• Title/Summary/Keyword: Butt weld

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Butt 용접부에서 잔류응력이 피로균열성장거동에 미치는 영향에 대한 실험적 연구 1

  • 최용식;김영진;우흥식
    • Journal of Welding and Joining
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    • v.6 no.4
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    • pp.27-34
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    • 1988
  • The objective of this paper is to investigate the effect of residual stress on fatigue crack growth behavior. For this purpose, submerged arc welding was performed on SM50A steel plate and post weld heta treatment (PWHT) was followed. Residual stress distribution on the weld plate was determined by a hole drilling method and a series of .DELTA.P-const. and .DELTA.K-decreasing fatigue test were performed on the three different regions, i.e. weld metal, HAZ and base metla. Following conclusins were achieved. 1. In "as welded" specimens, tensile residual stresses were produced in the center portion of the specimen while compressive residual stresses were produced near the edges. In PWHT specimens, however, most of the residual stresses were disappeared. 2. The fatigue crack growth behavior in low .DELTA.K region was considerably affected by the presence of residual stress in both "as welded" and PWHT specimens. 3. Because of the relaxation of residual stresses in PWHT condition, the values of m increased from 2.62-2.78 (in the "as welded" condition) to 3.57-3.91 (in the "PWHT" condition)3.91 (in the "PWHT" condition)condition)

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Improvement of Gap Bridging Ability in $CO_2$ Laser-GMA Hybrid Welding (조선용 강재의 $CO_2$레이저 GMA 하이브리드 용접에서 갭 브리징 능력 향상기술 개발)

  • Chae, Hyun-Byung;Kim, Cheol-Hee;Kim, Jeong-Han;Rhee, Se-Hun
    • Journal of Welding and Joining
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    • v.24 no.5
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    • pp.49-56
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    • 2006
  • For laser welding in shipbuilding industry, gap bridging capability is one of the most important characteristics to achieve the high productivity and good weld quality. Recently, laser-GMA hybrid welding process is regarded as a distinctive method to overcome the tight gap tolerance with improving the productivity. In this study, the influence of process parameters on the bead formation was experimentally analyzed and the relationship between the process parameters and geometric imperfections was investigated. It was revealed that undercut, excessive weld metal, excessive penetration and incompletely filled groove were the major geometric imperfections. The optimized wire feeding and arc pressure were necessary to ensure the gap bridging ability. The approach to select the process parameters was conducted for butt welding with up to 2mm joint gap, in which the sound weld beads were generated without changing the welding speed.

Estimation of Residual Stress Distribution for Pressurizer Nozzle of Kori Nuclear Power Plant Considering Safe End (고리 원전 가압기 노즐 용접부 잔류응력 예측 시 안전단 고려가 이종 금속 용접부 잔류응력 분포에 미치는 영향)

  • Song, Tae-Kwang;Bae, Hong-Yeol;Chun, Yun-Bae;Oh, Chang-Young;Kim, Yun-Jae;Lee, Kyoung-Soo;Park, Chi-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.32 no.8
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    • pp.668-677
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    • 2008
  • In nuclear power plants, ferritic low alloy steel nozzle was connected with austenitic stainless steel piping system through alloy 82/182 butt weld. Accurate estimation of residual stress for weldment is important in the sense that alloy 82/182 is susceptible to stress corrosion cracking. There are many results which predict residual stress distribution for alloy 82/182 weld between nozzle and pipe. However, nozzle and piping system usually connected through safe end which has short length. In this paper, residual stress distribution for pressurizer nozzle of Kori nuclear power plant was predicted using FE analysis, which consideded safe end. As a result, existing residual stress profile was redistributed and residual stress of inner surface was decreased specially. It means that safe end should be considered to reduce conservatism when estimating the piping system.

