Stamping rebound of metal die and countermeasures

From the development and manufacturing experience of all kinds of metal stamping dies, the drawing die is more difficult to deal with, because the material will produce flow, and the problem of stamping springback is sometimes very headache, there is no accurate and credible springback calculation formula, generally we rely on experience, for different materials, different R Angle to compensate. We are relatively clear about the influencing factors of rebound, if in the repair of the mold, for some conditions, we can still find effective ways to control rebound.


Factors affecting the springback of metal stamping parts

1. Mechanical properties of stamping materials

There are different strengths of metal stamping parts in the car body, from ordinary plates to high-strength plates, different plates have different yield strengths, the higher the yield strength of the plate, the more likely it is to rebound, especially DP series dual-phase high-strength steel.



2. Thickness of stamping material

In the forming process, the sheet thickness has a great impact on the bending property, with the increase of sheet thickness, the springback phenomenon will gradually decrease, this is because with the increase of sheet thickness, the material involved in plastic deformation increases, and then the elastic recovery deformation also increases, therefore, the springback becomes smaller.

With the continuous improvement of the 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 some understanding of the nature and size of parts springback in order to take corresponding countermeasures and remedial programs.

3. Shape and complexity of stamping parts

The rebound of different shapes of parts is very different, the shape of complex parts will generally increase a sequence of shaping, to prevent the formation is not in place, and there are more special shape parts are more prone to rebound phenomenon, such as U-shaped parts, in the analysis of the forming process, must consider the rebound compensation matters.

4. Stripper holding force of die parts

The blanking force of die stripper is an important process measure. By optimizing the blanking force continuously, the flow direction of the material can be adjusted and the stress distribution inside the material can be improved. The increase of blank holding force can make the part draw more fully, especially the part side wall and R Angle position, if the forming is sufficient, the internal and external stress difference will be reduced, thus reducing the rebound.

5. Mold drawing bar

Die drawing bar is widely used in today's process. Reasonable setting of drawing position can effectively change the direction of material flow and effectively distribute the feed resistance on the press surface, thus improving the formability of materials. Setting drawing bar on the parts prone to rebound will make the parts more fully formed, and the stress distribution is more uniform, so that the rebound is reduced.


Hardware stamping parts rebound control method

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

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



Stamping parts shaped parts rebound control and L-shaped parts rebound control

Generally, L-shaped parts are developed in the same mode with left and right countermeasures. In order to prevent lateral forces from causing the deflection of formed parts, the rebound rectification of L-shaped parts developed symmetrically is basically the same as that of U-shaped parts.

U-shaped parts stamping rebound control. General U-shaped parts are prone to rebound, such as the left/right front longitudinal girder inner plate front body parts of some models, this part has a rebound problem in the development process. After repeated analysis, and according to its bond relationship and communication with the designer, make changes to the parts, increase the length of the reinforcement, increase the shaping sequence in the mold itself, and schedule shaping 1 ~
3.5 mm. The stamping process sequence increases the shaping sequence, and the entire side wall of the parts is reshaped to ensure that the parts have no rebound phenomenon. As shown in FIG. 5, after the group flanging side punching, the shaping insert is added, and the mold insert is all made of Cr12MoV material to ensure that the treatment quenching hardness reaches HRC58 ~ 60. Finally determine the scheme, according to this scheme to change the mold, the field verification of the formed parts without springback phenomenon. According to the experience of developing models in the past, the rebound of some automobile molds can be judged.

In addition, the current general solution to sheet metal stamping springback process measures are as follows:

1. Correct bending

Correcting the bending force will make the impact pressure concentrate in the bending deformation zone, forcing the inner metal to be squeezed, after being corrected, the inner and outer layers are extended, and the rebound trend of the two extrusion zones after unloading can reduce the rebound.

2. Excessive bending

In bending production, due to elastic recovery, the deformation Angle and radius of the sheet material will become larger, and the way that the deformation degree of the sheet material exceeds the theoretical deformation degree can be used to reduce the rebound.

3. Pull and bend

The method is to apply tangential tension while bending the plate, change the stress state and distribution inside the plate, so that the entire section is in the plastic tensile deformation range, after unloading, the springback trend of the inner and outer layers offset each other, reducing the springback.

4. Local compression

The local compression process is to increase the length of the outer plate by thinning the thickness of the outer plate, so that the springback trend of the inner and outer layers counteracts each other.

5. Bend many times

The bending is divided into several times to eliminate rebound.


6, inside rounded passivation

Compress from the inside of the bend area to eliminate stamping rebound. When the plate U-shape bending, because the two sides of the symmetrical bending, the use of this method is better.

7, change the whole drawing into part bending forming

A part of the metal stamping part is bent and then formed by drawing to reduce springback. This method is effective for products with simple two-dimensional shapes.

8. Control residual stress

The metal mold increases the local convex hull shape on the surface of the tool during the pulling time, and then eliminates the increased shape during the later process, so that the residual stress balance in the material changes to eliminate rebound.

9. Put negative rebound

The stamping workpiece manages to produce a reserved negative rebound of the sheet material. After the upper die is returned, the part reaches the required shape by bouncing back.

In summary, Dongguan Changdong Mold Co., Ltd. in the design and manufacturing process of all kinds of stamping die, constantly summarize the stamping rebound encountered in the process of mold testing, and other mold testing problems. The company's team focuses on customers, and strives to control the number of stamping die trials, save customers' mold development cycle and save mold development costs for customers.