With the development of Additive Manufacturing process, lattice structures have recently been fabricated with fine quality. Lattice structures have unique performances which encompass various elastic responses. In this study, shear characteristics of the lattice structures (BCC and OTC) fabricated by SLM process, under optimized manufacturing conditions, were analyzed by 1/4 compression tests. As a result, several fracture modes and elastic configurations were found by comparing the compression test results of various lattice structures. In addition, the lattice structures possessed certain shear elasticity and normal elasticity among different types of lattices at elastic region when shearing. As the 1/4 compression test was simulating the lattice structure on concentrate load or shearing load, the test represented shock introspection characteristics of the lattice inner structure.
Microchannel-based chemical reactor is widely used to develop chemical products. High-efficiency reactors are required to produce high-quality chemical products. The reaction efficiency is highly related to the mixing ratio. In this paper, an inner structure model in the reactor was designed to improve the mixing ratio. Computational fluid dynamic (CFD) analysis was carried out for two-phase flow in a continuous flow reactor using a commercial software. A case model of the different inner structures was designed to evaluate the mixing rate. Velocity profiles, mixing ratio, and pressure fields of each model were obtained by two-fluid flow analysis using CFD. Based on the analysis results, a reactor model with a high mixing ratio was selected. Powder bed fusion based metal additive manufacturing process was performed to manufacture the 3D microchannel-based chemical reactor. It is expected that the proposed reactor could be applied to a high-efficiency reactor system to produce various chemical materials. For instance, it was possible to perform a chemical reaction based on a toxic material, such as, dimethylformamide solution, using the proposed 3D metal microchannel-based reactor.
We studied compressive behavior of two types of lattice structures having small-scale struts fabricated by utilizing a metal additive manufacturing process. Generally known, the lattice structure has some advantages such as lightweight and high specific mechanical strength, allowing diverse potential applications in the aerospace and mobility industries. In this work, we proposed two types of lattice such as body-centered truss (BCT) and octahedral truss (OCT) that were designed and fabricated for a compression test. From the experimental results, the OCT has much higher strength than the BCT, and all cases showed several buckling modes during the compressive behavior. Furthermore, ‘restructuring’ occurred with BCT, and the compressive force increased overall but fluctuated due to the restructuring by an increase of compression. Through this work, we found out that the BCT has the interesting compressive behaviors, and a repetitive bucking-restructuring was found. In fact, its strength could be increased continuously by the restructuring during compression. In conclusion, the BCT has key-characteristics of lightweight and re-strengthening, which are applicable to various applications in the industry.
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Numerical Study on the Quantitative Structure-Property Relation of Lattice Truss Metals Jiyeon Kim, Dongmyoung Jung, Yongwoo Kwon MATERIALS TRANSACTIONS.2022; 63(10): 1317. CrossRef
Analysis on Material Behavior of Metal Additive Manufactured Lattice Structures under Quarter Compression Test Qingye Jin, Simo Yeon, Yong Son, Sanghu Park Journal of the Korean Society for Precision Engineering.2021; 38(9): 667. CrossRef
Material extrusion (ME) type 3D printing has been widely utilized through various types of systems depending on the fabrication methods, materials, and precision to fabricate complex workpieces that cannot be made with conventional methods. This study provides basic considerations in response to the current demands on performance evaluation of ME type 3D printing related to dimensions as well as the realization of the guidelines to be established in the near future. As a simple specimen for these purposes, 2D and 3D hole-plates were designed and fabricated by using a ME type entry-level 3D printer. For evaluation of dimensions on the specimen, both specimens were measured by a calibrated tool-maker’s microscope which is to length standard. The measurement parameters were the center position of the holes, the diameter of the holes, and the circularity error of the holes.
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A Study on 3D Printing Conditions Prediction Model of Bone Plates Using Machine Learning Song Yeon Lee, Yong Jeong Huh Journal of the Korean Society for Precision Engineering.2022; 39(4): 291. CrossRef
Dimensional Characteristics of Hydraulic Actuator Curve based on 3D Printing Filament Materials Myung-Hwi Jung, Jeong-Ri Kong, Hae-Ji Kim Journal of the Korean Society of Manufacturing Process Engineers.2021; 20(1): 74. CrossRef
Effect of Fused Deposition Conditions on the Fracture Behavior of 3D Printed Tensile Specimens Bum Joon Kim Journal of the Korean Society for Precision Engineering.2020; 37(6): 421. CrossRef
Heat transfer characteristics in the vicinity of irradiated region of the beam of a selective laser melting (SLM) process affect the creation of the melted region during the deposition. The creation of the molten pool is greatly influenced by laser parameters and powder characteristics. The goal of the paper is to investigate the influence of laser parameters and powder porosity on thermal characteristics in the vicinity of the molten pool of the SLM process through repeated finite element analyses (FEAs). The power and the scan speed are chosen as the laser parameters. The laser is assumed to be a volumetric Gaussian heat flux model. Materials of the powder and the substrate are chosen as SUS17-4PH and S45C, respectively. Temperature dependent thermal properties for those material are used to perform the FEA. An appropriate efficiency of the heat flux is predicted by comparing the results of FEAs and those of experiments. The influence of laser parameters on temperature distributions in the vicinity of the melted region and the formation of the molten pool is examined. In addition, the effects of porosity of powders on heat transfer characteristics in the vicinity of the melted region are discussed.
