Magnetic Field Assisted Finishing PDF Download

Magnetic field assisted finishing (MAF) has been one of the most effective and widely used surface finishing process since its invention over five decades ago. The process contains a certain amount of magnetic particles along with abrasive particles (or magnetic abrasive particles) in a liquid medium, known as an MAF brush, filled in a machining gap between workpiece and magnetic poles subjected to a magnetic field. The relative motion between MAF brush and a workpiece results in abrasive action removing the irregularities and burrs from the workpiece surface to provide a nicer surface quality.MAF has been used extensively with a myriad of engineering materials such as metals, ceramics, metal alloys, glasses, etc. MAF is a suitable candidate for polishing freeform geometries as the MAF brush adapts and conforms to the surface that it is being subjected to since the MAF brush is flexible unlike conventional rigid finishing tools. Especially with additive manufacturing (AM) revolutionizing the manufacturing world with its unique abilities to fabricate complex geometries without any geometric limitations, the demand for surface finishing technology that can finish complex geometries is increasing. Also, since poor surface quality has been an omnipresent issue in AM produced components restricting it from producing functionally compatible parts for various industries, MAF can be a potential candidate to post-process AM components and improve the surface quality of AM fabricated parts. In this dissertation, several areas of MAF with the potential for improvement were explored. Addition of nano-scale solid lubricants, exfoliated graphene nano-platelets (xGnPs) in particular, was introduced for the first time in an MAF brush. The presence of xGnPs helped to reduce the abrasive wear by lubricating and protecting the sharpness of abrasive cutting edges. This resulted in a better surface quality of the final parts. The effect of xGnPs, however, varied with different abrasive sizes. 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 when larger abrasive particles were used but these were not as effective with the smaller ones. Hence, 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 xGnPs to abrasives, and indentation depth by abrasive particles, which enabled us to identify the change in the underlying mechanisms related to the abrasive size.As MAF process is a dynamic process with several parameters in play, a mathematical model to understand the fundamental material removal mechanism in MAF was introduced. Since the MAF brush is a magnetorheological fluid that can change its properties according to magnetic field and anything that can affect a magnetic field, it is crucial to understand the rheological properties of brush to correctly predict the underlying material removal mechanism in MAF. The rheological properties were studied and integrated to calculate the indentation depth that was eventually used to predict material removal rate (MRR) and surface roughness from the MAF process in this study. Finally, the formulated model was used to study the effect of parametric variations in MRR and surface roughness. Finally, oxide dispersion strengthened (ODS) MA956, an iron-chromium-aluminum alloy fabricated by selective laser melting (SLM), one of the most widely used metal AM process, was finished with magnetic field assisted finishing (MAF). The effect of laser processing conditions on part density and surface roughness was studied. Using multi-objective optimization, determination of optimal parameters that provide the highest density and lowest surface roughness was made. MAF was applied to the parts built with the obtained optimal processing parameters and the effect of initial roughness, iron particles size, and abrasive size on MAF performance was studied. Initial roughness had the most dominant effect followed by abrasive size. Final surface roughness of up to 0.36 Îơm with 76.4 % improvement in surface roughness was achieved after MAF on the post-processed samples with a certain initial surface quality.