Additive Manufacturing (AM) brought a revolution in parts design and production. It enables the possibility to obtain objects with complex geometries and to exploit structural optimization ...algorithms. Nevertheless, AM is far from being a mature technology and advances are still needed from different perspectives. Among these, the literature highlights the need of improving the frameworks that describe the design process and taking full advantage of the possibilities offered by AM. This work aims to propose a workflow for AM guiding the designer during the embodiment design phase, from the engineering requirements to the production of the final part. The main aspects are the optimization of the dimensions and the topology of the parts, to take into consideration functional and manufacturing requirements, and to validate the geometric model by computer-aided engineering software. Moreover, a case study dealing with the redesign of a piston rod is presented, in which the proposed workflow is adopted. Results show the effectiveness of the workflow when applied to cases in which structural optimization could bring an advantage in the design of a part and the pros and cons of the choices made during the design phases were highlighted.
Additive manufacturing technologies, compared to conventional shaping methods, offer great opportunities in design versatility, for the manufacturing of highly porous ceramic components. However, the ...application to glass powders, later subjected to viscous flow sintering, involves significant challenges, especially in shape retention and in the achievement of a substantial degree of translucency in the final products. The present paper disclosed the potential of glass recovered from liquid crystal displays (LCD) for the manufacturing of highly porous scaffolds by direct ink writing and masked stereolithography of fine powders mixed with suitable organic additives, and sintered at 950 °C, for 1–1.5 h, in air. The specific glass, featuring a relatively high transition temperature (Tg~700 °C), allowed for the complete burn-out of organics before viscous flow sintering could take place; in addition, translucency was favored by the successful removal of porosity in the struts and by the resistance of the used glass to crystallization.
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.
The present study illustrates the manufacturing method of hierarchically porous 3D scaffolds based on åkermanite as a promising bioceramic for stereolithography. The macroporosity was designed by ...implementing 3D models corresponding to different lattice structures (cubic, diamond, Kelvin, and Kagome). To obtain micro-scale porosity, flame synthesized glass microbeads with 10 wt% of silicone resins were utilized to fabricate green scaffolds, later converted into targeted bioceramic phase by firing at 1100 °C in air. No chemical reaction between the glass microspheres, crystallizing into åkermanite, and silica deriving from silicone oxidation was observed upon heat treatment. Silica acted as a binder between the adjacent microspheres, enhancing the creation of microporosity, as documented by XRD, and SEM coupled with EDX analysis. The formation of 'spongy' struts was confirmed by infiltration with Rhodamine B solution. The compressive strength of the sintered porous scaffolds was up to 0.7 MPa with the porosity of 68-84%.
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.
Recently, the possibility of producing medium-to-large batches has increased the interest in polymer powder bed fusion technologies such as selective laser sintering (SLS) and multi jet fusion (MJF). ...Only scant data about the characterization of parts produced by MJF can be found in the literature, and fatigue behavior studies are absent. This study analyzes the material properties of Polyamide 12 (PA12) powders and printed specimens using both SLS and MJF technologies. The morphology, crystalline phases, density, porosity, dimensional accuracy, and roughness are measured and compared; tensile and fatigue tests are performed to assess the effect of the technologies on the mechanical behavior of the produced structures. In addition, lattice structure specimens obtained by different geometric modeling approaches are tested to understand the influence of modeling methods on the fatigue life. The PA12 powders printed by both SLS and MJF mainly show by X-Ray Diffraction γ-phase and a small shoulder of α-phase. The crystallinity decreases after printing the powders both in SLS and MJF technology. The printed parts fabricated using the two technologies present a total porosity of 7.95% for SLS and 6.75% for MJF. The roughness values are similar, Ra ≈ 11 µm along the building direction. During tensile tests, SLS samples appear to be stiffer, with a lower plastic deformation than MJF samples, that are tougher than SLS ones. Fatigue tests demonstrate higher dispersion for MJF specimens and an enhancement of fatigue life for both SLS and MJF printed lattice structures modeled with a novel geometric modeling approach that allows the creation of smoother surfaces at nodal points. Scanning electron microscopy on fracture surfaces shows a brittle failure for the SLS tensile specimens, a more ductile failure for the MJF tensile specimens, a crazing failure mechanism for the SLS fatigue tested samples, and a crack initiation and slow growth and propagation for the MJF fatigue tested samples.
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•Comparison between PA12 Selective Laser Sintering and Multi Jet Fusion technologies.•Different failure mechanisms for SLS and MJF fatigue tested samples.•SLS bulk specimens behave better for stresses higher than 34 MPa.•MJF bulk specimens fatigue curve has a knee at 34 MPa.•Lattice structures modeled with Catmull–Clark algorithm have longer fatigue life.
