Performance Investigation of Cryo-treated End Mill on the Mechanical and in vitro behavior of Hybrid-lubri-coolant-milled Ti-6Al-4V alloy

Abstract Global demographic trends have signaled a growing need for biomedical implants such as artificial hips, dental implants, spine screws, coronary stents, and heart pacemakers. The reliability of a manufactured implant can be primarily ensured in terms of its surface integrity, dimensional accuracy, and biocompatibility. In the case of subtractive manufacturing of an implant, the required surface finish and complex geometrical features take the machining to a whole new level. However, the machining of mostly metallic biomaterials such as titanium and its alloys has always been challenged by their poor machinability. In this regard, the latest research has reported the outperformance of cryogenically treated non-coated and coated cutting tools and hybrid cooling environments, which resulted in a noteworthy improvement of machinability and biocompatibility of difficult-to-machine biocompatible materials. Therefore, the present research aimed to enhance the surface integrity and in vitro biocompatibility of Ti-6Al-4V alloy by using AlTiN coated solid carbide end mill in untreated and cryogenically treated condition with wet (using traditional cutting fluid as coolant), cryo (using liquid nitrogen as coolant), and hybrid-lubri-coolant (using a combination of cutting fluid and liquid nitrogen as coolant). The experimental findings were analyzed by RStudio software. The results reported that untreated end mill with cryo-lubri-coolant (C-LC) and cryo-treated end mill with hybrid-lubri-coolant (H-LC) achieved the targeted objectives of this research. However, the cryo-treated end mill with H-LC outperformed the untreated end mill with C-LC and produced better surface characteristics, confirmed by a morphological study of the H-LC-milled surface and cryo-treated end mill. The finding of the in vitro studies confirmed that the H-LC-milled surface exhibited superior biocompatibility and promoted the adhesion, growth, and proliferation of adipose-derived stem cells (ADSCs).