Additive manufacturing

With the advent of additive manufacturing (AM) and advanced fiber-reinforced composites, integrating orthotropic material behavior into the design phase is increasingly essential. Unlike isotropic assumptions typically used in topology optimization (TO), orthotropic materials exhibit direction-dependent properties that significantly impact mechanical performance, especially in the build direction due to AM layer-wise construction. Traditional workflows often separate design and manufacturing stages, leading to suboptimal structures when material anisotropy is ignored. This study proposes a design framework that embeds orthotropic elasticity into TO using the Solid Orthotropic Material with Penalization (SOMP) method. Material orientation, directly linked to part build direction, is treated as a variable influencing both product performance and process sustainability. A flat lamina case study illustrates how different fiber alignments affect mechanical behavior, while a second case involving a Formula SAE brake pedal demonstrates the feasibility of redesigning metal parts for composite AM. Key performance indicators (KPIs) are evaluated across material orientations to assess trade-offs in structural performance and manufacturing efficiency. Co-optimizing material orientation and geometry would allow to enhance stiffness-to-weight ratios and reduce waste and post-processing. The findings demonstrate the feasibility of further integrated product and process optimization using topology optimization of orthotropic materials.

Keywords: 3D Printing , CFRP , Design for Additive Manufacturing , Finite Element Method , Material Anisotropy , Sustainable manufacturing

Wire Arc Additive Manufacturing is based on a welding torch usually attached to a robotic arm with multiple degrees of freedom. Robot-based additive manufacturing allows non-planar and non-uniform thickness layers to be deposited where the slices have non-constant thickness. Thus, in addition to the motion settings, fine regulations of the welding parameters become necessary to obtain variable bead heights in the same slice. This paper aims to evaluate the user-accessible welding parameters' influence on the deposited material's dimensions during continuous Cold Metal Transfer (CMT) and its variant named CMT Cycle Step. In particular, the height and width of beads are investigated by varying the travel speed and the wire-feed rate (continuous CMT), as well as the size of the droplets by varying the number of CMT cycles and the wire-feed rate (CMT Cycle Step). In particular, the characterization of the material deposited during the CMT Cycle Step is not deeply studied in the literature. The experimental specimens are measured and the obtained values are numerically processed to yield empirical formulas that link the dimensions of the deposited material with the selected process parameters. The results show that CMT Cycle Step is more stable than continuous CMT, which confirms its higher suitability for accurate manufacturing.

Keywords: Bead Modeling , Cold Metal Transfer , Experimental characterization , Wire and Arc Additive Manufacturing

Planar slicing algorithms with constant layer thickness are widely implemented for geometry processing in Additive Manufacturing (AM). Since the build direction is fixed, a staircase effect is produced, decreasing the final surface finish. Also, support structures are required for overhanging portions. To overcome such limits, AM is combined with manipulators and working tables with multiple degrees of freedom. This is called Robot-Based Additive Manufacturing (RBAM) and it aims to increase the manufacturing flexibility of traditional printers, enabling the deposition of material in multiple directions. In particular, the deposition direction is changed at each layer requiring non-uniform thickness slicing. The total number of layers, as well as the volume of the support structures and the manufacturing time are reduced, while the surface finish and mechanical performance of the final product are increased. This paper presents an algorithm for non-uniform planar slicing developed in Rhinoceros and Grasshopper. It processes the input geometry and uses parameters to capture manufacturing limits. It mostly targets curved geometries to remove the need for support structures, also increasing the part quality.

