JP2009184019A - Spot joining apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spot joining apparatus and method that can keep joining quality constant regardless of positional deviation of a workpiece, the apparatus capable of being simplified. <P>SOLUTION: In the spot joining apparatus 50, a fixed arm 52 is fixed at a position where joining is to be performed. A joining tool 55 is fixed to the fixed arm 52 and rotatably installed around the axial line of rotation. A movable arm 53 is installed in the fixed arm 52 in a manner making angular displacement possible. A backing is provided in the movable arm 53 and is displaced in a direction approaching to or receding from the joining tool 55 in accordance with the angular displacement of the movable arm 53. The backing is formed on the surface part facing the joining tool 55 and is provided with a contact face with an area larger than the tip end of the joining tool 55. A driving source 59 is installed in the fixed arm 52, driving the movable arm 53 in a direction in which the backing at least comes close to the joining tool 55. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spot welding apparatus and a spot welding method for spot-joining workpieces by friction stir welding.

  FIG. 8 is a view showing a structure of a conventional spot welding apparatus 1 using friction stirring. The spot bonding apparatus 1 includes a bonding tool 5 having a pin at a tip, a rotation motor 4 that rotationally drives the bonding tool 5, and a pressing device 3 that raises and lowers the bonding tool 5 to apply a pressing force. .

  Next, a joining method will be described with reference to the drawing in FIG. 8A. First, two workpieces W1 and W2 are placed on the backing 7 in an overlapping manner. Next, while rotating the welding tool 5 with the rotation motor 4, the pressing tool 3 lowers the welding tool 5 together with the rotation motor 4. Then, the pin at the tip of the joining tool is pressed against the workpiece. When the pin is pressed, the pressing portion is softened by friction due to rotation, and the pin is inserted. By further rotating, the vicinity of the joining point is agitated by the inserted pin, and plastic flow occurs. After stirring for a predetermined time, when the joining tool 5 is raised by the pressing device 3, two workpieces are joined at the joining point and spot-joined.

  The spot welding apparatus 1 is attached to, for example, an arm wrist of a robot, and positions the bonding apparatus 1 at each joining point to continuously perform spot welding on one workpiece. However, the workpiece position varies from workpiece to workpiece, and as shown in FIG. 8B, the workpieces W1, W2 and the backing 7 may be arranged at positions separated from each other. If the welding tool 5 is lowered in such a state of being displaced, the workpieces W1 and W2 are pushed down with the pins at the tip of the welding tool 5, and the workpiece is deformed, so that the bonding quality is deteriorated. End up. Also, the pressing force is different, the joining quality differs for each workpiece, and a constant joining quality cannot be obtained.

  Further, in order to eliminate the misalignment and obtain a certain joining quality, a method of finely adjusting the position of the joining head 2 holding the joining tool 5, the rotation motor 4 and the pressing device 3 for each work can be considered. However, in this case, the control becomes complicated. Further, if the joining tool and the backing are separated and are joined to each other by displacing them, there is a problem that the apparatus becomes complicated and positioning becomes complicated.

  An object of the present invention is to provide a spot joining apparatus and a spot joining method capable of keeping the joining quality constant regardless of the displacement of the workpiece position and reducing the size of the apparatus.

The present invention includes a fixed arm that is fixed at a position where joining is performed;
A joining tool fixed to a fixed arm and provided to be rotatable around a rotation axis;
A movable arm provided on the fixed arm so as to be angularly displaceable;
A backing provided on the movable arm and displaced in a direction toward or away from the welding tool by angular displacement of the movable arm;
A backing formed with a contact surface having a larger area than the tip of the joining tool on the surface facing the joining tool;
A spot welding apparatus, comprising: a driving source provided on the fixed arm and driving the movable arm in a direction in which the backing approaches or separates from the welding tool.

In the present invention, the joining tool is provided at one end in the longitudinal direction of the fixed arm,
An angular displacement axis of angular displacement of the movable arm with respect to the fixed arm is formed at an intermediate position in the longitudinal direction of the fixed arm,
The drive source is provided at the other end of both ends in the longitudinal direction of the fixed arm.

  In the invention, it is preferable that the fixed arm is provided at a distal end portion of the robot arm.

Further, the present invention uses the spot bonding apparatus,
A joining tool placement step of placing the joining tool in the vicinity of the stacked workpieces;
After the joining tool placement step, a rotation start step for starting the rotation of the joining tool,
After the rotation start step, by causing the movable arm to be angularly displaced by the drive source, the clamping step of bringing the backing close to the joining tool,
The spot welding method is characterized in that the object to be joined is softened by the frictional heat between the joining tool and the object to be joined, stirred, and spot-joined at the joining point.

