Session: 03-08 Metals: New Processing Methods

Paper Number: 96634

96634 - A Study of Pre-Heating Stages in Electron Beam Melting Using Numerical Simulations 

Additive manufacturing by electron beam powder bed fusion (EBM) requires careful process thermal management. Particularly, unlike other powder bed fusion methods, significant pre-heating of the powder prior to melting is essential in order to ensure sufficient adhesion between the powder particles (through partial sintering and thermal expansion). This is required in order to avoid kinetic effects from a concentrated melting electron beam (AKA powder smoking). The pre-heating algorithm used in most EBM machines is material-specific with reliable results only for materials after rigorous testing procedures. Therefore, in order to allow reliable adaptation of new build materials in EBM, the pre-heating thermal management must be adequately studied and characterized. In this work, the thermal history of the pre-heated powder is studied using dedicated transient numerical simulations in finite elements. The first step in developing reliable pre-heating thermal simulations included a dedicated full-3D model of the ARCAM Q20+ machine build chamber, including all participating components (e.g. start-plate, heat shields, build stage, powder hoppers, etc.) in order to model the thermal boundary conditions. This model included a grey-body radiation cavity space, with several modified gap-conductance contact interactions tailored to the given geometry, in addition to 3D conduction. A series of dedicated validation experiments were performed using spatially distributed thermocouple measurements over the start-plate and heat shields over long duration pre-heating, and a good agreement was obtained between the experimental and computed results [1]. In the next step, the boundary conditions were analyzed and implemented onto a unique multi-stage additive pre-heating simulation with time-scale resolution of adaptable size. The additive model uses progressive element volume activation to introduce new powder layers mimicking an actual rake spread as in an EBM machine. The electron beam energy deposition is modelled using adaptive scaling which adjusts to the required time-incrimination resolution. Since this sort of computation may become too expensive depending on the time-scaling level of the moving heat source (the pre-heating beam travels at ~40-46m/s), the algorithm is adapted so the process may be solved in larger time-increments by scaling the energy deposition into several simultaneous line-blast energy sources. It is then possible to dictate in any certain portion of the transient, a reduction of the time-incrimination scale for short durations in order to assess some more local thermal phenomena where it is of interest. This approach enables generating a database of simulation results for different pre-heating cases (e.g. beam current, velocity and scan path) including 1^st and 2^nd pre-heating and post cooling or heating. These results can then be examined against complying pre-heating (only) experiments to assess the resulting "melt-safe" level of the pre-heated powder per material.

References

[1]      E.Landau, E. Tiferet, Y. Ganor, R. Ganeriwala, M.Matthews, D.Braun, M. Chonin and G. Ziskind."Thermal characterization of the build chamber in electron beam melting", Additive manufacturing, vol. 36, no. 101535, 2020.

Presenting Author: ERAN LANDAU Ben Gurion University and NRCN

Presenting Author Biography: Graduated BSc and MSc at Ben Gurion university, and is currently an active PhD student at Ben-Gurion university at the mechanical engineering department, studying unique pre-heating effects in electron beam melting (EBM) additive manufacturing in co-operation with the R&D Additive manufacturing lab at Rotem Industries LTD.

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