Material removal mechanism and surface integrity in ultraprecision cutting of porous titanium

Porous titanium presents unique material properties with a wide variety of mechanical and biomedical applications. Porous titanium components fabricated by near net-shape technologies require further machining processes to improve the surface quality and form accuracy, and in turn, the added value of the products. In this work, major factors dominating the surface integrity in ultraprecision cutting of porous titanium using single-crystal diamond tools were investigated. The results demonstrated that the presence of pores significantly changed mechanism of cutting. The chip morphology and surface topography depended on pore size and undeformed chip thickness. At an extremely small undeformed chip thickness, a majority pores were closed due to the welding phenomenon, leading to a sharp drop of surface porosity. In contrast, large pores cause craters on the machined surface and segmentation of chips and protruding lamella, especially at a large undeformed chip thickness. A coolant could lubricate the tool-workpiece interface and the shear deformation, which decreased cutting forces. On the other hand, the rapid cooling effect enhanced the work hardening effect and increase the hardness of the machined surface. Tool wear in cutting porous titanium is suppressed compared with that of pure titanium, especially in wet cutting.