Keywords: Multiaxial Deposition , Non-Uniform Slicing , Robot-based Additive Manufacturing

Polyether ether ketone (PEEK) is a thermoplastic polymer that presents notable thermal resistance, high mechanical strength, biocompatibility, durability, chemical resistance, and low density. PEEK can be additively manufactured by Power Bed Fusion (PBF) and Material Extrusion (ME) techniques. However, the latter is easier to operate and less expensive than the first solution. Printing parameters and thermal post-processing are fundamental aspects to improve the mechanical and thermal properties of the printed part. In the present study, the effects of two distinct thermal post-processing treatments and three different printing speeds on the mechanical properties of PEEK samples produced by ME were investigated. 45 specimens were manufactured, 15 for each printing speed and 5 for each thermal treatment. The results demonstrated that for the as-printed condition, higher printing speeds produced the greatest outcomes in terms of ultimate tensile strength and elastic modulus, whereas the lowest printing speed produced the maximum strain at break. The thermal post-processing treatments revealed that the one carried out at lower temperatures resulted in negligible changes, while the other significantly improved the mechanical performance of the material. The study's findings provide a solid foundation for printing and post-processing a cutting-edge polymer like PEEK to maximize its potential.

Keywords: Material Extrusion , Mechanical Properties , PEEK , Printing Speed , Thermal Post-Processing

Sustainability is fundamental in the field of additive manufacturing (AM) for improving eco-consciousness and driving evolution toward environmentally responsible production methods. Compared to traditional manufacturing processes, AM technologies can be more resource-efficient and offer innovative solutions for creating eco-friendly processes and products. Nevertheless, there is significant potential for improvement in additive manufacturing sustainability. The key factors driving this improvement include design optimization and increased awareness. Designers and engineers can create designs that optimize material efficiency and reduce support structures. Raising awareness and educating stakeholders about the environmental benefits of AM can promote responsible choices throughout the industrial process. The development of a tool to assess the environmental impact of AM processes could be a significant contribution to advancing sustainability in the AM field. The EcoPrintAnalyzer, introduced as a complementary plugin for UltiMaker Cura, offers data on the equivalent carbon dioxide footprint and energy consumption in material extrusion additive manufacturing. This tool facilitates informed decision-making regarding materials, designs, and settings, enabling users to optimize their AM processes for reduced waste and enhanced energy efficiency. Beyond aiding decision-making, the EcoPrintAnalyzer fosters environmental consciousness and encourages the adoption of sustainable practices within the AM ecosystem. The efficacy of the tool is demonstrated through the 3DBenchy model case study, showcasing its intuitive interface and seamless integration within the AM process workflow for immediate and comparative environmental impact assessments across different process configurations.

Keywords: additive manufacturing , carbon footprint , eco-design , material extrusion , sustainability assessment tool , sustainable development , UltiMaker Cura

Nowadays, universities address topics like CAD modeling and additive manufacturing to teach students important aspects of engineering and design. However, the development of a prototype is an iterative process composed of different phases that range from the definition of the problem to the evaluation of the concept The paper describes how to integrate all these phases for active learning in the course Computer-Aided Design and Mechanical Prototyping, which is part of the Master's Degree in Mechanical Engineering program at Politecnico di Milano. The final project assigned as a case study to students consists in the development of a rehabilitative hand exoskeleton. The paper presents how students faced the different phases of the development process till the final prototype and its evaluation with healthy subjects and some post-stroke patients. The methodology applied to the course was really appreciated by students, in particular, the experience of designing different devices from scratch. They were challenged in different areas, like mechanics, electronics, informatics, and manual work, which allowed them to range widely during the design and manufacturing process and to extend considerably their knowledge.

Keywords: additive manufacturing , CAD modeling , engineering education , hand exoskeleton , interactive applications

This article focuses on enhancing the range of motion (ROM) of the Tetra II joint, a spherical compliant joint consisting of three internally interconnected tetrahedron-shaped elements that achieve motion through elastic deformation. Despite its excellent precision, this specific design is constrained in terms of ROM due to internal contacts among the tetrahedral elements. To overcome this limitation, this study utilizes a computer-aided engineering (CAE) framework to optimize the configuration of the Tetra II joint and enhance its ROM. The resultant optimized joint, referred to as Tetra III, is subsequently compared to Tetra II in terms of both ROM and center shift. Finite element models (FEM) are employed to validate the optimization results and examine how various tetrahedron-shaped geometries impact the joint's performance. The newly optimized joint exhibits a significantly higher ROM compared to the previous version, while maintaining excellent precision and overall smaller dimensions. Finally, to demonstrate its manufacturability, the Tetra III joint is produced using selective laser sintering (SLS) technology, with Duraform PA serving as the construction material. The successful fabrication serves as a demonstrative example of the improved design of the Tetra III joint.

