http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
최병주(Byungjoo Choi),양재영(Jaeyoung Yang),이문구(Moongu Lee),전용호(Yongho Jeon) 한국생산제조학회 2021 한국생산제조학회지 Vol.30 No.1
Metal 3D printing is attracting attention as a new production technology. However, various problems need to be solved regarding it. In particular, defects occurring in the process of melting and solidification are relatively serious than those occurring in the traditional casting or cutting process. To solve this problem, this study introduced a tomography using a high-speed camera that can monitor the melting pool. This confirmed the possibility of finding defects by detecting an abnormality in the melting pool. In addition, if it is combined with the YOLO model, which is the latest object detection algorithm, it is judged that the integrity of the parts produced by the casting or cutting process can be secured by stopping or recovering the process through real-time inspection.
이강현(Kang-Hyun Lee),방경배(Gyung Bae Bang),김형균(Hyung Giun Kim),정경환(Kyung Hwan Jung),윤군진(Gun Jin Yun) Korean Society for Precision Engineering 2021 한국정밀공학회지 Vol.38 No.4
In the selective laser melting (SLM) process, a three-dimensional part is manufactured based on the formation of numerous molten tracks. Consequently, the generated melt pool in the scanning process of each track exhibits close relation to the internal defect formation and the quality of the fabricated part. In this study, a numerical model of single-track scanning of the SLM process is presented to analyze the melt pool characteristics for various process conditions. The presented model considers the thermal behavior of the powder material including the phase change and densification during the SLM process. The temperature-dependent energy absorption and the increase in effective energy absorptivity due to the keyhole mode melting are also incorporated in the heat flux model to evaluate the process conditions in the presence of high energy density. Moreover, the single-track specimens were manufactured under various process conditions for validation of the proposed model. The predicted melt pool dimensions, as well as the melting modes (Conduction/Keyhole), demonstrated good agreement with the experimental measurements. Based on the analysis results, the process boundaries (Keyhole/Lack-of-Fusion) for the SLM process of AlSi10Mg are provided and the potential application of the proposed model for exploring the process window is discussed.
Lee, Kang-Hyun,Yun, Gun Jin Techno-Press 2021 Advances in aircraft and spacecraft science Vol.8 No.1
Selective laser melting (SLM), one of the most widely used powder bed fusion (PBF) additive manufacturing (AM) technology, enables the fabrication of customized metallic parts with complex geometry by layer-by-layer fashion. However, SLM inherently poses several problems such as the discontinuities in the molten track and the steep temperature gradient resulting in a high degree of residual stress. To avoid such defects, thisstudy proposes a temperature thread multiscale model of SLM for the evaluation of the process at different scales. In microscale melt pool analysis, the laser beam parameters were evaluated based on the predicted melt pool morphology to check for lack-of-fusion or keyhole defects. The analysis results at microscale were then used to build an equivalent body heat flux model to obtain the residual stress distribution and the part distortions at the macroscale (part level). To identify the source of uneven heat dissipation, a liquid lifetime contour at macroscale was investigated. The predicted distortion was also experimentally validated showing a good agreement with the experimental measurement.
선택적 레이저 용융 공정의 공정변수 평가를 위한 용융풀 유한요소 모델
이강현,윤군진 한국군사과학기술학회 2020 한국군사과학기술학회지 Vol.23 No.3
Selective laser melting(SLM) is one of the powder bed fusion(PBF) processes, which enables quicker production of nearly fully dense metal parts with a complex geometry at a moderate cost. However, the process still lacks knowledge and the experimental evaluation of possible process parameter sets is costly. Thus, this study presents a finite element analysis model of the SLM process to predict the melt pool characteristics. The physical phenomena including the phase transformation and the degree of consolidation are considered in the model with the effective method to model the volume shrinkage and the evaporated material removal. The proposed model is used to predict the melt pool dimensions and validated with the experimental results from single track scanning process of Ti-6Al-4V. The analysis result agrees with the measured data with a reasonable accuracy and the result is then used to evaluated each of the process parameter set.
Lee, Kang-Hyun,Yun, Gun Jin Techno-Press 2021 Advances in aircraft and spacecraft science Vol.8 No.1
Selective laser melting (SLM), one of the most widely used powder bed fusion (PBF) additive manufacturing (AM) technology, enables the fabrication of customized metallic parts with complex geometry by layer-by-layer fashion. However, SLM inherently poses several problems such as the discontinuities in the molten track and the steep temperature gradient resulting in a high degree of residual stress. To avoid such defects, thisstudy proposes a temperature thread multiscale model of SLM for the evaluation of the process at different scales. In microscale melt pool analysis, the laser beam parameters were evaluated based on the predicted melt pool morphology to check for lack-of-fusion or keyhole defects. The analysis results at microscale were then used to build an equivalent body heat flux model to obtain the residual stress distribution and the part distortions at the macroscale (part level). To identify the source of uneven heat dissipation, a liquid lifetime contour at macroscale was investigated. The predicted distortion was also experimentally validated showing a good agreement with the experimental measurement.
Evaluation of an IVR-ERVC strategy for a high power reactor using MELCOR 2.1
Lim, Kukhee,Cho, Yongjin,Whang, Seokwon,Park, Hyun Sun Elsevier 2017 Annals of nuclear energy Vol.109 No.-
<P><B>Abstract</B></P> <P>The IVR-ERVC (In-Vessel Retention of molten corium through External Reactor Vessel Cooling) is an effective severe accident management strategy for reducing the possibility of a reactor containment failure by terminating the severe accident progress inside a reactor. However, the technical applicability and feasibility of the IVR-ERVC design for an advanced high-power reactor should still be validated considering the uncertainties of physical models, the initial conditions and assessment methodologies. In this paper, the severe accident progress of the APR1400 for a large break loss-of-coolant accident is analyzed using MELCOR 2.1 when the reactor cavity is fully flooded. The chronology of events, the thermal hydraulic behaviors and the core degradation behaviors are analyzed. As a result of the MELCOR calculation, a relatively large portion of particulate debris is relocated to the bottom of the lower head at the end of the debris-quench mode, preventing effective heat transfer to the ex-vessel wall. Because the lower head wall cannot be ablated by melting in the MELCOR, the in-vessel wall temperature is increased as compared to the melting point of the lower head. The heat flux is maximized at approximately 3.5e4s and it is compared to the results from the lumped parameter method.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The MELCOR 2.1 calculation of the IVR-ERVC for the APR1400 is carried out. </LI> <LI> The analysis result using MELCOR is compared to the LPM results. </LI> <LI> Absence of wall ablation model causes the very high temperature of in-vessel wall. </LI> </UL> </P>
작은 그루브 각을 가지는 맞대기 P-GMA 용접에서의 용접전류에 관한 연구
김륜한,나석주,김철희,Kim, Ryoon-Han,Na, Suck-Joo,Kim, Cheol-Hee 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.4
The purpose of this paper is to propose a mathematical model of welding current for the P-GMAW by modifying the well known GMAW model. Welding power circuit is simply modeled as a RL electric circuit and solved as an ODE equation. The welding current depends on the joint shape, molten pool and welding parameters. To compare the molten pool effect to the welding current, CFD numerical simulation technique was adopted. Welding experiment is also conducted with the same welding parameters as used in numerical simulations to verify the proposed welding current model. The current model which is considered molten pool shape, is more fit to experiment result.