• Journal of Welding and Joining
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• v.27 no.3
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• pp.52-59
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• 2009

Flash butt welding is applied in many industries. New technology was developed recently for joining billets which called "EBROS (Endless Bar Rolling System)". After reheating billets in furnace, two billets were joined using flash butt welding. The objective of this study was to investigate the effect of alloying elements on mechanical properties of flash butt welded zone of hot rolled steel bar. The tensile properties on welded zone of Fe-Mn steel and Fe-Mn-V steel were dropped as compared with non-welded zone. Fe-Mn-Nb steel was opposed to the former. It was found that the white band at the welded zone had high ferrite volume fraction and large ferrite grain size. The vertical white band between flash butt welded billets was transformed into an arrowhead it of steel bar. According to this band, softening has been appeared. There was a interesting phenomenon with HAZ of Fe-Mn-Nb Steel, 40nm scale of particles were observed and hardness of HAZ was higher than non-welded zone.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.74-82
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• 1999

Nowadays, the crank shaft motor vehicle has become essential as the important component. The machining precision was asked for manufacturing the shaft. They could be unstable in the quality by the conventional are welding. Both in-process quailty control and high reliability of the weld are the major concerns in applying friction wlding to the economical and qualified mass-production. No reliable nondestructive monitoring method is avaliable at present to determine the real-time evaluation of automatic production quality control for bar-to-bar friction welding of the crank shaft of O.D 24mm for motor vehicle. This paper, so that, presents the experimental examinations and statistical quantitative analysis of the correlation between the cumulative counts of acoustic emission(AE) during plastic deformation periods of the welding and the tensile strength and other properties of the bar-to-bar welded joints of O.D. 24mm shaft as well as the various welding variables, as a new approach which attempts finally to develop real-time quality monitoring system for friction welding, resulting in practical possiblility of real-time quality control more than 100% joint efficiency showing good weld with no micro structural defects.

• Proceedings of the KWS Conference
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• 1995.10a
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• pp.101-104
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• 1995

This paper deals with the development of fundamental design and manufacturing technique of hydraulic valve spool by optimizing of friction welding, the development of in-process real-time weld quality evaluation technique by acoustic emission and the evaluation of the mechanical properties and the fatigue life about the bar-to-bar dissimilar friction welded hydraulic valve spool steels.

• Transactions of Materials Processing
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• v.27 no.5
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• pp.296-300
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• 2018

T-type and H-type section steels were generally used in shipbuilding and offshore plants and were produced by welding technology. These section steels were produced by handwork, and the supplying amounts can't satisfy the demand amounts of the fabrication companies. In case of fillet welding, there are some gaps in weld-joint region due to no groove preparation processing and it can occur crack initiation in the welded region. It is important to evaluate the microstructural and mechanical properties of welded zone to solve these problems. To satisfy the demand amounts of T-bar parts, automatic welding technology was introduced and several conditions as a function of welding speeds were carried out to improve the manufacturing speed. Heat-affected zone may be affected by variation of heat input and cooling rate through automatic welding speed and welding speed is necessary to be optimized. In this study, fusion zone and heat-affected zone were investigated by microstructural and mechanical analysis and were evaluated whether the welded parts were sound or not.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.327-335
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• 1999

A batch process in which transfer bars are rolled in single bar units involves many problems in terms of quality, yield and threading stability. The endless rolling process is an effective solution to such problems. In this, study, an analysis model is proposed to calculate the distribution of normal stress in endless rolling process. The model was examined by comparing with the result of experiment. A device using the spring is developed for improving the welding quality.

• Journal of Welding and Joining
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• v.14 no.2
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• pp.57-64
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• 1996

In this paper, authors are trying to find optimum spot weldig conditions to minimize indentation of the plate surface which is crucial to quality of stainless rolling stocks. At first, to derive a simple equation to estimate the depth of indentation, a simplified one-dimensional bar model is proposed and validity of the model is confirmed by experiments. And also, to find proper welding conditions giving satisfied tensile strength of the welded joint, a simple formula is derived referring to the standard spot welding conditions by AWS. Optimization problem is formulated to find welding conditions such as welding current, time and applied force which give minimum indentation and proper tensile strength of joint, and solutions are found out. According to the results, the depth of indentation can be expressed by applied electrode froces and it can be shown that an optimum applied force exists.

