This study numerically obtains the thermal elastohydrodynamic lubrication (TEHL) solutions of different physical-property models of five lubricants and different thermal properties of the solids. The solution was computed at the nominal line contact for both Newtonian and non-Newtonian fluids. The density, viscosity, specific heat, and thermal conductivity were considered functions of temperature and pressure, whereas thermal expansivity was considered a function of pressure. The lubricant models were polyalphaolefin, polyglycol, and three mineral oils with different viscosity grades and the thermal conductivity of the solid materials was set to two different values. The operating parameters were represented by slide-to-roll ratio, load, and speed. The numerical solutions were represented by maximum film temperature and friction coefficient. When the physical and rheological properties of the lubricants were considered individually, the solutions were either over- or underestimated. The thermal conductivity formula model was applicable for calculation. When the physical properties were changed, the non-Newtonian fluids less affected the solutions than the Newtonian fluids, and solids with low thermal conductivity somewhat less affected them than those with high thermal conductivity. The mineral oil with high viscosity grade was sensitive to parameter changes. Overall, the qualitative behaviors of all oil types were almost identical in the lubricant models and solid properties.

This study presents the results of micro-oscillator fabrication using the transfer printing (TP) of gold (Au) thin films and inkjet printing of graphene oxide (GO) nanoparticles. The Au thin films are formed into a double-supported microbeam to function as a micro-oscillator on a polymer substrate. The Au microbeams have a thickness of 300 nm and a length of 250 or 300 μm. To improve adhesion strength between the substrate and the Au thin film, the Au thin film is transferred and printed onto a substrate pre-coated with a 30-nm-thick Au surface via atomic diffusion bonding. Furthermore, GO nanoparticles are deposited on the transfer-printed Au thin film and the convex part of the stamp using inkjet printing to enhance the mechanical properties of the micro-oscillator. The former deposition forms a double-layered beam of Au and GO. The Au/GO/Au-layered microbeam is fabricated on a pre-structured substrate by TP after another Au thin film is then deposited on this GO/Au surface. These micro-oscillators can be driven by electrostatic force at less than 10 kHz with 90–210 V of applied voltage, while the deflection of the micro-oscillator is measured by a laser displacement meter. The Au micro-oscillators have a damping ratio of 0.166, and a resonance frequency of 0.28 kHz. This resonance frequency is smaller than that estimated by finite element method analysis. This difference in resonance frequency is attributed to the Young's modulus of the Au thin film and structural defects due to van der Waal bonding. The modulus of the laminated thin film of Au and GO nanoparticles is higher than that of the Au thin film.

The contact between a tool and workpiece during machining has a significant effect on the vibration characteristics of machine tools. This study proposes a method for detecting contact between a tool and workpiece, and demonstrates applications of the detection. To detect the contact between the tool and workpiece, this study used the change in the contact electrical resistance in a metal-to-metal contact corresponding to the true contact area. The contact resistance between the tool and workpiece was connected in series with a buffer resistance, and the degree of separation was defined based on the change in the ratio of a voltage applied to the circuit under a constant current flow. Two types of applications were demonstrated in this study; one was an analysis of the influences of the contact state on the vibration characteristics, and the other was contact detection during milling operations. In the first demonstration, a contacting ratio was defined based on the contact time per unit time and degree of separation based on the tool-workpiece contact as detected during an excitation test, and the relationship between the contacting ratio and vibration characteristics was examined. It was confirmed that the natural frequency increases significantly when the contacting ratio exceeds 90%, and that the damping characteristics increase significantly when the contacting ratio is in the range of 0–10%. For the second demonstration, a milling test using a face mill with the same detection circuit confirmed that the system could detect contact during intermittent cutting and the changes in contact conditions associated with the occurrence of chattering vibration. It is expected that the developed method can be used to monitor machining conditions.

