What are the design requirements for the pressing surface of auto body parts?

2020-02-21 11:34:01

Two situations should be considered when designing the pressing surface: one is that one part of the pressing surface is the flange surface of the drawing part. The shape of the pressing surface of this kind of deep drawing part is determined, generally it does not change its shape, even if it is partially modified to improve the drawing forming conditions, it should be reshaped and corrected in the subsequent process; the other situation is that the pressing surface belongs to the supplementary part of the process. In the latter case, the design of pressing surface is mainly to ensure good drawing forming conditions. The design principle of pressing surface is:

（1） The shape of the pressing surface should be simplified as much as possible, and the horizontal plane pressing surface is better. On the premise of ensuring good drawing conditions, in order to reduce material consumption, it can also be designed into the shape of bevel, smooth surface (such as single surface, cone surface) or plane surface combination. But do not design it as the shape with big angle crossing, sharp change of height, or bulge or pit on the pressing surface. Because of the uneven distribution of material flow and plastic deformation caused by these shapes of pressing surface, there are wrinkling, accumulation, fracture and other phenomena in deep drawing.

(2) Horizontal pressing surface is widely used, and its resistance change is relatively easy to control, which is conducive to adjusting the die to a good pressing surface resistance state which is conducive to deep drawing forming, and the inward inclined pressing surface has less material resistance. Automobile stamping parts can be used in deep drawing parts with large plastic deformation. However, in order to ensure the strength of the blank holder ring, the inclination angle of the blank holder surface α is generally controlled to be less than 40 ° - 50 °. The flow resistance of the inclined pressing surface is large, and the plastic deformation of the blank can be increased when the automobile parts are drawing the shallow drawing parts. However, if the inclination angle φ is too large, the flow condition of the material will become worse and it is easy to crack.

(3) The section curve length of the pressing surface shall be less than that of the internal section of the drawing part. It is generally believed that when the elongation of each section reaches 3% - 5%, the shape of automobile body panel has better freezing property. The small elongation shall not be less than 2%. Therefore, the reasonable pressing surface is to ensure that the elongation of each section of the drawing part reaches more than 3%. If the length of the section curve of the pressing surface is not less than the length of the internal section curve of the drawing part, there will be surplus material, relaxation, wrinkles, etc. on the drawing part. It is also necessary to ensure that the elevation angle α of the pressing surface is greater than the elevation angle β of the punch, as shown in Figure 11-5. If this condition cannot be met, it is necessary to consider changing the pressing surface, or setting ribs or reverse forming shape at the bottom of the drawing part to absorb the surplus material.

(4) The pressing surface should make the forming depth small and the depth of each part close to the same. The pressing surface can make the material flow and plastic deformation tend to be uniform and reduce the forming difficulty.

(5) The pressing surface shall ensure the reliable positioning of the blank in the process of drawing and trimming, and the convenience of feeding and taking parts shall be considered.

In practical work, if the above principles cannot be achieved at the same time, the choice shall be determined according to the specific situation.