I believe many people have heard of stamping parts, especially in the machining industry. Stamping parts are widely used in industries such as electronics, mechanical manufacturing, home decoration, and automotive manufacturing. Stamping parts used in the automotive industry are collectively referred to as automotive stamping parts, which undergo both plastic deformation and elastic deformation during the processing. Today, the editors of Zhejiang Balford Electromechanical would like to discuss with you how to solve the springback problem of stamping parts?
I. Factors Affecting Springback of Stamping Parts and Solutions
Springback refers to the partial recovery of the deformed body's shape after unloading, where the shape and dimensions of the part do not match those of the stamping working surface, causing the part dimensions to exceed the allowable tolerance range, thereby affecting product precision.
During the processing of automotive stamping parts, both plastic deformation and elastic deformation occur. After unloading, the part will spring back to a certain extent. Springback refers to the deformation that occurs after the metal sheet is formed and removed from the die, affecting the final shape of the part. Springback directly affects the geometric accuracy of the workpiece, and it is also a defect that is difficult to minimize during the forming process.
1. Stress variation curve after unloading
(1) From ordinary steel sheets to high-strength steel sheets, stamping parts made of different materials and strengths have different yield strengths. The greater the yield strength of the sheet, the more prone it is to springback. For thick plate components, hot-rolled carbon steel plates or hot-rolled low-alloy high-strength steel plates are used as materials. The surface quality of hot-rolled plates is higher than that of cold-rolled plates, with smaller thickness, unstable mechanical properties, and lower elongation.
2. Stress variation before and after springback
(2) During the forming process, the thickness of the material has a significant impact on the bending performance of the sheet. When the sheet thickness increases, the springback phenomenon gradually decreases. As the sheet thickness increases, plastic deformation increases, elastic recovery deformation increases, and springback decreases.
3. Tangential stress of the plate punch
With the continuous improvement of thick plate quality levels, the dimensional accuracy problems of parts caused by springback are becoming increasingly serious. In order to understand the springback nature and dimensions of parts, corresponding countermeasures and measures should be taken for die design and process debugging.
The ratio of bending radius to sheet thickness for thick plates is relatively small, and the stress variation in the thickness direction cannot be overlooked.
Parts of different shapes exhibit significant differences in springback. Parts with complex shapes typically require an additional forming pass. When they are not fully formed, they spring back, and certain fractal parts are more prone to springback, such as U-shaped parts. Therefore, during analysis and forming, springback compensation must be considered.
(4) The larger the bending angle, the greater the accumulated springback value, and springback will generate tensile stress. The deformation length of the stamped part increases with the increase of the bending angle.
(5) When designing the die, the clearance between dies must not exceed twice the material thickness in the working parts, and the product should be integrated into it. To achieve better material flow, local forming of the die should be carried out after die machining. Especially for bending dies, the larger the working clearance, the greater the springback. When the sheet thickness range is small and springback is large, it is difficult to determine the die clearance accurately.
(6) The bending radius is proportional to the springback amount, so the greater the bending degree, the harder it is to form the bend.
(7) The forming process is a constraint that limits the springback value. Generally, the springback of bottoming bending is better than that of free bending. If the processing results of the same batch of stamped parts are identical, the bending force required for bottoming bending is much greater than that for free bending. Therefore, if both methods involve similar bending forces, the final results will differ. The greater the correcting force required for bottoming bending, the smaller the springback of the stamped part, and the correcting bending moment will elongate the fibers in the deformation zone to achieve the forming effect. When the bend is unloaded, the surface and internal fibers shorten, but the springback directions on both sides are opposite, thereby reducing the outward springback of the stamped part to a certain extent.