Browsing by Author "Mateus, A."
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- An Additive Manufacturing Solution to Produce Big Green Parts from Tires and Recycled PlasticsPublication . Domingues, J.; Marques, T.; Mateus, A.; Carreira, P.; Malça, C.Recycling is crucial for the conservation and improvement of the environment. The reduction of natural resource exploration and recovery of waste are examples of actions to contribute to a sustainable development. Waste from end-of-life tires and undifferentiated plastics represents an environmental problem due to the very high number of tons of used tires and plastics produced, but with a high economic potential because their incorporation into high value-added products is an issue of utmost importance. The manufacturing technologies oriented to the increase in quality levels, functional advantages, structural and financial gains of the produced products are currently a hot topic in industry. Similarly, the use of additive manufacturing technologies, instead of conventional techniques, e.g. moulding to process materials obtained from waste recovery, is a great industrial challenge. In order to promote greater environmental responsibility and to present innovative solutions for the management and sustainable destination of used waste recovery from tires and undifferentiated plastics, a composite made from the blend of 60% of tire waste granulate and 40% of polypropylene (PP) recycled was tested with the final purpose of generating components with added value. Both waste recovery materials were used in the micronized state. The thermal and mechanical behaviours of the synthesized composite were studied through DSC/TGA analysis and tensile testing. The implementation of additive manufacturing methodologies to process the blends between used tires granulated with a high incorporation of wastes from undifferentiated plastics was also explored in this work in order to produce big green parts without mould needed, such as urban furniture.
- Application of a Hybrid Additive Manufacturing Methodology to Produce a Metal/Polymer Customized Dental ImplantPublication . Silva, M.; Felismina, R.; Mateus, A.; Parreira, P.; Malça, C.In this paper an integrated methodology for implants personalized manufacturing is presented. This methodology materializes the hybrid material implants manufacturing through the integration of two or more advanced Additive Manufacturing (AM) technologies. Furthermore, high strength biomechanical implants with optimized geometry and mass can be manufactured by biomimetic concepts application. The combination of polymers and ceramics or polymers and metal materials (or metal alloys) allows a significant leap in the development and production of a great diversity of components and applications. The combination of advanced additive manufacturing processes, e.g. the Selective Laser Melting (SLM) or Selective Laser Sintering (SLS) and the StereoLithography (SL), make possible the production of parts with almost unlimited geometric freedom and custom multimaterial. The manufacturing flexibility and the processing capacity of the different combinations of materials - metal/polymer - obtained from hybrid additive manufacturing systems - SLM/SL - are demonstrated here by the manufacture of a dental bridge implant.
- Computer tool for maximizing the placement of congruent polyhedraPublication . Gaspar, M.; Alves, N.; Mateus, A.; Martins-Ferreira, N.Given multiple identical polyhedral objects and a parallelepiped container, how should one place the objects so that the largest number fits inside the container? This simple question is important in many applications, yet the answer is elusive. In fact, we know of no published solution for this very general formulation. Still, in many circumstances, further restrictions apply, resulting in a large number of variations requiring different algorithmic strategies. This paper is the continuation of [12] and focus on the fundamental concepts and tools that are used for this kind of problem, such as the no-fit polygon. We also present some of its many variations, giving in particular one that applies to the stereolithographic rapid prototyping technology.
- Cork Plastic Composite Optimization for 3D Printing ApplicationsPublication . Brites, F.; Malça, C.; Gaspar, F.; Horta, J. F.; Franco, M. C.; Biscaia, S.; Mateus, A.Among natural fillers, cork has been acknowledged as a suitable alternative of other cellular materials that are widely employed in engineering applications due to their low conductivity to heat, noise and vibration, high abrasion resistance and flexibility, high compressibility ratio, among other characteristics [1]. The eco-friendly features of natural fillers based composites make them a very promising and sustainable solution to large markets mainly if additive manufacturing technologies, such as 3D printing, are used [2]. Through 3D printers, engineers, designers and architects can create design and decor products with a free complexity of geometry. In this research work, plastic matrices of HDPE – obtained from conventional suppliers – were reinforced with different ratios of cork waste and natural cork powders – obtained from cork transformation industries – to find the optimum mixture for 3D printing. The effects of cork powders content in the plastic on the morphological, physical and mechanical properties of the composites were investigated through the density, optical microscopy, wettability, thermal analysis and tensile testing. Cork-based composites were processed by an extrusion system, and the mixture of polymer, adhesive and fillers is discussed. The results show that the addition of pure cork and cork waste can be processed with polymers such as HDPE, having adequate physical and mechanical properties.
