Research On The Mechanism For High Speed Machining Of Metals

High speed machining is an advanced manufacturing technology since it has manyadvantages such as high removal rates, a lower cost, an excellent dimensional accuracy andsurface quality. High speed machining is the direction for the future development ofmachining, and it has a broad applied prospects. The mechanism of high speed machining isthe theoretical basis for its application and development, thus it is of significant importancefor the development of manufacture industry. However, at recent, the correspondingtheoretical research of high speed machining lags behind the engineering application, and ithas not been developed into a comparatively integrated theory system. These seriously hinderthe development of national economy. Therefore, in this work, we carry out some systematicresearches around the mechanism of high speed machining.An experimental device is set up to realize high speed machining over a wide range ofcutting speeds. The chip morphology and microstructure of AISI1045steel and TiAl6V4alloy is investigated under different cutting speeds, and the results show that the transition ofchip morphology from continuous to serrated could be attributed to repeated thermoplasticshear-banding both for AISI1045steel and TiAl6V4.The stability analysis for thermoplastic shear deformation of the material in the primaryshear zone is carried out, where the coupling effects of material convection and tool-chipcompressive stress are taken into account. The results show that the transition of chipmorphology from continuous to serrated is not only dominated by strain hardening andthermal softening, but also controlled by thermal diffusion, viscous diffusion, elasticunloading and material convection. And the last four factors all hinder the formation ofserrated chip.Further microscopic observations of the chip free surface reveal that the segment spacingof the serrated chip increases as the shear band evolves. And hence a momentumdiffusion-based shear band evolution model is developed to predict the segment spacing. Inthis model, the relationship between the shear band evolution degree and cutting speed is established according to the numerical calculations.The finite element simulations for the high speed machining of TiAl6V4show that, thevariation tendency for tool-chip contact temperature with the cutting speed is quite different tothe finished workpiece surface temperature. Moreover, with decreasing the uncut chipthickness, the specific cutting energy increases nonlinearly. And the simulation results showthat this “size effect” phenomenon could be attributed to thermal softening effect of theworkpiece material.A new slip-line field model for orthogonal cutting of pressure sensitive materials isdeveloped. Analytical characterization for orthogonal cutting process is obtained, which cangive the explicit expressions for the shear angle, cutting force, and chip thickness. We find outthat the pressure sensitivity of materials has a significant influence on cutting process, whichmakes the machining much harder and more power-consuming.