As abrasive technologies are currently indispensable for production processes in the automotive, aerospace, optics, telecommunications, and healthcare industries, among others, it is essential that the application of abrasive processing to production be optimized and improved. To those ends, it is necessary to understand how to approach the task, as there are many processing factors to consider. However, priority is given to understanding the abrasive processing mechanism that determine finishing results, as well as the relationship between the processing factors and individual conditions. Measurement, analysis, and evaluation technologies are also important. Furthermore, the development of new abrasive tools or machining fluids and the active use of physicochemical phenomena are key to the development of advanced abrasive technologies.
Cutting-edge studies focusing on advanced abrasive technologies were collected for this special issue, which includes 12 papers covering the following topics:
- Quantitative evaluation of surface profile of grinding wheel
- Elucidation of grinding mechanism, based on grinding force
- Novel grinding wheel
- High-efficiency and high-accuracy grinding of difficult-to-cut materials
- Polishing technology using magnetic fluid slurry
- Application of ultrasonic waves or ultra-fine bubbles to coolants, and their effects on them
- Planarization technology for single-crystal silicon carbide
This issue is expected to help its readers to understand recent developments in abrasive technologies and to lead to further research.
We deeply appreciate the contributions of all authors and thank the reviewers for their incisive efforts.
Recently, carbon fiber reinforced plastics (CFRP) have been used in various applications such as airplanes and automobiles. In CFRP molding, there are unnecessary portions on the outer area. Therefore, a machining process is required to remove them. Cutting and grinding are conventionally used in the finish machining of CFRPs. End-milling allows the removal of most of these portions. However, uncut fibers easily occur during end-milling. In contrast, a precise machined surface and edge are easily obtained using a grinding tool. Therefore, this research has developed a novel cubic boron nitride (cBN) electroplated end-mill that combines an end-mill and a grinding tool. This is a versatile tool that can cut and grind CFRPs by changing the direction of rotation of the tool. In this study, the effectiveness of the developed tool is investigated. First, the developed tool machined the CFRP by side milling. Consequently, cBN abrasives that were fixed on the outer surface of the developed tool did not detach in certain cutting conditions. Next, in order to generate a sharp edge on the CFRP and restrict the increase in the CFRP temperature with the cBN electroplated end-mill, the optimum abrasive size and grinding condition were investigated through the design of experiments. Moreover, the effectiveness of the developed tool was verified by comparing it with a conventional tool. As a result, smaller burrs and uncut fibers were observed after final machining with the developed tool under the derived optimum condition than those with conventional tools. However, the desired surface roughness could not be achieved as required by the airline industry. Therefore, oscillating grinding was applied. In addition, the formula of the theoretical surface roughness while using the developed tool was derived using the theory of slant grinding. As a result, the oscillating condition that led to the required surface roughness was obtained by theoretical analysis. In addition, the required value for the airline industry was achieved by oscillating grinding.
Zirconia ceramics have excellent applicability in the aerospace, defense, new energy, automotive, electronics, and biomedical fields. However, few investigations have been conducted on the high-precision polishing of zirconia ceramics. In this work, a polishing method using a magnetic compound fluid slurry is proposed. First, the principle and the constructed experimental setup were presented. Then, the experiments were performed that characterized the surface profile after polishing, the effect of the working gap, and the effect of the concentration of carbonyl iron particles (CIPs) on the material removal and surface quality. The results showed that the material removal ability correlated positively with the surface roughness; the smallest working gap (0.5 mm) induced greater material removal ability and better surface roughness; higher CIP concentration enabled a higher polishing force to obtain higher material removal and better surface quality. The polishing results show that surface roughness Rz of 55 nm was obtained at the surfaces of zirconia ceramics, confirming that the proposed method has the potential for polishing of zirconia ceramics.