Compliant mechanism is a functional mechanism achieved by elastic deformation, which is expected to reduce the number of mechanical parts or assembly costs. Additive manufacturing using fiber-reinforced polymers (FRP-AM) is easy to fabricate a complex structure using materials with different elasticities. FRP-AM has an advantage in changing mechanical properties partially in fabricated structure. This is suitable for design of compliant mechanisms. For FRP-AM fabrication, it is necessary to consider the path continuity of fiber-reinforced materials. However, the conventional structural optimization method has difficulty in considering the fiber path continuity. The purpose of this study is to propose a simultaneous optimization of the structure and the continuous fiber path for compliant mechanism fabricated with FRP-AM. In the proposed method, by representing the target structure as a two-dimensional graph, the continuity of the fiber path is dealt with efficiently. Then, the graph is encoded into a binary tree, and genetic programming is adopted in the optimization process to obtain the structure that achieves the desired deformation. A case study was conducted to evaluate the proposed method. The compliant mechanism design of a robot end-effector, which initially consists of 9 walls with certain length, was optimized to achieve the target deformation, which finally consists of 18 walls with different length. The resulted FRP structures have continuous fiber paths. The deformation error against the target value was under 1% in FEM simulation. In addition, the optimized structure was fabricated. From the experiment on its deformation, the deformation error was about 20%. It was because the optimized structure deforms mainly due to bending of walls, which the simple approximation element is difficult to handle precisely. In addition, the gripping test was conducted, it was confirmed that the proposed optimization method is useful for design optimization of compliant mechanism fabrication with FRP-AM.

Bending angle obtained in laser forming process is much smaller than that in conventional die pressing or roller bending processes. Therefore, multi-stage forming is necessary to form deep drawn shapes and/or complex shapes by laser forming. However, laser irradiation varies material properties, posture, and stiffness of metal plates, and those influences are accumulated during the consecutive stages of process. Thus, thermo-elasto-plastic deformation models in theoretical analysis cannot predict the final shape precisely. Regarding this problem, authors propose a laser forming simulator, which employs the artificial neural network to correlate the process parameters and the deformation of metal plates, in this study. Teaching data for machine learning of the neural network is collected through the multi-stage laser bending experiments with stainless-steel plates and a high-power diode laser. The trained network is used to simulate the plate deformation to demonstrate the feasibility of proposed method. And the influences of network structure on machine learning are investigated, and the influences of conditions are discussed in aspect of prediction accuracy. Trained neural network acquired a relationship between the irradiating conditions and the deformation of plates, and work as a simulator to predict the shape of plates formed by consecutive bent at laser scanning paths. Prediction accuracy of the simulator was same as the accuracy of shape obtained by laser bending experiments.

In machining of rolled titanium alloy, the anisotropy in the cutting force induced by the rolling texture should be controlled to achieve high quality surface. The cutting tests on the normal direction (ND) plane of a rolled titanium alloy plate are conducted with changing the cutting direction with respect to the rolling direction. The deformation and the cutting force in micro cutting are discussed compared to those in cutting of single crystal titanium. Although the anisotropic effect on the cutting process is smaller than that of the single crystal workpiece, little deformation occurs around the boundary between the groove and the unmachined surface when cutting along the rolling direction. The material behavior is characterized by the shear plane cutting model. The shear angle and the shear stress on the shear plane depend on the cutting direction for the rolling direction.

The application of a cyber physical system (CPS) in a production system to improve the efficiency and effectiveness of its operation is called a cyber physical production system (CPPS). A digital twin (DT) is widely regarded as a cornerstone for the realization of CPPS, and many tools, methods and guidelines for developing DT have been proposed in recent years. However, DT alone is not sufficient for solving practical problems that occur in actual production systems (e.g., frequent rescheduling caused by unpredictable events, such as machine failure or engineering changes). Because DT is a digital representation of a physical object, it cannot individually provide a problem-solving procedure for unpredicted situations. Therefore, the integrated utilization of human experts’ knowledge with DT is indispensable for the realization of CPPS. This paper proposes a systematic method for acquiring experts’ knowledge that can be integrated with a DT to construct a production system that is robust against unpredicted changes in a production environment. In particular, the study focuses on the knowledge acquisition for the high-mix and low-volume production scheduling problem. This is because quick modification of the existing schedule considering complicated constraints among processes, resources, delivery time and so forth is regarded as a typical problem that only human experts can solve. Through a case study in the die machining industry, this study demonstrates the validity and limitations of the method and concludes that the proposed method is effective for acquiring experts’ knowledge.