  According to the present invention, the movable arm is provided on the fixed arm so as to be angularly displaceable. The joining tool is fixed to the fixed arm, and the backing is provided on the movable arm. The backing is formed on the surface facing the welding tool, with a contact surface having a larger area than the tip of the welding tool. The drive source is provided on the fixed arm. Thereby, the contact by the backing can be performed before the contact by the joining tool with respect to the objects to be joined arranged between the joining tool and the backing. Therefore, it can prevent that a to-be-joined object is pressed by the joining tool. Thereby, it can prevent that a to-be-joined object deform | transforms with the front-end | tip part of a joining tool. Therefore, the joining quality can be kept constant regardless of the positional deviation of the objects to be joined. Further, since the drive source is provided on the fixed arm, the apparatus can be reduced in size as compared with the case where the positioning and driving of the joining tool and the positioning and driving of the backing are performed respectively.

  Further, the driving source displaces the movable arm with respect to the fixed arm, thereby bringing the backing close to or away from the joining tool. Thereby, the joining tool and the backing can be moved together. Therefore, the apparatus can be downsized and the apparatus can be easily moved as compared with the case where the joining tool and the backing are moved to each other.

  According to the invention, the joining tool is provided at one end of the fixed arm in the longitudinal direction, and the angular displacement axis of the angular displacement of the movable arm with respect to the fixed arm is formed at a position in the middle of the fixed arm in the longitudinal direction. Is provided at the other end portion on the opposite side to the one end portion where the joining tool is provided, of the both ends in the longitudinal direction of the fixed arm. Thus, the joining tool and the backing can be arranged on both sides in the thickness direction of the article to be joined, and the drive source can be arranged on the opposite side of the article with respect to the angular displacement axis. Therefore, it is possible to prevent the drive source from coming into contact with the object to be bonded when the bonding tool and the backing are disposed on the object to be bonded. Thereby, arrangement | positioning of the joining tool and backing with respect to a to-be-joined object can be made easy.

  According to the invention, the fixed arm is provided at the tip of the robot arm. Thereby, the joining tool and the backing can be integrated and moved by the robot arm. The movement of the joining tool and the movement of the backing do not need to be performed independently, and the apparatus can be miniaturized.

  Further, according to the present invention, in the clamping process, the backing is brought close to the welding tool by angularly displacing the movable arm by the driving source after the welding tool arranging process. Thereby, the contact by the backing can be performed before the contact by the joining tool with respect to the objects to be joined arranged between the joining tool and the backing. Therefore, it can prevent that a to-be-joined object is pressed by the joining tool. Thereby, it can prevent that a to-be-joined object deform | transforms with the front-end | tip of a joining tool. Therefore, the joining quality can be kept constant regardless of the positional deviation of the objects to be joined. Further, the apparatus can be downsized as compared with the case where the positioning and driving of the joining tool and the positioning and driving of the backing are performed respectively.

It is a perspective view which shows the structure relevant to the spot joining apparatus of this invention. It is a front view which shows the structure of the spot joining apparatus 10 which is one Embodiment relevant to this invention. It is a front view which shows the spot joining apparatus 10 relevant to this invention at the time of joining. It is a figure which shows the structure of the spot joining apparatus 30 of other embodiment relevant to this invention. It is a figure which shows the state at the time of joining of the spot joining apparatus 30 of other embodiment relevant to this invention. It is a figure which shows the structure of the spot joining apparatus 40 relevant to this invention. It is a figure which shows the structure of the spot joining apparatus 50 which concerns on one Embodiment of this invention. It is a figure which shows the conventional spot joining apparatus 1. FIG.

  FIG. 2 is a diagram showing an overall configuration of a spot bonding apparatus 10 which is an embodiment related to the present invention. The spot bonding apparatus 10 is attached to the wrist of an arm of a 6-axis vertical multi-indirect robot, for example, and used as a spot bonding gun, for example, for spot bonding of an automobile body.

  The spot bonding apparatus 10 includes a bonding head 11, a gun arm 12, a bonding head support mechanism 21, and a backing pressing mechanism 20. The gun arm 12 has a bonding head 11 attached to the upper part via a bonding head support mechanism 21 and a backing pressing mechanism 20 attached to the lower part. The gun arm 12 is attached to the wrist 15 of the robot arm.

