Magnetic abrasive used for the internal finishing of capillary tubes, which prevents accumulation of contamination and erratic flow of the conveyed fluid, is a composite particle, consisting of iron and $Al2O3$ abrasive grains. The irregularity of the magnetic abrasive shape, due to the mechanical crushing process, causes nonuniform depth of cut of the abrasive and restricts the improvement of the finished surface quality. This has resulted in a narrow range of finishing performance. Moreover, the irregularity of the magnetic abrasive shape brings about difficulty in merely introducing it into capillary tubes. To break through these difficulties, this research proposes to develop a spherical iron-based magnetic abrasive, which carries $Al2O3$ grains on the surface, made by plasma spray. First, this paper examines the feasibility of the plasma spray to make the existing magnetic abrasive more spherical, and suggests the conditions needed to produce the spherical magnetic abrasive. Second, it studies the development of the new spherical magnetic abrasive made of separate particles: iron particles and $Al2O3$ abrasive grains, which carries the nonferrous abrasive on the outer surface alone. Their finishing performance, evaluated through the experiments using SUS304 stainless steel tubes, shows their applicability to magnetic abrasive finishing.

This paper presents the recent advancements and forthcoming challenges for abrasive machining with specific focus on the advancement of industrial applications. The most significant advancement of abrasive machining is in grinding applications of cubic boron nitride (CBN) abrasive. The advancement of CBN wheels, application of grinding models and simulation tools, development of high stiffness multi-axis grinding machines, and high-speed spindles have contributed to the growing industrial applications of grinding with plated and vitrified CBN wheels. Sustainability of abrasive machining also received more attention during the past two decades as global Fortune 500 corporations have included sustainability as a corporate goal. Abrasive machining will continue to be a critical process for manufacturing precision components in the decades to come. The advancement and adoption of additive manufacturing creates more unique challenges for abrasive machining of complex geometrical features which were impossible a few years ago. Furthermore, strategies for abrasive machining are needed to utilize the massive amount of process data available by connected factories. Therefore, it is expected that sustainability and data analytics for abrasive machining will become a more important focus for various manufacturers.

Transparent polycrystalline yttrium aluminum garnet (YAG) ceramics have garnered an increased level of interest for high-power laser applications due to their ability to be manufactured in large sizes and to be doped in relatively substantial concentrations. However, surface characteristics have a direct effect on the lasing ability of these materials, and a lack of a fundamental understanding of the polishing mechanisms of these ceramics remains a challenge to their utilization. The aim of this paper is to study the polishing characteristics of YAG ceramics using magnetic field-assisted finishing (MAF). MAF is a useful process for studying the polishing characteristics of a material due to the extensive variability of, and fine control over, the polishing parameters. An experimental setup was developed for YAG ceramic workpieces, and using this equipment with diamond abrasives, the surfaces were polished to subnanometer scales. When polishing these subnanometer surfaces with 0–0.1 μm mean diameter diamond abrasive, the severity of the initial surface defects governed whether improvements to the surface would occur at these locations. Polishing subnanometer surfaces with colloidal silica abrasive caused a worsening of defects, resulting in increasing roughness. Colloidal silica causes uneven material removal between grains and an increase in material removal at grain boundaries causing the grain structure of the YAG ceramic workpiece to become pronounced. This effect also occurred with either abrasive when polishing with iron particles, used in MAF to press abrasives against a workpiece surface, that are smaller than the grain size of the YAG ceramic.

Surface finishing is challenging in the context of additively manufactured components with complex geometries. Magnetic abrasive finishing (MAF) is a promising surface finishing technology that can refine the surface quality of components with complex shapes produced by additive manufacturing. However, there is insufficient study regarding the impact of MAF on microstructure–property relationships for additively manufactured builds, which is critical for evaluating mechanical performance. In this work, we studied the effects of different combinations of MAF and heat treatment steps on the microstructure–property relationships of Inconel 718 superalloys made by laser powder bed fusion (LPBF). The application of MAF was found to significantly reduce the surface roughness and refine the grain size of aged alloys. Moreover, MAF was able to increase the alloy elongation, which could be further influenced by the sequence of MAF and different heat treatment steps. The highest elongation could be achieved when MAF was performed between homogenization and aging processes. This work indicates that an effective combination of surface finishing and heat treatment is critical for the improvement of alloy performance. Furthermore, it demonstrates a promising solution for improving the performance of LPBF Inconel 718 by integrating MAF and heat treatment, which provides new perspectives on the post-processing optimization of additively manufactured alloys.

Magnetic field–assisted finishing (MAF) is used to polish free-form surfaces. The material removal mechanism can be described as a flexible “magnetic brush” that consists of ferromagnetic particles and abrasives that arrange themselves in the working gap between the magnet and the workpiece. Relative motion between the brush and the workpiece causes microcutting and improves surface finish. In this study, the contributions of the magnetic and polishing force components to the total force were evaluated. The effect of varying the polishing conditions, such as the working gap and the size of the ferromagnetic iron particles, on polishing forces, surface roughness, and material removal rate was also analyzed. It was observed that the polishing forces varied considerably with working gap. Also, the iron particle size was found to have a strong relation to the rate at which the surface roughness improved. Surface roughness values of 2–3 nm were achieved.

Core needle biopsy (CNB) is widely used in active surveillance, which is the current standard of care for low risk prostate cancers. A longer biopsy sample length may improve the accuracy of diagnosis. To increase the biopsy sample length, the magnetic abrasive finishing (MAF) technique was applied to decrease the needle inner friction force, which may hinder the tissue from entering the lumen of the biopsy needle. To assess the effectiveness of these MAF polished needles as compared to the unpolished needles, a method to measure the three components of axial force during hollow needle insertion—tip cutting force, inner friction force, and outer friction force—was developed. Six tissue-mimicking samples of different lengths were used to find the linear relationship between the sum of the cutting force and inner friction force and the phantom length or contact length. Linear regression method was used to extrapolate and estimate the tip cutting force and the inner friction force. With this method, the difference between the inner friction force of the needles with and without polishing was found. The results showed that the unpolished needles had an inner friction force 40–50% higher and a tip cutting force 22% higher than their MAF polished counterparts. We also found that MAF polished needles had an average of 9% longer contact length between the sample and the inner wall than unpolished needles, indicating that a longer sample can be extracted at a lower friction force. The results of our investigation implied that reducing the inner surface roughness of a biopsy needle could reduce inner friction forces.