In order to suppress the tearing of the material during the stamping process and ensure the progress of the plastic deformation process during fine blanking, the following three measures are taken:
1. Use the v-shaped tooth blank holder to press the material. Avoid sheet bending and warping;
2. Use a small stamping gap. The double-sided stamping gap of fine blanking is about 1%-1.5% of the material thickness, so that the material is always kept perpendicular to the stamping direction, so as to reduce the bending deformation of the deformation zone, and no tensile stress is generated, which constitutes the conditions for plastic deformation of compressive stress;
3. Use the blank holder force and the back pressure of the ejector rod to tightly compress the deformation area of the material to make it in a state of two-way compression, and increase the pressure of the material in the deformation area to increase the deformation of the material and suppress cracks and tears generation. The cutting edge of the die or punch is made into a very small rounded corner, and the radius of the rounded corner is generally 0.05mm~0.1mm, so as to reduce the stress concentration at the cutting edge and avoid or delay the generation of cracks.
The fine blanking process requires the equipment to provide stamping force, blank holder force and counter force at the same time, usually on a dedicated fine blanking machine.
Ordinary presses generally cannot provide these three forces and their motions at the same time, and are poor in rigidity and motion accuracy of the press, so it is not suitable for precision stamping on ordinary presses unless certain technical measures are taken, such as adding mechanical Or the hydraulic device provides blank holder force and counter pressure to realize fine blanking on general presses.
The hydraulic device is used to provide blank-holding force and counter-jacking force, and the pressure is evenly balanced. The pressure can be maintained or reduced during the fine-blanking process according to the process requirements, and the control is simple. The pressure is generally realized by hydraulic pressure.
A small gap is the main feature of a fine die. The size of the gap and its uniformity along the periphery of the cutting edge directly affect the quality of the shear surface of fine blanking parts. The fine blanking gap mainly depends on the thickness of the material, and is also related to the stamping profile and the material of the workpiece. The gap is too large and there is a tear on the sheared surface. This is because the gap is too large, the material in the deformation zone is subjected to a large tensile action, and produces tensile stress, and the tensile stress is the reason for inducing microcracks and tears. Therefore, the gap between the convex and concave dies of precision stamping should not be too large.
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