Geometric modeling and processing

This book is intended for students, academics, designers, process engineers and CMM operators, and presents the ISO GPS and the ASME GD&T rules and concepts. The Geometric Product Specification (GPS) and Geometrical Dimensioning and Tolerancing (GD&T) languages are in fact the most powerful tools available to link the perfect geometrical world of models and drawings to the imperfect world of manufactured parts and assemblies. The topics include a complete description of all the ISO GPS terminology, datum systems, MMR and LMR requirements, inspection, and gauging principles. Moreover, the differences between ISO GPS and the American ASME Y14.5 standards are shown as a guide and reference to help in the interpretation of drawings of the most common dimensioning and tolerancing specifications. The book may be used for engineering courses and for professional grade programmes, and it has been designed to cover the fundamental geometric tolerancing applications as well as the more advanced ones. Academics and professionals alike will find it to be an excellent teaching and research tool, as well as an easy-to-use guide. This 2nd, revised edition includes several improved features: - It highlights the tools provided in the recently published ISO GPS standards, such as ISO 22081-2021 and ISO 2692-2021. - New concepts and rules in accordance with the latest revision to the GD&T standard, ASME Y14.5.1-2019, Mathematical Definition of Dimensioning and Tolerancing Principles. - Most of the drawings have been redrawn and updated even further to the new standards. - Changes have been made to the text and illustrations to improve readability and clarify the content Additional contents and examples have been included. - The chapters dedicated to profile tolerance and tolerances (ISO 14405) have been extended and rewritten.

Keywords: Computer-Aided Design , engineering design , Geometric Product Specification , Geometrical Dimensioning , Geometrical Tolerancing , product design , SOLIDWORKS , Technical drawing

Knowledge of the cognitive processes underlying engineering design is essential for its comprehensive understanding and subsequent enhancement of the field. This paper contributes to building this knowledge by investigating the brain activity of engineering designers engaged in three visuospatial reasoning tasks of the Purdue Spatial Visualization Test (PSVT). These tasks assess three critical visuospatial factors for engineering design: spatial visualization, mental rotation, and spatial orientation. Brain activity is measured using electroencephalography (EEG) as a non-invasive neuroimaging method. The EEG results reveal significant differences in brain activity between the three tasks, considering three frequency bands (theta, alpha, and beta) and 14 electrodes spatially distributed across two hemispheres and seven cortical areas. Theta and beta task-related power (TRP) appear to be crucial in distinguishing among the visuospatial reasoning tasks at the neurocognitive level.

This chapter presents the dynamics and interplay of individual and collaborative use of ICT tools during a design project-based learning course. During the COVID-19 pandemic, five teams (8-9 members) with members from Croatia, Italy, Slovenia, and Austria worked in a geographically distributed context. The results show that students utilise both individual and collaborative working modes. However, the dynamics of ICT use differ throughout the course. Typical design tools for 3D modelling become predominant just in the later course phases. In contrast, visualisa tion tools are used more during the initial phases. Finally, findings suggest that remote collaboration requires continuous and frequent use of communication tools (video conferencing and instant messaging) throughout the whole course. The presented f indings can help educators and researchers in engineering education better structure their classes in post-pandemic settings.

Autologous ear reconstruction is a surgical procedure aimed at total or partial reconstruction of the ear of patients with microtia, which is a malformation or absence of the anatomical element. This procedure involves harvesting cartilage material from the patient at the costal level, cut and sculpt the tissue to create the skeleton of the ear, which is then inserted into a subcutaneous pocket in the malformed region. The sculping procedure takes inspiration from the geometry of the patient's contralateral healthy ear and can be very complex given the particularity of the elements to be reconstructed. Taking advantage of Reverse Engineering and Additive Manufacturing technologies, the authors, in collaboration with hospital staff, proposed patient-specific three-dimensional cutting guides that can facilitate the surgeon in sculpting the ear structure. In this work, a fully automated procedure for creating the printable digital model of such guides is proposed: at first is performed the segmentation of ear elements, which represent the starting data for the automated CAD modelling of the surgical guides. The automatic CAD modelling procedure was tested and validated by medical personnel.

