Rapid prototyping (RP) technology, such as Laser Engineering Net Shaping (LENS®), can be used to fabricate heterogeneous objects with various levels of gradient variations in material composition. These objects are engineered to achieve a potentially enhanced functional performance. Past research on the design of such objects has focused on representation, modeling, and desired functional performance. However, the inherent constraints in RP processes, such as system capability and processing time, lead to heterogeneous objects that may not meet the designer’s original intent. To overcome this situation, the research presented in this paper focuses on the identification and implementation of manufacturing constraints into the design process. Previous work on a 2D disk brake rotor design has shown that processing time is one of the critical factors that affect manufacturability. This paper focuses on incorporating the processing time into the optimization design for manufacturing of 3D heterogeneous objects. A node-based finite element modeling technique is used for the representation and analysis. The multi-criteria design problem corresponds to finding the nodal material compositions with minimized structural weight, maximized structural stiffness, and minimized extra processing time used to deposit the multi-material subjected to stress constraints. The optimizer used in this research is a self-adaptive, real-valued Evolutionary Strategy (ES), which is well suited for this type of multi-modal problem. A 3D I-beam made of two materials, aluminum for lightweight and steel for better strength characteristics, is used to illustrate the tradeoff between manufacturability and functionality.

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