1. Reasons for turning and twisting during stamping
In the progressive die, the outer shape of the punched part is formed by punching the leftover material around the punching part. The main reason for the turning and distortion of the punching parts is the influence of the punching force. When punching, due to the existence of the punching gap, the material is stretched on one side of the die (the material is warped upward) and compressed on the side of the male die. When using the unloading plate, use the unloading plate to compress the material to prevent the material on the die side from warping upwards. At this time, the force of the material changes accordingly. As the discharge plate increases its pressing force, the material on the punch side is stretched (compression force tends to decrease), while the material on the concave die surface is compressed (tension force tends to decrease). The overturning of the stamping part is caused by the stretching of the material on the die surface. Therefore, when punching, pressing and compressing the material is the key point to prevent the punching from turning over and twisting.
2. Methods to restrain stamping parts from turning over and twisting
- (1). Reasonable mold design. In the progressive die, the arrangement of the blanking sequence may affect the forming accuracy of the stamping parts. For the blanking of small parts of stamping parts, generally a larger area of punching is arranged first, and then a smaller area of punching is arranged to reduce the influence of the punching force on the forming of the stamping part.
- (2). Hold down the material. Overcome the traditional mold design and structure, open a material-containing gap on the discharge plate (that is, when the mold is closed, the discharge plate is attached to the concave mold, and the gap between the discharge plate and the concave mold where the material is contained is the material thickness t-0.03 ~0.05mm). In this way, the unloading plate moves smoothly during stamping, and the material can be compressed. The key forming part, the unloading plate must be made into a block-type structure to facilitate the solution of the wear (compression) loss of the pressing part of the unloading plate caused by long time stamping, and the material cannot be compressed.
- (3). Add a strong pressure function. That is to increase the size of the press part of the unloading insert (normal unloading insert thickness H+0.03mm) to increase the pressure on the material on the side of the die, so as to prevent the stamping part from turning over and twisting during punching.
- (4). The end of the punch edge is trimmed with a bevel or arc. This is an effective way to reduce cushioning and cutting power. By reducing the buffer cutting force, the tensile force on the material on the side of the die can be reduced, so as to achieve the effect of suppressing the turning and twisting of the stamping parts.
- (5). In daily mold production, care should be taken to maintain the sharpness of punching convex and concave die cutting edges. When the punching edge is worn, the tensile stress on the material will increase, and the tendency of the stamping part to turn over and twist becomes greater.
- (6). Unreasonable or uneven blanking clearance is also the cause of turning over and twisting of stamping parts, which needs to be overcome.
3. Handling of common specific problems in production
In daily production, there will be situations where the punching size is too large or small (it may exceed the specification requirements) and the size of the punch is quite different, except for the design size, processing accuracy and punching of the forming convex and concave mold. In addition to factors such as gaps, the following considerations should also be taken to solve them.
- (1). When the punching edge is worn, the tensile stress on the material increases, and the tendency of the stamping parts to turn over and twist increases. When turning over, the size of the punching hole will become smaller.
- (2). The strong pressure on the material causes plastic deformation of the material, which will cause the punching size to become larger. When the strong pressure is reduced, the punching size will become smaller.
- (3). The shape of the edge of the punch edge. If the end is trimmed with a bevel or arc, the punching force is not easy to turn over or twist because the punching force is slowed down, so the punching size will become larger. When the end of the punch is flat (no bevel or arc), the punching size will be relatively small.
In the specific production practice, specific analysis should be made for specific problems, so as to find out the methods to solve the problems.
The above mainly introduces the reasons and countermeasures of turning over and twisting of the punching parts during blanking.
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