Abstract: Virtual assembly has become a popular trend in recent years and is used for various purposes, including selective assembly and adaptive tooling. Monte Carlo approaches based on Finite Element Method (FEM) simulations are commonly used for production applications. However, during the design phase, when testing different configurations and design options, a variational method is more suitable. This paper aims to test different implementations of the Method of System Moments applied to the second-order tolerance analysis method when actual distributions, which are non-centered and non-normal, are used as input for the simulation. The study reveals that the simulation results can significantly vary depending on the simulation settings in some cases. As a result, a series of best practices are highlighted to improve the accuracy and reliability of the simulation outcomes.

Keywords: Assembly simulation | Computer-aided tolerancing | Tolerance stack-up | Virtual assembly

Abstract: In tolerancing activities focusing on the allocation of geometrical tolerances, many critical issues originate from the non-optimal assignment of responsibilities among the organization units involved. This paper aims to depict relations between different tolerancing activities and relevant specifications, assigning them to the proper actor and, therefore, expanding the ISO 8015:2011 “responsibility principle”. A classification among tolerancing activities, specifications, and media is proposed; a horizontal hierarchical framework among functional, manufacturing, and verification specifications and a vertical hierarchical framework along the supply chain are discussed. Examples of both hierarchical structures are presented.

Keywords: functional specification | functional tolerancing | geometrical product specification | ISO/TS 21619:2018 | manufacturing specification | manufacturing tolerancing | tolerance specification | verification specification | verification tolerancing

Abstract: This paper presents a possible functional geometric specification for a lifting airfoil including the definition of functional tolerance limits (tolerance synthesis) and an associated inspection procedure. The proposed specification scheme is derived from the analogy between the mating of the airfoil with a fluid field and the consolidated example of the mating of a prismatic element in its site. The airfoil thickness is defined as a non-constant size with non-constant tolerances and the airfoil shape is prescribed with a non-constant profile of a line tolerance applied to the median airfoil line. The tolerance synthesis is based on XFLR5 software and Computational Fluid Dynamics (CFD) simulations. The inspection procedure uses the data acquired with a laser probe elaborated in Geomagic Wrap, GOM inspect and MATLAB. The overall process has been applied to a case study allowing to define limits and proposing a set of possible improvements regarding, particularly, the geometric specification of the leading and trailing edges of the airfoil.

Keywords: Airfoil | Geometric Inspection | Geometric Specification | Tolerance Synthesis

Abstract: This paper proposes a tool to analyze the diffusion and knowledge of the ISO GPS language in both industry and academia. A survey has been designed based on the maturity model concept to achieve this goal. Six Key Performance Indicators (KPI) arguments have been defined: general concept, datum systems, geometric tolerances, dimensional tolerances, modifiers and indications, and tolerance stack-up. Per each of these, three assessments are proposed, and a rating is given based both on self-assessment and unbiased check questions. The result is a survey that takes between 10 to 15 min to be filled out. The assessment is based on both knowledge and usage. The defined survey, through testing, proved to be a simple and usable tool to test the actual diffusion and knowledge of the ISO GPS language thanks to its shortness and the different levels of analysis it allows.

Keywords: Geometric Specification | ISO GPS | Maturity Model | Survey

Abstract: Recent advancements in additive manufacturing technologies have significantly enhanced the capacity to accurately reproduce the shape and material properties found in nature. Furthermore, the behavior and functionality exhibited by natural systems can be effectively simulated using bio-inspired algorithms. An essential parameter that governs various life processes is the surface area to volume ratio. In industrial applications such as catalysis and heat exchange, this particular characteristic is intentionally augmented to enhance overall performance, thus fulfilling the functional requirements. In this study, a curve differential growth implementation was developed to obtain space-filling and self-avoiding paths. By applying successive iterations of the algorithm to an initial curve, a set of curves was generated. These curves were then organized in three-dimensional Euclidean space and combined into a NURBS surface. As a case study, the design of a coaxial counterflow heat exchanger employed the proposed modeling algorithm. The resulting model underwent a numerical simulation to assess the heat transfer rate and pressure drops. Material extrusion technology was used to manufacture a prototype for preliminary demonstration, although further studies are required to ensure watertight functional parts. Numerical results indicate that the proposed design exhibits a better heat transfer rate in a smaller size but leads to higher pressure drops when compared to three equivalent plain pipe solutions (with matching length, surface area, and heat transfer rate).