The present study is dedicated to the manufacturing of highly porous triply periodic minimal surface (TPMS) constructs, fabricated from recycled end of life borosilicate pharmaceutical glass ...employing masked stereolithography. The structures were prepared from a simple blend of photocurable resin with glass powder (<38 µm). The gyroid model was selected with the porosity varying from 75 to 90%. Hot stage microscopy was applied to examine the glass sintering behaviour to improve the translucency of the 3D scaffolds. The obtained 3D scaffolds were dip-coated with TiO2 and further utilized for the photocatalytic degradation of dyes. The photocatalytic efficiency of the 3D scaffolds was evaluated by the degradation of methylene blue in water. It was found that 3D scaffolds coated with TiO2 showed a 40% higher degradation rate in comparison to bare 3D scaffolds under UV irradiation, which determines the significant role of TiO2 in the organic dye degradation. The better efficiency of 3D scaffolds coated with TiO2, compared with uncoated BSG 3D scaffolds is attributed to a better recombination rate, and the migration of electrons to the surface of the scaffold, where the charges participate in the photodecomposition of MB dye. The efficiency of the scaffolds was assessed for five consecutive cycles. The degradation efficiency after the fifth cycle was 75%, confirming the stability of the system.
Innovative design methods and manufacturing technologies, such as lattice structures optimization and additive manufacturing, allow for the production of functional and extremely complex components. ...Recent literature shows limits in geometric modeling and data exchange, highlighting some improvements in the design of variable density lattice structures mainly for powder bed fusion technologies. Similar improvements are not available for material extrusion (MEX) technologies which show technological and numerical limits related to the computer numerical control programming language (G-code) generated by computer aided manufacturing (CAM) software. This work aims at overcoming the limits in fabricating graded density shell-based lattice structures for MEX technology by using the infill patterns available in the CAM software and editing the G-code based on a density map defined by volumetric models. Combining two usually separated phases, i.e., the geometric modeling and the CAM processing, several advantages are obtained, considering at the same time some of the technological constraints.The proposed approach is tested on a cubic sample and on a bracket fabricated by a fused filament fabrication technology. The results show that the method allows for the reduction of design efforts, amount of data exchanged, and processing time, obtaining an effective G-code and consistent components.
Pastes based on preceramic polymers have a great potential for direct ink writing of bioceramic scaffolds. In this paper, we discuss the fabrication of phase pure sphene (CaTiSiO5) bioceramics, ...developed by firing, at 1300°C, of silicone‐based printed scaffolds containing CaCO3 and TiO2 as active fillers. As a proof of the flexibility of the combination of preceramic polymers and additive manufacturing technologies, several lattice geometries of increasing complexity were successfully explored. In particular, the approach allowed the fabrication of sphene scaffolds with gyroid‐like structure exhibiting an impressive compressive strength, given the high porosity. Moreover, different lattice topologies of sphene scaffolds were compared also in terms of permeability.
Miniscrew-assisted rapid palatal expansion (MARPE) appliances utilize the skeletal anchorage to expand the maxilla. One type of MARPE device is the Maxillary Skeletal Expander (MSE), which presents ...four micro-implants with bicortical engagement of the palatal vault and nasal floor. MSE positioning is traditionally planned using dental stone models and 2D headfilms. This approach presents some critical issues, such as the inability to identify the MSE position relative to skeletal structures, and the potential risk of damaging anatomical structures.
A novel methodology has been developed to plan MSE position using the digital model of dental arches and cone-beam computed tomography (CBCT). A virtual model of MSE appliance with the four micro-implants was created. After virtual planning, a positioning guide is virtually designed, 3D printed, and utilized to model and weld the MSE supporting arms to the molar bands. The expansion device is then cemented in the patient oral cavity and micro-implants inserted. A clinical case of a 12.9-year-old female patient presenting a Class III malocclusion with transverse and sagittal maxillary deficiency is reported.
The midpalatal suture was opened with a split of 3.06 mm and 2.8 mm at the anterior and posterior nasal spine, respectively. After facemask therapy, the sagittal skeletal relationship was improved, as shown by the increase in ANB, A-Na perpendicular and Wits cephalometric parameters, and the mandibular plane rotated 1.6° clockwise.
The proposed digital methodology represents an advancement in the planning of MSE positioning, compared to the traditional approach. By evaluating the bone morphology of the palate and midface on patient CBCT, the placement of MSE is improved regarding the biomechanics of maxillary expansion and the bone thickness at micro-implants insertion sites. In the present case report, the digital planning was associated with a positive outcome of maxillary expansion and protraction in safety conditions.
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