A simple and time efficient model for atmospheric arc plasmas is presented in this work. It uses experimentally recorded emission spectra in order to estimate radial temperature and electron density profiles in welding arc plasmas. The plasma parameters are calculated using the Elenbaas-Heller and Saha equations, together with welding current, gas composition and simplified cylindrical arc geometry with a particular radius as input parameters. From these parameters an emission spectrum is calculated under the assumption, that the individual lines are mainly broadened due to the Stark effect. Here only second order perturbation theory for the Stark effect without any further influences of ion collision or other additional effects is considered. The comparison of measured and calculated spectra leads to a cost function. Its minimisation is used to find the radius of the arc model. This model was successfully applied for the estimation of plasma parameters in gas tungsten arc welding processes with argon and argon-helium as shielding gases. The calculated gas temperature and electron density profiles were compared with experimental data obtained by Thomson scattering. Further extension of the model for dynamic processes containing metal vapours and its application in feedback control are planned in the future.
In-orbit additive manufacturing (AM) is a promising approach for fabrication of large structures. It allows to expand and accelerate human space exploration possibilities. Extrusion-based AM was demonstrated in zero gravity, while the realization of such a process in orbit-like vacuum conditions is currently under exploration. Still, a solution for protection of the UV and IR radiation sensitive polymers is needed in order to prevent their early mechanical failure under space conditions. Vacuum arc plasma based process is widely applied on earth for thin protective coating deposition. Its major advantage is its scalability — from tiny size used in electric propulsion to large scale coating devices. The usability of the vacuum arc process in space conditions was shown in electric propulsion applications in nano-satellites. In this work we discuss and demonstrate the integration of vacuum arc process as a post processing step after Fused Filament Fabrication (FFF) for additive manufacturing and functionalization of long polymer structures. Here we address the concept for technical realization, which integrates the vacuum arc into additive manufacturing process chain. More over we present a laboratory prototype, which implements this concept together with a use case, where a previously printed PEEK structure is coated with aluminum based coating suitable for UV radiation protection.
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