Keywords: Additive Manufacturing | Bioinspiration | Biomimicry | Differential Growth | Geometric Modeling | Space-Filling Curves

Abstract: Multi-material additive manufacturing enables the opportunity to combine multiple materials within the same part, allowing for an expanded range of properties that can gradually change inside the design space. This category of materials is commonly referred to as functionally graded materials (FGMs). However, FGMs currently face several limitations and challenges in terms of design and manufacturing, such as compatibility, distribution design, and prediction of mechanical properties. Furthermore, when dealing with parts possessing complex micro/meso-structures, finite element simulation often becomes a costly and time-consuming process. Among various additive manufacturing technologies, fused filament fabrication allows the combination of multiple thermoplastic materials within the same nozzle during the deposition process, thereby creating FGMs. This process, known as coextrusion, enables the gradual deposition of materials adjacent to each other while changing their fractions. Moreover, the deposition direction shapes the distribution of materials within each deposited layer, influencing the material structure and the resulting mechanical properties. A recent study proposes a preliminary model describing the deposition mechanism, which has been confirmed by experimental tests. This model delineates the section of the material deposited based on the tool path and process parameters, such as layer thickness and hatching space. To expand upon these findings, this paper applies a homogenization approach based on finite element analysis to the deposition model. This approach enables the description of material mechanical properties based on the material fractions, tool path, and other process parameters. Additionally, this study presents a methodology to tailor the mechanical properties according to the printed part’s orientation around the print bed.

Keywords: FFF | FGM | Functionally graded materials | Fused Filament Fabrication | Homogenization | Multi-material coextrusion | Representative Volume Element | RVE

Abstract: Lattice structures are receiving a renewed interest in many areas such as biomedical and industrial fields, due to the capabilities of additive manufacturing technologies which allow for the fabrication of very complex shapes. Currently, several methods and tools are described in the scientific literature and some commercial software are introducing dedicated packages to reduce designer efforts for lattice structure design and optimization. However, by using commercial CAD/CAM tools in the fabrication of components filled by lattice structure, several critical issues remain and need to be taken into consideration. This work aims at manufacturing variable-density lattice structures via fused deposition modeling deriving the density map from a grayscale or color image. In the proposed approach, the shell-based lattice model is not achieved by CAD tools, but only during the CAM process, while the lattice relative density is computed by editing the G-code, modifying the extrusion flow according to the local grayscale of a volumetric CAD model, defined from an image. The main advantages are related to the absence of a graded lattice geometric model and the consistency of the toolpath. The method is tested on various images and patterns, and can find applications in artworks, embedded information on components, and functional 3D printed parts, such as the replication of the density map of a bone derived from a DICOM grayscale image.

Keywords: Additive manufacturing | Fused deposition modeling | Graded lattices | Heterogeneous objects

Abstract: Large parts produced by injection moulding are usually subjected to large deformations that may be reduced during assembly. The single parts manufacturing specification should refer to the as produced (free) state. On the other hand, the functional specification, derived from the assembly functional specification should address the “as assembled” state. Geometrical inspection, based on the functional specification requires dedicated fixtures to simulate the “as assembled” state. This contribution suggests a procedure, based on FEM simulation, to correlate the geometric specification at the “as assembled” state with the “as produced” (free) state, applied to an industrial case study. The result of the procedure are free state tolerance limits, e.g., manufacturing specification, that allows conformity of the part to the functional specification once assembled. The part may be inspected based on the manufacturing specification fixtureless during mass production. The result of the case study shows a significant reduction in position and orientation error due to the assembly process as it was expected.

