Automatic punching stroke search and compensation

The punching machine is a mechanical equipment that is widely used in leather cutting. To facilitate mass production, both the punching table and layout are designed to accommodate long strokes over a large area. This enables one-time automatic continuous punching of large leather sheets. However, as the punching layout increases in size, it becomes more difficult to maintain the equal distance of the die cutter and table plate. Moreover, the table plate is overlaid with a polypropylene (PP) punching pad that is approximately 25 mm thick. Although it acts as a buffer to preserve the sharpness of the die, it causes cumulative deformation and defects in the die after repeated punching. Additionally, there often exists a height deviation of approximately 1–2 mm between the die and the punching pad at different positions. As the thickness of the leather sheet is often between 0.1 and 2 mm, automatic punching has a few drawbacks; although the leather is cut completely according to the set depth in some areas, other areas of the sheet might be over- or under-cut. This results in excessive consumption of the die or punching pad or generates excessive waste at the locations where the cutting is incomplete. To determine the effective punching stroke for a large layout (1.2 m × 2.2 m), this study proposes the innovative method of using the object packing as the reference to obtain the actual depth of the punching point for each die through automatic search before automated mass production. The results are then recorded in the packing system. In addition, the control delay time of the hydraulic solenoid valve is obtained from signal analysis. This approach enables the adjustment of the punching depth, to punch and cut the leather material successfully in a large layout. Moreover, the depth of the die mark left in the punching pad is restricted to a value between 0.1 and 0.2 mm. This effectively increases the life of the die and reduces the consumption of the punching pad, greatly improving the accuracy and stability of the punching system.