Resistance spot welding apparatus

A resistance spot welding apparatus configured to weld a workpiece made of layered metallic plates, the resistance spot welding apparatus comprising:

• a first electrode configured to contact a first metallic plate among the metallic plates;
• a second electrode configured to contact a second metallic plate among the metallic plates, the second electrode being arranged such that the workpiece is interposed between the first electrode and the second electrode;
• and
• a pressure mechanism configured to apply air pressure to the first electrode towards the first metallic plate,
• wherein the pressure mechanism comprises:
• a piston coupled to the first electrode;
• a cylinder having an inner space that accommodates the piston;
• a first ventilation unit configured to supply the inner space with air for applying air pressure to the first electrode;
• a second ventilation unit configured to discharge air from the inner space as air pressure is applied to the first electrode;
• and
• an air supply system configured to supply air to the first ventilation unit and permit discharge of air from the second ventilation unit,
• wherein the first ventilation unit comprises first and second air passages independent from each other, communicating with the inner space, and respectively coupled to first and second apertures that are provided in the cylinder and face each other in a radial direction of the cylinder, and
• wherein the second ventilation unit comprises third and fourth air passages independent from each other, communicating with the inner space, and respectively coupled to third and fourth apertures that are provided in the cylinder and face each other in a radial direction of the cylinder.