수치해석을 활용한 마찰교반용접 공정의 온도 특성 분석 연구

김무선 한국산학기술학회 2019 한국산학기술학회논문지 Vol.20 No.12

Friction Stir Welding is a welding technique for metal materials that utilizes the heat generated by friction between the material to be welded and the welding tool that rotates at high speed. In this study, a numerical analysis method was used to analyze the change in the internal temperature of the welded material during friction stir welding. As the welding target material, AZ31 magnesium alloy was applied and the welding phenomenon was considered a flow characteristic, in which a melting-pool was formed. FLUENT was used as the numerical tool to perform the flow analysis. For flow analysis of the welding process, the welding material was assumed to be a high viscosity Newtonian fluid, and the boundary condition of the welding tool and the material was considered to be the condition that friction and slippage occur simultaneously. Analyses were carried out for various rotational speeds and the translational moving speed of the welding tool as variables. The analysis results showed that the higher the rotational speed of the welding tool and the slower the welding tool movement speed, the higher the maximum temperature in the material increases. Moreover, the difference in the rotational speed of the welding tool has a greater effect on the temperature change. 마찰교반용접(Friction Stir Welding) 기술은 금속 소재를 대상으로 하는 용접기술 중의 하나로 용접대상이 되는 소재와 고속으로 회전하는 용접툴 사이의 마찰로 인한 열을 활용하여 소재의 융점 이하 온도에서 접합하는 기술이다. 이번 연구에서는 마찰교반용접을 진행할 때, 용접 대상물의 내부 온도 변화를 분석하기 위한 방법으로 수치해석기법을 사용하였다. 용접소재로는 마그네슘 합금인 AZ31을 고려하였으며, 용접현상을 멜팅풀(melting-pool)이 생성되는 유동특성으로 간주하고 유동해석을 수행하기 위해 유동특성 수치해석 툴인 FLUENT를 이용하였다. 용접과정의 유동해석을 진행하기 위해 용접소재는 고점도 뉴턴 유체로 가정하였고, 용접툴과 용접대상 소재의 경계면은 마찰 및 미끄러짐이 동시에 발생하는 조건으로 경계조건을 선정하였다. 그리고 용접툴의 회전속도 및 용접속도를 변수로 하여 다양한 해석을 진행하였다. 해석 결과로부터 용접툴의 회전속도가 높을수록, 용접속도가 느릴수록 소재 내 최고온도가 증가함을 확인할 수 있었으며, 그 중 용접툴의 회전속도 차이가 온도 변화에 더 큰 영향을 보임을 확인하였다.

Recent Advances in Friction-stir Welding Process and Microstructural Investigation of Friction Stir Welded Pure Titanium

Jae-Deuk Kim,Eun-Geun Jin,Siva Prasad Murugan,Yeong-Do Park 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.4

The use of titanium and its alloys is increasing day by day, especially in aerospace, automobile, and defense fields. Friction stir welding is a prominent solid-state joining process, which produces non-melting low heat input welds with less residual stresses compared to the conventional welding process. The physical and chemical properties of Ti such as low thermal expansion and thermal conductivity, relatively high melting temperature(1668℃) and high reactivity makes the FSW a favorable joining process for Ti alloys. However, Ti friction stir welds reveal highly complexed microstructure evolution in the weld zone and exhibit several defects which can influence the mechanical properties of the weld. This paper aims at a review on the microstructural evolution and typical defects formation during the FSW of CP-Ti, with the brief review on the fundamentals of friction stir welding process and Ti and its alloys.

