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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.

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.

Ultrasonic abrasive machining is a machining method in which an ultrasonically-vibrated tool presses the workpiece via free abrasive grains and induces hammering motion of free abrasives. This machining technique is especially applicable to hard-and-brittle materials such as ceramic matrix composites and sufficient machining speed is practically achieved by performing micro-brittle fractures tens of thousands of times per second. Nevertheless, there are few studies that quantitatively evaluate the parameters of this machining method and their interactions. The problem is that this machining process is conducted manually and the machining conditions are determined by the experience of an operator. Hence, derivation of conditions to improve machining efficiency is required. In this study, the factor effects and their interactions among machining pressure, oscillator power and slurry flow, which are the typical parameters of ultrasonic abrasive machining, were evaluated by analysis of variance and the related experiments in monolithic SiC. As a result of analysis of variance and the related experiments, it was shown that the combination of machining pressure of 135 g/mm2, oscillator power of 100 W and slurry flow of 2500 mL/min remarkably improves the machining efficiency in monolithic SiC. It was also clarified that there are significant interactions between the machining pressure and the oscillator power and between the machining pressure and the slurry flow, respectively.

New energy saving methods are required to address global climate change and resource depletion. New structural materials such as Carbon fiber reinforced plastic (CFRP) are used also in nowadays machine tools applications for energy efficiency improvement by weight reduction. This research group succeed in being the first to develop the energy-saving machine tool using new structural materials, mainly CFRP. Furthermore, CFRP is expected to enhance thermal characteristics, which contributes to reduction of warm up drive and implement of idle reduction. First of all, the thermal deformation of the energy-saving machine tool is investigated through single axis feed motion by measuring a test bar. It is obtained that the thermal error is obviously suppressed and shows unique behavior in comparison with a based conventional machine tool. Next, the energy-saving performance is evaluated through machining test. Warm up drive minimization method is proposed in order to realize high precision form accuracy. The warm up drive time is estimated based on an estimation model, and the energy efficiency of warm up drive is improved 57.0% in comparison with the base machine.

This research has been conducted to develop computer aided manufacturing software, which can generate NC programs for a five-axis directed energy deposition (DED) type additive manufacturing system with following three focuses: 1. How to maintain consistent formation of a melt pool on the surface of the workpiece. 2. How to generate three-dimensional deposition path efficiently when a 3D part model is given. 3. How to control process parameters during additive operation. For focus 1, the work orientation has been controlled such that the surface to be deposited can remain perpendicular to the nozzle which is fixed to gravity direction and minimize distortion of the laser spot and powder distortion on the workpiece surface. For focus 2, a unique path generation method has been proposed based on the reverse play of a subtractive machining path, which removes the entire part to the null. For focus 3, preoperative process parameters control has been introduced to achieve the specified volumetric deposition rates along the additive tool path, which is equated with the material removal rates along the subtractive machining tool path. With methods mentioned above, the dedicated CAM system, CAMAM, has been prototyped and its feasibility has been verified experimentally by applying the NC program generation strategies to deposit several parts.

Electoadhesive (EA) gel can be applied to various mechatronics devices because it provides more degrees of freedom in mechanical design than other functional materials. While case studies have revealed much about these devices, the knowledge attained is still not integrated. We assembled new structured and controllable transmission and braking elements by fixing EA gel on plain and/or winding surfaces. This paper summarizes the characteristics of these devices from experimental findings on the initial pressure on the EA gel surface. The results showed that it is important for the initial pressure to be stable at approximately 0.5–1 kPa.

Single-crystal sapphire is utilized as a high-performance engineering material, especially in extreme and harsh environments. However, due to its extreme hardness and brittleness, the machinability of sapphire is still a challenge. By means of nanoindentation and plunge-cut experiments, the anisotropic brittle-ductile transition of the prismatic M-plane and rhombohedral R-plane is examined by analyzing crack morphologies and the critical depth-of-cut (CDC). The experimental results of the nanoindentation tests are correlated to the plunge-cut experiment. Both the prism plane and the rhombohedral crystal plane exhibit a two-fold symmetry of ductility with various crack patterns along the machined grooves. The direction-dependent plasticity of the hexagonal sapphire crystal is mainly connected to a twinning process accompanied by slip dislocation. Keywords: Sapphire, Anisotropy, Brittle-ductile transition, Orthogonal cutting

Directed Energy Deposition (DED), which is one of the Additive Manufacturing (AM) processes, can deposit metallic production efficiently by irradiating a high-power laser beam on a baseplate and supplying material powder simultaneously. DED has a problem in low mechanical strength due to residual pore inside of the production. However, the residual pore is also available to fabricate low density production as an opponent idea. If the residual pore could be increased intentionally and drastically, DED is applicable to foam metal fabrication. Foam metal could be produced continuously with high degree of freedom in shaping, if melt-pool can be foamed in DED. Therefore, this paper proposes a simple fabrication method for foam stainless alloy with DED by applying titanium hydride (TiH2) as a foaming agent for melt pool. TiH2 releases hydrogen in a high temperature environment as more than 500℃. Considering that high viscosity and low surface tension are required to stabilize pore generation, material powder also should contain a thickening agent (CaO: calcium oxide) and a surface active agent (Te: tellurium). According to the experimental results, an effect of CaO was hardly observed because the liquid stainless may already have high viscosity enough. On the other hand, Te certainly reduced the critical film thickness and prevented the pore collapse in stainless foam fabrication, according to the porosity rate calculation, the observation with a high speed camera, and the elemental distribution analysis. Furthermore, the proposed method successfully produced a foam structure in stainless steel with high porosity rate as 61% at maximum.

