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

Abstract

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.

A systematic review of voxelization method in additive manufacturing

“…Reference [12] proposes to extend the topology optimization model for multi-physics simulations, increasing the already good framework capabilities. A similar proposal is described in [14], where an integration of thermal influence during manufacturing process has been associated to an increase in the lattice degradation analysis results.…”

“…As a consequence of the wide lattice structures external surfaces (usually cells are made by thin cylinders), stair effect could be problematic. Reference [14] measures the qualitative properties of tensile specimen made in lattice structure and investigate stair-step and deposition path effects, by changing building angle to get the numerical elastic modulus and ultimate tensile strength variation. Moreover, due to their high structure complexity, finite element analysis would require a huge amount of computational power.…”

“…In industrial applications where weight reduction is mandatory, such as automotive and aerospace, lattice structures are widely used [56]. Reference [14] discusses a method to measure the property degradation using asfabricated voxel model. The 3D object is built relying on deposition path after a reconstruction starting from an STL file, taking into account the importance of used resolution to achieve an higher order of detail in the inner structure made of voids and gaps.…”

“…13). Besides, [14][15][16] use FDM to manufacture optimized specimens that are used in the experimental tests to validate the proposed models and methodologies. ABS plastic is cheap, easy to be found and is modelled by FDM machines, which are very wide spread in university and practitioners and a large community lie behind this technology.…”

“…Other important contributions to the field are given by [14,19]. The first one uses geometrical voxelization to access part degradation, based on the AM tool deposition path, while the second one uses cuboid elements as a computational unit to optimize and discretize the machine toolpath combining neighbour voxels depending on the stress amount detected using FEM analysis.…”