As part of AMELI, electron beam-based additive manufacturing is being investigated with an acceleration voltage of 150 kV instead of the usual 60 kV. So far, the expectations of the high acceleration voltage are fully met. The process stability is considerably increased and the beam quality is significantly improved. In addition, the beam quality is maintained at high beam power. This is the prerequisite for making the available high power usable at all. The beam quality not only has an influence on the additive process but also on the electron-optical analysis with the beam. To do this, it is necessary to know and optimize the properties of the beam. Characterizing the electron beam is generally very complex, only possible for lower powers and cannot take place in-situ. As part of AMELI, we have developed a method to determine the beam characteristics across the building area within seconds from just one electron-optical image of the powder bed. Since knowing the properties of the beam is essential for both, calibration and quality control, a patent application has been submitted for this method.
To explore the potential of electron-optical observation a four-detector system for detecting the emitted electrons was numerically optimized, constructed and successfully integrated into the PBF-EB system based on numerical simulation. Based on this multi-detector system and the information associated with it, it is now feasible to analyse the surface of the building area very precisely during the process. The surface topography can be reconstructed within seconds applying suitable algorithms. This allows the evaluation of material compaction and the detection of emerging instabilities. In addition, determining the topography is the basis for realizing the element contrast, which is intended to make evaporation effects visible during the process. Initial experiments on element contrast already demonstrate that this goal can be achieved, at least for certain alloys. Methods for locally designing properties by changing material compositions through evaporation can be uniquely monitored in the future.
In AMELI, we also develop a simulation framework to predict sophisticated digital processes for voxel based material design in complex geometries. In order to control the additive manufacturing process voxel by voxel, it is necessary to digitally map the essential features of the additive manufacturing process and optimize it layer by layer. By using efficient algorithms coupled with high-performance computing, we are now able to fully map the thermal process and optimize the beam guidance for each layer. We were able to reduce the necessary computing times to such an extent that the optimization of one layer takes only some minutes.
The high flexibility of the electron beam allows the powder to be melted point by point in an efficient way. We have succeeded in showing that highly developed point melting strategies in combination with the high beam quality lead to unimagined flexibility in the setting of the microstructure and thus the local properties. These point melting strategies can be easily varied locally. That is, in AMELI we already demonstrated voxel based material design. The texture in particular can be specifically adapted locally. This opens up a completely new degree of freedom for component design, as the mechanical properties can be locally adapted to the requirements at any point on the component.
