Factors affecting wrinkling of stamped parts and solutions
(1) Effect of stretching depth
The distribution of material flow resistance along the die opening is directly related to the drawing depth. At concave and convex curve positions, excessive stretching depth can cause uneven distribution of deformation resistance and form wrinkles, which should be avoided as much as possible.
(2) Adjust the size of the blank holder force
When wrinkles appear evenly around the workpiece, it should be judged that the pressing force is insufficient, and the wrinkles can be eliminated by gradually increasing the pressing force. When stretching conical and hemispherical parts, most of the material is in the air when stretching begins. It is easy to cause wrinkles on the side wall, so in addition to increasing the edge holding force, the pick-up and stretch ribs should also be added to increase the radial tensile stress in the plate and eliminate wrinkles.
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(3) Effect of radius of die fillet
If the fillet radius of the die is too large, the bending resistance of the blank flowing into the die and passing through the rounded corners of the die will be smaller, resulting in bending deformation. The smaller the bending resistance, the easier it is to cause wrinkles. The smaller the radius of the die, the greater the bending resistance to bending deformation, and the less likely it is to wrinkle, but it can easily cause cracking and napping of the part.
Through the accumulation of a large amount of practical production experience, it has been proved that the main cause of wrinkles in stamping parts is the accumulation of materials during the stretching process and the excessive speed of local material movement. When formulating actual solutions, the corresponding mechanisms of the mold should be adjusted from the above aspects, which will achieve good results.
Measures and methods to prevent wrinkling of stamped parts
The way to prevent wrinkling is to ensure that the mold can press the material during the stretching process of the metal stamping parts to ensure a reasonable flow speed of the sheet metal. If the sheet material flows too fast when the stamping part is stretched, it may cause wrinkles; on the other hand, if the sheet material flows too slowly, it may cause the stamping part to crack.
(1) Use a reasonable pressing device
When a pressing device is used, the pressing device tightly presses the deformed part of the blank and exerts pressing force on it to prevent the flange part from arching and causing wrinkles. The size of the pressing force must be appropriate. Pressing devices are divided into two categories: elastic pressing and rigid pressing. Elastic devices are suitable for shallow drawing and rigid devices are suitable for deep drawing.
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(2) Reasonable use of draw beads
Setting draw beads on the pressing surface is an effective and practical method to adjust and control deformation resistance. Drawbeads can well regulate the flow of materials, making the flow resistance of each part of the material uniform during the drawing process, so that the amount of material flowing into the cavity is suitable for the needs of the part, preventing wrinkling in the most cases and cracking in the least. The phenomenon. For curved tensile parts with complex shapes, especially those with small flanges, draw beads should be set to increase the radial tensile stress of the stretch to control wrinkling; the draw beads should be set in the radial direction. On the parts with smaller stress, that is, the parts where the sheet material flows easily. For parts with smaller flanges, in order to set draw beads, some material (process supplementary material) can be added appropriately, and this part can be removed during trimming. For drawn parts with large differences in drawing depth, the draw beads should be set in parts with less feed, so that excess material in this part can be prevented from being pulled into the die cavity, thereby preventing wrinkling.
03 Analysis of the causes of wrinkles in tensile parts
There are many reasons why tensile parts wrinkle during the stretching process. The main reasons are as follows:
(1) The drawing depth of the stamping parts is too deep, causing the sheet material to flow too fast during the feeding process, causing wrinkles.
(2) The R-angle of the die is too large during the stretching process of stamping parts, causing the punch to be unable to press the material during the stretching process, causing the sheet to flow too fast and cause wrinkles.
(3) The pressing ribs of stamping parts are unreasonable. The pressing ribs are too small and incorrectly positioned, which cannot effectively prevent the sheet material from flowing too fast and causing wrinkles.
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(4) The pressure of the ejector pin is too small, causing the stamping parts to be incompletely formed and causing wrinkles.
(5) The mold positioning design is unreasonable, resulting in the inability to press the material during the stretching process of the stamping parts or the pressing edge is too small, resulting in the inability to press the material during the stretching process, causing wrinkles.
(6) The gap between the convex and concave molds is too large, causing the material to be unable to be pressed during the stretching process, causing wrinkles.
The above are common causes of wrinkling during the stretching process of metal stamping parts, which require specific analysis in specific problems. Find the specific reasons based on the specific conditions of the stamping parts.
