Dongcheol Kim

A fuzzy pattern recognition based system for monitoring laser weld quality

In-process monitoring of welding has become important as the use of laser welding increases. Plasma and spatter are measured and used as signals for estimating the quality of a weld. The measurement system consists of three photodiode sensors (one IR and two UV) to detect the plasma and spatter signals in CO2 laser welding. The estimating algorithm was constructed using fuzzy pattern recognition considering the amplitudes as well as amounts of data beyond the tolerance boundary. Weld qualities were classified as optimal heat input, slightly low heat input, low heat input and misalignment of focus. Also, an algorithm for detecting spatter was created in order to find the partially produced pit. These algorithms were used for quality monitoring in tailored blank welds with a CO2 laser.

Resistance Spot Welding Characteristics of Mg Alloy Using Process Tape

Abstract Recently, studies about application of magnesium alloy sheet to automotive bodies are on the increase. For application to automotive bodies, researches about characteristics of resistance spot welding of magnesium alloy sheet are essential. Electrode life of resistance spot welding of magnesium alloy is very short due to sticking of magnesium alloy to copper alloy electrode. To increase electrode life, most effective method is inserting cover plate between electrode and magnesium sheet. But application of cover plate to actual process is difficult and decreases welding productivity. Process tape supplied automatically as cover plate can minimize lose of productivity and increase welding quality. In this study, resistance spot welding of magnesium alloy is carried out with applying process tape. Acceptable welding current region according to electrode force and welding time is determined. Key Words : Resistance spot welding, Mg alloy, Process tape, Cover plate, Electrode life 1. 서 론

Electrode Life Test of Resistance Spot Welding on Mg Alloy Using Dome Type Electrode

Abstract Magnesium alloy is used on parts of aircraft and electronic equipment because of the highest specific strength among the common metal materials. Recently, studies about appling magnesium alloy sheet to automotivebodies are on the increase rapidly. For application to automotive bodies, researches about characteristics of resistance spot welding of magnesium alloy sheet are essential. Magnesium alloy has low boiling point, so getting sound bead shape is difficult when appling varies welding processes. Resistance spot welding is also particular about setting optimum welding conditions because of spatter generation, pores and cracks occurrence in nugget. And life of electrodes is very short because of alloying with copper that main materialof electrodes. This requires frequent dressing and replacement of electrodes and decrease in productivity of resistance spot welding on magnesium alloy. Therefore in this study, for effective analysis of changes in tensile shear load and nugget size during electrode life test, evaluate detail characteristics of resistance spot welding on magnesium alloy sheet using dome type electrode.Key Words : Resistance spot welding, AZ31, Mg alloy, Dome type electrode

A study on tensile shear characteristics for weld-bonded 1.2GPa grade TRIP steels with changes in nugget diameter for automotive body application

High strength steels have been continually being developed to improve in fuel economy in automotive and ensure safety of passengers. New bonding and welding methods have been required for improving weldability on high strength steels. In this study, resistance spot welding and Weld-bond with nugget diameters of 4.0mm, 5.0mm, 6.0mm and 7.0mm were produced and tested, respectively. In order to confirm the effect of nugget diameters on tensile shear characteristic of the Weld-bond, tensile shear characteristics of Weld-bond were compared with those of resistance spot welding and adhesive bonding. Peak load of Weld-bond were increased as the nugget diameter increases. After appearing maximum peak load continuous fracture followed with second peak owing to load being carried by resistance spot weldment. Fracture modes of the adhesive layer in Weld-bond fractures were represented by mixed fracture mode, which are cohesive failure on adhesive part and button failure at resistance spot welds. The results showed that the tensile shear properties can be improved by applying Weld-bond on TRIP steel, and more apparent with nugget diameter higher than 5t.

Mechanical Behavior of Weldbond Joint of 1.2GPa Grade Ultra High Strength TRIP Steel for Car Body Applications

The effect of weldbond hybrid joining process on the mechanical behavior of single lap and L-tensile joints was investigated for the newly developed 1.2GPa grade ultra high strength TRIP(transformation induced plasticity) steel. In the case of single lap shear behavior, the weldbond joint of 1.2GPa TRIP steel showed lower maximum tensile load and elongation than that of the adhesive bonding only. It was considered to be due to the reduction of real adhesion area, which was caused by the degradation of adhesive near the spot weld, and the brittle fracture behavior of the spot weld joint. In the case of L-tensile behavior, however, the maximum tensile load of the weldbond joint of 1.2GPa TRIP steel was dramatically increased and the fracture mode was change to the base metal fracture which is desirable for the spot weld joint. These synergic effect of the weldbond hybrid joining process in 1.2GPa TRIP steel was considered to be due to the stress dissipation around the spot weld joint by the presence of adhesive which resulted in the change of crack propagation path.

