• Journal of Ocean Engineering and Technology
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• v.6 no.2
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• pp.113-124
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• 1992

The offshore industry created a need for quality wet weld repairs. Wet welding is a fast method of repair providing sound, structural quality welds. It requires less support equipment than a similar underwater dry weld repair or the alternative mechanical connections. Compared to welds made in air, underwater wet welds are plagued by increased hardness due to rapid quenching by the surrounding water. In this paper is described the experimntal study of improving the cooling rates of wet welds of TMCP steel plate by shielding around weld arc surroundings. The principal results of this experimental investigation can be summarized as follows : By shielding around weld arc surrounding, the cooling rates resulting from wet welds on TMCP steel plate could be lower than that of nonshielded wet welds and the fesibility on high quality of mecanical properties of wet weld on TMCP steel plate was carried out with shielded weld arc surrounding.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.2
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• pp.145-150
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• 2011

There is problem to reduce the car body weight for improving fuel consumption and $CO_2$ generation. As one of the solution, the multi material car body concept using aluminum alloys and high strength steels is proposed recently. Therefore, new welding processes by which these dissimilar material can be joined in high reliability and productivity are demanded. Laser spot welding was developed for joining of dissimilar metals. In the present work, Laser spot welding of zinc coated steel and aluminum alloy was investigated, and the process parameters were studied. Otherwise, the influences of process parameters on the weldability, the formation of intermetallic compound layer and the mechanical properties have been investigated. When intermetallic compound layer thickness was more than 1mm, specimen was failure in the interface.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.1
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• pp.109-115
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• 2004

The spatter and porosity could be occurred during$CO_2$CW laser welding of Primer- coated steel for shipbuilding. This study has suggested an alternative idea by examining of weld-defect formation mechanism. The primer-coated plate induced the spatter humping bead and porosity and these are main part of the welding defect. attributed to the powerful vaporizing pressure of primer attached on the base metal The zinc of Primer has a boiling point that is the lower temperature than melting point of steel zinc vapor will build up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Therefore introducing a small gap clearance in the lap position. the zinc vapor could escape through it and sound weld beads can be acquired. In conclusion, we suggested the occurred and prevented mechanism of weld defects with searching the factor.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.46-53
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• 2002

The expolitation of substitute material and new manufacturing technology of the automobile body panel for next generation cars have been steadily professed by advanced automobile companies. High strength steel of TRIP (Transformation of Induced Plasticity) type is developed in response to demands about crash safety and high strength of automobile. In this study, basic technologies can fix up problems occurring on the mass production and applied to the other forming methods will be prepared through rasping a property of TRIP material.

• Journal of Ocean Engineering and Technology
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• v.23 no.4
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• pp.58-63
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• 2009

Two kinds of welding methods are used for austenitic 304 stainless steel: laser welding and TIG welding. The difference in the corrosion characteristics of the welded zone between these two welding methods was investigated using electrochemical methods, such as corrosion potential measurements, polarization curves, cyclic voltammograms, etc. The Vickers hardnesses of all the welded zones (WM: Weld Metal, HAZ: Heat Affected Zone, BM: Base Metal) showed relatively higher values in the case of laser welding than for TIG welding. Furthermore, the corrosion current densities of all the welding zones showed lower values compared to TIG welding. In particular, the corrosion current density of the HAZ with TIG welding had the highest value of all the welding zones, which suggests that chromium depletion due to the formation of chromium carbide appears in the HAZ, which is in the range of the sensitization temperature. Thus, it can easily be corroded with a more active anode. Consequently, we found that the corrosion resistance of all of the welding zones for austenitic 304 stainless steel could apparently be improved by using Laser welding.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1162-1169
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• 2009

Two kinds of welding methods were carried out for 22APU stainless steel, one is a Laser welding and the other is the TIG welding. In this case, difference of corrosion characteristics of welded zone with two welding methods mentioned above was investigated with electrochemical methods such as measurement of corrosion potential, polarization curves and cyclic voltammogram etc.. Vickers hardness of all welded zone (WM:Weld Metal, HAZ:Heat Affected Zone, BM:Base Metal)in the case of Laser welding showed a relatively higher value than those of TIG welding. Futhermore their corrosion current density in all welding zone were also observed with a lower value compared to TIG welding. In particular corrosion current density of BM regardless of welding method indicated the lowest value than those of other welding zone. Intergranular corrosion was not observed at the corroded surface of all welding zone in the case of Laser welding, however it was observed at WM and HAZ with TIG welding, which is suggested that chromiun depletion due to forming of chromium carbide appears to WM and HAZ which is in the range of sensitization temperature. Therefore their zone can easily be corroded with more active anode. Consequently we can see that corrosion resistance of all welding zone of 22APU stainless steel can apparently be improved by using of Laser welding.

