On the Porous Structuring using Unit Cells

Abstract This study presents the characteristics of the eleven commonly used porous structures. The structures are designed using ten different unit cells. Some of the unit cells consist of free-form surfaces (e.g., triply periodic minimal surface). Some of them are straightforward in design (e.g., honeycomb structure). Some of them have a hybrid structure. The 3D CAD models of the structures are created using commercially available CAD software. The finite element analysis is conducted for each structure to know how it behaves under a static load. The structures are also manufactured using a 3D printer to confirm the manufacturability of them. It is found that some of the structures are easy to manufacture, and some are not. Particularly, metal-alloy-printed structures need a minimal thickness. However, the structures' printed or virtual models are evaluated by determining their respective mass, production cost, production time, Mises stress, and surface area. Using the values of mass, production time and cost, Mises stress, and surface area, the optimal structure is identified. Thus, the outcomes of this study can help identify the optimal porous structure for a given purpose

Ti-6Al-4V lattice structures produced by EBM: Heat treatment and mechanical properties

Abstract Additive manufacturing (AM) processes allow producing the complex components in a layerwise fashion. The complexity includes the design of lighter and stronger components by using lattice structures that can be quickly realized through AM technologies. However, the mechanical behaviour of lattice structures is not completely known, especially in the post-treated state. Thus, this work aims to explore the effect of post-treatment on the compressive strength of specimens with lattice structures. The samples are produced using Ti-6Al-4V powder processed by Electron Beam Melting (EBM). The outcomes of this work confirm the correlation between the heat treatment and final mechanical properties

Geometric Modeling of Cellular Materials for Additive Manufacturing in Biomedical Field: A Review

Advances in additive manufacturing technologies facilitate the fabrication of cellular materials that have tailored functional characteristics. The application of solid freeform fabrication techniques is especially exploited in designing scaffolds for tissue engineering. In this review, firstly, a classification of cellular materials from a geometric point of view is proposed; then, the main approaches on geometric modeling of cellular materials are discussed. Finally, an investigation on porous scaffolds fabricated by additive manufacturing technologies is pointed out. Perspectives in geometric modeling of scaffolds for tissue engineering are also proposed

Design for Additive Manufacturing: A Method to Explore Unexplored Regions of the Design Space

Additive Manufacturing (AM) technologies enable the fabrication of parts and devices that are geometrically complex, have graded material compositions, and can be customized. To take advantage of these capabilities, it is important to assist designers in exploring unexplored regions of design spaces. We present a Design for Additive Manufacturing (DFAM) method that encompasses conceptual design, process selection, later design stages, and design for manufacturing. The method is based on the process-structure-property-behavior model that is common in the materials design literature. A prototype CAD system is presented that embodies the method. Manufacturable ELements (MELs) are proposed as an intermediate representation for supporting the manufacturing related aspects of the method. Examples of cellular materials are used to illustrate the DFAM method.Mechanical Engineerin

Flow and thermal transport in additively manufactured metal lattices based on novel unit-cell topologies

The emergence of metal Additive Manufacturing (AM) over the last two decades has opened venues to mitigate the challenges associated with stochastic open-cell metal foams manufactured through the traditional foaming process. Regular lattices with user-defined unit cell topologies have been reported to exhibit better mechanical properties in comparison to metal foams which extend their applicability to multifunctional heat exchangers subjected to both thermal and mechanical loads. The current study aims at investigating the thermal-hydraulic characteristics of promising novel unit cell topologies realizable through AM technologies. Experimental investigation was conducted on four different topologies, viz (a) Octet, (b) Face-diagonal (FD) cube, (c) Tetrakaidecahedron, and (d) Cube, printed in single-cell thick sandwich type configuration in 420 stainless steel via Binder Jetting technology at same intended porosity. The effective thermal conductivity of the samples was found to be strongly dependent on the lattice porosity, however, no significant dependence on the unit-cell topology was demonstrated. Face-diagonal cube lattice exhibited the highest heat transfer coefficient and pressure drop, and consequently provided the lowest thermal-hydraulic performance. A procedure to incorporate the manufacturing-induced random roughness effects in the samples during numerical modelling is introduced. The numerical simulations were conducted on samples exhibiting the roughness profiles having statistically same mean roughness as the additively manufactured coupons and the results were compared to that obtained from the intended smooth-profiled CAD models that were fed into the printing machines. The analysis showed that inclusion of roughness effects in computational models can significantly improve the thermal performance predictions. Through this study, we demonstrate that additively manufactured ordered lattices exhibit superior thermal transport characteristics and future developmental efforts would require extensive experimentations to characterize their thermal and flow performance as well as local surface quality and AM-induced defect recognition. Experimental findings would also need to be supported by computational efforts where configurations which closely mimic the real AM parts could be modeled. A combined experimental-numerical framework is recommended for advancements in metal additive manufacturing-enabled enhanced heat transfer concepts

