Designing heterogeneous porous tissue scaffolds for additive manufacturing processes

A novel tissue scaffold design technique has been proposed with controllable heterogeneous architecture design suitable for additive manufacturing processes. The proposed layer-based design uses a bi-layer pattern of radial and spiral layers consecutively to generate functionally gradient porosity, which follows the geometry of the scaffold. The proposed approach constructs the medial region from the medial axis of each corresponding layer, which represents the geometric internal feature or the spine. The radial layers of the scaffold are then generated by connecting the boundaries of the medial region and the layer's outer contour. To avoid the twisting of the internal channels, reorientation and relaxation techniques are introduced to establish the point matching of ruling lines. An optimization algorithm is developed to construct sub-regions from these ruling lines. Gradient porosity is changed between the medial region and the layer's outer contour. Iso-porosity regions are determined by dividing the subregions peripherally into pore cells and consecutive iso-porosity curves are generated using the isopoints from those pore cells. The combination of consecutive layers generates the pore cells with desired pore sizes. To ensure the fabrication of the designed scaffolds, the generated contours are optimized for a continuous, interconnected, and smooth deposition path-planning. A continuous zig-zag pattern deposition path crossing through the medial region is used for the initial layer and a biarc fitted isoporosity curve is generated for the consecutive layer with C-1 continuity. The proposed methodologies can generate the structure with gradient (linear or non-linear), variational or constant porosity that can provide localized control of variational porosity along the scaffold architecture. The designed porous structures can be fabricated using additive manufacturing processes

Energy management system for biological 3D printing by the refinement of manifold model morphing in flexible grasping space

The use of 3D printing, or additive manufacturing, has gained significant attention in recent years due to its potential for revolutionizing traditional manufacturing processes. One key challenge in 3D printing is managing energy consumption, as it directly impacts the cost, efficiency, and sustainability of the process. In this paper, we propose an energy management system that leverages the refinement of manifold model morphing in a flexible grasping space, to reduce costs for biological 3D printing. The manifold model is a mathematical representation of the 3D object to be printed, and the refinement process involves optimizing the morphing parameters of the manifold model to achieve desired printing outcomes. To enable flexibility in the grasping space, we incorporate data-driven approaches, such as machine learning and data augmentation techniques, to enhance the accuracy and robustness of the energy management system. Our proposed system addresses the challenges of limited sample data and complex morphologies of manifold models in layered additive manufacturing. Our method is more applicable for soft robotics and biomechanisms. We evaluate the performance of our system through extensive experiments and demonstrate its effectiveness in predicting and managing energy consumption in 3D printing processes. The results highlight the importance of refining manifold model morphing in the flexible grasping space for achieving energy-efficient 3D printing, contributing to the advancement of green and sustainable manufacturing practices.Comment: 33 pages, 10 figures, Journa

Latest Developments in Industrial Hybrid Machine Tools that Combine Additive and Subtractive Operations

Hybrid machine tools combining additive and subtractive processes have arisen as a solution to increasing manufacture requirements, boosting the potentials of both technologies, while compensating and minimizing their limitations. Nevertheless, the idea of hybrid machines is relatively new and there is a notable lack of knowledge about the implications arisen from their in-practice use. Therefore, the main goal of the present paper is to fill the existing gap, giving an insight into the current advancements and pending tasks of hybrid machines both from an academic and industrial perspective. To that end, the technical-economical potentials and challenges emerging from their use are identified and critically discussed. In addition, the current situation and future perspectives of hybrid machines from the point of view of process planning, monitoring, and inspection are analyzed. On the one hand, it is found that hybrid machines enable a more efficient use of the resources available, as well as the production of previously unattainable complex parts. On the other hand, it is concluded that there are still some technological challenges derived from the interaction of additive and subtractive processes to be overcome (e.g., process planning, decision planning, use of cutting fluids, and need for a post-processing) before a full implantation of hybrid machines is fulfilledSpecial thanks are addressed to the Industry and Competitiveness Spanish Ministry for the support on the DPI2016-79889-R INTEGRADDI project and to the PARADDISE project H2020-IND-CE-2016-17/H2020-FOF-2016 of the European Union's Horizon 2020 research and innovation program