Keywords: Compliant assemblies | Deformable assemblies | FEM simulation | Geometrical Product Specification | Tolerancing

Abstract: Shaft-hole pattern fits based on the Boundary Condition design criterion allows a 100% acceptability rate, but they may be not economically convenient. If the rejection rate needs to be statistically quantified and the pattern is itself the alignment feature, therefore promoted as datum feature (Intrinsic datum system), there is no trivial solution to create a tolerance stack-up: a unique assembly function cannot be determined. The focus of this contribution is “2x” patterns: different methodologies to create tolerance stack-up assessing assemblability are discussed and verified through Monte Carlo simulation. An equation to transform the variability seen from the Intrinsic datum system to the one seen from an external arbitrary reference system is given. The mutual distance between any two elements of an “nx” pattern is discussed and the implication of multiplicity and datum system is highlighted. A case, derived from an industrial case study, will be discussed by comparing the result from the simulated manual and automated assembly. A path towards “nx” patterns generalization is also presented.

Keywords: Boundary Condition | Rejection rate | Tolerance analysis | Tolerancing | Virtual condition

Abstract: This work aims to propose a novel geometric modeling method to obtain lattice structures with internal walls and external skins that can be selectively activated. Internal walls can separate two adjacent cells, locally increase the stiffness of the component, and generate internal ducts; external walls are used to strengthen the entire structure and create a division from the outside. The proposed approach models a beam-based cellular structure with the introduction of internal walls according to an activation pattern that indicates whether a cell is communicating with the adjacent one through their connecting faces or not. The data structure describes the topology of the subdivision surface control polygon. The proposed method is then applied to a case study based on the hydraulic manifold applications. The possibility of building custom internal channels is exploited, with the advantage of obtaining smooth surfaces at the direction changes, with lower pressure drops, and a lightweight component due to the lattice structure that surrounds the channels. The resulting structure has a complex geometry that perfectly suits the manufacturing capabilities of additive manufacturing technologies.

Keywords: Additive manufacturing | Closed cells | Geometric modeling | Hydraulic manifold | Lattice structures

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

Keywords: additive manufacturing | coextrusion | fused deposition modeling | material extrusion | aterial modeling

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

Keywords: additive manufacturing | coextrusion | data exchange | functionally graded additive manufacturing | fused deposition modeling | multi-material additive manufacturing

Abstract: The precision livestock farming (PLF) has the objective to maximize each animal's performance while reducing the environmental impact and maintaining the quality and safety of meat production. Among the PLF techniques, the personalised management of each individual animal based on sensors systems, represents a viable option. It is worth noting that the implementation of an effective PLF approach can be still expensive, especially for small and medium-sized farms; for this reason, to guarantee the sustainability of a customized livestock management system and encourage its use, plug and play and cost-effective systems are needed. Within this context, we present a novel low-cost method for identifying beef cattle and recognizing their basic activities by a single surveillance camera. By leveraging the current state-of-the-art methods for real-time object detection, (i.e., YOLOv3) cattle's face areas, we propose a novel mechanism able to detect the ear tag as well as the water ingestion state when the cattle is close to the drinker. The cow IDs are read by an Optical Character Recognition (OCR) algorithm for which, an ad hoc error correction algorithm is here presented to avoid numbers misreading and correctly match the IDs to only actually present IDs. Thanks to the detection of the tag position, the OCR algorithm can be applied only to a specific region of interest reducing the computational cost and the time needed. Activity times for the areas are outputted as cattle activity recognition results. Evaluation results demonstrate the effectiveness of our proposed method, showing a mAP@0.50 of 89%.

