By using the automatic CO

2

gas protection welding with ABB welding robot for 12 mm thick Q345 steel plate with V groove

butt joint welding process testing was carried out to understand effects of different welding process parameters on microstructure and properties of welding joint. The results reveal that with wire feeding speed matching with welding velocity

droplet exhibits short-circuit transition with low spatter

so welding seam with desirable quality can be obtained. Absence of defects

such as gas hole

crack and undercut

can be observed in the surface of the joint. With increasing in feeding wire speed and welding current

the joint has the worse forming quality as a result of over-heating and oxidization tendency of joint leading to high spatter. When wire feeding speed is matched with welding velocity

microstructure of the joint is composed of fine white ferrite and black pearlite as well as a little uniformly distributed bainite. However

ferrite exhibits coarse bulky structure due to high heat-input with increasing in wire feeding speed. The optimized welding parameters for Q345 steel plate with 12 mm in thickness are presented as follows: current of 160 A

voltage of 22 V

feeding wire speed of 60 m/h

welding velocity of 3

6 mm/s and gas flow of 18 L/min

where hardness of the joint is distributed uniformly with good ductility.