Theoretical And Numerical Research On The Stability Of Ultra-high Speed Cutting Based On General Boundary Layer

As a important method in manufacture, ultrahigh-speed cutting is widelyused in aerospace and mold manufacture because of its advantages ofmachining efficiency and machining accuracy. High strain, high strain rate andlocal high temperature which happen in cutting will lead to appearance ofmaterial yield, instability and fracture. Under the loading of high strain rate forthermoplastic material, a narrow shear band with intense deformation appears.There are lots of similar deformation phenomenon such as terminal ballistics(impact dynamics) and ultrahigh-speed machining. Outstanding features ofdynamic shear bands are their thinness, with typical widths of10-100μm; highlocal shear strains, which can reach values of up to100; ultra-high local shearstrain rate, often in excess of106s-1. Local temperature rises of several-hundreddegrees; and high propagation speeds, sometimes in excess of1000ms-1. As forthis intense shearing, we often should take the factors below into consideration,namely large plastic deformation, rate sensitivity, hardening, heat conduction,thermal softening and inertial effects. To fulfill these targets, we should seekhelp from fluid dynamics. In this paper, a criterion including strain hardening, strain rate hardening,thermal softening and inertia effect with the aid of general boundary layer basedon combination of fluid dynamics and solid mechanics. The research in thispaper are divided into two parts:(1) Based on the general boundary layer and with the help of fluiddynamics and solid mechanics, the governing equations are formed includingNavier-Stokes equation, continuity equation for incompressible material, theevolution equation of strain in Eulerian filed, compatibility equation ofdeformation and energy equation. Then through employing the method ofnormalization in fluid dynamic boundary layer, the governing equations havebeen normalized and inertial effect has been introduced with the help of generalReynolds number (Re). And the introduction of general Reynolds numbermakes the criterion can be employed to estimate the stability of cutting, whichwill solve the problem that the inertial effect cannot be introduced into theinstability criterion (in the previous study, research shows that, in low and highcutting speed, the stability is determined by strain hardening, strain ratehardening and thermal softening; in ultrahigh cutting speed, inertial effectdominates the stability). At the end of this part, a thorough shearing criterionincluding strain hardening, strain rate hardening, thermal softening and inertialeffect is obtained.(2) In the second part, numerical simulation of high temperature nickelbase alloy has been conducted in commercial software ABAQUS/explicit and standard with large speed range, which can be up to360m/s. The chipmorphology in simulation can give us a intuitive understanding of the transitionof the cutting stability at different cutting stage. We can also obtain thefluctuation of cutting force with the increasing cutting speed. Because of thesame variation trend between fluctuation of cutting force and perturbationgrowth rate with increasing cutting speed, then the comparison will beconducted to validate reasonableness of the criterion created in the first part.