Ultrasonic-Assisted Innovative Polyurethane Tool to Polish Mold Steel

Abstract

High-quality die and mold production is becoming increasingly important in modern mass production. Surface quality is one of the most frequent and stringent customer specifications for machined parts, of which the major consideration and indication of quality is their surface roughness. In this study, a novel ball-ended polishing tool made of polyurethane impregnated with micro cubic boron nitride (CBN) was developed. The polishing tool was mounted on a three-axis machining center; the rotary polishing action was achieved via ultrasonics. Polishing experiments were conducted on specimens of hardened Stavax stainless mold steel. Four types of polishing tools – containing 10 wt% of pure CBN particles and Al₂O₃ coated CBN with two different degrees of hardness (Shore 25 and 45) – were fabricated; the results of the experiments were compared with those obtained using a traditional elastic-ball polishing tool. It was found that the surface quality achieved using the Al₂O₃ coated CBN tool was superior to that with pure CBN particles because the hardness of the polishing tool increased with the increase in the surface roughness of the workpiece. In addition, ultrasonic-assisted polishing yielded a better surface finish.