The continued effects of the global spread of COVID-19 have reaffirmed that restrictions on the movement of people and products have geopolitical consequences. In addition, the impacts involved in the decarbonization of the global environment have further strengthened the growing demand for the building of a sustainable society. These factors have had no small impact on the global economy and on global manufacturing as well. In this context, the demand for the realization of new manufacturing technologies that can respond to changes in social and economic environments has been growing.

This special issue focuses on recent advances in manufacturing technologies that maximize product quality and reduce costs, with an emphasis on the machinery industry. This special issue of the IJAT contains 12 papers. These include works on cutting technology, machining metrology, advanced machine tools, gear manufacturing technology, additive manufacturing, and more. The first five papers are proposals for new cutting technologies and elucidations of cutting phenomena. The next three papers are new proposals for machining measurements. The next two papers are on precision positioning technologies and a rack gear compensation technology. The last two papers are theoretical investigations into the basic phenomenon of additive manufacturing and its applications.

These papers were originally presented at the 10th International Conference on Leading Edge Manufacturing in the 21st Century (LEM21), held in Kitakyushu, Japan in 2021. The papers have been revised and expanded at the request of the editors.

The editors would like to thank all authors for their comprehensive efforts in making this special issue possible, and would like to thank the anonymous reviewers for their hard work. We wish them all the best in their future research in this field of manufacturing technology.

Titanium alloys are widely used as aerospace materials, especially for turbine blades, due to their excellent mechanical properties. In the high-efficiency machining of titanium alloy turbine blades, the feed rate for ball-end milling is limited to 1000 mm/min due to the low thermal conductivity and chemical reactivity of the titanium alloy. These characteristics result in tool damage and an increase in the cutting temperature, significantly reducing the machined surface accuracy. A new processing method is thus needed for achieving a high accuracy and high efficiency in titanium alloy machining. It has been reported that driven rotary machining of hardened steel improves the machined surface and increases the processing efficiency, suggesting that high-efficiency machining can be realized by employing hale machining with a rotary tool. In this study, hale machining was performed using a driven rotary tool and the effects of different cutting conditions and cutting environment on the machining characteristics were investigated. The results showed that the tool life was longest at a feed rate of 9000 mm/min among the three feed conditions because the number of times of adhesion and detachment decreased with the decreasing friction distance of the cutting edge. Furthermore, it was clarified that adhesion formation at the cutting edge was suppressed by lubrication with an oil mist in a minimum quantity lubrication environment. This lubrication effect reduced the tool damage and adherence at the cutting edge, significantly extending the tool life and improving the machined surface quality compared to the results obtained in a wet environment.

In this study, the effect of cutting fluid on tool wear in finished surface formation area was investigated when turning alloy 304 with a TiN coated carbide tool under different lubricant conditions and the transition of surface roughness caused by tool wear was investigated. In the case of water-soluble cutting fluid, the higher concentration emulsion caused a smaller wear width VB and larger VB’”. In the case of oily cutting fluid, the lower co-efficient of friction oil caused a smaller wear width VB and larger VB’”. In both cases of water soluble and oily cutting fluid, the cutting fluid of lower coefficient of friction caused a larger wear width VB in milling at the feed rate of around tool edge roundness. This tendency was consistent with the wear width VB” and VB’” in turning. In both cases of water soluble and oily cutting fluid, the cutting fluid of lower coefficient of friction caused a larger cutting force volatility. The feed marks were more irregular in lower coefficient cutting fluids.

Carbon fiber-reinforced plastics (CFRP), which are classified as functional resins, are rapidly replacing conventional materials because of their excellent properties. Typically, they have been used to fabricate components of airplanes or cars. In the field of medicine, the demand for micro-machined products manufactured with lathes is also increasing. However, owing to the significant tool wear caused by the carbon fiber, CFRP machining can result in burrs and inaccuracies in the finished product. The tool wear caused by carbon fiber must be reduced to ensure high dimensional accuracy. In this study, the possibility of combining conventional turning with electric current or electrical discharge machining was explored.

