Influencing factors of springback of metal stamping parts

Influencing factors of springback of metal stamping parts

1. Mechanical properties of stamping materials

There are metal stamping parts with different strengths on the car body. From ordinary plates to high-strength plates, different plates have different yield strengths. The higher the yield strength of the plates, the easier it is to spring back, especially the DP series dual-phase high-strength steels.

2. Stamping material thickness

During the forming process, the thickness of the sheet has a great influence on the bending performance. As the thickness of the sheet increases, the springback phenomenon will gradually decrease. This is because as the thickness of the sheet increases, the material involved in plastic deformation increases, and then the elastic recovery The deformation also increases, and therefore, the springback becomes smaller.

With the continuous improvement of the material strength level of thick sheet metal parts, the problem of dimensional accuracy of parts caused by springback is becoming more and more serious. Mold design and later process debugging require an understanding of the nature and size of part springback in order to adopt Corresponding countermeasures and remedial plans.

3. Shape and complexity of stamping parts

The springback of parts with different shapes is very different. For parts with complex shapes, a sequence of reshaping is generally added to prevent springback from being formed improperly. Some parts with special shapes are more prone to springback, such as U-shaped parts. In the analysis and forming process, springback compensation must be considered.

4. Blank holder force of stripper of mold parts

The stamping process of die stripper blank holder force is an important technological measure. By continuously optimizing the blank holder force, the flow direction of the material can be adjusted and the internal stress distribution of the material can be improved. The increase of blank holder force can make the part drawing more fully, especially the part side wall and the R angle position. If the forming is sufficient, the internal and external stress difference will be reduced, so that the springback will be reduced.

5. Mold drawbeads

Mold drawbeads are widely used in today’s processes. Reasonable setting of the drawing position can effectively change the direction of material flow and effectively distribute the feed resistance on the pressing surface, thereby improving the material formability and prone to springback. The drawing bead is set on the parts of the steel, which will make the parts more fully formed, the stress distribution will be more uniform, and the springback will be reduced.
Method for controlling springback of metal stamping parts

The best time to reduce or eliminate stamping springback is in the product design and mold development stages. With the aid of early CAE rebound analysis, the amount of rebound is accurately predicted, product design and process are optimized, and product shape, process and compensation are used to reduce springback. In the hardware mold debugging stage, the mold must be tested strictly in accordance with the guidance of process analysis. Compared with ordinary SE analysis, the workload of springback analysis and correction has increased by 30% to 50%, but it can greatly shorten the mold debugging cycle.

Springback is closely related to the drawing process. Under different drawing conditions (tonnage, stroke, feed volume, etc.), although the stamping parts have no forming problems, the springback after trimming will be more obvious. Springback analysis and drawing forming analysis are used The same software, but the key is how to set the analysis parameters and effectively evaluate the rebound results.

Springback control of special-shaped parts of stamping parts and springback control of L-shaped parts

The L-shaped part of the swing arm reinforcement plate of a certain car model, generally L-shaped parts are developed in the same mold with the left and right countermeasures. In order to prevent the lateral force from causing the formed part to deviate, the left and right symmetrical development of the L-shaped part rebound rectification Basically the same as U-shaped parts.

U-shaped parts stamping springback control. Generally U-shaped parts are prone to springback, such as the front part of the left/right front side rail inner panel of some models. This part has a springback problem during the development process. After repeated analysis and communication with the designer based on the overlap relationship, the parts are changed, the length of the ribs is increased, the plastic sequence is added to the mold itself, and the plastic is scheduled to be 1~
3.5 mm. The ordering of the stamping process increases the reshaping sequence, and the entire side wall of the part is reshaped to ensure that the part does not spring back. As shown in Figure 5, after the assembly, the flanging side punching sequence adds shaping inserts, and all the mold inserts are made of Cr12MoV material to ensure that the quenching hardness reaches HRC58-60. This plan is finally determined, the mold is changed according to this plan, and the molded parts are verified on the spot without springback. Based on the experience of developing models in the past, the springback of some automobile molds can be judged.
In addition, the current general technical measures to solve the rebound of sheet metal stamping are as follows:

1. Correct the bend

Correcting the bending force will concentrate the punching force in the bending deformation zone, forcing the inner layer of metal to be squeezed. After being corrected, the inner and outer layers are stretched. After unloading, the rebound tendency of the two squeezed areas can be offset to reduce the rebound.

2. Excessive bending

In bending production, due to elastic recovery, the deformation angle and radius of the sheet metal will become larger, and the sheet metal deformation degree exceeding the theoretical deformation degree can be used to reduce the springback.

3. Pull bend

This method is to apply tangential tensile force while bending the sheet to change the internal stress state and distribution of the sheet, so that the entire section is within the range of plastic tensile deformation. After these unloading, the springback tendency of the inner and outer layers cancels each other out, reducing Small rebound.

4. 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 rebound tendency of the inner and outer layers cancels each other out.

5. Multiple bends

Divide the bending into multiple times to eliminate springback.
6, the inner rounded corners are dull

Compress from the inside of the bend to eliminate punch springback. When the plate is bent in a U shape, this method is more effective because of the symmetrical bending on both sides.

7. Change the overall drawing into a partial bending shape

Part of the metal stamping parts are formed by bending and then drawn to reduce springback. This method is effective for products with simple two-dimensional shapes.

8. Control residual stress

The hardware mold adds a local convex hull shape on the surface of the tool during the drawing time, and then eliminates the added shape in the later process, so that the residual stress balance in the material is changed to eliminate springback.

9. Rebound

The stamped workpiece tries to make the sheet material produce the reserved negative rebound. After the upper mold returns, the part reaches the required shape by rebounding.