필렛 접합부를 갖는 알루미늄 합금 압출재의 마찰교반용접에 관한 연구

김환진,김현수,강성욱 한국기계기술학회 2020 한국기계기술학회지 Vol.22 No.6

In this study, experiments and simulations were performed for fillet joint friction stir welding according to tool shape and welding conditions. Conventional butt friction stir welding has good weldability because heat is generated by friction with the bottom of the tool shoulder. However, in the case of fillet friction stir welding, the frictional heat is not sufficiently generated at the bottom of the tool shoulder due to the shape of the tool and the shape of the joint. Therefore, it is important to sufficiently generate frictional heat by slowing the welding speed as compared to butt welding. In this study, experiments and simulations were carried out on an aluminum battery housing made by friction stir welding an extruded material with a fillet joint. The temperature of the structure was measured using a thermocouple during welding, and the heat source was calculated through correlation analysis. Thermal elasto-plastic analysis of the structure was carried out using the calculated heat source and geometric boundary conditions. It is confirmed that the experimental results and the simulation results are well matched. Based on the results of the study, the deformation of the structure can be calculated through simulation even if the tool shape and welding process conditions change.

Residual stresses analysis of friction stir welding using one-way FSI simulation

강성욱,장범선,송하철 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3

When certain mechanisms, such as plastic deformations and temperature gradients, occur and are released in a structure, stresses remainbecause of the shape of the structure and external constraints. These stresses are referred to as residual stresses. The base materiallocally expands during heating in the welding process. When the welding is completed and cooled to room temperature, the residualstresses are left at nearly the yield strength level. In the case of friction stir welding, the maximum temperature is 80% to 90% of themelting point of the materials. Thus, the residual stresses in the welding process are smaller than those in other fusion welding processes;these stresses have not been considered previously. However, friction stir welding residual stresses are sometimes measured at approximately70% or above. These residual stresses significantly affect fatigue behavior and lifetime. The present study investigates the residualstress distributions in various welding conditions and shapes of friction stir welding. In addition, the asymmetric feature is considered intemperature and residual stress distribution. Heat transfer analysis is conducted using the commercial computational fluid dynamics programFluent, and results are used in the finite element structural analysis with the ANSYS Multiphysics software. The calculated residualstresses are compared with experimental values using the X-ray diffraction method.

Temperature Behavior in Dissimilar Butt Joint During TIG Assisted Friction Stir Welding

방희선,엠 에스 엠조이,Bang, Hee-Seon,Bijoy, M.S. The Korean Welding and Joining Society 2011 대한용접·접합학회지 Vol.29 No.5

Three-dimensional finite element analysis is performed to study the temperature distribution phenomenon of TIG assisted friction stir welding (TAFSW) between dissimilar plates (Al 6061-T6 and stainless steel 304). TAFSW is a solid-state welding process that integrates TIG (Tungsten Inert Gas) into a friction stir welding (FSW), to preheat the harder material ahead of FSW tool during welding. In order to facilitate the industrial application of welding, 3D numerical modeling of heat transfer has been carried out applying Finite Element Method (FEM). The temperature distribution due to heat generation during TAFSW on dissimilar materials joint is analysed using in-house solver. Moving heat source along with frictional heat between the work specimens and tool surface is considered to calculate the heat input. The analytical model used predicts successfully the maximum welding temperatures that occur on the dissimilar materials during TAFSW. Comparison with the infra red camera and thermocouple measurement results shows that the results from the current numerical simulation have good agreement with the measured data.

밀링을 이용한 AI합금의 마찰 교반용접용 최적공구형상 및 치수개발에 관한 연구

장석기,신상현 한국마린엔지니어링학회 2001 한국마린엔지니어링학회지 Vol.25 No.4

Friction stir welding is a solid phase welding process that does not melt the metal when welding. The FSW is the most remarkable and potentially useful new welding technique that is still in development. Friction stir butt welding process on 2 mm thick Al 1050 plates by utilizing a milling machine was experimentally studied. With the optimized heat generating tool welds could be achieved that are void and crack free. It was found that the friction stir welded tensile test specimens failed in the HAZ outside of the weld metal, and that the tensile strength was above 90% of that of the base metal.

마찰교반용접시 Al 6061의 파괴인성의 평가에관한 연구

윤재영,송주현 한국기계기술학회 2023 한국기계기술학회지 Vol.25 No.6

In this study, we investigated the change in fracture properties after friction stir welding on Al606. In the L-T direction test, the fracture toughness of the unwelded base material was 275 MPa, and the specimen subjected to friction stir welding (FSW) was 227 MPa, showing that the fracture toughness decreased significantly with friction stir welding. In the T-L direction test, the difference between the base material and the weld material was not large, but the fracture toughness was shown to decrease during welding. In the comparison of the L-T direction and the T-L direction, it was found that both the base material and the weld material showed high fracture toughness in the L-T direction.In this study, the following conclusions were obtained after friction stir welding of Al 6061-T6.