Increasing use of NiTi alloy products makes it very important to improve the cutting performance of this material. This study presents the effect of cutting speed on radial shape recovery of work material which is supposed to deteriorate the dimension accuracy in cutting process of super-elastic NiTi alloy. The shape recovery of work material was investigated at the beginning of cutting process, during the stable part of cutting process and after feed stops respectively utilizing a high-speed camera and a cutting force dynamometer in orthogonal cutting experiments at various cutting speeds. The mechanism of the shape recovery was investigated by analyzing the crystallization phase state of work material before and after cutting using XRD and measuring the temperature distributions on the end surface of work material during orthogonal cutting experiments using non-reversible temperature indicating paints correspondingly. Results show that at relatively low cutting speed, the temperature of work material near the cutting point did not exceed the threshold temperature of phase transformation, and thus work material generated obvious shape recovery throughout the whole cutting process due to the phase transformation. Increasing cutting speed could increase the temperature of work material; when cutting speed increased to 100 m/min, the temperature of work material near the cutting point exceeded the threshold temperature of phase transformation, thus work material did not generate obvious shape recovery because it could not undergo any form of phase transformation during the stable part of cutting process and after feed stops. Consequently, increasing cutting speed could be proposed as an approach to improve dimension accuracy by inhibiting shape recovery of work material in cutting process of NiTi alloy.
Concave surfaces are widely used in the shells of smart devices, such as smartphones, watches, or molds. The quality of the concave surface is important in enhancing the value of these products. In order to improve the surface quality, the polishing process is crucial for removing defects on the concave surface and for smoothing the surface after machining or grinding. Magnetic assisted polishing is a promising method that can be used to meet the high standard of surface quality required. In this work, as a promising smart material in nano-precision polishing, magnetic compound fluid (MCF) slurry was used for the first time to polish a concave surface with a magnet that is magnetized in the radial direction. A simulation of the magnetic field distribution was performed in advance to clarify the polishing characteristics in theory. Subsequently, a polishing experiment was conducted to investigate the feasibility of this polishing method. Finally, the results demonstrated that both a curved surface and a flat surface could be polished successfully. Furthermore, the nano-precision PV value (the distance from the peak to the valley in the surface profile) and the surface roughness Ra were obtained for both areas, and this method was demonstrated to be capable of polishing concave surfaces and worthy of further research.
Currently, the demand for carbon fiber reinforced plastic (CFRP) has increased in various fields. However, there have been few studies investigating the machined surface quality, degradation in CFRP mechanical properties with machining temperature, or machining tool cost. In particular, the machining temperature is considered to affect the machined quality because the CFRP matrix is a resin. In this study, a cubic boron nitride (cBN) electroplated end mill was developed; this novel tool can switch between cutting and grinding without needing to change the tool. To observe the relationship between the amount of abrasive grain in contact with the CFRP and the occurrence of burrs, a grinding test was conducted with different clearance angles of the end mill and different abrasive grain sizes. The temperature during the grinding processes was measured, and the burrs were estimated after the grinding processes. From these results, the contact amount of the abrasive grit suitable for grinding was derived.
The development of grinding wheels that are capable of improving the grinding accuracy and the finished surface roughness via the grinding process is increasingly sought in industries. The refinement of grinding wheels comprising abrasive grains is an effective means of improving the ground surface quality. The general methods used for fabricating grinding wheels tend to facilitate the aggregation of fine abrasive grains, resulting in poor abrasive distribution. Therefore, we focused on the electro-spinning mode of Patterning with Electrostatically Injected Droplet (PELID), which is capable of forming micro resin fibers. Subsequently, we attempted to fabricate fibrous grinding wheels containing abrasive grains by using the twin nozzle PELID technique that applies this mode. We confirmed through experiments that resin fibers containing abrasive grains can be manufactured efficiently using PELID and succeeded in manufacturing fibrous grinding wheels containing abrasive grains.
In the grinding process, a grinding wheel surface is a tool that is directly applied to the workpiece. As the condition of the grinding wheel surface is determined by its dressing conditions, the ability to accurately measure the grinding wheel surface with an applied dressing would enable the prediction of the ground surface characteristics of the workpiece as well as the determination of optimum dressing conditions. Recently, a new dressing method called the multiple helical dressing was proposed, which has led to improvements in the grinding performance. However, there is still no method to quantitatively evaluate the changes in the grinding wheel surface condition caused by multiple helical dressings. In this study, we measured the grinding wheel surface applied with multiple helical dressings using a so-called measured focus position recalculation method to determine whether we can quantitatively evaluate the measured dressing grooves generated on the grinding wheel surface by multiple helical dressings, and the resultant undulated grinding wheel surface shapes. We ground an actual workpiece to demonstrate the effects of changes in the grinding wheel surface shape due to multiple helical dressings on the ground surface of the workpiece. The experimental results show that our proposed measuring method can accurately measure the changes in the grinding wheel surface condition due to multiple helical dressings. We also proposed a method to evaluate the dressing grooves to prove that we can quantitatively evaluate the measurement results of dressing grooves generated by multiple helical dressings. In addition, we evaluated undulated grinding wheel surface shapes as its cylindricities by extracting only the undulation shapes generated by multiple helical dressings. Finally, we performed groove grinding with a grinding wheel applied with multiple helical dressings to reveal the relationship between the ground surface of the workpiece and the grinding wheel surface condition, which demonstrated the effectiveness of multiple helical dressings.
