The tower crane large-tonnage support welding project utilizes a two-axis positioner at the welding workstation, where two robots simultaneously weld the tower crane support. The welding form of the dual robots is the overhead gantry structure (X/Y/Z three-axis) + cantilever structure (X/Z/rotating axis). All axes are external axes of the robot, which can be linked with the robot for welding, and both robots can independently or jointly with the positioner linkage. The gantry is equipped with a two-layer platform, which is used to store welding power source wire feeding barrels and other objects, which is convenient for personnel to conduct inspection and maintenance.