[Elenco soci]

Savio Gianpaolo

Professore Associato

Università degli Studi di Padova

Sito istituzionale
SCOPUS ID: 14048903400
Orcid: 0000-0001-5858-1483 View this author’s O

Pubblicazioni scientifiche

[1] Ożóg P., Elsayed H., Grigolato L., Savio G., Kraxner J., Galusek D., Bernardo E., Engineering of silicone-based blends for the masked stereolithography of biosilicate/carbon composite scaffolds, Journal of the European Ceramic Society, 42(13), 6192-6198, (2022). Abstract

Silicone resins, filled with phosphates and other oxide fillers, have been recently proposed as feedstock for the manufacturing of scaffolds with a composition resembling that of commercial Biosilicate® glass-ceramics. Silicones and engineered fillers enable the preparation of novel carbon-containing Biosilicate-based composites and, fundamentally, the easy application of additive manufacturing technologies. After successful demonstration of the applicability of direct ink writing of silicone-based pastes, the present paper is dedicated to preparation of highly porous scaffolds obtained by masked stereolithography, starting from a simple blend of silicone resin with commercial photocurable acrylates. Deviations in the desired phase assemblage were corrected by calibration of the silicone/fillers ratio. The more advanced printing technology, combined with ceramic transformation, allowed fabrication of scaffolds with a complex geometry and a distinctive control of overall porosity.

Keywords: Additive manufacturing | Biosilicate® glass-ceramic | Masked stereolithography | Polymer-derived-ceramics | SiOC

[2] Grigolato L., Rosso S., Meneghello R., Concheri G., Savio G., Design and manufacturing of graded density components by material extrusion technologies, Additive Manufacturing, 57, (2022). Abstract

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.

Keywords: Additive manufacturing | Functionally graded lattice structures | Material extrusion | Volumetric modeling

[3] Di Fiore A., Graiff L., Savio G., Granata S., Basilicata M., Bollero P., Meneghello R., Investigation of the Accuracy of Four Intraoral Scanners in Mandibular Full-Arch Digital Implant Impression: A Comparative In Vitro Study, International Journal of Environmental Research and Public Health, 19(8), (2022). Abstract

Background: We compare the accuracy of new intraoral scanners (IOSs) in full-arch digital implant impressions. Methods: A master model with six scan bodies was milled in poly(methyl methacrylate), measured by using a coordinate measuring machine, and scanned 15 times with four IOSs: PrimeScan, Medit i500, Vatech EZ scan, and iTero. The software was developed to identify the position points on each scan body. The 3D position and distance analysis were performed. Results: The average and ± standard deviation of the 3D position analysis was 29 μm ± 6 μm for PrimeScan, 39 μm ± 6 μm for iTero, 48 μm ± 18 μm for Mediti500, and 118 μm ± 24 μm for Vatech EZ scan (p < 0.05). Conclusions: All IOSs are able to make a digital complete implant impression in vitro according to the average misfit value reported in literature (150 μm); however, the 3D distance analysis showed that only the Primescan and iTero presented negligible systematic error sources.

Keywords: accuracy | CAD/CAM | dental implant | digital impression | full arch | intra-oral scanner

[4] Ferro P., Fabrizi A., Savio G., Meneghello R., Berto F., Metallurgical Characterization of Co-Cr-Mo Parts Processed by a Hybrid Manufacturing Technology, Physical Mesomechanics, 25(2), 155-167, (2022). Abstract

Abstract: The additive manufacturing technology offers new and incredible opportunities in the design of components. Nowadays, structural integrity assessment of additively manufactured components is a formidable challenge that needs to be faced out in order to allow such components to be launched in the market. One of the major drawbacks of additive manufacturing is poor surface finish and loose geometrical tolerance of built parts. In this scenario, hybrid manufacturing, which takes advantage of both subtractive and additive manufacturing, can be considered as a solution worthy of investigation in view of possible applications to save costs and time in the component production. The present work is aimed at assessing microstructural properties of Co-Cr-Mo specimens manufactured by the hybrid subtractive/additive technology, when the additive part is built over the machined one. The results show an excellent metallurgical coupling at the interface between the two differently processed parts.

Keywords: biomaterials | Co-Cr-Mo alloy | hybrid manufacturing | mechanical properties | microstructure | selective laser melting

[5] Graiff L., Savio G., Di Fiore A., Rosso S., Meneghello R., Uccheddu F., Evaluation of the Fatigue Strength of a CAD-CAM Nanoceramic Resin Crown on Titanium and Zirconia-Titanium Abutments, Applied Sciences (Switzerland), 12(3), (2022). Abstract

A computer-aided design/computer-aided manufacturing (CAD/CAM) resin block material for restoration of single-implant abutments can be milled and cemented on an optimized standard titanium abutment as a cheaper solution or, alternatively, individualization of the crown–abutment connection is required to fulfill the same mechanical requirements. The aim of this study was to evaluate how different structural and geometric configurations of the abutment influence the resistance of a nano ceramic resin crown (NCRC). During the test, 30 implants with an internal conical tapered configuration were considered. Each implant received a standard titanium abutment: in group 1, NCRCs were directly bonded to the titanium abutments; in group 2, NCRCs were cemented on a customized zirconia framework and then cemented on a standardized titanium abutment. Three crowns of each group were submitted to a static load test until failure. The remaining crowns were submitted to a fatigue test protocol with a dynamic load. The static and dynamic test showed earlier failure for group 1. In group 1, complete breaking of NCRCs was observed for all samples, with an almost total titanium abutment exposition. In the static tests, group 2 showed a mode of failure that involved only the crown, which partially debonded from the zirconia abutment. Within the limitations of the present preliminary study, it was possible to conclude that the shape of the abutment mainly influences the fatigue strength compared to the static tensile strength. The results of the performed test show that NCRC bonded to the customized zirconia abutments, and presented a 75% survival rate when compared to the same material bonded directly to a standard titanium abutment.

Keywords: CAD-CAM | Fatigue test | NCRC | Patient specific design

[6] Dasan A., Kraxner J., Grigolato L., Savio G., Elsayed H., Galusek D., Bernardo E., 3D Printing of Hierarchically Porous Lattice Structures Based on Åkermanite Glass Microspheres and Reactive Silicone Binder, Journal of Functional Biomaterials, 13(1), (2022). Abstract

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%.

Keywords: Additive manufacturing | Bioceramics | Glass microspheres | Silicones | åkermanite

[7] Dal Fabbro P., Rosso S., Ceruti A., Meneghello R., Concheri G., Savio G., Conformal Lattice Structures: Modeling and Optimization, Lecture Notes in Mechanical Engineering, 474-485, (2022). Abstract

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 verification methods 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: Additive manufacturing | Conformal lattice structure | Design for additive manufacturing | Size optimization | Virtual modeling

[8] Sponchiado R., Grigolato L., Filippi S., Concheri G., Meneghello R., Savio G., Heterogeneous Materials Additive Manufacturing: An Overview, Lecture Notes in Mechanical Engineering, 462-473, (2022). Abstract

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: Functionally graded materials | Heterogeneous objects | Multi material AM

[9] Righetti G., Zilio C., Savio G., Meneghello R., Calati M., Mancin S., Experimental pressure drops during the water flow into porous materials realized via additive manufacturing, Journal of Physics: Conference Series, 2116(1), (2021). Abstract

Open-cell foams offer several interesting possibilities in numerous technological fields. In fact, they present high surface area to volume ratio as well as enhanced flow mixing and attractive stiffness and strength. However, their complete and reliable characterization has not been completed yet. In fact, there is still no a comprehensive work that relates all the foam geometrical characteristics to their heat transfer and pressure drop features. This paper is the very first outcome of a larger study that aims at realizing open-cell foams via additive manufacturing, testing them, then generating a simulation model based on the real geometries to numerically optimize each parameter. The present manuscript presents the construction of the open-foam via 3D printing and the experimental pressure drop measurements when water flows through the foam.

[10] Dal Fabbro P., Rosso S., Ceruti A., Bozza D.B., Meneghello R., Concheri G., Savio G., Analysis of a preliminary design approach for conformal lattice structures, Applied Sciences (Switzerland), 11(23), (2021). Abstract

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 wire-frame 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: Additive manufacturing | Conformal lattice structure | Design for additive manufacturing | Size optimization | Virtual modeling

[11] Elsayed H., Rabelo Monich P., Savio G., Hartmann M., Boccaccini A.R., Galusek D., Kraxner J., Bernardo E., Alkali-free processing of advanced open-celled sinter-crystallized glass-ceramics, International Journal of Applied Glass Science, 12(4), 531-540, (2021). Abstract

The cooling of a melt corresponding to the eutectic between wollastonite (CaSiO3) and diopside (CaMgSi2O6) determines the synthesis of an interesting example of alkali-free bioactive glass, easily converted into glass-ceramics featuring two silicate phases, coupled also with åkermanite (Ca2MgSi2O7), by sinter-crystallization of fine glass powders at 1000°C. The fabrication of scaffolds by digital light processing of glass powders suspended in a photo-curable, sacrificial binder, is a well-established technique; the present paper aims at disclosing novel approaches, concerning the topology of scaffolds, offering components with remarkable strength, especially in bending conditions. As an alternative, glass-ceramic foams were fabricated by the firing of porous precursors derived from the gelation of suspensions of glass powders in alkali-free basic aqueous solution.

Keywords: additive manufacturing | alkali-free bioactive glasses | bioactive glass-ceramics | gel casting | scaffolds | sinter-crystallization

[12] Dasan A., Ożóg P., Kraxner J., Elsayed H., Colusso E., Grigolato L., Savio G., Galusek D., Bernardo E., Up-cycling of LCD glass by additive manufacturing of porous translucent glass scaffolds, Materials, 14(17), (2021). Abstract

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.

Keywords: Additive manufacturing | Direct ink writing | Glass recycling | LCD glass | Scaffolds

[13] Rosso S., Uriati F., Grigolato L., Meneghello R., Concheri G., Savio G., An optimization workflow in design for additive manufacturing, Applied Sciences (Switzerland), 11(6), (2021). Abstract

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.