The objective of this study is to achieve a high-precision and high-efficiency machining process for industrial components of the polyether ether ketone (PEEK) resin, such as the inspection socket of a connector or semiconductor packages. However, the drilling of holes in PEEK resin is challenging. Because PEEK resin is a thermoplastic resin, it can soften or melt owing to the heat generated during processing, which causes burrs and degrades the accuracy of the machined hole, thereby resulting in quality deterioration and hindering post-processing. Since the thermal conductivity of plastic materials including PEEK resin is lower than those of metals, the heat generated during processing does not dissipate to the outside of the workpiece, and the effect of the processing temperature on the processing accuracy is significant, particularly during drilling. Hence, a workpiece is cooled via a cold gas supply in this study. The effect of cold gas cooling on the machined hole accuracy and cutting state in the small-hole machining of PEEK resin is investigated. Results show that cooling the workpiece effectively decreases the cutting temperature and improves the machined hole accuracy. Under the experimental conditions, the combination of nonstep drilling and cooling enables high-precision drilling at approximately the same accuracy as step drilling.

This study quantitatively and theoretically clarifies the machining characteristics of the chisel engagement and the cutting-edge wear behavior in drilling in a workpiece superimposed with ultrasonic vibration. The machining phenomenon of drilling by this method considers being the same as drilling by ultrasonic vibration spindle from the viewpoint of the relative motion of the cutting edge and workpiece. However, the details have not been clarified yet. The chisel engagement behavior experiment at the initial stage of the drilling and cutting-edge wear experiment were carried out in this study. The chisel engagement behavior experiment revealed lower axial relative velocity results in a minor effect. In the cutting-edge life experiment, when the cutting fluid and the supply method were changed, the minimal oil with mist supply showed the same result as water-soluble with jet supply without breaking the drill. However, considerable wear was generated at the cutting edge in the initial drilling stage. When suitable ultrasonic vibration-assisted drilling was applied, initial wear decreased by 40% but could not be suppressed entirely. As a result of theoretical elucidation on this initial wear, it was proven that the flank face of the cutting edge contacted the workpiece when critical amplitude was exceeded. In the experiment to prove the validity of this theory, the initial wear occurred when the critical amplitude was exceeded. The cutting-edge wears increased in proportion to the working relief angle.

The deformation of the thermal workpiece in the end-milling process has a significant effect on the accuracy of machining. In-process direct measurement of workpiece deformation is difficult because process disturbances occur during machining. On the other hand, local temperatures of the workpiece can be easily and accurately measured using common measuring methods. This study aims to develop a monitoring method for workpiece deformations. A sensor-configured thermal simulation is proposed by combining local temperature measurements with thermal simulations to estimate the thermal states of the workpiece in small-lot production. Furthermore, an empirical modeling method is introduced to estimate the workpiece deformation from measured temperatures, thereby accelerating process time. A reliable estimation requires the selection of appropriate measuring points. Using multiple linear regression (MLR), a statistics-based selection method is proposed to establish a relationship between thermal deformation and temperatures of measuring points in various machining situations. During the end-milling process, the predicted time-series of deformations at the machining point and temperatures of the measuring points are regarded as output variables and input variables, respectively, in the finite element method (FEM)-based thermal simulation. The number of measuring points is determined by evaluating Akaike information criterion (AIC), and effective measuring points are selected using the p-value index. The proposed systematic construction method is evaluated using simulation-based case studies. The constructed temperature-based model for measuring workpiece deformation corresponded well to the FEM simulation. Therefore, the constructed model can represent workpiece deformation with the minimum number of measuring points.

The design and testing of different optical heads were performed to evaluate the pitch deviation of a diffraction scale grating with a small diffraction angle. Based on the proposed pitch deviation evaluation method employing optical angle sensors based on laser autocollimation, a modified optical head with position-sensitive detectors (PSDs) is first designed and constructed by following the conventional optical configuration. Owing to the small angle of diffraction of the first-order diffracted beams, the modified optical head has a large working distance, resulting in poor sensor stability. Therefore, a novel and compact optical head employing a pair of small prisms is designed and developed to shorten the working distance of the optical head. An additional modification was also made to the developed compact optical head in such a way that collimator objectives (COs) in the laser autocollimation units are removed to improve the sensor sensitivity. Experimental comparisons were conducted using the three types of optical heads to verify the feasibility of the developed optical angle sensor with PSDs.

