| With the increasing requirement of lighter vehicle body, lower fuel consumption and higher security, high-strength steel has been used more and more widely in automobile manufacturing field. But during the research and development process of vehicle structural product,which using the material of high-strength steel,due to the complicated structure of stamping parts and high yield strength and high tensile strength material properties of high-strength steel, The formability of stamping parts become very poor. The defects of crack, wrinkle and severe springback could arise on the stamping parts which increase the difficulties of product quality controlling and mould developing which severely restrict the application of high-strength steel. Therefore, how to control the defects in stamping the high-strength steel parts effectively has become the key to using it widely.Combining with the factory production practice, this paper selected the middle channel of a car using the material of DP450as the research subject and conducted high-strength steel stamping numerical simulation and springback control based on the AUTOFORM software. The purpose of this paper is to provide guidance for the actual production of high-strength steel cold stamping. The main research works are presented as the following points:1. Researched the formability of high-strength steel DP450based on the S-rail part. First, the forming characteristics of the S-rail part were analyzed:The straight-wall portion of the S-rail part was prone to cause a springback problem as a result of the uneven distribution of stress of the sidewall. The intermediate curved portion of the S-rail part was prone to wrinkle and thin due to the presence of outer flanging and inward flanging on each side. Therefore the curved portion was subjected to the compressive stress and tensile stress respectively. The simulation analysis results from the AUTOFORM software were in conformity with the theoretical analysis. The springback problem of the straight-wall portion of the S-rail part was more serious. In contrast with the straight-wall portion springback of DP450and other materials, the springback problem of the high-strength steel material was more serious. The straight-wall portion of S-rail parts was selected to analyze impacts of such process parameters as BHF, friction coefficient, punch fillet and die clearance on the springback of high-strength steel DP450. As the results suggested, the springback angle would decrease with the BHF and the friction coefficient increasing and it would increase with the punch fillet and mold gap increasing. When the BHF and drawbead were reasonable matched, the springback of the flange side part could be effectively controlled.2. Forming analysis and numerical simulation based on the middle channel using the material of the high-strength steel DP450.The researcher created a finite element model of the stamping part according to its preliminary forming program by characteristics of the channel structure and the material properties of high-strength steel and used the AUTOFORM software to simulate the whole forming process.The simulation results showed that the stamping part had crack and wrinkle forming defects, and the crack problem was particularly serious in both end portions of the stamping part. In order to solve the problem of high-strength steel forming defects, the researcher proposed a more reasonable forming program:adjust the fillet size at the bottom all around in the drawing process, optimize the process parameters of the drawing, and add the sizing process to the flanging process. The middle channel stamping program was drawing-trimming and punching-flanging and shaping. The simulation results demonstrated the feasibility of the program, and the forming defects were basically eliminated.3. Springback simulation of the whole forming process of the middle channel based on the AUTOFORM software. The simulation results showed that the product overall had a good springback, but the springback was out of tolerance in the local flange area. According to the actual processing of the product and the structural characteristics of the stamping part, the researcher used the flanging sizing process and added the sizing module to control local springback. The feasibility of the program was verified by the AUTOFORM software, and the designed optimization for the springback sizing surface effectively eliminated the springback in the local flange area.According to the structural characteristics of stamping parts and material properties of high-strength steel,design a reasonable stamping project. Numerical simulation analysis and optimization of stamping model by the AUTOFORM software could effectively predict and control the forming defects and springback problem of high-strength steel stamping parts, guide the actual production and enable every indicator of stamping parts using the material of high-strength steel to meet the criterion. |
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