Journal of the Korean Society for Precision Engineering

A Study on the Control of Manufacturing Variables in FDM Additive Manufacturing for Hair Tiles: TaeHyeon Yang, Jong Hoon Kim, Ki Hong Park, Wonsik Eom; J. Korean Soc. Precis. Eng. 2026;43(9):961-974.
Published online September 1, 2026; DOI: https://doi.org/10.7736/JKSPE.026.00050

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Hair-like surfaces in nature consist of high-aspect-ratio fibers with diameters below 100μm, falling to several tens of micrometers in softer hairs. These fine fiber arrays govern tactile softness, flexibility, surface texture, and mechanical response. Conventional fiber-spinning methods produce fine fibers effectively but offer limited control over the position, direction, and patterned arrangement of individual fibers. Here we propose a fused deposition modeling (FDM)-based strategy that combines melt extrusion with geometric drawing to fabricate PLA hair-like fibers. PLA melted fully at the processing temperature of 250oC, well below the thermal degradation onset near 330oC. DSC analysis showed that faster cooling suppressed thermodynamic crystallization, indicating that the final fiber structure is governed by drawing history and rapid cooling rather than by increased crystallinity. As the printing speed increased, the fiber diameter decreased nonlinearly, following D ≈ 106.3 v^-0.45, in excellent agreement with the D  v^-0.5 scaling predicted by the continuity equation. Tensile strength and modulus increased with printing speed, whereas elongation and toughness decreased, indicating drawing-induced molecular orientation. These results demonstrate that FDM can serve as a programmable platform for fabricating biomimetic hair-like fiber arrays with predictable diameter and mechanical properties.

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Development of a WA-DED Process for Low-angle Overhang Structures Using 3D Sand-printed Supports: Chang Young Choi, Hwi Jun Son, Seo Rim Park, Yeong Jae Kim, Young Tae Cho; J. Korean Soc. Precis. Eng. 2026;43(9):951-959.
Published online September 1, 2026; DOI: https://doi.org/10.7736/JKSPE.026.00044

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This study proposes a hybrid wire arc directed energy deposition (WA-DED) process that uses 3D sand-printed supports to overcome the limitations of low-angle overhang fabrication. WA-DED is a metal additive manufacturing process offering high deposition rates, cost efficiency, and suitability for large-scale components. However, because of its high heat input and molten pool instability, low-angle overhang and hollow structures remain difficult to fabricate, as the molten metal tends to collapse under gravity and thereby degrade geometric accuracy and surface quality. To address this issue, sand-printed supports were introduced. The supports provide tailored mechanical constraint and guide the solidification of the molten pool during deposition. Experiments were conducted to evaluate the feasibility of the proposed process at various overhang angles. The results show that the hybrid process markedly improves deposition stability and enables the fabrication of low-angle and curved overhang structures that conventional WA-DED cannot produce. These findings confirm the effectiveness of sand-supported WA-DED and highlight its potential for industrial applications requiring complex geometries, such as aerospace, marine, and energy components.

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Experimental Study on the Effect of Human-in-the-loop Integration on Large Language Model-based Process Control in Additive Manufacturing: Seongyoon Jeon, Taehwan Kim, Namhun Kim; J. Korean Soc. Precis. Eng. 2026;43(9):907-923.
Published online September 1, 2026; DOI: https://doi.org/10.7736/JKSPE.026.00041

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This study proposes a human-in-the-loop framework that integrates operator observations into a large language model (LLM) to control process parameters for defect handling in fused deposition modeling (FDM) 3D printing. Fully autonomous LLM-based control handles ambiguous sensor data poorly and cannot detect abnormal conditions that lie beyond the installed sensors. Operator observations may compensate for these limitations, but their actual impact on LLM decision-making has not been sufficiently validated. We therefore implemented the proposed framework and defined experimental scenarios involving erroneous parameter injection and environmental disturbances. The framework was evaluated in terms of LLM response quality and print quality. The LLM achieved over 80% response quality on the defined evaluation metrics and generated appropriate parameter adjustments, improving print quality by more than 55% on average. Comparative experiments further revealed that, without operator observations, the LLM sometimes failed to recognize defects. These findings demonstrate the effectiveness of human–LLM collaboration and provide a practical foundation for intelligent FDM process control.

