Slicing of tessellated models for additive manufacturing based on variable thickness layers

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Han, Dongmin
Kurfess, Thomas R.
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In contrast to machining or subtractive technologies, Additive Manufacturing (AM) is a set of technologies that fabricate a 3-D object by automatically adding material layer-by-layer. In AM systems, the Computer Aided Design (CAD) model is converted into layers in a process known as slicing. One of the limitations of AM is the geometrical inaccuracy and undesirable surface finish due to the layer-upon-layer application of material. Inclined features suffer significantly from this drawback, known as the stair-step effect. While decreasing the layer thickness can reduce the stair-step effect, the cost of considerably increasing processing time is unappealing to manufacturers. Flat layer additive manufacturing has a number of limitations: first, the trade-off between better surface finish and printing time; second, support structure are usually needed, which causes the unwelcome surface quality on the contact areas between the part and the support structure; and third, the use of flat layer leads to the anisotropy property, which affects the strength of the final parts. To overcome the limitations present in flat layer additive manufacturing, adaptive slicing and curved-layer slicing were proposed. Some research has focused on developing the algorithms that adaptively chooses the layer thickness based on the curvature and angle along the surface. Some has developed curved layer slicing by offsetting the top surface to generate the layers. But all of these works only apply to 3D models with lots of constrains and involve certain level of manual interventions. In addition, all of these works are only aiming at 3-axis FDM machines, while the proposed slicing procedure is not only applicable to 3-axis systems, but also suitable for 5-axis. This research proposes a new solution to slice tessellated CAD models with dynamic thickness layers. The proposed method negates the stair-step effect and provides smooth bonding between layers. It also provide the potential to be applied on 5-axis FDM machines with minimum modifications. In this procedure, the CAD models is divided into planar-curved regions and uniform slicing regions by the directions of the facet vectors. The top surface is extracted from the curved region and the facets are offset with different distance from the top surface to create slicing layers. As a result, the dimensional accuracy is improved using fewer layers compared to uniform slicing. Hence, the proposed method can significantly save print time without compromising quality. In addition, a more generic slicing procedure will be developed by applying the method locally to individual features on a single part. The contributions of the research are as follows: first, a dynamic thickness curved layer slicing algorithm for tessellated models was developed; second, this approach was implemented on a 3-axes Fused Deposition Modeling (FDM) platform; third, the surface integrity property was improved; and fourth, a more generic slicing algorithm was developed for more complicated models.
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