A welding station includes a welding gun that includes first and second caps. The welding gun is movable between a working position and a maintenance position. The working position corresponds to a welding operation on at least one workpiece. A maintenance tool assembly is configured to cooperate with the first and second caps in the maintenance position. The maintenance tool assembly includes a cap extractor, a cap dispenser and a cap dresser. The cap extractor is configured to remove the first and second caps from the welding gun. The cap dispenser is configured to provide a new cap to the welding gun for installation. The cap dresser is configured to shape the cap face. The maintenance tool assembly includes a lift actuator. A translate actuator is respectively configured to move the maintenance tool assembly in the lift and translate directions with respect to the welding gun.

A nugget diameter estimation method of a welded material bonded by resistance spot welding includes: a reference welding process of bonding a test material while measuring an expansion amount of the test material; a nugget diameter measurement process of measuring a nugget diameter of the bonded test material; a relational formula determination process of determining a relational formula between the measured nugget diameter of the test material and the expansion amount of the test material; a main welding process of measuring an expansion amount of the welded material, and bonding the welded material through energization while pressurizing the welded material with the pair of electrodes; and a nugget diameter estimation process of estimating a nugget diameter of the bonded welded material using the expansion amount of the welded material and the relational formula.

A flawless aluminum resistance welding system includes a welding gun that includes a gun body to engage a first welding tip and a second welding tip with an upper panel and a lower panel of an object to be welded. The welding gun further includes: a pressing actuator to press the upper panel of the object at a high pressure by the first welding tip during spot welding, a welding transformer to supply a welding current for the spot welding, an air balance cylinder to adjust an air pressure to make the second welding tip in a no-load balance state, and a linear guide unit to guide the second welding tip in up and down directions. The welding gun has an equalizing function and a bidirectional pressing structure in which the second welding tip rises with a reaction force when the first welding tip presses the upper panel.