Fused Deposition Modelling (FDM) is a relatively low-cost additive manufacturing process that is commonly characterised by poor dimensional accuracy and precision. Prior work indicates that dimensional errors may be the result of fundamental issues relating to how the filament behaves during deposition and not due to limitations in FDM machine design. Some studies have examined the cross-sectional area of single strands, highlighting the dimensional variation, but there have been no studies examining these changes in other orthogonal planes and along the whole strand length. This study seeks to characterise the behavior of deposited material, to explore the impact of different process parameters on single and multiple strand geometries. Single layer strands of Poly-Lactic Acid (PLA) are deposited through a 0.4 mm diameter nozzle at varying nozzle gap heights, filament volumetric velocities, and print head velocities. Image analysis is used to quantify the width, height, cross sectional shape, and qualitatively analyse strand geometries. Basic print repeatability is shown to be in the order of ±75μm at a strand length of 20 mm. By altering processing parameters, strand width variation of 2.6 mm has been demonstrated. Variations at the start and end of each strand are more significant than in the middle. Variations in shape becomes much more pronounced when printing multiple strands on top of each other. These results demonstrate the importance of careful process parameter selection on part quality, which to date has not been sufficiently well acknowledged.EPSRC Centre in Ultra Precision Engineering (EP/K503241/1