Micro Raman tomographic imaging (mRTI) is an excellent measurement technique that can nondestructively measure and image the fracture state of the crystal lattice inside materials with a high spatial resolution. mRTI has been successfully used for translucent materials such as wide bandgap semiconductor wafers. The applicability of this measurement method was evaluated by observing the wear damage in polycrystalline industrial ceramics materials. The influence of optical diffusion on the surface and inside of polycrystalline materials is a concern for the internal measurements by the optical beam. The quality degradation of spectral signals due to disturbances in the optical beam was confirmed by mRTI measurements on a commercial alumina plate. The application of surface polishing treatment was attempted to reduce the influence of surface optical diffusion. Three kinds of the surfaces were observed by mRTI, as the initial surface of the alumina plate, polished with #400 and #800 diamond abrasive lapping film, respectively. It was confirmed that the effective measurement depth range can be extended by reducing the surface roughness. However, we confirmed that excessive surface polishing may overwrite the damage on the measurement surface, making it difficult to observe the original damage.

Precision flat surfaces are required for the precision surface plates of measurement instruments and the sliding components of precision machine tools. Precision flat surfaces measuring several tens of millimeters square or more are often created via hand-scraping, which is a hand-finished work. Since a hand-scraped surface is rough, the surface form cannot be measured easily using a typical vertical incident interferometer. An oblique-incident interferometer based on Abramson interferometry has been developed previously for the surface form measurement of hand-scraped surfaces. However, the field of view of the developed oblique-incident interferometer is limited to dozens of millimeters square owing to the size of the optical components and imaging sensor; consequently, the field of view is smaller than the size of the entire hand-scraped surface. A stitching method is introduced herein to expand the size of measuring area of the oblique-incident interferometer. The surface forms of a hand-scraped surface with a partially overlapped area are obtained using an oblique-incident interferometer, and the discrepancies of the inclination and height offset between the surface form data are corrected to calculate the synthetic surface form. Pattern matching is performed when aligning the overlapping area, which reduces the alignment error of the optical system. The effectiveness of the stitching method for the oblique incident interferometer is evaluated based on the cross-correlation coefficient between the datum and corrected profiles.

Directed energy deposition (DED), a metal additive manufacturing process, has attracted considerable attention in various industries. In the past few decades, several studies have been conducted to enhance the quality of DED-produced parts. Various studies on powder- and laser-based DED have focused on eliminating the residual pores in the fabricated parts, which decrease the mechanical strength. In contrast, this study aims at intentionally increasing the residual pores to produce a porous structure in metals called as foam metal, which realizes lightweight and excellent energy absorption properties. Despite being well-known for their attractive properties, Foam metals are rarely used due to the technical difficulties in their production, which requires special devices and entails considerable cost. The simplicity of the DED process makes it a promising approach to fabricate foam metals because it is easy to foam at the fabrication point by mixing a foaming agent, such as titanium hydride (TiH₂), into the material powder. This study evaluates the DED foaming process in stainless steel alloys by changing the particle size of the TiH₂ powder and the scanning path to obtain the optimal conditions for enhancing the pore dispersion. The experimental results show that, when the particle size of the foaming agent is small, the number of pores and their distribution increases. Additionally, the mechanical properties are also evaluated through compression experiments, and the energy absorption ratio is found to be higher when a smaller foaming agent is used.

