Fused Filament Fabrication (FFF) has revolutionized metamaterial manufacturing, offering unprecedented control over material properties and structure. Despite extensive research on optimizing standard slicing parameters, the positioning of the seam location and the associated influences on the local and global mechanical properties of the metamaterials is an often overlooked aspect of printing thin-walled geometries.

Our study characterizes the nuanced relationship between seam positioning and the resulting geometry and mechanical integrity of FFF-printed metamaterials. While slicers commonly automate the optical concealment of seams, our research emphasizes the need to shift focus from visual aesthetics to mechanical optimization and the prevention of potential predetermined breaking points. The common practice of neglecting seam position in standard parameters can lead to structural weaknesses, especially in thin-walled metamaterials.

Using a state of the art Prusa 3D printer, we conducted a systematic study of seam positioning on PLA samples, keeping all other printing parameters constant. For the printed samples, the seam position was either placed at the edge of the sample, randomly distributed, or in the mid-plane. The influence of the seam position on the resulting geometry was determined using (segmented) computed tomography scans. The scans revealed irregular bonding and air gaps coinciding with the seam position, highlighting the hidden vulnerabilities introduced by seam placement. Samples of the three groups were mechanically characterized and compared using tensile tests, combined with digital image correlation analysis to gain further insight into the local and global strain distribution and defect propagation.

Our findings underscore the need to consider seam position as a fundamental factor in FFF printing, challenging the common practice of positioning the seam in the best optical manner.

This study serves as a call to action, advocating greater awareness in the community of the mechanical effects of seam positioning. By urging practitioners to move beyond automatic optical concealment, we aim to encourage a more informed and cautious approach to FFF printing. This increased awareness will be crucial for enhancing the mechanical performance and reliable characterization of printed metamaterials, fostering advancements in various engineering applications.