Surface Finish of the Injection Molding Tool Steel PX4 Using Ball Burnishing, Nickel-Plating, and Ball Polishing Processes

Abstract

The objective of this study is to improve the surface roughness of PX4 plastic injection mold steel using ball burnishing, nickel-plating, and ball polishing surface finish processes. The test specimens were first fine milled and then burnished by applying the optimal ball burnishing process parameters. The surface roughness value, Ra, of the specimens can be improved from about 1.0 µm on average to 0.086 µm on average, after ball burnishing. In order to protect the metal from oxidization, the burnished specimens were plated with nickel, to a thickness of about 10 µm. The surface roughness of the plated specimens was further improved by ball polishing. The optimal ball polishing parameters were determined after conducting Taguchi’s L18 matrix experiments, analysis of variation (ANOVA), and the full factorial experiments. The optimal flat surface polishing parameters for the plastic injection mold steel PX4 were as follows: rotation speed of 6,000 rpm using Al2O3 with grid no. 8000 (3 µm in diameter), a feed rate of 20 mm/min, a stepover of 100 µm, and a depth of penetration of 120 em (polishing force of 1.05 N). Using these parameters for ball polishing, the surface roughness value, Ra, of the burnished and plated specimens was improved from about 0.074 µm on average to 0.02 µm on average.