• Journal of Power System Engineering
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• v.11 no.1
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• pp.107-114
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• 2007

Underwater wet arc welds were experimentally performed on 11mm thick SS400 mild steel plate as base metal by using six different types of flux coated electrodes of 4.0mm diameter; KSKR, KSKT, USBL, JPUW, UWEA, and UWEB. As results, the developed flux coated underwater electrode had a good weldability compared with other domestic terrestrial electrodes. By rapid cooling rate, the hardness value of HAZ were increased by quenching effects. Mechanical properties for the multi-pass butt-welding specimen are also tested experimentally. The feasibility of the developed underwater electrode was experimentally studied and the results achieved in this wet arc welds have shown that the developed wet welding electrode UWEB can have a degree of integrity.

• Journal of Welding and Joining
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• v.27 no.6
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• pp.25-30
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• 2009

SBD (Strain-based design) of pipe lines have gained world-wide attention in recent years. The present research aims to evaluate the fracture characteristics of API (America Petroleum Institute) SBD X100 girth weldment that typically applied for cold climate and deep water offshore, with the focus on the influence of heat input changing with 6kJ/cm and 10kJ/cm from GMAW (Gas Metal Arc Welding). At a low heat input at 6kJ/cm, the weld metal had Multi-phase matrix (Acicular ferrite + Banite + Martensite) that could fill up both fracture toughness and strength as reported previously. Also, the weld metal exhibited 859MPa YS (Yield strength), 108J impact toughness at $-40^{\circ}C$ and 0.52mm CTOD (Crack Tip Open Displacement) at $-10^{\circ}C$. These results can be satisfied with the requirement of API SBD X100 girth weldment and Alaska pipe line project.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.4
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• pp.434-439
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• 2011

There are about 2.4million disabled in Korea, 2009. Also, Korean society entered into an aging society. Therefore disable and elderly are getting more involved in our society. This study proposes simple ramp design for wheel chair users and welding method and condition for manufacturing. In the middle of ramp, screw jack and motor are installed so that ramp can be moved left and right side. To make the ramp moves easily, ramp was fixed by installing LM guide on both sides. Ramp production for using Nd:YAG laser certain dissimilar welding in stainless steel sheet and cold reduced carbon steel. The output was fixed by 3kW, the speed was increased to 2~7m/min, Argon was used as shielding gas and the flow rate was changed to 10~30L/min. The proper welding condition is the output 3kW and welding speed 2~5m/min.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.5
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• pp.39-47
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• 2016

Nowadays, several welding processes are generally used to join parts together, and the materials are generally steel, aluminum, copper, stainless steel, and other difficult-to-weld materials. If a proper welding process is chosen, it is helpful for welding parts. However, there is no desirable technique for appropriately deciding on the welding process in the industry. Therefore, an appropriate method of selecting a welding process is needed for the novice worker in the industry. In this sense, a new analytic network process (ANP) technique is used for effective decision making in welding. By considering several criteria in ANP, a selection method is suggested to decide on the proper welding process. In the study, several criteria were considered for the proper welding of parts. By considering a matrix of prior interdependence effects among various welding processes, a decision-making method based on an ANP is accomplished using a weighting matrix, which is supposed to select an appropriate welding process. In addition, for appropriate decision criteria of the welding process, several factors, such as material, shape, precision, economics, and equipment, are used to accomplish the ANP algorithm. Moreover, the final weighting matrix is calculated following its ANP strategy. Furthermore, this decision-making technique is applied to both stainless razor spot joining and thick steel pipe joining. The results show its reliability and practicality, and the novice engineer and manager can use this technique to determine the best welding process.