In recent years, with the rapid development of computer technology and simulation analysis software, stamping CAE analysis technology has been widely used, from product development, stamping process analysis, DL drawing design, die debugging, to the solution of stamping production problems. Through simulation analysis and virtual manufacturing, the whole process is analyzed, problems are found in advance, causes are analyzed, solutions are put forward, products are further improved, process schemes are optimized, and process schemes are innovated. Therefore, a lot of design and manufacturing defects are avoided, product quality is improved, a lot of time is saved and development cost is reduced. There are many softwares in stamping CAE. At present, the commonly used special softwares are AutoForm, DYNAFORM and PAM stamp. The general software includes: MSC.MARC , ABAQUS, ANSYS-DYNA series, etc. In this paper, through some specific cases, using AutoForm software, introduces the application of CAE analysis technology, the shortcomings and future development direction.
Analysis of stamping process
Through CAE analysis, the defects such as cracking, wrinkling, stamping negative angle and slip line are determined to further optimize the product. (1) the parts shall not be cracked or wrinkled (Fig. 1), otherwise the product shall be changed. (2) the product should not have negative stamping angle and need to be optimized. After the stamping direction is determined, the software automatically calculates where the negative stamping angle exists and displays it by color. There is a negative punch angle in the red area shown in Figure 2. (3) there is a 5mm slip line on the edge line of the drawing part of the outer panel of a certain model during the drawing process, but the fillet does not slip out, which meets the process requirements, as shown in Figure 3.
Stamping process planning
Through the CAE analysis of the whole process, the process plan is determined, including drawing, flanging, shaping, trimming and punching direction, springback, etc. by optimizing the product, the process is shortened, the number of dies is reduced, and the die investment is reduced.
Material cost control
(1) determine the material grade. Select different materials, carry out CAE analysis, analyze and judge the results, determine the appropriate material brand of the product, and reduce the material cost.
Fig. 1 CAE analysis to determine the cracking and wrinkling of parts
Figure 2 negative angle of stamping parts
Drawing of a car’s outer panel slip line
Figure 4 stamping process planning
(2) optimize sheet metal layout. Through CAE analysis, optimize layout, improve material utilization and reduce cost. For the drawing blank of a product, the blank sheet is concave shape, and the material utilization rate of the product is 40.4% by adopting the rectangular blanking process; now the material utilization rate of the product is increased to 53.7% by adopting the non waste layout blanking process.
(3) waste utilization. Figure 5 (a) shows the roof of a panoramic skylight, figure 5 (b) shows the waste of skylight after trimming, figure 5 (c) shows the rear crossbeam of the roof, and figure 5 (d) shows the drawing part of the rear crossbeam of the roof, using the waste of skylight as the sheet material. From the simulation analysis, it can be seen that this scheme is feasible, and the material utilization rate of the top cover is increased from 43% to 50%.
Selection of stamping equipment
(1) determine the size of the sheet metal. By CAE analysis, the shape and size of the sheet metal are determined, the size of the die is calculated, and whether the size of the press table meets the requirements.
(2) calculate the forming force. By CAE analysis, the forming force is calculated to determine the tonnage of stamping equipment. The drawing part of the side wall reinforcement plate of a certain vehicle has the tensile strength of 590MPa, forming force of 1800t and edge pressing force of 300t.
(3) determine the number of processes and select the appropriate press production line through CAE analysis of the whole process.
Application of CAE analysis technology in stamping process design
CAE analysis technology of the whole process
Figure 6 shows CAE analysis process of inner plate of back door of a certain vehicle, and analyzes forming process in detail. Analyze whether there are defects in drawing and optimize, arrange the drawing bars reasonably, determine the size of sheet metal, judge whether the trimming punching direction is reasonable, choose the reasonable flanging pressing direction, analyze the springback state, etc.
Innovation of stamping process plan
The same product can have different stamping process plans, and the difference is very significant. If conventional process scheme is adopted, there is no risk; if innovative process scheme is adopted, the benefit is significant, but it may bring great risks. At this time, CAE simulation analysis is very necessary to judge the stamping process plan.
