• A new salient feature map is proposed to find critical points with respect to multi-axis tool orientation. • A relationship between the tool orientation compliance and the part orientation is revealed through a vector field-based approach. • A direct technique to compute a volumetric iso-tool orientation vector field for multi-axis tool path design. Part orientation is a crucial element that governs the impact of several manufacturing constraints in material extrusion-based additive manufacturing (AM). Although part orientation optimisation has been extensively investigated to improve the manufacturability in 2.5-axis AM configuration, its influence on material extrusion-based multi-axis AM remains underdetermined. In this paper, we propose a computational framework to find the optimal part orientation that maximises the compliance of the tool orientation vector field with respect to several constraints required for support-free multi-axis AM. By combining topological significance, mesh saliency and curvedness metrics, we introduce a new salient feature map to formulate the link between the part orientation and the tool orientation vector field compliance. Once the optimal orientation is computed, our method enables a direct computation of a compliant iso-tool orientation vector field for a set of input iso-tool path points. We demonstrate that the part orientation can indeed be changed to minimise tool angle variation whilst adhering to overhang angle constraints for a range of 3D mesh models. The effectiveness of the proposed method is validated by comparing our method with existing tool orientation vector field design methods. Our promising results reveal the potential in part orientation optimisation as a means to address manufacturing constraints in multi-axis tool path design.

In recent years, multi-axis fused filament fabrication has emerged as a solution to address the limitations of the conventional 2.5D printing process. By using a curved layering strategy and varying the print direction, the final parts can be printed with reduced support structures, enhanced surface quality, and improved mechanical properties. However, support structures in the multi-axis scheme are still needed sometimes when the support-free requirement conflicts with other constraints. Currently, most support generation algorithms are for the conventional 2.5D printing, which are not applicable to multi-axis printing. To address this issue, we propose a sparse and curved support filling pattern for multi-axis printing, aiming at enhancing the material efficiency by fully utilizing the bridge technique. Firstly, the overhang regions are detected by identifying the overhang points given a multi-axis nozzle path. Then, an optimization framework for the support guide curve is proposed to minimize its total length while ensuring that overhang filaments can be stably supported. Lastly, the support layer slices and support segments that satisfy the self-supported criterion are generated for the final support printing paths. Simulation and experiments have been performed to validate the proposed methodology.