Quantifying instabilities of a plasma cutting arc through analysis of schlieren images

In this paper the instabilities of plasma arc cutting was investigated using Schlieren images recorded with high speed CCD camera. Fluctuations of the arc width and of the light intensity in the boundary layer between the arc and the cold gas using Fourier transforms and wavelet analysis indicate that slight imperfections of the arc nozzle e.g. through erosion as well as its alignment with respect to the work piece can influence arc symmetry and fluid dynamic stability of the boundary layer. The results indicate that these diagnostic approaches can be used to evaluate different nozzle geometries which may lead to more stable arcs.