Keywords: Cattle identification | Computer vision | Deep learning | Low-cost sensors | Precision livestock farming

Abstract: The manufacturing process may lead non-rigid parts to endure large deformations which could be reduced during assembly. The manufacturing specifications of the single parts should refer to their free state or “as manufactured” state; the functional specifications should instead address the “as assembled” state. Therefore, a functional geometrical inspection requires dedicated fixtures to bring the parts in “as assembled” state. In this paper, through a linearized model that considers fixturing and elastic spring-back, we aim to correlate the functional specification to the manufacturing specifications. The model suggests a hybrid approach called “restricted skin model” that allows to reduce the degrees of freedom considering the form error when relevant. Firstly, the framework is verified in a mono-dimensional test case. Subsequently, it is verified including FEM simulation and actual measurement for two simple assemblies. The results show that the model can correctly interpret the theoretical assembly behaviour for actual applications. The use of the “restricted skin model” approach shows a negligible difference when compared to full FEM simulation with differences of 2.1 · 10−7 mm for traslations and 6.0 · 10−3 deg for rotations. The comparison with actual measurement values showed an error of ±0.2 mm at the assembly features. Furthermore, the linearized model allows a possible real-time application during production that enables to adjust manufacturing specification limits in case of process drifting.

Keywords: Compliant assemblies | Deformable assemblies | Geometrical Product Specification | Linearized model | Restricted skin model | Skin model | Tolerancing

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

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

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

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

Abstract: The increasing attention to numerical issues related to material modeling is still a strong incentive to develop sound mechanical models that can explain material behavior up to failure. A procedure to handle a robust geometric meso-scale reconstruction of concrete materials is here proposed, based on X-ray Computed Tomography (CT-scan or X-ray CT). This study applies X-ray CT on ordinary concrete made with limestone aggregates. In this case the technique allows to acquire the overall inner geometry and distribution of the aggregates and also voids, thanks to the difference in material density of the components. Solid models have been generated with such technique and discretized in space to be numerically studied via the Finite Element (FE) method. The numerical results are compared with uniaxial compression tests on the same scanned specimens. For the numerical analyses a specific non-associated elasto-plastic constitutive behavior, coupled with damage, is developed for the cement matrix, whereas the coarse aggregates are treated as elastic. The mechanical characteristics of the components are gathered through a specific experimental campaign. The study confirms that a predictive simulation of damage triggering and evolution in concrete under generic 3D stress states requires the characterization of the continuum at a meso-scale level. Comparisons between numerical and experimental results proves the soundness of the proposed constitutive description to evaluate the brittle behaviour of cementitious materials and to satisfactorily simulate damage triggering under generic 3D stress states.

Keywords: Concrete | Damage | Elasto-plasticity | FEM | Voids | X-ray micro-computed tomography

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

Abstract: Objectives: Implantoplasty (IP) is a treatment option for peri-implantitis. Mechanical concerns were raised on fracture resistance of implants subjected to this procedure. This study aimed to compare two methods of IP in terms of implant wear and fracture resistance, and of surface topography. Material and methods: Eighteen cylindrical screw-shaped dental implants (4 mm diameter, 13 mm length) with an external hexagonal connection were used. IP was performed on the first 6-mm implant surface with a sequence of burs or diamond sonic tips, both followed by an Arkansas finishing. IP duration and implant weight variation were recorded. Micro-computed tomography (micro-CT) was used to evaluate material loss. Implant fracture resistance was assessed by static compression test. Surface topography analysis was performed with a stylus profilometer. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDS) was applied for implant surface morphology and elemental characterization. Results: Micro-CT showed less material loss in sonic compared to burs. No statistically significant difference was found between the mean fracture resistance values reached in bur and sonic, both followed by Arkansas, and with respect to control. IP performed with burs led to a smoother surface compared to sonic. Equivalent final surface roughness was found after Arkansas in both IP procedures. SEM-EDS showed a deburring effect associated to sonic and revealed carbon and aluminum peaks attributable to contamination with sonic diamond tips and Arkansas bur, respectively. Conclusions: IP with sonic diamond tips was found to be more conservative in terms of structure loss. This could have a clinical relevance in case of narrow-diameter implants.

