Energy and cost assessment of 3D printed mobile case covers

Sustainable manufacturing emphasizes efficient production,whilst upholding economic, environmental, and societal commitments. One major challenge for sustainability arises in short lifecycle products such as mobile phone covers. The market demands quick product launch and responsive fulfilment, which is typically achieved through make-to-stock production using injection moulding. This approach necessitates production is based on demand forecasts, which frequently leads to overproduction and much unsold waste product. 3D printing technologies enable a make-to-order production model, allowing customers to self-manufacture mass customized products as needed. Moreover, in the framework of circular economy, 3D printing empowers the final user with full control of the end-of-life product disposal management. These capabilities suggest 3D printing may afford improved sustainability, but to-date there has been little empirical validation of this proposition. This paper addresses this gap through a comparison of 3D printed and injection moulded production, providing a detailed quantitative evaluation of energy and costs for both manufacturing approaches

Analysis of Density, Roughness, and Accuracy of the Atomic Diffusion Additive Manufacturing (ADAM) Process for Metal Parts

Atomic Diffusion Additive Manufacturing (ADAM) is a recent layer-wise process patented by Markforged for metals based on material extrusion. ADAM can be classified as an indirect additive manufacturing process in which a filament of metal powder encased in a plastic binder is used. After the fabrication of a green part, the plastic binder is removed by the post-treatments of washing and sintering (frittage). The aim of this work is to provide a preliminary characterisation of the ADAM process using Markforged Metal X, the unique system currently available on the market. Particularly, the density of printed 17-4 PH material is investigated, varying the layer thickness and the sample size. The dimensional accuracy of the ADAM process is evaluated using the ISO IT grades of a reference artefact. Due to the deposition strategy, the final density of the material results in being strongly dependent on the layer thickness and the size of the sample. The density of the material is low if compared to the material processed by powder bed AM processes. The superficial roughness is strongly dependent upon the layer thickness, but higher than that of other metal additive manufacturing processes because of the use of raw material in the filament form. The accuracy of the process achieves the IT13 grade that is comparable to that of traditional processes for the production of semi-finished metal parts

A Finite Element approach for the prediction of the mechanical behaviour of layered composites produced by Continuous Filament Fabrication ({CFF})

Continuous Filament Fabrication (CFF) is the additive manufacturing process for producing material reinforced with long fibres. Differently from other processes, CFF allows producing components in composite materials without using tools, moulds or post-processing operations and with a strengthened area only where it is strictly required. This innovative way of producing composites makes a new design approach necessary for better exploitation of the material. This work presents a preliminary study based on 3D Finite Element (FE) method to predict the mechanical behaviour of composite materials fabricated by CFF. With this aim, a FE model is developed to determine the actual material properties in terms of longitudinal, transverse and shear modulus. Comparisons between experimental and numerical tensile results at different fibre orientations validate the model. The robustness of the proposed approach is confirmed by the comparison with the experimental characterisation of composites produced with two different fibre reinforcements, Carbon and Kevlar®

Benchmarking of FDM Machines through Part Quality Using IT Grades

The diffusion of Fused Deposition Modeling (FDM) was recently boosted by the expiration of the FDM patent and the subsequent worldwide development of low cost FDM machines by a huge number of small companies. In most of the cases, FDM machines are worth what they cost. Thus the performance of expensive industrial FDM systems is better than that of low cost machines, also known as 3D printers. In this paper a benchmarking is carried out between a Dimension EliteTM by Stratasys and a 3D TouchTM by Bits from Bytes (BFB). The study and comparison is based on a reference part that was designed to fit into the building volume of most of low cost FDM machines. The part includes several classic geometries (planes, cylinders, spheres and cones) of different sizes to cover several ranges of basic sizes as defined by the ISO 286 standard. Geometric features appear both in the concave and convex shapes to account for all design possibilities. The proposed reference part allows to consider a higher number of features for each range of basic sizes with respect to other benchmarking models presented in the literature. Moreover the part does not require support structures for its production, allowing for manufacturing on 3D printers that come with a unique extruder. Replicas of the reference part are printed out of ABS (acrylonitrile butadiene styrene) material with different layer thicknesses using the compared machines. After inspecting the replicas by means of a Coordinate Measuring Machine (CMM), the dimensional accuracy of the compared FDM systems is reported through part quality using IT grades associated with the ISO basic sizes. GD&T values are also evaluated for some of the geometric features appearing on the reference part

