Innovative Magnetic-Field Assisted Finishing (MAF) Using Nano-Scale Solid Lubricant: A Case Study on Mold Steel

Magnetic-field assisted finishing (MAF) is a surface finishing process that utilizes a flexible brush composed of iron and abrasive particles typically mixed in a liquid medium. This paper presents an innovative approach to enhance the MAF performance by adding nano-scale solid lubricant into the brush. In particular, exfoliated graphite nanoplatelets (xGnPs), multi-layered graphene platelets with micro-scale diameter and nano-scale thickness, have been introduced into the brush. The modified brush consisting of iron particles, abrasives (cubic boron nitride, cBN), and xGnPs in silicone oil was applied to finish the surface of mold steel. While varying magnetic flux density, cBN particle sizes, and xGnP content in the MAF brush, a series of MAF experiments was conducted to examine their impact on the achieved surface quality on a workpiece and the life of MAF brush. For a given content of xGnPs in the brush, the quality of surface finish was improved and the life of MAF brush was extended significantly with larger abrasives in the brush. Furthermore, the effect of xGnPs with respect to abrasive size was investigated with various factors such as relative number and surface area coverage of xGnPs per abrasive, the relative size of xGnP to abrasives, and depth indented by abrasives on the workpiece, which enabled us to identify the change in the underlying mechanisms in relation to the abrasive size. The new MAF brush is also expected to improve the efficiencies of the overall MAF process in terms of energy consumption and material utilization.