Research On The High Speed Cutting Mechanism Based On The Dynamic Recrystallization Behavior Of Material

In the present work, the influence of workpiece material properties, varying with dynamic recrystallization, on mechanical balance of cutting process and tool wear of AISI 1045 steel during high speed cutting process are studied. Based on the mechanical equilibrium and energy minimum principle in cutting process, the equilibrium shear angle calculation model is established with considering the plastic deformation work dissipated in primary and secondary shear zone. And the calculation results shows good agreement with experiment measured. To establish a material constitutive model by using Zener-Hollomon (Z) parameter, which combined the impact of strain rate and temperature on flow stress, the isothermal compression tests are conducted, and the experiment output were analyzed and discussed in detail. The outputs illustrated that the constitutive model with Z parameters could better reflect the interaction of the work hardening and temperature softening in the process of deformation. Furthermore, the" comprehensive constitutive model containing material dynamic deformation and transition is established in this work with the analysis of critical strain and kinetics of dynamic recrystallization. A new constitutive model provides the necessary foundation for the further study of the influence of material behavior on mechanical equilibrium and tool wear in high speed machining. Through the analysis on shear angle model, the temperature, strain and strain rate of two shear zones, which changing with cutting angle from initial to equilibrium, are studied systematically. Results show that material will occurred from simple friction to plastic deformation, and then to the dynamic recrystallization with the change of secondary shear zone strain. The essential transformation reason for the chip morphology from continuous to serrated is the mechanical properties suddenly drops caused by the dynamic recrystallization of the material. Meanwhile, the formation of nanocrystalline grains occupied in the workpiece side of tool-chip contact interface because of the large plastic deformation occupying in serrated chip, and the finer grain size might accelerate the element diffusion behavior by the high grain boundary area. Based on this ideal, the mechanism of acceleration tool wear by nanocrystalline grains at chip root is analyzed and discussed. In order to further study the tool wear behavior, the finite element simulation method (FEM) is used by the secondary development of Marc software in three aspects(constitutive model, micro structure evolution, and diffusion wear model). The simulation results prove that the emergence of dynamic recrystallization in high speed cutting with serrated chip resulted in a crater wear on the rake face. Thus, the reduction of the tool diffusion wear and the improvement of tool life could be effectively realized through a reasonable design of cutting parameters or other methods to avoid the formation of serrated chip caused by dynamic recrystallization behavior.