Multiple Interaction Electron Beam Powder Bed Fusion for Controling Melt Pool Dynamics and Improving Surface Quality

Low surface quality of fabricated parts and long processing times are two commonly stated reasons against a more wide-spread adoption of electron beam powder bed fusion (PBF-EB) as a commercially viable manufacturing technique. Aside from the large particle size distribution (45-150 µm) of processed powders, the surface roughness, limited structural resolution and process instabilities are attributed to unwanted dynamics of the melt pool, like spattering, balling, evaporation and melt pool displacement. As a result, a contouring step using slow but stable melting parameters is usually added to the process to improve surface quality, leading to increased processing times.In this study, we demonstrate how the surface quality can be improved by supplying the energy for melt pool formation over multiple, timely separated interactions. To investigate the effect of this multiple interaction processing (MIP), series of single line melt structures with increasing number of interactions were fabricated, characterized and corresponding thermal diffusion simulations performed. The results show how MIP allows for lower melt pool temperatures during processing, reducing evaporation, spattering, balling, melt pool displacement and consequently surface roughness, while also reducing the required processing time. Lastly, we introduce a simple model to calculate appropriate MIP parameters for any kind of scan strategy.