Abrasive processing technologies support both the creation of new products and progressive production processes as finishing processing in various industries, such as the automotive, telecommunications, semiconductor, healthcare, energy, and aerospace industries. In this era of major changes, known as the Fourth Industrial Revolution, advanced abrasive processing technologies that produce cutting-edge devices, machinery, and equipment for a smart society are needed. The subjects related to abrasive processing are extremely diverse, including function generation processing and ICT fusion processing, in addition to the continuing basic subjects, including high-efficiency processing, difficult-to-cut material processing, ultra/high-precision processing, etc. The field of abrasive processing has recently been expanding from removal processing to additional types of processing, such as additive manufacturing. As a result, its importance is increasing as a technology indispensable for advanced industries such as healthcare and the production of power semiconductors, cutting-edge semiconductors, etc. On the other hand, new abrasive processing technologies, such as grinding wheel surface property analysis and highly efficient surface finishing methods, have developed along with the advancement of the elemental technologies that support abrasive processing using the latest measurement methods and ultra-precision technology. Furthermore, new research, such as work on energy-assisted or reaction-assisted grinding, has been conducted through the fusion of the materials science and physical chemistry fields. This special issue contains seven papers that cover the following topics.

- Abrasive jet processing

- Analysis of the surface profile of a grinding wheel

- Drilling of glass with a diamond tool

- Reaction-assisted grinding

- Barrel finishing

- High-speed polishing

We deeply appreciate the authors for their careful work and thank the reviewers for their incisive efforts in producing this special issue. We hope that it will help readers understand the latest research on abrasive processing, encouraging and providing hints for further research on abrasive processing technologies.

Powder jet machining is a blast machining process in which micrometer-order particles are projected onto a workpiece at near-supersonic speeds, to remove the workpiece (abrasive jet machining (AJM)) or to deposit the particles (powder jet deposition (PJD)). We report a novel dental treatment method for powder jet machining using hydroxyapatite, which is the main component of teeth, as deposited particles. The surfaces and interdental spaces of human teeth are not only flat, but also have complex groove structures. However, PJD and AJM exhibit impact-angle-dependent machining phases. Therefore, it is necessary to investigate the effect of the particle impact angle on machining, before dental treatment. Furthermore, because machining interacts not only with the particle impact angle but also with the particle impact velocity, a comprehensive investigation of the effects of the machining parameters is required, for delineating the phase-transition conditions. Accordingly, in this study, we conducted machining experiments using hydroxyapatite particles (particle diameter, 2.16 μm) and four different blasting angles of 30°, 45°, 60°, and 90°, to infer the machining amount. Machining efficiency was evaluated based on the amount of machining. The impact angles and velocities of the particles were calculated using computational fluid dynamics (CFD). Three-dimensional process mapping was performed using the machining amount, particle impact angle, and particle impact velocity, obtained from the experiments and CFD calculations. The results showed that PJD crossed to AJM at the impact angle of approximately 60°. Moreover, PJD exhibited high processing efficiency for impact angles above 60° and impact velocities in the 280–310 m/s range. In contrast, AJM exhibited high processing efficiency for impact angles below approximately 35° and impact velocities above 310 m/s.

The surface topography of ceramic grinding wheels used in creep feed grinding is examined in this study. Creep feed grinding experiments are performed using seeded gel (SG) grinding wheels. The three-dimensional surface of the grinding wheel is observed using a two-dimensional high-definition laser displacement sensor, and the effective cutting-edge number is calculated based on three-dimensional surface observations. Microscopic wear behaviors of grain cutting edges are examined based on scanning electron microscope (SEM) images. The cutting-edge area percentage is calculated based on SEM images via the discriminant analysis method. Results show that the micro self-sharpening phenomenon can be evaluated quantitatively. Micro sharp cutting edges on grains and normal grinding forces are suppressed. Subsequently, the relationship between the grinding characteristics and behaviors of the SG wheel working surface is investigated.