Fast tool servo (FTS) in ultra-precision diamond turning is an efficient technique for high-precision fabrication of freeform optics. However, the currently adopted constant scheme for control point sampling takes no account of the shape variation of the desired surface, which might lose some micro features and result in low form accuracy and non-uniform surface quality. Facing this issue, this manuscript proposes a novel adaptive control points sampling strategy, which improves the form accuracy and keeps as many as the micro surface features. In the optimization method, the sampling stepovers between two adjacent control points are actively adjusted to adapt to the surface profile variation. By adopting this method, the control point sampling induced interpolation error is constrained within the desired tolerance and eliminates the lack/over-definition of control points in the machining area. The feasibility of the proposed optimization method is demonstrated by both theoretical simulations and fabrication experiments of sinusoid freeform surfaces. Compared with the constant sampling method, both the theoretical predicted and experimental measured form error of the proposed method is remarkably reduced by about 35 % with the same amount of control points. This technique provides a new route to allocating control points in FTS diamond turning to achieve high form accuracy and machining efficiency in the fabrication of freeform optics.

This paper is concerned with performing job shop scheduling considering discrete uncertainty based on proactive approach. In production of large products, there often are cases where a work-in-process needs to undergo a reworking or a reprocessing depending on the result of an inspection process. Generally speaking, it is natural to cope with this type of uncertainty based on reactive approach, since it is discrete and makes a drastic change on the original production scenario. However, this may result in an unsatisfactory schedule which requires unreasonable overtime works or fails to keep due dates, etc., because the initial schedule is generated without considering the uncertainty and is updated considering only the information that is certain at the time of updating it. For this reason, we developed the following method based on proactive approach: (i) a set of consistent schedules each of which corresponds to a production scenario determined by an inspection result is generated by using genetic algorithm so that the weighted sum of overtime work, tardiness and makespan or earliness is minimized; (ii) the production starts based on the initial schedule that corresponds to the scenario in which no reworkings/reprocessings are necessary, and then the schedule is switched by the one which corresponds to the new scenario each time when it turns out that a reworking/reprocessing needs to be carried out. Comparison to reactive scheduling approach using numerical examples showed effectiveness of the proposed method.

Titanium alloy is widely used in different industrial applications. For the surface modification to improve the tribological properties, laser irradiation is a promising technology, which offers high efficiency, and high automation potential and geometrical flexibility. In this study, a novel method of surface modification for titanium alloys by carbonization using low fluence of laser irradiation in the atmosphere of PAO oil is proposed. Results show that the carbon content on the surfaces significantly increases with the laser shot number, with the laser irradiated spot showing little change of Ra. XPS analysis confirms that the carbon from the oil has bonded to the Titanium inside the alloy. By comparison with that irradiated without oil, the hardness of that irradiated in oil is much higher, demonstrating the feasibility of the surface modification of titanium carbide layer generation. To investigate the tribological properties, laser scanning irradiation in oil with different laser pulses were carried out to create laser modified areas and reciprocating ball-on-disk friction tests under oil lubrication were conducted. The laser modified areas show friction of 0.13, much lower than that of the unirradiated which is approximate 0.55, and the sliding lifetime of low friction is also increased with the laser pulse number. Moreover, by introducing patterning laser irradiation onto the uniformly irradiated area, the wear resistance can be further greatly improved, and the sliding lifetime can extend to 13 times of the optimal result of uniform irradiation.

Selective laser melting (SLM) is one of the additive manufacturing (AM) methods which is applicable to metal. This technique makes it possible to form complex internal shapes such as lattice structures. The lattice structure is expected to have weight reduction and vibration suppression effects on the product. In addition, a support structure is essential for the SLM fabrication process, which has the role of supporting the product and dissipating heat from the product. However, steep temperature gradients due to local laser irradiation and non-uniform heat conduction during the process can cause bending and cracking of the product. In particular, the support structure and lattice structure consisting of thin metal struts are greatly affected by process conditions, so it is necessary to select conditions suitable for stable and high-precision modeling. In this study, the influence of laser power and scanning speed on the mechanical characteristics of the support structure and lattice structure formed by SLM is investigated. In the tensile test of the support structure, a positive correlation with the volumetric energy density was confirmed, and suitable laser conditions were examined. In the compression test of the lattice structure, it was clear that the amount of energy absorption changed depending on the laser power, and the condition of 240 W achieved the maximum energy absorption.