CFRP (Carbon Fiber Reinforced Plastic) is a composite material formed using carbon fibers and epoxy resin matrices. It has low productivity and suffers from machining defects during precision machining. Laser machining of CFRP is associated with the problem of heat damage to the epoxy resin. EDM of CFRP can process various shapes with a shaped tool, however it has a lower material removal rate compared to laser, and the non-conductive epoxy resin layer on the surface must be removed before EDM processing. In this study, we have proposed a laser EDM hybrid machining in which CFRP was pre-processed with a laser and then post-processed by EDM. The laser pre-processing conditions were selected by adjusting the laser power and the number of repetitions to minimize thermal damage. According to EDM conditions, the size of the thermal damage area occurring in the epoxy resin, the change in the side gap, and the change in the processing time were investigated. Using the hybrid processing, micro-holes with a diameter of 150 μm were machined, and square-shaped micro-holes were also machined. To improve productivity, a multi-tool capable of processing four square shapes was manufactured, and multi-processing was performed.
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Fabrication of micro holes with confined pitting corrosion by laser and electrochemical machining: Pitting corrosion formation mechanisms and protection method Jian Yang, Yufeng Wang, Yong Yang, Yunfeng Liu, Wenwu Zhang Journal of Materials Processing Technology.2025; 335: 118677. CrossRef
Laser Drilling of Micro-Hole Array on CFRP Using Nanosecond Pulsed Fiber Laser Do Kwan Chung Journal of the Korean Society of Manufacturing Process Engineers.2024; 23(5): 92. CrossRef
Slot-die coating is a method of coating a wide layer of thin film on a substrate. It has the advantages of large-area coating with high reproducibility and uniform thickness. For this reason, it has been widely applied in various industrial manufacturing fields. To secure higher coating uniformity under various coating conditions, estimating and controlling the flow rate of the coating solution discharged to the substrate is crucial. In this study, a practical gravimetric flow rate measurement method for slot-die coating uniformity evaluation has been introduced. The gravimetric method is a technique for accurately and quickly estimating the flow rate through the mass change over time using a precision weighing balance. We analyzed the measurement principle and errors caused by fluid mechanics such as hydrodynamic force or capillary force. The dynamic properties based on fluid viscosity were also evaluated for flow rates from 5 to 50 μL/s. The repeatability of the fabricated measurement system was ~1.5 μL/s. Finally, it was confirmed that the settling time for high-viscosity fluid could be advanced by 56.4% through multi-step feedforward control.
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Precision Measurement and Control of Flow Rate for Coating Uniformity in Variable Slot Die Coating Yeeun Bae, Kyung-Taek Yoon, Hyun-Ho Lee, Moongu Lee, Hyun-Jung Kim, Young-Man Choi Journal of the Korean Society of Manufacturing Technology Engineers.2023; 32(5): 267. CrossRef
Tire-related crashes account for a large proportion of all types of car accidents. The causes of tire-related accidents are inappropriate tire temperature, pressure, and wear. Although temperature and pressure can be monitored easily with TPMS, there exists no system to monitor tire wear regularly. This paper proposes a system that can estimate tire wear using a 3-axis accelerometer attached to the tread inside the tire. This system utilizes axial acceleration, extracts feature from data acquired with the accelerometer and estimates tire wear by feature classification using machine learning. In particular, the proposed tire wear estimation method is designed to estimate tread depth in four types (7, 5.6, 4.2, and 1.4 mm) at speeds of 40, 50, and 60 kmph. Based on the data obtained during several runs on a test track, it has been found that this system can estimate the tread depth with reasonable accuracy.
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A Study on Wheel Member Condition Recognition Using 1D–CNN Jin-Han Lee, Jun-Hee Lee, Chang-Jae Lee, Seung-Lok Lee, Jin-Pyung Kim, Jae-Hoon Jeong Sensors.2023; 23(23): 9501. CrossRef
SFT, which has a high glass fiber content, is one of the effective methods to replace metal and secure weight reduction and price competitiveness. Also, paintless injection molding in which a functional pattern is applied to the mold surface can eliminate the cost of painting. In this study, three types of SFTs were manufactured by adding round glass fibers measuring Φ7 and Φ10 μm and flat glass fiber measuring 27 × 10 μm for the experiment. DOE (Design of Experiment) was conducted to confirm the change in the warpage of the product and the gloss of the micro pattern due to the cross-sectional shape of glass fibers and the major injection conditions. Based on the results, it was identified that the flat SFT had a very small warpage compared to the round SFTs, and the holding pressure was the main factor in the warpage of all three SFTs. The Φ7 μm SFT had the largest gloss value, and the Φ10 μm SFT and the flat SFT had similar average values. All SFTs demonstrated an enormous change in gloss according to the change in mold temperature. The flat SFT had the smallest standard deviation in both warpage and gloss.
Hydrogen production using water electrolysis is generally a well-known phenomenon. Hydrogen produced using the water electrolysis method is an environment-friendly energy source called ‘green hydrogen’ that does not emit any environmental pollutants when using renewable energy as an energy source. This study aims to improve the efficiency of hydrogen production by using the ion transportation effect induced by a rotating magnetic force. For this purpose, the experimental conditions for ion transport were determined through an experiment using a copper wire and the rotating magnetic force for water electrolysis was applied using an alkali aqueous solution. Based on the results, an increase in the number of bubbles generated by the rotating magnetic force increased was observed. It is assumed that the efficiency of hydrogen production using water electrolysis can be improved by the rotating magnetic force.