  The joining head 11 is fixed to the joining tool 18, the bracket 17 that supports the joining tool 18 so as to be rotatable about the rotation axis L thereof, and the rotation motor 16 that rotationally drives the joining tool 18 around the rotation axis L. The bracket 17 is attached to the joining head support mechanism 21. The joining head support mechanism 21 has, for example, a motor, and can raise and lower the bracket 17 and raise and lower the joining tool 18 along the axis L. In addition, raising / lowering of the joining tool 18 by this joining head support mechanism 21 is not used for pressing a workpiece | work at the time of joining, but is used for positioning to a workpiece | work. Therefore, a mechanism that manually moves up and down by a handle or the like instead of a driving source such as a motor may be used.

  The backing pressing mechanism 20 includes a backing 19, a backing pressing cylinder 13, and a drive source 14. The backing 19 is arranged facing the lower side of the joining tool 18, and a piston rod 25 of the backing pressing cylinder is fixed to the lower portion. The backing pressing cylinder 13 is a cylinder having a piston rod 25 that moves up and down along the rotation axis L of the joining tool 18, and the backing 19 is fixed to the tip of the piston rod 25. The backing pressing cylinder 13 is composed of, for example, a hydraulic cylinder, a pneumatic cylinder, or a ball screw. A driving source 14 is disposed adjacent to the backing pressing cylinder 13, and the driving source 14 is fixed to the gun arm 12. The drive source 14 is a hydraulic source when the backing pressing cylinder 13 is a hydraulic cylinder, a pneumatic source when the pneumatic cylinder is a pneumatic cylinder, and a servo motor when the ball screw is a ball screw.

  The joining tool 18 has a cylindrical shape, the central axis L is the rotational axis L, the lower end is tapered, and the pin 26 projects along the axis L from the center of the circular flat surface 18a at the tip. The workpieces W1 and W2 to be joined are, for example, aluminum alloys.

  The backing member 19 has a substantially rectangular parallelepiped shape, and a workpiece is mounted on the upper surface 19a. The upper surface 19a is formed with a slightly raised center. More specifically, the rectangular parallelepiped backing member 19 is arranged so that the center portion is perpendicular to the welding tool L, and the center in the width direction of the upper surface is slightly raised and extends in the longitudinal direction (FIG. 1). reference). This is because when the backing 19 is raised, the workpieces W1 and W2 are smoothly curved within the elastic deformation range.

  Further, a pressure sensor such as a load cell is embedded in the pressing member 19. The detection position of the pressure sensor exposed from the backing member upper surface 19a is arranged outside the position facing the circular flat surface 18a at the tip of the welding tool and at a position close to the circular flat surface 18a. This is because the most pressing force is applied at the position facing the circular flat surface 18a at the tip of the welding tool, and when the sensor is exposed at this position, the sensor is transferred to the back of the workpiece W2 when pressed and the aesthetic appearance is impaired. It is.

  Next, with reference to FIG. 2 and FIG. 3, the joining method of the spot joining apparatus 10 relevant to this invention is demonstrated.

  First, the rotating tool 16 rotates the welding tool 18 at a high speed, and the robot spots the pins 26 of the welding tool 18 so that the pins 26 of the welding tool 18 are arranged immediately above the predetermined bonding points of the workpieces W1 and W2 that are arranged in a stacked manner. The bonding apparatus 10 is positioned. At this time, as shown in FIG. 2, the distance h between the tip of the pin 26 and the workpiece surface is about 5 to 10 mm. Further, the displacement of the workpiece in the direction of the rotation axis L of the welding tool 18 (in this case, the vertical direction) is corrected by adjusting the vertical position of the welding head 11 by the welding head support mechanism 21.

  Next, the backing 19 is raised by the backing pressing cylinder 13. Then, as shown in FIG. 3, the workpieces W1 and W2 are pushed up and bent by the backing 19, and the pins 26 of the joining tool 18 are pressed against the joining points of the workpieces W1 and W2 while rotating.

  As described above, the backing member 19 is formed so that the upper surface 19a is slightly raised, and the curved surface of the upper surface 19a is substantially the same as the workpieces W1 and W2 that are curved when the backing member 19 pushes up the workpieces W1 and W2. It is in line with the shape. Therefore, when the backing member 19 is pushed up, the workpieces W1, W2 are smoothly curved and the workpieces W1, W2 are prevented from being plastically deformed.

