Drawing wrinkles refer to the rough and uneven surface of the workpiece during the drawing process, with excessively thick edges, which seriously affects subsequent processing. We need to pay attention to what causes drawing wrinkles and how to prevent them. Identifying these causes and methods can ensure our work proceeds normally and product quality is guaranteed.
When the material is drawn, the surrounding edge experiences excessive tangential stress, leading to material instability and causing uneven wrinkles along the edge of the product, known as wrinkling. Severe wrinkling can also make it difficult for the material to pass through the gap between the die and punch during drawing, increasing the drawing deformation force and even leading to cracking.
There are many reasons for wrinkling in drawn parts, mainly including the following: the blank to be drawn is not thick enough, so the pressure it can withstand is naturally smaller, making it highly prone to wrinkling during drawing; the corresponding elongation coefficient is not selected according to the texture of each blank, making the degree of deformation difficult to control, and if not controlled properly, deformation will occur; severe damage to the blank holder means it cannot apply uniform pressure to the blank, resulting in uneven pressure-bearing capacity and also causing wrinkling.
The thickness of the blank to be drawn should be relatively thicker, so that it can withstand the corresponding pressure during drawing, making it less likely to deform or wrinkle; selecting the appropriate drawing coefficient corresponding to the blank texture makes the degree of deformation easy to control; the blank holder ring needs frequent replacement or repair to ensure the blank receives equal pressure, reducing the likelihood of wrinkling.
1. When wrinkles appear on drawn parts, how can they be removed?
1. Extensive production practice experience has proven that the main causes of wrinkling in drawn parts are material accumulation during the drawing process and excessively fast local material movement. When designing the actual solution, adjustments to the corresponding mechanisms of the die should be considered from the above aspects, which can achieve good results.
2. The method to prevent wrinkling is to determine whether the die head can press the material during drawing, thereby determining the correct sheet metal flow speed. During the drawing process, if the sheet metal flows too fast during stamping, it will cause wrinkling; on the other hand, if the sheet metal flow speed is too slow, it may lead to cracking of the stamped part.
3. When wrinkles appear uniformly around the drawn part, it should be determined that the blank holder force is insufficient.
4. When drawing conical and hemispherical parts, at the beginning of the drawing process, most of the material is in a suspended state. Since this easily causes side wall wrinkling, in addition to increasing the blank holder force, draw beads should be enlarged to increase the tensile stress within the sheet.
5. If the die radius is too large, the bending resistance generated when the blank flows into the die and passes through the die radius will be smaller. The better the bending resistance, the more easily wrinkling occurs. If the die radius is small, the bending resistance generated by bending deformation is greater, making wrinkling less likely, but it can easily cause cracking and scratching of the part.
II. Precautions for the Use, Maintenance, and Repair of Drawn Parts
1. Before using drawn parts, conduct a strict inspection, clean off any dirt, and carefully check that the guide bushings of the drawn stamping parts and the die lubrication are in good condition.
2. According to the die installation procedure, mount the punch and die on the turntable, ensuring that the punch and die of the drawn stamping parts are oriented consistently. Particular care is required for drawn parts with directional requirements (non-circular and square shapes) to prevent incorrect installation or reversed mounting.
3. Regularly inspect the turntable and die mounting base of the press to ensure the concentricity and precision of the upper and lower turntables.
4. When installing the die, the operator should use tools made of softer metals (e.g., copper, aluminum, etc.) to prevent dropping and damaging the drawn stamping parts during installation.
5. When the cutting edges of the punch and die for drawing parts become worn, stop using them immediately and regrind them in a timely manner. Otherwise, the wear on the die edges will rapidly increase, accelerating die wear and reducing the quality of the stamped parts and the die's service life.
6. To ensure the service life of drawn parts, the die springs should also be replaced regularly to prevent spring fatigue damage from affecting the service life of the drawn stamping parts.
The above covers the causes and solutions for wrinkling in drawn parts. During the production and processing of drawn parts, attention should be paid to ensuring that the strip material operates under normal working conditions when using presses or stamping dies, and to prevent the strip from being fed along an incorrect position or not according to the corresponding clearance. We hope the above is helpful to the readers.