An interlaced toolpath strategy for void reduction in material extrusion additive manufacturing

Material Extrusion (MEX) is one of the most widely used Additive Manufacturing (AM) technologies due to its accessibility, versatility, and cost-effectiveness. However, the layer-by-layer and track-by-track nature of MEX printing makes it prone to defects, particularly voids between adjacent material tracks, which negatively impact structural integrity and surface quality. Among these, inter-track voids are the most prevalent in MEX-printed parts. This study investigates an interlaced toolpath strategy for Fused Filament Fabrication (FFF) to mitigate inter-track void formation. Unlike other void-minimisation strategies that rely on thermal post-treatments, laser-assisted deposition, or ultrasonic-enhanced printing, this method is a software-based approach that does not require hardware modifications or post-processing. A series of experiments were conducted using line-based toolpaths with interlaced deposition, varying second-pass extrusion rates and extrusion temperatures. The results demonstrate that the interlaced strategy reduces inter-track porosity by up to 65.5% while maintaining negligible changes in printing time. In addition, increasing the second-pass extrusion temperature by 5 °C further reduced porosity while limiting volumetric errors. These findings suggest that interlaced deposition strategies can be integrated into existing toolpaths to enhance print quality and mechanical performance in MEX-based AM. This method offers an effective solution for minimising porosity while maintaining precise material deposition, making it particularly relevant for applications requiring dense infill structures with high precision.