Automotive stampings - turning distortion
1. Reasons for turning and twisting during stamping
In the progressive die, the shape of the punch is formed by a method of punching the remaining material around the stamping. The main reason for the turning and twisting of the punching piece is the influence of the punching force. At the time of 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 punch. When the unloading plate is used, the material is pressed by the unloading plate to prevent the material on the side of the die from warping upward. At this time, the stress state of the material changes correspondingly. As the material is increased by the discharge plate, the material on the side of the punch is stretched (the compressive force tends to decrease), and the material on the die face is compressed (the tensile force tends to decrease). The inversion of the stamping is due to the stretching of the material on the die face. Therefore, when punching, pressing and pressing the material is the key to preventing the punching and twisting of the punch.
2. Method for suppressing the turning and twisting of stamping parts
(1). Reasonable mold design. In the progressive die, the arrangement of the blanking sequence may affect the accuracy of the forming of the stamping. For the blanking of the small parts of the stamping parts, generally, a large area of punching and cutting is arranged, and then a small area of punching and cutting is arranged to reduce the influence of the punching force on the forming of the stamping parts.
(2). Squeeze the material. Overcoming the traditional mold design structure, the material gap is opened on the discharge plate (that is, when the mold is closed, the discharge plate is attached to the die, and the gap between the discharge plate and the die at the receiving material is the material thickness t-0.03 ~0.05mm). In this way, the unloading plate moves smoothly during the punching, and the material can be pressed. In the key forming part, the unloading plate must be made into an inlaid structure to facilitate the grinding (pressure) damage caused by the pressing of the unloading plate caused by long-time pressing, and the material cannot be pressed.
(3). Add a strong pressure function. That is, the thickening size of the pressing portion of the unloading insert (normal unloading insert thickness H+0.03 mm) is used to increase the pressure on the material of the concave mold side, thereby suppressing the turning and twisting deformation of the stamping part during punching.
(4). The end of the punch edge is trimmed or curved. This is an effective way to reduce the buffering power. By reducing the cushioning force, the tensile force on the material of the die side can be alleviated, thereby suppressing the effect of turning and twisting the stamping part.
(5). In the daily mold production, attention should be paid to maintaining the sharpness of the punching and concave die edge. When the blanking edge is worn, the tensile stress of the material will increase, and the tendency of the stamping material to turn and twist will increase.
(6). Unreasonable punching gap or uneven gap is also the cause of the turning and twisting of the stamping parts, which needs to be overcome.
3. Handling of common problems in production
In daily production, there will be cases where the punching size is too large or too small (possibly out of specification) and the difference in size from the punch is large, except for the design dimensions, machining accuracy and blanking of the forming convex and concave molds. In addition to factors such as gaps, it should be considered from the following aspects.
(1). When the cutting edge is worn, the tensile stress of the material increases, and the tendency of the stamping parts to turn and twist is increased. When the material is turned, the punch size will become smaller.
(2). The strong pressure on the material causes plastic deformation of the material, which will lead to a larger punching size. When the strong pressure is reduced, the punching size will become smaller.
(3). The shape of the end of the punch edge. If the end portion is chamfered or curved, the punching force is less likely to cause turning and twisting due to the slowing of the punching force, and therefore, the punching size will become larger. When the end of the punch is flat (no bevel or arc), the punch size will be relatively small.
In specific production practices, specific analysis should be conducted on specific issues to find a solution to the problem.
The above mainly introduces the reasons and solutions for the turning and twisting of the punching parts during punching.