Technical Report Optimal topology for additive manufacture: A method for enabling additive manufacture of support-free optimal structures Martin Leary a,⇑ , Luigi Merli b , Federico Torti b , Maciej Mazur a , Milan Brandt a a RMIT Centre for Additive Manufacturing, School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melbourne, Australia b Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy article info Article history: Received 16 January 2014 Accepted 6 June 2014 Available online 20 June 2014 abstract Topology optimisation enables profound insight into the optimal material distribution for a given structural objective, applied loading and boundary conditions. The topologically optimal geometry is often geometrically complex and incompatible with traditional manufacturing methods. Additive manufacture can accommodate significantly more complex geometries than traditional manufacture; how- ever, it is necessary that specific design rules be satisfied to ensure manufacturability. Based on identified design for additive manufacture rules, a novel method is proposed that modifies the theoretically optimal topology as required to ensure manufacturability without requiring additional support material. By assessing the manufacturing time and component mass associated with feasible orientations of the proposed geometry, an optimal orientation can be identified. A case study is presented to demonstrate the usefulness of the proposed method. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Additive manufacture involves the progressive addition of material to generate component geometry; this differs fundamen- tally from traditional, subtractive manufacture whereby material is progressively removed from an initial geometry as required [1]. Additive manufacture has been labelled as a disruptive technology [2] due to the associated capacity to economically manufacture at very low batch sizes; and, the capability to manufacture highly complex geometries. This latter capability provides an opportunity to physically implement topologically optimal geometries, which are often highly complex, and therefore incompatible with traditional manufacturing methodologies. Topology optimisation enables identification of the optimal structural connectivity for a specific design scenario, boundary conditions and available spatial envelope. Topology optimisation is not based on a priori assumptions of material distribution, resulting in complex truss networks with high structural efficiency [3–5]. The geometric complexity of the topologically optimal design is typically incompatible with traditional manufacturing methods [6]. Additive manufacture therefore provides an opportunity to manufacture components that more closely approximate the optimal geometry than traditional methods. Despite the enhanced geometric freedom associated with additive manufacture, it is necessary that specific design rules be satisfied to ensure manufacturability [7–9]. Design for additive manufacture includes requirements associated with minimum feature size, manufacturable inclination angle, allowable bridging distance, and the robust accommodation of heat transfer. Typically, design for additive manufacture constraints are either accommodated by intuitive modification of the intended geometry [9], or by the use of support material to enable acute inclination angles and to transfer heat as required. The use of support material extends the envelope of feasible geometries, but incurs cost and time penalties [7]. A novel method is proposed in this work that modifies the theoretically optimal topology as required to enable additive manufacture according to the identified design for additive manu- facture constraints. The proposed method requires no manual intervention and results in a geometry that is manufacturable without necessitating the use of support material. By assessing the manufacturing time, component volume and platen support base associated with orientations of the proposed geometry, an optimal orientation can be automatically identified. 1.1. Topology optimisation Topology optimisation refers to the search for geometry that optimises an objective function, such as minimal mass or cost, subject to associated boundary conditions and constraints, such http://dx.doi.org/10.1016/j.matdes.2014.06.015 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +61 428955563. E-mail address: martin.leary@rmit.edu.au (M. Leary). Materials and Design 63 (2014) 678–690 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes