Lattice structure lightweight triangulation for additive manufacturing

Total hip arthroplasty (THA) is an increasingly common procedure that replaces all or part of the hip joint. The average age of patients is decreasing, which in turn increases the need for more durable implants. Revisions in hip implants are frequently caused by three primary issues: femoral loading, poor fixation, and stress shielding. First, as the age of hip implant patients decreases, the hip implants are seeing increased loading, beyond what they were traditionally designed for. Second, traditional implants may have roughened surfaces but are not fully porous which would allow bone to grow in and through the implant. Third, traditional implants are too stiff, causing more load to be carried by the implant and shielding the bone from stress. Ultimately this stress shielding leads to bone resorption and implant loosening. Additive manufacturing (AM) presents a unique opportunity for enhanced performance by allowing for personalized medicine and increased functionality through geometrically complex parts. Much research has been devoted to how AM can be used to improve surgical implants through lattice structures. To date, the authors have found no studies that have performed a complete 3D lattice structure optimization in patient specific anatomy. This paper discusses the general design of an AM hip implant that is personalized for patient specific anatomy and proposes a workflow for optimizing a lattice structure within the implant. Using this design workflow, several lattice structured AM hip implants of various unit cell types are optimized. A solid hip implant is compared against the optimized hip implants. It appears the AM hip implant with a tetra lattice outperforms the other implant by reducing stiffness and allowing for greater bone ingrowth. Ultimately it was found that AM software still has many limitations associated with attempting complex optimizations with multiple materials in patient specific anatomy. Though software limitations prevented a full 3D optimization in patient specific anatomy, the challenges associated such an approach and limitations of the current software are discussed.

Gas turbines play a critical role in industries such as power generation and aviation. Additive manufacturing has emerged as a game-changing technology for gas turbine components, offering superior design flexibility and performance enhancements. The present work provides an overview of a multistep approach for integrating lattice structures into a specific gas turbine component, the Nozzle Guide Vane (NGV), using additive manufacturing technology. The first step involves a comprehensive assessment of lattice structures’ influence on the mechanical and thermal properties of the exposed part of NGV. Through computational simulations and experiments, an ideal lattice geometry is determined, optimizing structural integrity and heat transfer properties while minimizing volume usage. The second step sets the baseline performances of the current NGV system components, which were investigated and selected for additive manufacturing analysis. The third step focuses on the overall effect of additive manufacturing capabilities in the NGV system. The fourth and final step optimizes the additive manufacturing process for fabricating gas turbine components with lattice structures. Laser Powder Bed Fusion (L-PBF) technology, united with advanced Topological Optimization analyses, and high-temperature alloys were selected to withstand the demanding gas turbine operating conditions. This multistep approach represents a significant step forward in gas turbine technology, capitalizing the advanced mechanical applications as lattice designs and additive manufacturing, aiming in enhanced performance, reduced weight, and improved efficiency. These developments hold the potential to achieve more sustainable and cost-effective energy generation and transportation systems.

A lattice structure is defined by a network of interconnected structural members whose architecture exhibits some degree of regularity. Although the overall architecture of a lattice may contain many members, its generation can be a simple process in which a unit cell composed of a small amount of members, in comparison to the overall structure, is mapped throughout the Euclidean space. However, finding the right lattice architecture in a vast search space that customizes the behavior of a design for a given purpose, subject to mechanical and manufacturing constraints, is a challenging task. In response to this challenge, this work investigates a Voronoi diagram-based tessellation of a body-centered cubic cell for applications in structural synthesis and computational design of 3D lattice structures. This work contributes by exploring how the Voronoi tessellation can be utilized to parametrically represent the architecture of a lattice structure and what the implications of the parametrization are on the optimization, for which a global direct search method is used. The work considers two benchmark studies, a cubic and a cantilever lattice structure, as well as the effect of isotropic and anisotropic material property models, stemming from applications to additive manufacturing. The results show that the proposed parameterization generates complex search spaces using only four variables and includes four different lattice structure types, a Kelvin cell, a hexagonal lattice, a diamond-core lattice structure, and a box-boom type lattice structure. The global direct search method applied is shown to be effective considering two different material property models from an additive manufacturing (AM) process.

