Ultra-precision surface finish of NAK80 mould tool steel using sequential ball burnishing and ball polishing processes

The sequential ball burnishing and ball polishing processes have been applied successfully to the ultra-precision surface finish of the NAK80 mould tool steel on a CNC machining centre. The optimal flat surface polishing parameters of the developed system for the NAK80 mould tool steel have been determined by conducting the experiments of the Taguchiʹs L18 orthogonal table, analysis of variation (ANOVA), and the full factorial experiments. The burnished surface roughness of the test specimens can be improved from about Ra 0.06 μm to 0.016 μm in average using the determined optimal polishing parameters. Applying the optimal flat surface ball burnishing and ball polishing parameters sequentially to a fine milled spherical lens mould cavity of NAK80 mould tool steel, the surface roughness Ra of the surface on the tested parts can be improved sequentially from about 1.0 μm in average to 0.020 μm in average.