Percorrer por autor "Leal, Rui"
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- Additive manufacturing tooling for the automotive industryPublication . Leal, Rui; Barreiros, F. M.; Alves, L.; Romeiro, F.; Vasco, J. C.; Santos, M.; Marto, C.Automotive industry faces new challenges every day, new design trends and technological deployments from research push companies to develop new models and facelifts in short term, requiring new tools or tool reshaping. Concerning the current world economic scenario, decreasing time for tooling up becomes as important as decreasing time-to-market. Such scenario opens up the horizons for new manufacturing approaches like additive manufacturing, in this case, applied for tooling up a stamping process on the automotive industry for the production of body panels. This approach enables the manufacturing of stamping inserts using similar high performance alloy steel as in conventional tooling, therefore, without losing tool mechanical properties. The stamping tools produced were tested by an automotive company in order to determine tool behaviour under real operating conditions, considering the high level demands of the stamping process. The results obtained enabled to conclude that metal additive manufacturing provided tools for the stamping process with excellent performance with a significant decrease on time-to-tooling.
- Effect of explosive mixture on quality of explosive welds of copper to aluminiumPublication . Loureiro, A.; Mendes, R.; Ribeiro, J.B.; Leal, Rui; Galvão, I.The aim of this research is to investigate the influence of explosive ratio and type of sensitizer on the quality of explosive welds between copper and aluminium alloy plates. The welds were performed on a partially overlapping joint configuration using an emulsion explosive (EE) with two different sensitizers, hollow glass microspheres (HGMS) and expanded polystyrene spheres (EPS). Welds with an improved surface were achieved by using the HGMS sensitizer. A higher wave amplitude was registered in welds produced with the EPS sensitizer. In turn, the dimension of the molten pockets was influenced by the explosive ratio, increasing in size with increases in the values of this parameter. The intermetallic content of these zones varied according to the sensitizer type.Unlike the CuAl2 phase, the Cu-richer phases CuAl and Cu9Al4were only identified inwelds performed using the EPS sensitizer. An increase in hardness was observed at the interface of all welds, which resulted from both the presence of intermetallic phases and the plastic deformation of the materials promoted by the impact. This effect was most evident on the aluminium alloy side. All the welds had a greater strength than copper, i.e. the weakest material of the joint.
- Effect of friction stir processing parameters on the microstructural and electrical properties of copperPublication . Leal, Rui; Galvão, I.; Loureiro, A.; Rodrigues, D. M.Friction stir processing (FSP) is an innovative technology, based on friction stir welding (FSW) operative principles, which can be used for changing locally the microstructure and the mechanical properties of conventional materials. In this work, the copper alloy C12200 was friction stir processed using two distinct tools, i.e. a scrolled and a conical shoulder tool, in order to promote different thermomechanical conditions inside the stirred volume, and consequently, varied post-processed microstructures. The influence of the tool geometry and tool rotation and traverse speeds on the microstructural and electrical properties of the processed copper alloy was analysed. The processing conditions were found to have an important influence on the electrical conductivity of the processed material. The differences in electrical conductivity were explained based on dislocations density effects. The effect of the dislocations density on electrical conductivity of the processed material was found to prevail over the effect of the grain boundaries.
- Formation of intermetallic structures at the interface of steel-to-aluminium explosive weldsPublication . Carvalho, G.H.S.F.L.; Galvão, I.; Mendes, R.; Leal, Rui; Loureiro, A.The formation of intermetallic structures at the interface of carbon steel to 6082 aluminium alloy explosive welds and their influence on the weldability of these two materials were studied. The morphology, the microstructure, the chemical and phase compositions of the welds were characterised by several types of microscopy techniques. The interface characterisation proved that explosive mixtures with a lower detonation velocity were revealed as being more suitable for achieving consistent welds since jet entrapment was prevented and continuous molten layers were not formed at the weld interface. It was also found that the physical properties of the intermetallic phases generated at the weld interface have a strong influence on the weldability of steel-to-aluminium explosive welds. Specifically, it was shown that the formation of aluminium-rich intermetallic phases at the weld interface increases the solidification time of the interfacial molten material, decreasing the weldability of these two materials. The formation of these intermetallic compounds should be avoided by reducing the interaction between the flyer and the baseplate as well as by avoiding excessive molten layers.
- Influence of base material properties on copper and aluminium–copper explosive weldsPublication . Carvalho, G. H. S. F. L.; Galvão, I.; Mendes, R.; Leal, Rui; Loureiro, A.The influence of base material properties on the interfacial phenomena in copper and aluminium–copper explosive welds was studied. Two explosive mixtures with different detonation velocities were tested. Sound aluminium–copper joints with effective bonding were achieved by using an explosive mixture with a lower detonation velocity. High energy explosives led to extensive interfacial melting, preventing the production of consistent dissimilar welds. Unlike to the similar copper joints, the aluminium–copper welds presented very asymmetrical interfacial waves, rich in intermetallic phases and displaying a curled morphology. The interaction of the materials in dissimilar welding was found to be completely different depending on the positioning of each alloy in the joint, i.e. positioned as the flyer or as the baseplate.
