Study of the current path in gas metal arc welding for the generation of a dynamic phenomenological system model

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The regulation of the arc length in gas metal arc welding is an important part of control concepts in many welding power sources to adjust a stable welding process. Up to now, estimations and statistical values from the current-voltage characteristics are used as input for the arc length determination. Here, often for simplicity a one-dimensional arc model is assumed where mainly the arc column length can be vary whereas variations in the arc sheath regions, wire electrode and contact tube are neglected. However, in particular the arc sheath regions must be expected to contribute considerably to the power input and to cause additional voltage fluctuations. Therefore, the detailed experimental study of the current path from the contact tube over wire, droplet, arc including sheathes up to the work piece is aimed in the research project. The different parts of this path should be analysed separately by specific experimental techniques as well as by determining and using the different time scales of the underlying physical mechanisms. In particular, the study of the whole path by time series of electrical signals and measuring the complex impedance should be coupled with optical and spectroscopic investigations of the arc and probe measurements at the droplet depot. A description of the current path in form of a process model will be available as a result of the basic study which describes the dynamic and interdependent behaviour of the subsystems. Herewith the prerequisites for a considerable improvement of the arc length control in gas metal arc welding processes in contrast to existing solutions will be provided. In addition, the results can be used in following studies to improve the physical models of arc attachment and sheath regions at melted electrodes under the impact of metal evaporation.