- Cyclic plastic behaviour of 7075 aluminium alloyPublication . Nogueira, F.; Cunha, J.; Mateus, A.; Malça, C.; Costa, J. D.; Branco, R.This paper aims at studying the cyclic plastic behaviour of the 7075-T651 aluminium alloy under fully-reversed strain-controlled conditions. Tests are conducted under strain-control mode, at room temperature, in a conventional servo-hydraulic machine, from smooth samples, using the single step method, with strain amplitudes (∆ε/2) in the range ±0.5 to ±2.75%. This material has exhibited a mixed behaviour, i.e. cyclic strain-hardens at higher strain amplitudes (∆ε/2/>1.1%) and cyclic strain-softens at lower strain amplitudes (∆ε/2<1.1%). A linear relationship between the degree of cyclic strain-hardening and the strain amplitude has been established for higher strain amplitudes. Fatigue-ductility and fatigue-strength properties agree with those found in the open literature for the same loading conditions.
- Development of Heterogeneous Structures with Polycaprolactone-Alginate Using a New 3D Printing System – BioMED βeta : Design and ProcessingPublication . Biscaia, S.; Dabrowska, E; Tojeira, A.; Horta, J.; Carreira, P; Morouço. P; Mateus, A.; Alves, N.Direct Digital Manufacturing of implantable biomedical devices is the strategy for designing and constructing three dimensional (3D) structures. DDM (i.e., biomanufacturing) technologies have been widely used to construct complex 3D structures (scaffolds), where chemicals, biomaterials, and cells are deposited in a layer-by-layer fashion. These technologies control size, microarchitecture and pores interconnectivity in scaffolds, essential to transporting oxygen and nutrients for cell survival. As the Tissue engineering field progresses, new types of printers have been designed to accomplish functional engineered tissue constructs. However, the availability of innovative 3D biomanufacturing technologies for hard tissue and organ engineering is scarce and with several equipment limitations. In this work, a new biomanufacturing system, BioMEDBeta, composed of three different fabrication modules (thermoplastic micro-extrusion, multi-head deposition of hydrogels and electrospinning) was used to fabricate (3D) scaffolds using layer-by-layer alternated deposition of polycaprolactone and alginate hydrogel. The BioMEDBeta system demonstrates the possibility of obtaining scaffolds with well-defined architecture, using both natural and synthetic polymers. Nevertheless, there are still parameters to optimize related with the design of 3D constructs and materials processing.
- Development of SLM cellular structures for injection molds manufacturingPublication . Malca, C.; Santos, C.; Sena, M.; Mateus, A.Using selective laser melting (SLM) is possible to manufacture molds with cellular internal structures with different porosity degree. Furthermore, internal geometry design can be improved as a function of the desired structural and thermal stress solicitations. In this work two types of cellular internal structures – hexagonal and cub-octahedral – were developed and manufactured using the SLM process. These topologies were generated with the purpose of creating a high degree of internal porosity and getting satisfactory results in terms of thermal and mechanical behavior whencompared with similar dimensional bulk structures. The mechanical and thermal behaviors of each cellular topology were evaluated numerically and experimentally through compression and thermal tests. From numeric and experimental results, it can be concluded that hexagonal cellular internal topology provides a higher mechanical strength when compared to the cub-octahedral cellular structure while the thermal analysis shows that cub-octahedral topology is more efficient for heat dissipation. Both cellular topologies have demonstrated, however, to be appropriate for use in injection mold structures. In addition, the use of these cellular topologies provides light weight structuring with an approximate 58% weight reduction, which represents a considerable saving of material total cost to manufacturing of an injection mold.
