In-situ microwave tomography for parts' cooldown monitoring in powder bed fusion of polymers

Temperature monitoring during the cooldown in powder bed fusion of polymers is essential to qualify parts, and is an absolute novelty in the field. This is because the direct reading of the parts' temperature is hindered by the powder. In this work, an innovative temperature monitoring technology based on microwave tomography is used to assess the part cooldown history in an industry-grade EOS P110 machine. So, relative and absolute readings of the temperature field can be carried out even for parts surrounded by powder. For the first time, several cooldown rates could be experimentally measured depending on the different polymer state: 0.56 degrees C min-1 in the liquid phase, 1.2 degrees C min-1 during supercooling, 0.83 degrees C min-1 in the solid phase. This technology will allow the development of a new generation of smart PBF machines that can better sense and hence control the entire PBF process, including the cooldown phase, which is often neglected but has the highest impact on the final mechanical performances of parts.