Lapping with a lapping tape refers to a finishing process in which a new tape is continuously supplied to its processing area and pressed down with a pressure roller during its relative motions. In response to the growing demand for lapping high-hardness materials with high efficiency, lapping tapes with superabrasive grains formed in a textured structure with a bond have been recently utilized. In this study, we supply a working fluid that has passed through the slit between ultrasonically oscillating blades to processing points. Variations of sound pressure generate cavitation in the working fluid. Impulse waves due to the collapse of cavitation bubbles inhibit chips from getting adhered to the chip pockets of the lapping tape. We have lapped hardened SUJ2 with plural lapping tapes of different characteristics. In lapping with a lapping tape using diamond abrasive grains, we have improved the time constant for the changes in surface roughness in relation to the lapping time from 18.9 s to 7.6 s by superimposing ultrasonic oscillations; consequently, the lapping speed improved. We have compared the effects of ultrasonic oscillations for three types of lapping tapes and discovered that fewer abrasive grains and lower chip adhesion firmness due to the abrasive grains formed in a textured structure increased the effects of ultrasonic oscillations.
In a previous study, we developed an abrasive-free polishing method named catalyst-referred etching (CARE) and used it for the planarization of silicon carbide (SiC) (0001). In this method, Si atoms at step edges are preferentially removed through a catalytically assisted hydrolysis reaction to obtain an atomically smooth and crystallographically well-ordered surface. However, the removal rate is low (< nm/h) and needs to be improved. In this study, we proposed an ultraviolet (UV) light assisted CARE method. In this method, UV light is irradiated onto a SiC surface to generate holes and oxidize the surface. The oxidized area, consisting of SiO2, can be quickly removed to form a nano-pit owing to the higher removal rate of SiO2 compared to that of SiC. The periphery of the nano-pits works as a reaction site, leading to a higher removal rate. To enhance the oxidation rate and form nano-pits, we applied electrochemical bias to the SiC substrate. However, the removal rate did not improve significantly when the bias voltage was higher than 3.0 V. This is because the electrochemical potential of Pt increased with the anodic potential of SiC, which oxidized the Pt surface and degraded the catalyst capability. To avoid this issue, we modified the catalytic pad, where an in-situ refreshment of the Pt surface is possible. As a result, the removal rate increased up to 200 nm/h at a bias of 7.0 V, which is 100 times higher than that of the CARE without UV irradiation. The proposed method is expected to contribute to the enhancement in the productivity and quality of next-generation SiC substrates.
Grinding forces and power are important parameters for evaluating grinding process performance, and they are typically measured in grinding experiments. Forces are typically measured using a load cell or a dynamometer, whereas power is measured using an electrical power sensor to monitor the power of the spindle motor. Direct readings of the measurements include the net grinding force and power components for material removal and non-grinding components such as the impingement of a grinding fluid. Therefore, the net components must be extracted from the direct readings. An approach to extracting the net grinding forces and power is to perform additional spark-out grinding passes with no down feed. The forces and power recorded in a complete spark-out pass are used as the non-grinding components. Subsequently, the net grinding components are obtained by subtracting the non-grinding components from the corresponding totals for actual grinding passes. The approach becomes less accurate when large depths of cut, particularly large depths of cut and short grinding lengths, are involved. A new experimental approach is developed in this study to measure the non-grinding force and power components and to extract the net components. Compared with the existing approach, the new approach is more accurate for grinding with large depths of cut or short grinding lengths. In this approach, two additional grinding passes on an easy-to-grind material, one with and the other without a grinding fluid, are conducted using the same setup and condition as those in the actual test material to measure the forces and power for obtaining the non-grinding components. Subsequently, these non-grinding components are used as the non-grinding components of the actual material and subtracted from the total force and power components of the actual material to obtain the net values. To illustrate the application of the approach, surface grinding experiments are conducted to collect the forces and power. The extracted net power is consistent with the power predicted with the extracted net forces.
