A review of void reduction strategies in material extrusion-based additive manufacturing

Material extrusion (ME) is one of the most common Additive Manufacturing (AM) techniques in use today due to low equipment and feedstock costs and a broad range of compatible materials. However, parts manufactured by ME can exhibit undesirable internal voids produced by incomplete material filing within part layers. Voids are detrimental to part performance as they compromise mechanical, visual, and dimensional properties. The size and distribution of the voids depend on various parameters, such as the cross-sectional shape of deposited material tracks, the shape of a layer, and the layer infill strategy. A range of voids reduction strategies have been investigated in the literature based on pre-deposition, in-situ, or post-process approaches. This review provides a comprehensive insight into how voids are formed, identified and reduced via different reported approaches. Gaps in the literature are identified for the perspective of future research.