Keywords: bone implant interactions | CT imaging | surface chemistry

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

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

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

Abstract: The biomechanics of the abdominal wall depends on muscular activation, tissue mechanical behavior and Intra-Abdominal Pressure (IAP). In this work, a numerical model of a human abdomen is presented, based on abdominal wall geometry from medical images. Specific constitutive formulations describe tissues mechanical behavior. Connective tissues are modelled as hyperelastic fiber-reinforced materials, while muscular tissues are described by means of a three-element Hill's model. The abdominal cavity is represented by a volume region interacting with the abdominal wall. Numerical analyses are developed by applying a muscular contraction, inducing a volume reduction of the abdominal cavity and a simultaneous IAP increase. Numerical results of abdomen displacement at IAP corresponding to an abdominal crunch are compared with experimental results acquired via 3D laser scanning on a healthy subject. Numerical and experimental results are mutually consistent and show that muscular activation induces a raising in the region adjacent to linea alba along the posterior-anterior direction and a lowering along lateral-medial direction of the abdominal wall sides. The numerical model developed in this work allows a coherent representation of the abdominal wall mechanics.

Keywords: 3D laser scanning | Finite element modeling | Muscle activation | Numerical analysis | Tissue constitutive modeling

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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.

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

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

Abstract: Rapid-prototyping is usually considered as a powerful tool in geometric and functional optimization of a product. In such an approach, focus is exclusively on the real component, and not on the rapid prototype which represents it. This work takes part on a wider study which focuses on a rational, systematic approach in obtaining an "optimized rapid prototype", with particular regard to emptying strategies without loss of structural and geometric properties. In detail, a set of tensile tests have been performed on different types of specimen, which reproduce a set of corresponding emptying strategies: each type of specimen is characterized by a different percentage of porosity (40, 60 and 80%), obtained by the combination of particular values of two parameters: reticular structure and its density. As a result, the correlation between mechanical strength and geometric structure has been evaluated, allowing the identification of a profitable emptying strategy, in terms of cost and weight. © Springer-Verlag London 2013.

Keywords: Cellular structures | Light weight structures | Polyamide tensile properties | Rapid prototyping | Selective laser syntering

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

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

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

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

Abstract: The present paper describes the design features, potential indications and a clinical application of a newly designed device for jaw motion rehabilitation, the Spring-Bite. This device is characterized by a first class lever mechanism, which allows performing passive jaw motion rehabilitation at constant load without an active participation by the patient. Spring-Bite was developed for the management of temporomandibular joint (TMJ) hypomobility and its application may be much useful in the post-operatory phases of TMJ or orthognathic surgeries as well as in patients with reduced muscular force.

Abstract: The significantly growing use of Additive Manufacturing (AM) enables the fabrication of innovative parts, characterized by lightness and good mechanical properties. The biomedical field takes great advantage of these capabilities: in particular, the ability of producing porous or lattice structure-based parts allows to obtain prostheses with human bone like stiffness, with a positive influence in patient's lifestyle. The knowledge of the mechanical behavior of materials used in AM and producible geometries is an essential requirement to profit and improve this characteristic: in particular, recent studies focus on the correlation between strength parameters and relative porosity of the part. In a previous work a set of tensile tests have been performed on different types of specimens, reproducing a set of corresponding emptying strategies, with different resulting porosity rates, and a linear predictive model has been proposed. Aim of this work is to integrate the already acquired data, providing an interpretation on previous results by numerical simulations: the influence of porosity rate on mechanical properties was investigated by performing both global and local Finite Element Analyses, finding out an explanation on inverse proportionality between material strength properties and porosity rate. The methodology proved to be a profitable way in the optimization of lattice structures for Additive Manufacturing. © 2012 Elsevier Ltd.