A relaxation scheme for TSP-based 3D printing path optimizer

2016-2017 > Academic research: refereed > Refereed conference paper201804_a bcmaAccepted ManuscriptPublishe

Process Planning for Concurrent Multi-nozzle 3D Printing

Additive manufacturing (AM) processes possess excellent capabilities for manufacturing complex designs as single uniform parts with optimum material utilization. However, the processes are still not widely used in industry to make large parts. The main reason for this slow adoption is the low material deposition rate during printing. Increasing the material deposition rate by increasing the layer thickness or utilizing larger diameter nozzles results in deterioration of the surface quality of the part. This is known as the “staircase effect”; thus there is a trade-off between the print time and the surface finish of a part. A majority of the research efforts focused on minimizing this trade-off aim to minimize the print time by optimizing the layer thickness based on the evaluation of local geometry of the part. Another approach adopted in minimizing this trade-off is to utilize multiple nozzles concurrently for increasing the material deposition rate. The processes leveraging this approach use independent nozzles with relative motion between them and are seen to be more suitable for parts with a large footprint in the X-Y plane. This thesis further explores this direction of research by utilizing multiple nozzles, mounted on the same print-head, for concurrent printing to increase the deposition rate. The algorithm developed here requires a rotational axis. A 4-axis multi-nozzle toolpath generator, a G-code simulator and a proof-of-concept machine were therefore developed as part of this thesis

From 3D Models to 3D Prints: an Overview of the Processing Pipeline

Due to the wide diffusion of 3D printing technologies, geometric algorithms for Additive Manufacturing are being invented at an impressive speed. Each single step, in particular along the Process Planning pipeline, can now count on dozens of methods that prepare the 3D model for fabrication, while analysing and optimizing geometry and machine instructions for various objectives. This report provides a classification of this huge state of the art, and elicits the relation between each single algorithm and a list of desirable objectives during Process Planning. The objectives themselves are listed and discussed, along with possible needs for tradeoffs. Additive Manufacturing technologies are broadly categorized to explicitly relate classes of devices and supported features. Finally, this report offers an analysis of the state of the art while discussing open and challenging problems from both an academic and an industrial perspective.Comment: European Union (EU); Horizon 2020; H2020-FoF-2015; RIA - Research and Innovation action; Grant agreement N. 68044

Topological optimization of structures produced through 3D printing of fiber reinforced cementitious materials

Dissertação de mestrado integrado em Engenharia CivilTopology optimization can play an important role in the Architecture, Engineering and Construction (AEC) sector. This technology along with digital manufacturing can be a game changer in the future of civil construction, allowing to build, in a short time period, lighter constructions with very geometry complexity but keeping the same of even better structural functioning. These optimized structures when coupled with a material with high capacity efforts redistribution, e.g. fibre reinforced cementitious material (FRC), can partially or totally substitute the conventional reinforcement, consequently less raw material is use, contributing for a better sustainable development. Following this idea, this dissertation will focus on study topology optimization processes along with the use of FRC materials. Initially a comparison between some topology optimization software’s will be carried out, in order to proper evaluate to most suitable for the realization of the present work. In a second stage, considering only the linear behavior of the material, different topology optimization analyses will be done. These analyses will be based on the geometry and the intended structural application (support and load conditions), in addition to the optimization goal (design variable and constraint). This part aims to assess the influence of height / length ratio (H/L ratio) of the beam, in the optimization outcome. After that, a study of the influence of reinforcement amount in the optimization will be done. Afterwards, some finite element analysis (FEA) for one of the optimized structures will be performed and assessed using distinct approaches for obtaining the tensile stress – strain relationship, namely by adopting the ultimate limit state (USL) and service limit state (SLS) tensile diagrams according to the recommendations presented in FIB Model Code 2010. These simulations will serve to evaluate the nonlinear behavior of the FRC structure. For this study six FRC with different strength classes were considered. Finally, an optimized structural element obtained through the FEA was sliced for 3D printing and the influence of the nozzle dimensions, i.e. printing resolution was checked.A otimização da topologia pode desempenhar um papel importante no setor de Arquitetura, Engenharia e Construção (AEC). Esta tecnologia aliada à manufatura digital pode completamente revolucionar o futuro da construção civil, permitindo construir, num curto espaço de tempo, construções mais leves, mas mantendo o mesmo ou ainda melhor funcionamento estrutural. Estas estruturas otimizadas quando conjugadas a um material com alta capacidade de redistribuição de esforços, por ex. materiais cimentícios reforçado com fibras (FRC), pode substituir parcial ou totalmente o reforço convencional, onde consequentemente menos matéria-prima será utilizada, contribuindo-se assim, para um melhor desenvolvimento sustentável. Seguindo essa ideia, esta dissertação terá como foco estudar processos de otimização de topológica juntamente com o uso de materiais FRC. Inicialmente será realizada uma comparação entre alguns softwares de otimização de topológica, a fim de avaliar adequadamente o mais adequado para a realização do presente trabalho. Em uma segunda etapa, considerando apenas o comportamento linear do material, serão realizados diferentes processos de otimização topológica. Essas otimizações serão baseadas na geometria e na aplicação estrutural pretendida e no objetivo da otimização. Esta parte visa avaliar a influencia da relação altura/comprimento da viga (relação H/L), no resultado da otimização. Posteriormente, algumas análises de elementos finitos (FEM) para uma das estruturas otimizadas serão realizadas e avaliadas usando duas abordagens distintas para a obtenção da relação tensão de tração – deformação, uma para estado limite último (ELU) e estado limite de serviço (ELS), seguindo as recomendações presentes no FIB Model Code 2010. Estas simulações servirão para avaliar o comportamento não linear da estrutura de FRC. Para este estudo foram considerados seis FRC com diferentes classes de força. Finalmente, para um elemento estrutural otimizado anteriormente, foi realizada uma simulação de impressão 3D, de modo a estudar a influencia do tamanho do bico de impressão, ou seja, a resolução de impressão foi verificada

