A Feature-Specific Local Cooling System to Control Tensile Strength and Dimensional Accuracy in Fused Filament Fabrication

There is in-depth understanding of the effects and interactions of various process parameters on the mechanical properties and dimensional accuracy of parts produced through fused filament fabrication (FFF). Surprisingly, local cooling in FFF has been largely overlooked and is only rudimentarily implemented. It is, however, a decisive element of the thermal conditions governing the FFF process and of particular importance when processing high-temperature polymers such as polyether ether ketone (PEEK). This study, therefore, proposes an innovative local cooling strategy, which allows for feature-specific local cooling (FLoC). This is enabled by a newly developed hardware in combination with a G-code postprocessing script. The system was implemented on a commercially available FFF printer and its potential was demonstrated by addressing typical drawbacks of the FFF process. Specifically, with FLoC, the conflicting requirements for optimal tensile strength versus optimal dimensional accuracy could be balanced. Indeed, feature-specific (i.e., perimeter vs. infill) control of thermal conditions resulted in a significant increase in ultimate tensile strength and in strain at failure in upright printed PEEK tensile bars compared with those manufactured with constant local cooling-without sacrificing the dimensional accuracy. Furthermore, to improve the surface quality of downward-facing structures the controlled introduction of predetermined breaking points at feature-specific part/support interfaces was demonstrated. The findings of this study prove the importance and capabilities of the new advanced local cooling system in high-temperature FFF and provide further directions on the process development of FFF in general.