  In addition, since the area of the backing upper surface 19a is much larger than the circular flat surface 18a at the lower end of the welding tool, even if the workpieces are displaced, the pressing force is applied by lowering the welding tool 18. Compared with the case where the pressing force is applied, the pressing force is applied by raising the backing 19 to reduce the variation in the pressing force due to the displacement of the workpiece.

  When the rotating pin 26 is pressed against the workpiece, the workpiece is softened by frictional heat, and the pin 26 is inserted. When the pin is inserted and rotated, the base material is agitated and plastic flow is induced. Further, when the circular flat surface 18a at the lower end of the joining tool comes into contact with the workpiece surface, it is also stirred here. The pressing force at this time is detected by the pressure sensor. When the predetermined pressing force is reached, the pressing of the backing member 19 by the backing pressing cylinder 13 is stopped and the predetermined pressing force is applied for a predetermined time. As a result, the workpieces W1 and W2 are sufficiently stirred at the joining point.

  When pressed for a predetermined time, the backing 19 is lowered by the backing pressing cylinder 13. Then, the workpieces W1 and W2 that are curved upward and elastically deformed are returned to their original positions by the elastic restoring force, and the pin 26 is pulled out from the joint point. The joints of the workpieces W1 and W2 from which the pins 26 have been pulled out are cooled, and the workpieces W1 and W2 are integrated into a spot in the plastic flow region.

  When the joining at this joining point is completed, the robot moves the spot joining apparatus 10 to the next joining point. At this time, when the position of the next bonding point is shifted in the axis L direction (in this case, the vertical direction) from the previous bonding point, the vertical position of the bonding head 11 is adjusted by the bonding head support mechanism 21. Thereby, it is not necessary to control the vertical position of the joining apparatus 10 with a robot, and joining points can be joined continuously and smoothly in the same workpiece.

  FIG. 4 is a diagram showing a spot bonding apparatus 30 according to another embodiment related to the present invention. FIG. 5 is a diagram illustrating a state at the time of bonding in a spot bonding apparatus 30 according to another embodiment related to the present invention. Unlike the spot bonding apparatus 10 described above, the spot bonding apparatus 30 is a spot bonding apparatus that is installed on the floor and used instead of a spot gun that is mounted on the wrist of a robot. In this spot bonding apparatus 30, the shape of the backing 31 is different from the backing 19 of the spot bonding apparatus 10 described above, but the other configurations are substantially the same, and thus the corresponding configurations are denoted by the same reference numerals. The description is omitted.

  In the spot bonding apparatus 10, the backing 19 has a curved upper surface. However, the backing 31 of the spot bonding apparatus 30 is large enough to place the workpieces W 1 and W 2 as shown in FIG. The upper surface is flat. Even in such a configuration, the workpieces W1 and W2 can be spot-bonded by raising the backing 31 and pressing the workpieces W1 and W2 against the welding tool with a predetermined pressing force.

  Next, a spot bonding gun 40 which is another embodiment related to the spot bonding apparatus of the present invention will be described with reference to FIG. The spot joining gun 40 is a welding gun that performs a pressurizing operation used for spot welding or the like, and is obtained by applying the configuration of the present invention to a type of gun called a C gun.

  The spot bonding gun 40 includes a gun arm 48, a pressure receiving tool 47 that is a backing of the bonding tool 46, a rotation motor 44, a fixing portion 41, and a ball screw 45. The gun arm 48 includes a fixed portion 41 and a movable portion 42, and a joining tool 46 is rotatably held at the tip of the fixed portion 41. A rotation motor 44 is fixed to the tip, and a welding tool 46 is connected to the output shaft of the rotation motor 44 with the rotation axis line aligned. Further, a ball screw 45 is fixed to the fixing portion 41 in parallel to the rotation axis of the welding tool 46. The ball screw 45 includes a screw shaft 45 a and a nut member 45 b, and the screw shaft 45 a is rotationally driven by a pressurizing motor 43 fixed to the fixing portion 43. The movable portion 42 is fixed to the nut member 45b, and the screw shaft 45a rotates, whereby the movable portion 42 moves up and down in the direction of the rotation axis of the welding tool 46 together with the nut member 45b. A pressure receiving member 47 is provided at the distal end of the movable portion 42 so as to face the joining tool 46.

  Such a joining gun 40 is equipped on the wrist of a 6-axis articulated robot, for example. At the time of joining, the spot welding gun 40 is positioned by a robot so that the workpiece is placed on or above the pressure receiving member 47, and the pressing motor 43 is rotated while the welding tool 46 is rotated by the rotating motor 44. The movable part 42 is raised and joined. As described above, in the spot bonding gun 40, since the pressurizing motor 43, which is the drive source of the movable part 42, is arranged on the fixed part 41, the weight of the movable part 42 can be greatly reduced, and positioning during pressurization is possible. It became possible to easily improve control capabilities such as accuracy and pressure.

