Journal of the Korean Society for Precision Engineering

Development of CNN-LSTM Based Surface Roughness Prediction Model in Feature Machining Process of Ti-6Al-4V for Aerospace Components: Su In Choi, Joo Sung Yoon; J. Korean Soc. Precis. Eng. 2026;43(8):845-851.
Published online August 1, 2026; DOI: https://doi.org/10.7736/JKSPE.026.00032

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Ti-6Al-4V titanium alloy is widely utilized in aerospace components, such as torque tubes and turbine blades, due to its outstanding strength-to-weight ratio and corrosion resistance. However, controlling surface roughness during machining is challenging because the alloy's low thermal conductivity and high chemical reactivity result in unpredictable variations in Ra. Traditional contact-based measurement methods are not only time-consuming but also incompatible with in-process monitoring, creating a disconnect between production and quality control. This study introduces a CNN-LSTM hybrid model for predicting surface roughness in Ti-6Al-4V shape machining, utilizing multi-sensor CNC data. The model effectively captures spatial correlations among nine sensors and temporal dependencies in sequential operations. We implement a stratified time-series split validation that maintains chronological order while ensuring a representative distribution of Ra values, reflecting realistic deployment conditions. Data were collected from machining tests on features of a torque tube part, comprising 4,154 samples with Ra values ranging from 0.57 to 0.74 μm. The CNN-LSTM model achieved R² = 0.8512, RMSE = 0.0199 μm, and MAE = 0.0096 μm, outperforming Random Forest, XGBoost, and standalone neural networks. These results demonstrate the feasibility of non-contact, in-process surface roughness prediction in aerospace manufacturing, facilitating proactive quality control without interrupting operations.

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Performance Enhancement of Polymer Electrolyte Membrane Fuel Cells Using Porous Inserts in Flow Channels: Dongjin Kim, Jaejoong Kim, Geon Go, Suhyun Min, Seungwoo Lee, Taehyun Park; J. Korean Soc. Precis. Eng. 2026;43(7):787-793.
Published online July 1, 2026; DOI: https://doi.org/10.7736/JKSPE.026.00002

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This study proposes a novel flow-field design strategy that incorporates porous inserts into the bipolar plate (BP) flow channels to address flooding and improve the performance of polymer electrolyte membrane fuel cells (PEMFCs). The BPs were fabricated by maintaining the traditional flow-field structure while varying the number and arrangement of melamine foam inserts, with the electrochemical performance changes analyzed comparatively. The findings revealed that the configuration featuring five porous inserts achieved the highest performance enhancement, with a peak power density increase of approximately 13.4% compared to the conventional cell. This improvement is attributed to localized pressure gradients created by the porous inserts, which facilitated transverse gas transport toward the gas diffusion layer and reduced flooding in the flow channels. However, excessive insertion resulted in increased flow resistance and mass transport limitations, leading to performance degradation. The study also confirmed the impact of insert arrangement on PEMFC performance. Overall, the introduction of porous inserts into BP flow channels, without the need for additional machining processes, offers an effective method for managing water and gas transport in PEMFCs, providing valuable insights for flow-field optimization and the development of high-performance fuel cell systems.

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Ethanol Concentration Measurement and Classification Using Near-infrared Spectroscopy and a Random Forest Model: Min Seok Park, Ye Chan Cho, Min Seok Jeong, Jae-Hoon Jun; J. Korean Soc. Precis. Eng. 2026;43(5):499-504.
Published online May 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.118

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Ethanol poses a significant threat to driver safety, as its effects vary with blood alcohol concentration (BAC). Common methods for estimating BAC include breath alcohol analysis, which calculates BAC from the alcohol concentration in exhaled breath, and direct blood sampling. However, these methods have notable limitations. This study aims to classify alcohol concentration using non-invasive optical signal data obtained from biomimetic samples with varying alcohol levels. To replicate the high scattering characteristics of biological tissue, scattering effects were induced in the samples, and absorbance was measured using near-infrared (NIR) wavelengths, which penetrate biological tissue more deeply. A Random Forest (RF) model was trained using the measured absorbance values to classify alcohol concentration levels. The Area Under the ROC Curve (AUC) for each concentration level indicated effective model learning, and the classification results on the test set demonstrated statistically significant accuracy. These findings suggest that the RF model can classify alcohol concentrations non-invasively and without the loss of samples. Furthermore, incorporating additional optical properties beyond absorbance may improve the accuracy of future non-invasive alcohol concentration classification models.

