Stamping conditions of the stretching die:
① Excessive edge holding force. When the edge pressing force is too large, wrinkling will not occur on the flange surface. The roughness of the anti wrinkle pressure plate surface, mold fit, gap, rp, rd, type and coating conditions of processing oil, and the distribution of the edge holding force caused by the buffer pin all affect the anti wrinkle pressure. If all of the above conditions for deep drawing are appropriate, the blank holder force will decrease and rupture will not occur before wrinkling. When the edge pressing force is too large, it is easy to determine because the flange surface will be fully illuminated.
② Poor lubrication. Deep drawing processing is closely related to lubrication, especially when it involves thinning and deep drawing processing, it is necessary to control the temperature rise of the product. If it is a deep drawing process with good conditions, the selection of lubricating oil is not a problem; Deep drawing processing with poor conditions can cause cracking if the lubricating oil is not selected properly.
③ Poor shape of the blank. During the trial drawing stage, determining the shape of the blank is one of the important tasks. The shape of the blank must be limited to the minimum size. When using square blanks for cylindrical drawing, the ultimate drawing rate is about 0.58. In addition, if the drawing rate is too strict, the scars on the RP area will rupture, and cutting corners can prevent rupture. When drawing a square cylinder, it can be done with a square billet first, which can produce beautiful products. However, if the drawing limit is reached, cracks will occur near the rcp. If it has already broken, a part of the four corners of the blank can be cut off. But if cut too much, it will cause flange wrinkling, which becomes the cause of wall cracks.
④ Poor positioning of the blank. Even if the shape of the blank is good, if the adjustment position is not good or the placement direction is incorrect, the convex mold and the blank will be misaligned, which will also cause cracks or wrinkles. In addition, when using a 500 ton hydraulic press to form large-sized deep drawing parts (material SUS304), low viscosity oil can be used for deep drawing. When using high viscosity oil for deep drawing, the rp part will crack when the drawing reaches 1/4 of the height. Compared to soft steel plates, stainless steel is more susceptible to speed, but if sufficient cooling and lubrication are carried out, other issues are more important in practical operation than speed. When performing high-speed punching, even with general clearance, the entire shear surface of the cut is ideal.
⑤ Poor mold installation. The defect is caused by poor installation of the mold and misalignment of the upper and lower molds. Recently, almost all molds are equipped with guiding devices, and faults caused by misalignment of molds are very rare.