Reactive two-step additive manufacturing of ultra-high temperature carbide ceramics

Thanks to the increasingly widespread additive manufacturing technology and promising properties, the use of Lattice Structures (LS) is becoming increasingly frequent. LS allows the components to be designed with tunable stiffness, which can unlock the control of natural frequencies. However, crucial challenges must be faced to integrate LS into the typical design process. In the present work, an experimental and numerical study of LS-enabled tuning of natural frequencies in mechanical components is proposed. In a first step, the difficulties arising with the large amount of FEM nodes, that are required to predict LS complex shapes in detail, are overcome by modeling LS with an elastic metamaterial whose stiffness properties are determined through ad hoc finite element analyses. After that, a simplified investigation can be conducted on the modal properties of components with fixed external shape and variable internal LS filling, based on Triply Periodic Minimal Surfaces (TPMS) lattices. In those conditions, the parameters of the LS core can be tuned to control and optimize the global modal frequencies of the entire geometry. In addition, the admissible range of frequencies can be estimated. Optimized plates results are validated through an experimental test campaign on additively manufactured specimens made with Selective Laser Melting (SLM) technology. The samples are hammer-tested with various boundary conditions while laser sensors measure the oscillation data of selected points. Finally, estimated and identified natural frequencies were compared. The described model is suitable to be implemented in an automated tool for designers.

PurposeIn this era of Fourth Industrial Revolution, also known as Industry 4.0, additive manufacturing (AM) has been recognized as one of the nine technologies of Industry 4.0 that will revolutionize different sectors (such as manufacturing and industrial production). Therefore, this study aims to focus on “Additive Manufacturing Education” and the primary aim of this study is to investigate the impacts of AM technology at selected South African universities and develop a proposed framework for effective AM education using South African universities as the case study.Design/methodology/approachQuantitative research approach was used in this study, that is, a survey (questionnaire) was designed specifically to investigate the impacts of the existing AM technology/education and the facilities at the selected South African universities. The survey was distributed to several students (undergraduate and postgraduate) and the academic staffs within the selected universities. The questionnaire contained structured questions based on five factors/variables and followed by two open-ended questions. The data were collected and analyzed using statistical tools and were interpreted accordingly (i.e. both the closed and open-ended questions). The hypotheses were stated, tested and accepted. In conclusion, the framework for AM education at the universities was developed.FindingsBased on different literature reviewed on “framework for AM technology and education”, there is no specific framework that centers on AM education and this makes it difficult to find an existing framework for AM education to serve as a landscape to determine the new framework for AM education at the universities. Therefore, the results from this study made a significant contribution to the body of knowledge in AM, most especially in the area of education. The significant positive responses from the respondents have shown that the existing AM in-house facilities at the selected South African universities is promoting AM education and research activities. This study also shows that a number of students at the South African universities have access to AM/3D printing lab for design and research purposes. Furthermore, the findings show that the inclusion of AM education in the curriculum of both the science and engineering education is South Africa will bring very positive results. The introduction of a postgraduate degree in AM such as MSc or MEng in AM will greatly benefit the South African universities and different industries because it will increase the number of AM experts and professionals. Through literature review, this study was able to identify five factors (which includes sub-factors) that are suitable for the development of a framework for AM education, and this framework is expected to serve as base-line or building block for other universities globally to build/develop their AM journey.Research limitations/implicationsThe survey was distributed to 200 participants and 130 completed questionnaires were returned. The target audience for the survey was mainly university students (both undergraduate and postgraduate) and the academics who have access to AM machines or have used the AM/3D printing lab/facilities on their campuses for both academic and research purposes. Therefore, one of the limitations of the survey is the limited sample size; however, the sample size for this survey is considered suitable for this type of research and would allow generalization of the findings. Nevertheless, future research on this study should use larger sample size for purpose of results generalization. In addition, this study is limited to quantitative research methodology; future study should include qualitative research method. Irrespective of any existing or developed framework, there is always a need to further improve the existing framework, and therefore, the proposed framework for AM education in this study contained only five factors/variables and future should include some other factors (AM commercialization, AM continuous Improvement, etc.) to further enhance the framework.Practical implicationsThis study provides the readers and researchers within the STEM education, industry or engineering education/educators to see the importance of the inclusion of AM in the university curriculum for both undergraduate and postgraduate degrees. More so, this study serves as a roadmap for AM initiative at the universities and provides necessary factors to be considered when the universities are considering or embarking on AM education/research journey at their universities. It also serves as a guideline or platform for various investors or individual organization to see the need to invest in AM education.Originality/valueThe contribution of this study towards the existing body of knowledge in AM technology, specifically “AM education research” is in the form of proposed framework for AM education at the universities which would allow the government sectors/industry/department/bodies and key players in AM in South Africa and globally to see the need to invest significantly towards the advancement of AM technology, education and research activities at various universities.

