A Study on Thermal and Mechanical Characteristics in Hybrid Fillet Welding (CO2 Laser+MIG) of Mild Steel

Abstract

This thesis presents a theoretical and experimental investigation of laser arc hybrid welding. The arc welding is one of the main welding process in shipbuilding, and this process has many merit such as stability of arc, gap bridging, less expensive and economical efficiency etc. But the limited welding speed and angular distortion after welding is inevitable in shipbuilding stage. Especially with the thinner plate which were used as pure car carrier deck in thickness 6 to 15mm had more welding deformation.

Even though the shipbuilders try to increase the productivity and high quality, the deformation caused by arc welding made many problem and low speed decreased the productivity. The manufacturer have to pay additional man-power and man-hour for straightening, which sometimes creates processing problem. To overcome this problem, a distortion control method should be applied to reduce the welding deformation at each welding stage and new welding technology should be applied to increase productivity.

It is necessary to develop the accurate welding method to reduce the welding deformation and to increase the productivity. For this purpose, this paper suggest the laser arc hybrid welding a better method to overcome the problems caused by conventional arc welding. Laser arc hybrid welding was introduced and observed the weldability and feasibility in fillet joints for complementing the disadvantages of conventional arc welding.

The application possibility of laser arc hybrid welding to fillet joints of mild steel are confirmed. The welding speed of laser arc hybrid welding reached up to 2m/min and the welding deformation reduced about 50%. After more comprehensive investigation, It is found that laser arc hybrid welding process could be used successfully in shipbuilding.