Keywords: Computational geometry | Design for additive manufacturing | Design workflow | DfAM | Geometric modeling | Size optimization | Topology optimization

[14] Grigolato L., Filippi S., Cantarella D., Lione R., Moon W., Rosso S., Meneghello R., Concheri G., Savio G., Concept selection and interactive design of an orthodontic functional appliance, International Journal on Interactive Design and Manufacturing, 15(1), 137-142, (2021). Abstract

Demand for innovation represents a driver not only in the industrial field but also in niche markets such as orthodontics. Among different type of orthodontic devices, functional appliances are used for the correction of class II skeletal malocclusion, mostly in young patients. In a previous study based on a systematic design approach, several concepts were generated for this device. This work shortly introduces the concept selection and the interactive design process of the device. The concept consisting of two-side guiding surfaces, obtained by TRIZ inventive principles, has been selected by the decision matrix. This concept consists in guiding the jaw movements without any connections between the parts of the device. Operating on patient morphometrics parameters, the proposed approach allows to establish a virtual interaction during the design of the device by facilitating the collaboration between orthodontist, dental technician, designer and the software, through a dedicated user interface. Dedicated algorithms were also developed to simulate the occlusion correction and the mandible path, and to support the geometric modelling in a virtual environment. As a result, the proposed approach allows manufacturing patient-customized devices using a digital interactive workflow in an innovative way.

Keywords: Concept selection | Functional appliances | Interactive design | Morphometric parameters | Orthodontics

[15] Cantarella D., Quinzi V., Karanxha L., Zanata P., Savio G., Del Fabbro M., Digital workflow for 3d design and additive manufacturing of a new miniscrew-supported appliance for orthodontic tooth movement, Applied Sciences (Switzerland), 11(3), 1-9, (2021). Abstract

The introduction of digital workflows and their combination with miniscrew assisted appliances has opened new and enthusiastic perspectives in modern orthodontics. However, in all digital workflows currently in use for orthodontic tooth movement, the miniscrews are inserted first in the maxillary bone, often by means of a surgical guide, and then the appliance is fabricated and secured over the miniscrews with different fixation mechanisms. By doing so, some adaptation problems can be encountered while securing the appliance over the miniscrews, and the chairside time required can therefore be significant. In the present study, we introduce a digital workflow for the design and fabrication of a new appliance, customized on the individual morphology of maxillary bone by using patient Cone Beam Computed Tomography CBCT, for sagittal and vertical orthodontic tooth movement (DIVA, divergent anchors). Differently from the existing protocols, the appliance is cemented first intraorally, serving as a surgical guide for the subsequent insertion of miniscrews. In this way, the adaptation problems are avoided and the chair-side time is reduced.

Keywords: 3D printing | CAD/CAM | Digital orthodontics | DIVA | Laser melting | Miniscrew | Tooth anchorage

[16] Rogolino A., Savio G., Trends in additively manufactured microfluidics, microreactors and catalytic materials, Materials Advances, 2(3), 845-855, (2021). Abstract

The interest in microfluidics, that is the manipulation of fluids with volumes in the range of μL or below, has increased exponentially in the past decades, due to their relevance to diagnostics, sensors, drug-design and pilot plant prototyping. Common manufacturing processes in clean rooms for microfluidic substrates are well established, but still expensive and competence-demanding. Additive manufacturing is a promising alternative, given the inherent simple geometry and the small dimensions of microfluidic devices, which in turn allow ease of design and production along with a reduction of time and costs of the manufacturing processes. In this paper the state of the art in additive manufacturing of microfluidics and microreactors is presented, showing how vat photopolymerization, multimaterial jetting and extrusion-based additive manufacturing possess the best features in this field. An overview of the most remarkable applications obtained so far is provided, highlighting the best performance in layer height resolution achieved and the printing of dynamic devices. Furthermore, potentiality of additive manufacturing in the fabrication of catalysts for chemical reactions is reviewed. Finally, it is claimed how the rise of additive technologies in small-scale manufacturing in the future will definitely occur due to their cheapness, accessibility and ease of customization. This journal is

[17] Cantarella D., Karanxha L., Zanata P., Moschik C., Torres A., Savio G., Del Fabbro M., Moon W., Digital planning and manufacturing of maxillary skeletal expander for patients with thin palatal bone, Medical Devices: Evidence and Research, 14, 299-311, (2021). Abstract

The miniscrew-assisted rapid palatal expansion approach has given new opportu-nities for the treatment of maxilla transverse deficiency by providing an alternative to the surgical approach for adult patients. However, the presence of a thin palatal bone can compromise the success of such approach. Recently, the digital planning of the miniscrew-assisted appliances has offered unique advantages in terms of safety and accuracy of the overall process. The aim of this study is to describe the digital planning and MSE fabrication with cad-cam technology using 6 mini-screws in cases with a palatal bone thickness of less than 2.5 mm.

Keywords: Digital orthodontics | MARPE | Maxillary transverse deficiency | MSE | Palatal expansion

[18] Rosso S., Curtarello A., Basana F., Grigolato L., Meneghello R., Concheri G., Savio G., Modeling Symmetric Minimal Surfaces by Mesh Subdivision, Lecture Notes in Mechanical Engineering, 249-254, (2021). Abstract

Thanks to the great diffusion of additive manufacturing technologies, the interest in lattice structures is growing. Among them, minimal surfaces are characterized by zero mean curvature, allowing enhanced properties such as mechanical response and fluidynamic behavior. Recent works showed a method for geometric modeling triply periodic minimal surfaces (TPMS) based on subdivision surface. In this paper, the deviation between the subdivided TPMS and the implicit defined ones is investigated together with mechanical properties computed by numerical methods. As a result, a model of mechanical properties as a function of the TPMS thickness and relative density is proposed.

Keywords: Additive manufacturing | Design for additive manufacturing | Lattice structures | Triply periodic minimal surfaces

[19] Rosso S., Meneghello R., Biasetto L., Grigolato L., Concheri G., Savio G., In-depth comparison of polyamide 12 parts manufactured by Multi Jet Fusion and Selective Laser Sintering, Additive Manufacturing, 36, (2020). Abstract

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.

Keywords: Fatigue | Lattice structure | Multi Jet Fusion | Polyamide 12 | Selective Laser Sintering

[20] Ferro P., Rosso S., Savio G., Meneghello R., Berto F., Razavi S.M.J., Crack Arresters Design for Fatigue Strength Improvement of Additively Manufactured Components, Proceedings of the 2020 IEEE 10th International Conference on "Nanomaterials: Applications and Properties", NAP 2020, (2020). Abstract

Additive manufacturing applied to polymeric as well as metallic materials offers a lot of advantages, today not yet fully explored. They can potentially enhance the structural efficiency of the components, which means, for a given loading condition, the section uses as little material as possible. As a matter of fact, the complete freedom in parts shape design could be exploited to increase the fatigue strength of structural components by crack arresters (CAs) design. From classical fracture mechanic theories, it is well known that when the fatigue crack meets a hole, the consequent sudden reduction of the stress concentration ahead of the crack tip promotes the arrest of the crack propagation itself. Using additive manufacturing, it is now possible to design structural components with CAs in the vicinity of crack initiation points like notches. This paper is aimed at exploring, with preliminary experiments supported by numerical analyses, this possibility. It was found that crack arresters effectively enhance the fatigue life of a notched component provided that their shape and position are designed properly.

Keywords: Additive Manufacturing | Crack arrester | Crack growth | Fatigue | Stop-hole | Stress concentration

[21] Ferro P., Meneghello R., Savio G., Berto F., A modified volumetric energy density–based approach for porosity assessment in additive manufacturing process design, International Journal of Advanced Manufacturing Technology, 110(7-8), 1911-1921, (2020). Abstract

Soundness of additively manufactured parts depends on a lot of process and geometrical parameters. A wrong process design leads to defects such as lack of fusion or keyhole porosity that have a detrimental effect on the mechanical properties of the printed parts. Process parameter optimization is thus a formidable challenge that requires in general a huge amount of experimental data. Among the others, heat source power and scan speed are the most defects-affecting parameters to be optimized. The energy density is used in literature to quantify their combination. Unfortunately, in different works it was demonstrated that it fails if used as design parameter mainly because it does not take into account the material properties and the interaction between heat source and the powder bed. In this contribution, a modified volumetric energy density equation that takes into account the powder-heat source interaction to optimize the combination of power-scan speed values for porosity assessment in powder bed fusion process design is proposed and verified on both AlSi10Mg alloy and Maraging steel 300.

Keywords: Additive manufacturing | Aluminium alloy | Energy density | Maraging steel | Porosity | Selective Laser Melting

[22] Ferro P., Fabrizi A., Berto F., Savio G., Meneghello R., Rosso S., Defects as a root cause of fatigue weakening of additively manufactured AlSi10Mg components, Theoretical and Applied Fracture Mechanics, 108, (2020). Abstract

Additive manufacturing is an emerging technique that is not only subjected to the interest of academic world because of its peculiar characteristics to obtain new material properties and optimized 3D geometries, but it also finds the interest of the industrial sector because of the possibility to build advanced components never realized until now. Among the additive manufacturing processes, Laser Powder Bed Fusion process is perhaps the most used in producing components out of metallic materials. In particular, thanks to its low density and its hypoeutectic favourable composition, AlSi10Mg alloy is particular suitable for the production of lightweight components by additive manufacturing. However, for safety reasons, their mechanical, static and cyclic, characteristics need to be well understood and predicted. Unfortunately, they are dramatically influenced by process parameters that in turn may promote killer defects dangerous for the fatigue strength of load bearing mechanical components. This contribution is aimed at highlighting the influence of defects on the fatigue resistance of AlSi10Mg samples produced by laser powder bed fusion. The combination of process parameters were obtained that maximizes the fatigue strength and reduces the scattering of the results.

