| Hot stamping die, the core part of hot stamping, fatigue failure prematurely occurred that severely restricts the production cost of automobile parts. Therefore, it is an effective way to cut production costs by reducing die fatigue damage and improving the life of die. Factors of die fatigue life include not only the heat cycles and stress cycles in the stamping process, but also the surface oxidation of die in the long term cycles. The combined effect of these factors will adversely affect the surface of die, and reduce fatigue life of die. Therefore, in order to improve die life we should first improve the quality of the die surface. Now, surface coating technology is an advanced technology to optimize the mechanical properties of the die surface. In this paper, the thermal and machine fatigue properties of hot stamping die surface has been systematically studied, by introducing the PVD (Physical Vapor Deposition) coating to strengthen common hot stamping die (H13) surface. And designing "Stamp-slid-keep pressure" experiment that simulating stamping process, the service performance of the mold material (H13) with PVD coating has been obtained by comparing the thermal-machine fatigue properties of die material surface with CrN coating and uncoated. And further compared the corresponding performance of 45 steel material in the same working conditions. By combined with finite element model to explore the optimized effects of PVD coating in improve the thermal-machine fatigue properties of different die materials. The above studies provide an effective guidance for the die surface coating technology treatment and application in the actual production process.In order to ensure the reliability of simulation and subsequent analysis, based on typical thermal-machine fatigue test, the typical mold materials key service data and elementary performance of fatigue durability has been studied. First, the effects of hot stamping temperature to die life has been studied, considered the effect of die surface stress to the quality of the die surface, and measured the coating surface roughness, coating thickness and coating hardness of the coating relevant elementary parameters. By SEM and high optical microscope observed the coating and mold material after the test, and explored the impact of comprehensive factors to the microscopic characteristics of coating and die material.Next in importance, as the main research tool, Abaqus finite element analysis software is used to build the corresponding finite element model and achieve the whole simulation system considering the thermal-force coupling and coating model is introduced. The stamping experiment device with heating function is designed, so as to verify the stress trend of model and the influence of temperature. Good agreement with the data of simulation and experiment under influence of thermal-force coupling, verify the results of the finite element simulation is reasonable and effective.Further, through Ncode fatigue life analysis software, the results of finite element analysis is used to predict the fatigue life. Comparing the results of fatigue life can analysis the optimized effect on mold fatigue life of PVD coating. After optimization of the mold surface relative the surface without optimization, fatigue life is improved. According to the experimental results, the anti fatigue effect of the surface optimization of mold material relative the surface without optimization is obviously improved, which proves that the PVD coating has a significant effect on improving service life of die surface. The surface optimization technology has certain enlightenment to the surface optimization of hot stamping die as well as provides a reference to the surface treatment of the actual mold surface. |
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