What is the Springback and What are Influencing Factors of Springback on Metal Stamping Parts?
After the load is removed, and the shape of the deformed parts gets restored partially, which is the springback. In other words, springback is the geometric change to the part after the forming process while the part has been released from the forces of the forming tool. Upon completing the forming of the sheet metal, stretch-drawn and deep-drawn parts spring back, accordingly having some influence on the dimensions’ accuracy of the finished part and affecting the assembly precision of the part. The final shape of the stamping part is influenced by the springback, making it difficult to produce the stamping part. Therefore, the manufacturing industry is confronted with some practical issues:1>. after the springback, the prediction of the final part’s geometry; 2>. how to compensate for these effects with appropriate tools.
After applying new materials, the number of new issues are increasing. Forming parts made from new materials are much easier to be influenced by the springback than parts made from traditional deep-drawn steel. Regarding classic sheet metal defects, for example, wrinkles and cracks, the stresses in the sheet metal are more crucial. If the springback occurs, these models are not enough to predict the possible deformation. If so, the strain is decisive and a considerably higher accuracy is very much important.
While the development of tools, the springback is compensated by the software, to remove the part from the tool straight away in the necessary dimensions. Simulation software could not only discover the springback early on, it could also compensate accordingly. By means, tooling processes are accordingly improved and manufacturing cost are decreased. Thus, springback compensation minimizes the risk of expensive changes to processes or stamping die later on.
The springback of metal stamping parts is a difficult problem for automotive stamping parts, especially high-strength steel materials with a yield strength over 600Mpa. Nowadays, it’s still a big difficulty to solve out the springback of stamping parts. Below are several influencing factors.
1. Material Properties
From an ordinary plate to the high strength plate, different sheets are with the different yield strength. The higher the yield strength of the sheet metal is, the more likely it’s to springback, such as S500MC, DP780(with good forming properties). Compared with cold-rolled sheet materials, the hot-rolled sheet material has the worse surface quality, the tolerance of the thickness is larger, the mechanical properties of material are not more stable, and the elongation rate of the material is lower.
2. Material Thickness
During the forming process, the sheet material thickness affects greatly on the bending performance. The thicker the plate is, the less the rebound phenomenon would be, which is because as the thickness of the sheet increases, the amount of the plastic deformation material increases, the elastic recovery deformation also increases, and the resilience decreases accordingly.
3. Parts Shape
Different parts’ shapes are with different springback. For parts with complicated shapes, in order to prevent the springback caused by the incomplete forming process, normally one process(shaping) is added accordingly. However, some special shaped parts, such as u-shaped parts, are more possible to rebound. Therefore, it’s very important and necessary to consider the springback compensation In the analysis of the forming process.
4. Bending Radius
The relative bending radius is proportional to the springback value. That is to say, the greater the curvature of metal stamped parts, the less possible it’s to be bent.
5. Bending Center Angle
The larger the value of the bending center angle is, the bigger the springback cumulative value is, causing the serious springback. With the increase of the bending center angle, the deformation length of stamping parts increases correspondingly.
6. Forming Technique
The forming process is a very important aspect, restricting its springback value. Normally, the springback effect of correcting bending is better than that of free bending.
7. Matched Condition of the Stamping Die’s Clearance
In the relative working components, the metal stamping die should be designed with a gap of twice the thickness of the material, and the part shall be accommodated in the gap. To better achieve the material flow, the parts of stamped dies shall be developed after finishing the die’s manufacturing. Especially for bending die, the larger the clearance of the working component is, the great the springback is.
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