The door outer panel is a medium-sized outer cover in the body-in-white, and the main ridgeline feature on the side of the vehicle generally runs through the front and rear door outer panels.Since the door is a moving part, it involves the matching of multiple flatness and gaps, and it is also the part most intuitively observed by users, and its forming quality requirements are very strict.In order to realize the dynamic shape of the whole vehicle, most mainstream automobile factories have made the characteristic ridgeline design more and more protruding, the angle between the profiles on both sides of the ridgeline is getting smaller and smaller, and the ridgeline fillet radius is on the premise of meeting the national standard. The corner radius is designed according to the limit value of 2.5 mm, which puts forward higher requirements on the stamping process, especially the more complex rear door outer panel. Based on this type of rear door outer panel, the reasons for wrinkling defects in the B-pillar area during traditional stamping process are analyzed, and the improved stamping process is adopted to eliminate the wrinkle defects of the parts and meet the requirements of the forming quality of the parts.
1 Rear door outer panel structure
Figure 1 shows the shape of the outer panel of the rear door of a certain model. There are two characteristic ridgelines. Both sides of the ridgeline are curved surfaces with a certain angle. The included angle of the main ridgeline is about 134°, and the radius of the ridgeline is R2.5 mm . There are steps in the B-pillar area of the whole vehicle. The radii of the two rounded corners of the steps are R1.2 mm and R2 mm respectively. The structure of the intersection of the main ridgeline and the B-pillar area is shown in the circle in Figure 1, which is visible after the front door is opened. . According to the requirements of the quality standard of Kangzin, there should be no obvious surface defects after single piece and after painting, and the defect level should not be higher than Class C.
2 Wrinkling analysis and optimization of the B-pillar area of the rear door outer panel
2.1 Stamping process of rear door outer panel
Aiming at the stamping process design of the door outer panel, the stamping direction, process supplement, drawing depth and process arrangement are discussed. For the rear door outer panel, except for the B-pillar area, the process supplement is relatively simple. Generally, deep drawing, trimming and straight flanging are required. If there are special requirements for pressing, the side flanging process needs to be added; for the B-pillar of the rear door outer panel In the area, the supplementary section and related parameters of the traditional process are shown in Figure 2. Due to its modeling characteristics, it cannot be directly deep-drawn and formed. It needs to be formed by deep-drawing, trimming, step shaping and flanging. , b value is generally 0.5~2 mm, R1 is 3~6 mm, R2 is 5~8 mm, h is 0~2 mm; A value is 0~10°. The smaller the value of each parameter, the closer the drawing process supplement is to the final part shape, the smaller the shaping amount, and the more serious the corresponding drawing thinning rate, on the contrary, the smaller the deep drawing thinning rate, but the corresponding secondary shaping amount increases. It is easy to produce surface defects and springback; the idea of process design is generally to adjust various parameters to minimize the amount of shaping under the premise of ensuring the quality of deep drawing.
2.2 Wrinkle analysis
The B-pillar area of the rear door outer panel adopts the above-mentioned stamping process, and the drawing process adopts the minimum drawing depth under the premise of ensuring the overall thinning rate > 3%. After deep drawing, secondary shaping was performed on the step. The results are shown in Figure 3. The thinning rate after deep drawing was 28.4%, and the thinning rate of the cusp area after shaping reached 30%. Severely wrinkled, the part is formed in a state of simultaneous wrinkling and cracking.
The local forming process of the ridgeline is shown in Figure 4. The material at the ridgeline is pressed down by the shaping inserts. As the shaping depth increases, the materials on both sides of the ridgeline are unevenly distributed, and local materials accumulate, and finally they are stacked together. Severe warpage occurs at the edge of the material. After shaping to the end, the wrinkled material cannot be unfolded, and the parts are wrinkled.
The local stress state during the shaping process is shown in Figure 5. Due to the deep-drawing effect of the shaping insert on the sharp point of the ridge line, the primary and secondary stresses are greater than 0, and the state is in the state of tensile stress. After shaping, the material at the sharp point area is thinned. . The primary and secondary stress values in the local area below the insert are all less than 0, and it is in a state of compressive stress. According to the maximum shear stress criterion, if the equivalent compressive stress value exceeds the critical value of instability, the plastic deformation condition is reached, and the local material is compressive instability. , causing parts to wrinkle.
In order to solve the wrinkling of the parts, the following measures can be considered:
- ①Reduce the excess material after deep drawing, that is, the deep drawing forming is as close to the part as possible, and at the same time reasonably distribute the reshaped materials on both sides of the ridge line;
- ② Change the stress state of the wrinkled area, Reduce compressive stress and eliminate material wrinkling;
- ③ impose constraints on wrinkled materials to inhibit material instability.
2.3 Wrinkle optimization
Combined with the above analysis, using the shaping process shown in Figure 6, a movable blanking plate is added to the lower die. During forming, the upper die insert goes down to contact the blanking plate, and only a small part of the material is shaped before contacting the blanking plate, and then Press the sheet together, and apply tensile stress to the end of the sheet to improve the stress state and reduce the compressive stress. The stress distribution during the forming process is shown in Fig. 7. Compared with the process before optimization, the compressive stress is significantly reduced. The free end of the material is restrained by the pressing plate, and the instability of the material is restrained. At the same time, one forming is reduced in the deep drawing process to ensure uniform shaping on both sides of the ridgeline before the clamping.
The shaping process is shown in Figure 8. There are no wrinkles during the entire shaping process. The relative height of the steps decreases during deep drawing. The thinning rate at the sharp point of the ridge line is reduced to 16%, and the final thinning rate after shaping is 26.3%. , greatly improving the stability of the deep drawing process. The actual production adopts this process, and the final part has no local wrinkle and cracking phenomenon, and the forming quality meets the requirements as shown in Figure 9.
Through the analysis of the traditional forming process and the improved process of the B-pillar area of the rear door outer panel, the following conclusions are drawn.
- (1) When using the traditional process method, wrinkling defects occur in the B-pillar area of the rear door outer panel, and the thinning rate also reaches the limit state, and the formed parts cannot meet the quality requirements.
- (2) In order to ensure deep drawing, the local process supplement is “multi-material” relative to the part. During the shaping process, the part of the excess material is in a state of compressive stress, which leads to compression instability, and the unstable part is unconstrained, and the final part is wrinkled. defect.
- (3) By using deep drawing “shallow” forming (meaning that there is no wrinkling due to the material clamping process guarantee, the deep drawing can be shallower than the traditional process, which can reduce the drawing thinning rate and make the deep drawing The process is more stable), and the subsequent use of the clip shaping process not only optimizes the thinning rate of deep drawing, but also solves the wrinkling defect, and the forming quality of the parts meets the requirements, which has certain guidance for the stamping process design and quality optimization of such parts. significance.
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