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Functional Grid Patterning on Silicon Substrates via Femtosecond Laser Processing for Physically Enhanced Raman Spectroscopy of Polystyrene Particles: Sang Seon Lee, Jae Cheol Park; J. Korean Soc. Precis. Eng. 2026;43(3):307-313.
Published online March 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.128

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The practical application of Raman spectroscopy is often constrained by its low signal sensitivity, particularly for low-concentration liquid samples. This study introduces a straightforward platform that enhances Raman signals by physically concentrating analytes, providing an alternative to complex substrate fabrication and chemical treatments. We employed a femtosecond pulse laser to create functional micro-grid patterns on a silicon (Si) substrate. This laser process induces localized ablation and simultaneous oxidation, resulting in three-dimensional, hydrophilic microstructures of nonstoichiometric silicon oxide (SiO_2-x). These grid structures effectively confine aqueous sample droplets through a pinning effect, functioning as a microwell array that traps and concentrates suspended polystyrene (PS) particles. This physical concentration mechanism achieved a notable signal enhancement, with a maximum factor of 5.2 for PS particles, without the need for sample dehydration. This work presents a simple, cost-effective, and highly reproducible alternative to conventional SERS for analyzing low-concentration liquid samples, demonstrating strong potential for integration into microfluidic systems.

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Experimental Study on Porosity Behavior during DED Additive Manufacturing of S45C/H13 Dissimilar Metals: Si Heon Lee, Ha Jin Choi, Min Woo Yeon, Hyun Na Kim, Sae Hun Jeong, Chul Kyu Jin, Do Young Kim; J. Korean Soc. Precis. Eng. 2026;43(3):231-236.
Published online March 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.00027

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This study examines the porosity behavior during the directed energy deposition (DED) of dissimilar metals S45C and H13. We analyzed the effects of deposition parameters, including laser power, feed rate, and powder characteristics, on pore formation, taking into account the unique properties of these metals. Our findings indicate that laser power is the primary factor influencing porosity. At a low power of 200 W, insufficient energy input, along with differences in thermal conductivity and chemical composition between S45C and H13, led to incomplete melting and lack-of-fusion, resulting in high porosity. As the laser power increased to 400-600 W, the melt pool stabilized, enhancing interfacial bonding and significantly reducing porosity. However, at an excessive power of 800 W, rapid melting and solidification of the powder caused gas entrapment and pore formation, which increased porosity, particularly due to the differing thermal conductivities of S45C and H13. Therefore, our results suggest that maintaining an adequate laser power of 400-600 W is essential for achieving a stable melt pool and minimizing porosity in the DED process for dissimilar S45C and H13 metals.

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Model-based Hysteresis and Cross-coupling Compensation for Precision Control of Piezoelectric Fast Steering Mirror: Hyo Geon Lee, Jae Woo Jung, Sang Won Jung, Jae Hyun Kim, Seonbin Lim, Youngjin Park, Jaehyun Lim, Kijun Seong, Daehee Lee, Seunggu Kang, No-Cheol Park, Jun Young Yoon; J. Korean Soc. Precis. Eng. 2026;43(2):139-149.
Published online February 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.091

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This paper presents model-based hysteresis and cross-coupling compensators designed for precise control of a piezoelectric fast steering mirror (FSM). The hysteresis compensators are developed by inversely modeling the variation in the force constant relative to various excitation voltages, enabling the system to maintain linear response characteristics across a broad range of input amplitudes. The cross-coupling compensator is formulated by creating a decoupling matrix that cancels out coupling effects, generating signals of equal magnitude and opposite phase for each axis. The implementation of these compensators reduces the hysteresis band and magnitude uncertainty in the FSM dynamics by over 89.6% and 74.2%, respectively, while also significantly suppressing cross-coupling effects by more than 85.5%. Furthermore, the performance of the proposed compensators is validated in a closed-loop control system, demonstrating a notable reduction in cross-axis vibrations and improved tracking performance in response to step reference inputs and highfrequency sinusoidal trajectories.

