Improvement of Stability and Self-Regulation of Welding Arc by Power Source with Nonlinear Characteristic

Abstract

A power source characteristic is proposed for improving the stability and self-regulation of the wleding arc in a constant feeding speed system. The welding system 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 steady solutions which are correlated with singular points in the phase-plane are first sought for various characteristics of the power source. The stability of steady solutions is discussed by considering the behavior of, variations from the steady solutions. Our object is to improve the stability and self-regulation of the welding arc. These problems are investigated by studying the solution in the transient state, which, with the lapse of time, ultimately yields the steady solution. For this purpose, it is particularly useful to investigate the trajectory of the solution in the phase-plane and the time response of the solution in the transient state.
When the power source has a constant voltage characteristic, the time response of the welding arc may usually be quick. However, a slight deviation of the arc voltage from the singular point may produce such a large value of variation of the arc current that the spray arc cannot be sustained. When the power source has a drooping characteristic or a constant current characteristic, it may usually, but not necessarily, take a long time for the representative point to reach the vicinity of the singular point. From the analytical results, it will be deduced that a nonlinear characteristic of power source is useful for improving the stability and self-regulation of the arc.
We have developed a nonlinear characteristic power source consisting of transistors and function generators, and performed the experiments by making use of the power source. The arc phenomena are observed by means of the high speed motion pictures. The validity of the theoretical results is confirmed by the experimental investigations.