Methodology to assess interlayer quality in the material extrusion process: A temperature and adhesion prediction on a high performance polymer

Abstract

The material extrusion additive manufacturing process consists in extruding a molten polymer along a path with trajectories defined from a 3D definition of the part. One of the major drawbacks of this process is the reduction of the mechanical properties of the parts compared with those made by conventional manufacturing methods such as injection molding. On the one hand, this reduction of properties is linked to the presence of macroporosities in the part and, on the other hand, to the limited adhesion between the deposited layers. These two phenomena strongly depend on the thermal history of the polymer. This work proposes to determine the thermal conditions leading to sufficient adhesion, and to the manufacture of parts with sufficient final interfilament strength. An instrumented bench was developed from a 3D printer in order to investigate the cooling, at the filament scale, of parts printed in PEKK material. In parallel, heat transfers in the material extrusion process were simulated using a model, which was validated with the experimental data obtained using the bench. The adhesion was also modeled by describing the phenomena of coalescence and healing of the interface. The physical properties necessary for the models were characterized taking into consideration their thermodependency. A parametric study then quantifies the influence of each parameter on the temperature of the polymer, as well as on the interlayer adhesion, thus contributing to the definition of the process window.