The coating process of high-performance films, such as electrodes for lithium-ion batteries, requires high-precision transfer of settling slurries and high-viscosity liquids. This is because transfer characteristics, such as low pulsation and quantitative transfer, have a significant impact on product performance. A single eccentric screw pump is used in this coating process. One component of this pump is a complex-shaped rotor. This rotor must have high precision and high wear and chemical resistance. To meet these requirements, we applied alumina ceramics, which have excellent material properties, to the constituent materials of the rotor. However, for rotors with hypocycloid-curved surfaces, the development of a highly accurate and highly efficient alumina ceramic grinding technology is required. For this purpose, a free-form grinding technique using small-diameter ball-end electroplated diamond grinding wheels is indispensable. In the present study, we carried out machining experiments on inclined and cylindrical surfaces as a basic study. As a result, by increasing the grinding speed with a high-speed spindle, we achieved the precision, quality, and efficiency required for rotor grinding.
Bacterial growth is one of the common causes of putrefaction and deterioration of water-soluble machining fluid. The 16S ribosomal DNA metagenome analysis of the bacterial species composing the microbial flora present in the machining fluid derived after processing demonstrated a high amount of species belonging to the Pseudomonas genus. Therefore, we prepared two types of ultrafine bubbles water (gas species: air and CO2) containing different types of gas and confirmed the bactericidal effect on Pseudomonas aeruginosa (ATCC 10145), a typical Pseudomonas species. The grinding fluid was prepared using sterile purified water containing ultrafine bubbles (hereafter referred to as UFB) as diluted water, and the Pseudomonas aeruginosa was inoculated to obtain 106 CFU/mL. The sterilization rate of the number of bacteria was determined immediately after immersion in each fluid and subsequently after two hours. The sterilization rate was determined to be 100% in the test group using the ultrafine bubbles water of CO2 (CO2-UFB water). As a comparative control, a similar test was performed on Staphylococcus aureus IFO12732, and the sterilization rate was determined as 0%. Fluorescence microscopic observation of bacteria after immersion in the CO2-UFB water demonstrated damage to the cell wall as the cause of death of the Pseudomonasaeruginosa. Therefore, CO2-UFB demonstrated sterilization of machining fluid by killing Pseudomonasaeruginosa in the machining fluid. The bactericidal mechanism of UFB involved the induction of damage in bacterial cell walls. This can be attributed to crushing due to the increase in the particle size of UFB.
This paper proposes a fault-tolerant aircraft control method based on a self-constructed fuzzy neural network for quadcopters with multiple actuator faults. We first introduce the actuator failure model and the model uncertainty. Subsequently, we establish a framework for a self-constructed fuzzy neural network observer with an adaptive rate to obtain the estimated value of the nonlinear term of the module uncertainty. We also design a multivariable sliding mode fault-tolerant controller to ensure the stability of the aircraft under this fault condition. Finally, we conduct experiments using the Pixhawk 4 flight controller installed on the QBall-X4 UAV experimental platform, such that the use of the flight controller’s fault coprocessor and redundant sensor design reduces the crash that occurs during the debugging of the control algorithm. Compared to the existing intelligent fault-tolerant control technology, our proposed method employs fewer fuzzy rules, and the number of these rules can be adaptively adjusted when the system model changes. In the experimental test, the aircraft was still able to fly stably under multi-actuator failure and interference conditions, thereby proving the stability of the proposed controller.
This study was carried out to investigate the surface roughness in infeed centerless grinding process. The experiment was performed to determine the influence of several technological parameters on the surface roughness. The grinding wheel of Hai Duong Company, Vietnam, was used to machine the SCM435 steel. The experimental matrix was designed using central composite design (CCD). The machining parameters that were used as the input parameters in this study include the workpiece center height, dressing feed rate, regulating wheel velocity, and infeed rate. From the experimental data, an initial model of the surface roughness was built as a quadratic function. Further, a Box-Cox transformation was used to develop a new model from the initial surface roughness data with better accuracy than that of the initial model. The accuracy of the proposed model was verified by comparing the values of the mean absolute error, mean square error, and determination coefficients. This direct approach can be applied for the investigation of other factors during machining processes and can be used in the optimization of machining processes.