Directed Energy Deposition (DED) of metal materials has been widely studied with Inconel 718 using in aerospace industry. Void generation in a deposited part causes deterioration of the mechanical strength. Hence, void should be avoided in the DED process. In this study, a mechanism of void generation was investigated through the dynamic observation by high-speed camera, the thermal observation and the evaluation of the porosity. The experimental result shows that solidification time has an influence on the void generation.

Direct energy deposition attracts attention from automobile and aerospace industries because of its applicability to complex shape production. Although the meltpool temperature has to be controlled to enhance shape accuracy, industries remain hesitant over introducing a complex process monitoring system because of high cost and necessity of frequent maintenance. In order to keep the meltpool temperature constant, this paper proposes optimal laser power command generation by creating a finite-element thermal conductivity model for a gradient descent calculation. The experimental results clearly indicate that the obtained laser power command enhances the shape accuracy of the deposited objects.

Error factors in sensorless cutting force estimation under ball-screw-driven stage were discussed. In addition, their influence on estimation accuracy was experimentally evaluated through several end milling tests. Because rigid body-based formulation is difficult in ball-screw-driven stage, estimation principle of cutting force needs to be formulated considering interaction between rotation and translation to enhance estimation accuracy of the cutting force. Simulation results revealed that phase lag element between current and position/angle response was non-negligible in higher frequencies as well as measurement error of acceleration due to numerical differential. Therefore, both phase lag compensation and high-resolution encoders are necessary. Fluctuations of disturbance force and acceleration synchronizing rotation of servomotor were classified in terms of their period: comparatively low-frequency fluctuations ranging from submillimeter to millimeter resulting from mechanical elements; high-frequency fluctuations with period of several micrometers resulting from interpolation error of encoder signal. The former can be eliminated more effectively than the latter, because preliminary identification is possible based on position dependency and repeatability. On the other hand, the latter needs to be eliminated by signal processing, because preliminary identification including phase is difficult. The result of milling tests revealed that it was possible to enhance estimation accuracy of the cutting force by constructing estimation system considering the above error factors.

We fabricated a calcium fluoride (CaF2) whispering gallery mode (WGM) microcavity with a computer controlled ultra-precision cutting process. We observed a thermo-opto-mechanical (TOM) oscillation in the CaF2 WGM microcavity, which may influence the stability of the optical output when the cavity is employed for Kerr comb generation. We studied experimentally and numerically the mechanism of the TOM oscillation and showed that it is strongly dependent on cavity diameter. In addition, our numerical study suggests that a microcavity structure fabricated with a hybrid material (i.e. CaF2 and silicon), which is compatible with an ultra-high Q and high thermal conductivity, will allow us to reduce the TOM oscillation and stabilize the optical output.

Polydimethylsiloxane (PDMS) is difficult to machine by conventional cutting process because of its low elasticity and high adhesion. We proposed the cryogenic micromachining method assisted by liquid nitrogen cooling for direct fabrication of 3D micro channels on PDMS substrate in short time. In this paper, the cryogenic cutting mechanism is clarified through some verification experiments. Moreover, Pre-Deformation-assisted Cryogenic Micromachining (PDCM) method is also proposed for fabricating the unique shapes of channels and its validity is evaluated experimentally. The results of cutting tests show that 3D unique micro channels can be processed precisely and rapidly on PDMS.

Intelligent machine tools require the functions of high-accurate process monitoring and adaptive control to fit the optimum process condition in each workpieces. For realizing these functions, the various techniques to monitor the cutting process and control it using additional sensors have been proposed and widely studied. Authors propose the sensorless cutting force control method using parallel disturbance observer. The performance of our proposed method is evaluated through simulation and experiments using a linear motor driving table.

Semiconductor process technology increasingly requires high accuracy and efficiency. In the case of processing thin fragile substrate such as silicon wafer, it has to be fixed with low strain. In addition, its fixture device can be used under vacuum condition because some processes are carried out in vacuum. It is required to develop a new fixture device for vacuum transportation of silicon wafer. ERG is the functional material whose friction characteristic varies according to the intensity of applied electric field. The surface friction of ERG can be changed quickly and reversibly applying the electric field. In other words, it becomes easy to fix and release a substrate by control of electric field. In this study, ERG is applied to a fixture element of silicon wafer available for vacuum process. The ERG fixture element was trial-manufactured and its performance under vacuum condition was evaluated experimentally. The result shows that the ERG effect emerges in vacuum and ERG can fix silicon wafer sufficiently. Moreover, numerical analysis of electric filed was carried out to obtain the optimal pattern of the one-sided electrodes used for the ERG fixture element. It is clear that the optimal width of electrodes exists according to the gap of electrodes and the thickness of ERG.

