Improving mechanical performance in material extrusion parts via optimized toolpath planning

Abstract

The material extrusion (MEX) additive manufacturing (AM) process is often overlooked for producing parts in load-bearing applications due to poor inter- and intra-layer bonds. These bonds are weak relative to the deposition direction, creating an overall anisotropic mechanical performance. However, this anisotropy presents an opportunity to tune part performance through the toolpath. Especially with a composite material, changing the deposition direction to preferentially align mechanical anisotropy with load paths could provide a route to increased performance. In a more general sense, any set of design objectives could be used to generate an orientation field (e.g., load paths for strength, routes for thermal conductivity, etc.) to control alignment of deposition directions.In combination with the inherent geometric flexibility of AM, there is an opportunity to simultaneously optimize part topology and its printing toolpath. As a step towards this goal, this paper presents a toolpath planning algorithm, based on streamline placement algorithms used in computational fluid dynamics, for generating optimized toolpaths where every deposition is aligned to an arbitrary orientation field. In particular, the algorithm is designed to continuously connect a discrete orientation field to improve deposition (and therefore composite reinforcement) length. The presented algorithm is then compared to more typical MEX infill patterns using topology- and toolpath orientation-optimized structures undergoing both tension and three-point bending loads. The toolpath planning strategies are evaluated in terms of (1) alignment to the orientation field and (2) mechanical performance. Relative to more conventional toolpath planning methods, the presented algorithm produces toolpaths with better alignment to the optimized orientation fields (>97%), and the printed parts demonstrate increased mechanical efficiencies.