The main welding line has the characteristics of high automation, high welding precision, stable takt time, etc. It mainly completes the welding tasks of the under body assembly and BIW assembly; By virtue of programmable logic controller (PLC) control, the whole process is automated. The main components are robot, electrode trimmer, water gas unit RIP and HIP, internal conveying system, positioning jig, handling gripper, gun change plate, servo resistance welding gun, arc welding gun, automatic stud welding gun, SPR, FDS, automatic sealing equipment, automatic loading equipment APC, line side loading and unloading cart with fine positioning, safety fence, etc.