Different grinding wheel surface conditions affect the ground surface roughness and grinding resistance during the grinding process. In addition, as the grinding wheel surface condition changes depending on the dressing conditions, the difference in the dressing conditions significantly affects the grinding characteristics. However, the dressing condition is affected by factors such as the dressing lead, depth of dressing cut, and tip shape of the dresser. Thus, optimum dressing conditions are difficult to achieve. Furthermore, even if the dressing is applied under the same dressing conditions, the grinding wheel surface condition will differ as the tip wear of the dresser progresses. There is a need for a method to quantitatively evaluate the relationship between the dressing conditions, grinding wheel surface condition, and grinding characteristics while considering the difference in the tip shape of the dresser. Thus, the relationship between the tip shape of the dresser and dressing conditions was evaluated using the dressing overlap ratio. This study aimed to evaluate the effect of different dressing overlap ratios on the grinding wheel surface condition and grinding characteristics with different grain sizes. Consequently, even if the tip shape of the dresser changes, the effect of the different dressing conditions on the grinding wheel surface condition and grinding characteristics could be quantitatively determined using the dressing overlap ratio. Furthermore, the relationship between the calculated successive cutting-point spacing, area of active abrasive grains, and grinding characteristics could be quantitatively evaluated for grinding wheels with different grain sizes.

Our laboratory has been exploring the development of tools for drilling holes in glass plates, and the drilling techniques to be adopted for it. A devised tool shape that could prevent the occurrence of cracks at the exit holes achieved high quality through hole drilling of 100 holes or more using only the drilling cycle. However, crack-free drilling beyond this number of holes cannot be performed. This is due to the adhesion of the residual chip on the tool surface when the number of holes increases. Therefore, further improvement of chip discharge is needed to achieve crack-free drilling. In this report, we consider that chip discharge results from the flow of the machining fluid. To investigate the cause of chip discharge, we analyzed the flow of the machining fluid in the hole using computational fluid dynamics and the supposed chip discharge conditions. The results obtained in this study are summarized as follows. (1) In the case of a cylindrical tool, the Z-axis directional flow of the machining fluid did not occur in the hole. This is because the tool does not have bumps to agitate the fluid on the side, and the gap between the tool and the inner surface of the hole is narrow. (2) The plate side widened the gap between the tool and inner surface of the hole. Therefore, the fluid was likely to flow in the Z-axis direction in the hole. (3) For the tool with the plane side bit, the flow entered the hole from one plane side and exited the hole from the other plane side. (4) When the tool end is spherical, the Z-axis directional flow of the fluid occurs at the tool end. (5) The fluid flow of the devised tool weakened as the drilling depth increased. To improve the chip discharge performance of the designed tool, the Z-axis directional flow of the machining fluid must occur in an area deeper than 2 mm.

The demand for optical glass lenses is rising owing to the increase in image resolution. Optical glass is a hard and brittle material. Thus, an efficient and precise grinding method is required for optical glass to improve lens quality and productivity. There are a few methods of producing crack-free machined surfaces; however, they provide only limited grinding efficiency. To resolve this issue, the authors’ group has proposed the reaction-induced slurry-assisted (RISA) grinding method, which expands the range of ductile-regime grinding by utilizing the chemical–mechanical action of a cerium oxide slurry. In this study, the grinding performance of RISA grinding is experimentally evaluated for different pH levels. The results are compared using Tukey’s test, where surface roughness is considered as the characteristic value and the pH value as the analyzed factor. The result shows that RISA grinding efficiently produces a high-quality surface when the slurry is alkaline. The adhesion of cerium oxide abrasives to the wheel in RISA grinding follows the same mechanism as slurry aggregation. In addition, adhesion is more likely to occur when the alkalization of the slurry promotes aggregation. The tank in the slurry supply unit is replaced with a rotating tank to ensure stable RISA grinding with a highly aggregable slurry while preventing aggregation. The performance evaluation shows that a high-quality surface with a surface roughness of less than 10 nm in most parts is obtained. Moreover, the critical depth of cut stably increases by a factor of 5.8.