Keywords: CAE , Compliant mechanisms , Flexure , PRBM , SLS , Spherical joint , Tetrahedron

This article presents a new design for a two-degrees-of-freedom compliant robotic wrist for upper limb prostheses that matches the maximum range of motion of a human wrist by utilizing cross axis flexural pivot (CAFP) as compliant joints. The wrist design is manufactured using additive manufacturing technology as a single, monolithic component. An optimization routine that utilizes the bi-beam constraint model technique to synthesize compliant joints in the wrist design is presented and verified using finite element analysis (FEA). This optimization routine includes the computation of passive contact profiles through the centroid approach to prevent buckling in the CAFP compliant beams caused by external forces. Furthermore, an accurate analysis of various tendon routing paths for the actuation of the wrist is conducted, providing a flexible and reliable solution to avoid unnecessary power consumption. The proposed wrist is lightweight, cost-effective, easy to maintain, and thanks to the utilization of CAFP joints, it is frictionless and immune to backlash. Experimental tests are conducted to verify the FEA results and confirm the range of motion achieved by the joint (i.e., <inline-formula><tex-math notation="LaTeX">$\pm 80^{\circ }$</tex-math></inline-formula> of flexion/extension, <inline-formula><tex-math notation="LaTeX">$\pm 40^{\circ }$</tex-math></inline-formula> of ulnar/radial deviation). Overall, this article demonstrates the development of a novel compliant robotic wrist that offers several advantages over traditional prostheses, including a wider range of motion, increased flexibility, and reduced maintenance costs.

Keywords: 2-DOF , Additive manufacturing , compliant mechanisms (CMs) , cross axis flexural pivot (CAFP) , monolithic design , Motion control , Optimization , prosthetic wrist , Prosthetics , Read only memory , Robots , Wrist

Additive Manufacturing is becoming a widespread manufacturing system in several industrial fields such as automotive, aerospace, biomedical, etc. Design for Additive Manufacturing represents the branch of research that considers the technological constraints from the early stages of design, arriving at a geometrical model to be exported in G-code. The limitations of additive manufacturing are related to the complexity of the process, the high costs, the processing time, and the difficulties of ensuring adequate geometric and dimensional tolerances. A data-driven approach can be a solution to improve the Design for Additive Manufacturing. Artificial Intelligence and Machine Learning methods are employed in the literature to shorten the time for assessing the optimal combination of parameters and supporting decision-making. The current state of the art shows three macro-areas to apply Machine Learning methods in Design for Additive Manufacturing. These applications concern Geometrical Design Level, Process Configuration Level, and Process Monitoring Level. This paper aims to identify and classify the Machine Learning methods and algorithms most used in Design for Additive Manufacturing practices, analyzing parameters, results, processes, and materials involved.

Keywords: Additive Manufacturing , Artificial Intelligence , Design for Additive Manufacturing , Machine Learning

Approximately 50% of the adult global population is projected to suffer from some form of metabolic disease by 2050, including metabolic syndrome and diabetes mellitus. At the same time, this trend indicates a potential increase in the number of patients who will be in need of implant-supported reconstructions of specific bone regions subjected to inflammatory states. Moreover, physiological conditions associated with dysmetabolic subjects have been suggested to contribute to the severity of bone loss after bone implant insertion. However, there is a perspective evidence strengthening the hypothesis that custom-fabricated bioengineered scaffolds may produce favorable bone healing effects in case of altered endocrine or metabolic conditions. This perspective review aims to share a comprehensive knowledge of the mechanisms implicated in bone resorption and remodelling processes, which have driven researchers to develop metallic implants as the cobalt-chromium (Co-Cr) bioscaffolds, presenting optimized geometries that interact in an effective way with the osteogenetic precursor cells, especially in the cases of perturbed endocrine or metabolic conditions.

