Friction stir spot welding device and friction stir spot welding method

A friction stir spot welding device which welds an object to be welded, by softening the object by friction heat and by stirring the object, the friction stir spot welding device comprising:

• a pin member which has a solid cylinder shape, is rotatable around an axis of the pin member, and is advanceable and retractable along the axis of the pin member;
• a shoulder member which has a tubular shape with a circular cross-section, is rotatable around an axis of the shoulder member, and is advanceable and retractable along the axis of shoulder member, the pin member being insertable into the shoulder member;
• a rotation driving unit which rotates the pin member around the axis of the pin member and rotates the shoulder member around the axis of the shoulder member:
• a tool driving unit which causes the pin member to be advanced and retracted along the axis of the pin member, and causes the shoulder member to be advanced and retracted along the axis of the shoulder member;
• a position detector which detects an axial position of a tip end surface of the pin member or an axial position of a tip end surface of the shoulder member;
• and
• a controller which
• sets as a reference position the axial position of the tip end surface of the pin member or the axial position of the tip end surface of the shoulder member which is detected by the position detector at a time point when the tip end surface of the pin member or the tip end surface of the shoulder member contacts an obverse surface of the object, when a welding process for the object is initiated,
• controls the tool driving unit to make the tip end surface of the pin member and the tip end surface of the shoulder member coplanar with each other, when the welding process for the object ends,
• controls the tool driving unit to reduce a pressing force applied to the object by the pin member and a pressing force applied to the object by the shoulder member in a next welding process, and/or controls the rotation driving unit to reduce a rotational speed of the pin member and a rotational speed of the shoulder member in the next welding process, in a case where a first position which is the axial position of the tip end surface of the pin member or the axial position of the tip end surface of the shoulder member, which is detected by the position detector, is within a first region which is inward of the object relative to the reference position, when the welding process for the object ends.

A friction stir spot welding method which welds an object to be welded, by softening the object by friction heat and by stirring the object, the friction stir spot welding method comprising:

• (A) setting as a reference position an axial position of a tip end surface of a pin member or an axial position of a tip end surface of a shoulder member which is detected by a position detector at a time point when the tip end surface of the pin member or the tip end surface of the shoulder member contacts an obverse surface of the object, wherein the pin member has a solid cylinder shape, is rotatable around an axis of the pin member, and is advanceable and retractable along the axis of the pin member, and the shoulder member is disposed to surround an outer peripheral surface of the pin member, has a tubular shape with a circular cross-section, is rotatable around an axis of the shoulder member, and is advanceable and retractable along the axis of the shoulder member;
• (B) causing a tool driving unit to advance and retract the pin member or the shoulder member along the axis of the pin member or the axis of the shoulder member, in a state in which the object is pressed by a preset pressing force applied by the pin member or the shoulder member, and causing a rotation driving unit to rotate the pin member or the shoulder member at a preset rotational speed, to partially stir the object and weld the object;
• (C) driving the tool driving unit to make the tip end surface of the pin member and the tip end surface of the shoulder member coplanar with each other, when the welding process for the object ends,
• (D) detecting a first position by the position detector, the first position being an axial position of the tip end surface of the pin member or an axial position of the tip end surface of the shoulder member, after (C);
• and
• (E) changing setting to reduce a pressing force applied to the object by the pin member and a pressing force applied to the object by the shoulder member in a next welding process, and/or to reduce a rotational speed of the pin member and a rotational speed of the shoulder member in the next welding process, in a case where the first position is within a first region that is inward of the object relative to the reference position.