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Effects of Deposition Strategy and Preheating Temperature on Thermo-Mechanical Characteristics of Inconel 718 Super-Alloy Deposited on AISI 1045 Substrate Using a DED Process Ho Kim, Kwang-Kyu Lee, Dong-Gyu Ahn, Hyub Lee Materials.2021; 14(7): 1794. CrossRef
We propose a novel fin-tube expanding process using a spiral-grooved-expanding ball, prepared by the metal additive manufacturing process, to improve heat exchange performance in a fin-tube type heat exchanger. In this study, deformation of inner grooves in a tube, was minimized during the expanding process. For this, we developed lab-scale expanding equipment, and a spiral-grooved-expanding ball, was newly designed and fabricated. Comparing to a conventional tube expanding process, it was deduced that a deformation rate of groove height was reduced to approximately 8.3%, when the proposed process was used. Through this fundamental study, we validate that the developed process can be used to fabricate large-surface grooved tubes, for application to a high efficiency heat exchanger.
Recently, many studies have been conducted on the nano-scale fabrication technology using twophoton-absorbed polymerization induced by a femtosecond laser. The nano-stereolithography process has many advantages as a technique for direct fabrication of true three-dimensional shapes in the range over several microns with sub-100 nm resolution, which might be difficult to obtain by using general nano/microscale fabrication technologies. Therefore, two-photon induced nano-stereolithography has been recently recognized as a promising candidate technology to fabricate arbitrary 3D structures with sub-100 nm resolution. Many research works for fabricating novel 3D nano/micro devices using the two-photon nano-stereolithography process, which can be utilized in the NT/BT/IT fields, are rapidly advancing.
The wear problem of wheel flange occurs at sharp curves of rail. This paper proposes a procedure for optimum design of a wheel profile wherein flange wear is reduced by improving an interaction between wheel and rail. Application of optimization method to design problem mainly depends on characteristics of design space. This paper compared local optimization method with global optimization according to sensitivity value of objective function for design variables to find out which optimization method is appropriable to minimize wear of wheel flange. Wheel profile is created by a piecewise cubic Hermite interpolating polynomial and dynamic performances are analyzed by a railway dynamic analysis program, VAMPIRE. From the optimization results, it is verified that the global optimization method such as genetic algorithm is more suitable to wheel profile optimization than the local optimization of SQP (Sequential Quadratic Programming) in case of considering the lack of empirical knowledge for initial design value.
A nano-stereolithography is the direct patterning process with a nanoscale resolution using twophoton absorption induced by a femtosecond laser. However, in the majority of the works, the fabrication of 3D microstructures have been done only onto transparent glass due to the use of an oil immersion objective lens for achieving a high resolution. In this work, the coaxial illumination and the auto-focusing system are proposed for the direct patterning of nano-precision patterns on an opaque substrate such as a silicon wafer and a metal substrate. Through this work, 3D polymer structures and metallic patterns are fabricated on a silicon wafer using the developed process.
Two-photon stereo lithography is recognized as a promising process for the fabrication of three-dimensional (3D) microstructures with 100 ㎚ resolution. Generally, beam-scanning system has been used in the conventional process of two-photon stereo lithography, which is limited to the fabrication of micro-prototypes in small area of several tens micrometers. For the applications to 3D high-functional micro-devices, the fabrication area of the process is required to be enlarged. In this paper, large-area two-photon stereo lithography (L-TPS) employing stage scanning system has been developed. Continuous scanning method is suggested to improve the fabrication speed and parameter study is conducted. An objective lens of high numerical aperture (N.A.) and high strength material were employed in this system. Through this work, 3D microstructures of 600*600* 100 ㎛ were fabricated.
Two-photon stereo lithography (TPS) is recognized as a useful process for the fabrication of three-dimensional microstructures. Recently, the need for a two-photon curable resin with high strength increases as 3-D microstructures of high aspect ratio or large scale of several hundreds micrometers are required for applications of nano/micro devices in IT/BT. In this work, process parameters of TPS employing the SU-8 which is a representative two-photon curable resin with high strength have been studied for the precise fabrication of 3-D microstructures with high strength. The pre-baking and post-baking processes are studied and the parameter study of the SU-8 in TPS is conducted. Through this work, very small roughness of 12 ㎚ and the minimum aspect ratio of ~1 which provides a precise accumulation of layers could be obtained. Using the conditions studied in this work, some 3-D examples are fabricated.
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