Keywords: 3D-printed scaffolds , cobalt-chromium (Co-Cr) bioscaffolds , customized medicine , endocrine metabolic and immune disorders , regenerative medicine , tissue engineering , translational medicine

The Laser Powder Bed Fusion (LPBF) is an Additive Manufacturing (AM) technology suitable to produce almost free-form metallic components. At Legnaro National Laboratories (LNL) of the Italian National Institute for Nuclear Physics (INFN), the LPBF process was recently used to produce parts of the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source for the SPES Isotope Separation On-Line (ISOL) facility. In this work are presented the feasibility assessment and production steps of tantalum cathodes produced via AM; in addition, the results concerning both the dimensional–geometrical measurements and the preliminary high-temperature test are reported.

The growing cooperation between physicians and engineers have been producing increasingly sophisticated anatomical phantoms for the training and planning of Structural Heart Surgery. Trans-Septal Puncture (TP) is a percutaneous, non-invasive cardio chirurgical procedure used to access the heart Left Atrium from the Right Atrium through the Fossa Ovalis (FO), a region of the Inter Atrial Septum with reduced thickness. TP is technically challenging and requires dedicated teaching and a skillful operator; as a result, application of phantoms to TP training have been gaining increasing interest. The aim of the present work is to investigate the current state of the art in TP simulators. The Scopus and PubMed databases were analyzed and the bibliography of the most impacting articles was reviewed. The results can be summarized as follows: i) mold casting and additive manufacturing (AM) are the only technologies documented for phantoms creation; ii) silicone rubbers and Polyvinyl Alcohol Cryogel are the most used materials for mold casting while Polyjet polymers are the most used material for AM; iii) quantitative data on force and haptic feedback from IAS and FO simulacra is scarcely documented; iv) procedure image guidance can be simulated during the training.

Keywords: Additive Manufacturing , Material Characterization , Medical Phantoms , Silicone Casting , Trans-Septal Puncture

The use of customized surgical guides for the removal of bone tumors is an increasingly common practice in advanced hospitals. These devices are modeled directly on the 3D model of the patient's anatomy and produced using additive techniques; therefore, they have the ability to perfectly anchor to the bone anatomy and allow the tissue of the tumor mass to be removed according to cutting paths predetermined by the physician during preoperative planning. This work proposes a semi-automatic framework for modeling custom surgical guides composed of two main modules: 1) a web application, called Precise, that allows the surgeon to visualize and manipulate 3D anatomical models and enter a set of cutting planes that determine the correct tumor resection paths and other useful information for modeling the surgical guide; 2) a fully automatic procedure that based on this information creates the guide's STL model. The entire procedure aims to create a specific type of cutting guide designed to guide an oscillating saw in a series of planar cuts, thus isolating the tumor. The cutting guides produced are composed of three main elements: a base, the blade slot, and pin's holes.

Keywords: Medical 3D Model , Medical Application , Rapid Prototyping , Surgical Planning

The increasing demand for designing complex structures using Functionally Graded Material boosts the research on reliable joining processes. For several industrial applications in the automotive, tooling, and petrochemical industries, the joining of a stainless steel with a low-alloy steel is often required to obtain a variation of mechanical and corrosion properties when different parts of the same structure are subjected to different working conditions. Welding a stainless steel with a low-alloy steel is a challenging operation because it is not easy to control the microstructure of the welded joint and to avoid metallurgical defects such as hot cracks. Moreover, traditional welding methods can only be applied to relatively simple geometries. To design and produce multi-material components, characterised by complex geometries, Selective Laser Melting process capabilities can be exploited. In this paper, an AISI 316L stainless steel is joined to 16MnCr5 steel by carefully tuning the process parameters. Metallurgical investigations coupled with Energy Dispersion Spectroscopy analyses allowed to evaluate the soundness of the joint and the effect of the process thermal cycle on the alloy microstructures and properties. The results are very promising and show that a careful selection of process parameters allows to obtain a continuous joint.

