In the stamping process of stainless steel stub-end, the outer edge part of the blank is usually a non-deformation area due to the constraint of the blank holder force or because the ratio of the outer edge width to the diameter of the flanging hole is large, and the vertical wall part has been deformed and is a force transmission area. The bottom of the hole is the deformation zone. The deformation zone is in a state of bidirectional tensile stress (the stress in the thickness direction is negligible), and the deformation zone becomes thinner under the action of tensile stress, which is the same as bulging.
Small punch punching, especially the flanging positioning problem, can be said to be almost difficult to solve. If the prefabricated holes are not punched, the flanging height can be guaranteed and the positioning is not a problem, and the operation is also very convenient; but the vertical edge of the stainless steel flanging pipe may be inconsistent in height, and there may be cracks in some materials. According to the mechanical properties of 08F steel materials According to the performance analysis, the strength limit is compared with the flow limit, and the possibility of cracks is not very large. According to the existing experience, there may be crack marks except for the inconsistent height of the vertical side, but it does not affect the extension. Therefore, it is decided not to Punch prefabricated holes.
The round hole stainless steel stub-end belongs to the elongation type flanging. When the stainless steel stub-end is subjected to tensile stress in the tangential direction of the deformation zone of the blank, a tangential tensile strain is generated. According to the yield criterion, it can be determined that the edge of the hole is the first place where plastic deformation occurs, and the thickness becomes the most serious, so cracks are most likely to occur. When the stainless steel stub-end is deformed, the deformation zone is subjected to radial tensile stress, and the radial strain value generated is relatively small.
For the inner hole flanging of non-circular holes, the stress and strain distribution in the deformation zone along the flanging line is not uniform. Under the same flanging height, the tangential tensile stress and tangential elongation deformation are larger in the part with smaller curvature radius; while the tangential tensile stress and tangential elongation deformation in the part with larger curvature radius are smaller. The straight part is similar to the bending deformation. Due to the continuity of the material, the deformation of the curved part will extend to the straight part, so that the tangential elongation deformation of the curved part can be alleviated to a certain extent.
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