Evaluation of the flexural behaviour of 3D printed multimaterial beams

Among Additive Manufacturing (AM) processes, Fused Deposition Modelling (FDM), more popularly renown as 3D printing1, allows the fabrication of multimaterial parts by extrusion of multiple thermoplastic filaments that are then deposited layer after layer. In such a way parts are built bottom to top and the different materials can be deployed in each cross section according to strategies aiming at optimizing the reinforcement through the exploitation of the design freedom of AM technologies. Most diffused commercial materials for FDM are Acrylonitrile Butadiene Styrene (ABS) and the biodegradable PolyLactic Acid (PLA), that are amorphous polymers characterized by similar mechanical properties. The use of semicrystalline polymers in FDM is often avoided because of the higher amount of shrinkage which causes the warpage of the deployed layers during manufacturing. The innovative aspect of this paper is the use of a filament made of a Polyammide (PA) blend as a reinforcement in multimaterial beams of PLA that are fabricated by FDM. The flexural behaviour of the composite beams is evaluated by three point bending tests according to the ASTM D790 method. Owing to the lack of a specific reference for 3D printing, dimensions of the specimens are assumed equal to those of injection molded specimens. Their nominal overall dimensions are 3.25 x 12.7 x 127 mm. In this preliminary study, test specimens are 3D printed with a core of PA having a rectangular cross section, whose width (w) and height (h) are varied. Bending tests show that the PA core increases both the flexural stiffness and the flexural strength of the PLA beam. Experimental results are compared with those of the finite element (FE) simulation of the bending test performed by using Abaqus/CAE software. 3D printing issues are also considered and discussed along with the influence of the layer by layer fabrication on the beam resistance

Surface Roughness Characterisation and Analysis of the Electron Beam Melting (EBM) Process

Electron Beam Melting (EBM) is a metal powder bed fusion (PBF) process in which the heat source is an electron beam. Differently from other metal PBF processes, today, EBM is used for mass production. As-built EBM parts are clearly recognisable by their surface roughness, which is, in some cases, one of the major limitations of the EBM process. The aim of this work is to investigate the effects of the orientation and the slope of the EBM surfaces on the surface roughness. Additionally, the machine repeatability is studied by measuring the roughness of surfaces built at different positions on the start plate. To these aims, a specific artefact was designed. Replicas of the artefact were produced using an Arcam A2X machine and Ti6Al4V powder. Descriptive and inferential statistical methods were applied to investigate whether the surface morphology was affected by process factors. The results show significant differences between the upward and downward surfaces. The upward surfaces appear less rough than the downward ones, for which a lower standard deviation was obtained in the results. The roughness of the upward surfaces is linearly influenced by the sloping angle, while the heat distribution on the cross-section was found to be a key factor in explaining the roughness of the downward surfaces

Experimental validation of topology optimization of Additive Manufactured polymeric beams subjected to three-point bending test

Topology Optimization (TO) is a powerful tool for the optimization of product geometry and weight for compliance with structural requirements. The shapes generated by TO are generally complex and intricated, but nowadays they can be produced by Additive Manufacturing (AM) or 3D Printing. 3D Printing is the term that is widely used to address layered manufacturing in the case of consumer applications with polymeric materials, while AM mostly refers to industrial applications. The basic algorithm for TO is based on the Solid Isotropic Material with Penalisation (SIMP) method. The increasing importance of AM has recently driven researchers to develop modified versions of the SIMP algorithm for considering the constraints and peculiarities of layered manufacturing, such as the use of lattice structures with intermediate densities or the need to include support structures in the case of overhanging features. Owing to the diffusion of AM and 3D Printing, SIMP methods have also been implemented in many commercial computer aided design and engineering (CAD/CAE) software packages. Specific TO software is also available outside CAD packages. However, the anisotropic nature of layered technologies brings additional challenges for TO methods, especially in the case of load bearing structures. There is the need of improving the performances and the accuracy of TO by considering the peculiarities of the adopted AM techniques and the properties of the specific material. In this work a commercial TO software, SolidThinking Inspire, is used to optimize the geometry of polymeric beams subjected to a three-point bending test under different loading levels. Two different AM technologies are considered to produce the beams: powder bed Selective Laser Sintering (SLS) and material extrusion 3D Printing. Several polymeric materials are used and for the specific AM process the TO calculations are defined by considering the mechanical properties declared by the supplier on the material datasheet. The results of TO are then validated by fabricating and testing replicas of the optimized beams with the corresponding material and process. Starting from the CAD model of a three-point bending beam with some design space for TO, the TO is then executed with different load levels for the different materials and the optimized beam is then fabricated using the corresponding AM process. Finally, the results of the three-point bending test performed on the replicas of the optimized beams are compared to the TO results. Correlation and differences between the experimental behaviour of the beam and the flexural resistance predicted by TO are analysed and discussed