Keywords: 16MnCr5 , AISI 316L , Functionally Graded Material , Microstructure , Selective Laser Melting

Autologous ear reconstruction is a surgical procedure which aims to restore the anatomy of the outer ear whenever there are malformations due to congenital defects (microtia) or as a result of trauma and burns. Reconstruction involves the cutting, carving, and modeling of a portion of costal cartilage harvested from the patient. The aesthetic results of the surgery are highly dependent on the manual skill of the surgeon, which therefore needs a wide range of surgical experience. Appropriate simulation and training tools are essential to acquire adequate familiarity with the procedure without compromising the patient's aesthetic appearance. In such a context, the present work aims to create replicas of the costal cartilage that allow a realistic simulation of the surgery, thus taking into account important characteristics of the cartilage tissue such as the behavior to cut and suture, hardness, etc. The problem is approached with well-established Additive Manufacturing and Reverse Engineering techniques, which are increasingly being used in the medical field, addressing both the problem of identifying the most suitable materials and the possibility of providing medical personnel with simple interactive procedures for the fabrication of multilayer replicas, without the need to turn to expert CAD modelers.

Keywords: CAD modeling , Costal cartilage mold , Ear reconstruction , Medical simulation

Additive Manufacturing is widely applied in aerospace, automotive and marine engineering. Indeed, large-scale components are often required in these applications, such as for non-structural parts of aircraft, spare parts or small lots of cars or marine components. Fused Deposition Modelling is one of the Additive Manufacturing processes used to affordably convert digital models into mockups, prototypes, and functional parts: a slicing software converts the object's digital model into a list of instructions for the machine. However, commercial slicing software packages often fail to accurately estimate the time required to produce models, especially when their size is significant: the errors could be up to several hours, which cannot be adequate in a real-life industrial context where production must be scheduled in a precise way. This manuscript compares the build time estimation of several commercial slicing software considering a real-life part. Furthermore, the evaluation of the manufacturing setting mainly affects the error in estimating the build time achieved through a Design of Experiment approach. The more time-impacting printing parameters have been detected, allowing fine helpful tuning to increase the accuracy of the build time in commercial slicing software. A case study included in the manuscript supports the analyses. Proper setting of the commercial slicing software can significantly improve the accuracy of the printing time.

Keywords: Additive Manufacturing , Design of Experiment , Fused Deposition Modelling , Slicing , Time Estimation

This study aims to evaluate the advantages and criticalities of applying additive manufacturing to produce climbing holds replicating real rocky surfaces. A sample of a rocky surface has been reproduced with a budget-friendly 3D scanner exploiting structured light and made in additive manufacturing. The methodology is designed to build a high-fidelity replica of the rocky surface using only minor geometry modifications to convert a 2D triangulated surface into a 3D watertight model optimised for additive manufacturing. In addition, the research uses a novel design and uncertainty estimation approach. The proposed methodology proved capable of replicating a rocky sample with sub-millimetre accuracy, which is more realistic than conventional screw-on plastic holds currently used in climbing gyms. The advantages can be addressed in terms of customisation, manufacturing cost and time reduction that could lead to real outdoor climbing experiences in indoor environments by coupling additive manufacturing techniques and reverse engineering (RE). However, operating the scanner in a rocky environment and the considerable size of the climbing routes suggest that further research is needed to extend the proposed methodology to real case studies. Further analysis should focus on selecting the best material and additive manufacturing technology to produce structural components for climbing environments.