There have been frequent fatal accidents of firefighters at fire scenes. A firefighting robot can be an alternative to humans at a fire scene to reduce accidents. As a critical function of the firefighting robot, it is mandatory to autonomously detect a fire spot and shoot water. In this research, a deep learning model called YOLOv7 was employed based on thermal images to recognize the shape and temperature information of the fire. Based on the results of the test images, which were not used for learning purposes, a recognition rate of 99% was obtained. To track the recognized fire spot, a 2-DOF pan-tilt actuation system with cameras was developed. By using the developed system, a moving target can be tracked with an error of 5%, and a variable target tracking test by alternately covering two target braziers showed that it takes about 1.5 seconds to track changing targets. Through extinguishment experiments with a water spray mounted on the pan-tilt system, it was observed that the temperature of the brazier dropped from 600 degrees to 13 degrees. Based on the obtained data, the feasibility of a robotic firefighting system using image recognition was confirmed.
A pneumatic tube system is a system that transmits and receives objects quickly inside pipes and is used in urgent situations or when transferring or returning objects. It is mainly used in hospitals, large marts, and automation systems. For long-distance transportation (up to 10 km) high pressure is used at industrial plant industrial sites. A large amount of flow rate and high pressure are used to generate instantaneous pressure and flow to the opposite side, where the transport target is stored in a separately manufactured carrier and transported. Specially manufactured carriers considering significant frictional force in the straight, curved, rising, and lower sections during long-distance transport are employed. The other party experimentally generates reverse pressure to lower the care speed inside the transfer pipe that arrives at a high speed and operates the worker valve to reduce the speed, but the valve must be operated every time according to pressure and distance changes. In the present work, a method of arriving at a carrier in a stable pipe through speed reduction by controlling the flow rate and reverse pressure depending on the distance from the transmission unit and calculating the reverse pressure compared to the teleportation speed is presented.
We have developed a direct conductive patterning method with micro-scale line widths using the laser-induced-forward transfer (LIFT) and liquid metal. As this method does not need post-thermal processing, there is no thermal damage even on heat-sensitive polymer substrates by low-power laser irradiation on the dynamic release layer (DRL). Unlike other liquid metal patterning processes, this procedure can easily achieve fine line widths of a few tens of micrometers corresponding to laser spot size. The solid-state UV pulse laser with 266 nm wavelength and 20 ns pulse duration was used to transfer Eutectic Gallium Indium (EGaIn) liquid metal and the results for the single and multi-pulse laser irradiation were investigated to determine the effective process conditions. The applicability of flexible circuit fabrication and selective circuit repair was successfully tested on Polyimide (PI) substrate. After the LIFT process, the electrical properties of liquid metal on the pattern were measured to be approximately 5~8 x 10-3 Ω/m of resistance.
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Study on Micro Grooving of Tungsten Carbide Using Disk Tool Min Ki Kim, Chan Young Yang, Dae Bo Sim, Ji Hyo Lee, Bo Hyun Kim Journal of the Korean Society for Precision Engineering.2024; 41(2): 123. CrossRef
In the scheduling of assembly lines with human-robot collaboration, variations in workload caused by differences in the available working hours of workers and robots must be minimized. A scheduling method that considers buffers shared by automated guided vehicles and cooperative assembly by multiple workers is proposed herein. In particular, cooperative work requires an assembly schedule that minimizes the make span and satisfies the delivery date, while accounting for the possibility of work partitioning, the number of workers, as well as their available time slots and skills. Hence, it is difficult to obtain an exact optimal solution within a reasonable computation time using existing methods such as mathematical programming. Heuristic or metaheuristic approaches are effective for solving this problem. However, these approaches are not suitable for cooperative assembly by multiple workers. Therefore, a genetic algorithm supported by dispatching rules with four genes is proposed. Computational experiments are conducted based on multiple worker skills. The results showed that when the worker skills are the same, the genetic representation of the job name and part processing order is effective, whereas when the worker skills are different, the genetic representation of the cooperative process with the worker for each operation is effective.
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Development of a Statically Balanced Lifting Device for Repetitively Transporting Construction Materials Byungseo Kwak, Seungbum Lim, Jungwook Suh Journal of the Korean Society for Precision Engineering.2024; 41(12): 929. CrossRef
Stretchability enables the device to be patched to a curved surface or to be folded several times to maximize usability. Among many methods, the pre-strain method is advantageous in that the stretchability as much as the pre-strain applied to the substrate is guaranteed even without material improvement. When the pre-strain is restored to its original state, the thin film gets wrinkled or the substrate gets buckled. Wrinkles and buckling that appear in this way are affected by the physical properties and dimensions of the substrate, and it is necessary to analyze their effect. In this study, a theoretical approach was used and a nonlinear post-buckling analysis was performed using a finite element method. The analysis was divided into two steps: the pre-strain step and the recovery step. According to the analysis results, it was possible to predict and analyze the wrinkle and buckling behavior due to pre-strain according to the physical properties and dimensions of the substrate. The pre-strain analysis method can be applied to multi-layer structures with three or more layers and can be used as a method to analyze wrinkle suppression and wrinkle shape control in future studies.
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