In recent years, the field of manufacturing has become increasingly diversified and complex to meet various requirements, such as improved manufacturing accuracy, productivity, environmental friendliness, and automation/intelligence in manufacturing sites. Consequently, the fusion of different fields as well as interdisciplinary research has become indispensable for the creation of innovative manufacturing technologies that can realize advanced production systems.

This special issue comprises seven outstanding research papers that focus on advanced precision engineering in manufacturing systems, covering the following topics:

- Advanced cutting technologies

- Advanced machine tools and elements

- Surface finishing technologies

- Non-traditional machining and additive manufacturing

- Nano-scale surface finishing

- Advanced surface processing

All research papers were originally presented at the 19th International Conference on Precision Engineering (ICPE2022), held in Nara, Japan, in 2022. The editors hope that the research papers included in this special issue will offer valuable insights to readers for their future research in the field of manufacturing technology.

Each paper underwent a rigorous peer-review process, and the editors would like to express their deep appreciation for the efforts and excellent work of all the authors and anonymous reviewers who contributed to the realization of this special issue. Finally, it is our sincere hope that the papers in this special issue will further contribute to the advancement of our future society.

In this study, a novel methodology was proposed to investigate the influence of the built-up layer (BUL) formation on the stress state distribution in the primary shear zone (PSZ) using analytical model and particle image velocimetry (PIV) analysis. Orthogonal cutting tests were performed under a range of uncut chip thicknesses and cutting speeds using two uncoated cemented carbide tools with different rake angles. A series of shear strain, shear strain rate, and velocity distributions in PSZ were obtained by PIV analysis. Al7075-T6511 was used as the workpiece. Subsequently, the influences of cutting conditions on the BUL/built-up edge (BUE) formation and the plastic deformation in PSZ were investigated. Using these results, the parameters of the proposed analytical model were identified, and the influences of the BUL/BUE formation on the stress state distribution were investigated. From the experimental results, it was found that in the cutting speed range below 2 m/min, only BUE is formed, and the uncut chip thickness and tool rake angle have a significant influence on its formation. The agreement between the measured and calculated results demonstrated the effectiveness of the proposed methodology. The results confirmed that the BUE formation has little effect on the bell-shaped distribution of shear strain rate, but has a significant influence on the thickness of PSZ, chip sliding velocity near the outlet boundary of PSZ, maximum shear strain rate, stress state, and temperature in PSZ. It was also confirmed that the stress triaxiality plays an important role in the BUE formation. These results provide a deeper understanding of the BUL/BUE formation.

This study presents a novel method for estimating the surface integrity of end-milled workpieces. It is well known that the mechanical properties of machined surfaces in cutting affect the quality of the final product. In particular, hardness and residual stress often require strict control; however, nondestructive inspection remains a challenge. This study proposes a method to estimate the hardness and residual stress of end-milled surfaces by analyzing cutting forces and images of the tool during machining to obtain approximate temperature and stress distributions. These state quantities are highly correlated with the dislocation density and its distribution on the machined surface, which in turn is strongly correlated with residual stress and surface hardness. Despite this strong correlation, few research studies have been conducted on the topic. In the proposed method, cutting forces, measured by a dynamometer, are analyzed to estimate the specific cutting forces and edge force coefficients. Simultaneously, the flank wear width is recorded using an image-based on-machine measuring device installed in the machine tool. From this information, the average stresses at the primary and tertiary cutting zones are estimated, while the cutting temperature in the primary cutting zone is roughly estimated by considering the traditional shear-angle prediction theory. Using these estimations, hardness and residual stress are calculated based on a simple linear regression model. Parameter identification for the model is performed based on measured hardness and residual stress in end-milling experiments. The model was validated against experimental measurements, which showed that the proposed method can accurately estimate hardness and residual stress, although it was observed that the selection of explanatory variables has a significant effect on accuracy.

