Stamping springback is a problem that accompanies all stamping processing industries, but its degree varies, here are 12 tips for you! depending on whether it is within the allowable range of the product. It mainly affects the shape, precision, and size of stamping products, and has little effect on surface quality.
Influencing Factors of Stamping Springback
- Material Properties
The strength of stamping parts is different, from ordinary plates to high-strength plates, different plates have different yield strengths. The higher the yield strength of the sheet, the easier it is to spring back.
The material of thick sheet parts is generally hot-rolled carbon steel plate or hot-rolled low-alloy high-strength steel plate. Compared with a cold-rolled thin sheet, the hot-rolled thick sheet has poor surface quality, large thickness tolerance, unstable material mechanical properties, and lower elongation of the material.
- Material Thickness
In the stamping forming process, the sheet thickness has a great influence on the bending performance. As the thickness of the sheet increases, the springback phenomenon will gradually decrease. Because as the thickness of the sheet metal increases, the material participating in the plastic deformation increases, and the elastic recovery deformation also increases, so the springback becomes smaller.
- Part Shape
The springback of parts with different shapes is very different. Parts with complex shapes generally need to be shaped in order to prevent the stamping springback if the forming is not in place. Parts with special shapes are more prone to springback, such as U-shaped parts. Therefore, stamping springback compensation must be considered during the analysis of the forming process.
- Part Blank Holder Force
Blank-holding force The stamping forming process is an important technological measure. By continuously optimizing the blank-holding force, the flow direction of the material can be adjusted and the internal stress distribution of the material can be improved. The increase of the blank holder force can make the part drawing more full, especially the side wall and R angle position of the part. If the forming is sufficient, the internal and external stress difference will be reduced, thereby reducing the stamping springback.
- Stamping Springback Control of Special-shaped Parts
During the development process of the left and right threshold parts of the front floor, there is a phenomenon of stamping springback of 4°. In the process route, the plastic 4° is also added, and the third sequence of plastic surgery is added. At the same time, the material of the mold plastic insert is Cr12MoV, and the hardness needs to reach HRC58-62.
- Stamping Springback Control of L-shaped Parts
The L-shaped part of the swing arm reinforcement plate of a certain car model, generally the L-shaped parts are developed with the same mold as the left and right countermeasures. In order to prevent the lateral force from causing the deviation of the formed part, the left and right symmetrical development of the L-shaped part is rectified. It is basically the same as the U-shaped part.
- U-shaped Part Rebound Control
Generally, U-shaped parts are prone to springback. After repeated analysis and communication with the designer according to the overlapping relationship, make changes to the part, increase the length of the rib, add a shaping sequence to the mold itself, and plan to shape the shape by 1 to 3.5 mm.
The shaping sequence is added to the process sequence, and the entire side wall of the workpiece is completely shaped to ensure that there is no springback phenomenon of the workpiece. Therefore, plastic inserts are added in the flanging and side punching sequence after assembly, and all mold inserts are made of Cr12MoV material to ensure that the quenching hardness reaches HRC58-62. It is verified on-site that there is no rebound phenomenon of formed parts.
Stamping Parts Springback Control Methods
The best time to reduce or eliminate springback is during the product design and tooling development stages. With the help of analysis, accurately predict the amount of springback, optimize product design and process, and use product shape, process, and compensation to reduce springback.
In the mold debugging stage, the mold must be tested in strict accordance with the guidance of the process analysis. Compared with ordinary SE analysis, the springback analysis and correction workload increases by 30% to 50%, but it can greatly shorten the mold debugging cycle.
Springback is closely related to the drawing-forming process. Under different drawing conditions (the tonnage of the punch, stroke, feed rate, etc.), although there is no forming problem in the stamping parts, the springback after trimming will be more obvious. Springback analysis and drawing forming The analysis uses the same software, but the key is how to set the analysis parameters and evaluate the springback results effectively.
In addition, the current common technological measures to solve the springback of sheet metal stamping are as follows:
- Correct Bending
Correcting the bending force will concentrate the stamping force in the bending deformation area, forcing the inner layer of metal to be squeezed. After being corrected, both the inner and outer layers will be elongated.
- Heat Treatment
Annealing before bending, reducing its hardness and yield stress can reduce springback, and also reduce bending force, and then harden after bending.
- Excessive Bending
In stamping and bending production, due to elastic recovery, the deformation angle and radius of the sheet will become larger. Springback can be reduced by deforming the sheet beyond the theoretical deformation.
- Material Hot Bending
Using heating and bending, and choosing the right temperature, the material has enough time to soften, which can reduce the amount of springback.
- Inner Fillet Passivation
Compress from the inside of the bend to eliminate springback. When the plate is bent in a U shape, this method is more effective due to the symmetrical bending on both sides.
- Electromagnetic Treatment
The shape and size errors caused by springback can be corrected by impacting the surface of the stamped material with electromagnetic pulses.
- Stretch Bend
The method is to apply tangential tension while bending the sheet, change the stress state and distribution inside the sheet, and make the entire section within the range of plastic tensile deformation. After unloading, the springback trends of the inner and outer layers cancel each other out, reducing Small rebounds.
- Local Compression
The local compression process is to increase the length of the outer sheet by reducing the thickness of the outer sheet so that the springback tendency of the inner and outer layers cancels each other out.
- Multiple Bending
The bending form is divided several times to eliminate springback.
- Change the Overall Drawing into Partial Bending
A part of the part is bent and then drawn to reduce springback. This method is effective for products with simple two-dimensional shapes.
- Control Residual Stress
When drawing, add a local convex shape on the surface of the tool, and then eliminate the added shape in the subsequent process, so that the residual stress balance in the material will change to eliminate springback.
- Negative Rebound
When machining the surface of the tool, try to make the sheet negative springback. After the upper mold returns, the workpiece reaches the required shape by springback.