Silicon carbide (SiC) has been used as a material for semi-conductor, molds, and micro-electro-mechanical systems (MEMS) because of its superior thermal, electrical, and mechanical properties. However, micro machining of SiC is very challenging due to its hardness and brittleness. This paper presents an experimental study of micro hole drilling of SiC. In this study, polycrystalline diamond (PCD) was used as a tool to overcome the hardness of SiC. The micro PCD tool with a diameter of 110 μm was fabricated by micro electrical discharge machining (EDM). Micro drilling was conducted with varying machining parameters such as tool rotational speed and feed rate. Effects of surface roughness of the tool and lubrication method were also investigated.
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In this study, a novel size adjustable robot that could overcome an unstructured environment was introduced. To provide the robot with a volume-modifiable function, negative Poisson’s ratio structure with a unique characteristic about deformation of material was applied to the design of the body frame. The robot could simultaneously adjust its width and length with only one directional control with the help of the negative Poisson’s ratio structure. An omni-directional mobile mechanism was adopted to drive its wheels and allow flexible movement in a narrow space. However, during the procedure to adjust the size of the robot, a slip phenomenon occurred, resulting in an unnecessary movement. To solve this problem, the unnecessary offset was measured through repetitive tests and applied to the robot to compensate the position shift. To verify the performance of the robot, a test bed with a narrow space was fabricated. Extensive experiments were conducted to evaluate environmental recognition and size adjustment function by calculating the width of the narrow space and scaling the robot"s body. Results confirmed that the robot sufficiently achieved the motion objective to move in a narrow space with its size adjustment function.
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Auxetic and Holonomic Mobile Robot for Enhanced Navigation in Constrained Terrains Cheonghwa Lee, Jinwon Kim, Hyeongyeong Jeong, Hyunbin Park, Baeksuk Chu Journal of Field Robotics.2025; 42(8): 4414. CrossRef
The objective of this study was to numerically accomplish the cooling performance of an electric vehicle driving motor depending on cooling channel design. Cooling performances of novel cooling channels were compared based on the temperature of coils and cooling channels as well as convection heat transfer coefficient in electric vehicle driving motors. Local axial positions of cooling channels at three different cases were marked for numerical comparison of heat transfer coefficients. Owing to forced convection by the boundary and flow conditions, the heat transfer coefficient of Case 3 at the location where pin-fins were attached in the cooling channel was improved 85.02 and 65.77% compared to Cases 1 and 2, respectively. In Case 3 with pin-fins having 50% of cooling channel length, the maximum temperature of the coil was 4.25% lower than that of Case 2 with pin-fins having 30% of the cooling channel length and 6.98% lower than that of Case 1 without pin-fins in the cooling channel. As a result, pin-fins finally diminished the maximum temperature of coils in Cases 2 and 3. Ultimately, Case 3 showed the best cooling performance for improving vehicle driving durability and developing next-generation electric vehicle cooling system technologies.
The performance prediction and grain burn-back analysis of rocket motor are important steps in the designing of a solid propellant rocket motor. The grain burn-back analysis of the solid grain identifies the burning surface area at each burning step in order to predict pressure-time history of the rocket motor. In this study, the shape of propellant grains was conveniently designed based on a solid modeling program of conventional purpose and the internal ballistics analysis was performed using a Matlab code which was developed to analyze the grain burn-back for this shape model. Upon carrying several analyses for rocket motors, it was confirmed that the developed code is suitable and useful.
The main function of aircraft ejection system is that it separates the store from the aircraft. The ejection force is important for the safety of the aircraft when the store is ejected, because the store can be lifted by air flow affected by the aircraft’s speed. If the ejection force is low, the aircraft can be damaged by the floating store. The ejection force of the suspension system should be designed in order to release the store safely. In this study, the ejection force of the pyrotechnic suspension using the cartridge to eject the store was researched. This research was performed, based on the precedent study about the over-center linkage mechanism and the pressure drop by the orifice. The ejection force was calculated, after analyzing mathematical fundamentals about the pressure in the system of the suspension and analyzed through AutoDyn and ADAMS software. Finally, the theoretical results were compared with the ejection test results of the suspension system.