The lattice structure is a type of cellular materials [1] that has truss-like structures with interconnected struts and nodes in a three-dimensional (3D) space. Compared to other cellular materials such as random foams and honeycombs, the lattice structures exhibit better mechanical performance [2]. Some examples of lattice structures are shown in Figure 8.1. The first one is a randomized lattice structure. Due to the disordered lattice cells, the properties of this type of lattice structures are stochastic and difficult to control. But it can be used as implants in orthopedic surgeries. The second and the third are lattice structures with periodic unit cells. The difference is that the strut thickness of the second one is uniform, which is called homogeneous lattice structures. However, the third one has non-uniform strut thickness for specific loading conditions, which is called heterogeneous lattice structures. By properly adjusting the material in vital parts of the lattice structure, the heterogeneous periodic lattice structure can have a better mechanical performance than the homogeneous one with the same weight. Plenty of design and optimization methods [3-5] have been proposed for lattice structures to pursue better performance in different engineering applications. For example, the lattice structure is applied to achieve lightweight [3, 4], energy absorption [6], and thermal management [7]. Due to the complexity of the geometry, the fabrication of lattice structures had been the most critical issue. However, with the development of Additive Manufacturing (AM) processes, the difficulty in the fabrication was largely relieved.

Characterization of L-PBF lattice structures geometric defects

Purpose The purpose of this study is to introduce methodologies for detailed characterisation of process-induced defects in 3D printed lattice structures, independent of the manufacturing process. Detailed characterisation of imperfections, particularly internal voids, including their geometry and distribution, provides insights into their impact on the mechanical properties of lattice structures. Furthermore, the correlation between defect severity, distribution and printing conditions, such as the printing direction, can be captured using the proposed methods. These correlations can be used to optimise printing parameters and lattice designs to achieve workpieces with minimal imperfections. Design/methodology/approach Due to the significant role of polymers and their composites in diverse industrial sectors, such as bioengineering, and the existing research gap regarding the impact of process-induced defects on the mechanical properties of polymeric lattices, the cellular structures were fabricated from the polymer in this study using the selective laser sintering process. To characterise additive manufacturing-induced defects in polymeric lattice structures, X-ray computed tomography is employed to scan the printed lattices, and image processing techniques using MATLAB scripts are developed to extract and analyse the characteristics of inspected defects, including their morphology and distribution. Findings This study reveals that polymeric lattice structures manufactured by powder bed fusion exhibit various defects, including geometry-related imperfections and internal voids. Geometry-related defects are more pronounced near strut junctions, with significant variations in strut thickness and cross-sectional shape. The analysis of voids’ morphology indicates that the lack of fusion during additive manufacturing leads to their formation, with voids exhibiting diverse shapes, sizes and orientations. This highlights the importance of detailed characterisation of process-induced voids and their incorporation into the structural analyses to improve the accuracy of the mechanical performance predictions for lattice structures. Originality/value The novelty of this work lies in the detailed characterisation of voids within manufactured polymeric lattices, including their 3D dimensions, aspect ratio and orientation. This comprehensive analysis of process-induced voids offers new insights into their impact on the mechanical performance of lattice structures, addressing the limitations of prior research that often simplified voids as spheres and overlooked the influence of void geometry on the mechanical properties of lattices. Furthermore, the methods developed for defect characterisation, especially for internal voids, are applicable to any lattice unit cell topology, regardless of the additive manufacturing method or material used.

PurposeThis study aims to evaluate and compare the macroscopic properties of commercial acrylonitrile-butadiene-styrene (ABS) processed by two different types of additive manufacturing (AM) machines. The focus is also on the effect of multiple closed-loop recycling of ABS.Design/methodology/approachA conventional direct-drive, Cartesian-type machine and a Bowden, Delta-type machine with an infrared radiant heating system are used to manufacture test specimens molded in ABS. Afterward, multiple closed-loop recycling cycles are conducted, involving consecutive AM (four times) and recycling (three times). The rheological, mechanical, morphological and physicochemical properties are investigated.FindingsThe type of machine affects the quality of the produced parts. The machine containing an infrared radiant system in a temperature-controlled chamber produces parts showing higher mechanical properties and filling fraction, although it increases the yellowing. Closed-loop recycling of ABS for AM is applicable for at least two cycles, inducing a slight increase in tensile modulus (ca. 5%) and in tensile strength (ca. 13%) and a decrease in the impact strength (ca. 14%) and melt viscosity. An increase in the filling fraction of the AM parts promotes an increase in tensile strength and tensile modulus, although it does not influence the impact strength. Furthermore, multiple closed-loop recycling does not affect the overall chemical structure of ABS.Practical implicationsControlling the environmental temperature and using infrared radiant heating during AM of ABS improves the quality of the produced parts. Closed-loop recycling of ABS used in AM is feasible up to at least two recycling steps, supporting the implementation of a circular economy for polymer-based AM.Originality/valueThis study shows original results regarding the assessment of the effect of different types of AM machines on the main end-use properties of ABS parts and the influence of multiple closed-loop recycling on the characteristics of ABS fabricated by the most suited AM machine with an infrared radiant heating system and a temperature-controlled environment.

