Graph-based spot melting sequence for electron beam powder bed fusion

Powder bed fusion processes are nowadays able to manufacture parts with a high geometric complexity. However, it is still challenging to realize these complex geometries defect-free as well as with homogeneous properties using classic line-based melting strategies. Electron beam powder bed fusion offers the promising opportunity to achieve this goal by spot melting, i.e., jumping from melt spot to melt spot with a very high velocity. The fundamental idea is, that homogeneous properties result, if all melt spots are independent from each other regarding their thermal history. The corresponding sequence of melt spots controls the temperature field and thus the microstructure leading to the mechanical properties. The main challenge is to develop a spot melting sequence resulting in independent spots while ensuring other process restrictions, like machine dependent jump lengths. In this contribution, a new heuristic algorithm to generate a spot melting sequence is developed. It bases on the subdivision of complex geometries into consecutively melted groups. The groups are transformed into graphs, connecting the spots inside the groups with all possible jumps meeting certain machine restrictions. A heuristic algorithm to identify Hamiltonian cycles is adapted to determine the final spot melting sequence. We demonstrate the applicability of the heuristic algorithm on complex geometries by one layer of a fuel nozzle combined with temperature simulations.