Investigation of the Anode Attachment Process in Plasma Arc Cutting

The anode attachment process in plasma arc cutting is still not well understood in spite of decades of industrial use. Previously, several approaches were made to analyze the attachment mechanisms including imaging, discharge current and voltage measurements as well as the use of thermocouples. In this paper a different approach is described to evaluate the attachment position. Six electrically separated water-cooled copper plates arranged in layers are used as an anode emulating a workpiece. The current through each layer is measured individually using current Hall sensors. The thus obtained information about the current distribution across each plate is used to deduce the anode attachment position inside the workpiece. This diagnostics allows a quick determination of the influence of process parameter variations like the cutting current, gas flow rate, cutting speed or the torch distance on the current distribution inside the workpiece. Using this setup, it is observed that no single attachment appears; the current is divided to flow through all anode segments. The torch distance and cutting speed proved to have the biggest influence on the anode current distribution. Comparison between measurements conducted with the new setup and an experiment using steel plates instead of copper plates is provided.