Line III consists of feeding shelf, leveling and grooving device, hydraulic notching and punching device, hydraulic plate-shearing machine and hydraulic folder. The electrical control part is mastered by computer and this control system is equipped with closed-loop feedback system, so it helps improve manufacturing precision and stability. The maximum feeding speed is 16m/min. The length tolerance is ± 0.5mm and the diagonal tolerance is ± 0.8mm. It features in high degree of high automatition, high efficiency and saving materials. So it is very suitable for mass production of square duct.