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Investigated New Thin Films based on Zn-doped MgO for Optoelectronic Devices: Nadjat Chaouch, Amira Sbaihi, Said Lakel, Abdelghani Lakel, Said Benramache; J. Korean Soc. Precis. Eng. 2026;43(9):987-996.
Published online September 1, 2026; DOI: https://doi.org/10.7736/JKSPE.026.00019

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In this work, Mg1-xZnxO thin films were deposited on glass substrates by the pneumatic spray technique at 450°C using a 0.15 M precursor solution of magnesium acetate and zinc acetate. The effect of Zn content (x = 0, 0.3, 0.5, and 0.7%) on the structural, morphological, optical, and electrical properties of the films was examined. XRD analysis showed that all films adopted a cubic MgO structure with diffraction peaks from the (111), (200), and (220) planes, and the crystallite size grew from 8.12 to 12.49 nm as the Zn content increased. SEM images indicated that moderate Zn incorporation improved film homogeneity, whereas higher Zn contents promoted agglomeration and surface roughening. The films transmitted well in the visible region, and the optical band gap widened from 3.56 to 3.93 eV at x = 0.3. The Urbach energy also rose with Zn content, reaching a maximum of 0.695 eV at x = 0.7, which indicates greater structural disorder. FTIR spectra confirmed that Zn incorporation modifies the chemical bonding network. The sheet resistance increased markedly with Zn content, demonstrating the strong influence of Zn doping on the optical and electrical properties of MgO thin films.

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Evaluating the Environmental Benefits of 3D Printing Based Part Production for Low-volume Automotive Applications: Na Kyong Yun, Sung Won Choi, Gyung Bok Kim, Hyo Jae Kong; J. Korean Soc. Precis. Eng. 2026;43(9):1007-1013.
Published online September 1, 2026; DOI: https://doi.org/10.7736/JKSPE.026.00016

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3D printing is emerging as a promising solution for the automotive industry, as it offers economic advantages in small-batch, high-variety production and mitigates climate impact by eliminating mold fabrication. This study compares the carbonemission reduction potential and economic feasibility of fused deposition modeling (FDM)—the most widely used polymer 3D printing process—with those of conventional injection molding at the actual component level. The analysis shows that the environmental burden of mold manufacturing in injection molding is substantial, confirming the advantage of FDM in low-volume production. Specifically, for production volumes below 645 units, FDM performs better in reducing carbon emissions. These findings indicate that FDM can serve as a sustainable alternative for low-volume manufacturing in automotive applications.

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Microwave-induced Enhancement of Interlayer Strength in FDM-printed Nylon6/Carbon Fiber Composites: Si Woo Kim, Ho Geun Nam, Jong Wan Ko; J. Korean Soc. Precis. Eng. 2026;43(5):517-526.
Published online May 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.112

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Among 3D printing techniques, fused deposition modeling (FDM) is known for its design flexibility, rapid fabrication, and the ability to produce complex geometries without molds. However, weak interlayer adhesion often results in poor mechanical strength along the build (Z) direction, limiting its use in structural applications. Instead of altering printing parameters or switching technologies, we propose a simple microwave-irradiation post-treatment to enhance interlayer bonding in FDM-printed parts. By optimizing microwave power and exposure time, we significantly improved interlayer fusion while maintaining the original geometry. Cross-sectional microscopy before and after treatment confirmed markedly improved interlayer bonding (Unbonded interfacial area fraction: 56.82% → 15.51%; -41.31 percentage points, -72.7%). Correspondingly, the Z-direction tensile strength increased from 42.38 to 49.11 MPa (+6.73 MPa, +15.9%). This straightforward post-processing method effectively addresses a key limitation of FDM, thereby expanding its potential for structural and industrial applications.

