Topology Optimization of Manufacturable Rib-Type Structures for Casting and Molding
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Rib-like features originate from structural mechanics principles of bending efficiency and were reinforced by casting and injection-molding constraints (thick walls cause sink marks, voids, long cooling times) and refined through stress-flow analysis, making them ubiquitous with modern manufacturing designs/processes. In this work we present a new approach to creating rib-patterns derived algorithmically via topology optimization (TO), yielding ribs that are not resembling typical parametric primitives while still catering to the engineering intuition and satisfying manufacturing constraints. Additive manufacturing technologies, inherently disposing an extreme design freedom, have contributed significantly to realize TO-based designs. However, a great percentage of TO-designed industrial structures still concern cast parts. In this case, manufacturability is ensured by enforcing corresponding manufacturing constraints in the optimization problem. Pull-Out and Member Size constraints (maximum/minimum thickness, gap size) are usually applied to guide the optimized shape towards rib-type patterns. Although such constraints are well-tested in different TO frameworks, their geometric definition may deviate from the logic of the intended geometric pattern, resulting in non-manufacturable designs. In Ansys Mechanical, we developed a novel formulation for two geometric constraints that contribute most to the formation of rib-type designs, namely the Maximum Thickness and the Gap Size constraints. We provide the possibility to approximate the thickness inside some plane, instead of the standard 3-dimensional definition. This choice improves significantly the manufacturability of cast/molded parts, providing rib-designs that respect the user-defined specifications.
