12 major questions about sheet metal bending and forming technology
In the sheet metal workshop, how did an originally flat metal plate transform into an extremely precise bend? This bending process may seem simple at first glance, but in fact, it contains more than a dozen commonly seen quality traps!
The bent edge is not straight and the size fluctuates
After bending, the edge appears curved or the size is different every time. This is a common problem. This is generally due to omissions in the process design. There is no crimping or pre-bending process before bending, so the internal stress of the material cannot be released in advance. Another key factor is mold wear. If the degree of wear of the rounded corners of the punch and the concave mold is different, it will cause the material to be unevenly stressed during bending, thus affecting the straightness.
In order to solve this problem, the crimping step must be accurately added to the process route, that is, a shallow mark should be made first at the bending line. At the same time, the workshop must establish a rigorous mold inspection system, regularly measure and grind the fillet radii of the convex and concave molds to ensure their symmetry, and adjust the equipment so that the bending force can be evenly distributed on the work.
Surface scratches and corner cracks on the workpiece
Scratches appear on the outer surface of the workpiece after machine tool processing, which has a direct impact on the appearance of the finished product. The main reason is that the surface of the die is not smooth enough, or the bending radius of the die is too small, which causes strong friction with the plate during the molding process. Improving the hardness and polishing level of the mold is the key. Use more wear-resistant mold steel and polish it on time.
Micro cracks appear on the outside of the bending angle. The reason may be that the inner bending radius is set too small, resulting in machining bending problems that exceed the ductility limit of the material. Soft metals like aluminum and copper are particularly sensitive to this. The solution is to reasonably increase the fillet radius of the punch according to the thickness and material of the plate, and ensure that the burr faces the inside of the bend to prevent stress from tearing away from the burrs.
Hole deformation and surface thinning due to bending
When bending operations are carried out using holes as positioning, the holes are easily deformed and lose their circular shape. This is because during the bending process, the outside of the material bears tension, while the inside bears pressure, which causes the positioning holes to be pulled and deformed. Shape bending should be preferred to replace simple elastic bending, or a mesh-like grid pattern should be processed on the ejector plate to increase friction and prevent the workpiece from sliding and shifting during bending.
The outer surface becomes significantly thinner in the bending area, and even stretch lines appear. This is often because the die entrance fillet radius is too small, and the material is severely scraped when flowing through. Increasing the die fillet radius can significantly improve the material flow and make the material flow smoother. For important appearance parts, it is necessary to calculate and select a reasonable fillet, and perform multi-pass progressive bending if necessary.
The end surface of the part bulges and the holes are displaced
After the workpiece is bent, there is a problem with machining and bending . The end face is uneven and the middle part is bulging. The reason for this is that during the bending operation, the outer surface shrinks, while the inner surface extends, causing deflection in the length direction. As for the solution, it is to increase the pressure in the final stage of stamping so that the convex and concave molds can compact the workpiece with sufficient force. At the same time, the fillet radius of the die needs to match the outer corner of the workpiece, and the contact area of the ejection device must be sufficient and the ejection force must be strong enough.
After the workpiece is bent, the center lines of the two holes on it are shifted. This is due to the material rebound causing the bending angle to change, which then affects the hole position. In addition to using compensation angles during mold design to pre-control the amount of springback, the mold structure can also be improved, such as using a bending die with a correction function to implement strong micro-correction at the end of the stroke to stabilize the angle and hole position.
Loss of precision and deformation in width direction
After bending, the position accuracy of multiple holes cannot be ensured. This may be due to an error in the calculation of the expansion diagram size, or the process positioning is not qualified. It is necessary to recheck the unfolded dimensions and consider adding positioning pins to the bending die. For complex parts, the processing sequence can be changed, bending first and then drilling, or adding a dedicated correction process to ensure accuracy.
The reason for the bowing or twisting of the workpiece in the width direction is that the stretching and shrinkage of each point in the width direction of the plate is not consistent, and can be suppressed by increasing the pressure during bending. In addition, when blanking, attention should be paid to allowing the fiber direction of the material to show a certain angle (such as 45 degrees) toward the bending line. This can effectively reduce the deformation caused by anisotropy.
Deflection of cutout parts and comprehensive process countermeasures
After the part with a cutout is bent, the whole part flexes downward, and the cutout releases the local stress, causing the two sides to open outward and the bottom to be concave. Improving the structural design of the product and reducing unnecessary cuts is the best solution. If the structure cannot change the machining bending problem , reserve a process connection part at the cutout, and then cut off the excess connection part after the whole body is bent and formed.
A systematic project is the quality control of sheet metal bending, which involves material science, mold engineering, and process planning. From the calculation to achieve accuracy, the mold design to be reasonable, to the equipment operation specifications and maintenance, every link is indispensable. The workshop must establish standard operating procedures and conduct continuous training for operators to stably produce high-quality products.
What is the most difficult bending quality problem you encountered during actual work? Is it the control of springback or the deformation of the thin plate? You are welcome to share your experience in the comment area. If you think these solutions are effective, please like and support.
暂无评论内容