Quantifying effects of material extrusion additive manufacturing process on mechanical properties of lattice structures using as-fabricated voxel modeling

During additive manufacturing processes, part geometry is approximated because the layer by layer deposition procedure can yield stair-step irregularities between layers. Moreover, since finite-sized filaments are deposited in the material extrusion process, air gaps are generated among the filaments. These lead to geometrical errors in additively manufacturing parts and degradation of the parts' mechanical properties, such as elastic modulus and strength, based on slicing and material deposition strategies. Geometric errors that arise during the manufacturing procedure have a particularly significant impact on fabricated lattice structures, which consist of a network of small struts, because they have large bounding surfaces that must be approximated during fabrication. In addition, since the struts in lattice structures are generally small, voids among filaments affect the structures' mechanical properties significantly even if they are small. In order to avoid property degradation it is necessary to consider these phenomena during lattice structure design. In this paper, an as-fabricated modeling approach for a material extrusion process is proposed, for use in modeling and assessing the effects of geometric degradation on additively fabricated lattice structures. The approach implements a voxel based modeling technique to consider stair steps and deposition paths at each layer. Using the proposed method, numerical models for evaluating mechanical properties are generated. Estimated mechanical properties using the as-fabricated voxel modeling approach are compared with experimental results. The effects of the stair step and deposition path phenomena on mechanical properties are quantified and demonstrate good correspondence with experiments, particularly for elastic modulus.