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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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A Study on Fabrication of PCD Boring Tool Body based on Metal 3D Printing Technology: Ho Min Son, Dong Gyu Kim, Min-Woo Sa; J. Korean Soc. Precis. Eng. 2026;43(2):189-196.
Published online February 1, 2026; DOI: https://doi.org/10.7736/JKSPE.025.107

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The future mobility industry is increasingly utilizing advanced tools for cutting and machining lightweight parts to enhance the fuel efficiency of automotive engines. Machining companies are turning to polycrystalline diamond (PCD) tools to boost productivity in the production of these lightweight components. PCD tools provide exceptional machining performance and a long service life, making them ideal for high-mix, low-volume production, which often involves customized requirements for various materials. To further improve efficiency, this study explores the application of metal 3D printing technology in the manufacturing of PCD tools. This technology allows for the creation of PCD tools with superior cutting performance and wear resistance, tailored for high-speed machining of lightweight materials, including complex shapes. Thus, research into this area is essential. In this study, we manufactured boring tools by brazing PCD tips onto three different laminated structures created using Fused Deposition Modeling (FDM), a method within metal 3D printing technologies. We then evaluated the fabricated boring tools through comparative machining experiments against existing sintered PCD boring tools. The results indicated that the 3D-printed solid tools demonstrated no significant differences in machining accuracy or surface quality compared to the conventional tools.

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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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A Review on Performance Improvement of Solid Oxide Cells via Atomic Layer Deposition: Min Seong Gwon, Kyoungjae Ju, Jihwan An; J. Korean Soc. Precis. Eng. 2025;42(12):987-995.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.00017

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Atomic Layer Deposition (ALD) has emerged as a promising technique for fabricating thin films that enhance the performance of solid oxide fuel cells and solid oxide electrolysis cells. ALD allows for precise control over film thickness and composition at the atomic level, resulting in uniform and dense thin films. These characteristics enable the deposition of thin, homogeneous layers of various materials onto the porous electrode surfaces of solid oxide cells, thereby increasing electrochemical activity and reducing activation losses. Additionally, thin-film electrolytes produced through ALD can achieve high ionic conductivity and low ohmic losses, facilitating a reduction in the operating temperature of solid oxide cells. This review summarizes recent research trends in applying ALD technology to the fuel electrode, air electrode, and electrolyte of solid oxide cells and discusses design strategies aimed at improving efficiency and long-term stability.

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Tensile Behavior of 3D Printed Specimens by Small Punch Test: Bum Joon Kim; J. Korean Soc. Precis. Eng. 2025;42(10):879-884.
Published online October 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.121

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The purpose of this study is to evaluate the deformation behavior of 3D printed specimens using the small punch tensile test method. Traditional tensile tests for assessing mechanical properties require a significant amount of material to produce uniaxial tensile specimens. In contrast, the small punch test method only requires 10 x 10 x 0.5 mm (width x length x thickness) thin plate specimens, providing a substantial economic advantage in specimen sampling and production. This method is particularly beneficial when it is impossible to produce specimens of the same size as uniaxial specimens, as it allows tensile testing with just the minimum sample required. In this study, we utilized fused deposition modeling 3D printing and considered various 3D printing parameters, such as layer height and volume fraction, while manufacturing the specimens. We then compared and analyzed the effects of these variables on tensile strength as measured by the small punch tensile test. Furthermore, we focused on investigating the applicability of this method to the deformation behavior of 3D printed specimens. We also examined the impact of laminating conditions, including layer height, printing speed, and laminating direction, on the failure modes observed after the small punch tensile test.

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Suppression of Interfacial Side Reactions and Performance Enhancement of NCA Cathodes via LNO Deposition Using Particle ALD: Min-ji Kim, In-suk Song, Hyo-jun Ahn, Sun-min Kim, Young-Beom Kim; J. Korean Soc. Precis. Eng. 2025;42(10):851-859.
Published online October 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.025

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Improving the interfacial stability between cathode active material (CAM) and solid electrolyte (SE) is essential for enhancing the performance and durability of all-solid-state batteries (ASSBs). One promising method to achieve this is through surface coating with a chemically stable ion conductor, which helps suppress interfacial side reactions and improve long-term cycling stability. In this study, we deposited a uniform LiNbO3 (LNO) protective layer on NCA using particle atomic layer deposition (Particle ALD). This technique utilizes a self-limiting growth mechanism to ensure precise thickness control. We characterized the structural and chemical properties of the coated CAM with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), confirming the successful formation of a uniform LNO layer. Electrochemical evaluations revealed that LNO@NCA exhibited significantly improved capacity retention, maintaining 68.1% after 50 cycles at a 1C rate, compared to just 56.5% for the uncoated sample. This enhancement is attributed to the LNO layer's effectiveness in mitigating electrochemical side reactions. These findings demonstrate that Particle ALD-derived LNO coatings are an effective strategy for stabilizing CAM|SE interfaces and extending the cycle life of high-energy ASSBs.

