Exploring the impact of build direction on overhang design constraints for multiaxis material extrusion

Purpose Material extrusion (MEX) additive manufacturing often requires support structures to enable manufacture of steep overhanging features. Multi-axis deposition (often enabled by a robotic arm) offers novel toolpath planning methods that can significantly reduce or eliminate supports. However, there is currently a lack of established design guidelines for the process. Design/methodology/approach This study investigates the relationship between achievable, support-free overhangs and the multi-axis build direction. Although altering build directions mid-print can increase the layer-to-layer overlap of an overhanging feature, the deposition paths on the overhanging surface may be less supported with respect to gravity. To interrogate these effects, a 6-degree-of-freedom robotic arm MEX platform printed test pieces with overhang angles (relative to the build direction) increasing from 0° to 75° at build directions varying from 0° (i.e., XY-planar) to 60° with respect to the global Z-axis. Findings Characterization of printed surface quality revealed no statistically significant difference in the fidelity of the overhanging surface as the build direction was changed. These results suggest that the overhang threshold observed in traditional XY-planar printing (typically 45°) remain consistent regardless of build direction (e.g. a build direction of 60° successfully printed a relative overhang of 45°), indicating that deposition quality was not negatively impacted by gravitational forces. Originality/value This study provides insight into how tool orientation can be optimized to maximize part accuracy and minimize support material requirements; after quickly screening for the XY-planar overhang threshold, designers can freely select multi-axis build directions throughout part geometries, provided the overhanging surfaces are below that relative threshold.