A welding gun assembly including a housing that defines a first chamber and a second chamber. The assembly also includes a first piston moveably disposed in the first chamber and a second piston moveably disposed in the second chamber. The assembly includes an intensifying rod that can move at least partially into the first chamber due to movement of the second piston within the second chamber. The assembly includes a controller with a pressure sensor operable to detect pressure within the first chamber. The controller is operable to increase pressure within the first chamber up to a predetermined extension pressure while the intensifying rod is disposed outside of the first chamber. The controller is further operable to increase pressure within the second chamber to thereby move the intensifying rod into the first chamber to thereby increase pressure within the first chamber above the predetermined extension pressure.