Laser Weldability and Formability of Hot Rolled Steels for Hydroforming Applications (하이드로포밍용 열연 강재의 레이저 용접성 및 성형 특성)

  • Lee Won-Beam;Lee Jong-Bong
    • Journal of Welding and Joining
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    • v.22 no.6
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    • pp.19-24
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    • 2004
  • The laser welding and its analysis of thin-sheet carbon steels were carried out with high power $CO_{2}$ laser. The main factor of weld quality of laser welding is gap and edge quality. This work was preformed to focus on the gap tolerance problem during laser welding. First, bead on plate welding of thin sheet was examined to investigate the effect of laser welding variables, and to obtain optimum welding condition. Butt welding was also carried out to show the effect of gap on the laser weldability of thin sheet. In order to investigate the effect of gap on formability of welded thin sheet, LDH test was caried out. At high welding speed, the partial penetration was obtained by low heat input. Otherwise, porosity was formed in the bead at low weld speed because of too much heat input. The optimum welding condition of welding was derived from bead width, penetration and hardness property. The maximum gap tolerance on laser welding was observed to be about 0.2mm. This gap size has good relationship with beam size of laser spot(about 0.3mm). The formability of welded sheet was about $80{\%}$ value of base metal and the gap size has not affected on the formability, although weld quality is dependent on the gap size.

Design and Output Characteristic of AC Pulse Current for MIG Welding of Ai Sheet (박판 Al MIG 용접용 AC펄스 전류 파형의 설계 및 출력특성)

  • 조상명;김태진;이창주;임성룡;공현상;김기정
    • Journal of Welding and Joining
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    • v.21 no.2
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    • pp.57-63
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    • 2003
  • Since new types of vehicles or structures made from thin aluminum alloy are under rapid development and some products are already on the market, welding of aluminium sheet is increasing. MIG(Metal Inert Gas), MIG-Pulse, TIG(Tungsten Inert Gas) welding are the typical Ai welding. MIG welding has the advantage of high speed, but it is difficult to apply to the thin plate, because of bum-through by the high heat input and spatter. MIG-Pulse welding can weld without spatter and burn-through, but when the gap exists at the welding joint, there is quite a possibility of bum-through. TIG welding is difficult to weld at a high speed. AC Pulse welding alternates between DCEP(Direct Current Electrode Positive) and DCEN(Direct Current Electrode Negative). DCEN is higher wire melting rate than DCEP, while lower temperature of droplet than DCEP. In AC Pulse welding, far fixed welding current, wire melting rate increases as the EN ratio increases. For fixed wire feed rate, welding current decreases as the EN ratio increases. Because of these features, the temperature of droplet, the depth of penetration, the width of bead decrease and the reinforcement height increases as EN ratio increases, and these are able to weld at a high speed, lower heat input. It is the purpose of this study that design of AC pulse current waveform for MIG welding of Al sheet and estimation of output characteristic.

Effect of Forced Cooling condition along with Welding on Welding Angular Distortion (용접 후면 강제냉각조건이 용접각변형에 미치는 영향)

  • Park, Jeong-Ung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.4
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    • pp.2021-2026
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    • 2013
  • In this study, the effect on the welding angle distortion was reviewed by carrying out a thermal elastic-plastic analysis while changing the cooling condition(width, length, and distance from weld torch to cooling torch) the back of the welding zone for the butt weld joint. The review results revealed that maximum 57% of reduction in the angle distortion was achieved when the distance between weld torch and cooling tip of 25mm, cooling length of 80mm, and cooling width of 30mm were maintained.

Development of Rotor Shaft Manufacturing Process using a Large Friction Welding (대형마찰용접을 이용한 로타샤프트 제조공정개발)

  • Jeong, H.S.;Lee, N.K.;Park, H.C.;Choi, S.K.;Cho, J.R.
    • Transactions of Materials Processing
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    • v.16 no.4 s.94
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    • pp.266-270
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    • 2007
  • Inertia welding is a solid-state welding process in which butt welds in materials are made in bar and in ring form at the joint face, and energy required for welding is obtained from a rotating flywheel. The stored energy is converted to frictional heat at the interface under axial load. The quality of the welded joint depends on many parameters, including axial force, initial revolution speed and energy, amount of upset, working time, and residual stresses in the joint. Inertia welding was conducted to make the large rotor shaft for low speed marine diesel engine, alloy steel for shaft of 140mm. Due to material characteristics, such as, thermal conductivity and high temperature flow stress, on the two sides of the weld interface, modeling is crucial in determining the optimal weld parameters. FE simulation is performed by the commercial code DEFORM-2D. A good agreement between the predicted and actual welded shape is observed. It is expected that modeling will significantly reduce the number of experimental trials needed to determine the weld parameters.