Multi-point scanning measurement, which is effective in eliminating motion errors of the stage in on-machine profile measurement, requires multiple displacement sensors of equal pitch to measure displacements simultaneously. However, it is not easy to arrange small sensors with high alignment accuracy when applying the multi-point method at a narrow pitch. In addition, if many sensors can be arranged in parallel, improvement in measurement accuracy can be expected. Therefore, a new micro electro mechanical system (MEMS) device for straightness measurement, one that integrates 10 cantilever displacement sensors, has been proposed. This device can be expected to solve the problem involved in the multi-point method because of the characteristics of MEMS, as the semiconductor processing method can make mechanical structures with high accuracy and it can easily make the device with many identical structures. The device is designed to measure waviness less than 100 μm in height. Ten cantilevers of 11 mm length are fabricated in parallel with 1.8 mm pitch on a side of a base substrate 20 mm square. The strain induced by a displacement of the probe placed near the front edge of the cantilever is detected as a change in the resistance of the piezo resistor at the foot of the cantilever. In the fabrication process of this device, crystal anisotropic etching is performed for 12 hours to form probes 250 μm high. A new fabrication process is also proposed in which a protective process is added to prevent damage to the circuits already formed during the etching. A prototype is investigated, and it is found that the resistance value increases about 0.45% in proportion to the displacement of 100 μm. It is therefore confirmed that this device has the basic ability to detect displacement.

High-precision positioning can be obtained by reducing sliding friction and securing support rigidity. A prototype of a biaxial positioning table with non-contact drive by magnetic force and flexible mechanism support was developed to meet these requirements. The magnetic poles of a permanent magnet and an electromagnet were placed opposite to each other with an appropriate gap between them, and the attraction force between the two poles was used as the actuator for fine feed. The table was supported with a flexible mechanism composed of metal (A2017) beams with notches and elastic hinges assembled into a square frame shape. The permanent magnets were commercial neodymium magnets, and the electromagnets were self-made of S45C core bars. Two types of attraction force, maximum and minimum, were set depending on the number of neodymium magnets and the magnetic pole gap. The relationship between the applied current and attraction force for each type was calibrated using an electronic balance. Upon increasing and decreasing the applied current to the electromagnets, a linear relationship was shown between them. The relationship between the attraction force and the X- and Y-axes displacements was simulated by finite element analysis. Based on both results, the relationship between the applied current and displacement was estimated. The fine-feed experiment was conducted in both directions of the X- and Y-axes by applying current to electromagnets in a stepwise sequence. The displacements of total strokes in the long-stroke feed on applying the maximum attraction force were 340 μm and 315 μm for the X-axis and 160 μm and 133 μm for the Y-axis. These values are 2.0–2.8 times larger than the estimated displacement. Additionally, 3%–12% of the other axes interference occurred between the X- and Y-axes. In the high resolution feed applying the minimum attraction force, the displacement per step was 75 nm and 78 nm for the X-axis and 35 nm and 39 nm for the Y-axis. Cooperative feed with a combination of long stroke and high resolution was verified to be feasible.

Racks are typically curved after cutting their gear teeth, and a straightening process is required to correct the distortion due to machining. In this study, key factors in the straightening of curved racks by three-point and four-point bending are examined with to automate the correction. The relationship between load and deformation is plotted in real time to determine the unloading point to correct the target deflection for straightening. The parameters constituting the above-mentioned relationship are important for achieving precise correction. The load and deflection at the central loading point are known to be suitable parameters for three-point bending. The smaller the deflection required for correction, the higher is the precision of the displacement sensor required for three-point bending. In the case of four-point bending, the bending moment and bending angle should be selected. In addition, a four-point bending jig is required to load the uniform bending moment during the correction. A modified four-point bending jig is made and the effectiveness was examined.

This paper describes a method to represent and predict the melting and solidifying shape of metal powder materials in the selective laser melting (SLM) method of metal addition manufacturing using a small number of physical properties. This is a processing method to complete a three-dimensional modeling object by layer-by-layer stacking. A laser beam is used to create objects with minimal voids and distortion by appropriately setting the scanning speed, output intensity, spot diameter, hatch spacing, and other conditions. Repeating actual experiments to determine the optimal build conditions increases the cost of operating the machine, such as electricity and labor, and the cost of materials when a modeling failure occurs. In recent years, attempts have been made to determine the optimal build conditions by analyzing the melting and solidification phenomena of metallic materials through precise simulations. However, it is necessary to set many physical property values as the parameters. Many physical property values are difficult to measure, and if these values are incorrect, the analysis results can differ significantly. In this study, a theoretical model for predicting the cross-sectional area and cross-sectional thickness of the melt pool using a single-track laser was developed using a small number of physical properties, such as melting point, thermal conductivity, and latent heat. To further examine the validity of the theoretical model, experiments were conducted for comparison purposes. In this experiment, 5 × 1 × 1 mm rectangular specimens were stacked and fabricated by a metal additive manufacturing machine using different laser beam irradiation conditions. The fabricated samples were cut, polished, and etched with nital, and the melt pool shapes were measured. Finally, experimental and theoretical values were compared to confirm the validity of the constructed theoretical model. This indicates that the proposed model can predict the melt pool shape.

