P. Dal Fabbro, S. Rosso, A. Ceruti, D. Boscolo Bozza, R. Meneghello, G. Concheri, G. Savio. Analysis of a Preliminary Design Approach for Conformal Lattice Structures. Applied Sciences 2021, 11(23), 11449

An important issue when designing conformal lattice structures is the geometric modeling and prediction of mechanical properties. This paper presents suitable methods for obtaining optimized conformal lattice structures and validating them without the need for high computational power and time, enabling the designer to have quick feedback in the first design phases. A wireframe modeling method based on non-uniform rational basis spline (NURBS) free-form deformation (FFD) that allows conforming a regular lattice structure inside a design space is presented. Next, a previously proposed size optimization method is adopted for optimizing the cross-sections of lattice structures. Finally, two different commercial finite element software are involved for the validation of the results, based on Euler–Bernoulli and Timoshenko beam theories. The findings highlight the adaptability of the NURBS-FFD modeling approach and the reliability of the size optimization method, especially in stretching-dominated cell topologies and load conditions. At the same time, the limitation of the structural beam analysis when dealing with thick beams is noted. Moreover, the behavior of different kinds of lattices was investigated.

Keywords: Conformal lattice structure, Size optimization, Additive manufacturing, Virtual modeling Design for additive manufacturing

R. Sponchiado, L. Grigolato, S. Filippi, G. Concheri, R. Meneghello, G. Savio. Heterogeneous Materials Additive Manufacturing: An Overview. In Design Tools and Methods in Industrial Engineering II. Lecture Notes in Mechanical Engineering. Springer, Cham, 2022. pp 462-473

Advancements in additive manufacturing technology have made it possible to create machines that allow the use of a wider range of materials, even simultaneously in the production of a single piece. The production of heterogeneous objects allows to include multifunctionality within the domain by varying the composition in a gradual or net fashion. This paper analyzes the AM technologies that allow multi-material, emphasizing the constrains and the possible applications with the goal of identifying guidelines for design methods development. From the analysis we observe important innovations that permitted to easily process polymeric materials, especially with material extrusion and material jetting. However, the use of ceramic powders and metallic materials for the creation of heterogeneous objects requires the development of methods which remain very limited by the process conditions.

Keywords: Multi material AM, Functionally graded materials, Heterogeneous objects

P. Dal Fabbro, S. Rosso, A. Ceruti, R. Meneghello, G. Concheri, G. Savio. Conformal Lattice Structures: Modeling and Optimization. In Design Tools and Methods in Industrial Engineering II. Lecture Notes in Mechanical Engineering. Springer, Cham, 2022. pp 474-485

One of the open issues in additive manufacturing is the design of conformal lattice structures, leading to an optimal layout of the struts in the design domain. This paper aims to compare different struts distributions in conformal lattices via low computational power methods in a CAD environment. Four approaches for a wireframe virtual model definition are presented for a simple cubic conformal lattice structure. An iterative variable diameter optimization method and two linear structural analyses based on mono-dimensional elements and different theories are compared. These verificationmethods widen the capability of checking the results so the user can compute the deformation of 3D periodic structures, or other visual results, without spending a huge amount of time and computational power. Results show that both the analysis methods give reliable results and the struts layout based on trivariate NURBS shows the most flexible solution allowing for a real-time variation of the boundary condition.

Keywords: Conformal lattice structure, Size optimization, Additive manufacturing, Virtual modeling, Design for additive manufacturing

R. Sponchiado, F. Uccheddu, L. Grigolato, P. Dal Fabbro, G. Savio. A Design Method for Custom Functionally Graded Lattice Orthoses. In Advances on Mechanics, Design Engineering and Manufacturing IV. Lecture Notes in Mechanical Engineering. Springer, Cham, 2023. pp 265–275

Additive manufacturing allows the creation of highly customized and complex objects that could not be achieved with traditional methods. These characteristics of the production method make the products perfectly suitable for the design of orthotics, where the customization of the device and the speed of production are essential. For example, it may be necessary to create locally more or less rigid orthose depending on the anatomic area or its local function. The 3D printing of objects can be performed with variable properties within their domain by means of the so called Functionally Graded Additive Manufacturing (FGAM). This article presents a new method for the production of reticular orthoses which begins with the acquisition of the area of interest using a 3d scanner, followed by the generation of the reticular structure locally densified according to ergonometric models, and the finalization of the model with truss thickening and application of a closure system. Some models were then reproduced with AM techniques such as SLA and MJF and tested in daily use.

