• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.1
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• pp.45-53
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• 2003

For the improvement of welding performance, high-efficiency inverter system was designed and applied that system to the conventional large scale Flashbutt welder. The inverter systems are consists of full bridge PWM power control system and DSP controller. This inverter system has increased switching frequency of power control system of Flashbutt welder. For the test of application effects, we compared an our inverter control system with a conventional thyristor control system. In the results, we confirmed that our system has decreased the welding spatter amouts and improved welding performance.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.793-799
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• 2004

In track a third weakness point is joint part, turnout part, curve part. One of them joint part of rail have been known to the most weak point by loosen of joint bar and fish bolt due to impulse and vibration by wheel contact at times. In addition happen to deformation and failure at end of rail, failure and miniature of ballast gravel. Finally impact between wheel and rail become origin cause of a welded rail, noise and vibration. riding condition deterioration, besides track failure. In the present domestic, Thermite and Gas pressure weldings have been used to continuous welded rail(CWR), however stiffness and confidence in quality is lower than Flash butt welding method. FRW have the excellent capacity, however have a shortcoming large scale of machine and power equipment. Therefore we will introduce Mobile Flash Butt Welder can weld in track.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.384-389
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• 2002

This study was aimed to evaluate the weldability and optimize the welding conditions for flash butt welding of 780MPa grade steel applied to the automotive bumper reinforcement. And then the relationship between the welding conditions and the joint performance relating specifically to coil-joining steel would be established. The effect of welding conditions between flashing and upsetting process was elucidated. Microstructure observation of the joint indicated that the decarburized band was mainly changed with upsetting process. Width of HAZ was also related to the upsetting conditions rather than the flashing conditions. Generally maximum hardness at HAZ was correlated with $C_{eq}$ of steel and the empirical relationship was obtained to estimate the HAZ properties. Tensile elongation at the joint was usually decreased with increasing the initial clamping distance. Investigation of fracture surface after tensile and bending tests reveal that the origin of cracking at the joint was oxide inclusions composed of $SiO_2$, MnO, $Al_2$ $O_3$, and/or FeO. The amount of inclusions was dependent on the composition ratio of Mn/Si in steel. If this ratio was above 4, the amount of inclusions was low and then the resistance to cracking at the joint was enough to maintain the joint performance. It was obtained that the flashing process influenced the conditions for the energy input to establish uniform or non-uniform molten layer, while the upsetting conditions influenced the joint strength. Heat input variable during flashing process was also discussed with the joint properties.

• Journal of the Korean Society of Safety
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• v.7 no.1
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• pp.65-72
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• 1992

Objective of this research is to evaluate fracture behaviors of fresh-butt welded metal by the acoustic emission technique. The specimens used are medium carbon steel(SM45C), mild steel (SS41) and stainless steel(SUS304), which have different weldability. The similar welding and dissimilar welding processes are considered, in the former SM45C, SS41 and SUS304 are used, in the later the following metals are used SM45C and SS41, SM45C and SUS304 and SS41 and SUS304. The characteristics of fracture in weld metal are eshmated by the tension test with nominal speciemns, the fracture toughness test with compact tension specimens and fractography analysis. The results of tension test show for base metals and similar welding materials that the yield strength and ultimate strength of similar welding materials are increased, the elongation of those are decreased. The weldability of SUS304 is better than that of SM45C and SS41 In similar welding materials. Mechanical properties of dissimilar welding mateiiths we lower than those of similar welding materials. In dissimilar welding materials, the weldability of SM45C and SUS304 is better than that of SM45C and SS41, and also weidability of SS41 and SUS304 is better than SS41 and SM45C. Comparing mechanical properties with AE counts, it is found that AE conuts appeared on a small before the limit load of elasticity(P$_{e}$), and apper greatly near yield strength region in tension test. These results could contribute to the safety analyses and the evaluation of strength for welding structure.e.

• Journal of the Korean Society of Safety
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• v.9 no.1
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• pp.9-18
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• 1994

In this study, we conducted experimental tests to evaluate fracture behaviors of fresh-butt welded metal by Acoustic Emission technique. We selected similar welding and dissimilar welding process, the one welded for SM45C, SS41 and SUS304 of each material, the other for SM45C and SS41, SM45C and SUS304 and SS41 and SUS304. The fracturing processes of weld metal were estimatied through the fracture toughness test with compact tension specimens and fractography analysis. In ASTM test method E-399, type I curves for materials of this study were obtained by load-cod diagram of fracture toughness test. and 5% offset load( $P_{5}$) was estimated as the estimated crack initial load( $P_{Q}$), The estimated crack initial load( $P_{Q}$) of similar welding materials generally lower than base matal, and then SM45C appeared greatly in decreasing rate of PB, SS41 and SUS304 appeared in order. $P_{Q}$ of dissimilar welding materials were lower than the similar welding materials. $P_{Q}$ of welding of SM45C and SS41 appeared in small, SUS304 and SS41 appeared greatly in dissimilar welding materials. In fracture toughness test, AE counts increased before the inflection point of the slope, decreased after that. It was found that increasing of AE counts were due to the microcrack formation at the crack tip near the $P_{5}$ point through AE data. For welding materials in this study, both low and high AE amplitude appeared simulataneously. It was confirmed that the low AE amplotude was due to formation of micro void, micro crack or micro dimple, the high AE amplitude was caused by microvoid coalescence and quasi-cleavage fracture through analyses of fractograpy.apy.apy.apy.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.163-169
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• 2003

