Design of flexible lattice structures: a design for additive manufacturing perspective

Research output: ThesisLicentiate Thesis

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Abstract

Recent years has seen an unprecedented growth in emerging technologies like Additive manufacturing (AM), augmenting the manufacturing capabilities through a multitude of opportunities while also introducing unique constraints, such as support structures, and post-processing requirements. Taking full advantage of the potential of AM demands product designs to be optimised for both opportunities and constraints specific to AM, requiring evolution from the traditional design for manufacturing to design for additive manufacturing (DfAM). Although majority of studies related to product design within DfAM focus specifically on stiffness maximisation, the domain of flexibility remains under-explored. One of the ways to explore the domain of flexibility, is through flexible structures which are often seen in the applications that require structural flexibility, such as in robotics for locomotion, foot orthotics in health care applications, cranial helmets in shock absorber applications, among others. Among the range of flexible structures that make it possible to achieve flexibility in such applications, lattice structures have been frequently researched due to the design freedom offered by their structural arrangement, relative ease of computation, and tunability of desirable mechanical properties. Although these structures have been investigated to harness the structural flexibility that they offer, a significant gap in research has been observed when focusing on the interplay between the design of flexible lattice structures and DfAM. Addressing this gap, the objective of the presented research is to advance the state-of-the-art in DfAM by enhancing knowledge on how to design flexible lattice structures specifically tailored for AM.
To fulfill the research objective, this research follows the design research methodology (DRM), and involves three studies combining both quantitative and qualitative data collection and analysis methods. The first study is a broader study involving a systematic literature review in DfAM, and the subsequent studies are empirical studies involving laboratory and computation-based experiments with a narrow focus on the design of flexible lattice structures within the context of DfAM.
The systematic literature review revealed that when DfAM is concerned, different design strategies are available for general lattice structures and its variants such as functionally graded lattice structures, conformal lattice structures, multi-material lattice structures, mostly supporting in geometric modelling and finite element-based design evaluation. Other available design strategies enable design optimisation specifically focusing on gradient based TO and multi-scale structural optimisation, address design implications such as cost reduction, and enable incorporation of design parameters and AM specific constraints. However, there is a scarcity of design strategies enabling manufacturing analysis-based design evaluation and other forms of design optimisation (e.g., size and parametric optimisation), with none addressing design rules and guidelines for lattice structures. Thus, the outcomes of the first study provide insights into the existing design strategies, and potential gaps, assisting in their adaptation or extension into the narrower field of flexible lattice structures.
The second and third studies combinedly revealed factors influencing the design of flexible lattice structures, and their effect on structural performance, i.e., compressive behaviour - an indicator of flexibility. The second study revealed that printing orientation is a crucial design parameter showing its substantial impact on deformation behaviour and material failure of lattice structures with no notable effect on plastic deformation that relies more on lattice structure topology - another important design parameter. The third study revealed that manufacturing deviations in as-printed parts is a crucial manufacturing constraint, especially for thin strut-based structures typically seen in lattice structures for light-weighting applications. This study revealed the deviations in geometry (tapered strut geometry with elliptical cross-section compared to their geometrical model), and material of as-printed parts and demonstrated their impact on the compressive behaviour of printed parts. The third study also proposed a finite element based numerical model to incorporate these deviations enhancing the prediction accuracy of the compressive behaviour, thus, assisting in the design of flexible structures.
The presented research has both academic and industrial contribution. Theoretically, it contributes to knowledge within the field of DfAM by providing improved understanding of the influencing factors, and their effect on structural performance when designing flexible lattice structures within the context of DfAM. Industrially, it offers invaluable insights that can aid engineering designers and practitioners in creating flexible lattice structures for various applications, such as upholstery design in furnitures, foot orthotics for patients, among others. For instance, the presented research provides insights related to geometrical and numerical modeling, design tolerances, and numerical simulation based structural analyses specific to flexible lattice structures tailored for AM.
Although this thesis has explored the domain of DfAM to broaden its scope by venturing into the design of flexible lattice structures, future work is needed to design these structures for practical industrial use, making it essential for the future research to focus on developing a simulation driven design approach using the insights produced in this thesis, while also venturing into advanced numerical modelling, advanced lattice designs, and performing scale-up studies within industries.
Original languageEnglish
QualificationLicentiate
Supervisors/Advisors
  • Johansson, Glenn, Supervisor
  • Nordin, Axel, Supervisor
Award date2024 Feb 1
Place of PublicationLund
ISBN (Print)978-91-8039-904-3
ISBN (electronic) 978-91-8039-905-0
Publication statusPublished - 2023 Dec 20

Subject classification (UKÄ)

  • Production Engineering, Human Work Science and Ergonomics

Free keywords

  • Design for additive manufacturing
  • DfAM
  • Lattice structures
  • Flexibility
  • Compuational methods
  • Numerical modelling
  • Engineering design process

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