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Study on Repair of SKD 61 Using Directed Energy Deposition with H13 and P21 Powders: Bit-na Yun, Min-seong Ko, Hyo-jeong Kang, Do-Sik Shim; J. Korean Soc. Precis. Eng. 2024;41(11):849-856.
Published online November 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.073

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In this study, we investigated characteristics and mechanical properties of SKD61 repaired using the direct energy deposition (DED) process. Mechanical properties of the repaired product can vary depending on the base material and powder used in the DED process. To prepare for DED repairing for a damaged part, we conducted experiments using two different powders (H13 and P21). Experimental results showed that both powders were deposited without defects in the surface or interface between the deposited zone and the substrate. Hardness measurements indicated that the repaired region of the Repaired-H13 sample exhibited higher hardness than the base material, while the Repaired-P21 sample showed a sharp increase in hardness in the heat-affected zone (HAZ). Additionally, tensile test results revealed that the Repaired-H13 sample had lower tensile strength and elongation than the base material, whereas the Repaired-P21 sample demonstrated higher tensile strength and yield strength with a higher elongation than the Repaired-H13 sample. In case of Repaired-H13, it was confirmed that interfacial crack occurred due to a high hardness difference between the repaired part and the substrate.

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Microstructure and mechanical properties of P21 tool steel fabricated via laser powder bed fusion
A. Rajesh Kannan, V. Rajkumar, S. Maheshwaran, N. Siva Shanmugam, Wonjoo Lee, Jonghun Yoon
Materials Letters.2025; 398: 138930. CrossRef

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Mechanical Property Test Results for Additive Manufactured Specimens of Stainless Steel 316 L after Heat Treatment: Kyungnam Jang, Seunghan Yang, Dae Seung Park; J. Korean Soc. Precis. Eng. 2024;41(7):551-559.
Published online July 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.035

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Additive manufacturing (AM) technology, also known as 3D printing, is a highly promising technology that can drive innovation in various industrial areas, including the nuclear industry. Although the nuclear industry is traditionally conservative when it comes to adopting new technologies, it is crucial that AM technology is eventually applied for a variety of reasons. To overcome the barriers that currently hinder the adoption of AM in the nuclear industry, it is essential to ensure the reliability of AM products. One key factor is ensuring that AM products have mechanical properties equivalent to those of traditionally manufactured products. This paper presents the results of mechanical property tests conducted on additive manufactured specimens of stainless steel 316 L after heat treatment. We performed tensile tests, hardness tests, and microstructure analysis on specimens produced using two types of metal AM technologies: powder bed fusion (PBF) and directed energy deposition (DED). The results of the tests indicate that certain weaknesses, such as anisotropy and brittleness, in AM products can be improved through three types of heat treatments. In particular, AM products produced using the PBF method and subjected to heat treatments show potential for application in the nuclear industry in terms of materials.

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Additional Ionomer-coated Layer for Self-humidifying Polymer Electrolyte Membrane Fuel Cells: Gyutae Park, Dongjin Kim, Junseo Youn, Junghyun Park, Hyoun-Myoung Oh, Taehyun Park; J. Korean Soc. Precis. Eng. 2023;40(12):997-1001.
Published online December 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.097

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In this study, we aim to develop a self-humidifying polymer electrolyte membrane fuel cell (PEMFC) by depositing platinum (Pt) on a membrane using sputtering. After we coated it with a Nafion^® ionomer solution. This is considered a solution that can prevent membrane degradation in low humidity conditions. By introducing this self-humidifying concept, we can expect improved performance compared to conventional PEMFCs. By managing the water content of Nafion^®, we aim to improve both the stability and performance of the PEMFCs. This research contributes to the development of more efficient and reliable PEMFC systems, showing promise for advances in this field.