Keywords: Additive manufacturing | ALSi10Mg | Fatigue strength | Fractography | Laser powder bed fusion | Porosity

[23] Righetti G., Savio G., Meneghello R., Doretti L., Mancin S., Experimental study of phase change material (PCM) embedded in 3D periodic structures realized via additive manufacturing, International Journal of Thermal Sciences, 153, (2020). Abstract

The interest in Phase Change Materials (PCMs) has been continuously growing, since they were identified as a suitable way to store large quantities of thermal energy. Despite many PCMs being available on the market, almost all present a relatively low thermal conductivity, which limits the efficiency and the convenience of their use inside Latent Thermal Energy Storage (LTES) units. This paper proposes a novel method to overcome the low thermal conductivity drawback: additive manufacturing was used to realize three innovative 3D metallic periodic structures, with different base pore sizes (10, 20, and 40 mm) and constant porosity, to be filled with a suitable PCM. The samples were experimentally tested by analyzing the temperature field in a paraffin wax, which has a melting temperature of around 55 °C. Furthermore, several videos and images were taken during the charging (i.e. heating and melting) process, obtained by electrical heating (three heat fluxes corresponding to 10, 20, and 30 W were applied) and the discharging (i.e. solidification and cooling) process, where the heat was only rejected by natural convection with ambient still air. The coupling of PCMs and aluminum structures was demonstrated to enhance both the charging and the discharging processes.

Keywords: Additive manufacturing | PCM | Periodic structures | Phase change materials | Thermal energy storage

[24] Di Fiore A., Savio G., Stellini E., Vigolo P., Monaco C., Meneghello R., Influence of ceramic firing on marginal gap accuracy and metal-ceramic bond strength of 3D-printed Co-Cr frameworks, Journal of Prosthetic Dentistry, 124(1), 75-80, (2020). Abstract

Statement of problem: The marginal gap and ceramic bond strength of metal-ceramic restorations are important for success. However, studies evaluating the marginal gap and ceramic bond strength of fixed partial dentures (FPDs) produced with 3D printing technologies such as selective laser melting (SLM) are scarce. Purpose: The purpose of this in vitro study was to investigate the marginal gap of cobalt-chromium (Co-Cr) alloy frameworks produced by SLM technology before and after ceramic firing. Additionally, the metal-ceramic bond strength was evaluated with the Schwickerath crack-initiation test according to the International Standards Organization (ISO) 9693-1:2012. Material and methods: Conventional impressions were made, and the definitive cast of a patient requiring a 4-unit FPD was scanned. After designing the FPD, the files were sent to a service center for the fabrication of a metal master model, 80 Co-Cr frameworks, and 80 flat specimens (25×3×0.5 mm) with SLM technology. The marginal gap between frameworks and the abutment tooth of the metal master model was nondestructively measured by using an optical coordinate-measuring machine. A total of 80 sets, consisting of 1 framework and 1 flat specimen, were sent to 80 dental laboratory technicians for ceramic firing. Detailed instructions for correct manipulation of the framework and flat specimen were provided. The marginal gap was remeasured, and the 3-point bend test was used to evaluate metal-ceramic bond strength. Results: Only 28 of the 80 dental technicians returned the specimens within a prespecified time and/or in adequate condition. The mean ±standard deviation marginal gap of the framework before ceramic firing was 25 ±9 μm and 34 ±12 μm after firing. The difference was statistically significant (P=.001). The mean ±standard deviation 3-point bend strength was 33 ±9 MPa. Conclusions: Ceramic firing affected the marginal gap; however, all Co-Cr frameworks had a marginal gap lower than 120 μm, which is reported to be a clinically acceptable limit. Most of the specimens (80%) had a metal-ceramic bond strength value higher than the 25-MPa ISO 9693 requirement. Five of 28 dental laboratory technicians were not able to comply with ceramic firing instructions.

[25] Di Fiore A., Stellini E., Savio G., Rosso S., Graiff L., Granata S., Monaco C., Meneghello R., Assessment of the different types of failure on anterior cantilever resin-bonded fixed dental prostheses fabricated with three different materials: An in vitro study, Applied Sciences (Switzerland), 10(12), 1-9, (2020). Abstract

background: resin-bonded fixed dental prosthesis (RBFDP) represents a highly aesthetic and conservative treatment option to replace a single tooth in a younger patient. The purpose of this in vitro study was to compare the fracture strength and the different types of failure on anterior cantilever RBFDPs fabricated using zirconia (ZR), lithium disilicate (LD), and PMMA-based material with ceramic fillers (PM) by the same standard tessellation language (STL) file. Methods: sixty extracted bovine mandibular incisives were embedded resin block; scanned to design one master model of RBFDP with a cantilevered single-retainer. Twenty cantilevered single-retainer RBFDPs were fabricated using ZR; LD; and PM. Static loading was performed using a universal testing machine. Results: the mean fracture strength for the RBFDPs was: 292.5 Newton (Standard Deviation (SD) 36.6) for ZR; 210 N (SD 37.6) for LD; and 133 N (SD 16.3) for PM. All the failures of RBFDPs in ZR were a fracture of the abutment tooth; instead; the 80% of failures of RBFDPs in LD and PM were a fracture of the connector. Conclusion: within the limitations of this in vitro study, we can conclude that the zirconia RBFDPs presented load resistance higher than the maximum anterior bite force reported in literature (270 N) and failure type analysis showed some trends among the groups.

Keywords: Adhesive restorations | CAD/CAM | Digital dentistry | Fracture | Lithium disilicate | PMMA | Resin bonded bridge | Zirconia

[26] Ferro P., Meneghello R., Razavi S.M.J., Berto F., Savio G., Porosity Inducing Process Parameters in Selective Laser Melted AlSi10Mg Aluminium Alloy, Physical Mesomechanics, 23(3), 256-262, (2020). Abstract

Abstract: Additive manufacturing techniques areknown for the unrivalled geometric freedom they offer todesigners. It is one of the mainstays of “metal 3D-printing”,compared to casting, which, in contrast, implies morerestrictions because some shapes do not cool evenly or may needmoulds or forms. Despite the possible presence of defects insideadditive manufactured components, such as oxide films, pores orunmelted powder, they can be strongly reduced or controlled byprocess parameters optimization. That seems not true for acasting component, in which defects can vary a lot from zone tozone according to the solidification conditions. Porosityinducing process parameters in selective laser melted AlSi10Mgaluminium alloy are carefully analysed with the aim to findoptimal conditions that guarantee the maximum material densityand the best mechanical properties. Finally, a model is proposedthat correlates the amount of pores with the alloy ultimatetensile strength.

Keywords: Additive manufacturing | Aluminium alloy | Mechanical property | Porosity | Selective laser melting

[27] Pellizzoni P., Savio G., Mesh simplification by curvature-enhanced quadratic error metrics, Journal of Computer Science, 16(8), 1195-1202, (2020). Abstract

Polygonal meshes have a significant role in computer graphics, design and manufacturing technology for surface representation and it is often required to reduce their complexity to save memory. An efficient algorithm for detail retaining mesh simplification is proposed; in particular, the method presented is an iterative edge contraction algorithm based on the work of Garland and Heckberts. The original algorithm is improved by enhancing the quadratic error metrics with a penalizing factor based on discrete Gaussian curvature, which is estimated efficiently through the Gauss-Bonnet theorem, to account for the presence of fine details during the edge decimation process. Experimental results show that this new algorithm helps preserve the visually salient features of the model without compromising performance.

Keywords: Computational Geometry | Discrete Curvature | Mesh Simplification

[28] Filippi S., Grigolato L., Savio G., UX Concerns in Developing Functional Orthodontic Appliances, Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 12202 LNCS, 229-241, (2020). Abstract

In the orthodontic field, UX concerns can take an important role in boosting innovation from the designers, engineers, dentists, dental technicians and patients’ points of view. In the last months, these concerns spread over the development of functional orthodontic appliances for the correction of skeletal class II malocclusions. This paper focuses on two phases: the data collection before starting the development and the evaluation of the design results. The UX concerns developed through the involvement of the Quality Function Deployment and the irMMs-based UX evaluation method 2.0, including the meQUE questionnaire 2.0. This paper describes the UX role, the related activities and the impact of its involvement in the design process.

Keywords: Functional orthodontic appliances | irMMs-based UX evaluation method 2.0 | meCUE questionnaire | Quality function deployment | User experience

[29] Cantarella D., Savio G., Grigolato L., Zanata P., Berveglieri C., Giudice A.L., Isola G., Del Fabbro M., Moon W., A new methodology for the digital planning of micro-implant-supported maxillary skeletal expansion, Medical Devices: Evidence and Research, 13, 93-106, (2020). Abstract

Introduction: 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. Methods: 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. Results: 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. Conclusion: The proposed digital methodology represents an advancement in the planning of MSE positioning, compared to the traditional approach. By evaluating the bone morphol-ogy 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.

Keywords: CBCT | CBDP | Cephalometrics-based digital planning | MARPE | Miniscrew-assisted rapid palatal expansion | MSE | TAD | Virtual planning | Workflow

[30] Uriati F., Da Rin Betta F., Ferro P., Rosso S., Savio G., Concheri G., Meneghello R., High Density AlSi10Mg Aluminium Alloy Specimens Obtained by Selective Laser Melting, Lecture Notes in Mechanical Engineering, 871-878, (2020). Abstract

Additive manufacturing technology offers new design possibilities compared to traditional casting processes applied to metallic materials. Not only there are no limits in shape, but a higher microstructure control is allowed compared to traditional processes. Irrespective of the sample dimensions, the solidification defects induced by SLM process depend only on process parameters and do not vary from zone to zone of the component like in a casting component: the higher the casting dimensions and thickness variations, the lower the microstructure homogeneity resulting from different cooling conditions inside the casting itself. The effect of process parameters on porosity, in selective laser melted AlSi10Mg aluminium alloy, is carefully analysed with the aim to find optimal conditions that guarantee the maximum material density and the best mechanical properties.

Keywords: Additive manufacturing | Aluminium alloy | Mechanical properties | Porosity | Selective laser melting

[31] Grigolato L., Filippi S., Barattin D., Cantarella D., Moon W., Meneghello R., Concheri G., Savio G., Conceptual Design of a Functional Orthodontic Appliance for the Correction of Skeletal Class II Malocclusion, Lecture Notes in Mechanical Engineering, 329-341, (2020). Abstract

The current requests for continuous innovation represent a challenge in every industry as well as in the field of orthodontics. Aim of this work was to develop new concepts of a functional appliance for the correction of class II skeletal malocclusion through a systematic design methodology. Staring at the existing devices in this field, taking into account the literature and the patient’s needs, the customers’ requirements were identified by Quality Functional Deployment. Systematic methods such as morphological method, theory of inventive problem solving and other creative methods were used for generating concepts some of which are presented at the end of the paper.