In order to develop domestic railway technology, it is necessary that manufacturing technology of turnout should be kept up with update level, because turnout is the core component of high speed railway. Manganese crossing made of high manganese alloy steel is a important component of turnout. So far, this could not have been welded with rail steel due to metallic problem in Korea. However, joint technology hereunder between manganese crossing and rail by using Flash Butt Welding which is developed by Kangwon Railtech Co., Ltd is the state of the art and enable to realize rail continuousness in turnout section, speed up train velocity, reduce maintenance cost, and enhance riding quality.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.1067-1069
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• 2001

자동차 분야에 있어서 자동차 바퀴의 림(rim)용접에서 flash butt 용접이 널리 이용되고 있는 데 이 분야 역시 경량화에 따른 고강도 강재의 채택이 불가피하게 대두되고 있고, 고장력강의 flash butt 용접이 중요한 이슈가 되고 있다. 좋은 용접품질 획득을 위한 균일한 가열을 위해 전류의 시간적 편차가 큰 thyristor에 의한 제어는 큰 flash를 유발할 수 있어서 고장력강과 같은 경우에서 산화물의 발생을 유발시킬 수 있기 때문에 주의하지 않으면 안된다. 따라서 flashing과 upset의 균일성을 획득하기 위해서는 용접전류의 편차가 크지 않도록하는 기술과 최적의 전류를 공급하는 기술, 그리고 용융량과 배출량의 함수적 제어가 중요한 데 이를 위해서 인버터 방식의 전류제어기술이 개발되면 큰 효과를 기대할 수 있다. 본 논문에서는 DSP controller를 이용하여 사이리스터 위상제어를 다이오우드 정류기와 직류 링크 캐패시터, PWM 인버터로 구성해 인버터 방식의 정전류제어 기술을 개발하여 용접성을 비교 실험하여 결과를 보여준다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.240-248
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• 2004

Recently, the customer's demands for automotive steel sheet have been diversified and sterned more. Therefore, as the tendency of auto industry light-weight, one among these requirements is the trend for high strength together with the thinness of automotive steel sheet. Because Mn added essentially in producing high strength steel sheet is bonded strongly with oxygen, the Fine oxidation layer was created at the welding face after the flash butt welding operated in entry section of pickling line. Thereby it was caused the crack or breakage of welding part in process of cold rolling. At this research, in order to protect the contact Mn with oxygen in atomosphere it was considered to fire oxygen with LNG and the related researches have been gone forward with the find out concrete and to apply them to operation.

• Journal of Welding and Joining
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• v.7 no.2
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• pp.60-69
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• 1989

The present study was aimed at investigating the effect of welding parameters such as welding current, electrode force(or squeeze force) and parts cleaning on the sound weld, and establishing the most reliable weld conditions for HWP(Heavy Water Reactor) fuel end capping with the resistance upset butt welding. Major results obtained are as follows. 1. The amount of sound weld was increased with increasing weld current(5.0-11KA) because the activated diffusion with increasing heat generation played an important role in eliminating the porosity and weld line in the weld interface. 2. It was found that weld current was not significantly influenced by the electrode force although the increase of it caused a slight increase of weld current and upset deformation. 3. Acetone rinsing before drying for the Zircaloy-4 end cap cleaning produced the reliable sound weld because it would remove the remaining solvent and surface films, and provided the uniform contact between the end cap and the tube. 4. The optimum welding conditions for fuel end capping by a resistance upset hytt welding are obtained as follows. weld current: 10-11KA, electrode force: 62-90KPa parts cleaning: vapor degreasing.rarw.water, acetone rinsing.rarw.drying.

• Journal of Welding and Joining
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• v.9 no.4
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• pp.60-68
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• 1991

The weld quality of end cap welds in Pressurized Heavy Water Reactor (PHWR) Fuel is extremely important for the fuel performance in the nuclear reactor. The quality of resistance upset welds is currently evaluated mainly by the metallographic examination although it reveals only two weld cross-sections in a circumference welds. This investigation was, firstly, carried out to determine whether the ultrasonic examination would be applied to detect weld defects in the end cap welds and, secondly, to measure the mechanical strength of upset butt welds as a function of phase shift percentage. The major results obtained in this study are as follows: 1. The weld current and amount of upset shrinkage linearly increased with increasing the phase shift percentage. 2. Above the phase shift 55%, the defects in the welds were completely eliminated with increasing the phase of sound weld was over the thickness of cladding tube. 3. The ultrasonic testing well detected such defects in the end cap welds as upset external crack, upset split, corner crack and irregular weld flash comparing with the results of metallography. 4. The micro-fissure in the corner of the end cap welds was reliably detected by ultrasonic testing. 5. The mechanical strength in the welds increased with increasing phase shift percentage but the fracture did't occur in the welds above 55%.