Refill friction stir spot welding method and refill friction stir spot welding device

1. A friction stir spot welding method of performing friction stir spot welding of a pair of workpieces having a coating film formed on at least one welding surface by using a refill friction stir spot welding device including a rotary tool,

the rotary tool including a pin member that rotates around a predetermined axis and is provided to be able to advance and retract in a direction of the axis, a shoulder member that rotates around the axis while surrounding an outer periphery of the pin member and is provided independently of the pin member so as to be able to advance and retract in the direction of the axis, and a clamp member that has an end face able to press a surface of one of the pair of workpieces by coming into surface contact with the surface and is provided to surround an outer periphery of the shoulder member, the method comprising:

a coating film removal step of removing the coating film by plunging a distal end of the shoulder member into the one workpiece up to a position closer to the surface than the welding surface, while rotating the shoulder member around the axis, and rotating the shoulder member in a state in which the surface of one of the pair of workpieces, with the welding surfaces being overlaid on each other, is pressed by the end face of the clamp member; and

a welding step of performing friction stir spot welding of the pair of workpieces after the coating film removal step by using the pin member and the shoulder member,

wherein the coating film includes a resin.

2. The friction stir spot welding method according to claim 1 , wherein in the coating film removal step, the coating film is thermally decomposed by heat generated by rotation of the shoulder member.

3. The friction stir spot welding method according to claim 1 , wherein in the coating film removal step, after the distal end of the shoulder member is plunged into the one workpiece up to a standby position located closer to the surface than the welding surface while the shoulder member is rotated around the axis, the distal end of the shoulder member is made to stand by for a predetermined time while being located at the standby position.

4. The friction stir spot welding method according to claim 3 , further comprising a return step of returning the distal end of the shoulder member from the standby position to the surface position of the one workpiece between the coating film removal step and the welding step.

5. A friction stir spot welding method of performing friction stir spot welding of a pair of workpieces having a coating film formed on at least one welding surface by using a refill friction stir spot welding device including a rotary tool,

the rotary tool including a pin member that rotates around a predetermined axis and is provided to be able to advance and retract in a direction of the axis, a shoulder member that rotates around the axis while surrounding an outer periphery of the pin member and is provided independently of the pin member so as to be able to advance and retract in the direction of the axis, and a clamp member that has an end face able to press a surface of one of the pair of workpieces by coming into surface contact with the surface and is provided to surround an outer periphery of the shoulder member, the method comprising:

a coating film removal step of removing the coating film by plunging a distal end of the shoulder member into the one workpiece up to a position closer to the surface than the welding surface, while rotating the shoulder member around the axis, and rotating the shoulder member in a state in which the surface of one of the pair of workpieces, with the welding surfaces being overlaid on each other, is pressed by the end face of the clamp member; and

a welding step of performing friction stir spot welding of the pair of workpieces after the coating film removal step by using the pin member and the shoulder member,

wherein in the coating film removal step, the distal end of the shoulder member is plunged at a first speed from the surface of the one workpiece to a reference position located closer to the surface than the welding surface of the one workpiece while the shoulder member is rotated around the axis, and the distal end of the shoulder member is plunged from the reference position to the welding position at a second speed lower than the first speed.

6. The friction stir spot welding method according to claim 1 , further comprising a preliminary step of standing by for a predetermined time while rotating the shoulder member around the axis in a state in which the surface of the one workpiece is pressed by the end face of the clamp member before the coating film removal step.

7. A refill friction stir spot welding device that performs friction stir spot welding of a pair of workpieces having a coating film formed on at least one welding surface, the device comprising:

a rotary tool;

a tool driving unit configured to drive the rotary tool; and

a control unit configured to control the tool driving unit,

wherein the rotary tool includes a pin member that rotates around a predetermined axis and is provided to be able to advance and retract in a direction of the axis, a shoulder member that rotates around the axis while surrounding an outer periphery of the pin member and is provided independently of the pin member so as to be able to advance and retract in the direction of the axis, and a clamp member that has an end face able to press a surface of one of the pair of workpieces by coming into surface contact with the surface and is provided to surround an outer periphery of the shoulder member,

the control unit includes a processor and a storage medium readable by the processor, the storage medium storing a control program which executes:

coating film removal control in which the processor controls the tool driving unit to remove the coating film by plunging a distal end of the shoulder member into the one workpiece up to a position closer to the surface than the welding surface, while rotating the shoulder member around the axis, and rotating the shoulder member in a state in which the surface of one of the pair of workpieces, with the welding surfaces being overlaid on each other, is pressed by the end face of the clamp member, and

welding control in which the processor controls the tool driving unit to perform friction stir spot welding of the pair of workpieces after the coating film removal control by using the pin member and the shoulder member, and

the coating film includes a resin.

8. The friction stir spot welding method according to claim 1 , further comprising:

an alignment step of aligning the distal end of the shoulder member and a distal end of the pin member to a surface position of the one workpiece prior to the coating film removal step; and

a return step of returning the distal end of the shoulder member and the distal end of the pin member to the surface position of the one workpiece at the alignment step between the coating film removal step and the welding step.