Research On Finite Element-Cellular Automaton Coupling Simulation For Dynamic Recrystallization Of Surface Change Layer In High Speed Dry-hard Cutting

In the process of high speed dry-hard cutting, because of the strong interactions of multi-field coupling, the workpiece and tool are all in the high-speed transient state at the local high stress, high strain, high strain rate and high temperatures, which brings many new challenges of mechanism and traditional cutting mechanism. Numerous studies also show that the change layer exists in the machined surface in high speed dry-cutting. Thus, it is important to clarify the formation mechanism of high speed dry-cutting for searching the material's microstructure evolution of the cutting deformation zone at high temperature and high strain rate.In this paper, using the method of combining the numerical simulation and experimental research to explore the interior of the grain microstructure evolution through studying the GCrl5 hardened steel and 45 steel. So this research can provide the theoretical basis for reasonably choosing cutting parameters, controlling change layer formation, improving workpiece surface quality and optimizing high speed cutting process. The main contents are as follows:Obtaining the dynamic recrystallization kinetics model of GCr15 hardened steel and 45 steel at high temperature and high strain rate, the experiment of dynamic compressive properties of GCr15 hardened steel and 45 steel are carried out at 20?-800? and strain rate of 2000s-1?8000s-1by using the Split Hopkinson Pressure Bar, the stress-strain curves are obtained. By analyzing and fitting the experimental date and micro-analysis of materials science, the dynamic plastic constitutive equations of the two material are established and the dynamic recrystallization kinetic models are built of the GCrl 5 hardened steel and 45 steel at the conditions of high temperature, high-speed deformation and thermal coupling. These results can provide accurate data and parameters for the cellular automata to simulate the microstructure formation process of change layer in high speed dry-hard cutting.The high-speed cutting experiments are carried out for hardened GCrl 5 steel and 45 steel, and the obtained micro-machined surface was observed by using SEM to observe the existence of the phenomenon of delamination of the change layer, and analyze the microstructure characteristics and thickness of each layer, Exploring the impact of change layer in different cutting conditions. The finite element models of high speed machining of GCrl5 hardened steel and 45 steel are developed, and the temperature and stress-strain data are extracted under different cutting conditions.Using MATLAB programming language, turning the dynamic recrystallization evolution of GCrl5 hardened steel and 45 steel at high temperature and high strain rate into cellular automata model and coupling finite element simulation data with the model, to achieve microstructure evolution simulation of grain growth in high-speed cutting conditions. The XRD experiments are carried out to calculate the grain size of surface change layer to verify the correctness and accuracy of the model through comparing the experimental results and the simulation results.According to the simulation results with the Cellular Automata model to discuss the effects of dynamic recrystallization grain size of surface change layer in different high-speed cutting conditions (cutting speed and tool flank wear), then discussing the influence of the grain size for the change layer. This research can provide the theoretical basis for reasonably choosing cutting parameters, controlling change layer formation and optimizing high speed cutting process.