- Geometric Study of Surface Finishing of Selective Laser Melting MouldsPublication . Nhangumbe, M.; Gouveia, J.; Sousa, E.; Belbut, M.; Mateus, A.Selective laser melting, which is based on the principle of material incremental manufacturing, has been recognised as a promising additive manufacturing technology. The principle of additive manufacturing lies in fabricating a part or an assembly of parts, layer by layer through a bottom to top approach. The technology is suited for creating geometrically complex components that can not possibly or feasibly be made by any other means. This technique has a weak point related to the surface finishing. Therefore, during the construction of layer by layer, there is a need to use techniques such as milling to remove material. This hybrid approach allows the fabrication of parts with internal complex structures and very good surface finishing. To plan and optimize the successive additive and subtractive phases, we need a quick tool to determine when the geometry of a piece is suitable for surface finishing by a 3 axes milling machine. This problem can be reduced to a layer by layer subproblem of approximately covering a slice of the object by circles of the diameter of the smallest drill available that can reach its depth. This reduction to the plane allows us to use a medial axis approach. The medial axis of a planar domain, defined as the set of centers of maximal circles contained in the domain, relates very closely to the notion of generalized Voronoi diagram, and has been proposed in several milling applications that involve motion planning. We propose to use it, and certain extensions of it, as a practical way of determining the best possible finishing quality at a slice. To that end we have to find which of the available construction strategies best suits our needs to determine exactly or approximately the medial axis of a polygon and its extensions.
- A Hybrid Processing Approach to the Manufacturing of Polyamide Reinforced Parts with Carbon FibersPublication . Silva, M; Pereira, A. M.; Alves, N.; Mateus, A.; Malça, C.The use of thermoplastic composites reinforced with long or continuous fibers underwent an amazing increase due to advantages such as good mechanical performance, high temperature resistance, recyclable and chemical stability when compared with simple thermosetting matrices. These advantages allowed for the replacement of thermosetting systems by composites that led to the discovery of new applications. However, the processing procedure of thermoplastics reinforced with prepregs yarns entails some technological and scientific challenges mainly due to its high viscosity that results in difficulty and complexity in impregnating the reinforcements. Concerning engineering components market requirements, the polyamide thermoplastic matrices reinforced with carbon fibers have a huge demand due to the versatility of the applications where they can be used. This work presents, therefore, the development of a low-cost device that combines the Fused Filament Fabrication (FFF) additive manufacturing technique together with the processing and consolidation of thermoplastic prepregs yarns for manufacturing parts made of polyamide reinforced with carbon fibers without need of post-processing operations. To evaluate the mechanical properties of the polyamide reinforced with carbon fibers, samples were manufactured and three point bending and tensile tests were done. From results it was demonstrated the very high structural strength to both bending and tensile loads of tested material.
- Optimization of a Wood Plastic Composite for Architectural ApplicationsPublication . Martins, G.; Antunes, F.; Mateus, A.; Malça, C.The actual demand for sustainable construction has fostered the research of alternative products made of new materials, such as composites based on renewable resources obtained directly from nature or, most importantly in this context, from the wastes of industries thus encouraging the implementation of recycling processes. This study reports the optimization of wood plastic composites (WPC) made of industrial residues of pine sawdust, high density polyethylene (HDPE) and maleic anhydride-grafted-polyethylene (PE-g-MA) as coupling agent. These composites were specifically designed for the production of an innovative shading system to apply in the forefront of buildings, thus requiring an adequate combination of material properties concerning resistance to weather conditions, with mechanical and functional performance of the final products. The composites were optimized to enable their production and the fabrication of the shutter units through sequential extrusion processing. The optimization of the composites started with a thorough characterization of the raw materials and the mixtures were prepared after analysing the effect of the concentration of pine sawdust in the polymeric matrix, with variable amounts of the coupling agent. Torque rheometry was used to determine the most adequate viscosities for extrusion processing. The composites with optimized contents of pine sawdust and additives were characterized using SEM, FTIR, DSC-TGA, tensile testing, measurements of water contact angle and water absorption capacity. This allowed determining the respective microstructure, chemical interactions, thermal stability, mechanical properties, surface wettability and swelling capacity.