Optimization of material extrusion additive manufacturing process parameters for polyether ketone ketone (PEKK)

Polyether ketone ketone (PEKK) is a high-performance thermoplastic used in the fused filament fabrication (FFF) process to manufacture end use parts for the biomedical and aerospace industries. While other high-performance polymers such as polyetherimide (PEI) and polyether ether ketone (PEEK) have been studied extensively in literature, minimal studies have investigated the effects of FFF process parameters on PEKK. Tensile properties of FFF-printed PEKK was most affected by build orientation followed by number of contours in our previous study, although effects of build orientation on various properties of materials have been examined extensively, only few studies focused on number of contours. This study aims to understand if the selected parameters from our previous study affect other properties of PEKK, and if employing more contours can further improve these properties. A Taguchi orthogonal array varying contours in 4 levels and all other factors in 2 levels were used for this study. Optimum process parameters that maximize properties including compressive, flexural, thermomechanical, dynamic mechanical, and surface roughness were determined, and samples were printed using those settings to verify the statistical model. For the first time in literature, analysis was performed to understand if process parameters affected porosity and that, in turn, influenced mechanical properties. Comparison of flexural properties with injection-molded counterparts revealed that through optimization of process parameters, even the cost-effective printers used in this study could produce parts with properties almost equal to injection-molded parts in the direction of measurement. In addition, a coefficient of linear thermal expansion varied significantly with changes in process parameters and the variation was attributed mostly to porosity within samples and alignment of rasters with the direction of measurement. A clear relationship between number of contours, porosity, and mechanical properties was observed for most responses. Overall, number of contours was the most significant process parameter as more contours reduced porosity and improved mechanical and dynamic mechanical properties.