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Study on the Reduction of Charge in Electrostatically Charged Particles Using a Neutralizer: Deokhyeong Kim, Sungbin Lee, Geonho Kim, Seonghyun Ko, Heesung Park; J. Korean Soc. Precis. Eng. 2026;43(1):105-111.
Published online January 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.096

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This study examines the charge reduction characteristics of charged particles using a neutralizer to prevent accidents from electrostatic discharge and enhance process efficiency. The research measures the number of charges, elimination efficiency, and penetration rate under various voltage polarity conditions with a DC-type bipolar electrostatic eliminator. The results indicate that electrostatic neutralization is most effective under negative high voltage (-HV) conditions, while the mesh penetration rate increases and charge accumulation occurs under positive high voltage (+HV) conditions. Furthermore, partial charge neutralization is observed under both positive and negative high voltage (±HV) conditions due to the sequential emission of positive and negative ions. This study quantifies the mitigation of electrostatic charge using a neutralizer, offering insights for optimizing filtration systems and improving process stability. Future research will refine electrostatic control mechanisms by considering additional parameters such as particle size, material properties, and flow conditions.

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Effect of Flash-light Sintering Voltage on the Microstructure and Chemical Properties of Lithium Lanthanum Titanate Thin Films Prepared by Electrostatic Spray Deposition: Sun Min Kim, In Suk Song, Hyo Jun Ahn, Min Ji Kim, Young-Beom Kim; J. Korean Soc. Precis. Eng. 2026;43(1):55-60.
Published online January 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.056

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All-solid-state batteries (ASSBs) utilizing non-flammable inorganic electrolytes are gaining significant attention due to safety concerns associated with conventional lithium-ion batteries. Among various oxide electrolytes, lithium lanthanum titanate (LLTO) demonstrates high ionic conductivity at room temperature but is prone to lithium loss at elevated sintering temperatures. In this study, we employed electrostatic spray deposition (ESD) at 250℃, followed by flash light sintering within milliseconds using a xenon lamp. This approach enabled the production of dense and highly crystalline LLTO thin films with minimal lithium evaporation. Scanning electron microscopy (SEM) analysis confirmed reduced porosity at 650V, while X-ray photoelectron spectroscopy (XPS) revealed stable lithium content. Additionally, X-ray diffraction (XRD) indicated the formation of a cubic perovskite structure that is beneficial for ionic transport. This rapid and scalable process shows promise for producing high-quality LLTO electrolytes, thereby enhancing the safety and performance of next-generation ASSBs.

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Development of the Fretting Corrosion Test Equipment for the Automotive Electrical Connector: Jeong Hyun Kim, Sang Hoon Lee; J. Korean Soc. Precis. Eng. 2026;43(1):21-28.
Published online January 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.029

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Fretting corrosion results from microscopic abrasion of connector contacts and is influenced by environmental conditions in automotive applications. This study designed and fabricated test equipment capable of evaluating fretting corrosion characteristics at low temperatures. A temperature–humidity environmental chamber was used, and a compact test jig box was created to fit inside it. The specimen was positioned outside the box and fully exposed to low temperatures, while the driving components were enclosed inside the box. To ensure their reliable operation, warm air was supplied using vortex tubes, maintaining the internal box temperature above 0oC even when chamber conditions reached −40℃. A hemispherical-tip jig was also produced to enable consistent specimen preparation. Experiments conducted at −40℃ used a constant current–resistance method to measure output signals. The system successfully captured accurate and stable resistance changes corresponding to displacement cycles. These findings indicate that the developed equipment provides stable low-temperature operation and reliable measurement performance. Therefore, the system is expected to support fretting corrosion characterization across a wide range of environments, including low-temperature, high-temperature, and temperature-cycling conditions.