In this study, the manufacturing process of multi-material parts by simultaneous mechanical joining and three-dimensional (3D) printing of plastic parts was developed. In this process, a metal part with a hole sets on a lower 3D printed plastic part having a projection, and an upper plastic part is deposited on the metal part, while caulking is formed by a 3D printer. The effect of 3D printing conditions and a dimension of caulking on the joint strength was evaluated through the tensile shear and three-point bending tests. It was observed that squashing the projection while printing the upper part effectively improved the strength. The strength decreased as the clearance increased, whereas the shape of the projection was changed to a cylinder and a cone to ease positioning while preventing a decrease in the strength.

The ocular movements of skilled and unskilled engine lathe operators were analyzed as a preliminary step in developing a method for supporting the transfer of skills in engine lathe machining. An attempt was made to elucidate the difference in skilled and unskilled workers operating a lathe with a digital position display device (digital readout display meter) that can display the machining status of the workpieces. The impact of the digital position display device was investigated by evaluating and comparing the quality of each production from the operations. In addition, because skillful estimation is necessary for most manufacturing tasks, the differences between the ranges of visual examination of workers were analyzed while a workpiece was being measured.

A composite algorithm combined with fuzzy proportional-integral-derivative (PID) control and acceleration closed-loop control is proposed to address the defects of slow response speed, strong oscillation, and long adjustment time of the current height following control system for a laser cutting head. The fuzzy PID control can satisfy the different requirements for the control parameters in each stage of the height follow-up adjustment process for the laser cutting head via the adaptive adjustment of the PID parameters. Accordingly, the height following error can be attenuated to the set positioning accuracy range. The acceleration closed-loop control can improve the acceleration and deceleration performance of the system through the positive and negative feedback regulation of the motion acceleration of the laser cutting head to achieve high-speed servo. An experimental bench of height follow-up control system for laser fabrication is developed to verify the effectiveness of the algorithm. Through experimental verification, compared with the conventional digital PID incremental algorithm, this composite control algorithm can accelerate the response speed of height follow-up control system for the laser cutting head, improve the dynamic performance of the system, and realize fast and precise servo control of laser cutting head height under the premise of ensuring positioning accuracy. The proposed algorithm is expected to lay a foundation for the development of the new intelligent laser processing system.

Wire-based direct energy deposition (W-DED) techniques in metal additive manufacturing allow part-fabrication at higher deposition rates and lower costs. Given the lack of any support mechanism, these processes face challenges in fabricating overhanging features. The inherent overhang capability of weld-beads and higher-order kinematics can help realize certain complex geometries. However, significant challenges like non-uniform slicing, constrained deposition-torch accessibility, etc., limit the efficacy of these approaches. The present work describes a deformation-aided deposition process designed to overcome some of these limitations and to manufacture complex metallic components. It is based on a sequential combination of deposition and bending processes: a shape fabricated through W-DED deposition is bent to form the required shape. The cycle of deposition and bending is repeated until the final desired geometry is realized. The anisotropic and deterministic behaviors of the deposited components are analyzed in terms of springback and the punch force. Finally, the benefit of current hybrid process is demonstrated through a few illustrative geometries.

Using computational fluid dynamics (CFD) technology, a stable manufacturing method for polymeric nanofiber non-woven fabrics based on an improved melt-blowing method and flash spinning is realized to achieve mass productivity. Subsequently, a method to predict filter efficiency using two production methods based on the effects of thickness, filling rate, and fiber diameter on filtration performance is developed to establish a filter design via CFD technology. CFD models featuring uniform fiber diameters are proposed. Next, the pressure loss and flow resistivity are calculated using CFD flow analysis software, as in a filter experiment. The proposed fiber diameter distribution model yields results similar to the experimental value, and the relationship among filling rate, fiber diameter, and flow resistivity is verified. The non-woven filter fabricated in this study demonstrates superior filtration properties, based on the results. Additionally, a method to satisfy both low pressure loss (low flow resistivity) and high filtration efficiency is discussed. Although the pressure loss increases, the filter yields a value below the standard for high-performance face masks, since the fiber diameter is on the nano-order.