Abstract
The current study evaluates the capabilities of electron-optical (ELO) in situ imaging with respect to monitoring and prediction of manufacturing precision in electron beam powder bed fusion. Post-process X-ray computed tomography of two different as-built parts is used to quantitatively evaluate the accuracy and limitations of ELO imaging. Additionally, a thermodynamic simulation is performed to improve the understanding of ELO data and to assess the feasibility of predicting dimensional accuracy numerically. It is demonstrated that ELO imaging captures the molten layers accurately (deviations <100 μm) and indicates the creation of surface roughness. However, some geometrical features of the as-built parts exhibit local inaccuracies associated with thermal stress-induced deformation (deviations up to 500 μm) which cannot be captured by ELO imaging. It is shown that the comparison between in situ and post-process data enables a quantification of these effects which might provide the possibility for developing effective countermeasures in the future.
Highlights
The accuracy of additive manufacturing (AM) processes is usually assessed by manufacturing of benchmark artifacts [1,2,3] with standardized and differently sized geometrical features
The strong influence of process parameters has been shown by Smith et al [5] for the dimensional accuracy of truss structures manufactured by PBF-EB
All three geometries show missing material on the top side of the parts. The amount of this missing material for ELO and simulation is very similar to the X-ray computed tomography (XCT) data of the as-built part which indicates that the theoretical thermal shrinkage included into ELO and simulation data was sufficiently accurate
Summary
Process that enables the tool-free production of complex shaped parts Despite this great asset, the application of AM technologies in industrial production is still hindered by an inferior geometrical and dimensional accuracy compared to conventional manufacturing technologies. The strong influence of process parameters has been shown by Smith et al [5] for the dimensional accuracy of truss structures manufactured by PBF-EB Another important factor that up to now has hardly been considered when discussing geometrical and dimensional accuracy is the effect of the chosen scanning strategy, especially for the manufacturing of complex shaped parts. Most of the machines in the field only provide limited control over the scanning strategy to the operator This circumstance impedes the absolute assessment of an AM technology as a whole based on manufacturing of an arbitrary geometry, e.g., a benchmark artifact.
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