Keywords: CAD Modelling , Ear Reconstruction , Reverse Engineering , Surgical Guide

The growing attention of people to aesthetics has led to a greater demand for dental whitening treatments. Several solutions can be utilized to obtain the desired visual whiteness of teeth but, according to literature, at-home supervised treatments are the standard in dental bleaching. They require soft plastic trays to contain a whitening gel, with active chemical agents, and keep it in contact with the patient's teeth. The fitting, comfort, and tightness of trays play a fundamental role in the treatment. Any gel leakage can compromise the effectiveness of the treatment and damage soft tissues. Commonly, the trays are ready-made or based on physical dental impressions and manually modified by the dental technician. These procedures have low repeatability and do not always ensure high accuracy. This work presents an automatic digital algorithm to design customized whitening trays. Starting from a digital scan acquisition of the patient's dental arches, it generates the 3D models of the bespoke trays, in approximately two minutes per arch, ready to be produced by additive manufacturing and thermoforming technologies. The evaluation of the method involved 20 patients. The results emphasize that the custom trays were comfortable and ensured high levels of tightness and fitting.

Keywords: automatic product design , custom teeth trays , dental whitening , digital process

This work aims at the development of a streamlined and robust CAD procedure to design load-bearing implants. The methodology used to reach this result is explained in the paper: 3D digital anatomy reconstruction of defective structures of the patient is performed with the help of a statistical shape model; subsequently, a CAD modelling tool based on implicit modelling (i.e., nTopology) is used to implement a repeatable semi-automatic procedure that can be performed by a competent user with little effort and limited manual operations. Once that the main shape of the implant is defined, lattice geometries are generated to improve mechanical properties of the implant. The procedure requires as inputs the reconstructed anatomy of the patient and a series of clinical indications on the type of implant that needs to be designed. The paper discusses the development of the whole procedure; achieved results, which include the application of the whole framework on multiple case studies, are presented. The procedure allows the design of a whole implant in 20 minutes circa.

Keywords: CAD Design Automation , Custom Implant; Additive Manufacturing , Implicit Modelling , nTopology

The huge possibilities generated by the introduction of rapid prototyping techniques in the medical field has paved the way for collaborations between physicians and engineers to produce personalized medical devices, tailored to the specific anatomy of the patient. Specifically, in the field of autologous auricular reconstruction, i.e. the reconstruction of the external ear using the patient's costal cartilage, the authors worked towards the development of new patient-specific intraoperative devices, to support the surgeon during the procedure. The surgical guide design was then supported by the development of automated techniques for their modelling. In this work, a new hybrid technique for the CAD modelling of surgical guides is proposed. The idea is not to totally eliminate the intervention of the physician in defining the shape of the surgical guides, but rather to simplify their interaction with design tools. The proposed method is based on the straightforward adaption of a two-dimensional template developed by evaluating various auricular biometric parameters to approximate ear structure. The template is coupled to a parametric automatic procedure that generates the surgical guides' CAD model. The template was created outside of commercial CAD modeling software packages to make the procedure more accessible, and it is managed using a well-designed graphical user interface. With specialized questionnaires to evaluate the surgeon's satisfaction, the interface was put to the test, and the results were positive.

