Research on production stability of machine cover outer plate
Based on the investigation of the precision fluctuation of the cover outer plate, this paper introduces the reasons and analysis ideas of the precision fluctuation. It focuses on the importance of the die structure in the continuous batch production. It meets the setting principle of the six degrees of freedom of the parts, effectively improves the automation production efficiency, and has a certain reference significance for the early mold structure design.
Wen / Li welcome, Wang Zhiguang, sun Jijun, technical center of Great Wall Motor Co., Ltd
Based on the investigation of the precision fluctuation of the cover outer plate, this paper introduces the reasons and analysis ideas of the precision fluctuation. It focuses on the importance of the die structure in the continuous batch production. It meets the setting principle of the six degrees of freedom of the parts, effectively improves the automation production efficiency, and has a certain reference significance for the early mold structure design.
Research background
During the pT2 stage of chb025a model, during the production rhythm of the whole line of the elevator cover outer plate, the flanging edge lines of the finished products were misplaced, warped, and the flanging height of the front bumper and the front windshield were out of tolerance, which seriously affected the appearance quality of the single piece and the pass rate of the single piece, and seriously affected the quality of the hood assembly. In order to ensure the model development node to be mass produced on time, a special problem investigation team was set up This is a survey.
Research objectives
Solve the problems of single piece flanging edge line dislocation, edge warping, flanging height out of tolerance and precision drop, improve the automatic production rhythm of engine hood outer panel, and achieve the company’s development target of 8.3 pieces / min for single piece stamping and 95% pass rate of outer plate in SOP stage.
Field investigation
Current situation description
At the end of Pt stage, in order to improve the production efficiency of single piece, the stamping workshop optimized the beat of all parts. When the beat of the outer plate of the machine cover was increased from 7.7 pieces / min to 8.3 pieces / min, there were quality problems in the outer plate of the machine cover, such as unsmooth edges, warped edges, concave surface products and so on. The single piece pass rate of the machine cover outer plate dropped from 95% to 80%, which seriously affected the single-piece straight through of the stamping workshop The rate and the work of the post station were carried out smoothly.
Investigation and analysis
As shown in Figure 1, in view of the surface product and accuracy problems of the single cover, the first breakthrough point is the change factors of human, machine, material, method and measurement, and the changes of machine equipment and human factors are found; then, confirm the position where the single part of the lower cover occurs, the edge lines of the front windshield part of the cover are misplaced, the edges of the front protection part of the cover are not smooth, and the edges of the left and right sides of the cover change in different degrees It is found that the flanging height of the outer plate of the machine cover has little change on the left and right sides, but the flanging height of the front protection part of the cover is out of tolerance, which was (8 ± 0.7) mm, but the flanging height of the front protection part is about 10 mm. However, the original flanging height of the front windshield side of the hood outer panel was (8 ± 0.7) mm, and now the flanging height of the front windshield is about 6 mm, which seriously exceeds the tolerance.
Figure 1 problem analysis of cover
The single piece of the outer plate of the old machine cover in stock was used for inspection, and there was no surface product problem. The accuracy of the single piece of inventory was sent for inspection. The full clearance and surface difference around the machine cover were all qualified, and the flanging height was also within the specified qualified range. After comparing and checking the recent mold change records, there is no product design change and mold abnormal change record for the whole sequence mold of the cover outer plate. Therefore, it is determined that the cause of this problem is caused by the single piece production instability of the outer plate of the machine cover. So what is the reason for the single piece instability of the cover outer plate? By using the elimination method, the recent change point is the single piece beat of the cover outer plate. The investigation found that after the automatic production rhythm of the whole line of the machine cover outer plate was increased from 7.7 pieces / min to more than 8.3 pieces / min, there were different degrees of edge line dislocation, edge warping and the flanging height of the front cover and front windshield parts out of tolerance.
When the beat is adjusted to 7.7 pieces / min, the surface products and precision of the cover are good. When 8.3 pieces / min is used to produce the outer plate of machine cover, the phenomenon of single piece and flanging height out of tolerance will appear in different degrees, and the optimization of automatic trajectory will only be more beneficial to the production stability. After reviewing the process layout of chb025a cover outer plate, it is found that Op10 is drawing, OP20 is side repairing on left and right sides of machine cover, front bumper and front windshield side are in the form of forward repair and two-stage cutter, op30 is full forward turning under the premise of two φ 16mm locating pins on the front windshield side, and op40 is the four corners of the cover outer plate. In order to reduce the problem of chromium damage caused by slag on the outer plate of the conventional machine cover, the process of setting two-stage waste knives at the front and rear sides of the feeding is adopted. At this time, no waste knives are arranged in the feeding direction, but two cutting scraps knives are set at the left and right sides of the machine cover near the feeding direction. Since the left and right sides of the machine cover and the front protection side are equipped with waste knives, the parts can be positioned by using the waste knife symbolic surface, but there is no waste knife on the front windshield side. At this time, it will be determined according to the shape of the parts, whether the parts have instability caused by the improvement of production efficiency. Generally, there is an angle of about 15 ° between the radian of the outer panel of the machine cover and the feeding direction, even if there is no scrap knife on the front windshield side, it can ensure that the parts will not offset to the feeding side under the high production efficiency. However, the radian of the outer plate of chb025a machine cover is flat, only 5 ° only. After the production rhythm is increased, the parts will move in different degrees, resulting in the defects of surface products and the over tolerance of flanging height.