Improvement of side wall die of Guangzhou Honda

2022-08-15
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Improvement of the side wall mold of Guangzhou Honda

after studying the cracking and deformation of the outer side wall components of model a, Guangzhou Honda successfully put forward suggestions for the improvement of the side wall mold, which not only solved the problem, but also laid a foundation for the smooth production in the future

at the initial stage of the new mold for the rear fender of the side wall of model a (Figure 1), we found that the side wall parts produced by stamping steel plates with different coil blanking were in different states, and some parts were thinned to a certain extent at the vertical wall of the rear door (part a in Figure 2). After confirming the material quality, we found that the material performance and specification were within the qualified range. Therefore, the new mold needs to be adjusted to adapt to the fluctuations of material properties and specifications

Figure 1 a model side wall rear fender

at first, technicians alleviated the occurrence of adverse phenomena to a certain extent by implementing countermeasures such as gaskets, air cushion pressure and closing height, but still failed to make the quality of parts reach a stable state. After careful analysis and summary, we have determined the mold repair plan: by grinding the inner R angle of the rear door drawbead to reduce the feed resistance and increase the material flow, so as to improve the thickness thinning state of the parts. However, this practice will damage the local chrome plating layer of the blank holder, so it is necessary to track the quality of the parts and re chrome plating in a timely manner. In addition, as the drawbead is loosened, the flow of material outside the drawbead increases, which may cause the drawbead to flow within the trimming line, which will expand the range of the Drawbead on the trimming surface (Part B in Figure 2) at the rear door frame of the whole vehicle. Moreover, after some drawbeads are loosened, the leveling force of the drawbead may be reduced, and the drawbead will become deeper. The trimming surface here is a surface of appearance grade C (Part C in Figure 2), so the quality must be tracked and tested after modification

schematic diagram of defective parts in Figure 2

for the improvement of thinning at a and deformation at C in Figure 2, if the adjustment range is too large, it will often cause other related defects. It is necessary to find an improved balance point in the process of mold adjustment

the influence of trimming process mold on the deformation and cracking of side wall parts

taking the trimming and shaping process of our factory as an example, according to the existing process arrangement, the side wall parts usually have the main shape contour after drawing, and the trimming mold plays the role of trimming and shaping

in the trimming process, when the upper mold is pressed down, the trimming process of the rear fender area of the side wall is (Figure 3): the pressing plate presses the part; Cutting insert cutting waste; Reshape the R corner with the reshaping insert to make the R fillet smaller. In general, the conditions required for shaping are very high, and drawing deformation will not occur. In addition, the method of increasing the drawing height is often adopted in domestic mold design. By compensating the materials required for the reduction of R fillet during shaping, and properly carrying out compression deformation, the R angle size can be stabilized. It can be seen from Figure 4 that if material compensation is made for the reduction of R angle, there will be a force f2x in the deformation area shown in the figure, and the force is very small. In addition, in the process of plastic surgery, there are also trimming and integral polyether polyurethane urea (PEUU) in the rear window of the side wall, which has better biological stability and better use potential. Therefore, there is force f1x in the deformation area

Figure 3 mold structure at the back door of side trimming process

Figure 4 stress in the deformation area of trimming process

according to the above analysis, we can analyze the stress of section A-A in Figure 4 as shown in Figure 5. The stress in the deformation area is: the pull force F1 on the material caused by trimming/shaping at the rear window, the pull force F2 caused by shaping at the rear door, the pressing force n of the pressing plate, and the friction force F caused by the pressing force

Figure 5 decomposition of stress section in the deformation area

it can be concluded from Figure 5 that if the appearance surface is required to be free of deformation, the material in the appearance surface area should be in a stress balance state. Theoretically, the deformation area is zero (Fig. 6). Here, according to the numerical qualitative analysis, it can be deduced as:

f2+f1+f=0 ①

f ≤ μ N ②

from the two formulas ① and ②,

f2+f1 ≤ μ Internalized in the heart n

where: μ Is the friction coefficient between the die and the material when the pressing force of the pressing plate is n

from the above analysis, it can be seen that by controlling the friction between the mold and the material, the material at the deformation part can be in a state of zero stress

Figure 6 force on differential unit in all directions

modification countermeasures

1 Adjustment of shaping force and trimming force

the adjustment of shaping force and trimming force is actually the adjustment of F1 and F2 forces

(1) adjust the pressing plate at the rear windshield of the side wall

test method: paste lead tape along the edge of the windshield of the pressure plate to verify the surfacing effect of the pressure plate along the edge of the windshield, and it is found that the deformation of other related parts is aggravated

(2) adjust the flanging clearance at the rear door

test method: polish the flanging position of the lower die to increase the gap between the upper die shaping insert and the lower die, and adjust the R-angle shaping force through the gap change. Finally, it is found that the deformation does not change significantly

through the above two experiments, we found that the adjustment of F1 and F2 forces is not obvious, the magnitude and direction of F1 and F2 forces cannot be determined theoretically, the influence on the deformation area is also very complex, and there is a risk of affecting the appearance accuracy of the whole vehicle in the repair

2. Adjust the size of the pressing force

adjust the size of the pressing force, which can only be achieved by adjusting the n value

(1) adjustment of mold closing height

increasing or decreasing the closing height directly affects the fitting degree of the upper and lower dies. The shaping force and trimming force will decrease. At the same time, due to the rise of the bottom dead center, the stroke of the polyurethane spring is slightly reduced, and the pressing force n of the pressing plate is also reduced. In addition, the shaping R angle cannot meet the requirements, and the local shear continues, and the deformation position does not change significantly

