In-situ electron optical measurement of thermal expansion in electron beam powder bed fusion

Thermal expansion plays an important role during additive manufacturing by electron beam powder bed fusion because it strongly affects the quality of the manufactured parts. However, prediction and control of thermal expansion is a difficult task due to the high complexity of part geometries and the corresponding temperature distribution. Therefore, powerful process monitoring tools are required to improve insight into the process. In the current study, the capabilities of in-situ acquisition of electron optical images are assessed with respect to measurement of thermal expansion. For this purpose, a large series of electron-optical images was recorded during cooling down of a PBF-EB build job. The subsequent image analysis revealed that the image quality is high enough to monitor thermal shrinkage of the part and to quantify thermal strain with remarkable accuracy. These findings are very promising and give rise to new applications of in-situ electron-optical observation with regard to temperature management and validation of numerical frameworks.