  Next, a spot bonding gun 50 according to an embodiment of the present invention will be described with reference to FIG. The spot bonding gun 50 is obtained by applying the configuration of the present invention to a type of gun called an X gun used for spot welding or the like.

  The spot bonding gun 50 includes a gun arm 51, a bonding tool 55, a rotation motor 57, a pressure motor 59, a pressure receiving tool 54 as a backing, and a ball screw 58. The gun arm 51 includes a fixed arm 52 and a movable arm 53. The fixed arm 52 and the movable arm 53 extend substantially in parallel with each other, and are connected via an angular displacement shaft 60 so as to be angularly displaceable, so that the tip end portion can be opened and closed.

  The joining tool 55 is rotatably held at the distal end of the fixed arm 52, and the rotation motor 57 is fixed to the proximal end side. The output shaft of the rotation motor 57 and the joining tool 55 are connected by a power transmission mechanism 56 using a belt, and a rotational force is transmitted. A pressing motor 59 and a ball screw 58 are provided behind the rotating shaft 60 (to the right in FIG. 7). The screw shaft 58a of the ball screw 58 has a lower end portion connected to the movable arm 53 so as to be angularly displaceable. A pressurizing motor 59 is connected to the fixed arm 52 so that the upper end portion can be angularly displaced, and an output shaft is a nut member of the ball screw 58. 58b. Therefore, by rotating the nut member 58b of the ball screw 58 with the pressurizing motor 59, the proximal end portion of the fixed arm 52 and the proximal end portion of the movable arm 53 are moved close to and away from each other, whereby the distal end portion of the gun arm 51 is moved. Opened and closed.

  The spot bonding gun 50 is also used by being mounted on the wrist of a robot, for example. At this time, the base end portion of the fixed arm 52 of the gun arm 51 is fixed to the wrist of the robot.

  When spot welding is performed, the spot welding gun 50 is positioned by a robot so that the workpiece is placed on the pressure receiver 54 or above the pressure receiver 54, and the welding tool 55 is rotated by the rotation motor 57. The gun arm 51 is closed by the pressurizing motor 59 and the workpiece is clamped and joined.

  As described above, also in the spot bonding gun 50 of the present embodiment, since the pressurizing motor 59 is provided on the fixed arm 52, the weight of the movable part can be greatly reduced, and the control ability at the time of pressurization is easily improved. Can be made. Furthermore, in the present embodiment, the rotation motor 57 is disposed at the base end portion of the fixed arm 52, and the rotation of the rotation motor 57 is transmitted by the power transmission mechanism 56. It is possible to reduce the restrictions on the workpiece shape and the parts that can be joined.

The following embodiments are possible for the present invention.
(1) Arrange the objects to be joined between the backing and the welding tool, and press and hold the objects to be joined between the tip of the welding tool and the backing with the joining tool rotated around the rotation axis. In the spot welding method of softening and stirring the object to be welded by frictional heat generated by the rotation of the welding tool, and spotly joining the two objects to be joined at the joining point
At the time of joining, the spot welding method is characterized in that the joining tool is rotationally driven in a state of being fixedly held with respect to the rotation axis direction, and the backing is moved in a direction close to the joining tool to press the objects to be joined. .

  In a state where the welding tool is fixedly held, the backing is moved toward the welding tool and the object to be joined is pressed. That is, as shown in FIG. 1A, the tip of the welding tool is pressed against the workpiece by raising the backing side having a large contact area to the workpiece and pushing up the workpiece. In the above-described prior art, when the object to be bonded is displaced and the backing and the object to be bonded are separated, the object to be bonded is deformed by pressing the object to be bonded with the pin at the tip of the bonding tool. As a result, the pressing force differs depending on the amount of displacement, and a certain joining quality could not be obtained.However, in the present invention, the backing with a large contact area against the workpiece is lifted and pressed. Even when the bonded object is displaced, a substantially constant pressing force can be applied, and the bonding quality can be kept constant regardless of the displacement of the bonded object.

  As described above, since the backing having a large contact area to the workpiece is lifted and pressed, even if the workpiece is displaced, a substantially constant pressing force can be applied, The joining quality can be kept constant regardless of the misalignment of the joined object.

