The Research On Plastic Deformation Behaviors Of PM Component During Surface Strengthening

In recent years, powder metallurgy(PM) components have been widely used in automobile and mechanism, which is due to the advantages of PM components,such as the net shape capability, low cost and high efficiency.However, because of the PM components have a quantity of pores, it severely impair the strength, which cause the PM components can't bear the heavy-duty during the operation, and result in the large limitation of its applied range.Therefore, densify the pores, improve the structure, increase combination mechanical property of PM components becomes the important aim of PM strengthening. Combines the plastic forming and surface strengthen technic, this paper have studied the plastic deformation and densification law of PM component during surface rolling.It shows that surface rolling is a kind of appropriate strengthening technic for PM component, which are engaged in heavy-duty and undergo pulsating stress. The processing technic of surface rolling has great potentiality and developable prospect on increasing surface strengthen and reducing cost.Based on the PM plastic theory, the Shima-Oyane criterion has been choosed for the process of PM surface rolling using MSC.Marc FE software. According to the theoretical analysis and experiments, it obtained the plastic constitutive relationship of the PM component. Then the FE model has been established correctly. The change of relative density, stress and strain during surface rolling have been shown, that the densification occurred mainly on the surface of PM component, the relative density increased when the amount of feed increased. At the same time, the deformation and stress of pore during surface rolling have also been simulated, which illustrated the densification laws of pore when it bear rolling pressure. It also shows that the process of surface rolling can bring a significant influence on densify pores.The experimental method has been used to study the process of surface rolling of PM sintered material. The experimental study indicates the rules of plastic deformation and densification according to the comparing results of physical and mechanical properties that before and after surface rolling. That is surface rolling can densify pores that in the areas near the surface, but remain the density in core. It also shows that the hardness values also raised and the microstructure have the trend of refinement. Besides, the influencing laws of different processing parameters were studied, containing rotate speed, amount of feed and friction condition. The result applied theoretical foundation for optimizing the process of PM surface rolling.In brief, the results this paper explained have an important effect on expanding and deepen the precision plastic forming theory of PM material, enlarging application range of PM surface rolling processing and developing numerical simulation technology for PM components.