Machinability analysis for drilling Ti6Al4V ELI under sustainable techniques: EMQL vs LCO2

Abstract

As a result of the widespread use of Ti6Al4V ELI in the medical industry for implants that are subjected to high loads, these biomedical implants must be accurately machined to prevent unfavourable joint or muscular inflammatory conditions. This oftentimes involve drilling holes into the implants for joint assembly during surgery. It is well known that titanium is a very difficult to machine material and therefore, requires appropriate cooling and lubrication during machining. With the help of SEM and line-scan EDS analysis, the current study focuses on analysing various sustainable machining techniques, such as electrostatic minimum quantity lubrication (EMQL) and liquid carbon dioxide (LCO2 cryogenic coolant), while drilling Ti6Al4V ELI (Grade 23) holes in terms of hole surface quality, wear mechanisms, and chip morphology. Poor surface quality of the hole was produced under EMQL cutting, with around 42–71% larger surface roughness values (Rz) compared to cryogenic LCO2 conditions. The hole surface consisted of different defects such as adhesion, microfractures, smearing etc., as a residue of the drilling operation under both EMQL and cryogenic LCO2 conditions. Tool life was significantly improved under LCO2 cutting environment (approximately by 416%) in comparison with EMQL technique. Adhesion and abrasion were found to be the main tool wear modes. Likewise, the machined chips exhibited cracks and adhered particles further demonstrating that EMQL coolant did not provide sufficient lubrication and heat extraction capability. Cryogenic LCO2 coolant outperformed EMQL lubrication for all machinability indicators, according to the study, making it a superior cutting environment for machining Ti6Al4V. Moreover, cryogenic LCO2 coolant dissipates into air during the machining process rendering it a sustainable and environmentally friendly machining coolant fluid.