A Study on an Electro-Magnetic System far Arc Rotating in MIAB Welding (MIAB용접에서 아크 회전을 위한 전자기 시스템에 관한 연구)

  • 최동혁;김재웅
    • Journal of Welding and Joining
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    • v.19 no.4
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    • pp.391-398
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    • 2001
  • MIAB welding method uses a rotating arc as its heat source and is known to be efficient in pipe butt welding. The arc is rotated around the weld line by the electro-magnetic force resulting from the interaction of arc current and magnetic field. This paper is concerned with the experiment of initial stage for process control, monitoring for weld quality, and the design of coil system which is efficient of flux generation and concentration. A coil system for the generation of magnetic flux was designed and constructed. Magnetic flux density and arc rotating behavior are important factors in MIAB welding, so the relations between these factors and process parameters were investigated. Various experiments were performed for the steel pipes(48.1mm O.D and 2.0mm thickness). The magnetic flux density is increased by increasing exciting current and decreasing gap size. The maximum of arc rotating frequency is affected by exciting current and gap size. However, the variations of arc rotating frequency during welding and then the melting process are mainly influenced by welding current. Thus, it is considered that the results of this study can be used as important data on the monitoring for weld quality and the design of efficient coil system.

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Prediction of Welding Imperfection with Idealization of Welding and Their Accuracy (용접이상화에 의한 용접부정의 예측과 정도)

  • Lee, Jae-Yik;Chang, Kyong-Ho;Kim, You-Chul
    • Journal of Welding and Joining
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    • v.31 no.5
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    • pp.15-19
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    • 2013
  • In order to reduce a grand compute time in prediction of welding distortion and residual stress by 3D thermal elastic plastic analysis, idealization of welding that is methods to heat input simultaneously in all weld metal on the same welding direction is carried out on two weld joints(butt welding and fillet welding). Then, the accuracy of acquired results is investigated through the comparison of the high accuracy prediction results. The thermal conduction analysis results by idealization of welding, the temperature is raised accompany with beginning of heat input because all of weld metal is heated input at the same time. On the other side, the temperature witch predicted with high accuracy is raised at the moment heating source passes the measuring points. So, there is difference of time between idealization of welding and considering of moving heat source faithfully. However, temperature history by idealization of welding is well simulated a high accuracy prediction results.

Friction Stir Welding in Extrusion Aluminum Carbody of HEMU-400X (Highspeed EMU-400km/h eXperiment) (차세대 분산형 고속전철용 압출재 알루미늄 합금의 마찰교반접합)

  • Chang, W.S.;Chun, C.K.;Kim, H.J.;Park, I.G.;Paik, J.S.;Ro, Y.H.
    • Proceedings of the KSR Conference
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    • 2008.06a
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    • pp.980-985
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    • 2008
  • Since its invention at TWI in 1991, Friction Stir Welding (FSW) has become a major joining process in the aerospace, railway and ship building industries especially in the fabrication of aluminium alloys. In an attempt to optimize the friction stir welding process of Al alloys for extrusion Aluminium carbody of HEMU-400X (Extrusion Aluminum 6xxx series), effects of joining parameters such as tool rotating speed, plunging depth and dwelling time on the weld joints properties were evaluated. Experimental tests were carried out for butt joined Al plates. A wide range of joining conditions could be applied to join Al alloys for Extrusion Aluminum 6xxx series without defects in the weld zone except for certain welding conditions with an insufficient heat input. The microstructures of welds have dynamic-recrystallized grain similar to stir zone in FSW weld. For sound joints without defects, at the rotation speed of 700 rpm with different welding speeds, the tensile strengths of the Stir Zone(SZ) were almost the same, 80% of those of the base metal. (JIS Z 2201)

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