The relationship between blanking gap and shear quality

Source：Suzhou Meiyuan Ruite Precision Machinery Co., Ltd. Time：2022-06-16 Browse：3423

Whether the blanking gap in the blanking process is reasonable will determine whether the upper and lower cracks on the fracture surface overlap, whether the shear force is balanced, and the size of the burr. Therefore, the mold design, manufacture and installation must ensure that the gap is uniform, and the gap between the convex and concave molds in the same manufacturing process should be kept within a reasonable range. Otherwise, the mold will appear part of the gap is too large and too small quality phenomenon.

Effect of Gap on Section Quality
1. Reasonable blanking gap
When the convex and concave gaps are appropriate, the cracks generated near the edges of the convex and concave die along the direction of the maximum shear stress can meet during the blanking process. At this time, although the section is not perpendicular to the surface of the material, it is still relatively straight, smooth and burr Smaller, the section quality of the part is better.

2. Punching gap is too small
When the gap is reduced, the bending moment is small and the compressive stress component is high in the deformation zone. The cracks generated near the edge of the die enter the compressive stress zone below the punch and stop developing; the cracks generated near the edge of the punch enter the compressive stress zone on the upper surface of the die and stop developing. The upper and lower cracks do not overlap. The material between the two cracks will be sheared a second time. When the upper crack is pressed into the die, it is squeezed by the wall of the die, resulting in a second bright band, and at the same time, part of the material is extruded, forming thin and high burrs on the surface. If the gap is too small, although the slump angle is small and the arch is small, the quality of the section is also defective. If there is an interlayer in the middle of the section, the two ends are bright bands, and there are long burrs on the end face.

3. Punching gap is too large
When the gap increases, the tensile stress in the material increases, so that the tensile fracture occurs early, so the fracture band becomes wider; the bright band becomes narrower; the bending deformation increases, so the slump and arch also increase. When the gap is too large, due to the large bending moment and the high tensile stress component, the cracks generated near the edges of the convex and concave molds will not coincide. The slope of the fractured layer generated after separation increases, and two oblique angles α1 and α2 appear on the section of the workpiece, and the section quality is not ideal. Moreover, due to the large slump angle, the large arch, the small bright band, and the high and thick burrs, the quality of the blanking parts is reduced.

4. The gap is uneven
The side with a small gap presents the cross-sectional feature of an excessively small gap, and the side with a large gap presents the cross-sectional feature of an excessively large gap

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