Keywords: 3D Modelling , Autologous Ear Reconstruction , CAD , Microtia , Personalized Medicine , Reverse Engineering

The design of a sailing yacht is mostly based on the traditional design techniques of trial-and-error which takes time and requires iterative corrections to reach the final result. Moreover, several design teams with different and complementary expertise are required. If the standpoint is the one of the designs of a pleasure yacht, most of the activities can be solved through the related standards. While, concerning regatta's yacht, more deep investigations become mandatory and intensive application of digital design instruments is now a common practice in modern yacht design. In this paper, a parametric procedure has been set up aimed to design and numerically compare sailing hulls performances. The hull shape design follows the classical approach based on the definition of the main curves frame and the generation of a parametric surface. Preliminary information about the hull resistance can be quickly obtained with a dedicated module of the software. Once a satisfactory shape has been modeled, detailed investigations can be automatically executed with commercial fluid dynamics software. The procedure has been successfully applied to the design of a new boat belonging to a specific class-called 1001VELAcup R3- which is two people racing dinghy designed according to a box rule with limitations on materials, dimensions and total sail area. The availability of experimental data suggested the numerical investigation about the influence of the hull geometry on the sailing performances.

Keywords: CAD modeling , Numerical investigation , Yacht design

Industrial Robots (IRs) are increasingly adopted for material subtraction or deposition functions owing to their advantages over machine tools, like cost-effectiveness and versatility. Unfortunately, the development of efficient robot manufacturing processes still faces unsolved issues related to the IRs poor positioning accuracy and to the tool path generation process. Novel engineering methods and tools are needed for CAD based programming of accurate paths and continuous robot motions to obtain the required manufacturing quality and tolerances. Within this context, to achieve smoothness along the tool path formed by linear G-code segments, the IR controllers' approximation strategies, summarily reported in the manufacturer's manuals, must be considered. The aim of this paper is to present the preliminary work carried out to identify the approximation algorithms of a Kuka IR when executing linear moves. An experimental study is conducted by varying the controller settings and the maximum translational velocity. The robot behavior has been acquired thanks to the controller tracing function and then processed to yield relations readily employable for the interpretation of G-Code commands and the subsequent generation of proper robot motion instructions. The obtained formulas allow to accurately predict the robot geometric path and kinematics within the corner transition between two linear segments.

Keywords: Corner smoothing , G-code translation , Manufacturing robots , Path approximation , Robot programming

Design For Assembly (DFA) aims at improving product design facilitating assembly phases via the application of evaluation metrics and design guidelines. However, DFA analyses are usually performed manually and the adoption of supporting tool is poor. This paper investigates the application of algorithms allowing to extract from CAD assembly models the required data to perform automated DFA analyses, thus providing a tool to support designers' everyday works. In particular, attributes from geometric feature recognition algorithms, solids properties and assembly parts' semantics are leveraged and mapped to the parameters required to accomplish DFA evaluations. The proposed approach is illustrated on a 3D printer for home use. At first, a manual DFA analysis has been performed on the product identifying product BOM, components properties, assembly cycle and times according to models in the literature. Then, the CAD model of the printer has been processed with some geometric algorithms to verify the possibility to extract the required data to be used as input to the DFA analysis. The test case has demonstrated the feasibility of the approach, even if some design considerations and improvement directions still need the critical evaluation of the designer.

Keywords: Assembly semantics , Design For Assembly , Feature recognition , Part recognition

The production of large-sized optical components with complex shapes requires several phases, including surface finishing. Currently, mainly skilled workers can correctly perform this operation, divided into the successive steps of grinding and polishing, leading to long production times, poor reproducibility of results, and exposure to human error. For this reason, the industry is trying to move towards automation involving, for example, high-precision machine tools and machining centers. However, these solutions require high investment costs and long setup times. Using robotic cells helps to reduce these expenses, manufacture larger components, and increase the flexibility in the production chain. In this research, we present an unconventional approach to the robot-assisted grinding of optical samples made of borosilicate crown glass. The samples were guided by a six-degree-of-freedom industrial robot on a rotating grinding disc while imposing to them different trajectories with complex geometry. We avoided regular grinding patterns, which are easily recognizable by human eyes and affect the quality assessment, by superposing multiple relative movements between the machined surface and the abrasive grains. The ground surfaces of the samples were characterized based on average roughness values, profile error data, and surface topography images. Finally, we selected the best robotic grinding procedure matching the trajectory and strategy with optimal surface quality, processing time, and productivity. The suggested methodology not only shortens the manufacturing sequence by eliminating manual methods but also provides components with optical properties within the required specifications for subsequent polishing steps.

