Mechanical property variance amongst vertical fused filament fabricated specimens via four different printing methods

Amongst additive manufacturing processes, fused filament fabrication (FFF) is one of the most affordable and cost-efficient technologies that can produce complex shaped components with an increasing number of printable polymers such as the polyaryletherketone family, polyetherimide and polyphenylene sulfide. Despite the gain in popularity, there is a lack of standardisation in specimen preparation and mechanical testing of FFF samples. This study investigates the effect of different methods of printing vertical tensile specimens on the mechanical properties when the material and the printing parameters are fixed. A slow crystallising polyetherketoneketone grade was selected as the printing material to exclude the effect of crystallisation on the interlayer bonding strength, leaving the temperature-dependent amorphous molecular diffusion across the layers as the governing mechanism. Vertical tensile specimens made by four printing methods - individually printed, machined and connected (based on ISO 527-2-1A and ISO 527-2-1BA) - were assessed. Individually printed vertical specimens were found to have the highest mean tensile strength, owing to the high level of diffusion induced by the very short layer time. The strengths of specimens printed via the other three methods are less sensitive to the effect of layer time, due to the lower rate of change during cooling and its relationship with the local temperature at the interlayer surface. This study highlights the importance of the disclosure of FFF printing methods along with any reported mechanical data. (c) 2021 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.