Auto duct line 3 consists of a metal frame, leveling and beading machine, hydraulic punching machine - punching sharped and square mouth, hydraulic shearing machine and hydraulic folding machine. Electrics controlled by automatic computer controller with a closed-loop feedback system which obviously improve the precision and stability of production. The maximum operating speed is 16m/min. Length error of ±0.5mm and diagonal error of ±0.8mm.