Drop transfer in short-circuit welding

Abstract

This paper considers the physical processes which may occur when a liquid weld metal drop comes in contact with a liquid metal pool. Experiments with drops of aqueous KCl solutions and mercury, combined with a theoretical analysis of the effects of surface tension and Lorentz forces, lead to the following conclusions. Drops larger than a critical size, which is a function of the capillary constant and wire diameter, will transfer to the pool and smaller drops will lead to stable menisci. Surface tension alone will complete the interaction in approximately k(M/4πT)1/2 s, where M and T are the drop mass and surface tension in CGS units and k similar 3·7. An electric current I can result in a repulsive force on drops of radius less than approximately μ0I2/16π2T (MKS units). The magnetic pinch instability can dominate surface tension effects under extreme conditions, and magnetically induced streaming can make otherwise stable menisci unstable. Applied to short-circuiting MIG welding systems, these results show how proper attention to the current and weld metal surface tension can lead to reduced spatter and better process control.