Very high speed cutting of Ti–6Al–4V titanium alloy – change in morphology and mechanism of chip formation

The chip formation for a Ti–6Al–4V alloy was studied at high cutting speeds combined with large uncut chip thicknesses (0.1–0.25 mm). Orthogonal cutting tests were conducted by using uncoated carbide tools on a specific ballistic set-up with cutting speeds from 300 m/min to 4400 m/min (5–75 m/s). A hypothesis on the mechanism of chip generation is proposed for this speed range validated by high-speed imaging system enabled direct observation of cutting process. A transition, from serrated more or less regular with localized shearing and possible presence of cracking, to discontinuous at very high speed is observed.The inclination of the segment Φseg is shown as resulting from the primary shear angle Φ that can be modified by compression between the tool and the uncut part. A maximum value of 60° for Φseg is reached with increasing speed after which it decreases to 45° at very high speed.The cutting speed appears as the most important factor when compared with the uncut chip thickness, in determining the formation of chips by affecting the frequency of segmentation, the shear angles and the crack length.The significant reduction of cutting forces occurring with increases in cutting speed was firstly explained by the conflicting work hardening–thermal softening processes and then depended on whether the deformation phase of the chip segment is occurred.

► The Ti–6Al–4V alloy is machined with a cutting speed from 300 m/min to 4400 m/min. ► Orthogonal cutting conditions are realised on a specific ballistic device. ► The different chip morphologies are illustrated and studied. ► The high cutting speed effects on the morphology of the segmented chips are analyzed. ► Mechanisms of chip formation are proposed according to the high cutting speed.