Analysis of tool wear in cryogenic machining of additive manufactured Ti6Al4V alloy

Electron Beam Melting (EBM) technology applied to the titanium alloy Ti6Al4V is attracting interest in the biomedical industry since it allows producing surgical implants requiring a reduced number of subsequent machining steps. Even if the microstructural features of the EBM Ti6Al4V induce higher tool wear than the wrought Ti6Al4V, no evidences can be found in literature concerning the tool wear analysis when machining the EBM alloy, especially under dry and cryogenic cutting conditions, which are of particular interest for the biomedical industry allowing the reduction of the parts cleaning steps. The aim of the paper is to evaluate the tool wear mechanisms arising when semi-finishing turning the EBM Ti6Al4V under dry and cryogenic conditions using a coated tungsten carbide insert at varying cutting speed and feed rate. The tool wear behaviour was investigated at fixed turning times using different analysis techniques. Scanning electron microscopy analyses were performed to measure the flank wear at the nose region, and energy dispersive X-ray spectroscopy was employed to investigate the workpiece material elements adhered on the cutting edge and rake face of the tool. 3-D optical profilometer analysis of the rake face was carried out to evaluate the abrasive and adhesive wear; the width of the adhered layer was measured by removing through chemical etching the workpiece material from the insert, allowing the quantification of the adhesive wear in comparison to the abrasive one. The obtained results demonstrate that the higher cutting speed and feed rate the higher the tool wear; nevertheless, it was found the cryogenic cooling allowed reducing the adhesive wear mechanism of the workpiece material on the tool cutting surfaces in comparison with dry cutting, proving the feasibility of utilizing the cryogenic cooling to reduce the tool wear when machining the EBM Ti6Al4V.