Design, analysis, and application of a cellular material/structure model for metal based additive manufacturing process.

Powder bed fusion additive manufacturing (PBF-AM) has been broadly utilized to fabricate lightweight cellular structures, which have promising potentials in many engineering applications such as biomedical prosthesis, aerospace, and architectural structures due to their high performance-to-weight ratios and unique property tailorabilities. To date, there is still a lack of adequate understanding of how the cellular materials are influenced by both the geometry designs and process parameters, which significantly hinders the effective design of cellular structures fabricated by PBF-AM for critical applications. This study aims to demonstrate a cellular structure design methodology that integrates geometrical design and process-material property designs. Utilizing both analytical modeling and empirical modeling, this research aims to significantly improve the design flexibility and robustness of the metal PBF-AM cellular structures. Experimental designs were carried out to establish the process-material property knowledge for the Ti6Al4V using the EOS M270 laser powder bed fusion (LPBF) system. Utilizing optical microscopy, scanning electron microscopy (SEM), micro-tensile testing and micro-hardness testing, the characteristics of thin struts with different strut dimensions and orientations under different process conditions were characterized and compared with those of the bulk materials from LPBF. The results clearly indicated significant effects of strut geometries (dimension and orientation angle) on their qualities. Struts with large orientation angle (i.e. more aligned to the build direction) exhibit lower process robustness and are sensitive to process parameters. Due to the resolution limitation of the LPBF process, the geometrical accuracies of the struts increases drastically when the designed dimension is smaller than 0.2mm, with minimum achievable dimensions around 0.2mm for the process parameters investigated in this study. On the other hand, the struts with smaller dimensions tend to exhibit higher mechanical properties, which might be associated with the smaller grain size and lower porosities. There also does not appear to be a single set of process parameters that would result in minimum porosities for struts with various dimensions. Utilizing center-joint based unit cell design, an analytical model for unit cells with designable numbers of struts was established in the attempt to enhance geometry designabilility of the geometries. Timoshenko beam theory was verified to be the most accurate modeling method, although for large strut orientations Euler-Bernoulli beam theory might suffice. The analytical model for elastic modulus was verified by finite element analysis (FEA) and experiments. Additionally, predictable size effect was modeled for the cellular structures with the center join connectivity of 8 (octahedral). Utilizing the material property database for the cellular designs, the integrated material performance/structural geometry model was demonstrated for both single strut sand small cellular patterns. It was shown that the integrated model is able to provide improved prediction to the properties of cellular structures

Ti-6Al-4V lattice structures produced by EBM: Heat treatment and mechanical properties

Additive manufacturing (AM) processes allow producing the complex components in a layerwise fashion. The complexity includes the design of lighter and stronger components by using lattice structures that can be quickly realized through AM technologies. However, the mechanical behaviour of lattice structures is not completely known, especially in the post-treated state. Thus, this work aims to explore the effect of post-treatment on the compressive strength of specimens with lattice structures. The samples are produced using Ti-6Al-4V powder processed by Electron Beam Melting (EBM). The outcomes of this work confirm the correlation between the heat treatment and final mechanical properties