Keywords: Borosilicate crown glass , Industrial robot , Superposed trajectories , Surface grinding , Surface quality

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

Preface and Acknowledgements (Editorial)

Keywords: Editorial

In the Model-Based Enterprise (MBE) paradigm, digital product models are the primary source of information to support the design, analysis, and manufacturing of products. The master geometry of these product models is generally built procedurally in a CAD system, typically as history-based parametric geometry. However, some model conversion and exchange processes imply losing procedural information (i.e. the internal structure that represents how the model was built). In this position paper, we review the state of the art in procedural CAD model exchange and discuss an approach for conveying procedural information during model exchange. Although not available in practice, the approach is currently theoretically feasible, as the exchange of procedural information is already supported in modern neutral formats. Finally, we develop our position by advocating for defining Conformance Classes to facilitate the practical development of the ISO 10303 AP 242 standard, thus enabling official implementations that can provide full exchange capabilities for procedural CAD models.

Keywords: Neutral formats , Procedural CAD models , STEP

Composite sandwich panels with honeycomb, corrugated, tetrahedral, trapezoidal, 3D periodic and hybrid lattice cores have long been studied for their use in various industrial fields. In this study, several numerical analyses were conducted in ANSYS APDL environment in order to analyze the effect of a novel bi-directional corrugated core configuration on the flexural performance of a CFRP sandwich panel. In particular, the sandwich core is obtained by repeating a regular unit cell in two different directions to form a three-dimensional lattice structure. In order to determine the optimal values of the geometrical parameters of the core unit cell and to evaluate how the layout of the composite laminate could affect the mechanical performances of the structure, a numerical study was conducted by using the Group Search Optimizer (GSO) algorithm, a metaheuristic animal-inspired optimization algorithm used to solve various real-world problems. The obtained results show that the GSO algorithm is very effective to optimize the main geometrical parameters of the composite sandwich panel with the novel bi-directional corrugated core. More generally, the implemented procedure provides an open framework to solve complex optimization problems that are very difficult to solve using exact methods, making the GSO algorithm particularly attractive for many industrial applications.

Keywords: ANSYS , Finite element analysis , Group search optimizer , Numerical optimization

In this work a Reverse Engineering based approach has been implemented aiming to reconstruct the 3D shape of a strongly damaged and no longer usable impeller of a submersible centrifugal pump. After obtaining the 3D model, new designs of the impeller were investigated in terms of structural stability and corrosion resistance by changing the geometry and the material. Obtained results show the used approach can be very useful both to reproduce, by Additive Manufacturing, no longer available spare parts, so allowing to extend the useful life of old machineries and to reduce costs resulting from plant shutdowns, but also to improve the performances of old designs, making use of different materials and new manufacturing processes.

Keywords: CAD , Centrifugal pump , Impeller , Modal analysis , Reverse Engineering

The paper presents a preliminary design activity and virtual prototyping of an innovative boat equipped with hydrofoils and hybrid propulsion, with the aim of extending the foil technology from the field of competition boats to recreational day-cruiser yachts and creating a craft with minimal environmental impact. Hydrofoils allow boats to rise from the water, greatly reducing resistance and increasing performance. The current work dealt with the preliminary design of a daysailer with foil technology and hybrid propulsion that allow to combine green and comfortable navigation both under sail and motor and that, when required, can sail in a more performing way by exploiting the foil technology and the thrust of the wind. After having deepened the theory and physics of sailing on foils, a MATLAB code was created to integrate the stability equations that characterize hydrofoil sailboats: connecting the acting forces and allowing to define the dimensions of the geometries, the code was fundamental in speeding up the iterative preliminary design process. The next step was to model the geometry of the hull and the appendages in the CAD environment and, subsequently, the wing movement mechanism so that it could both manage the incidence of the wings and retract the foils when the boat is moored. The hull, profiles, and wings were subsequently placed in a CFD and VPP virtual environment for testing their resistance. Future developments will include a detailed design and the physical prototyping of a first boat for water testing.

