release of the applied pressure by the earth function electrode 28.

  In the subsequent second welding step, the welding current-carrying circuit 30 of the welding current circuit 30 is pressed with the welding position of the welding member 50 shown in FIG. 6A held between the lower welding electrode 22 and the upper welding electrode 25. The second switch 33 is turned on. As a result, a current i is caused to flow from the upper welding electrode 22 to the lower welding electrode 22 from the welding power source 31 as shown in FIG. The current i is a junction point a between the thin plate 51 and the first thick plate 52 between the lower welding electrode 22 and the upper welding electrode 25 pressurized by the lower welding electrode 22 and the upper welding electrode 25, that is, the nugget 55 and the first thickness. It flows through the energization path passing through the junction point b located at the contact portion between the plate 52 and the second thick plate 53. The nugget 55 formed at the junction point a between the thin plate 51 and the thick plate 52 has a high current density flowing through the junction point b where the first thick plate 52 and the second thick plate 53 are in pressure contact. Is heated and melted, and the formation of the nugget 56 at the junction point b is started. The nugget 56 gradually increases as the energization progresses.

  After energization for a preset time T, the nugget 56 becomes large, and the first thick plate 52 and the second thick plate 53 are welded. Then, the second switch 32 is turned OFF, and the lower welding electrode is switched from the upper welding electrode 22 to the lower welding electrode. The formation of the nugget 56 is stopped by cutting off the current i to the 23 side.

  Here, if the amount of heat generated at the junction b of the first thick plate 52 and the second thick plate 53 is too small, a sufficiently large nugget 56 cannot be obtained, resulting in insufficient welding strength, while the amount of generated heat is low. If it is excessive, the occurrence of splattering will be caused, and there is a concern that the welding strength will be insufficient. Therefore, an energization time T at which the optimum welding quality at the joint point b between the first thick plate 52 and the second thick plate 53 can be ensured is tested in advance. It is preferable to set based on simulation or the like.

  Next, the upper welding electrode 22 is moved from the pressurizing position to the retracted position by the operation of the pressurizing actuator 23 to separate the upper welding electrode 25 from the thin plate 51 of the welded member 50, and the welded member 50 is opened, that is, uncrank. To do.

  The spot welding apparatus 10 with the welded member 50 opened holds both the upper welding electrode 25 and the earth function electrode 28 in the retracted position, and the first switch 32 and the second switch 33 are both OFF. It moves to the next spot position of the welded member 50 by position control, positions the welded position of the welded member 50 between the lower welding electrode 22 and the upper welding electrode 25, and lower welding electrode 22 is positioned. The workpiece 50 and the spot welding device 10 are positioned by contacting the thick plate 53, the same operation is repeated, and a nugget 55 is formed between the thin plate 51 and the first thick plate 52, and the first thick plate 52 is formed. A nugget 56 is formed between the first thick plate 53 and the second thick plate 53, and spot welding is performed.

  As described above, in the first welding step, the lower welding electrode 22 and the upper welding electrode 25 sandwich and pressurize the welding position, and the ground function electrode 28 is in contact with the thin plate 51 and the first and second plates 51 and 25 are in contact with each other. The thin plate 51 and the first thick plate 52 are energized by energizing between the upper welding electrode 25 and the earth function electrode 28 for a preset energization time t at which an optimum welding condition is obtained at the junction point a between the thick plates 52. By forming the nugget 55 at the joining point a, sufficient welding strength between the thin plate 51 and the first thick plate 52 can be obtained. In the next second welding process, the upper welding electrode 25 and the lower welding electrode 22 are set at a preset energization time T at which an optimum welding condition is obtained at the joint point b between the first thick plate 52 and the second thick plate 53. Between the first thick plate 52 and the second thick plate 53, and a nugget 56 is formed at the junction b between the first thick plate 52 and the second thick plate 53, thereby obtaining a sufficient welding strength between the first thick plate 52 and the second thick plate 53. . That is, the welding strength of the thin plate 51 and the first thick plate 52, and the first thick plate 52 and the second thick plate 53 is obtained, and the welded member 50 in which the thin plate 51, the first thick plate 52, and the second thick plate 53 are overlapped. Uniform and stable welding quality can be obtained.

  The spot welding apparatus 1 includes a lower welding electrode 22 that faces the second thick plate 53 of the member to be welded 50 and an upper welding electrode that sandwiches and pressurizes the member to be welded 50 in cooperation with the lower welding electrode 22. 25, a ground function electrode 28 that contacts and separates the thin plate 51 of the member 50 to be welded and pressed by the lower welding electrode 22 and the upper welding electrode 25, and a member to be welded by the lower welding electrode 22 and the upper welding electrode 25. In a state where 50 is sandwiched and pressurized, current is passed between the upper welding electrode 25 and the earth function electrode 28 contacting the thin plate 51, and the upper and lower welding electrodes 25 and 25 are in contact with each other while the earth function electrode 28 is away from the thin plate 51. It can be formed with a simple configuration including a welding energization circuit 30 that energizes between the side welding electrodes 22.

