Free Bending
Free bending is the most commonly used method. Free bending utilizes the two edges of the die opening and the edge of the punch tip for bending, with the bending angle determined by the depth of the punch's penetration into the die. Free bending requires less bending force, and the mold is subjected to less stress, extending its service life. However, its disadvantage is that inconsistencies in sheet metal thickness and mechanical properties, as well as the rolling direction of the steel plate, can cause variations in the bending angle.
Correction Bending
Correction bending involves the punch precisely pressing the rounded corners and straight edges of the workpiece. During the downward movement of the punch, the blank angle will be smaller than the die angle, resulting in negative springback; at the end of the stroke, the punch and die correct the blank, ensuring that its rounded corners, straight edges, and bending radius are all in close contact with the punch. Therefore, correction bending can effectively overcome springback, resulting in high bending accuracy.
Three-Point Bending
This part is processed using a CNC press. It only requires programming, and the entire process can be completed with a single clamping and positioning. The programming time is at most two or three hours, and the processing time is only a few minutes, with high processing accuracy. The hydraulic cushion pressure is evenly distributed over the entire bending length, ensuring that the bending force of the punch is also evenly distributed along the entire bending length. Each punch is elastically supported, thus automatically adapting to the straightness of the die and ensuring a constant pressure distribution, which improves the accuracy of the bending angle and the straightness of the bending edge. The bending angle error of the three-point bending method is ±15 degrees, equivalent to the accuracy of correction bending. Bending thickness can reach 20mm. When the plate thickness exceeds 3mm, the three-point bending method is the best method for achieving the desired bend. This is because, otherwise, to obtain the same bending accuracy, only correction bending can be used, but its bending force will exceed the pressure limit that the mold can withstand.