조선용 AH36강의 디스크 레이저-MIG 아크 하이브리드 용접성에 관한 연구

Abstract

Laser-arc hybrid welding is noted as a promising joining process since it can compensate for the drawbacks or weaknesses in laser welding and arc welding by utilizing both features. Laser welding has gained great popularity as promising joining technology with high quality, high precision, high performance, high speed, good flexibility and low deformation or distortion, in addition to the recognition of easy and wide applications owing to congeniality with a robot, reduced man-power, full automation, systematization, production lines, etc.. The defects or drawbacks of lasers and their welding are high costs of laser apparatuses, difficult melting of metals that have high reflectivity and thermal-conductivity, small gap tolerance and easy formation of welding defects such as porosity in deeply penetrated weld fusion zones. Arc welding is most widely used in joining applications because the machines are cheap and easy in operation, and the welding processes are highly stable and effective. The drawbacks are shallow penetration of weld beads in most cases, slower welding speeds, easier formation of humping weld beads at high speed welding, etc.. Laser-arc hybrid welding has been receiving considerable attention because it can achieve many advantages such as deeper penetration, higher welding speeds, wider gap tolerance, better weld bead surface appearance and reduced welding defects leading to a smaller amount of porosity in addition to complements of the drawbacks of both individual processes. In this study disk laser and MAG arc were used for hybrid welding of AH36 steel for shipbuilding industries.

First of all, we carried out bead on welding for SS400 changing defocused distance, flow rate of front and back shield gas, process parameters such as welding voltage, pulse waveform, laser power, welding current and speed. Optimal welding conditions decided from the results were shield gas : front gas(20ℓ/min), back gas(15ℓ/min), distance between laser and arc(DLA) : 3mm, laser power(P) : 5 and 6kW for SS400, 6kW for AH36.

Second, butt welding for SS400 and AH36 were conducted changing welding speed and current. Then penetration properties were analyzed and optimal parameters for each materials were decided based on experimental results. From these results, Using of high current and speed induces undercut but these undercut can be suppressed by increasing heat input.

Last, microstructure and mechanical properties of weld such as hardness, tensile strength and elongation were measured and compared to those of base metal. As a result same mechanical properties were obtained in weld. Conclusionally, it was possible to obtain indefective one-pass full penetration welding for AH36.