Keywords: Conceptual design | Functional appliance | Morphological method | Quality function deployment | TRIZ

[32] Rosso S., Meneghello R., Concheri G., Savio G., Scale and Shape Effects on the Fatigue Behaviour of Additively Manufactured SS316L Structures: A Preliminary Study, Lecture Notes in Mechanical Engineering, 879-890, (2020). Abstract

The freedom in geometry given by additive manufacturing allows to produce cellular materials, also called lattice structures, with unit cells and mesoscale features that are impossible to obtain with traditional manufacturing techniques. The geometric modeling of lattice structures still presents issues such as robustness and automation, but, with a novel modeling approach based on subdivision surface algorithm, these troubles were limited. Furthermore, the subdivision method smooths surfaces, avoiding sharp edges at nodal points and increasing performances in fatigue properties. The aim of this work is twofold; a. The subdivision surface method is validated through fatigue tests on specimen additively manufactured by selective laser melting technology in SS316L stainless steel; dynamic tests were carried out on two types of lattice structures based on cubic cell: one obtained with a traditional modeling method, one obtained with a subdivision surface approach. b. Additional tests on bulk cylindrical samples, allowed to propose a preliminary model that describes the fatigue behaviour of additively manufactured lattices as a function of the bulk material properties, considering the shape and scale effects coming from stress concentration factor, increased area, surface roughness and porosity of the part. Results show that the subdivision surface approach improves the fatigue life of lattice structures, as expected. More, the lattices have a worse fatigue life compared to the bulk samples due to the scale and shape effects, that results in a higher sensibility to surface and internal defects related to the manufacturing process.

Keywords: Additive manufacturing | Fatigue behaviour | Lattice structure | Scale effect | Shape effect

[33] Longo F., Savio G., Contiero B., Meneghello R., Concheri G., Franchini F., Isola M., Accuracy of an automated three-dimensional technique for the computation of femoral angles in dogs, Veterinary Record, 185(14), 443, (2019). Abstract

Aims: The purpose of the study was to evaluate the accuracy of a three-dimensional (3D) automated technique (computer-aided design (aCAD)) for the measurement of three canine femoral angles: anatomical lateral distal femoral angle (aLDFA), femoral neck angle (FNA) and femoral torsion angle. Methods:Twenty-eight femurs equally divided intotwo groups (normal and abnormal) were obtained from 14 dogs of different conformations (dolicomorphic and chondrodystrophicCT scans and 3D scanner acquisitions were used to create stereolithographic (STL) files, which were run in a CAD platform. Two blinded observers separately performed the measurements using the STL obtained from CT scans (CT aCAD) and 3D scanner (3D aCAD), which was considered the gold standard method. C orrelation coefficients were used to investigate the strength of the relationship between the two measurements. Results: A ccuracy of the aCAD computation was good, being always above the threshold of R 2 of greater than 80 per cent for all three angles assessed in both groups. a LDFA and FNA were the most accurate angles (accuracy >90 per cent). Conclusions: The proposed 3D aCAD protocol can be considered a reliable technique to assess femoral angle measurements in canine femur. The developed algorithm automatically calculates the femoral angles in 3D, thus considering the subjective intrinsic femur morphology. The main benefit relies on a fast user-independent computation, which avoids user-related measurement variability. The accuracy of 3D details may be helpful for patellar luxation and femoral bone deformity correction, as well as for the design of patient-specific, custom-made hip prosthesis implants.

Keywords: 3D computation | accuracy | dogs | femur

[34] Di Fiore A., Meneghello R., Graiff L., Savio G., Vigolo P., Monaco C., Stellini E., Full arch digital scanning systems performances for implant-supported fixed dental prostheses: a comparative study of 8 intraoral scanners, Journal of Prosthodontic Research, 63(4), 396-403, (2019). Abstract

Purpose: Compare the accuracy of intraoral digital impression in full-arch implant-supported fixed dental prosthesis acquired with eight different intraoral scanner (Ios). Methods: A polymethyl methacrylate acrylic model of an edentulous mandible with six scan-abutment was used as a master model and its dimensions measured with a coordinate measuring machine. Eight different Ios were used to generate digital impression: True Definition, Trios, Cerec Omnicam, 3D progress, CS3500, CS3600, Planmeca Emelard and Dental Wings. Fifteen digital impressions were made. A software called “Scan-abut” was developed to analyse and compare the digital impression with the master model, obtaining the scanning accuracy. The three-dimensional (3D) position and distance analysis were performed. Results: Mean value of the 3D position analysis showed that the True Definition (31 μm ± 8 μm) and Trios (32 μm ± 5 μm) have the best performance of the group. The Cerec Omnicam (71 μm ± 55 μm), CS3600 (61 μm ± 14 μm) have an average performance. The CS3500 (107 μm ± 28 μm) and Planmeca Emelard (101 μm ± 38 μm) present a middle-low performance, while the 3D progress (344 μm ± 121 μm) and Dental Wings (148 μm ± 64 μm) show the low performance. The 3D distance analysis showed a good linear relationship between the errors and scan-abutment distance only with the True Definition and CS3600. Conclusions: Not all scanners are suitable for digital impression in full-arch implant-supported fixed dental prosthesis and the weight of the output files is independent from the accuracy of the Ios.

Keywords: Accuracy | Dental implant | Digital impression | Full arch | Intraoral scanner

[35] Savio G., Meneghello R., Concheri G., Design of variable thickness triply periodic surfaces for additive manufacturing, Progress in Additive Manufacturing, 4(3), 281-290, (2019). Abstract

Minimal surfaces are receiving a renewed interest in biomedical and industrial fields, due to the capabilities of additive manufacturing technologies which allow very complex shapes. In this paper, an approach for geometric modeling of variable thickness triply periodic minimal surfaces in a CAD environment is proposed. The approach consists of three main steps: the definition of an initial mesh, the adoption of a subdivision scheme and the assignment of a variable thickness by a differential offset. Moreover, the relationship between relative density and mesh thickness was established for two types of minimal surfaces: Schoen’s gyroid, Schwarz’ Primitive. The proposed method improves the main issues highlighted in literature in the modeling of cellular materials and allows to easily obtain a consistent polygonal mesh model satisfying functional requirements. Two test cases were presented: the first shows a gradient thickness gyroid; in the second the relative density obtained by topology optimization was adopted in our modeling approach using a Schwarz’ Primitive. In both cases, guidelines for selecting the geometric modeling parameters taking into account the specific additive manufacturing process constraints were discussed. The proposed method opens new perspectives in the development of effective CAD tools for additive manufacturing, improving the shape complexity and data exchange capacity in cellular solid modeling.

Keywords: Cellular materials | Design for additive manufacturing | Geometric modeling | Triply periodic minimal surfaces

[36] Todros S., de Cesare N., Pianigiani S., Concheri G., Savio G., Natali A.N., Pavan P.G., 3D surface imaging of abdominal wall muscular contraction, Computer Methods and Programs in Biomedicine, 175, 103-109, (2019). Abstract

Background and Objective: The biomechanical analysis of the abdominal wall should take into account muscle activation and related phenomena, such as intra-abdominal pressure variation and abdomen surface deformation. The geometry of abdominal surface and its deformation during contraction have not been extensively characterized, while represent a key issue to be investigated. Methods: In this work, the antero-lateral abdominal wall surface of ten healthy volunteers in supine position is acquired via laser scanning in relaxed conditions and during abdominal muscles contraction, repeating each acquisition six times. The average relaxed and contracted abdominal surfaces are compared for each subject and displacements measured. Results: Muscular activation induces raising in the region adjacent to linea alba along the posterior-anterior direction and a simultaneous lowering along lateral-medial direction of the abdominal wall sides. Displacements reach a maximum value of 12.5 mm for the involved subjects. The coefficient of variation associated to the abdomen surface measurements in the same configuration (relaxed or contracted) is below 0.75%. Non-parametric Mann-Whitney U test highlights that the differences between relaxed and contracted abdominal wall surfaces are significant (p < 0.01). Conclusions: Laser scanning is an accurate and reliable method to evaluate surface changes on the abdominal wall during muscular contraction. The results of this experimental activity can be useful to validate numerical models aimed at describing abdominal wall biomechanics.

Keywords: Abdomen surface | Abdominal wall | Deformation | Laser scanner | Muscle contraction

[37] Ciocca L., Meneghello R., Savio G., Scheda L., Monaco C., Gatto M.R., Micarelli C., Baldissara P., Manufacturing of Metal Frameworks for Full-Arch Dental Restoration on Implants: A Comparison between Milling and a Novel Hybrid Technology, Journal of Prosthodontics, 28(5), 556-563, (2019). Abstract

Purpose: To determine the trueness and precision of frameworks manufactured with a selective laser melting/milling hybrid technique (SLM/m) and conventional milling by comparing the implant-platform/framework interface with those of the original computer-aided design (CAD). Materials and Methods: Using a virtual 6-implant-supported full-arch framework CAD drawing, 27 titanium replicas were manufactured by 3 independent manufacturing centers (n = 9/center) using a hybrid SLM/m technology (labs 1 and 2) or the conventional milling technique (lab 3). Using an opto-mechanical coordinate measuring machine, the frameworks’ misfit distribution and patterns were analyzed, and the position error between paired platform positions within each framework was evaluated to calculate the misfit tendency for each group. A multilevel analysis using a mixed-effects model was conducted (α = 0.05). The trueness was evaluated as the dimensional difference from the original, while the precision as the dimensional difference from a repeated scan. Results: The 3 dimensional misfits differed significantly among the 3 groups, with the milled group exhibiting the least accurate outcome (p = 0.005). The mean 3D positioning errors ranged from 8 to 16 µm and from 9 to 22 µm for the SLM/m technique (labs 1 and 2, respectively), and from 20 to 35 µm for conventional milling (lab 3). Regarding the misfit distribution pattern, the misfit increased with the distance between paired platform positions in all groups. Conclusions: All groups had 3D misfits well within the error limits reported in the literature. The 3D misfits of new hybrid (SLM/milling) and conventional (milling) procedures differed significantly among them, with the milling technique the less accurate and precise. The largest errors in all groups were found between the most distant implants, resulting in a correlation between the framework span and the inaccuracies.

