Original Article Proc IMechE Part B: J Engineering Manufacture 1–11 Ó IMechE 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954405417728309 journals.sagepub.com/home/pib Comparison of the chip formations during turning of Ti64 b and Ti64 a + b Vincent Wagner 1 , Floran Barelli 2 , Gilles Dessein 1 , Raynald Laheurte 3 , Philippe Darnis 3 , Olivier Cahuc 3 and Michel Mousseigne 4 Abstract For a number of years, the rise in the number of titanium alloy grades and therefore of microstructures has hampered the productivity of titanium parts. In order to understand the phenomena involved, this study presents a comparison of the chip formations between two microstructures obtained from the same alloy. The first part presents the two alloys, their microstructures and their methods of production. The chip formation of each material is then presented and shows two completely different processes. The first process is classical, for which shear mechanisms appear to be cycli- cal. Conversely, the second process depends on the orientation of the microstructure when the shear occurs. For a bet- ter understanding of the phenomena, the effect of cutting speed and feed is also discussed. Finally, in the last section, chip formations for the two microstructures are summarized and perspectives are presented. Keywords Titanium alloys, machining, chip formation, Ti64 b structure Date received: 12 January 2017; accepted: 22 July 2017 Introduction For many years in the aeronautical industry, the machining of titanium alloys has been very problematic due to their low machinability. Moreover, the high diversity of alloys (Ti-64, Ti-1023, Ti-5553, Ti-17, etc.) does not allow application of the same cutting condi- tions or the same cutting tools on all titanium alloys. Different points explain this low machinability. The first is its low thermal conductivity which is always lower than the cutting conductivity of the cutting tool mate- rial. Consequently, the temperature is directed to the tool and rapid wear occurs. The second point is the chemical affinity of the titanium alloys with the cutting tool materials, favoring the diffusion of wear and limit- ing the tool life. Added to this is the behavior of tita- nium: its high mechanical properties and its high surface integrity sensitivity. To control these points, the cutting conditions chosen are always very low, reducing produc- tivity. Over a number of years, certain works have explored chip formation for different alloys. The first among them focused on Ti64, an a + b structure, and were conducted by Komanduri and Von Turkovich, 1 Komanduri 2 and Cotterell and Byrne. 3 These works describe chip formation in a homogeneous structure where the cutting process is never modified by material heterogeneity. Other works addressed chip formation during titanium alloy machining, with the turning of b metastable alloy, 4,5 in milling of Ti1023 6 or in turning with high pressure lubricants. 7 However, all these arti- cles concern the machining of bi-modal structures where a nodules occur in the beta matrix (Figure 1). The aim of this work is to provide a comparison of the chip formation of two structures generated with the same alloy. After the experimental set-up presentation and the highlighting of differences between the two structures, the chip formation for each structure is exposed. The following section concerns the effect of the cutting conditions on chip formation and chip geo- metry. The relation between chip formation and cutting 1 Laboratoire Ge ´nie de Production, Ecole Nationale d’Inge ´nieurs de Tarbes, Universite ´ de Toulouse, Tarbes Cedex, France 2 HAM France Andreas Maier, Peillonnex, France 3 Universite ´ de Bordeaux, CNRS, I2M Bordeaux, 351 cours de la Libe ´ration, Talence, France 4 Institut Cle ´ment Ader (ICA), Universite ´ de Toulouse, CNRS, UPS, INSA, ISAE-SUPAERO, Mines-Albi, 3 rue Caroline Aigle, Toulouse, France Corresponding author: Vincent Wagner, Laboratoire Ge ´nie de Production, Ecole Nationale d’Inge ´nieurs de Tarbes, Universite ´ de Toulouse, 47, Avenue d’Azereix, BP 1629, 65016 Tarbes Cedex, France. Email: vincent.wagner@enit.fr