Design for Polymer Additive Manufacturing Processes with Coupled Process Responses Using Novel Numerical and Empirical Based Modelling and Optimization Tools
Creators: Mostafa, Khaled
Publisher: name: University of Alberta Library
Year: 2022

<p>Additive manufacturing (AM) is a process of joining materials to make parts from 3D model data by successive layer by layer material addition. AM has triggered a paradigm shift towards parts and assemblies design methodologies, materials development and utilization, and additional part functionalization. The workflow to produce an additively manufactured part consists of three steps: preprocessing, build cycle, and post-processing. Design for additive manufacturing (DfAM) or preprocessing is crucial in additive manufacturing and significantly impacts the process outcomes like part&#39;s strength, geometry, and manufacturing time which translates to cost. DfAM consists of different sub-steps: part design, process parameters optimization, and path planning. The promised advantages of AM will not get realized, and the results can be significantly costly unless the rules for DfAM are implemented. Additionally, new design strategies should be developed to overcome the inherent limitations of each AM process.Functional additively manufactured parts are evaluated based on three main criteria; mechanical performance, geometrical accuracy, Physical efficiency (thermal, fluid, and weight), and cost. Part design, process parameters, and path planning required to produce cost-effective and successful functional parts must be carefully designed and optimized to overcome the inherent tradeoffs of the selected process. The ultimate goal of DfAM is to produce parts with &quot;as-built&quot; geometrical measurements and mechanical performance that match the &quot;as designed&quot; CAD part design specifications. The challenges facing design for polymer additive manufacturing process outcomes are coupled, process parameters are interdependent, commercially promised resolution is different from manufacturing resolution, and lack of simulation, modelling and optimization tools.The thesis&#39;s primary research question is &quot;Can the DfAM tools and optimized process parameters produce a feasible as-built part comparable to the as-designed CAD par specifications?&quot;. The research domain of this thesis includes two subdomains. The first subdomain is the process parameter optimization, and the second domain is part design optimization to improve mechanical properties, geometrical accuracy and minimize cost and weight. This thesis studies two polymer AM processes to apply and investigate the different challenges, namely Projection stereolithography (PSLA) and fused deposition modelling (FDM).For the first subdomain, the thesis investigates the effect of the PSLA process parameters on the mechanical properties, geometric accuracy, and surface roughness of the manufactured part in light of a novel introduced curing model to estimate the accumulated exposure energy per each layer. Developed analytical and empirical models are integrated to predict the final part’s geometrical distortion, material properties, and surface roughness. Newly introduced terminologies like irradiance affected zone and critical energy for mechanical properties are used to develop curing schemes to improve geometrical accuracy while maintaining the mechanical properties to ensure the part integrity during manufacturing. Then mechanical properties can be enhanced during post-curing. A novel high-resolution fluorescence induced irradiance measurement methodology is introduced to measure and capture the irradiance profile projected from one micromirror and quantify the effect of building plat irradiance map non-uniformity on geometrical accuracy. The effect of part location on the geometrical accuracy and the effect of grayscale pixels on minimizing that effect is experimentally explored. A novel 3D geometry prediction algorithm is developed to simulate the geometrical distortion in different features and surface roughness. A three-stage integrated optimization algorithm with a newly introduced cross-layers optimization method and irradiance compensation algorithm is presented.For the second subdomain, the thesis investigates the effect of part 2D design parameters on the mechanical properties and cost of manufactured parts by the FDM process. A cost-based methodology is used while considering the part design parameters to manufacture parts optimized for strength and cost. A novel algorithm called the reverse CAD algorithm is introduced, which converts the machine input G-code file back to a CAD model. The Reverse CAD provides an accurate assessment of the geometric and mechanical behaviour of the printed part as it also incorporates the effect of slicing parameters. Finally, a novel framework to grade both the size and relative density of standard and custom unit cells simultaneously within a lattice structure as a function of the cell spatial coordinates. It was found that dual grading enhances compressive strength, modulus of elasticity, absorbed energy, and fracture behaviour of the lattice structure at the same part weight.</p>