  Further, the lower welding electrode 22 is disposed on the welding apparatus main body 20 disposed in the welding robot 1 via the yoke 21, and the pressure actuator 23 and the earth function electrode actuator 26 are disposed on the welding apparatus main body 20 to perform spot welding. The apparatus 10 can be easily attached to the welding robot 1.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the lower welding electrode at the time of spot welding of the thin plate 51 and the first thick plate 52 in the first welding step and welding of the first thick plate 52 and the second thick plate 53 in the second welding step. Although the case where the applied pressure and current by the upper welding electrode 25 and the upper welding electrode 25 are constant has been described as an example, spot welding of the thin plate 51 and the first thick plate 52 in the first welding step and the first thick plate in the second welding step It is possible to appropriately change the applied pressure, current, energization time, and the like at the time of welding between 52 and the second thick plate 53. The first thick plate 52 and the second thick plate 53 do not have to have the same thickness, rigidity, or the like, and the first thick plate 52 and the second thick plate 53 may be thinner than the thin plate 51.

DESCRIPTION OF SYMBOLS 1 Welding robot 10 Spot welding apparatus 20 Welding apparatus main body 21 Yoke 22 Lower side welding electrode (1st welding electrode)
23 Pressurizing actuator 25 Upper welding electrode (second welding electrode)
26 ground function electrode actuator 28 ground function electrode 30 welding energization circuit 31 welding power source 32 first switch 33 second switch 50 member to be welded 51 thin plate 52 first thick plate 53 second thick plate

Claims (5)

In the spot welding method of spot welding a member to be welded in which a thin plate, a first thick plate having a thickness greater than the thin plate, and a second thick plate are sequentially stacked,
The member to be welded is sandwiched and pressed by a first welding electrode that is disposed opposite to the second thick plate and a second welding electrode that is in contact with the second thick plate,
A first welding step of spot-welding the thin plate and the first thick plate by energizing between the second welding electrode and the earth function electrode in contact with the thin plate in the sandwiched pressure state;
Spot welding the first thick plate and the second thick plate by energizing between the second welding electrode and the first welding electrode in a non-energized state between the second welding electrode and the earth function electrode. A spot welding method comprising: a second welding step. In the spot welding method of spot welding a member to be welded in which a thin plate, a first thick plate having a thickness greater than the thin plate, and a second thick plate are sequentially stacked,
The member to be welded is sandwiched and pressed by a first welding electrode that is disposed opposite to the second thick plate and a second welding electrode that is in contact with the second thick plate,
A first welding step of spot-welding the thin plate and the first thick plate by energizing between the second welding electrode and the earth function electrode in contact with the thin plate in the sandwiched pressure state;
Second welding for spot welding the first thick plate and the second thick plate by energizing between the second welding electrode and the first welding electrode in a state where the ground function electrode is not in contact with the member to be welded. A spot welding method comprising: a step. In a spot welding apparatus that spot welds a member to be welded in which a thin plate, a first thick plate having a plate thickness larger than the thin plate, and a second thick plate are sequentially stacked,
A first welding electrode facing the second thick plate of the member to be welded;
A second welding electrode facing the first welding electrode on the same axis and facing the thin plate of the member to be welded to clamp and press the member to be welded in cooperation with the first welding electrode;
An earth function electrode that contacts and separates from the thin plate of the member to be welded and pressed by the first welding electrode and the second welding electrode;
A current is passed between the second welding electrode and the earth function electrode in contact with the thin plate in a state where the member to be welded is sandwiched and pressurized by the first welding electrode and the second welding electrode, and the earth function electrode is A welding energization circuit for energizing between the second welding electrode and the first welding electrode in a non-contact state away from the thin plate;
A spot welding apparatus comprising: A pressing position for holding and pressing the second welded electrode coaxially with the first welding electrode in close proximity to the first welding electrode and cooperating with the first welding electrode, and a retracted position for separating the thin plate from each other A pressure actuator that reciprocates between
An earth function electrode for reciprocating the earth function electrode between an abutting position where the earth function electrode is brought into contact with the thin plate of the member to be welded and pressed by the first welding electrode and the second welding electrode and a retracted position away from the thin plate An actuator,
The spot welding apparatus according to claim 3, further comprising: A welding apparatus main body supported by the welding robot, and a yoke extending to the welding apparatus main body,
The first welding electrode is disposed at a tip of the yoke;
The spot welding apparatus according to claim 4, wherein the pressure actuator and the earth function electrode actuator are disposed on the welding apparatus main body.

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