Owing to recent interest in the production of flexible devices, it is necessary to develop a more convenient approach in which silicon (Si) thin film transistors (TFTs) are fabricated directly onto the flexible substrates at low substrate temperatures. Unfortunately, the physical limitations of conventional plasma-enhanced chemical vapor deposition (PECVD) under low pressures becomes a critical obstacle. In this study, Si film deposition using PECVD under atmospheric pressure excited by very high-frequency electrical power was investigated to overcome this issue. Tetramethylsilane [Si(CH₃)₄] is used as a source gas that is much safer than silane (SiH₄) gas. We investigated the effects of the reactive gas concentration and specific energy (the ratio of input power to unit volume of the reaction gas) on carbon incorporation into the resultant films. Based on the results, we discuss the possibility of forming Si films with sufficiently low carbon content, which is applicable to Si TFTs.

Electrochemical machining was performed on two cemented carbides with different compositions using unipolar and bipolar short-pulse voltages to investigate the effects of the composition and pulse conditions on the machining characteristics. In the case of cemented carbides with high cobalt and low tungsten carbide (WC) contents, machining progressed even when a unipolar voltage was used. This is believed to be due to the dissolution of the binder, that is, Co, which causes the WC and WO₃ particles to drop out. Machining progressed more easily when a bipolar voltage was used than when a unipolar voltage was used. This is attributed to the effective removal of WO₃. The unevenness of the machined surface was also reduced with bipolar voltage. The negative pulse duration had to be sufficiently but appropriately long, because too long a duration increased the wear of the tool electrode. Even when bipolar pulse voltages were used, similar to the machining of general materials, a shorter positive pulse duration resulted in more precise machining. However, in the case of cemented carbide with low Co and high WC contents, the removal did not progress when a unipolar pulse voltage was applied. On the other hand, the machining progressed when a bipolar voltage was applied. However, if the positive pulse duration was excessively long, the amount of removal decreased. This is believed to be because the longer positive pulse duration increased the amount of WO₃ generated, thereby inhibiting the current flow. Therefore, it is necessary to set an appropriate positive pulse duration to avoid the excessive production of WO₃.

Additive manufacturing (AM) technology is extensively applied in various industries, including manufacturing, and is constantly advancing. Compared with subtractive manufacturing methods such as cutting or grinding, the AM is a cost-effective technique with minimal material wastage, and it can produce intricate shapes within a short timeframe. However, research on AM methods involving additional modeling or printing on the surfaces of three-dimensional objects is insufficient. By employing additive modeling, a diverse range of colors and materials can be utilized without requiring support structures, thereby expanding the possibilities of layering-based expression. This study experimentally investigated additive printing systems using a six-degree-of-freedom parallel mechanism stage and a fixed material extrusion head. A slant direct-drive parallel mechanism for a prototype additive printing system was proposed and designed. The developed prototype system enables additional modeling on curved and spherical surfaces of three-dimensional objects. An experimental surface modeling on these objects was conducted. This paper reports on the performance of the motion mechanism, motion range, and positioning accuracy of the modeling stage. Furthermore, the fabricated models were experimentally examined and validated to assess the results of the modeling process.

Electroporation using microstructured electrodes, which generate a localized high electric field, allows molecules (genes) to be introduced into cells; however, there are some technical issues with the fabrication process and material in terms of cytotoxicity and cost. In this study, polypyrrole (PPy), a biocompatible and conductive polymer, is nano- and micro-structured for an electrode of electroporation by electrochemical polymerization. Nano- and micro-scale dots of PPy are generated by a specific pulse waveform of applied voltage in a considerably low concentration of pyrrole (monomer) solution. The conductivity of PPy is changed from 4 to 16 S/cm by dopant concentration with a range of 0.025 M to 0.2 M. It is demonstrated that electroporation using the PPy and ITO electrodes introduce test agent of molecules (Propidium Iodide) into HeLa cells, where 10 and 50 V of pulse voltage is applied. The electroporation using nano-scale dots of PPy electrodes provides a 40% higher introduction rate than that of the micro-dots of PPy electrodes. The introduction rate in electroporation using the nano-scale dots of PPy can be maintained above 95% regardless of the application time of voltage, whereas that of the micro-scale dots of PPy electrodes increases with the application time. It is reasonable to assume that the nano- and micro-structured PPy electrodes are effective in electroporation, as the introduction rates on these PPy electrodes are higher than that of the ITO electrode. However, the cell viability in the electroporation using the nano-scale of PPy electrodes decreases by approximately 30% with application time. Both the introduction rate and cell viability slightly decrease with the conductivity of the PPy electrode; therefore, they are dominated by surface morphologies of the PPy electrode and applied voltage as compared to that of electrode conductivity. Nevertheless, it is demonstrated that the nano- and micro-structured PPy electrodes improve the efficiency of electroporation owing to the locally concentrated electric field.

