Spot welding apparatus

1. A spot welding apparatus comprising:

a first fixed welding electrode;

a second movable welding electrode which is moved by a pressure actuator, and the second movable welding electrode is disposed to face the first fixed welding electrode and configured to clamp and press at least three workpieces together with the first fixed welding electrode; and

a control pressing force applicator configured to apply a control pressing force to a workpiece of the at least three workpieces by bringing a pressing force applying unit disposed adjacent to the first fixed welding electrode into contact with a lower surface of a thinnest workpiece of the at least three workpieces;

wherein spot welding is performed by applying current between the first fixed welding electrode and the second movable welding electrode while the workpiece is clamped and pressed by the first fixed welding electrode that is in contact with the workpiece, the pressing force applying unit of the control pressing force applicator that is in contact with the workpiece, and the second movable welding electrode that faces the first fixed welding electrode and is in contact with the workpiece; and

wherein the control pressing force applicator includes:

a control pressing force applying actuator that has a movable shaft which moves reciprocally; and

a control pressing force applying arm that comprises a non-magnetic material and includes:

a base end arm that has a base end connected to the movable shaft and extends in a direction at an angle with respect to the movable shaft;

the base end arm is formed of a U-shaped plate surrounding only half of the second movable welding electrode and has a semi-circular cross-section shape that allows the second movable welding electrode to move therethrough;

a pair of ends of the U-shaped plate of the base end arm are each connected to the movable shaft which extends below the actuator;

an arm that has a base end connected to a distal end of the base end arm and extends in an axial direction of the first fixed welding electrode;

a movable receiving unit that has a base end connected to a distal end of the arm and has a distal end on which the pressing force applying unit is provided; and

wherein the control pressing force applicator is configured to apply the control pressing force to the workpiece by moving the movable shaft of the control pressing force applying actuator and thereby bringing the pressing force applying unit provided on the distal end of the arm into contact with the workpiece.

2. The spot welding apparatus according to claim 1 , wherein the arm comprises a non-magnetic material.

3. The spot welding apparatus according to claim 1 , wherein the control pressing force applying arm has an outer surface having a corrugated heat transfer structure.

4. The spot welding apparatus according to claim 2 , wherein the control pressing force applying arm has an outer surface having a corrugated heat transfer structure.

5. The spot welding apparatus according to claim 1 , wherein the non-magnetic material includes a non-magnetic stainless steel.

6. The spot welding apparatus according to claim 2 , wherein the non-magnetic material includes a non-magnetic stainless steel.

7. The spot welding apparatus according to claim 3 , wherein the non-magnetic material includes a non-magnetic stainless steel.

8. The spot welding apparatus according to claim 4 , wherein the non-magnetic material includes a non-magnetic stainless steel.

9. The spot welding apparatus according to claim 1 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

10. The spot welding apparatus according to claim 2 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

11. The spot welding apparatus according to claim 3 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

12. The spot welding apparatus according to claim 4 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

13. The spot welding apparatus according to claim 5 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

14. The spot welding apparatus according to claim 6 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

15. The spot welding apparatus according to claim 7 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

16. The spot welding apparatus according to claim 8 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

17. The spot welding apparatus according to claim 1 , wherein the base end arm extends in a horizontal direction at an angle with respect to the movable shaft.

18. The spot welding apparatus according to claim 1 , wherein the movable receiving unit of the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

19. The spot welding apparatus according to claim 1 , wherein the base end arm of the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.

20. The spot welding apparatus according to claim 2 , wherein the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water,

wherein the movable receiving unit of the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water, and

wherein the base end arm of the control pressing force applying arm includes a water passage in which cooling water flows and is cooled by the cooling water.