Run-to-run process control of magnetic abrasive finishing using bonded abrasive particles

Abstract

In this study, magnetic abrasive finishing, a polishing method using novel bonded magnetic abrasive particles, is implemented in the nanometer-scale surface polishing of STAVAX (S136) die steel workpieces, which are widely used for precision lens molds. With the aid of run-to-run control, a process control method, nanometer-scale mold surface quality is achieved and maintained over multiple runs. A specially designed magnetic quill equipped with an electromagnet was connected to a computer numerical control machining center to construct the polishing setup. Based on Preston’s equation and a set of preliminary experiments, design of experiment and analysis of variance were used to select and evaluate the relevant control parameters for the process. The finishing results show that the magnetic abrasive finishing has a nanometer-scale finishing capability (down to 8 nm surface roughness). Under run-to-run control with the selected parameters, the surface roughness values were successfully maintained below the target values (10 and 50 nm for Ra and Rmax, respectively), which shows that the proposed magnetic abrasive finishing scheme is readily adaptable to ultraprecision polishing applications, which are subject to disturbances for a relatively long period of time.