Image-based and in-situ measurement techniques for the characterization of the damage behavior of additively manufactured lattice structures under fatigue loading

PurposeThis paper aims to investigate the feasibility of supportless printing of lattice structures by metal fused filament fabrication (MF3) of Ti-6Al-4V. Additionally, an empirical method was presented for the estimation of extrudate deflection in unsupported regions of lattice cells for different geometric configurations.Design/methodology/approachMetal-polymer feedstock with a solids-loading of 59 Vol.% compounded and extruded into a filament was used for three-dimensional printing of lattice structures. A unit cell was used as a starting point, which was then extended to multi-stacked lattice structures. Feasible MF3 processing conditions were identified to fabricate defect-free lattice structures. The effects of lattice geometry parameters on part deflection and relative density were investigated at the unit cell level. Computational simulations were used to predict the part quality and results were verified by experimental printing. Finally, using the identified processing and geometry parameters, multi-stacked lattice structures were successfully printed and sintered.FindingsLattice geometry required considerable changes in MF3 printing parameters as compared to printing bulk parts. Lattice cell dimensions showed a considerable effect on dimensional variations and relative density due to varying aspect ratios. The experimental printing of lattice showed large deflection/sagging in unsupported regions due to gravity, whereas simulation was unable to estimate such deflection. Hence, an analytical model was presented to estimate extrudate deflections and verified with experimental results. Lack of diffusion between beads was observed in the bottom facing surface of unsupported geometry of sintered unit cells as an effect of extrudate sagging in the green part stage. This study proves that MF3 can fabricate fully dense Ti-6Al-4V lattice structures that appear to be a promising candidate for applications where mechanical performance, light-weighting and design customization are required.Originality/valueSupportless printing of lattice structures having tiny cross-sectional areas and unsupported geometries is highly challenging for an extrusion-based additive manufacturing (AM) process. This study investigated the AM of Ti-6Al-4V supportless lattice structures using the MF3 process for the first time.

<p>Lattice structures are used in a variety of high-value engineering applications; for example, in automobile, aerospace and biomedical applications, due to their light weight, high specific strength, stiffness, heat transfer control and energy absorption. Additive Manufacturing (AM) technologies, such as Selective Laser Melting (SLM), offer radical net-shape manufacturing solutions for metallic structures directly from digital data. The prediction of AM lattice structure mechanical properties prior to manufacture is both cost and time-consuming; particularly as existing models do not readily accommodate the effects of manufacturing defects and lattice node geometry on column buckling. The critical buckling load of columns was algebraically and numerically simulated for a full Design of Experiments (DOE) of independent variables, including column length, column radius, node radius and material type. This simulation data quantifies the effect of independent variables on critical buckling load and demonstrates the limitations of algebraically prediction. This research can be extended to allow the simulation of the load carrying capacity of entire lattice structures; and to accommodate the effect of manufacturing variation on the associated load carrying capacity of AM lattice structures.</p>

CFD and strength analysis of novel biomimetic lattice structure designed for additive manufacturing and post-processing

Additive Manufacturing (AM), popularly called 3D Printing, is a scientific term indicating the Rapid Prototyping (RP) technologies developed in 1980s. AM technologies can directly fabricate a complex 3D object from three-dimensional Computer Aided Design (3D CAD) model by adding layer-by-layer of material. Advances in AM technologies are capable of manufacturing highly complicated geometries of product without the need for process planning, the reduction of product development time and cost, the removal of tooling compared to conventional manufacturing technologies. The production of lattice structures is quickly performed by AM technologies in order to attain a product with lightweight and stronger and to provide the high specific mechanical properties such as strength and energy absorption. However, the current product modelling technologies have many difficulties for generation of lattice structure model. Thus, the paper proposes a new approach that allows to create different configuration types of conformal and non-conformal lattice structure model.