1. Reasons for flipping and twisting during stamping

In a progressive die, the shape of the stamping part is formed by punching and cutting the remaining material around the stamping part. The main reason for flipping and twisting of punched parts is the influence of punching force. During punching, due to the existence of punching gaps, the material is stretched on one side of the concave mold (material warps upwards) and compressed on the side next to the convex mold. When using a discharge plate, use the discharge plate to compress the material to prevent the material on the concave mold side from warping upwards. At this time, the stress state of the material will change accordingly. As the unloading plate increases its pressing force, the material on the convex die side is stretched (the compression force tends to decrease), while the material on the concave die surface is compressed (the stretching force tends to decrease). The flipping of stamping parts is caused by the stretching of the material on the concave die surface. So when punching, pressing and compressing the material is the key to preventing flipping and twisting of the punched part.

2. Methods for suppressing flipping and twisting of stamping parts

(1) Reasonable mold design. In progressive dies, the arrangement of the cutting sequence may affect the accuracy of stamping parts. For the cutting of small parts of stamping parts, generally, a larger area of punching and cutting is arranged first, and then a smaller area of punching and cutting is arranged to reduce the impact of punching force on the forming of stamping parts.

(2) Press down on the material. Overcoming the traditional mold design structure, a material holding gap is created on the discharge plate (i.e., when the mold is closed, the discharge plate adheres to the concave mold, while the gap between the discharge plate and the concave mold at the material holding point is t-0.03-0.05mm in material thickness). In this way, the unloading plate moves smoothly during stamping, while the material can be compressed. The key forming parts of the discharge plate must be made into an embedded block structure to facilitate solving the wear (compression) damage caused by long-term stamping at the pressing part of the discharge plate, which cannot compress the material.

(3) Add strong pressure function. Namely, thicken the size of the unloading insert pressing part (the normal unloading insert thickness is H+0.03mm) to increase the pressure on the material on the concave mold side, thereby suppressing the flipping and twisting deformation of the stamping part during punching.

(4) Trim the end of the convex die edge with an inclined or curved surface. This is an effective method to slow down the punching force. Reducing the buffering and cutting force can reduce the tensile force on the side material of the concave mold, thereby achieving the effect of suppressing the flipping and twisting of the stamped parts.

(5) In daily mold production, attention should be paid to maintaining the sharpness of the punching convex and concave mold edges. When the cutting edge is worn, the tensile stress on the material will increase, resulting in an increase in the tendency of the stamped part to flip and twist.

(6) Unreasonable or uneven punching clearance is also a cause of flipping and twisting of stamping parts, which needs to be overcome.

3. Handling of common and specific problems in production

In daily production, there may be situations where the punching size is too large or too small (possibly exceeding the specification requirements) and there is a significant difference from the punch size. In addition to considering the design dimensions, processing accuracy, and punching clearance of the forming convex and concave molds, the following aspects should also be considered to solve the problem.

(1) When the cutting edge is worn, the tensile stress on the material increases, and the tendency of the stamped part to flip and twist increases. When flipping occurs, the punching size will decrease.

(2) The strong pressure on the material causes plastic deformation, which can lead to a larger punching size. When reducing strong pressure, the punching size will decrease.

(3) The shape of the end of the convex die blade. If the end is trimmed with an inclined or curved surface, the punching force slows down, making it difficult for the punched part to flip or twist, resulting in a larger punching size. When the end of the punch is flat (without inclined or curved surfaces), the punching size tends to decrease relatively.

In specific production practice, specific analysis should be conducted on specific problems to find solutions.

The above mainly introduces the reasons and solutions for flipping and twisting of punched parts during punching.