Influence of Grinding Parameters and Substrate Bias Voltage in Dry Surface Grinding with TiN-Coated Single Layer Galvanic cBN Wheel

According to some patented literatures, grit pull-out in single layer galvanic wheels can be arrested by a physical vapor deposited (PVD) coating on the wheels. It has been assumed, therein, the uniform high energy bombardment of TiN caused a reinforcement of the bond as well as increased the stability of the cBN layer on the core. However, an in-depth study on the performance of PVD coated grinding wheel is still lacking. The present research deals with exploring the effect of grinding parameters and substrate bias voltage on the performance of TiN coated galvanic cBN wheels compared to their uncoated counterpart in dry surface grinding of AISI 52100 hardened bearing steel. TiN was deposited at the bias voltages of 0, -60, and -90V in an in-house PVD coating system. The coating microstructure and post-grinding condition of the wheels were observed using scanning electron microscopy (SEM) and phase detection was carried out using grazing incidence X-ray diffraction (GIXRD). With the increase in negative bias voltage, highly dense and compact structure of TiN was observed along with a reduction in column size. GIXRD indicated the formation of nickel-titanium intermetallics at the interface of TiN and nickel bond. Amongst the grinding parameters, downfeed was found to be the most influential factor on the grinding forces and specific grinding energy. Both downfeed and wheel velocity exhibited significant percentage contributions to the maximum grit depth of cut. The uncoated wheel was found to undergo many grit fractures and some pull-out during grinding. TiN deposited at 0V bias could not prevent the fracture. However, when TiN was deposited at the bias voltages of -60V and -90V, such failures were noticeably restricted due to the high energy ion-bombardment and diffusion of Ti and TiN within the nickel bond and the cBN grits.