Replace drawing process with forming process
The first mock exam is: left / right connecting plate, symmetrical shape, material DC52D+Z-60 /60, material thickness 1.4mm, conventional stamping process plan, butt joint, double drawing and drawing process. The five processes are drawing, trimming, trimming, trimming, flanging and side turning. Innovative process plan, the butt joint, the first mock exam, the forming process and the three processes are blanking, punching, forming, trimming, punching and cutting, as shown in Figure 7.
Figure 5 waste utilization
Figure 6 CAE analysis process of back door inner plate of a certain vehicle
Figure 7 innovation process plan
Figure 8 CAE simulation and actual forming drawing
CAE analysis is carried out for forming process, mainly for forming process. As shown in Figure 8, no wrinkle and crack occurs. The right figure of figure 8 shows the actual production of forming parts, and the forming process scheme has been successful. The new technology can save two sets of dies. The structure of the mould is simple, the product quality is good, and the utilization rate of the material is increased by 6%. The product quality is improved, the investment in mold is reduced, the material cost and production cost are reduced, and the effect is very significant.
(2) butt drawing process of upper and lower part of car back door panel. The upper and lower parts of the back door panel are not processed in the same set of molds, and each product is generally processed in 4 processes. In order to reduce the investment and improve the efficiency, this paper creatively puts forward the butt drawing process of the upper and lower parts of the car back door panel, which adopts one sheet and four processes. Figure 9 (a) shows the shape of the upper and lower parts of the back door panel, and Figure 9 (b) shows the shape of the upper and lower butt drawing parts of the back door panel. Through CAE analysis, it can be seen that there is no wrinkle crack defect, the slip line is in a reasonable range, there is no impact line, so the scheme is feasible and has been mass produced.
Figure 9 butt drawing process for upper and lower part of car back door panel
(3) surface compensation technology of automobile exterior parts. After forming, the sheet metal generally has to rebound, especially the surface parts, because of the gentle shape, weak structural strength, insufficient deformation and springback. After the forming of high-strength sheet and aluminum alloy sheet, the springback is also relatively large, and the size is out of tolerance seriously, resulting in many times of mold rectification and high cost. Now mold manufacturers try to predict springback through CAE analysis, and solve this problem through springback compensation technology. There are also many successful cases. The actual results are close to the analysis results, and the die test is successful.
There are many factors affecting springback, such as process, material, punch and die clearance, equipment tonnage, product shape, die manufacturing accuracy, and surface compensation technology. At present, most die manufacturers adopt the method of combining CAE simulation analysis with experience, which is not mature enough and has not completely changed the state of repeated die testing.
Application of CAE Technology in die debugging
Solution of wrinkle at the corner of front door inner panel
Figure 10 (a) shows the wrinkle area of the front door inner panel, and (b) shows the shape of the product reinforcement position. If the corner is wrinkled and the feed resistance is increased, it will crack. Finally, to change the product, the location of the shape and size of the stiffener should not only consider eating the wrinkle, but also meet the requirements of beautiful appearance. After detailed CAE analysis, the shape and position of the product reinforcement are determined, and the change is successful at one time.
Figure 10 front door inner panel corner wrinkle problem
Wrinkling of left and right floor connecting plate of a car
The left and right parts of the product are not completely symmetrical. After butt drawing, the left and right parts are cut in the middle, and the wrinkle is obvious in the area shown in Figure 11. A rib was added in the supplementary part of the intermediate process, and the wrinkle was eliminated by CAE analysis. With this scheme, the mould can be changed successfully at one time.
Figure 11 wrinkling of left and right bottom plate connecting plate
Application of CAE analysis technology in hydroforming process
Figure 12 (a) shows the product shape of the front subframe main pipe of a car, (b) is the process flow diagram, (c) is the formability of CAE analysis, and (d) is the wall thickness distribution of the pipe analyzed by CAE. The problems in the debugging process are very close to the analysis process. Through adjusting the process parameters, the qualified product parts are obtained. The mold debugging is relatively smooth and has been mass produced.