Experimental investigation of chemical mechanical polishing (CMP) process parameters through polishing of optical glass

Due to the high precision and surface accuracy, optical quartz glass’s chemical mechanical polishing (CMP) is a challenge. Quartz glass, also known as fused silica (SiO2), is a popular optical material due to its high transmission range, hardness, strength, and chemically inertness properties. This work studied the effect of normal load and spindle speed on the material removal rate (MRR) and surface roughness (Ra) of fused silica glass. The MRR and roughness values of the quartz glass workpiece are evaluated by the chemical and mechanical action of cerium oxide abrasives due to the application of normal load and velocity. Further, pressure and relative velocity values are used to understand and verify Preston’s Theory. The MRR has been estimated based on the weight difference of the quartz glass before and after polishing. Surface roughness (Ra) values are measured using Taylor-Hobson Phase Grating Interferometer. The minimum value for surface roughness achieved is 9.4 nm, and the corresponding value of MRR is 50.226 nm/minute. It is also observed that MRR is greatly affected by the normal load applied and spindle speed compared to the surface roughness of the workpiece. The plot shows the linear relation of MRR with the normal load. MRR is directly proportional to the PV (Pressure x Relative Velocity) values which show the validity of Preston’s equation.