The current method of gait analysis has several limitations for determining gait stability, such as a complicated preparation process, repeated experimental procedures that are time-consuming, and financial burden of experiments. This study investigated whether gait stability could be analyzed using only the COM-COP (Center of Mass-Center of Pressure) inclination angle connecting COM and COP. COM and COP coordinates were obtained from a motion analysis system for a total of 40 elderly and young subjects. The COM-COP inclination angle that changed in real time during level walking was then analyzed to obtain gait stability on each of sagittal and frontal planes using these coordinates. As a result, the gait symmetry index on the sagittal plane did not show a statistically significant difference between young and elderly subjects (First Step, p = 0.189; Second Step, p = 0.711). On the frontal plane, elderly subjects showed 0.39 degrees (p = 0.058) and 0.5 degree (p = 0.03) larger side-to-side sway angles in the first and second steps than young subjects, respectively. Gait stability can be analyzed using a more simplified experimental method with minimum amount of data in future gait analysis.
Recently, porous structures of nano/microfibers are receiving great attention because of their excellent mechanical properties, surface area to volume ratio, and permeability. In this study, thick microfiber mats were fabricated using a melt-electrospinning process in a controlled manner. A melt-electrospinning equipment including a three-axis precision motion control with pneumatic dispensing was constructed. The diameter and deposition pattern of melt-electrospun microfibers with respect to the barrel temperature and pressure were investigated. Based on identified effects of process conditions on microfiber geometry, thick microfiber mats with various properties were successfully fabricated using melt-electrospinning with snake scanning and iterative layering. Their mechanical properties and porosities were then compared and analyzed.
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Study of an Electrospinning Process Using Orthogonal Array Trieu Khoa Nguyen, Van-Tho Nguyen International Journal of Precision Engineering and Manufacturing.2024; 25(10): 2153. CrossRef
Recent developments in additive manufacturing (AM) process have led us to fabricate many mechanical and electrical components or devices into complex geometries. Within existing AM processes, laser is widely used as an energy source to selectively sinter particles with a powder bed fusion (PBF) process or cure photopolymers with a vat photopolymerization (VPP) process. This study investigated the applicability of the SLS process for silver nanoparticles (Ag NPs)-photopolymer inks to fabricate micro-scale conductive patterns. With Ag NPs-photopolymer inks prepared with different mixture ratios and pasted on a polyethylene terephthalate (PET) substrate, a pulse width modulation (PWM) signal-controlled 405 nm laser was applied to these inks to selectively sinter and cure the Ag NPs and the photopolymer simultaneously. The final conductive patterns were obtained after a rinse in ethanol to remove un-sintered and un-cured regions of the inks. Microstructures, thickness profiles, pattern width, electrical resistance, and resistivity of the fabricated patterns were investigated by varying the PWM duty and the laser exposure time. Effects of different numbers of scan lines in the pattern and nanoparticle mixture ratios were also investigated. The proposed method is cost effective and easy with fast patterning capabilities. It will leverage practical advances in AM industries.
Due to the pandemic of SARS-CoV-2 (COVID-19) virus, the demand for personal protective equipment (PPE), including face shield, ventilator value, and so on, has abruptly increased in the world. The collapse of the global supply chain of PPE has led to a shortage of the PPE. An additive manufacturing process has emerged as one of solutions to overcome such shortage. The objective of this study was to develop a reusable protective face shield using a material extrusion (ME) process. Five types of face shield were designed. Effects of the design on effective stress distribution, deformation, and specific rigidity were investigated through finite element analyses. To examine the influence of the design on deposition and post-processing characteristics, five types of face shield were fabricated from a ME apparatus. Post-processing characteristics and building time were greatly improved when Design 1 was adopted. In addition, the overall weight, wasted material, and buy-to-fly (BTF) ratio were significantly reduced when Design 1 was applied. Finally, results of wearing and droplet spreading experiments showed that the fabricated face shield for Design 1 was applicable to protection of droplet spreading.
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Investigation of Applicability of Additive Manufacturing Processes to Appropriate Technologies for Developing Countries Dong-Gyu Ahn Academic Society for Appropriate Technology.2021; 7(2): 188. CrossRef
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