Optimal Design for Additive Manufacturing of Heterogeneous Objects
Author: Hu, Yuna
Supervisor: Fadel, Georges M.
Institution: The Graduate School of Clemson University
Rapid prototyping (RP) technologies, such as Laser Engineering Net Shaping (LENS®) and Ultrasonic Consolidation (UC), can be used to fabricate heterogeneous objects composed of more than one material, wherein spatially varied microscopic structural details produce continuously or discretely changing mechanical or thermal properties on a macroscopic scale. These objects are engineered to achieve a potentially enhanced functional performance. Past research on the design of such objects has focused on representing and optimizing the material distribution to obtain a desired functional performance. However, the inherent constraints in RP processes are critical when building heterogeneous objects. The research goal in this dissertation is to develop an approach, Design for Additive Manufacturing (DfAM), to identify and implement the manufacturing constraints related to the fabrication of heterogeneous objects in the design phase. By incorporating these constraints early in the design process, the solution can satisfy not only the required functionalities but also conform to the manufacturing constraints, thus ensuring manufacturability. Two manufacturing constraints for the point-wise LENS® process, -the achievable volume fractions and the processing time-, and the two constraints for the layer-wise UC process, -the possible volume fraction values and the gradient material direction, are identified and incorporated into the DfAM design approach. A node-based and an element-based finite element (FE) representation are extended in this dissertation to model the point-wise (in LENS® process) and layer-wise (in UC process) material distribution of heterogeneous objects, in addition to the geometric information. Evolutionary-based optimizers such as a Genetic Algorithm (GA-based) algorithm and an Evolution Strategy (ES-based) algorithm, using zeroth-order searching methods, are applied because of their ability to handle the type of multi-modal problems encountered in the design of heterogeneous objects. The multi-criteria design problem, consisting of finding the optimal material compositions at nodes or within elements, -that satisfy the requirements of functional performance and manufacturability-, is set up and solved. Two hypothetical applications, a bi-material 2D disk brake rotor and a 3D I-beam structure consisting of aluminum and steel, are used to illustrate how to incorporate effectively the identified manufacturing constraints into the design process and how to deal with the tradeoff between manufacturability and functionality.