Generating structurally efficient forms for digital fabrication: a pathway to manufacturing-ready design
Creators: name: Bi, Minghao
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400510
subject: Structural engineering

description: For centuries, engineers and architects have been striving to explore the design limit of spatially intriguing structures. However, enthralling visions often end up aborted due to the challenges in manufacturing and construction. In the past few decades, research attention has been drawn to developing digital fabrication techniques, where manufacturing is assisted by digitally controlled robotics. More advanced manufacturing technologies have become accessible and mature, allowing designers to reimagine the form-finding process in the conceptualisation stage. Combined with topology optimisation, structurally efficient forms can be fabricated without extra cost due to geometrical complexity. Although showing great potentiality, digital fabrication of structurally efficient forms is still at the infant stage and demands research attention for further development.

This thesis provides systematic approaches to improving the quality, efficiency and manufacturability of structurally optimised designs. The study examines the characteristics of different advanced manufacturing technologies and reflects their manufacturing constraints within the design framework. The generated structural designs are tailored to the requirements of the fabrication process, minimising the need for post-processing and extra design modifications. The thesis presents three inter-related research projects targeting different aspects of advanced manufacturing technologies.

The first research project presents a novel method that restrains the formation of overhanging features in the topology optimisation framework, creating self-supporting designs for additive manufacturing applications. The overhang problem is formulated as a layer-wise relationship, and elements whose modification does not create an overhang are selected as candidates for the element update scheme. Numerical results under different overhang conditions and comparisons between self-supporting and non-self-supporting designs are presented. Subsequently, the effectiveness of the proposed method is further validated by the fabrication of 3D printed models. The results suggest that the self-supporting designs are comparable to non-self-supporting counterparts in structural performance. Without needing sacrificial support, the printing time and material usage can be saved by more than 40%.

The second research project addresses various manufacturing constraints of 3D concrete printing within the topology optimisation framework. Firstly, a layer-wise sensitivity scheme is proposed to satisfy the overhang angle limit, generating self-supporting designs in the user-defined print direction. Secondly, a novel continuous extrusion constraint is implemented to facilitate continuous printing operation. Thirdly, the anisotropy of the 3D concrete printing process is simulated in the optimisation process by employing a transverse isotropic material model. Fourthly, domain segmentation is introduced as a design feature to simulate modular construction. Finally, the feasibility and robustness of the algorithm are demonstrated by constructing a topology optimised chair using 3D concrete printing in the laboratory. The proposed strategy is innovative as a self-supporting design framework for 3D concrete printing is currently missing in the literature. By addressing the manufacturing constraints, the proposed method significantly improves the quality and efficiency of 3D concrete printing designs.

The third research project presents a novel framework to generate a globally continuous toolpath for solid and partial infill designs. For solid infill, outward contour and double offset schemes are used to generate smooth curves as the primary volume-filling paths; the remaining unfilled areas are covered by extending zigzag lines from the closest contours. Subsequently, a contour layer-wise connection is carried out based on the depth-first-search algorithm to formulate a globally continuous path. A post-processing step is also presented to optimise the coverage and curvature of the toolpath design. The concept is extended for partial infill settings by trimming and joining rectangular grid lines. Finally, topology optimised structures are fabricated using the proposed algorithm in two interesting experiments: topology optimised table printed from thermoplastic polyurethane and topology optimised chair printed from 3D concrete printing. Comparison with algorithms in the literature suggests that the proposed algorithm for solid infill shows significant improvement in print quality and efficiency. A continuous toolpath design for partial infill settings is also innovative in this field.

The research outcomes demonstrate how structurally optimised forms can be digitally fabricated without needing formwork and human intervention. The contribution of the research to the relevant field is summarised as (1) the topology optimisation framework for 3D concrete printing and continuous toolpath for partial infill are innovative and fills the gap in the literature; (2) the self-supporting topology optimisation for additive manufacturing and continuous toolpath for solid infill show improved performance compared to existing work. The thesis sheds light on the integration of topology optimisation and digital fabrication in civil and architectural applications.