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Study on Fatigue Life Prediction of Crossed Roller Bearings: Gilbert Rivera, Dong-Hyeok Kim, Dong Uk Kim, Seong-Wook Hong; J. Korean Soc. Precis. Eng. 2025;42(12):1088-1098.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.097

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This paper presents a method for estimating the fatigue life of crossed roller bearings (XRBs). XRBs feature a single row of rollers arranged alternately at right angles, making them ideal for applications that require high precision and a compact design. In rolling-element bearings, fatigue life is a crucial design parameter for ensuring long-term reliability and performance. However, existing fatigue life estimation models for XRBs in the literature are limited to basic rating life, with no models available for reference rating life. To address this gap, we developed a comprehensive fatigue life prediction model specifically for XRBs. We formulated a corresponding dynamic load rating to align with the values provided by bearing manufacturers and calibrated an unknown adjustment factor for XRBs using a commercial program. Additionally, a parametric study was conducted to investigate the impact of varying diametral clearance, external loads, roller dimensions, and roller profile parameters on the fatigue life of XRBs.

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A Review of in Operando Measurements of Local Temperature for Lithium-ion Batteries: Soyoung Park, Woosung Park; J. Korean Soc. Precis. Eng. 2025;42(12):1021-1035.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00024

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Sensing the internal temperature of lithium-ion batteries is particularly useful for reliable battery operation as both electrochemistry and mass transport are dictated by local temperature. In this article, we review in operando techniques to monitor the internal temperature of lithium-ion batteries during charging and discharging. We categorize existing techniques into two groups: invasive and non-invasive approaches. Invasive techniques include optical fibers, thermocouples, and resistance temperature detectors as a thermometer. Non-invasive methods cover the temperature estimation techniques, namely electrochemical impedance spectroscopy as well as X-ray thermometry. For both approaches, we review working principle of thermometry, pros and cons of each thermometry, and recent studies to tackle relevant technical challenges. This review provides useful information for internal temperature measurements, offering chances for thermally reliable battery operation.

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A stress prediction method for lithium-ion batteries using segmented Gaussian process regression
Shengchuan Cheng, Chengjie Zhou, Ren Zhu, Hongyuan Zeng, Heng Li
Journal of Power Sources.2026; 684: 240362. CrossRef

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Electrochemical Evaluation of PrO_x Capping Layer in LT-SOFCs via Sputtering Process: Ji Woong Jeon, Geon Hyeop Kim, Hyeon Min Lee, Jun Geon Park, Gu Young Cho; J. Korean Soc. Precis. Eng. 2025;42(12):1003-1010.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00014

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Solid Oxide Fuel Cells (SOFCs) are energy conversion devices known for their significantly higher power density compared to other fuel cell types. However, their high operating temperatures pose challenges related to thermal stability. To address this, research is focusing on Low-Temperature SOFCs (LT-SOFCs), which function at lower temperatures and exhibit enhanced electrochemical performance. While various electrode materials are utilized in SOFCs, platinum (Pt) stands out for its excellent electronic conductivity and catalytic activity. Unfortunately, at the operating temperatures of SOFCs, Pt tends to agglomerate, leading to a rapid reduction in the triple phase boundary (TPB) and a subsequent decline in electrochemical reactions. In this study, LT-SOFCs were fabricated with a Praseodymium Oxide (PrOx) capping layer applied to a porous Pt cathode using sputtering, with various thicknesses achieved by adjusting the deposition time. The electrochemical performance of the LT-SOFCs was measured at 500^oC. Additionally, the degradation behavior of the LT-SOFCs was assessed by applying a constant voltage of 0.5 V for 48 hours. Scanning Electron Microscopy (SEM) analysis was also conducted on the PrOx capping layer thin films under the same operating conditions.