Keywords: CAD/CAM | implant prosthesis | opto-mechanical measurement | oral rehabilitation | precision | trueness

[38] Savio G., Curtarello A., Rosso S., Meneghello R., Concheri G., Homogenization driven design of lightweight structures for additive manufacturing, International Journal on Interactive Design and Manufacturing, 13(1), 263-276, (2019). Abstract

The diffusion of design tools suitable for regular lattice structures was recently stimulated by the spread of additive manufacturing technologies that enable the fabrication of complex geometries, exceeding the limits of traditional manufacturing methods. Fillet radii play a fundamental role in the design of lattice materials, reducing the stress concentration and improving fatigue life. However, only simplified beam and 2D models are available in the literature, which are unable to capture the actual stiffness and stress concentrations in the cell nodes of the 3-D beam based lattice structures with fillets. In this paper, four types of polyamide 12 cells, fabricated by selective laser sintering technology, based on cylindrical elements, are studied by finite element (FE) analysis, evaluating the influence of struts and fillet radii on the mechanical properties. In order to study a single cell, specific boundary conditions, simulating the presence of adjacent cells, were adopted in FE analysis. As a result, a model describing mechanical properties as a function of geometrical characteristics is obtained. By this model, it is possible to replace the complex shape of a lattice structure with its boundary, simplifying numerical analyses. This approach, called homogenization, is very useful in the design process of lightweight structures and can be adopted in optimization strategies. Numerical outcomes show that the effect of fillet radius is not negligible, especially in cells having a large number of struts. Moreover, experimental tests were also carried out showing a good agreement with the numerical analysis. Finally, an interactive design process for lattice structures based on experimental and numerical outcomes is proposed.

Keywords: Additive manufacturing | Finite element analysis | Homogenization | Lattice structures | Polyamide 12 | Tensile tests

[39] Righetti G., Savio G., Meneghello R., Doretti L., Mancin S., Optimized 3D periodic structures for advanced latent thermal energy storages ((LTESs) via additive manufacturing, Refrigeration Science and Technology, 2019-August, 1805-1812, (2019). Abstract

The use of a Latent Thermal Energy Storage (LTES) system using suitable Phase Change Materials (PCMs) is an effective way of storing energy because of its high-energy storage density and isothermal nature of the storage processes. Unfortunately, PCMs present a few unfavorable thermophysical properties, among those the low thermal conductivity, which are limiting the development of efficient, reliable and convenient LTESs. However, LTES represents a promising technology, which can unlock unprecedented opportunities for multiple-sources energy integration, waste heat recovery, and efficient energy management. This paper aims at investigating new 3D periodic structures obtained via metallic additive manufacturing developed to enhance the phase change process during both loading and unloading processes of different paraffin waxes and sugar alcohols. The tests were run by imposing 20 W during the loading process and the monitoring the temperature distribution within the PCM.

Keywords: Additive manufacturing | PCM | Phase change | Renewable energy | Thermal energy storage

[40] Rosso S., Savio G., Uriati F., Meneghello R., Concheri G., Optimization approaches in design for additive manufacturing, Proceedings of the International Conference on Engineering Design, ICED, 2019-August, 809-818, (2019). Abstract

Nowadays, topology optimization and lattice structures are being re-discovered thanks to Additive Manufacturing technologies, that allow to easily produce parts with complex geometries. The primary aim of this work is to provide an original contribution for geometric modeling of conformal lattice structures for both wireframe and mesh models, improving previously presented methods. The secondary aim is to compare the proposed approaches with commercial software solutions on a piston rod as a case study. The central part of the rod undergoes size optimization of conformal lattice structure beams diameters using the proposed methods, and topology optimization using commercial software tool. The optimized lattice is modeled with a NURBS approach and with the novel mesh approach, while the topologically optimized part is manually remodeled to obtain a proper geometry. Results show that the lattice mesh modelling approach has the best performance, resulting in a lightweight structure with smooth surfaces and without sharp edges at nodes, enhancing mechanical properties and fatigue life.

Keywords: Additive Manufacturing | Case study | Lattice structures | Modeling approaches | Optimisation

[41] Savio G., Rosso S., Curtarello A., Meneghello R., Concheri G., Implications of modeling approaches on the fatigue behavior of cellular solids, Additive Manufacturing, 25, 50-58, (2019). Abstract

According to recent studies, a new paradigm in the geometric modeling of lattice structures based on subdivision surfaces for additive manufacturing overcomes the critical issues on CAD modeling highlighted in the literature, such as scalability, robustness, and automation. In this work, the mechanical behavior of the subdivided lattice structures was investigated and compared with the standard lattices. Five types of cellular structures based on cubic cell were modeled: struts based on squared or circular section, with or without fillets and cell based on the subdivision approach. Sixty-five specimens were manufactured by selective laser sintering technology in polyamide 12 and tensile and fatigue tests were performed. Furthermore, numerical analyses were carried out in order to establish the stress concentration factors. Results show that subdivided lattice structures, at the same resistant area, improve stiffness and fatigue life and reduce stress concentration while opening new perspectives in the development of lattice structures for additive manufacturing technologies and applications.

Keywords: Design for additive manufacturing | Fatigue | Geometric modeling | Lattice structures | Selective laser sintering | Subdivision surface

[42] Savio G., Meneghello R., Rosso S., Concheri G., 3D model representation and data exchange for additive manufacturing, Lecture Notes in Mechanical Engineering, 412-421, (2019). Abstract

The unique capabilities of additive manufacturing (AM) technologies highlight limits in commercial CAD tools. In this manuscript, after a synthetic description of the main AM technologies based on international standards classification, geometric modeling methods and data exchange file formats available in the literature are presented. Twelve geometric models have been studied to evaluate the effectiveness of the file format, noting the file dimension and the time to open and close the file. As a result, a roadmap in the development of new tools for design in AM is drawn, taking into account the new possibilities offered by AM technologies.

Keywords: Additive manufacturing | Data exchange | Design for additive manufacturing | Geometric modeling

[43] Ciocca L., Meneghello R., Monaco C., Savio G., Scheda L., Gatto M.R., Baldissara P., In vitro assessment of the accuracy of digital impressions prepared using a single system for full-arch restorations on implants, International Journal of Computer Assisted Radiology and Surgery, 13(7), 1097-1108, (2018). Abstract

Purpose: This study describes a method for measuring the accuracy of the virtual impression. Methods: In vitro measurements according to a metrological approach were based on (1) use of an opto-mechanical coordinate measuring machine to acquire 3D points from a master model, (2) the mathematical reconstruction of regular geometric features (planes, cylinders, points) from 3D points or an STL file, and (3) consistent definition and evaluation of position and distance errors describing scanning inaccuracies. Two expert and two inexpert operators each made five impressions. The 3D position error, with its relevant X, Y, and Z components, the mean 3D position error of each scanbody, and the intra-scanbody distance error were measured using the analysis of variance and the Sheffe’s test for multiple comparison. Results: Statistically significant differences in the accuracy of the impression were observed among the operators for each scanbody, despite the good reliability (Cronbach’s α = 0.897). The mean 3D position error of the digital impression was between 0.041 ± 0.023 mm and 0.082 ± 0.030 mm. Conclusions: Within the limitations of this in vitro study, which was performed using a single commercial system for preparing digital impressions and one test configuration, the data showed that the digital impressions had a level of accuracy comparable to that reported in other studies, and which was acceptable for clinical and technological applications. The distance between the individual positions (#36 to #46) of the scanbody influenced the magnitude of the error. The position error generated by the intraoral scanner was dependent on the length of the arch scanned. Operator skill and experience may influence the accuracy of the impression.

Keywords: Accuracy | CAD–CAM | Digital impression | Opto-mechanical measuring

[44] Longo F., Nicetto T., Banzato T., Savio G., Drigo M., Meneghello R., Concheri G., Isola M., Automated computation of femoral angles in dogs from three-dimensional computed tomography reconstructions: Comparison with manual techniques, Veterinary Journal, 232, 6-12, (2018). Abstract

The aim of this ex vivo study was to test a novel three-dimensional (3D) automated computer-aided design (CAD) method (aCAD) for the computation of femoral angles in dogs from 3D reconstructions of computed tomography (CT) images. The repeatability and reproducibility of three manual radiography, manual CT reconstructions and the aCAD method for the measurement of three femoral angles were evaluated: (1) anatomical lateral distal femoral angle (aLDFA); (2) femoral neck angle (FNA); and (3) femoral torsion angle (FTA). Femoral angles of 22 femurs obtained from 16 cadavers were measured by three blinded observers. Measurements were repeated three times by each observer for each diagnostic technique. Femoral angle measurements were analysed using a mixed effects linear model for repeated measures to determine the levels of intra-observer agreement (repeatability) and inter-observer agreement (reproducibility). Repeatability and reproducibility of measurements using the aCAD method were excellent (intra-class coefficients, ICCs ≥ 0.98) for all three angles assessed. Manual radiography and CT exhibited excellent agreement for the aLDFA measurement (ICCs ≥ 0.90). However, FNA repeatability and reproducibility were poor (ICCs < 0.8), whereas FTA measurement showed slightly higher ICCs values, except for the radiographic reproducibility, which was poor (ICCs < 0.8). The computation of the 3D aCAD method provided the highest repeatability and reproducibility among the tested methodologies.

Keywords: Canine | Computed tomography | Femur | Repeatability | Reproducibility | Three-dimensional constructions

[45] Savio G., Meneghello R., Concheri G., Geometric modeling of lattice structures for additive manufacturing, Rapid Prototyping Journal, 24(2), 351-360, (2018). Abstract

Purpose: This paper aims to propose a consistent approach to geometric modeling of optimized lattice structures for additive manufacturing technologies. Design/methodology/approach: The proposed method applies subdivision surfaces schemes to an automatically defined initial mesh model of an arbitrarily complex lattice structure. The approach has been developed for cubic cells. Considering different aspects, five subdivision schemes have been studied: Mid-Edge, an original scheme proposed by the authors, Doo–Sabin, Catmull–Clark and Bi-Quartic. A generalization to other types of cell has also been proposed. Findings: The proposed approach allows to obtain consistent and smooth geometric models of optimized lattice structures, overcoming critical issues on complex models highlighted in literature, such as scalability, robustness and automation. Moreover, no sharp edge is obtained, and consequently, stress concentration is reduced, improving static and fatigue resistance of the whole structure. Originality/value: An original and robust method for modeling optimized lattice structures was proposed, allowing to obtain mesh models suitable for additive manufacturing technologies. The method opens new perspectives in the development of specific computer-aided design tools for additive manufacturing, based on mesh modeling and surface subdivision. These approaches and slicing tools are suitable for parallel computation, therefore allowing the implementation of algorithms dedicated to graphics cards.

