Support-free fabrication of overhanging structures in laser powder directed energy deposition using hybrid planar and nonplanar slicing

Abstract

This study aims to address the challenge of support-free fabrication of large-angle overhanging structures in laser powder directed energy deposition (LP-DED), where geometric constraints and process instability often lead to failure. A hybrid slicing strategy integrating planar and nonplanar toolpaths is proposed and implemented on an eight-axis robotic LP-DED system. By coordinating the motion of a six-degree-of-freedom robotic arm and a two-degree-of-freedom positioner, the laser/nozzle axis is maintained approximately aligned with the gravity vector during deposition. A B-Rep-based slicing method using STEP models is adopted to generate smooth and continuous toolpaths for complex geometries. The proposed method enables stable support-free fabrication of representative overhanging structures, including spherical shells, truncated cones and blade geometries. Using 304 stainless steel as the demonstration material, consistent deposition was achieved across different geometries, with acceptable dimensional accuracy and surface quality. The experimental results confirm the feasibility and process stability of the proposed hybrid planar and nonplanar slicing strategy for support-free LP-DED fabrication of complex overhanging structures. This study proposes a geometry-dependent support-free fabrication strategy for LP-DED by combining multi-axis motion control with adaptive slicing. The approach enables stable deposition while maintaining acceptable surface roughness for complex structures.