(2) adjustment of polyurethane working stroke

by adding 5mm shims to the polyurethane spring between the upper die pressing plate and the upper die base, the stroke of the polyurethane spring can be increased, thereby increasing the compression force n. Test results: the deformation is slightly improved

(3) improve polyurethane spring

polyurethane elastic elements have certain shortcomings, which require pre tightening and compression to achieve the elastic pressure required by the design. This situation often affects the quality of stamping parts, making the mold structure design more complex. At the same time, it occupies too much mold space, which increases the cost of mold manufacturing. In addition, the performance of polyurethane spring with unsteady pressure may also lead to many problems of parts. To this end, our factory began to use nitrogen springs in stamping dies

the characteristic of nitrogen spring is that in a small space, it can produce a large initial elastic pressure without preloading. The pressing plate has elastic pressure when it contacts with the nitrogen spring plunger at the beginning. One nitrogen spring can replace multiple ordinary springs. For the mold with the same working stroke, the height of the mold with nitrogen spring is much smaller than that with ordinary spring; The spring pressure can be basically kept constant throughout the whole journey; According to the requirements of different stamping processes, the size of the elastic pressure and the position of the force point can be accurately adjusted. In the mold design and debugging, it is very convenient to realize the elastic pressure and balance; Improve the quality of stamping parts and ensure the stability of stamping parts quality. Figure 7 shows the performance comparison between the working spring and the nitrogen spring of polyurethane China Zhongwang, which participated in the optimization design of component structure, material experiment, 2D drawing, section improvement, sample vehicle trial production, etc

Figure 7 Comparison of changes of polyurethane and nitrogen spring pressure affected by compression stroke

3 Distribution and adjustment of pressing force

when drawing parts, we hope to get as full and uniform plastic deformation as possible, so as to avoid deformation caused by local bias flow or excessive flow resistance, resulting in thinning and out of tolerance; During shaping, the material flow in the shaping process is much smaller than that during drawing, and the material flow resistance is also smaller, and the material thinning caused by plastic deformation is smaller. Compared with the material flowing while drawing and thinning during drawing, the material in the trimming process tends to flow as a whole in local areas (Fig. 8), so the improvement of the cracking or thinning out of tolerance of the side wall parts mainly corresponds to the adjustment of the drawing die, while the improvement of the appearance deformation of the parts needs to take into account the comprehensive consideration of drawing and subsequent processes

figure 8 measured material flow during the commissioning of side trim parts

the trimming process has a major impact on the appearance quality of the rear fender. Through the distribution of the pressing force of the pressing plate, the stress on the material during trimming and shaping is controlled, so as to control the overall flow of the local area of the material, which can ensure the appearance quality of the product

(1) on the premise that the overall pressure of the pressing plate is certain, the local stress of the part is increased by local welding of the pressing plate, but at the same time, other parts that are not welded are avoided, resulting in the reduction of the pressing force. However, this may reduce the deformation of the compacted parts and increase the deformation of the non compacted parts. In a more serious state, the zinc powder coating in the compacted area may fall off or appear indentation, resulting in new bad appearance

(2) by grinding and grinding the pressing plate, the surface area of the parts can be expanded, but at the same time, the pressing force is reduced due to dispersion, or the pressing plate is pushed by other convex areas, and the polished area is avoided, but the deformation is intensified

(3) through the method of gradually fitting after welding, the pressing force is optimally distributed and the deformation degree is as small as possible. This requires the fitter to burn and weld correctly, and carefully and properly research and match. It is a work that requires the fitter to have high skills. Of course, with the use of three-axis milling machine tools and various advanced equipment, the dependence of this die repair technology on fitters will be gradually reduced until it is completely eliminated

management after the new mold is put into production

1 Improvement of fitter skills of mold repair personnel

the overall skill level of fitter of mold repair personnel directly affects the progress of mold repair. Take the burning and welding of the pressing plate of the side trimming die as an example. If the required repair cycle is too long, it will take several days from the transportation of the die to the mold repair area for mold opening, the transfer of the pressing plate, the burning and welding of the pressing plate, the grinding of the pressing plate ground and the machine fitting of the pressing plate, to the trial production after the fitting quality is determined. The main reason is that the DuPont medical and pharmaceutical packaging teams are also committed to providing technical support to global medical device manufacturers. Some of the work hours are too long, and these jobs need to be undertaken by experienced fitters. If experienced fitters are understaffed or can only work in the morning shift, or they are too old and lack physical strength, the implementation of the mold maintenance plan will become a bottleneck, and the subsequent work cannot be carried out

2. Equipment accuracy management

the total clearance of the machine tool is a comprehensive index that directly reflects the accuracy and safe use performance of the main drive of the machine tool, including the total wear between the slider adjusting screw nut pair, the connecting rod semi-circular bearing pair, the eccentric connecting rod drive pair, and the low-speed and high-speed drive pairs

3. New material introduction

introduce steel plates with high lubrication performance to increase the processing performance of materials. The delay of deep drawing of highly lubricated materials can reduce the resistance of material flow, increase the overall fluidity of materials, and thus reduce cracking

conclusion

with the rapid development of China's automobile industry, automobile enterprises continue to launch new models, which correspond to a large number of advanced and new models

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