Gyro finishing is a mass-finishing process in which fixed workpieces are finished by contact with the flow of abrasive media owing to the rotation of the barrel. The process is used to finish large complex-shaped workpieces, such as large gears and parts constructed using additive manufacturing. In our previous study, we proposed a cover plate positioned above a workpiece to restrict the upward motion of abrasive media after contact with the workpiece, thereby improving the finishing speed. In this study, plates were added at the side of the workpiece to restrict the flow of the abrasive media toward the side of the workpiece and further improve the finishing speed. First, we evaluated the effect of the side plates using a simple-shaped workpiece. The difference in the surface roughness during a 5 min process was evaluated under certain conditions of the side cover plates. We confirmed that the finishing speed can be increased by using a side cover plate whose front was positioned behind the workpiece center because of the restriction of motion of the abrasive media. In contrast, the finishing speed decreased when a side cover plate whose front was positioned in front of the workpiece center was used because of the interruption in the transmission of force from the barrel wall to the abrasive media near the workpiece, owing to the side cover plates. Subsequently, the effect of the side cover plates placed at a suitable position was evaluated based on variations in the surface roughness during the process. We confirmed that the finishing speed increased by approximately a factor of 1.5 when the side cover plates were used owing to restrictions in the motion of the abrasive media. Finally, a spur gear was finished with cover plates, as a sample of practical workpieces. The finishing speed was determined based on the difference in the surface roughness of the gear teeth during the process. The finishing speed increased when a side cover plate whose front was positioned behind the workpiece center was used. Therefore, it can be concluded that the use of side cover plates is an effective technique to improve the finishing speed in gyro finishing.

An increased removal rate is required to improve the production efficiency during the polishing of ultrahard-to-process materials. The rotational speed of the polishing pad is increased to increase the removal rate. However, research has not been extensively conducted on polishing with a high-speed rotation because slurry is rarely supplied to a polishing area by the centrifugal force generated through polishing pad rotation. In this study, we developed a high-speed rotational polishing system with slurry confinement and friction-state control. The casing and spiral groove of the polishing pad were designed to confine the slurry in a polishing area, and friction-state control was adopted to maintain the spindle torque generated by friction between the pad and wafer at the target spindle torque. Based on the experiments investigating the supply efficiency, the developed polishing method can supply sufficient slurry to the polishing area by the optimized spiral groove pattern and perform polishing without slurry shortage at a high-speed pad rotation of 10000 min^-1. In addition, the results of polishing experiments for a sapphire wafer revealed that friction-state control and wafer rotation could stabilize the polishing state effectively. The proposed polishing system can achieve a higher removal rate than the conventional polishing system.

The substation inspection robot follows the set path when working autonomously, and accurate positioning of the robot while moving is required to ensure that the route does not deviate. This study briefly introduces a substation inspection robot, an odometer-based positioning algorithm, radio frequency identification (RFID), and a machine vision-based positioning algorithm, and improves the former algorithm by RFID. Subsequently, the three positioning algorithms were compared. The results showed that the RFID+machine vision-based positioning algorithm exhibited the highest accuracy among the three algorithms tested under the same cycle number, and its positioning error remained stable as the cycle number increased.

In manufacturing industries, customers demand a wide variety of products, with high quality and fast delivery. Production scheduling systems have become critical for efficient operation. However, scheduling problems in manufacturing are generally large and complex with many constraints. It is difficult to create an optimal production schedule that satisfies all constraints within a reasonable timeframe. This study targets a factory with multiple working machines and two overhead cranes. Our research aims to obtain a solution algorithm to avoid interference of overhead cranes and machine competition and a production plan that minimizes the total makespan for each job. As the problem must be solved within a reasonable timeframe, we have developed the solution algorithm using metaheuristics and scheduling simulation. In general, metaheuristic algorithms must strike a balance between an intensive search for good solutions and a search for diverse solutions. Accordingly, we propose a new algorithm using path relinking in a scatter search. This method was demonstrated to be effective in obtaining good solutions with little variation in numerical experiments. In this paper, we describe previous research, our target process, and new solution algorithm and discuss algorithm design methods based on computer experiments.