Adaption of a topographical measurement system for beam welding processes with high temporal and spatial resolution

Both typical beam welding processes laser beam welding LBW and electron beam welding EBW feature the deep penetration welding process. Theses processes rely on a vapor capillary with a delicate, highly dynamic equilibrium of various opposing forces. The direct observation of the vapor capillary's inner surface is hindered with growing capillary depth by the thermal optical emissions with high intensities due to the high temperatures inside the capillary. Even with the use of high intensity laser based illumination and band pass filters adjusted for the laser wavelength, it is merely possible to observe only the upper most part of the capillaries opening. The lack of observability, especially with high temporal resolution to assess the highly dynamic effects contributes to the state of the capillary models that actually are describing quasi-static modes or implement the less dynamic effects that can be observed with state of the art methods.The topographical measurement system, developed by the Institut für Strahlwerkzeuge Universität Stuttgart IFSW, uses the process inherent thermal emission of the capillary governed by the complex refractive index of the base material to reconstruct the inner geometry of the visible capillary surface. This is achieved by using the dependence of the emissivity between emission angle and polarization that is described by the Fresnel equations (Sawannia et al., 2018). The measurement system uses the fact that the quotient of two or more polarization components of the emission from a surface increment is depending on the angle of surface inclination but are almost independent of the surface temperature (Weberpals et al., 2011). Based on the results of the application of the measurement principle with laser beam welding, an adaption to electron beam welding is developed to assess the observability of capillaries with large depth and to contribute in the improvement of capillary models in the wake of the development. To allow the use of the improved measurement system to capture the EBW process capillary with unmatched spatial and temporal resolution, a complete new optical observation beam path was developed and fitted insight a custom-made pressurized chamber inside an electron beam welding machine.