Abstract
It is attractive to combine topology optimization (TO) with additive manufacturing (AM), due to the design freedom provided by AM, and the increased performance that can be achieved with TO. One important aspect is to include the design rules associated with the process restrictions of AM to prevent the requirement of relatively large support volumes during printing. This paper presents a TO filter that enforces a minimum overhang angle, resulting in an optimized topology that is printable without the need for support structures. The filter is based on front propagation, which, as it is described by a PDE, allows for a straightforward application on unstructured meshes, to enforce an arbitrary overhang angle. Efficient algorithms developed for front propagation are used in combination with adjoint sensitivities, in order to have a minor influence on the total computational cost. The focus of this work is on the implementation of the filter for high resolution 3D cases, which requires development of the front propagation for tetrahedral elements, and its parallelization.
Highlights
Additive manufacturing (AM) offers tremendously more design freedom compared to conventional manufacturing techniques, and geometric complexity has a much lesser relative impact on production cost
The filter is based on front propagation, which, as it is described by a PDE, allows for a straightforward application on unstructured meshes, to enforce an arbitrary overhang angle
A second arrival-time field, TAM, is constructed that includes information on the overhang limitation of an actual additive manufacturing (AM) process (Fig. 1c). It is constructed by using a front propagation that results in TAM = Tlayer in printable regions, but delays the propagation when the direction of propagation is lower than a given overhang angle αoh
Summary
Additive manufacturing (AM) offers tremendously more design freedom compared to conventional manufacturing techniques, and geometric complexity has a much lesser relative impact on production cost. The local boundary angle control methods usually converge to sub-optimal local minima, generating saw-tooth like structures that are not manufacturable, whereas the physics-based constraints, potentially providing more details, are numerically expensive since they generally involve one or more finite element analyses to model the printing process. A second arrival-time field, TAM, is constructed that includes information on the overhang limitation of an actual AM process (Fig. 1c) It is constructed by using a front propagation that results in TAM = Tlayer in printable regions, but delays the propagation when the direction of propagation is lower than a given overhang angle αoh (i.e. violating the overhang limitation). The value of τ (x) is a measure for the distance to the closest manufacturable region, giving an indication of how much material it would require to support a certain location This continuous measure of overhang is beneficial for gradient-based optimization used in topology optimization
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