Keywords: Additive Manufacturing | Cellular structures | Finite Element Analysis | Polyamide | Selective Laser Sintering

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

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.

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.

Abstract: This is a case of unilateral masseter muscle hypertrophy (MMH) treated with botulinum toxin (NHAI - normalised hemi-facial asymmetry index improvement from 5.48 to 3.04). After 19 months, the treatment was repeated because of hypertrophy relapse (NHAI increase up to 6.82). The volume variations in the masseter area were monitored during 25 months using a laser scanner to compute facial volume. In order to relate the cause of hypertrophy and relapse to the presence of parafunctional activities, a nocturnal electromyography (EMG) study was conducted with positive results (nocturnal parafunctions of patients 4074.99 μV to be compared with a control group value of 1644.63 μV). The lack of the left inferior molars and the consequent right occlusal support seemed to justify the hypertrophy of right masseter (MMRight-POC [percent overlapping coefficient] 91.9%). However, the prosthetic rehabilitation did not prevent relapse in the same muscle. The EMG analysis of both the muscular activation (MMRight-POC 66.0% after relapse) and inhibition activity in Maximum Voluntary Clench (MVC) resulted in contradictory conclusions. At present, the available knowledge regarding MMH physiopathology is very limited and does not support a therapeutic rationale for relapse prevention. © 2009 by CHROMA, Inc.

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

Abstract: BACKGROUND: Current methodologies in the prevision of post-surgical features of the face in orthognathic surgery are mainly 2-D. An improvement is certainly given by the introduction of CT, but its acceptance is controversial due to its high biological cost. As an alternative, in this study an effective procedure for the construction of a 3-D textured digital model of the face and dental arches of patients with dentofacial malformations using a 3-D laser scanner at no biological cost is presented. METHODS: A 3-D Laser scanner Konica-Minolta VIVID 910 is used to obtain multiple scans from different perspectives of the face of patients with dentofacial malocclusions requiring orthognathic surgery. These multiple views are then recombined, integrating also the maxillary and mandibular arch plaster casts, to obtain the 3-D textured model of the face and occlusion with minimal error. RESULTS: A viable methodology was identified for the face and occlusal modeling of orthognathic patients and validated in a test case, confirming its effectiveness: the 3-D model created accurately describes the actual features of the patient's face; the proposed methodology can be easily applied in the clinical routine to accurately record the steps of the surgical treatment and to perform accurate anthropometric analyses of the facial morphology, and thus constitute the necessary database for the development of previsional tools in orthognathic surgery. CONCLUSIONS: The proposed method is effective in recording all the morphological facial features of patients with dentofacial malformations, to develop a facial modification database and tools for virtual surgery.

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.

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

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.

Abstract: An important aspect in developing "intelligent" CAD systems is related to methodologies which are reliable both in handling the relevant information and in modelling the design processes themselves. The intrinsically dynamic nature of these last makes particularly difficult choosing the most suitable methodology to use. This paper describes a prototype Design System, which is capable of generating and dynamically modifying models of design processes and product data that can be considered as Engineering Knowledge Data Bases. The system, implemented in LPA-Prolog++, is based on a hybrid approach that enforces both the Object-Oriented and the Frame paradigms. Frames are mainly devoted to the implementation of the computational model required by the components involved in the design process, while classes are used to assure the inheritance of properties when objects are instantiated or specialized. Information in the Knowledge Data Base is structured using two types of frames: dataFrames, that support the static computational model of the low level components; and linkFrames, that allow for the collection of the low level components into more complex ones without restraining the activation sequence of the pointed frames. In addition, the management of history slots was added to the system in order to associate to the data and process models, at an atomic level, all information related to the rationale of the choices made. The functionality of the system is presented by means of relevant test cases. © 2001 Elsevier Science Ltd.

Keywords: Computer-aided design | Dynamic management | Product data