Keywords: 3D scanning , Additive manufacturing , Climbing holds , Fused deposition modelling , Reverse engineering , Uncertainty quantification

In the last decades, the adoption of assistive devices has been spreading among different application fields, starting from the rehabilitative medicine to the industrial field. In particular, exoskeletons aimed to ease the operations performed by workers have been developed in order to reduce the entity of work-related musculoskeletal disorders, limiting the inconvenience caused to the workers and reducing therapy-related costs faced by the employer or the healthcare system. However, commercial full-body exoskeletons equipped with efficient, low-weight actuation systems require a huge investment (both for purchase and maintenance), which only a few companies are willing to pay. In order to achieve high performance while limiting costs and complexity, a custom cycloidal reduction was designed: because of its back-drivability and scalability, it represents a low-cost solution capable of maximizing the overall performances of the assistive device. In this paper, the methodology to define a custom low-cost yet efficient cycloidal drive actuation is hence proposed, as well as its implementation in the design of a low-back exoskeleton based on backbone kinematics.

Keywords: additive manufacturing , back-drivable reduction , cycloidal transmission , fast pro-totyping , FEM , low-back exoskeleton

This work aims at investigating the causes affecting the dimensional and geometrical accuracy of holes in metal binder jetting stainless steel parts. Parallelepiped samples with a through hole were produced using AISI 316L and 17-4PH powders, differing for diameter (3, 4, 5 mm), and position of the axes with respect to the building plane (6, 9, 12 mm distance). Dimensions and geometrical characteristics were measured at green and sintered state by a coordinate measuring machine, determining the dimensional change and the geometrical characteristics. As expected, the shrinkage of linear dimensions is anisotropic; moreover, change in volume and sintered density are significantly affected by the position in the printing chamber. Higher shrinkage was measured along building direction (Z) – 18.5 ÷ 19.5%, than in the building plane – 16.5 ÷ 17.5%, and slightly higher shrinkage – 0.5 ÷ 0.8% was measured along powder spreading direction (X) than binder injection direction (Y). A variation up to 3% in relative density of sintered parts depending on the position in the building plane was observed in 316L. The dimensional change of diameters generally confirmed the shrinkage predicted by the model previously developed—difference between real and expected dimensional changes lower than 3%, except for three geometries (4 ÷ 6%). The cylindricity form error of sintered parts was strongly underestimated by the prediction model (up to 0.15 mm), but underestimation was considerably reduced (generally lower than 0.05 mm) adding the cylindricity form error due to printing. Dimensional and geometrical accuracy of holes are strongly affected by shape distortion of the parallelepiped geometry, in turn due to layer shifting and inhomogeneous green density during printing, and to the effect of frictional forces with trays during sintering. Gravity load effect was also observed on the holes closest to the building plane. Future work will improve the reliability of the prediction model implementing the results of the present work.

Keywords: Additive manufacturing , Dimensional and geometrical accuracy and precision , Metal binder jetting , Shrinkage on sintering

This work aims at evaluating the dimensional precision and the accuracy achievable through the Metal Binder Jetting Additive Manufacturing process. An artifact was designed, and 36 replicates were produced using a 17-4PH stainless steel powder aiming at evaluating different feature sizes. The dimensions of the samples were measured by a coordinate measuring machine (CMM) before and after sintering. At green state, the distribution of measured dimensions parallel to the building direction was centered on the nominal dimension, while the distribution of measured dimensions parallel to the building plane was shifted from the nominal ones. Dimensions of cavities were found to be significantly smaller than nominal ones (Z position for fundamental deviation), whereas the dimensions of outer features were larger than the nominal sizes probably on the reason of excessive binder saturation. The dimensional precision ranged from IT9 to IT11. After sintering, the inaccuracy increased with the distance of samples from the building plane, in turn related to non-uniform shrinkage on sintering. Additionally, sintering determined worsening in the dimensional precision, which ranged from IT11 to IT15.

Keywords: Design for AM , Dimensional Precision and Accuracy , Metal Binder Jetting