Influence of Material Models on Serrated Chip Formation in Simulation of Machining Ti-6Al-4V Titanium Alloy T. Özel 1 *, S. Yildiz 1 , J. Ciurana 2 1 Rutgers University, Department of Industrial and Systems Engineering, New Jersey, USA 2 University of Girona, Mechanical Engineering and Industrial Construction Department, Girona, Spain *ozel@rutgers.edu Abstract Titanium and its alloys are today used in aerospace, automotive and medical device in- dustries. Ti-6AL-4V alloy is the most suitable Ti alloy used because it offers great me- chanical characteristics such as high strength-to-weight ratio, toughness, superb corro- sion resistance and bio-compatibility. However, Ti alloys are difficult-to-machine materi- als with considerable manufacturing problems. Due to the low thermal conductivity, temperatures rapidly reach high values affecting phase-transformation and causing se- vere tool wear. In this study, the feasibility of using finite element analysis to investigate the cutting tool micro-geometry effects in machining of Ti6Al4V titanium alloy is ex- ploited. 2-D finite element modeling of machining has been considered to investigate the influence of material models for Ti-6AL-4V titanium alloy on tool forces, chip formation and temperatures and stresses using PcBN tools with a distinct edge radius. Serrated and cyclical chip formation has been simulated using damage models in processes simulations and compared with experimental results from literature. 1 INTRODUCTION Titanium and its alloys (mainly titanium al- loy Ti-6Al-4V) are increasingly used in aerospace industry because of good combina- tion of high specific strength, toughness, cor- rosion resistance and compatibility with polymer composite materials. The literature search reveals that extensive work has been done in chip formation mechanism [1-7], adia- batic shearing and modeling [8-11] and tem- perature measurement [12], performance of carbide, ceramic, PcBN tools and possible modes of tool wear [13-19,27,28] during ma- chining of titanium alloys. More comprehensive literature review in machining of titanium alloys can be found in [20-23]. It is commonly reported that titanium is a difficult -to machine material with consider- able manufacturing problems. When thermal conductivity and diffusivity of the workpiece ma- terial is low, the heat generated from the de- forming workpiece is concentrated at the tool tip. This leads to localized high temperatures that weaken the cutting edge. The result is plastic deformation of the tool and loss of the cutting edge. Titanium is highly chemically reactive and, therefore, has the tendency to weld to the cutting tool during machining, thus leading to chipping and tool wear. Chip segments Figure 1: Micrograph pictures of chip formation in orthogonal cutting of Ti6Al4V. The upper right image shows adiabatic shear bands, while lower right one shows a crack with no shear [11]. Quick-stop experiments are used where a cut- ting operation is abruptly halted and the instan- taneous chip formation is captured (see Fig.1). Such chip pictures indicate highly serrated shape with regions of high plastic deformations (adiabatic shear bands) and cracks mixed. Such segmented but continues chips are often formed, especially at high cutting speeds [5, 7]. Low thermal conductivity of titanium alloys causes the temperature at the tool tip to rise very rapidly during cutting process. Conse- quently, at elevated temperatures (around 800