• Proceedings of the KWS Conference
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• 1995.04a
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• pp.114-117
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• 1995

A study of friction welding of high speed steel(SKH51) bar for blade side to carbon steel(STC3) bar for shank side was carried out experimentally through tensile test, hardness lest, microstructure, and acoustic emission (AR) test. So, this paper deals with optimizing the welding conditions and the real-time quality(strength) evaluation of friction welded joints by acoustic emission technique.

• Journal of the Korea Institute of Building Construction
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• v.5 no.3 s.17
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• pp.131-138
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• 2005

The study is focused on the settling the developing direction of korean gas pressure welding machine which can be applied in korean construction sites with moderate and high performance. Gas pressure welding is more economical and has good performances than other steel bar jointing methods, as arc welding and mechanical joint etc. Therefore in Japan, the gas pressure welding, which has less loss of steel bars and low performance of joints, when connecting the D29 and thicker steel bars, Is one of the typical connection of steel reinforcement. But in Korea, the gas pressure welding method is not widely used caused by the shortage of skilled workers, and this situation in Korea can not be solved in short period. The training of the skilled workers takes long period(around $6\~10$ years), and there is no certification system for gas pressure welding. So to activate the gas pressure welding in Korea, the development of the automatic gas pressure welding machine is necessary, which gives regular performance of the steel bar joints and can be operated by not sufficient skilled workers. The automatic gas pressure welding machine was developed in Japan, but this machine has many problems when applied in korean construction sites. Therefore, it is necessary to develop a korean automatic gas pressure welding machine to overcome this problems. To develop korean automatic gas pressure welding machine, the problems, which shows when applied in korean construction sites, need to be investigated. According to the investigation, counterproposals are presented for the pragmatical development of the korean automatic gas pressure welding machine.

• Journal of Advanced Marine Engineering and Technology
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• v.17 no.4
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• pp.38-48
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• 1993

A study on friction welding of stainless steel bar(SUS431) to chrome molybdenum steel bar(SCM21) was accomplished experimentally through analysis for relations among friction welding conditions, tension test, hardness test, microstructure test and acoustic emission test. The results obtained are summarized as follows ; 1. Through friction welding of SUS431 bar to SCM21 bar, the optimum welding condition by considering on strength and toughness was found to be the range of heating time of 3-5 sec when the number of rotating speed of 2000rpm, heating pressure of 10kg/$mm^2$, and upsetting time of 4 sec. 2. Quantitative ralationship was identified between heating time($T_1$, sec) and tensile strength (${\sigma},\;kgf/mm^2$) of the friction welded joint and the relation equation is $\sigma$=52.62$T_1{^{0.06}}$. 3. Through AE test, quantitative relationship was confirmed between heating time($T_1$, sec) and total AE(N, counts) during welding, and the relation is computed as follows ; N=30413.6$e^{0.06T1}$. 4. It was confirmed that the quantitative ralationship exists between the tensile strength of the welded joints and AE cumulative counts. And the relation is computed as the following ; ${\sigma}$=16.37(ln N)- 116.4. 5. When ONZ=36500-41500 counts by $OT_1Z$=3~5sec, it was identified by experiment that the range of welded joint tensile strength is 55.6-57.7kgf/$mm^2$/ whose joint efficiency is more than 100%, and it was experimentally confirmed that the real-time nondestructive quality(strength) evaluation for the friction welded joints could be possible by acoustic emission technique.

• Journal of Ocean Engineering and Technology
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• v.10 no.3
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• pp.24-33
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• 1996

Up to now, most of studies on mechanical properties in friction welded components are about tensile and bending strength. However the fatigue studies on the friction-welded components subjected to repeated stress are not available. The purposes of this study are the development of fundamental design and the development of in-process real-time weld quality evaluation technique by acoustic emission for the bar-to-bar dissimilar friction welding of hydraulic valve spool steels.