Abstract
Metal inert gas/metal active gas (MIG/MAG) welding is generally used in many fields because of its high efficiency. Metal inert gas welding is expected but has not been used in pure Ar shielding gas because of arc instability. Shielding gas including O2 or CO2 has been used to secure the arc stability. However, these gases cause the quality of joints to deteriorate. Therefore, the authors have investigated the case of instability using a high speed video camera system to achieve a stable MIG welding in pure Ar shielding gas. The observation showed that the unstable welding behaviour was due to the instability of a column of liquid metal generated at the wire tip. To shorten the column of liquid metal, the authors developed a welding process which uses a small amount of oxygen and a coaxial multilayer solid wire (coaxial hybrid solid wire) where the melting behaviour can be controlled. A stable welding can be achieved by employing these methods.