Impact of additive manufacturing on engineering education – evidence from Italy

Purpose - The purpose of this paper is to evaluate how the direct access to additive manufacturing (AM) systems impacts on education of future mechanical engineers, within a Master's program at a top Italian University. Design/methodology/approach - A survey is specifically designed to assess the relevance of entry-level AM within the learning environment, as a tool for project development. The survey is distributed anonymously to three consecutive cohorts of students who attended the course of "computer-aided production (CAP)", within the Master of Science Degree in Mechanical Engineering at Politecnico di Torino. The course includes a practical project, consisting in the design of a polymeric product with multiple components and ending with the production of an assembled prototype. The working assembly is fabricated by the students themselves, who operate a fused deposition modelling (FDM) machine, finish the parts and evaluate assemblability and functionality. The post-course survey covers diverse aspects of the learning process, such as: motivation, knowledge acquisition, new abilities and team-working skills. Responses are analyzed to evaluate students' perception of the usefulness of additive technologies in learning product design and development. Among the projects, one representative case study is selected and discussed. Findings - Results of the research affirm a positive relationship of access to AM devices to perceived interest, motivation and ease of learning of mechanical engineering. Entry-level additive technologies offer a hands-on experience within academia, fostering the acquisition of technical knowledge. Research limitations/implications - The survey is distributed to more than 200 students to cover the full population of the CAP course over three academic years. The year the students participated in the CAP course is not tracked because the instructor was the same and there were no administrative differences. For this reason, the survey administration might be a limitation of the current study. In addition to this, no gender distinction is made because historically, the percentage of female students in Mechanical Engineering courses is about 10 per cent or lower. Although the answers to the survey are anonymous, only 37 per cent of the students gave a feedback. Thus, on the one hand, impact assessment is limited to a sample of about one-third of the complete population, but, on the other hand, the anonymity ensures randomization in the sample selection. Practical implications - Early exposure of forthcoming designers to AM tools can turn into a "think-additive" approach to product design, that is a groundbreaking conception of geometries and product functionalities, leading to the full exploitation of the possibilities offered by additive technologies. Social implications - Shared knowledge can act as a springboard for mass adoption of AM processes. Originality/value - The advantages of adopting AM technologies at different levels of education, for diverse educational purposes and disciplines, are well assessed in the literature. The innovative aspect of this paper is that the impact of AM is evaluated through a feedback coming directly from mechanical engineering students

Investigation of the Mechanical Properties of a Carbon Fibre-Reinforced Nylon Filament for 3D Printing

Additive manufacturing (i.e., 3D printing) has rapidly developed in recent years. In the recent past, many researchers have highlighted the development of in-house filaments for fused filament fabrication (FFF), which can extend the corresponding field of application. Due to the limited mechanical properties and deficient functionality of printed polymer parts, there is a need to develop printable polymer composites that exhibit high performance. This study analyses the actual mechanical characteristics of parts fabricated with a low-cost printer from a carbon fibre-reinforced nylon filament. The results show that the obtained values differ considerably from the values presented in the datasheets of various filament suppliers. Moreover, the hardness and tensile strength are influenced by the building direction, the infill percentage, and the thermal stresses, whereas the resilience is affected only by the building direction. Furthermore, the relationship between the mechanical properties and the filling factor is not linear

Enhancing the dimensional accuracy of a low-cost 3D printer

3D printing is widely used in the entertainment industry by filmmakers, effect studios and game designers to easily and fast fabricate characters or objects that are first virtually modelled through Computer Graphics. There are several commercial proposals in the field of low-cost 3D printers, with prices starting from a few hundred euros for kits that the users should assemble by themselves. However, their performances in terms of part accuracy are quite limited and are basically the consequence of a lack of optimization both in mechanical terms as in software. Starting from these considerations, an optimization project was assigned to the students of the Specializing Master in Industrial Automation of the Politecnico di Torino. The Master is developed in collaboration with COMAU S.p.a., a company worldwide leader in automation expecially for the automotive sector. The task of enhancing the performances of the 3D printer Prusa i3, that is supplied in the assembly box, was assigned to sixteen engineers attending the Master who were divided into 4 groups. The activities have led to the birth of four new 3D printers: Fluo, Ghost, Metallica and Print-Doh. In order to assess and validate the improvements, a benchmarking activity was carried out to evaluate the dimensional accuracy of the four printers. The benchmarking was based on the manufacturing of an innovative reference artifact whose geometrical features are designed to fit within different ISO basic sizes. Each group printed a replica of the reference part with their own new printer and then the replicas were measured by means of a coordinate measuring machine (CMM). Measures were used to compare the performances of the four printers and the results of the benchmarking considers the dimensional accuracy of the replicas in terms of ISO IT grades, but also the form errors of the geometrical features through GD&T tolerances