A Geometry-based Approach for Support-free Additive Manufacturing of Structures with Large Overhang Angles and Closed Features

Architected materials derive performance characteristics from material properties and internal geometry. These materials are increasingly prevalent across a wide variety of domains. Many intricate feature geometries associated with architected materials can be explored using additive manufacturing (AM) processes. However, current AM methods generally cannot fabricate geometries with completely closed voids without introducing a support structure. This paper describes a new, support-free approach to AM capable of creating structures with closed voids. This work limits part geometry to three-dimensional (3D) geometries defined by a revolution about a single axis. This limitation enables planar analysis within a three-degree-of-freedom (3-DoF) task space. Part geometry in 3-DoF task space is constrained to a convex arch. Task space geometry is divided into an ordered set of sub-regions, considering feasible deposition orientations and collision constraints. The use of 3-DoF task space provides planar translation and rotation of the component during fabrication. The introduction of this rotational DoF addresses AM overhang constraints imposed by gravity. Methods for generating, ordering, and layering sub-regions suitable for printing a part with a closed hole are presented. Layers derived in the 3-DoF task space analysis are then extended to 3D deposition paths using the axis of revolution defined by the original part. The method of hole closure relies on the concept of a "keystone" which requires a 45° nozzle offset for collision-free deposition within keystone-adjacent sub-regions. The feasibility of deposition using a 45° nozzle offset is explored experimentally, and results demonstrate feasibility.