Once all components of the stamping and drawing die have been manufactured and finished, the assembly stage can begin. Due to the high precision and minimal tolerances of die components, the correct assembly sequence must be arranged to ensure the normal operation of the stamping and drawing die. Below, the team at Balford provides a brief introduction to the causes of wrinkling during the stamping and drawing die fitting process and the corresponding solutions:
I. Factors Affecting Wrinkling in Stamped Parts and Their Solutions
1. Effect of Drawing Depth
The resistance to material flow along the die opening is directly related to the drawing depth. At concave and convex positions, excessive drawing depth can lead to uneven deformation resistance distribution, resulting in wrinkling. This situation should be avoided as much as possible.
2. Adjusting the Blank Holder Force
If wrinkles are uniformly generated around the workpiece, it indicates insufficient blank holder force, which can be eliminated by gradually increasing the blank holder pressure. When drawing conical and hemispherical parts, most of the material is in a suspended state at the beginning of the drawing process. Since the side walls are prone to wrinkling, it is necessary not only to increase the blank holder force but also to add draw beads to increase the radial tensile stress within the sheet, thereby eliminating wrinkles.
3. Effect of Die Radius
If the die radius is too large, the blank undergoes bending deformation as it flows into the die cavity over the die radius, resulting in lower bending resistance. The lower the bending resistance, the more easily wrinkling occurs. Conversely, a smaller die radius results in greater bending resistance and a lower likelihood of wrinkling, but it may cause cracking and scratching of the part.
Through extensive production practice and accumulated experience, it has been proven that the main causes of wrinkling in stamped parts are material accumulation during the drawing process and excessive material movement speed in certain areas. When developing practical solutions, the aforementioned aspects should be considered and the corresponding die mechanisms adjusted to achieve effective results.
II. Measures and Methods to Prevent Wrinkling in Stamped Parts
The method to prevent wrinkling is to ensure that the die can hold the material during the drawing process of the metal stamping part, thereby controlling the flow speed of the sheet metal. If the material flows too quickly during stamping drawing, it will cause wrinkling; on the other hand, if the material flows too slowly, it will cause stamping cracks.
1. Use a reasonable blank holder device
When using a blank holder device, the blank holder tightly presses the deformed portion of the blank and applies blank holder force uniformly to prevent the flange area from arching and causing wrinkling. The blank holder force should be appropriately sized. Blank holder devices are divided into two types: elastic blank holders and rigid blank holders. Elastic devices are suitable for shallow drawing, while rigid devices are suitable for deep drawing.
2. Proper use of draw beads
Setting draw beads on the blank holder surface is an effective method to regulate and control deformation resistance. Draw beads can effectively regulate material flow, ensuring uniform material flow resistance for all parts during the drawing process, so that the amount of material flowing into the die cavity meets the requirements of the part, preventing wrinkling and cracking. For complex-shaped curved surface drawing parts, especially those with small flanges, draw beads should be set to increase the radial tensile stress during drawing to control wrinkling.
Draw beads should be positioned where the radial tensile stress is relatively low, i.e., where the sheet metal flows easily. For parts with small flanges, additional material (process addendum) can be appropriately added to accommodate the draw beads, and this portion is removed during trimming. For drawing parts with significant differences in drawing depth, draw beads should be set at locations with less material inflow to prevent excessive material from being drawn into the die cavity, thereby preventing wrinkling.
3. Analysis of causes of wrinkling in drawn parts
There are many causes of wrinkling during the drawing process, with the main reasons as follows:
1. The drawing depth of the stamping part is too deep, causing the sheet metal to flow too quickly during material feeding, resulting in wrinkling.
2. The die radius (R angle) is too large during the drawing process of the stamping part, preventing the punch from holding the material properly during drawing, causing the sheet metal to flow too quickly and form wrinkles.
3. Improper blank holding of the stamped part, with draw beads that are too small or incorrectly positioned, fails to effectively prevent excessive material flow that leads to wrinkling.