Vacuum additive manufacturing of polyether ether ketone: Prediction of mechanical properties and forming mechanism

Abstract

Polyether ether ketone (PEEK) 3D printing technology has enormous potential uses in space exploration and engineering because of the exceptional qualities of material and ability to withstand the harsh conditions of the space environment. Considering the significant influence of the vacuum environment on the thermal history and resin rheology of the 3D printing process, this study establishes a predictive model using response surface methodology (RSM) to correlate axial tensile strength with critical process parameters under 10 Pa vacuum environment (VAC) and standard atmospheric pressure (ATM). Moreover, the relationship between tensile strength and process parameters across different environmental pressures is analyzed using analysis of variance (ANOVA) and univariate analysis. To further understand the intricate behaviors of PEEK during 3D printing, cooling and non-isothermal crystallization models, the neck growth model, and the pore growth model were developed for both VAC and ATM conditions. These models were validated through crystallinity assessments, microstructural cross-section analysis, and monofilament extrusion tests. Experimental results reveal that the theoretical model provides an accurate depiction of heat and mass transfer processes in VAC and ATM conditions. The results calculated using the theoretical model systematically elucidate the influence mechanisms of the vacuum environment on heat and mass transfer, resin rheological behavior, and defect formation. The study explains the different effects of process parameters on the tensile properties under VAC and ATM pressure conditions and proposes a defect formation mechanism for vacuum-printed samples, attributed to the expansion of initial pores within the filament driven by the pressure difference between the internal and external environments.