An investigation on the material removal mechanism, surface porosity, and surface integrity in ultrasonic vibration assisted turning of porous stainless steel 316L

The machining of porous materials is commonly accompanied with high and irregular cutting forces, high cutting temperature, poor surface integrity, and severe tool wear. The porous materials are considered difficult to be machined. Porosity reduces the rate of heat transfer; moreover, it impairs the continuous cutting and therefore leads to cyclic loads. The main objective of the present study is to investigate the influence of superimposing ultrasonic vibration to the cutting motion of the cutting tool on the surface integrity of the porous materials. For this purpose, the mechanism of chip removal in vibration assisted machining of porous materials was analyzed and porous stainless steel 316L specimens were machined by ultrasonic vibration assisted turning. It was illustrated by the porosimetry of the machined surfaces that the surfaces machined by conventional turning had higher rate of surface porosity compared with ultrasonic vibration assisted turning. In the latter process, the SEM images of the machined surfaces manifested the existence of a kind of rubbing mechanism and material overlaps, which was attributable to the friction existing between the cutting tool with micro scale reciprocating motion and the surface of the workpiece. The overall impact of imposing ultrasonic vibration to the cutting tool motion in the cutting direction was the achievement of a trade-off between preserving the porosity and improvement of the surface quality. This effect was bolstered by increasing the vibration amplitude.