Keywords: Additive manufacturing, Orthotics, Functionally graded materials, Custom manufacturing.

R. Sponchiado, S. Rosso, P. Dal Fabbro, L. Grigolato, H. Elsayed, E. Bernardo, M. Maltauro, F. Uccheddu, R. Meneghello, G. Concheri, G. Savio. Modeling Materials Coextrusion in Polymers Additive Manufacturing. Materials. 2023; 16(2):820

Material extrusion additive manufacturing enables us to combine more materials in the same nozzle during the deposition process. This technology, called material coextrusion, generates an expanded range of material properties, which can gradually change in the design domain, ensuring blending or higher bonding/interlocking among the different materials. To exploit the opportunities offered by these technologies, it is necessary to know the behavior of the combined materials according to the materials fractions. In this work, two compatible pairs of materials, namely Polylactic Acid (PLA)-Thermoplastic Polyurethane (TPU) and Acrylonitrile Styrene Acrylate (ASA)-TPU, were investigated by changing the material fractions in the coextrusion process. An original model describing the distribution of the materials is proposed. Based on this, the mechanical properties were investigated by analytical and numerical approaches. The analytical model was developed on the simplified assumption that the coextruded materials are a set of rods, whereas the more realistic numerical model is based on homogenization theory, adopting the finite element analysis of a representative volume element. To verify the deposition model, a specific experimental test was developed, and the modeled material deposition was superimposed and qualitatively compared with the actual microscope images regarding the different deposition directions and material fractions. The analytical and numerical models show similar trends, and it can be assumed that the finite element model has a more realistic behavior due to the higher accuracy of the model description. The elastic moduli obtained by the models was verified in experimental tensile tests. The tensile tests show Young’s moduli of 3425 MPa for PLA, 1812 MPa for ASA, and 162 MPa for TPU. At the intermediate material fraction, the Young’s modulus shows an almost linear trend between PLA and TPU and between ASA and TPU. The ultimate tensile strength values are 63.9 MPa for PLA, 35.7 MPa for ASA, and 63.5 MPa for TPU, whereas at the intermediate material fraction, they assume lower values. In this initial work, the results show a good agreement between models and experiments, providing useful tools for designers and contributing to a new branch in additive manufacturing research.

Keywords: additive manufacturing, fused deposition modeling, material extrusion, coextrusion, material modeling.

F. Leoni, P. Dal Fabbro, S. Rosso, L. Grigolato, R. Meneghello, G. Concheri, G. Savio. Functionally Graded Additive Manufacturing: Bridging the Gap between Design and Material Extrusion. Applied Sciences. 2023; 13(3):1467

Nowadays, the use of 3D printing is becoming a key process for on-demand and customized manufacturing. One of the most flexible 3D printing techniques is fused deposition modeling (FDM), where the combination of multiple materials was recently introduced. A quantum leap in part design is possible by integrating local variations between materials that allow for expanded functionality to be built into a single part. Therefore, the process of co-extrusion and material mixing is becoming more and more popular. The process of management and design of the engineered part are still complicated, and there are no commercially available tools that follow the process from design to production of these highly engineered products. This paper proposes a methodology to fill this gap and allow any designer to be able to produce multi-material parts by editing a G-code (computer numerical control programming language) with engineered gradients for FDM technology. More specifically, the proposed approach is based on the modification of the G-code according to a volumetric model describing the local combination of two or more materials. This original aspect allows for a wide extension of the current software capabilities. To explain and test the method, a simple test case was investigated, in which two components of an earphone are consolidated and developed gradually by combining polylactic acid and thermoplastic polyurethane. The results show the effectiveness of the proposed approach within the limits of the material coextrusion additive manufacturing process.

Keywords: fused deposition modeling, additive manufacturing, functionally graded additive manufacturing, data exchange; coextrusion, multi-material additive manufacturing.

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CAE Conference Poster – Dal Fabbro – Design of Optimized Conformal Lattice Structures
CAE Conference Poster – Sponchiado – Material coextrusion modeling and characterization in additive manufacturing