In-process thermal monitoring of the extrusion additive manufacturing process with high temperature polymers

Lack of repeatability and undetected print defects during printing in Material Extrusion (MEX), can limit the uptake of the technology for manufacturing. Many of the conventional polymer manufacturing processes such as injection moulding and extrusion rely on sensors and in-situ process monitoring tools to control, provide feedback and adjust parameters during the process. MEX requires tight control of both the heating and cooling of the polymer in order to achieve high performance parts. For this reason, monitoring the layer temperature is of greater importance, such that (1) it allows the validation of thermal models; (2) can inform on the presence of defects in printing and potentially reduce their presence through a closed loop monitoring system; and (3) helps maintain control over important parameters such as viscosity and crystallinity. Although the literature presents often validated thermal models, the details of how these measurements are obtained are rarely presented. This study discusses in detail the challenges of measuring the layer temperature during printing of pure and Carbon fibre (Cf) based Polyaryletherketone (PAEK) polymers using an Infrared (IR) camera and proposes two data processing methods as well as a discussion of results with an optimum method recommended.