Investigations on the chip formation mechanism and shear localization sensitivity of high-speed machining Ti6Al4V

Abstract

This study develops a combined numerical and experimental approach to get deeper insights into chip formation mechanism for high-speed machining of titanium alloy Ti6Al4V. The numerical investigation of high-speed machining is implemented with the aid of finite element analysis software Abaqus/Explicit, in which the Johnson-Cook (JC) fracture model with an energy-based ductile failure criterion is adopted. Meanwhile, the experiments of high-speed orthogonal cutting are carried out to validate the numerical results. The cutting speeds are selected ranging from 50 to 3,000 m/ min, and the uncut chip thickness is fixed at 0.1 mm. The variables investigated include the serrated degree and serrated frequency of chips in addition to the cutting force. The results show that both the serrated degree and serrated frequency have positive correlations with the cutting speed. An important regularity for the transformation of chip morphology from serrated to unit at a critical cutting speed has been achieved, and the critical value for Ti6Al4V is about 2,500 m/min. The research also finds that the cutting force decreases with the increasing cutting speed, while its fluctuant frequency and amplitude increase sharply. Furthermore, the influences of JC fracture constants (the five constants in JC fracture model) on chip formation are investigated based on the finite element method, which is the main original and innovative highlight of this study. The shear localization sensitivity is firstly proposed to describe the influences of JC fracture constants on the chip formation process. When the JC fracture constants decrease, the shear localization sensitivity is positive which means that the serrated degree increases and vice versa. The sensitivity analyses indicate that the influences of initial failure strain D 1 and exponential factor of stress triaxiality D 2 on chip formation process are more conspicuous than the rest three ones. This paper is enticing from both the engineering and the analytical perspectives aimed at predicting the evolution of serrated chip formation and chip morphology transformation in metal cutting process. Keywords Finite element method . JC fracture model . Shear localization sensitivity . High-speed machining . Ti6Al4V Nomenclature A Initial yield stress (MPa) a c Uncut chip thickness (mm) B Hardening modulus (MPa) C Strain rate dependency coefficient d Pitch of two neighboring trapezoids in serrated chips (mm) D Damage variable d 1 Diameter of slot milling cutter (mm) d 2 Width of workpiece (mm) D 1 Initial failure strain of JC fracture model D 2Exponential factor of JC fracture model D 3Triaxiality factor of JC fracture model D 4Strain rate factor of JC fracture model D 5Temperature factor of JC fracture model fChip serrated frequency

Effects of cutting conditions on the milling process of titanium alloy Ti6Al4V

“…In recent years, as a new method, the finite element method draws more and more attention [15][16][17][18][19]. It is a powerful tool to study the complex milling mechanisms [20][21][22][23]. However, the different cutting mechanisms of Ti6Al4V under up-milling and down-milling are not understood fully.…”

Investigations on deformation and fracture behavior of workpiece material during high speed machining of 7050-T7451 aluminum alloy

“…In result, the temperatures between toolÀchip interface under different cutting speeds are extracted through finite element method [28]. The finite element model (FEM) for orthogonal cutting as shown in Fig.…”

Onset and evolution of discontinuously segmented chip flow in ultra-high-speed cutting Ti-6Al-4V

“…Here, to show clearly the whole evolution process of the chip flow pattern from low to ultra-high cutting speeds and, thus, to reveal the underlying mechanism of the initiation of discontinuously segmented chip flow, the morphology images of the chips obtained at low cutting speeds are shown together with that obtained at high cutting speeds, although the lowseed cutting experimental results for Ti-6Al-4V have been widely reported [34][35][36].…”