Keywords: Cellular materials | Lattice structures | Mesh modelling | Subdivision surfaces

[46] Lops D., Meneghello R., Sbricoli L., Savio G., Bressan E., Stellini E., Precision of the connection between implant and standard or computer-aided design/computer-aided manufacturing abutments: A novel evaluation method, International Journal of Oral and Maxillofacial Implants, 33(1), 23-30, (2018). Abstract

Purpose: The aim of this in vitro study was to verify whether or not stock and computer-aided design/ computer-aided manufacturing (CAD/CAM) abutments show similar precision in the connection with the respective implants. Materials and Methods: Ten CAD/CAM titanium abutments were compared with 10 stock titanium abutments. Each abutment fit a regular-platform implant (Institute Straumann). Implants and abutments were measured independently and then connected. During the connection procedure, the torque was measured using a six-axes load cell. Then, outer geometric features of the implant-abutment connection were measured again. Finally, the assembly was sectioned to provide the analysis of inner surfaces in contact. The geometric measurements were performed using a multisensored opto-mechanical coordinate measuring machine. The following parameters were measured and compared for the CAD/CAM and stock titanium abutment groups, respectively: width of interference and interference length between the conical surfaces of the implant and abutment; and volume of material involved in the implant-abutment connection. Results: Interference width mean ± SD values of 18 ± 0.5 and 14 ± 0.5 μm were calculated for the stock and CAD/CAM titanium abutment groups, respectively. The difference was statistically significant (P = .02). Furthermore, the interference length mean ± SD values of 763 ± 10 and 816 ± 43 μm were calculated for stock and CAD/CAM titanium abutment groups, respectively. The difference was also statistically significant (P = .04). Finally, the volume of material involved in the implant-abutment connection was compared between stock and CAD/CAM titanium abutment groups; the mean ± SD values of 0.134 ± 0.014 and 0.108 ± 0.023 mm3 were significantly different (P = .009). Conclusion: Both standard and CAD/CAM abutment groups showed a three-dimensional (3D) seal activation after the screw tightening. Nevertheless, stock titanium abutments showed a significantly higher volume of material involved in the implant-abutment connection compared with that of CAD/CAM titanium abutments.

Keywords: CAD/CAM abutments | Implant-abutment connection | Stock titanium abutments

[47] Savio G., Rosso S., Meneghello R., Concheri G., Geometric modeling of cellular materials for additive manufacturing in biomedical field: A review, Applied Bionics and Biomechanics, 2018, (2018). Abstract

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.

[48] Savio G., Pal R.K., Meneghello R., D'angelo L., Concheri G., Shape &amp; curvature error estimation in polished surfaces of ground glass molds, Optical Engineering, 56(2), (2017). Abstract

In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamental task to control geometrical errors. Nevertheless, the more significant geometrical functional aspect related to the optical properties is the curvature, which is rarely investigated in the manufacturing process of lenses. Algorithms for the assessment of shape and curvature errors on aspheric surface profile are presented. The method has been investigated on profiles measured before and at different steps of the membrane polishing process. The results show how surface roughness, shape, and curvature change during the polishing process as a function of the machining time.

Keywords: Curvature | Glass | Grinding | Polishing | Roughness | Shape

[49] Zampieri P., Curtarello A., Maiorana E., Pellegrino C., Rossi N.D., Savio G., Concheri G., Influence of corrosion morphology on the Fatigue strength of Bolted joints, Procedia Structural Integrity, 5, 409-415, (2017). Abstract

This note summarizes some recent investigation results on the behavior of corroded steel bolted joints under uniaxial fatigue loading. Fatigue test specimens, were made up using S355 structural steel plates joined together with preloaded M12 bolts of class 10.9 with a geometry that corresponds to the Δσ = 112 MPa EC3 detail category. The accelerated corrosion process was accomplished using an electrolyte consisting of an aqueous 5% NaCl solution whereby the specimens were treated. In particular, during the corrosion process specimens were repeatedly immersed for 2 minutes in the electrolyte and then removed keeping them 60 minutes long in free air at 35 °C. An atmospheric corrosion in marine-industrial environment is well-represented through corrosion test. Fatigue loading tests and surface morphology measurement of uncorroded and corroded specimens were performed and the results were compared.

Keywords: bolted joints | Corrosion Fatigue | fatigue | fatiuge tests | material degradation

[50] Savio G., Meneghello R., Concheri G., Optimization of lattice structures for additive manufacturing technologies, Lecture Notes in Mechanical Engineering, 0, 213-222, (2017). Abstract

Additive manufacturing technologies enable the fabrication of parts characterized by shape complexity and therefore allow the design of optimized components based on minimal material usage and weight. In the literature two approaches are available to reach this goal: adoption of lattice structures and topology optimization. In a recent work a Computer-Aided method for generative design and optimization of regular lattice structures was proposed. The method was investigated in few configurations of a cantilever beam, considering six different cell types and two load conditions. In order to strengthen the method, in this paper a number of test cases have been carried out. Results explain the behavior of the method during the iterations, and the effects of the load and of the cell dimension. Moreover, a visual comparison between the proposed method and the results achieved by topology optimization is shown.

Keywords: Additive Manufacturing | Cellular Structure | Computer-Aided Design (CAD) | Design Methods | Lattice Structures

[51] Graiff L., Savio G., Turchetto M., DI Fiore A., Stellini E., Meneghello R., In vitro preliminary accuracy assessment of the impression in full arch implant rehabilitation measured by intraoral scanner, Dental Cadmos, 85(4), 193-203, (2017). Abstract

OBJECTIVES. The purpose of this preliminary in vitro investigation was to evaluate the accuracy of an intraoral scanner in fully edentulous arches rehabilitated with 6 implants; in this clinical condition it is particularly difficult to ensure sufficient accuracy standards. MATERIALS AND METHODS. For this study a reference metal master model was provided: it had 6 implant analogs inserted to simulate a fully rehabilitated edentulous arch with implants. A scanbody made of PEEK (Polyether Ether Ketone) was inserted in each analog and the positions of each scanbody were calibrated by means of a Coordinate Measuring Machine (CMM). The master model, fitted with the scanbodies and a silicone gingiva, was acquired with the True Definition Scanner (TDS). Several series of scans were taken, each of them consisting of 10 close acquisitions, in order to arrange the calibration of the master model and the series of scans with TDS in the same day. From the mesh of each scan, a segmentation was performed to identify known points referable to both plane and cylinder shapes of the scanbodies. This operation was automatically performed by implementing a dedicated algorithm developed in the Rhinoceros 5.0 software. RESULTS. The results herein are related to one set of 10 acquisitions of the master model. Dimensional analysis assessed the effective diameter of the scanbodies measured by TDS and was compared with the reference diameter measured using a CMM, thus obtaining the dimensional error in the body diameter of the scanbody. The values of dimensional errors varied from a minimum of 15 μm to a maximum of about 39 μm, with standard deviations of up to 9 μm. The location analysis allowed to determine the average location error of the scanbodies centers with respect to the reference positions: they were in a range from 14 to 21 μm, with standard deviations of less than 10 μm. CONCLUSIONS. Within the limitations of this in vitro study, the intraoral scanner under investigation proved to be able to scan a 6 implants full arch with a level of accuracy in line with other data reported in scientific literature, or even with smaller error rates. This level of accuracy is capable of fulfilling the accuracy requirements considered clinically acceptable.

Keywords: Full arch digital impressions | Implants | Intraoral scanner | Scanning dimension errors | Scanning position errors

[52] Savio G., Baroni T., Concheri G., Baroni E., Meneghello R., Longo F., Isola M., Computation of Femoral Canine Morphometric Parameters in Three-Dimensional Geometrical Models, Veterinary Surgery, 45(8), 987-995, (2016). Abstract

Objective: To define and validate a method for the measurement of 3-dimensional (3D) morphometric parameters in polygonal mesh models of canine femora. Study Design: Ex vivo/computerized model. Sample Population: Sixteen femora from 8 medium to large-breed canine cadavers (mean body weight 28.3 kg, mean age 5.3 years). Methods: Femora were measured with a 3D scanner, obtaining 3D meshes. A computer-aided design-based (CAD) software tool was purposely developed, which allowed automatic calculation of morphometric parameters on a mesh model. Anatomic and mechanical lateral proximal femoral angles (aLPFA and mLPFA), anatomic and mechanical lateral distal femoral angles (aLDFA and mLDFA), femoral neck angle (FNA), femoral torsion angle (FTA), and femoral varus angle (FVA) were measured in 3D space. Angles were also measured onto projected planes and radiographic images. Results: Mean (SD) femoral angles (degrees) measured in 3D space were: aLPFA 115.2 (3.9), mLPFA 105.5 (4.2), aLDFA 88.6 (4.5), mLDFA 93.4 (3.9), FNA 129.6 (4.3), FTA 45 (4.5), and FVA −1.4 (4.5). Onto projection planes, aLPFA was 103.7 (5.9), mLPFA 98.4 (5.3), aLDFA 88.3 (5.5), mLDFA 93.6 (4.2), FNA 132.1 (3.5), FTA 19.1 (5.7), and FVA −1.7 (5.5). With radiographic imaging, aLPFA was 109.6 (5.9), mLPFA 105.3 (5.2), aLDFA 92.6 (3.8), mLDFA 96.9 (2.9), FNA 120.2 (8.0), FTA 30.2 (5.7), and FVA 2.6 (3.8). Conclusion: The proposed method gives reliable and consistent information about 3D bone conformation. Results are obtained automatically and depend only on femur morphology, avoiding any operator-related bias. Angles in 3D space are different from those measured with standard radiographic methods, mainly due to the different definition of femoral axes.

