Part-scale thermal evolution and post-process distortion of Inconel-718 builds fabricated by laser powder bed fusion

Abstract

In-situ monitoring and assessment of thermal evolution during the layer-by-layer build process of a laser powder bed fusion (L-PBF) additive manufacturing system play a pivotal role to help understand the process-structure-property correlation of the L-PBF. Interlayer temperature refers to the layer temperature after the powder is spread but before scanning a new layer commences. It represents the part heating due to the processing of the previous layers and acts as the initial temperature under which a new layer is scanned. Therefore, interlayer temperature is essential for the derivation of process control to minimize keyholes and other thermal-related defects. In addition, measurements of interlayer temperature can be used for validating part-scale thermal modeling or for detecting part defects. This paper presents an experimental study of the evolution of interlayer temperature through in-situ thermographic imaging during the fabrication of twin square-canonical parts of Inconel 718 using the EOS M280 system. Post-process distortion measurements of the fabricated parts are also obtained to provide insights into the correlation to geometric features of the part. The experimental results show that the evolution of the interlayer temperature highly correlates with the unique geometric features of the part and the support structure used to build the part. During the processing of the square-canonicals, the interlayer temperature reached as high as 325 °C, which is significantly higher than the preheated substrate temperature of 80 °C under which the first layer of the part is scanned. Measurements of the build after manufacturing show that the largest normal displacement of the part's outer wall surface reached about 17 % of its thickness. The results also show that the peak distortion and peak interlayer temperature do not occur at the same layer and are due to different causes.