Gas metal arc welding (GMAW) processes are characterized by a high number of simultaneously running physical processes. The process capability is mainly determined by the properties of a metal vapour influenced arc and the material transfer. In recent years, experimental as well as numerical methods are being used increasingly in order to understand the complex interactions between the arc and material transfer. In this paper, we discuss the influence of metal vapour on GMAW processes in spray as well as pulsed material transfer mode. With respect to the high complexity of the process, experimental and numerical methods are combined in a targeted manner in order to obtain a high level of expressive capability with moderate numerical and experimental effort. The results illustrate the high influence of the changing vaporization rate not only on the arc properties but on the arc attachment at the filler wire. It could be shown, that in many cases the metal vapour concentration in the arc region has a greater influence on the arc properties and the material transfer than different shielding gas components like oxygen, hydrogen or helium. Gas metal arc welding (GMAW) processes are characterized by a high number of simultaneously running physical processes. The process capability is mainly determined by the properties of a metal vapour influenced arc and the material transfer. In recent years, experimental as well as numerical methods are being used increasingly in order to understand the complex interactions between the arc and material transfer. In this paper, we discuss the influence of metal vapour on GMAW processes in spray as well as pulsed material transfer mode. With respect to the high complexity of the process, experimental and numerical methods are combined in a targeted manner in order to obtain a high level of expressive capability with moderate numerical and experimental effort. The results illustrate the high influence of the changing vaporization rate not only on the arc properties but on the arc attachment at the filler wire. It could be shown, that in many cases the metal vapour concentration in the arc region has a greater influence on the arc properties and the material transfer than different shielding gas components like oxygen, hydrogen or helium.