Problems In Cold Bending Forming Process

Cold forming process is known as an "art", and its products are widely used in various fields.At present, some industry experts have carried out in-depth theoretical research on it, and some researchers have carried out computer simulation on the molding process, and achieved certain results. But the cold bending forming process is a very complex process, there are still many problems to be solved in the design and production, these problems are often found in the debugging and production process.

Take the wide section sheet forming as an example, if the design is not reasonable, the deformation defects such as edge wave, bag wave, longitudinal bending, corner fold, crack and distortion will appear in the debugging process. The redesign of the processing roll after the occurrence of problems will inevitably cause a great waste of human and material resources. If we can understand the mechanism of these defects, try to avoid these defects in the design process, or after the occurrence of defects on the basis of the original reasonable improvement of the roll, so as to reduce or even eliminate these defects, we can still achieve the desired goal of roll design.

The following is the cause of the problems in the actual operation of cold bending forming and some simple analysis

1. The generation of bag wave is mainly due to the transverse tensile stress and transverse strain generated in the bending process of the plate, while the strain along the thickness direction of the plate is relatively small, according to the Poisson relation of the deformation of the material, it is inevitable to shrink along the longitudinal deformation in the part where the deformation is concentrated.In this experiment, this phenomenon mainly occurs at four deformation angles, so the longitudinally-contracted part exerts compressive force on the central plate, and under the action of force, instability occurs in some areas and bag-like bulge occurs, which is often referred to as bag-shaped wave.The bag wave is mainly elastic deformation.

2. The edge wave (hereinafter referred to as edge wave) is a kind of more common defects than pocket wave, it produces is mainly two kinds of effect of synthesis: the first with the pocket in front of the wave are the same, the mechanism of is due to the cross section bending part of the material by transverse tensile stress, transverse tensile strain, strain in the thickness direction is not big, according to the relationship between poisson appear longitudinal contraction, and edge wave generated by the edges due to compression stress;The second is that the material at the edge is first stretched and sheared under the action of external force, and then compressed and sheared again, generating plastic deformation and resulting in edge wave.These two effects add up to form a side wave.

3. There are many reasons for longitudinal bending, one of the most important reasons is that the edge of the section is affected by the tension force when bending the side, trying to lengthen the entire section along the longitudinal, but the tension force is not enough to stretch the entire rigid section, leading to the rolling workpiece front end appears up or down bending phenomenon.

Analysis and solution:

1. The front and the back track have a greater impact on the bag-shaped wave than the middle track, especially the back track.The appearance of bagged waves can be eliminated by adopting more forming paths.The width of the edge of the section has a certain influence on the bag-shaped wave. In the design, the relational expression F<250t2/(W-88t) can be referred to.Thin plates are more prone to pocket waves than thick plates. The bag wave can be slowed by applying tension to the sheet.

2. Edge waves may occur in all channels, and the previous channel has a great influence on the appearance of edge waves. Thinner plates are more likely to have edge waves than thicker plates, while wider ones are more likely to have edge waves.In order to reduce or eliminate edge waves, it should be noted that the width of section edge should not be too large at the early stage of design, and the ratio of section edge width to plate thickness can be referred to close to or less than 40 for design.The bending Angle can be assigned according to the empirical formula.If the edge wave occurs during rolling, it can be alleviated or eliminated by adding part of the pass.

3. The following track number has a great influence on longitudinal bending. With the same section and roller configuration, the thick plate is more prone to longitudinal bending than the thin plate.In order to reduce or eliminate the longitudinal bending, we should pay attention to the reasonable distribution of deformation in the design, and the deformation of the following few lines is not too large. Longitudinal bending can be reduced or eliminated by prebending, increasing the number of passes, using a straightener, changing the spacing between brackets, using rollers, adjusting the gap between rollers, etc.