Fabrication of Complex Support-Free, Thin-Walled, Hollow Curved Structures Via 6-Axis Robotic Material Extrusion

Robotic additive manufacturing (AM) presents a transformative alternative to traditional-based 3D printing, particularly for fabricating complex, free-form geometries without support structures. This study optimizes the (AM) process parameters for manufacturing unsupported, thin-walled hollow 90-degree curved tubes using a six-degree-of-freedom robotic arm integrated with a material extrusion additive manufacturing system. A Taguchi L₁₆ orthogonal array was employed to explore the effects of robot speed, nozzle temperature, extrusion speed and layer height. Part quality was evaluated using a comprehensive five-metric framework: process time, mass, surface roughness, geometric deviation, and mechanical peak compressive load. Analysis of variance revealed that layer height is the dominant factor governing process efficiency (86.4% contribution), surface roughness (74.6%), and geometric accuracy (41.7%). On the contrary, mechanical strength was primarily controlled by extrusion speed (34.4% contribution) and robot speed (12.2%), where higher extrusion rates resulted in denser parts with superior interlayer adhesion. Validation experiments on complex twisted hollow curves demonstrated that the optimized robotic process reduced material consumption by 61.5% and production time by 70.1% compared to traditional 3D printing, which depends on sacrificial support structures. This work establishes a robust, data-driven protocol for the efficient, supportless fabrication of functional thin-walled structures.