Polydimethylsiloxane (PDMS) is one of the important materials for microfluidic chips. The pattern of micro channels on the PDMS plate is usually fabricated through the photolithography and micro molding process. However, the photolithographic method requires multi chemical and mechanical processes and resultant long process time. The micro milling process is a feasible method for rapid fabrication of various patterns of micro channels. However, micromachining has not yet been applied to soft polymer materials. It is difficult to machine elastic materials such as PDMS because of their low toughness. In order to machine a micro grooves on soft polymer materials, the cutting process applying cryogenic cooling is proposed because the elastic properties of soft polymer materials remarkably change from rubbery state to glassy state below the glass transition temperature. In this study, the freezing milling method using liquid nitrogen is applied to the micro grooving of PDMS. The result of a cutting test shows that micro grooves can be shaped easily and machined accurately in PDMS by the proposed method.

The linear motor driving mechanism has been adopted as a positioning mechanism of machine tools to realize high speed and precise positioning because of friction-free and no backlash. However, when two or more linear motors are used, minute differences between the thrust forces of each motor causes the generation of micro vibration and the change of velocity of each linear motor generated by yawing around the center of gravity. This study proposes interaction-mode-control method for the machine tool table driven by three linear motors to control the three modes defined as the position of the center of gravity, bending and yawing independently. The interaction-mode-control method is a new technique for applying interaction modes defined according to the workspace to the real control system through modal conversion. From the results of simulation and experiments, it is confirmed that the three modes are controlled independently and, therefore, bending and yawing can be suppressed using interaction-mode-control. Moreover, to combine the interaction-mode-control method with disturbance observer and feedforward control, this control system has high robustness and precise positioning can be realized.

Electro-rheological gel (ERG) is a new functional material whose surface friction and adhesive properties vary according to the intensity of the applied electric field. In a recent study, one-sided patterned electrodes were applied to the ERG and the change in surface frictional and adhesive property under the electric field, which is called the ERG effect, was experimentally confirmed. The ERG with one-sided patterned electrodes is considered to be suitable for application to a fixture device for micro milling. In this study, a prototype of the ERG fixture device was developed and its performance was experimentally investigated. The proposed ERG fixture devices can be useful for fixturing both metallic and nonmetallic workpieces, such as glass. Micro shrinkage of the ERG occurs in proportion to the voltage applied to the ERG material. Using this characteristic, the alignment of the workpiece can be also adjusted. The developed ERG fixture device was applied to the micro grooving process of a thin glass workpiece, and successful results were obtained.

Chatter vibration must be avoided to ensure the cutting accuracy in milling. Several studies have proposed analytical prediction methods for chatter stability based on a frequency-domain milling model and a modal analysis. However, the prediction accuracy is difficult to enhance because the modal parameters vary according to the spindle rotation and heat generation. In addition, necessity of special measurement devices for the modal analysis leads to high cost and complicated operations overwhelming the operator. In this paper, we propose a novel analytical method for identifying stable spindle rotations against chatter vibration in milling, which only requires once milling test without any measurement devices. Chatter frequency gradually gets larger with higher spindle rotation and drastically shifts at the stable spindle rotation, at which the locally largest depth of cut can be applied. Based on this characteristic of chatter frequency, the stable spindle rotations can be captured only from the servo information by decreasing spindle rotation continuously and observing frequency shifts with disturbance observer in the spindle control system. The disturbance observer is a technique to estimate the load torque only from the servo information, which is utilizable to monitor a fluctuation in cutting torque due to chatter. By applying time-frequency analysis to the estimated cutting torque, the drastic shift of chatter frequency can be captured. The experimental results show that the chatter frequency shift can be clearly captured at stable spindle rotations by applying a time-frequency domain analysis on the estimated disturbance torque.

This paper deals with axial ultrasonic vibration-assisted machining with workpiece bending. It was proposed as a novel machining method for the reduction of the chippings at the machined holes during micro through-hole drilling of chemically strengthened glass. In micro through-hole drilling of chemically strengthened glass, machining accuracy and efficiency tend to be low because the material's high hardness and brittleness cause rapid tool wear and large chippings at the inlet and outlet of the machined holes. In order to machine small holes with high accuracy, the reduction of the tensile stress that causes large chippings at the outlet of the machined holes is an issue of primary importance that deserves investigation. In the proposed machining method, the glass plate is bent slightly to be convex upward through the application of a compressive stress at the posterior surface of chemically strengthened glass, with a specially designed jig. Using this proposed method that can reduce the tensile stress, the chipping size at the outlet of the machined holes was successfully reduced with applied compressive stress values of 38.9 MPa. In conclusion, it has been clear that the axial ultrasonic vibration-assisted machining with workpiece bending has the potential for achieving high-precision and high-efficiency machining for chemically strengthened glass.