Design and numerical simulation of the drawing die

Design and numerical simulation of drawing die for automobile cover parts

automobile cover parts (hereinafter referred to as cover parts) refer to the surface parts (outer cover parts) and (internal parts) of the sheet steel heteromorphic body covering the automobile engine, chassis, cab

and car body. Compared with general stamping parts, they have the characteristics of thin materials, complex shapes, large structural dimensions, high surface quality requirements and high production costs. It also has its own characteristics in the stamping process design, mold design and mold manufacturing process of the panel, which generally needs to go through multiple processes (such as drawing, punching, trimming, flanging, shaping, etc.). In the whole production, drawing forming is a key process, and the die of drawing forming determines the success or failure of drawing and the quality of workpiece. In the past, the temperature tended to rise after reaching the fixed value of 1. Single piece pressing was adopted, and the production efficiency, material utilization rate and equipment utilization rate were relatively low. The drawing process is improved, and the central symmetrical method of the first mock examination and two pieces is used to redesign and mold, which greatly improves the utilization rate of equipment and production efficiency [2]

1 stamping process analysis

(1) rember stamping process rember

the material of the part is cr340, the thickness of the sheet is 1mm, the tensile strength is 750 MPa, and the elongation is 16%. The structural shape of the parts is shown in Figure 1 from 1962 to 1981 according to the data of the National Transportation Safety Commission of the United States. The structure of this part is complex, and it needs many processes to complete. According to the process analysis of this workpiece, the process route is: blanking → drawing → punching and trimming → cam trimming → turning → punching and separation. The specific process diagram is shown in Figure 2

there are many local forming of this part, which is the result of punching, drawing, flanging and trimming. In the drawing process, the first mock examination and two pieces are used to draw symmetrically. In order to ensure that all the spatial shapes of the drawn parts can be drawn out at one time, there should be no "dead zone" that cannot be touched by the punch, that is, it is necessary to ensure that all the punch can enter and minimize the drawing depth difference as far as possible, so as to reduce the material fluidity and the uneven distribution of deformation. Process supplement is an indispensable part of the drawing process, but the process supplement should be minimized to improve the utilization of materials. In addition to the needs of drawing process and pressing surface, the requirements of trimming and flanging process should also be considered in the process supplement. The process supplementary surface and vertical trimming line of the workpiece are shown in Figure 3:

(2) drawing simulation results and formability analysis

the material selected for drawing simulation is the same as the above, and the slab size is 920mm × 200mm, the friction coefficient is 0.1, the blank holder force is initially determined to be 95kn, and the punch speed is 5000mm/s. After defining the motion and boundary conditions of each part of the die, submit the work to LS-DYNA for calculation. Considering the deformation characteristics of the panel, the forming limit diagram and thickness change diagram are selected as the main indicators to evaluate the formability

the layout of the equivalent drawbead is shown in Figure 4, the parameters of the drawbead are shown in Figure 5, and the simulation results are shown in Figure 6. From the forming limit diagram, it can be seen that the forming effect of some materials at the bottom of the sheet is still not ideal, and the crimping phenomenon still exists, but the crimping edge is finally cut off by trimming, so it has little impact. The sheet thickness variation diagram is shown in Figure 7. From the sheet thickness variation diagram, it can be seen that the thickness of some parts of the bottom fillet is thinned by 0.9814mm, and the maximum thinning amount is 18.21%. The material thinning is not serious; At some places of the blank pressing edge, the thickness of the sheet becomes 1.3132mm, and the thickening amount is 9.43%, which belongs to the normal range

2 drawing die design

(1) 3D solid modeling of UG []

through the parameters obtained from the above numerical simulation, the automobile panel rember is modeled, and the surface design and die structure design are carried out. When modeling, the punch and die with trimming are generated by numerical simulation and the calculated blanking clearance. Through the curve on the digital analog, use the curve operation offset/project to offset the required curve, then use the from feature -extrude for deep drawing, and use the trim command of the digital analog profile to get the profile. In this way, the female die is obtained first, and then the punch and female dies can be obtained by roughly the same command from the blanking gap, as shown in Figure 8

because UG has parameterization function, it is easy to modify. At the same time, it is suggested that each step should be started from sketch, so as to meet the requirements of parameterization design and facilitate the modification of errors. According to the method of drawing punch and die above, three-dimensional parts such as lower die base and blank holder can be drawn. Fig. 9 is a three-dimensional mold assembly drawing of the panel drawing die based on the drawing of each part of the mold