Keywords: Green , Hybrid , Hydrofoil , Virtual prototyping

Nowadays, 10–34% of patients undergone Total Knee Arthroplasty (TKA) continues to have pain and reduced mobility. New technologies in TKA have been developed to reproduce the native anatomy, respecting the natural joint line, by means of customized implants or following the kinematic alignment. In this context, the present research aims at defining a method to create customized implants. In particular, three different situations have been studied. The first condition is the healthy knee, that is used as reference for further analysis. For the second situation, an off-the-shelf prosthesis has been virtually implanted, following the kinematic joint line. In the third solution, a custom-made knee implant has been created. In all the three cases, FEA has been performed to study how load transmission and stability change after TKA. To reach the goal, high resolution Magnetic Resonance (MR) images of a healthy knee have been employed. Three-dimensional models of the knee have been reconstructed through a segmentation process, starting from DICOM images. Hence, the three situations have been studied. Distribution of pressure and stress are comparable in the two solutions, since they both maintain the natural joint line. Improving the kinematic function is crucial to increase patient satisfaction. According to the patient's anatomy, the surgeon can choose between the standard and the personalized prosthesis. The studied customized approach allows to overcome the limits of conventional TKA since it permits to create geometries, which accommodate a variety of anatomical variations.

Keywords: 3D modeling , Customized knee implants , FEA , Kinematic alignment

Tracheomalacia (TM) is a tracheal weakening that causes the cartilage structure to collapse during breathing. The term tracheobronchomalacia (TBM) is used when the bronchi are also implicated in the disease. This illness can be treated in a variety of methods, including the insertion of stents in the cartilage-restricted region. Stents are commercially available in numerous sizes (diameter and length), different shapes and materials. The shape of the stent is chosen based on where the disease is located, while the size is derived from measurements on CT images or by endoscopic investigations. This task is extremely critical for the patient's health since improper stent can have serious and even deadly repercussions for the patient. Therefore, it is necessary to choose a stent that fits the patient's anatomy as closely as possible. To this end, it is possible to employ a three-dimensional model of the investigated anatomy and choose the most suitable type of stent following measurements made on the model itself. In this work, a method to assist physicians in the choice of the stent to be used in TM or TBM patients, is proposed. By analyzing the tracheobronchial tree and measuring successive cross-sections along the centerline of the lumen, the automated procedure allows to localize the diseased area and to identify the optimal shape and size of the stent to be implanted. Four case studies of paediatric patients were performed and the results were validated by a team of physicians specialized in the treatment of upper and lower airways.

Keywords: 3D modelling , Airway obstruction , Reverse engineering , Stent

When dealing with craniofacial impairments, restoring the morphological condition is as crucial as restoring the functional ones to avoid psychosocial disabilities for the patient. For this aim, the accurate location of the midsagittal plane is essential for performing reliable symmetry analyses and guiding effective surgery planning. To provide a fully automatic and landmark-independent approach, capable of providing a midsagittal plane for craniofacial skeleton even from anatomical models with high asymmetries, an innovative method, called MaWR-method, was developed by the authors in a previous work. This paper further investigates the MaWR-method by evaluating its capacity to produce a successful outcome even in the worst-case scenario that may be considered in maxillofacial surgery, namely panfacial fractures. In all the test cases considered in this work, the method proved robust and reliable in its original design. It provided a consistent result requiring no user involvement, even when dealing with extreme asymmetries because of extensive and complex fractures.

Keywords: Feature recognition , Mid-sagittal plane , Symmetry analysis , Symmetry plane detection