[53] Sivolella S., Brunello G., Ferroni L., Berengo M., Meneghello R., Savio G., Piattelli A., Gardin C., Zavan B., A novel in vitro technique for assessing dental implant osseointegration, Tissue Engineering - Part C: Methods, 22(2), 132-141, (2016). Abstract

By definition, osseointegration means close contact between bone and implant. Bone response is related to implant surface properties. Various surfaces have been studied and applied to improve the biological properties of the implant and thereby favor the mechanism of osseointegration. This strategy aims to promote osseointegration by means of a faster and stronger bone formation, improving stability during the healing process, and thus allowing for earlier loading of the implant. Dental implant osseointegration has so far been studied in various animal models. The development of a method based on tissue engineering for assessing the osseointegration process in vitro could prove a valid biomimetic alternative to sacrificing animals. In this study, flat cylindrical dental implants with moderately rough surfaces and machined implants were set in bovine bone blocks. Then, adipose-derived stem cells (ADSCs) were three dimensionally cultured onto these blocks in osteo-endothelial medium for up to 30 days to mimic the osseointegration process in vitro. Scanning electron microscopy (SEM) and gene expression were used to examine stem cell commitment. Mechanical pull-out tests were also performed. SEM analysis identified cells with an osteoblast morphology adhering to the surface of the implants after their removal. Gene expression analysis showed that ADSCs seeded onto the bone blocks were able to express osteoblast and endothelial markers. The implants with the moderately rough surface generated higher pull-out strengths when compared with the machined implants. Nevertheless, the pull-out test values were higher for implants placed in bone blocks with ADSCs than for those set in scaffolds without stem cells. Our results demonstrate the validity of the method adopted and its potential for use in the in vitro assessment of the biological behavior of dental implant surfaces.

[54] Di Fiore A., Meneghello R., Savio G., Sivolella S., Katsoulis J., Stellini E., In Vitro Implant Impression Accuracy Using a New Photopolymerizing SDR Splinting Material, Clinical Implant Dentistry and Related Research, 17, e721-e729, (2015). Abstract

Purpose: The study aims to evaluate three-dimensionally (3D) the accuracy of implant impressions using a new resin splinting material, "Smart Dentin Replacement" (SDR). Materials and Methods: A titanium model of an edentulous mandible with six implant analogues was used as a master model and its dimensions measured with a coordinate measuring machine. Before the total 60 impressions were taken (open tray, screw-retained abutments, vinyl polysiloxane), they were divided in four groups: A (test): copings pick-up splinted with dental floss and fotopolymerizing SDR; B (test): see A, additionally sectioned and splinted again with SDR; C (control): copings pick-up splinted with dental floss and autopolymerizing Duralay® (Reliance Dental Mfg. Co., Alsip, IL, USA) acrylic resin; and D (control): see C, additionally sectioned and splinted again with Duralay. The impressions were measured directly with an optomechanical coordinate measuring machine and analyzed with a computer-aided design (CAD) geometric modeling software. The Wilcoxon matched-pair signed-rank test was used to compare groups. Results: While there was no difference (p=430) between the mean 3D deviations of the test groups A (17.5μm) and B (17.4μm), they both showed statistically significant differences (p<.003) compared with both control groups (C 25.0μm, D 19.1μm). Conclusions: Conventional impression techniques for edentulous jaws with multiple implants are highly accurate using the new fotopolymerizing splinting material SDR. Sectioning and rejoining of the SDR splinting had no impact on the impression accuracy.

Keywords: Accuracy | Edentulous jaw | Implant impression technique | Impression copings | Passive fit | Splinting material

[55] Savio G., Gaggi F., Meneghello R., Concheri G., Design method and taxonomy of optimized regular cellular structures for additive manufacturing technologies, Proceedings of the International Conference on Engineering Design, ICED, 4(DS 80-04), 235-243, (2015). Abstract

Additive manufacturing technologies enable the fabrication of innovative parts not achievable by other technologies, such as cellular structures, characterized by lightness and good mechanical properties. In this paper a novel modeling and optimization method is proposed to design regular cellular structures. The approach is based on generative modeling of a structure by repeating a unit cell inside a solid model, obtaining a beam model, and on an iterative variation of the size of each section in order to get the desired utilization for each beam. Different structures have been investigated, derived by six cell types in two load conditions. Taxonomy of cell types as a function of relative density and compliance were proposed in order to support the design process for additive manufacturing of cellular structures.

Keywords: Additive manufacturing | Cellular structure | Computer aided design (CAD) | Design methods | Simulation

[56] Savio G., Meneghello R., Concheri G., A heuristic approach for nesting of 2D shapes, Proceedings of the 37th International MATADOR 2012 Conference, 49-52, (2013). Abstract

In several manufacturing processes, the cutting of 2D parts from sheets is an important task. The arrangement of the parts in the sheets, supported by computers, is called nesting and is addressed to minimize the wasted material. In literature some approaches are proposed, based on genetic or heuristic algorithms which emphasize different characteristics, e. g. the time complexity or the wasted material. In shipbuilding the parts to be arranged have significantly different sizes, which are often difficult to pack in a fast way using the standard methods in literature. In this work an approach is proposed, able to arrange parts with very different dimensions, which is based on the identification of a suitable starting rotation that ensures a solution in a reasonable time. The main steps are: A) importation of the model files of the parts to be packed, b) identification of a preliminary orientation and sorting of the parts (starting position), c) optimization of the position of the parts, ensuring a minimum distance between them. For the starting rotation, three different orientations are considered: i) the original orientation, ii) the x axis coincident with the minimum inertia axis, iii) the x axis aligned with the maximum edge. The orientation is selected in order to obtain the minimum area of the bounding box. The implementaiton of the method has been investigated and the results show the advantages of the approach: reduction of waste material and time for performing the nesting. © Springer-Verlag London 2013.

Keywords: CAD/CAM | CAPP | Cutting-stock | Nesting | Packing | Shipbuilding

[57] Savio G., Concheri G., Meneghello R., Lines of curvature and umbilical points: Computation method and applications, Applied Mechanics and Materials, 421, 489-495, (2013). Abstract

A method for computing lines of curvature and umbilical points is proposed. These properties, derived for NURBS surfaces, are useful in shape modeling for both aesthetic and functional characteristics evaluation. Moreover, the application to the ship-hull design and to the progressive additional lens design, of umbilics and lines of curvature are investigated. © (2013) Trans Tech Publications, Switzerland.

Keywords: Computer aided design | Curvature | Differential geometry | Freeform surfaces | Lines of curvature | Principal direction | Progressive addition lens | Sculptured surfaces | Shape interrogation | Shipbuilding | Umbilical points

[58] Savio G., Concheri G., Meneghello R., Progressive lens design by discrete shape modelling techniques, International Journal on Interactive Design and Manufacturing, 7(3), 135-146, (2013). Abstract

The free-form technologies, recently introduced in the manufacturing process of ophthalmic lenses, allow the production of high performance and custom progressive addition lenses (PALs). In this work a method for the parametric design and analysis of PAL, based on discrete shape modelling, is proposed. Both the optical (e.g. power and addition) and the geometrical (e.g. inset, corridor length, amplitude of the distance and near vision area) parameters have been taken into account. In addition the method developed for the analysis of surface optical properties, especially with regard to the astigmatic surface power, has proved an essential tool for the analysis of results. Moreover the exchange data formats for the CNC manufacturing process were described. The influence of different parameters on the optical properties are analyzed and discussed. In this context a key role on the resultant optical properties of the designed PAL is covered by the distribution of the curves in the intermediate area and by the curvature equation along the corridor. Surface power and astigmatic surface power show similar behaviour to other commercial progressive additional lens but, moreover, the designer can specify the distribution of astigmatism in the intermediate region. Compared to the methods proposed in literature, this one shows more opportunities in the design parameters definition and allows highly customized lens, designed on the main habits of the wearer. Finally the method was applied to the manufacturing process of glass mould for PAL and the results of optical parameters measurements are proposed. © 2012 Springer-Verlag France.

Keywords: Curvature | Free-form surface | Geometric modelling | Progressive Addition lens PAL | Umbilics

[59] Meneghello R., Savio G., Raffaeli R., Cerardi A., Turchetto M., Planchenstainer L., An integrated methodology for the functional design of dental prosthesis, International Journal on Interactive Design and Manufacturing, 7(2), 103-114, (2013). Abstract

In this work it is proposed an integrated methodology for the functional design and simulation of removable complete dentures. This methodology develops in four phases: virtual and physical prototyping, contact forces and areas analysis and functional optimization of teeth and arches geometry. A virtual environment for the modeling of the prosthesis (NM-Tooth) was developed: it includes a database of 3D CAD models of artificial teeth and allows to simulate the fabrication techniques used in dentistry. In particular, it is possible to create a full denture virtual model by a semi-automatic procedure, where a preliminary occlusal configuration is set up. By using rapid-prototyping techniques, a physical model of the prosthesis is manufactured which is utilized for the experimental, in vitro, analysis. The analysis phase includes the study of the occlusion forces in relation to the identification of contact areas; a multi-axial force measuring system allows the detection of forces acting on the physical model. Simultaneously, with a reverse engineering procedure, the relevant contact areas in the virtual model are related with the load configuration. According to the experimental output, it is possible to modify the preliminary geometry both of the arches and of the individual tooth. This integrated methodology is an original instrument to study the dental prosthesis and acquire information for its functional improvement. © 2012 Springer-Verlag France.

Keywords: Bite force | CAD modeling | Complete dentures | Contact analysis | Occlusion simulation | Virtual dentistry

[60] Savio G., Meneghello R., Concheri G., D'Angelo L., Process optimization in glass polishing based on a material removal model, Advanced Science Letters, 19(2), 539-542, (2013). Abstract

In the industrial world there are different production processes for the manufacturing of spectacle lens. Nowadays casting is the most common lens manufacturing method. Here, the mould production is based on three stages: grinding, polishing and hardening, where, in the second step, different sets of process parameters play a key role in quality, time and cost. To optimize the polishing process of moulds a model for the correlation between the material removal and the process parameters is proposed. The model is developed for CNC ball polishing of free-form surfaces, where the pad, made of a polyurethane layer superimposed to a rubber bulk, moves along a scanning path, in a suspension of cerium oxide. The material removal can be derived through pressure and sliding velocity between polishing pad and workpiece and consequently can be related to the CAD-CAM- CNC parameters e.g., tool and workpiece shape, dimension and modulus of elasticity, feed rate, feed step, tool rotational speed and radial tool deformation. The model has been validated on ground glass flat samples polished varying the process parameters and it shows a satisfactory estimation of material removal as a function of the process parameters. © 2013 American Scientific Publishers.All rights reserved.