A novel slicing strategy to print overhangs without support material

Fused deposition modeling (FDM) 3D printers commonly need support material to print overhangs. A previously developed 4-axis printing process based on an orthogonal kinematic, an additional rotational axis around the z-axis and a 45° tilted nozzle can print overhangs up to 100° without support material. With this approach, the layers are in a conical shape and no longer parallel to the printing plane; therefore, a new slicer strategy is necessary to generate the paths. This paper describes a slicing algorithm compatible with this 4-axis printing kinematics. The presented slicing strategy is a combination of a geometrical transformation with a conventional slicing software and has three basic steps: Transformation of the geometry in the .STL file, path generation with a conventional slicer and back transformation of the G-code. A comparison of conventionally manufactured parts and parts produced with the new process shows the feasibility and initial results in terms of surface quality and dimensional accuracy

Hybrid additive manufacturing with MIG-deposit of aluminium alloy enhanced by friction stir processing

Hybrid additive manufacturing (HAM) is an additive manufacturing (AM) process that integrates multiple metal processing/shaping techniques. This thesis work focuses on the development of a HAM process that combines the MIG welding technique, to produce the initial AM via multi-layer deposit, with friction stir processing (FSP) technique, to enhance the properties of the deposited layers. In order to validate this hybrid concept, filler wire of aluminium alloy AA5183, with diameter of 1.2 mm was deposited on a base plate of aluminium alloy AA5083, with thickness of 6 mm. The initial AM component was produced with three overlapped layers, resulting in a plate of about 400 x 130 x 9 mm, over the base plate. Each layer was produced with parallel and partially overlapping string passes with MIG. The resulting AM component was then processed by FSP, in parallel passes aligned with the initial MIG passes. The effect of the HAM process on the strength and microstructure of the final component was then investigated. It was observed that the initial AM microstructure was refined, with evident dynamic recrystallization in the stirred region by the probe of the FSP tool. There are evidences that the porosities produced by MIG were removed by the FSP. In terms of mechanical properties, the ductility increased in comparison to the initial AM material, in both transversal and longitudinal directions. Concerning the strength, the ultimate tensile (UTS) and yield strength 〖(σ〗_y) are higher than the initial AM material in the longitudinal direction, but lower than the initial AM material in the transversal direction. This fact is mainly due to the overlap ratio between the FSP passes, along the transversal direction, which did not reach continuous overlapping of the stirred zones. Based on a global analysis, encompassing several mechanical properties, the overall quality of the HAM sample improved in comparison to the initial AM