Effect of Initial Grain Size on Friction Stir Weldability for Rolled and Cast CoCrFeMnNi High‑Entropy Alloys

Sangwon Park,Hyunbin Nam,Youngsang Na,Hyoungseop Kim,문영훈,강남현 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.5

This study investigated the influence of the initial grain size on the plastic deformation and tunnel defects that occurredfrom friction stir welding of CoCrFeMnNi high entropy alloys (HEAs). The rolled and cast HEAs had a grain size of 2.8and 308 μm, respectively. After friction stir welding, the cast HEA weld had a grain size of 1.8 μm, which was coarser thanthat of the rolled HEA weld (1.4 μm). Therefore, the dynamic recrystallization ratios were 60.7 and 99.6% for the rolled andcast HEAs, respectively. The cast HEA weld with a large grain size contained a higher density of high-angle boundaries andtwins than the rolled HEA weld with the small grain size. The cast HEA had a larger resistance to plastic deformation owingto the larger fraction of Σ3 twin boundaries than the rolled HEA during friction stirring. This was associated with the highstrain hardening rate during tensile testing and to the significant amount of W dissolved from the stirring tool in the castHEA weld. Thus, the cast HEA weld had a higher tunnel defects ratio than the rolled HEA weld. The total unbonded ratiosof the rolled and cast HEA welds were 0.2 and 7.2%, respectively, indicating that the rolled HEA had better weldability thanthe cast HEA.

마찰교반점접합한 5454-O 알루미늄합금 판재의 접합부 거시조직 및 기계적 특성에 미치는 접합인자의 영향

최원호,권용재,윤성욱,강명수,임창용,서종덕,홍성태,박동환,이광학,Choi, Won-Ho,Kwon, Yong-Jai,Yoon, Sung-Ook,Kang, Myoung-Soo,Lim, Chang-Yong,Seo, Jong-Dock,Hong, Sung-Tae,Park, Dong-Hwan,Lee, Kwang-Hak 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.6

Friction stir spot welding between 5454 aluminum alloy sheets with the different thicknesses of 1.4 and 1.0 mm was performed. In the welding process, the tool for welding was rotated ranging from 500 to 2500, and plunged to the depth of 1.8 mm under a constant tool plunge speed of 100 mm/min. And then, the rotating tool was maintained at the plunge depth during the dwell time ranging from 0 to 7 sec. The pull-out speed of the rotating tool was 100 mm/min. The increase of tool rotation speed resulted in the change of the macrostructure of friction-stir-spot-welded zone, especially the geometry of welding interface. The results of the tensile shear test showed that the total displacement and toughness of the welds were increased with the increase of the tool rotation speed, although the maximum tensile shear load was decreased. However, the change in the dwell time at the plunge depth of the tool did not produce the remarkable variation in the macrostructure and mechanical properties of the welds. In all cases, the average hardness in friction-stir-spot-welded zone was higher than that of the base metal zone. By the friction stir spot welding technique, the welds with the excellent mechanical properties than the mechanically-clinched joints could be obtained.

Welding strain analysis of friction stir-welded aluminum alloy structures using inherent strain-based equivalent loads

Hyung Suk Mun,Sung-Il Seo 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.9

Friction stir welding is a solid-state welding method commonly used for aluminum alloy or lightweight metal. It has the advantages of low welding strain, high welding quality, and low residual welding stress while requiring no protection gas. Welding strain analysis of friction stir welding using finite element analysis has been the subject of many studies that focused on the substance fluid using threedimensional computational fluid dynamics; however, this approach is inefficient for large structures and requires much time for analysis. To address this drawback, this study proposes a faster method for analyzing extruded aluminum material that exploits the advantages of the inherent strain-based equivalent load.