Keywords: CMP | Freeform surfaces | Glass | Material removal | Model | Optimization | Polishing | Process modeling

[61] Savio G., Meneghello R., Concheri G., Optical properties of spectacle lenses computed by surfaces differential quantities, Advanced Science Letters, 19(2), 595-600, (2013). Abstract

The surface optical properties of an ophthalmic lens are closely related to curvature parameters and conse- quently they can be derived by the geometric characterization of the lens surface. Adopting this approach it is possible to verify a spectacle lens by contact probe measurements without light transmission based instruments. Moreover, this method can be applied in the design stage to verify the surface optical properties of complex surface geometries as in progressive lens design. In this work, in order to derive the optical properties of a spectacle lens, a method based on quadratic fitting to assess the curvature properties of discrete surfaces is proposed. The procedure has been validated on several discrete surfaces, and subsequently error fitting functions were derived. © 2013 American Scientific Publishers All rights reserved.

Keywords: Curvature | Differential quantities | Freeform surface | Spectacle lenses | Surface optical properties

[62] Giovanzana S., Savio G., Meneghello R., Concheri G., Shape analysis of a parametric human lens model based on geometrical constraints, Journal of Modern Optics, 58(19-20), 1770-1780, (2011). Abstract

Several simple models, such as conicoid models, are usually adopted to describe the surfaces of the human crystalline lens; unfortunately they do not provide a continuous junction between the anterior and the posterior surface of the lens and then they cannot qualify for biomechanical simulation. Vice versa, more complex mathematical models give a continuous junction between the anterior and the posterior surface, but do not provide a geometrical or optical interpretation of the coefficients of the model. In this work we propose a continuous curvature lens model in which the coefficients are derived by geometrical constraints. In this way, both the continuity in the junction zone and a geometrical-physical interpretation of the coefficient involved in the model are obtained. Shape, volume and curvature of the proposed model were compared with four models presented in the literature: two independent conic equations, two interdependent figuring conicoid equations, conic patches model and modulated hyperbolic cosine. © 2011 Copyright Taylor and Francis Group, LLC.

Keywords: curvature | geometrical constraint | human crystalline lens | shape | volume

[63] Savio G., Meneghello R., Concheri G., Cerardi A., A study on the material removal mechanisms in ball polishing, Proceedings of the 11th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2011, 2, 353-356, (2011). Abstract

The manufacturing process of freeform glass components for precision optics is usually based on contour CNC grinding and polishing operations. To predict the geometrical precision of the production process, a correlation between the geometrical error and the process parameters is required. This is even more important in the polishing operation which is the final stage of the process. In this work a model for material removal estimation in deterministic polishing of glass moulds is proposed and validated. The model is developed for CNC ball polishing of free-form surfaces, where the pad, made of a polyurethane layer superimposed to a rubber bulk, moves along a scanning path, in a suspension of cerium oxide. As many models in literature the removed material can be estimated by pressure and sliding velocity between polishing pad and workpiece. Adopting the Hertz theory these physical characteristics can be related to the CAD-CAM-CNC parameters, e.g. tool and workpiece shape, dimension and modulus of elasticity, feed rate, feed step, tool rotational speed and radial tool deformation. The model validation was performed on ground glass flat samples polished with different process parameters, measuring the removed material by a contact probe profilometer. The developed model shows a satisfactory estimation of removal material as a function of the process parameters.

[64] Cerardi A., Meneghello R., Concheri G., Savio G., Advanced characterization of free-form surfaces in high precision machining, Proceedings of the 11th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2011, 2, 309-312, (2011). Abstract

Precision free-form components are functionally complex objects with very accurate surfaces. In the manufacturing of these parts the complete and correct characterization of geometrical errors is an important aspect since it allows the adoption of preventive actions to control errors causes such as the thermo-mechanic behaviour of the machine tool, the removal mechanism of the cutting operation, the wear of the tool, the lubricant action, etc. In this work an advanced method of geometry characterization has been adopted to investigate the various contributions of the geometric error, resulting from the machining of any free-form geometry. The method allows the effective estimation of the size contribution error as well as form, orientation and position deviation. The method consists in an iterative process that minimize the distance of the cloud of points measured to an optimized offset of the nominal model of the component. At the end of minimization process, optimal parameters are used for the complete shape characterization of the part.

[65] Savio G., Meneghello R., Concheri G., A surface roughness predictive model in deterministic polishing of ground glass moulds, International Journal of Machine Tools and Manufacture, 49(1), 1-7, (2009). Abstract

The introduction of deterministic NC grinding and polishing operations, in the manufacturing of free-form glass components for precision optics, requires the characterization of surface topography evolution as a function of process parameters. In this work, a model based on Reye's wear hypothesis is proposed for the assessment of surface roughness prediction as a function of operating parameters, in the deterministic polishing process of glass moulds. According to Reye's hypothesis, the removed material per unit area is proportional to the work due to the friction force: the removed material per unit area can be computed by adequately integrating the areal material ratio function (Abbott-Firestone curve) of the surface and can be associated with the amplitude roughness parameter; the work due to the friction force per unit area is proportional to the integral of the product of pressure and velocity in the time interval and can be derived from the process parameters by means of the Hertz theory. The model assessment was performed on ground glass flat samples polished with different operating parameters, mapping the surface roughness using an atomic force microscope (AFM). The developed model shows a satisfactory estimate of surface roughness evolution during the polishing process and confirms the experimental results found in the literature for the Preston coefficient. © 2008 Elsevier Ltd. All rights reserved.

Keywords: Abbott-Firestone | Glass | Material ratio | Polishing | Roughness | Surface texture

[66] Savio G., Meneghello R., Concheri G., A new model for surface roughness evolution in the chemical mechanical polishing (CMP) process, Laser Metrology and Machine Performance VIII - 8th International Conference and Exhibition on Laser Metrology, Machine Tool, CMM and Robotic Performance, LAMDAMAP 2007, 252-261, (2007). Abstract

Surface polishing is a typical example of a machining process based on mixed chemical-mechanical phenomena, as pointed out in the recent literature on the polishing process (CPM - Chemical Mechanical Polishing). In this work, a model is proposed for the assessment of surface roughness evolution in the polishing process of glass moulds, used in the manufacturing of ophthalmic lenses, in order to identify the influence of the operating parameters on the material removal rate (MRR). In this model the evolution of surface roughness during the polishing process is based on Reye hypothesis. According to such hypothesis, the removed material in a specific time interval is proportional to the friction work: the removed material per unit area can be computed by adequately integrating the bearing ratio curve (Abbott-Firestone) of the surface; the friction work per unit area is proportional, according to the dynamic friction coefficient, to the integral of the product of pressure and velocity in the time interval. A similar result can be also obtained adopting other wear models, e.g. the Preston or Archard approaches. The model validation was performed on ground glass flat samples polished with increasing values of MRR. Pressure and velocity distributions on the sample surface were established according to the polishing machine operating parameters by means of the Hertz theory; the surface roughness of the sample was mapped using an atomic force microscope (AFM). The developed model shows a satisfactory estimate of surface roughness evolution during the polishing process and confirms the experimental results found in literature.

[67] Meneghello R., Concheri G., Savio G., Comelli D., Surface and geometry error modeling in brittle mode grinding of ophthalmic lenses moulds, International Journal of Machine Tools and Manufacture, 46(12-13), 1662-1670, (2006). Abstract

The selection of modeling and machining parameters for glass mould fabrication in ophthalmic lenses production, has required the definition of a theoretical-empirical model of the ground surface in order to predict the overall geometry errors of the surface. The accurate control of the geometrical errors and of the surface texture for the mould functional surface is crucial for the subsequent polishing operation, which is responsible for the final geometry, surface finish and cost. The basic hypotheses validation has been accomplished by measuring the micro-geometric parameters P, W and R and by characterizing the macro-geometry comparing the nominal profile and the measured profile. The correspondence among theoretical hypotheses and experimental results allows realistic predictions of the attainable surface texture during a contour grinding operation and the adoption of preventive actions in order to compensate the geometrical errors due to modeling and tool path generation parameters. © 2005 Elsevier Ltd. All rights reserved.

Keywords: Brittle mode | Geometry error | Glass | Grinding | Process modeling | Surface roughness

[68] Concheri G., Savio G., Meneghello R., Curvature estimation for optical analysis, Proceedings of the 6th International Conference European Society for Precision Engineering and Nanotechnology, EUSPEN 2006, 1, 87-90, (2006). Abstract

In the productive process of moulds for ophthalmic lenses, the availability of a specialized tool for the analysis of the optical property of 3D virtual models of ophthalmic lenses and relevant injection moulds, may reduce the tests on physical prototypes during the design phase. The optical properties of interest are usually power and astigmatism of the lens surface. Both of them are proportional to the geometric curvature of the lens surfaces. Therefore the identification of the optical properties of a surface can be brought back to the computation of the minimum and maximum curvature maps on lens surface. Some commercial software tools able to perform curvature analysis on both physical and virtual models exist, but they show some limitations: methods and algorithms used to compute the desired parameters are not declared, the size of the area used to compute the desired parameter cannot be set by the operator and no estimate on the accuracy of the computed results is given. These last two issues are crucial: the area considered in the analysis should be related to the area actually used; the accuracy of the adopted algorithm should be verified and compared with the eye sensitivity to geometric errors of the lens surface. Aim of the present work is to describe the functioning principles of a software tool for curvature analysis and optical properties computation of either virtual models expressed as high resolution meshes or physical prototypes of lenses sampled using a Coordinate Measuring Machines (CMMs), that overcomes the cited limitations. Such tool will be included into an integrated tool for design, analysis, manufacturing and verification of ophthalmic lenses.