A Review of In-situ Temperature Measurements for Additive Manufacturing Technologies

Abstract

Additive manufacturing (AM) encompasses a rapidly advancing host of technologies used for building parts with complex geometrical shapes layer-by-layer from a wide range of materials such as polymers, glasses, ceramics, metals, and metal-alloys. A wide variety of AM processes are used to build parts on test beds using processes such as material extrusion and laser or e-beam irradiation of powders and liquids, depending on the industrial or commercial application. Unfortunately the dimensional and compositional quality of AM built parts highly depends on the technology, and can even significantly vary between different AM machines of the same technology, due to a lack of process feedback and control. Improvements have been made by performing computational modeling and ex-situ characterization such as x-ray diffraction, focused ion beam cross-sectioning, x-ray computed tomography, and electron microscopy. These techniques, however, are time consuming, expensive, and do not allow in-situ monitoring of parts as they are built. In-situ temperature measurements are promising as they monitor the build temperature and can provide feedback for better process control. Thermal imaging is widely-used for in-situ temperature measurements, but is limited to qualitative data due to the unpredictability of emissivity as temperature and composition dynamically change. Two-color pyrometry and mm-wave radiometry measurements promise to circumvent these problems but have their own dimensional limitations. These methods and others will be compared and contrasted, and future improvements of in-situ temperature measurements will also be discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Certain commercial equipment, instruments, or materials are identified in this paper in order to adequately describe the experimental procedure. Such identification does not imply recommendation or endorsement by the authors, Sandia National Laboratories, or NCSL International, nor does it imply that the materials or equipment identified are the only or best available for the purpose.