ORIGINAL ARTICLE Chip formation modeling using traction-separation cohesive model Xavier Soldani 1 & Héctor López-Gálvez 1 Received: 18 May 2018 /Accepted: 25 October 2018 # Springer-Verlag London Ltd., part of Springer Nature 2018 Abstract Numerical models of machining require criterion (maximum equivalent strain, maximum shear stress, or damage fracture models) to separate the chip from the workpiece. In this work, we propose to use cohesive element methodology to remove the chip from the machined material. The paper is focused on the determination of cohesive parameters for the numerical modeling of chip formation process applied to titanium alloy. A numerical study is presented to calibrate the number of elements necessary in the cohesive zone thickness, the values of traction-separation energy, and the cohesive interaction parameter used in the 2D cutting model; the calibration is realized comparing numerical results of cutting forces and chip morphology with experimental analysis. Keywords Numerical modeling . Ti6Al4V . Cohesive elements . Chip separation . Traction-separation energy . Orthogonal cutting 1 Introduction The excellent combinations of the mechanical (high strength at elevated temperature and high modulus of elasticity), phys- ical (high corrosion resistance), and thermal properties (low thermal conductivity) of titanium alloys make them extremely attractive for the aeronautical, biomedical, energy, or automo- tive industries. Nevertheless, Ti6Al4V results in a material that is difficult to machine; its machining always induces pre- mature tool wear, poor surface quality, and high cutting ener- gy. The poor machinability of Ti6Al4V was one of the reasons that further limited its use during the last decades [1]. The multiplication of experimental studies [2–8] and numerical works [9–18] on titanium machining makes it possible to un- derstand the mechanisms of chip formation, to predict cutting forces, and to analyze temperature distribution [15], residual stresses [19], or tool wear [2]. High-speed machining of titanium alloys produces chip serration and segmentation due to apparition of adiabatic shear bands at the primary shear zone. Many authors have studied the phenomena of segmentation of Ti alloys. Among the con- tributions, we can cite the experimental investigations realized by Komanduri et al. [2], Nabhani [3], Gente et al. [4], Molinari et al. [17], Cotterell et al. [6], Sun et al. [7], Ducobu et al. [8], and Arulkirubakaran et al. [20]. In 1981, Komanduri et al. [2] carried out experimental work on machining of Ti6Al4V for cutting speeds lower than 5 m/s; authors studied the effect of the cutting conditions on the shear band formation in the material. Gente et al. [4] stud- ied the chip formation in orthogonal cutting for a wide range of cutting speeds (from 5 to 100 m/s). The quick-stop tech- nique allowed them to investigate the effects of cutting con- ditions on chip segmentation intensity. Authors concluded that the chip segmentation is not due to the catastrophic adiabatic shear but to the crack propagation. In the same year, F. Nabhani [3] also used the quick-stop technique in machining tests of Ti6Al4V but to study the wear mechanisms for differ- ent cutting tools and coatings. In 2002, Molinari et al. [5] presented an experimental work of orthogonal cutting applied to titanium alloy. The use of both lathe and ballistic device permits to study the effects of cutting speed in a large range of values (from 0.01 to 73 m/s). Authors observed clearly that the velocity affects drastically the localization of strain; for low values of the cutting speed, the instability process in the chip is weak and, by the way, the strain localization is not significant. For high values of cutting speed, adiabatic shear bands induc- ing phase transformation were well observed. Finally, they * Xavier Soldani xsoldani@ing.uc3m.es 1 Department of Mechanical Engineering, Universidad Carlos III de Madrid, Avda. Universidad 30, 28911 Leganés, Madrid, Spain The International Journal of Advanced Manufacturing Technology https://doi.org/10.1007/s00170-018-2940-7