On the mechanism of evaporation-determined arc-cathode coupling in GMA welding

  • Über den Wirkzusammenhang der Verdampfungsbestimmten Kopplung von Lichtbogen und Kathode beim MSG-Schweißen

Simon, Marek Sebastian; Reisgen, Uwe (Thesis advisor); Uhrlandt, Dirk (Thesis advisor)

Düren : Shaker Verlag (2021)
Book, Dissertation / PhD Thesis

In: Aachener Berichte Fügetechnik 1/2021
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2021

Abstract

In gas metal arc welding (GMAW) process simulation, it is desired to predict the energy transferred to the process as well as the weld pool geometry. For this reason, the coupling of the arc to the welded material is of high interest, both at the cathode and anode. Although there exists a substantial body of work on the coupling of the arc to the cathode, the present models cannot be applied in the conditions of GMAW welding, as they give unphysical results. In particular, the current models usually result in very high cathode surface temperatures, i.e. above boiling temperature of the metals. After relevant experiments are presented and discussed, it is concluded that the current state of the art does not reflect the observations and that therefore a new approach needs to be developed. Furthermore, a dialectic argument is developed, namely that the coupling of the arc to the cathode in diffuse attachment of GMAW must be strongly determined by evaporation. The argument concludes that the current transfer is mainly carried by metal ions that are evaporated from the cathode surface and ionized in the near cathode plasma, and that this current transfer must be limited to below boiling temperature. The core hypothesis is that this limit results from a decrease of the ionization degree, due to cooling of the near cathode plasma by the cold metal vapor. Based on this argument, a mathematical model for the Evaporation-Determined Arc-Cathode Coupling (EDACC), is introduced in detail. The properties of the model are then analyzed by applying it to a simplified computational fluid dynamics (CFD) weld pool simulation and it shows that the model is in line with the observed cathode surface temperatures below boiling. Finally, also an outlook is given on possible applications of this new understanding of the arc-cathode coupling, as well as a discussion of open questions and current limitations of the model.

Identifier

Downloads