Estimated reading time: 12 minutes
In order to improve the quality of multi-station progressive stamping and reduce the cost of mold manufacturing, the forming processes such as bending, deep drawing, trimming, shaping, and flanging are involved in the stamping process of an automobile door guide rail structure and spring back unloading were carried out. The finite element numerical simulation is carried out, and the forming defects such as carrier distortion, deep drawing crack, flanging crack, and springback that may occur in the forming process are predicted, the causes of the defects are analyzed, and corresponding solutions or control measures are put forward. Re-modeling, the ideal simulation results are obtained. Based on the numerical simulation results, a multi-station progressive stamping test was carried out, and a certain door guide rail structure with qualified forming quality was successfully punched out in one mold, which can meet the requirements of mass production.
The rapid development of the automobile industry has put forward higher requirements for the production efficiency, parts quality, and parts cost of auto parts. Parts processing has been more and more widely used. However, the quality of multi-station progressive stamping is affected by many factors, such as the geometry of the blank, the form of the carrier, the structure of the mold, the process parameters, etc. The mold designed based on experience often causes the parts to wrinkle and crack during the forming process. and springback and other defects, the forming quality is difficult to control, it is necessary to repeatedly try and repair the mold during the manufacturing process, and the product manufacturing cost is high and the cycle is long. Through the effective use of numerical simulation methods, the elastic-plastic deformation of the sheet during the forming process can be calculated, the forming defects can be accurately predicted, an optimized forming process or die structure can be obtained, and the forming quality can be finally improved.
Taking a front longitudinal beam reinforcement plate of an automobile as an example, the stamping process of the progressive die is simulated, and the problems such as the deformation of the conveyor belt and the inaccurate unfolding of the blank that may occur in the production are predicted, and the material belt formed by the progressive stamping is optimized. . The full-process finite element numerical simulation of the 13-station stamping forming of a high-strength steel plate automobile mounting seat is carried out. By correcting the shape of the blank and the convex hull, the problem of easy cracking during forward and reverse drawing is solved, and the forming quality is improved. . But so far, there is no research report on defect prediction and quality control in the whole process of multi-station progressive stamping. In this paper, a certain automobile door guide rail structure is taken as the research object, and the finite element modeling of its multi-station progressive stamping forming process and springback unloading is carried out by using Dynaform software, and the possible carriers that may appear in the forming process are completely predicted through numerical simulation. Forming defects such as distortion, deep drawing cracks, flanging cracks, and springback are effectively controlled according to the causes.
Finite Element Modeling And Numerical Simulation
The schematic diagram of the structural parts of a car door guide rail is shown in Figure 2:
The material is DX53D galvanized sheet with a thickness of 1.2mm. The guide rail structure is used for the electric glass lifter of the car. The curved profile of the part must be consistent with the curvature of the door glass, and the grooves, bayonet, and other local features match with other parts. These parts must ensure good Forming quality and dimensional accuracy. Through the process analysis of the guide rail structural parts, the stamping process scheme of 13 stations, double-sided carriers, double-row layout, and simultaneous stamping of left and right parts is finally determined. The layout design is shown in Figure 3:
Establishment of Finite Element Mesh Model
According to the stamping and forming process of the guide rail structure, the finite element numerical simulation is carried out for the involved bending-deep drawing, segment trimming, shaping, flanging, punching, trimming, and cutting processes. The segmented trimming or punching is built in a model, and the specific simulation process of the progressive stamping forming process is press bending-deep drawing forming → trimming → shaping, flanging → trimming, and cutting. Since the trimming process only removes the material along the trimming line without the simulation process, it is not necessary to establish a mesh model of the punching tool. and 4(b):
Numerical Simulation Process And Quality Control
According to the simulation process of stamping and forming guide rail structural parts and the established finite element model, the numerical simulation is carried out, the forming defects affecting the product quality in the stamping process are predicted, and the quality control is studied.