  (2) A spot joining method characterized by elastically deforming an object to be joined when the backing is moved in a direction close to the joining tool.

  Since the object to be joined is lifted and elastically deformed and pressed, as shown in FIG. 1 (2), when the pressing of the backing is released, the object to be joined can be easily detached from the joining tool by the elastic restoring force. it can.

  Further, since the object to be bonded is lifted and elastically deformed and pressed, when the pressing of the backing is released, the object to be bonded can be easily detached from the bonding tool by the elastic restoring force.

(3) The object to be joined is placed between the backing and the joining tool, and the joining tool is pressed with the tip of the joining tool and the backing while the joining tool is rotated. In a spot joining apparatus that softens and stirs the object to be joined with frictional heat, and spot-joins two stacked objects to be joined at the joining point.
The backing is provided so as to be movable in the direction of approaching and separating from the joining tool. At the time of joining, the joining tool is fixedly held, and the backing is moved in the direction of approaching the joining tool to move the object to be joined. A spot bonding apparatus characterized by pressing.

  Even when the object to be joined is displaced, a substantially constant pressing force can be applied, and the joining quality can be kept constant regardless of the position displacement of the object to be joined.

  In addition, the rotary drive source is fixed to the fixed part and is configured to press only by moving the backing at the time of joining, so it is possible to greatly reduce the weight of the movable part of the pressure shaft. Sometimes it is possible to easily improve the control capability (positioning accuracy, pressure).

(4) a fixing portion that rotatably holds the joining tool;
A movable part having a backing and provided movably with respect to the fixed part;
A spot welding apparatus, comprising: a rotation driving source that is fixedly held by a fixing unit and that rotationally drives the welding tool.

  The rotational drive source is fixed to the fixed portion, and only the backing is moved and pressurized at the time of joining. In other words, since the rotary drive source is not provided on the pressurization side, the weight of the movable part of the pressurization shaft can be greatly reduced, and the control capability (positioning accuracy, pressurization) during pressurization is easy. Can be improved.

(5) The rotational drive source is fixed to the fixing portion so as to be spaced apart in a direction perpendicular to the rotation axis of the welding tool,
A spot welding apparatus comprising a transmission means for transmitting a rotational force of a rotational drive source to a welding tool.

  The rotational drive source is separated from the joining tool, and is configured to transmit the rotational force by a transmission means such as a belt or a gear. As a result, the tip of the spot bonding apparatus provided with the bonding tool can be reduced in size, and the restrictions on the workpiece shape and the bondable part that are the objects to be bonded can be reduced.

  In addition, since the rotational drive source is separated from the welding tool and is configured to transmit the rotational force with a transmission means such as a belt or gear, the tip of the spot welding device provided with the welding tool can be reduced in size and joined. Constraints on workpiece shapes and parts that can be joined are reduced.

DESCRIPTION OF SYMBOLS 10, 30, 40, 50 Spot welding apparatus 11 Joining head 13 Back pressing cylinder 18, 46, 55 Joining tool 19 Back 20 Back pressing mechanism

Claims (4)

A fixed arm that is fixed at a position where joining is performed;
A joining tool fixed to a fixed arm and provided to be rotatable around a rotation axis;
A movable arm provided on the fixed arm so as to be angularly displaceable;
A backing provided on the movable arm and displaced in a direction toward or away from the welding tool by angular displacement of the movable arm;
A backing formed with a contact surface having a larger area than the tip of the joining tool on the surface facing the joining tool;
A spot welding apparatus comprising: a driving source provided on the fixed arm and driving the movable arm in a direction in which the backing approaches or moves away from the welding tool. The joining tool is provided at one end in the longitudinal direction of the fixed arm,
An angular displacement axis of angular displacement of the movable arm with respect to the fixed arm is formed at an intermediate position in the longitudinal direction of the fixed arm,
2. The spot bonding apparatus according to claim 1, wherein the driving source is provided at the other end of both ends in the longitudinal direction of the fixed arm.   The spot bonding apparatus according to claim 1, wherein the fixed arm is provided at a tip portion of a robot arm. Using the spot bonding apparatus according to any one of claims 1 to 3,
A joining tool placement step of placing the joining tool in the vicinity of the stacked workpieces;
After the joining tool placement step, a rotation start step for starting the rotation of the joining tool,
After the rotation start step, by causing the movable arm to be angularly displaced by the drive source, the clamping step of bringing the backing close to the joining tool,
A spot joining method characterized by softening, agitating, and spot-joining at a joining point by a frictional heat between a joining tool and an article to be joined.

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