The differences of weld pool formation, convection and stability in normal and high speed GMAW processes are researched. Three main factors are responsible for the humping formation.

The low momentum of the backward fluid flow, the balanced surface tension normal force along the liquid channel, and the capillary stability contribute to the disappearance of humping in twin wire GMAW process.

The influence of current ratio on humping suppression in the twin wire GMAW process is discussed. In order to obtain sound weld bead, the trailing wire current should not be larger than the leading wire current.