- Deep Drawing Fracture Control
When using the finite element model shown in Fig. 4(a) to perform the bending-deep drawing simulation, serious cracks occurred at the fillet position in the middle of the box-shaped part, as shown in Fig. 5:
After analysis, the serious cracking phenomenon is mainly due to the mutual restriction of the flow of the material in the middle area to the grooves at both ends during forming, and the tensile stress is greatly increased, resulting in the stress at the center fillet position quickly reaching the limit point and causing cracking. Therefore, three long process holes are punched in the middle position of the blank relative to the deep drawing crack area (considering the punch structure, the width is 6 mm) to improve the deep drawing formability, and at the same time, the parameters of the too-small fillet at the drawing crack are selected. Step by step modification in the form of transition rounded corners, as shown in Figure 6：
- Carrier Distortion Control
The carrier plays a vital role in the multi-station progressive stamping process. Once the carrier is deformed, the feeding accuracy of the strip cannot be guaranteed, which seriously affects the stamping quality. However, during bending-deep drawing, the carrier has distortion defects (as shown in Figure 7):
The simulation results shown show that the carrier distortion is well controlled, almost no arching occurs during the stamping process, it will not go beyond the guide block due to distortion, and the contact between the side of the strip and the guide block is greatly improved. The improvement ensures the smoothness and precision of feeding.
- Flanging Rupture Control
Using the model shown in Figure 4(b) to carry out a numerical simulation of flanging forming, during the flanging process, one end of the workpiece cracked, as shown in Figure 9:
In order to avoid the occurrence of this cracking phenomenon, while optimizing the flanging and trimming line, the rounded corners of the punch that are too small are corrected to increase the stretched area and avoid excessive concentration of tensile stress. The rounded corners are shown in Figure 10(c), using a transition of 3mm→2mm rounded corners. The improved flanging forming simulation results are shown in Figure 11, indicating that the flanging rupture problem has been effectively solved.
- Rebound Control
Springback is an inevitable phenomenon in sheet metal forming. When the springback of the stamping workpiece exceeds the allowable range, it is necessary to take corresponding measures to control it, otherwise, the geometric accuracy of the parts will be difficult to meet the requirements. Therefore, in the design of the progressive stamping process of the guide rail structural parts, the shaping process is selected to control the dimensional accuracy of the parts with high precision requirements and large springback. Make accurate predictions. The springback analysis model of the workpiece is established on the basis of the sheet metal forming simulation, and the springback analysis is carried out by the multi-step implicit analysis method. The simulation results are shown in Figure 12:
From 12, it can be seen that the workpiece is in a certain twisted state after the trimming rebound, and unloading. The rebound at the A, B, C, D, and E positions is relatively large, and the precision requirements are high. The inlaid die structure is selected to be used. Shaping and shaping can be carried out by means of pressure correction, mold insert profile compensation, etc. For the parts that need to be reshaped, the design of segmental trimming to remove the material should be conducive to the release of internal stress in these parts. The specific shaping parts and the blank after segmental trimming are shown in Figure 13:
Finally, the multi-station progressive stamping forming process of the guide rail structure is re-modeled. From the simulation results shown in Fig. 14, it can be seen that the ideal forming simulation results are obtained through the adoption of quality control measures.
The progressive stamping forming material strip and the glass guide rail structural parts of the left and right doors of the automobile door obtained by the test are shown in Figure 15:
It can be seen from Figure 15(b) that the formed guide rail structure has good forming quality, no wrinkles, cracks, scratches, indentations, and other defects, and the surface of the workpiece is smooth. The progressive die has been put into actual production, the feeding is smooth, the operation is stable and reliable, the dimensional accuracy of the product meets the requirements, and the production efficiency is high, reaching 36 pieces/min, which can meet the requirements of large-scale automated production.
By means of numerical simulation, the quality control method of multi-station progressive stamping forming of guide rail structural parts is studied, various defects that may occur in the forming process are predicted, and corresponding solutions or control measures are proposed. conclusion as below:
- The distortion of the carrier can be effectively controlled by setting a constraining structure or increasing the constraining force in the severely deformed area.
- If there is a large area at the bottom of the deep-drawing workpiece that needs to be removed, a process hole can be set in this area, and trimming is performed after the deep-drawing forming, which can effectively improve the deep-drawing property of the material and prevent the occurrence of cracks.
- During deep drawing, proper correction of the local fillet parameters of the mold can solve the cracking while ensuring the use of a large blank holder force to avoid wrinkling defects.
- For elongation flanging, the contact area of the punch fillet is subjected to the concentration of tensile stress, which is prone to rupture. By increasing the contact fillet of the punch and optimizing the shape of the blank before flanging, the flanging can be effectively avoided. the emergence of the phenomenon.
- Based on the numerical simulation results of workpiece springback, for the parts with large springback after trimming springback after unloading, the design of segmental trimming before shaping should be conducive to the release of internal stress.