(2) structural design of drawing die []

the guide between the blank holder ring and the female die of the drawing die is to cast bosses and grooves on the blank holder ring and the female die, and install a guide plate on it, with a guide gap of 0.3mm. The punch and blank holder are guided by four guide plates, which are placed at the smooth part of the punch. As it is drawn and formed on the hydraulic press with hydraulic pad, the female die is fixed under the movable workbench, the male die is fixed on the lower workbench, and the blank holder is pushed out by the cushion block. During mold test, ensure that the contact area of all formed joints reaches more than 80%

working process of the die [2]: the structure of the drawing die is shown in Figure 10, which adopts the flip structure of punch and blank holder ring at the bottom and concave die at the top. When working, the air cushion column rises to make the cushion block jack up the blank holder ring to rise to a certain position, and put the materials on and off according to the fixed position. The movable workbench drives the female die downward, so that the female die and blank holder ring compress the material parts, and the female die and blank holder ring descend together, so that the material parts contact with the convex and concave die, and the pressure forming, pressure maintaining, and drawing processes are completed

1 slider; 2 M12 screws; 3 pressing ring; 4 lifting lugs; 5 upper mold base; 6 guide plate; 7 M24 screw; 8 lower bottom plate; 9 limit key; 10 lower backing plate; 11 convex module; 12 lower mold base; 13 air cushion column; 14 cushion block; 15 M10 screw

the drawing die adopts a flip structure, which is conducive to the positioning of blank holder and blank on the die, and is conducive to improving the quality of drawing parts, and the discharging and taking of parts are smooth

developed auto panel ldquo; 1 coal is hard to find rdquo; It has become an urgent task for all steel mills. Rember's stamping process and the designed drawing die of the panel have been used in production practice. Figure 11 shows the rember products of automobile panels produced by using the stamping process formulated above and the designed drawing die

3 conclusion

(1) in the drawing process, DYNAFORM is used to simulate and analyze the sheet metal forming process and accurately predict the possible defects in the forming process, which has a certain guiding role for die design, reduce the workload of die testing and repair, reduce the development cost and shorten the development cycle

(2) the combination of CAE and UG 3D modeling and assembly functions is used to design the mold more effectively and quickly

(3) the developed process route has been successfully used in production, and the appearance and assembly size of the produced panel can well meet the technical requirements, and the surface is free of wrinkles and strains. The production of the drawing die proves that the die design is reasonable and reliable

references

[1] Hu Shiguang, Chen Hezheng Principle of sheet metal cold pressing (Revised) [m] Beijing: National Defense Industry Press, 1989

[2] Ju Shupu Drawing process and die design of back corner [j] Mold technology, 1999.4:37~39

[3] Zeng Xiangyang, Xie Guoming, Wang Xueping. UGNX foundation and application course [m]. Beijing: Electronic Industry Press, 2004.

[4] Tan Jianzhou, Wu Bojie Using UG Ⅱ to design drawing parts of automobile panel [j] modern manufacturing engineering, 2002, (1): 29 ~ 30

[5]Ahmetoglu M A,AltanT,provement of part quality in stamping by cintrolling blank-holder force and pressure[J]. Journal of Materials Proce -ssing Technolog -y,1992,33():.

[6]siegert K, Ziegler m, Wagner osed loop control of the friction force de is still not cleared EP drawing process [j], Journal of materials processing technology, 1997, 71 (1):126-133

[7]Obermeyer E J,Majlessi S A.A review of recent advances in the application of blank-holder force towards improving the forming limits of sheet metal parts[J]. Journal of Materials Processing Technology,1998,75();. (end)