This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

Topology optimization is a powerful free-form design tool to systematically optimize structures for various applications. Often this results in complex shapes that are difficult or impossible to manufacture by conventional manufacturing processes. Additive manufacturing methods like the selective laser melting are predestined for such applications because of the design freedom provided by a tool-free, layer-wise production. Even though additive manufacturing grants great freedom in shape and structural design, there are some restrictions of additive manufacturing that need to be considered during the design phase of components. These restrictions that strongly differ from conventional processes are highly material dependent and must be adjusted for any change of printing material or even alloy. It is possible to directly integrate manufacturing restrictions into topology optimization simulations to only generate geometries fitting these constraints. In this paper a novel approach to avoid internal support structures in fluid flow optimizations is presented. Internal supports are needed to avoid building errors like sagging or dross formation. These occur when restrictions regarding the maximum overhang length or overhang angle perpendicular to the building direction are violated. This is often found in horizontally aligned channels. The removal of internal supports during the post processing of printed components is time consuming and expensive. For complex geometries it can even become impossible because a direct access to the support structures is needed. For this reason, much effort has been put into the implementation of restrictions to avoid specific overhang angles and lengths in topology optimizations in the past, which are transferable to fluid flow optimizations. An application of these conventional approaches leads to significant changes in the channel geometry which causes a deviation from the optimal flow profile. Therefore, this paper presents a new empirical approach that does not influence the channel geometry. Instead, channels that violate manufacturing restrictions are divided into smaller channels of equal mass flow that are directly printable and simultaneously provide an optimal flow profile. A general formulation in connection with the conventional SIMP method is aimed at to allow a transfer to related processes or an adaptation to different materials.