High Current Arc Welding Technology of Aluminum Alloy

Abstract Aluminum alloy, Al5083-O, is one of candidate materials for the LNG storage tank, because of its excellent weldability, cryogenic characteristics, and corrosion resistance. The good weldability of Al5083-O is very important in LNG storage tank manufacturing. In this study, high current metal inert gas(MIG) welding process was used to get one pass welding of thick plate aluminum alloy. Bead on plate(BOP) welding was performed to evaluate the effect of welding conditions on the height of bead and depth of penetration. The optimum welding conditions were derived to get one pass welding of the thickness of 14.5mm. The mechanical properties of the welded joint were evaluated. The cross-sectional macro test, tensile test, and bending test satisfied the class rule.Key Words : Aluminum alloys, Metal inert gas welding, Full penetration weld 1. 서 론 LNG(Liquified Natural Gas)는 타연료 대비 높은 연료 효율 및 저탄소 배출로 인해 사용량이 급증하고 있으며 이러한 수요를 만족하기 위해 전 세계적으로 LNG 선박의 건조가 활발히 진행되고 있다 1) . LNG는 주로 환경조건이 열악한 해역 및 북극지방에 많이 매장되어 있기 때문에 LNG 선박의 저장탱크는 높은 파도에 의한 충격이나 운항 중 유빙 충돌 등과 같은 외부충격에 견딜 수 있어야 하고 특히 극저온 특성이 우수한 소재가 사용되어야 한다. 이러한 요구조건을 만족시키는 LNG 탱크의 소재로는 9% Ni강, 오스테나이트계 스테인리스강 및 Al5083-O재를 사용하고 있으나 철계 소재의 경우 중량 증가에 따른 선박 무게의 증가로 그 한계성을 나타내었고, 이에 따라 LNG 탱크의 소재로 경량금속인 Al5083-O재의 사용이 고려되고 있다

Corrosion Assessment of Al/Fe Dissimilar Metal Joint

The use of light-weight Al alloys in the automotive industry is increasing to meet requirements for fuel efficiency and emission reduction. Joining Al alloy to the conventional steel sheet is also very important issue with the increased use of Al alloy, and several joining processes have been introduced to enhance joining strength between dissimilar metals. This paper deals with a galvanic corrosion in the dissimilar metal joining. Salt spray tests up to 2000 hours were conducted on a self-piercing rivet, spot welded, adhesive bonded and weld-bonded joints, and cross-sections and tensile shear strength according the salt spray duration were analyzed at every 500-hour. Self-piercing rivet joint had relative low initial strength but the joint strength did not change regardless of the salt spray duration. The strength of other joints (spot welded, adhesive bonded and weld-bonded joints) decreased with the increase of salt spray duration and the corrosion behaviour of each joint was discussed.

Development of Push-pull Type Arc Welding Wire Feeder

Abstract It is difficult to feed welding wire stably, when the distance between welding wire feeder and welding torch is far enough. In order to solve this problem, arranging a extension wire feeder between them could be one of useful methods. However, the welding wire could be twisted up in the extension cable between extension and terminal wire feeders in the case that RPM of extension wire feeding motor is higher than that of terminal motor. In this study, feeding problem of normal push-pull wire feeding system occurred at low welding current range less than 250A. In order to solve the problem, two new wire feeding systems of push-pull type were introduced. Welding wire feeding tests were preformed in the range of 150A to 400A with the developed push-pull feeding system. In addition, weldability test was performed at the welding current of 200A, 300A, and 400A. The welding wire twisting problem that was observed in the normal feeding system did not occur in the new push-pull wire feeding system.Key Words : Arc welding, Welding wire, Wire feeder, Push-pull type feeder, Welding torch

Gas metal arc weldability of 1.5 GPa grade martensitic steels

The gas metal arc weldability of 1.5 GPa grade martensitic (MART) steel was evaluated using both inverter direct current (DC) and DC pulse power type welders, under conditions of different welding currents, welding speeds, and shielding gasses. By investigating the bead appearance, tensile strength, and arc stability, it was determined that DC pulse power is better than inverter DC power for arc welding of 1.3 mm thick 1.5 GPa grade MART steel. Further, from the results of the weldability for various shielding gases, it was determined that mixed shielding gas is more effective for welding 1.5 GPa grade MART steel than is pure inert gas (Ar) or active (CO2) gas. In the case of pure shielding gas, no sound bead was formed under any conditions. However, when the mixed shielding gas was used, sound and fine beads were obtained.

Effect of Welding Time on Resistance Spot Weldability of Aluminum 5052 Alloy

In the study, the effect of welding time on resistance spot weldability of aluminum 5052-H32 alloy was analyzed through simulation and experiments. The resistance spot weldability was evaluated by measuring the tensile shear strength, nugget size, and hardness of welds with variations in the welding time. The simulated results of parameters such as tensile shear strength and nugget size obtained using the SORPAS program were compared with the experimental results. Furthermore, a simulation was performed to calculate the temperature inside the weld nugget based on the distance from the center of the nugget. Hence, an optimum welding time to retain the required weld strength of the aluminum 5052-H32 alloy was obtained.