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Parametric Studies of Ionomer Content in PEMFC MEA with Different Humidity: Byung Gyu Kang, Hyeon Min Lee, Ye Rim Kwon, Sun Ki Kwon, Ki Won Hong, Seoung Jai Bai, Gu Young Cho; J. Korean Soc. Precis. Eng. 2025;42(12):975-980.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00006

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The ionomer content in the catalyst layer is a crucial design factor that affects the performance of polymer electrolyte membrane fuel cells (PEMFCs). However, the optimal ionomer content can vary based on the surrounding humidity levels. This study systematically evaluated the influence of the ionomer-to-carbon (I/C) ratio (0.00, 0.55, and 0.91) on PEMFC performance under fully humidified (RH 100%) and low-humidity (RH 25%) conditions. Membrane-electrode assemblies (MEAs) were fabricated using a spray coating technique, and their electrochemical properties were analyzed through polarization curves and electrochemical impedance spectroscopy (EIS). Under RH 100%, the MEA with an I/C ratio of 0.55 achieved the highest peak power density of 519.8 mW/cm², indicating a successful balance between proton conductivity and gas transport. Conversely, under RH 25%, the best performance of 203.9 mW/cm² was observed at an I/C ratio of 0.91. This shift is attributed to improved water retention at higher ionomer content, which reduced membrane dehydration and lowered both ohmic and Faradaic resistances. These findings highlight the dual role of the ionomer in facilitating proton transport and managing water balance, emphasizing the necessity of optimizing the I/C ratio according to operating conditions for stable and high-performing PEMFC operation.

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Tape-casting Process Electrochemical Characteristic Test for Fabrication of LST-GDC for Anode Supported SOFCs: Min Ji Kim, Chunghyun Kim, Young-Beom Kim; J. Korean Soc. Precis. Eng. 2025;42(11):937-942.
Published online November 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.073

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In this study, we developed a composite anode support composed of La-doped SrTiO₃ (LST) and Gd-doped CeO₂ (GDC) using a tape casting process for solid oxide fuel cells (SOFCs). By adjusting the pore former content in the slurry, we constructed a bilayered structure consisting of a porous anode support layer (ASL) and a dense anode functional layer (AFL) with the same material composition. The number of tape-cast sheets was controlled to tailor the overall thickness, and lamination followed by co-sintering at 1250^oC resulted in a mechanically robust bilayer. We characterized the microstructural evolution concerning sintering temperature and pore former content using SEM, while XRD confirmed the phase stability of LST and GDC. The measured electrical conductivity at 750^oC ensured sufficient electron transport. To enhance interfacial adhesion and suppress secondary phase formation, we introduced a GDC buffer layer and a pre-sintering treatment prior to electrolyte deposition. A full cell with a YSZ electrolyte and LSCF cathode achieved a stable open circuit voltage of approximately 0.7 V and demonstrated continuous operation at 750^oC. These findings highlight the suitability of LST-GDC composite anodes as thermochemically stable supports, potentially enabling direct hydrocarbon utilization in intermediate-temperature SOFCs.

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Electrochemical Impedance Analyses of ePTFE-reinforced Polymer Electrolyte Membrane-based PEMFC with Varying Thickness and Relative Humidity: Gyutae Park, Subin Jeong, Youngjae Cho, Junseo Youn, Jiwon Baek, Jooyoung Lim, Dongjin Kim, Taehyun Park; J. Korean Soc. Precis. Eng. 2025;42(11):901-907.
Published online November 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.052

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The polymer electrolyte membrane fuel cell (PEMFC) generates electrical energy through electrochemical reactions and is a key technology for sustainable energy. The electrolyte membrane significantly affects performance under varying conditions. This study examines the impact of membrane thickness and relative humidity (RH) on PEMFC performance using j-V curves and electrochemical impedance spectroscopy (EIS). Experiments were conducted with membrane thicknesses of 30, 15, and 5 μm under RH conditions of 100%-100% and 100%-0%. Under RH 100%-100%, performance improved as the membrane thickness decreased, with values of 954, 1050, and 1235 mW/cm² for the 30, 15, and 5 μm membranes, respectively. The 5 μm membrane demonstrated a 23% performance improvement over the 30 μm membrane. Under RH 100%-0%, performances were 422, 642, and 852 mW/cm², with degradation rates of 55.8%, 39.0%, and 32.1%. The 5 μm membrane exhibited the lowest degradation rate, indicating superior performance under low humidity. These results suggest that thinner membranes generally enhance performance and maintain efficiency even in dry conditions.