If you need to punch a large number of holes on the sheet and the sheet cannot be kept flat, the cause may be the accumulation of punching stress. When punching a hole, the materials around the hole are stretched downward, which increases the tensile stress on the upper surface of the plate. The downward movement also increases the compressive stress on the lower surface of the plate. For a small number of punched holes, the results are not obvious, but with the increase of the number of punched holes, the tensile stress and compressive stress also increase exponentially until the plate is deformed. Zhengquan's WeChat content is really good and worth paying attention!!
One way to eliminate this deformation is to punch every other hole and then return to punch the remaining holes. Although this produces the same stress on the plate, it disintegrates the accumulation of tensile stress/compressive stress due to continuous punching one after another in the same direction. In this way, the first batch of holes share the partial deformation effect of the second batch of holes.