Deterioration surveys of large structures such as furnaces have been mainly conducted by visual inspection, but it is desirable to automatically detect deterioration using point clouds captured by the terrestrial laser scanner. In this study, we propose flexible methods for detecting various scales of cracks, delamination, and adhesion on furnace walls by using a machine learning technique. Since small cracks have few geometrical features, they are detected from the reflection intensity images generated by projecting a point cloud onto a two-dimensional plane. For detecting cracks on the image, we use the U-Net fine-tuned by crack images denoised with a median filter. For detecting delamination and adhesion, a wall surface is approximated by a smooth B-spline surface, and deterioration is detected as differences between the point cloud and the approximated surface. However, in this method, the resolution of the B-spline surface has to be carefully determined according to the expected deterioration sizes. To robustly detect deterioration at various scales, we introduce multiscale 3D features, and detect deterioration using both multiscale 3D features and 2D features. In actual walls, it is difficult to distinguish between cracks and delamination because delamination grows from cracks. To detect both types of deterioration in a uniform manner, we combine the two detectors and propose an integrated detector for detecting deterioration at various scales. Our experimental results showed that our methods could stably detect various scales of degradation on furnace walls.

In this study, we developed a method for automatically generating computer-aided design (CAD) models of injection molding dies. The method only required 3D CAD models of products in the Standard Triangulated Language (STL) format as the input information. We also developed a system for automatically generating numerical control (NC) programs by automating the system process planning necessary for machining the injection molding dies. The method generated CAD models of the injection molding dies by dividing the STL files of the products into triangular meshes on a specified split plane. For injection molding dies with several free curved surfaces, we acquired the tool positions of a ball end mill (as approximated by a spherical shape) and flat drill (as approximated by a cylindrical shape) from the geometrical relationships of the triangles constituting the CAD model. We generated a CAD model of an injection molding die using the proposed method with respect to the CAD model of a product shape to verify the validity of the developed system. Then, we machined the product based on the NC programs and tool position. In addition, we injection molded a product with a machined die to mold it into its original product shape.

A simple material contact sensor on the forming tool was devised for sheet hydroforming. The applicability was investigated for the shallow forming of aluminum alloy sheet. A flat bottom axisymmetric die or a conical one was used. An antistatic electric tape was used as contact sensor. It is flexible and attached to the die cavity in the radial direction. Electrical resistance of the tape between the center and the contact position of the material changes as the forming progresses. The change in voltage of the resistance part corresponding to the contact length was captured continuously. The strain at the center of the circular test piece was also continuously measured using a strain gage for large deformation. A short contact length was captured for the flat bottom die, since the test piece deforms into a dome shape, and the tip of the dome contacts to the center of the die cavity. On the other hand, the captured length was longer in the forming with the conical die. The repetitive separation and contact motion of the test piece to the die in impact forming due to the impulsive water pressure was successfully captured by the contact sensor. The accuracy was relatively coarse due to that the diameter of the die cavity was small. However, it was found that the simple contact sensor can be applied to evaluate the deformation behavior of the material. The measured maximum strain of the test piece was larger in impact forming, and the strain concentration occurred. This may be due to the negative strain rate sensitivity of the material.