| Hot stamping process is a kind of sheet metal forming technology at high temperature which based on die quenching process, in which the sheet metal stamping is formed at high temperature, and the workpiece is quenched using the mould. In hot stamping process, the blank at pressing progression is heated up to austenitizing temperature and above. This will significantly reduce the requirement of the forming force and promote deformation ability in single process. Before pressing, the high temperature austenite has been fully homogenization. After pressing, the mould will be closed keeping pressure for a period of time, in order to rapidly cool and harden the forming part, improving the mechanical properties and microstructure morphology. Hot stamping process can effectively eliminate the technology problems such as fracture, springback, large deformation resistance which easily appear when forming high strength steel using traditional process, and greatly improve the high strength steel forming ability. Hot stamping process can effectively improve the collection of forming process, which has positive significance for reducing process complexity and improving the production efficiency. Obviously, hot stamping process is a new technology which highly collected variety of process and variety of technology. It greatly expands the scope of the application of high strength steel, making which won a wide application prospect and huge market potential.In this paper, hot stamping will be given a systematic and in-depth study in the aspects of technology principle, technological process, performance of boron steel after quenching, mold temperature control technology, mold cooling system optimization design and related key technology research.Aiming at the chosen boron steel material, the mechanical properties and microstructure morphology after quenching are selected as key points. The heat treatment parameters (austenitizing temperature, holding time) and cooling medium (water, copper block, steel block) has been made a permutation and combination. And series of experiments with simplified process are carried out. Then the mechanical property is tested and microstructure is observed. Through contrast analyzing the experiments results, the influence law of process parameters on the materials performance after quenching is studied. And recommended proposals for applicable heat treatment parameters are give out.By analyzing the technology principle and the heat transferring process between the different parts of mold, the reasonable experimental simulation of hot stamping is presented and the experimental device is set up. Based a U-part forming process, hot stamping experiments are carried out. Using the mold temperature data obtained in experiment, the mold temperature distribution pattern during the single process and the variation rule during continuous process are studied. Combined experimental situation, the numerical simulation model is built based the software ABAQUS. With appropriate settings of related interfacial property, the mold temperature distribution pattern and its history variation rule are simulated using numerical method. The reliability of numerical model is checked by contrast with the former experiment result.Based on thermal-mechanical coupled simulation, response surface method and PSO (Particle Swarm Optimization) optimization algorithm, the iniluence rule of mold cooling system parameters on cooling efficiency, temperature uniformity and fatigue life is analyzed. Using the regression analysis with least square method, the response surface models are set up including average temperature of mold surface, the standard deviation of mold surface temperature and the maximum equivalent stress on mold. By means of ANOVA and random experiment, the availability of these response surface models are proved. Three optimization design strategies are proposed including cooling efficiency first, mold average temperature first and fatigue life first. Based the established response surface model, the related optimal models are set up respectively. The optimal calculation of object function is carried out using self-developed optimal design program. As a result, recommend parameters of mold cooling system layout are obtained. It is experiment verified using numerical method. The optimal result is proved having positive significance on improve the related index such as cooling efficiency by comparing with the original design method.Based on experimental test result, a material model is self-developed which coupled the calculation of thermal-mechanical-phase field. Importing it into the numerical simulation process using the ABAQUS subroutine function, the three field coupled simulation of hot stamping is realized. According to the hot stamping technological characteristics, the numerical model for U-part hot stamping process is built. It is studied that the influence of forming temperature on blank thickness, on the springback deformation, on residue stress field and on the phase transformation. It is obtained that the variation rule of formed parts process index with process conditions. It is experimental studied on the U-part hot stamping process. With the experiment result, it is analyzed the influence rule of forming temperature and mold cooling method on the mechanical properties and microstructure morphology. This provided a theory basis and scientific instruction for process specification of hot stamping part. |
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