Forced Drop Transfer Arc Welding by Power Source with Periodically Varying Nonlinear Characteristic

Abstract

This paper deals with effects of power source characteristic on the stability of the drop transfer arc in a constant feeding speed system. The key to minute drop transfer is socalled "pinch effect" which automatically squeezes the drops off the electrode. The forced drop transfer is achieved by pulsing the current between the globular and spray transfer current ranges. Droplets are ejected one by one from the electrode tip at a regular frequency synchronizing with the frequency of current supplied from a power source with periodically varying nonlinear characteristic. Hence, with a sufficiently short arc, drop transfer is reasonably stable and associated with an absence of spatter. The forced transfer by drop mode may occur at average current levels far below the transition current.
The welding arc is described by nonlinear differential equations. The phase-plane analysis is used for the present investigation. The current and voltage of the arc constitute the coordinates of a representative point in the phase-plane. The behavior of the forced drop transfer arc is investigated by illustrating the geometrical configuration of integral curves in the phase-plane. When the current and length of the are keep on varying periodically in the steady state, the representative point moves along the limit cycle repeatedly. From the analytical results, it may be inferred that a nonlinear characteristic of power source is useful to stabilize the drop transfer arc.
Experiments are also carried out by making use of power sources which contain transistors and integrated circuits, and the forced drop transfer arc phenomena are observed by means of the high speed motion pictures. The validity of the theoretical results is confirmed by the experimental investigations.