Investigation on the machinability of nitriding mold steel by applying in-situ laser assisted diamond cutting

Abstract

Mold steel is a typical material in precision molding for the massive production of optical lenses. It has the outstanding mechanical properties and superior corrosion resistance. However, it is a huge challenge for ultra-precision diamond cutting mold steel due to the active chemical affinity between the diamond tool and steel, which causes the deteriorated surface integrity and catastrophic tool wear. In this research, we adopted a novel hybrid machining technology, which is in-situ laser assisted diamond cutting (In-situ LADC), for ultra-precision machining nitriding mold steel. Pulsed plasma nitriding treatment provides a dense nitrided compounds layer in workpiece surface to suppress the chemical reaction between the iron atom of steel and carbon atom of diamond. Furthermore, the surface nitriding layer is softened by the laser radiating to improve the machinability of workpiece. Experimental results showed that the laser thermal effect obviously decreased the hardness and elastic modulus of nitrided layer, which enhanced the material removing in ductile mode. Compared with the ordinary cutting (OC), the machined surface roughness Ra is decreased from 29 nm to 12 nm. The maximum profile error PV is also decreased from 161 nm to 64 nm. The mechanism of tool wear was changed from the rapidly abrasive wear to mildly adhesive wear, which significantly increased working life by 29 %.