Topology optimization considering overhang constraint in additive manufacturing

Structural topology optimization (Bendsoe and Kikuchi, 1988; Bendsoe and Sigmund, 2003; Deaton and Grandhi, 2014; Cheng and Olhoff, 1981; Xie and Steven, 1993) [1-5] provides a numerical tool for structural design with optimum performance. However, these structures could be too complex to be fabricated. Additive manufacturing (AM) enables the fabrication of these complex structures and is perfectly suitable for realizing the full potential of TO. However, AM has its manufacturing constraints too. The overhang constraint is one of these constraints. Components with small overhang angles or hanging features may deform, droop or warp, when fabricated using laser or electron beams in a layer-wise manner. This paper proposes a new approach to obtain optimum structural topology with consideration of the overhang constraint. We develop an effective method to estimate structural boundary normals of the optimum and intermediate designs with zigzag and blurry boundaries in SIMP by fitting local element density distribution with linear surfaces. By controlling the horizontal length of structural component, the hanging feature and too thin component are effectively suppressed. The element-wise overhang angle constraints and hanging feature constraints are aggregated as two single constraints on the volume fraction of the elements that violate these element-wise constraints. The structural topology optimization problem is solved by MMA. Numerical examples are given to demonstrate the effectiveness of the proposed algorithm. (C) 2018 Elsevier Ltd. All rights reserved.