- Influence of friction stir welding parameters on the microstructural and mechanical properties of AA 6016-T4 thin weldsPublication . Rodrigues, D.M.; Loureiro, A.; Leitão, C.; Leal, Rui; Chaparro, B.M.; Vilaça, P.In present work friction stir welds produced in 1 mm thick plates of AA 6016-T4 aluminium alloy, with two different tools, were analysed and compared concerning the microstructure and mechanical properties. For each tool, the welding parameters were optimized in order to achieve non-defective welds. Assuming a relation between the welding parameters and the energy input per unit of length of the weld [Seidel TU, Reynolds AP. Visualization of the material flow in AA2195 friction stir welds using a marker insert technique. Metall Mater Trans A 2001;32A:2879-84; Sato YS, Urata M, Kokawa H. Parameters controlling microstructure and hardness during friction stir welding of precipitation-hardenable aluminum alloy 6063. Metall Mater Trans A 2002;33(3):625-35; Lim S, Kim S, Lee CG, Kim S-J. Tensile behavior of friction-stri-welded Al 6061-T651. Metall Mater Trans A 2004;35(9):2829-35; Yang B, Yan J, Sutton MA, Reynolds AP. Banded microstructure in AA2024-T351 and AA2524-T351 aluminum friction stir welds: Part I. Metallurgical studies. Mater Sci Eng A 2004;364(1-2):55-65; Peel MJ, Steuwer A, Withers PJ, Dickerson T, Shi Q, Shercliff H. Dissimilar friction stir welds in AA5083-AA6082. Part I: process parameter effects on thermal history and weld properties. Metall Mater Trans A 2006;37:2183-193; Gerlich A, Su P, Yamamoto M, North TH. Effect of welding parameters on the strain rate and microstructure of friction stir spot welded 2024 aluminum alloy. J Mater Sci 2007;42(14):5589-601; Lombard H, Hattingh DG, Steuwer A, James MN. Optimising FSW process parameters to minimise defects and maximise fatigue life in 5083-H321 aluminum alloy. Eng Fract Mech 2008;75(3-4):341-54], the welds produced were classified as "hot" and "cold welds". The results obtained showed that the "hot" welds, obtained with the maximum tool rotational speed and the minimum traverse speed, have improved mechanical properties relative to the "cold" welds that were in undermatch condition relative to the base material. The differences in mechanical properties between the two types of welds are explained based in TEM microstructural analysis. Despite the undermatched characteristics of the "cold" welds relative to the base material, formability tests demonstrated that these welds improve the drawing performance of the welded sheets.
- INFLUÊNCIA DA GEOMETRIA DA FERRAMENTA E DAS PROPRIEDADES DE LIGAS DE ALUMÍNIO NA QUALIDADE DAS SOLDADURAS POR FRICTION STIR WELDINGPublication . Manuel, Neves; Beltrão, Daniel; Leal, Rui; Galvão, Ivan; Domingos, José; Loureiro, AltinoO estabelecimento de juntas T entre ligas de alumínio de séries diferentes tem grande importância no caso de estruturas com elevada rigidez, mas com peso reduzido. O processo de soldadura Friction Stir Welding (FSW) apresenta elevado potencial para esta tarefa. O objetivo deste trabalho é investigar a influência da geometria da ferramenta, das propriedades dos materiais e de parâmetros do processo na qualidade de soldaduras FSW dissimilares. A qualidade das soldaduras foi investigada com base na análise da evolução da força axial, binário e ciclo térmico gerado durante a soldadura, bem como na resistência mecânica e sanidade das mesmas. A utilização de ferramentas com pino progressivo, independentemente da posição relativa dos materiais base (placa ou reforço), requer maior força axial da ferramenta, maior rácio velocidade de rotação sobre velocidade de avanço da mesma e maior binário, mas proporciona soldaduras sem defeitos, ao contrário das ferramentas de pino simples.
- Mechanical behaviour of similar and dissimilar AA5182-H111 and AA6016-T4 thin friction stir weldsPublication . Leitão, C.; Leal, Rui; Rodrigues, D.M.; Loureiro, A.; Vilaça, P.The tensile behaviour of similar and dissimilar friction stir welds in 1 mm thick sheets of two aluminium alloys (AA5182-H111 and AA6016-T4) is analysed in this paper. The heterogeneity in properties across the welds was studied by performing microhardness tests and microstructural analysis. The tensile tests were performed in samples extracted longitudinal and transverse to the weld direction. It was found that the tensile behaviour of the welds depends mainly on the grain size in the TMAZ, for the AA5182-H111 alloy, and on precipitate distribution, for the AA6016-T4 alloy. In all types of welds, the HAZ preserves the same properties of the base materials. The global mechanical behaviour of the AA5182-H111 similar welds is very similar to that of the base material. However, for the AA6016-T4 similar welds and for the AA6016-T4-AA5182-H111 dissimilar welds a 10-20% strength reduction relative to the base materials and important losses in ductility were reported.
- Microstructural and mechanical characterisation of 5XXX-H111 friction stir welded tailored blanksPublication . Tronci, A.; McKenzie, R .; Leal, Rui; Rodrigues, D. M.Friction stir welds in 1 mm thick plates of AA 5182-H111 and AA 5083-H111 aluminium alloys are analysed in this paper. The welds were produced using a large range of welding conditions, namely, different process control modes (position and load control), tool parameters (different geometries and dimensions) and process parameters (rotation speed, advancing speed and axial load). Visual inspection and metallographic and mechanical analysis demonstrate that it is possible to obtain consistently good quality welds in very thin plates under a large range of welding conditions. Important relations between base material properties, tool geometry and the final properties of the welds were established.
- SOLDADURA POR EXPLOSÃO DE ALUMÍNIO A COMPÓSITO TERMOPLÁSTICO REFORÇADO COM FIBRASPublication . Silva, Miguel; Mendes, Ricardo; Leal, Rui; Galvão, Ivan; Beltrão, Daniel; Amaro, Ana; Loureiro, AltinoFoi investigada a utilização de soldadura por explosão para ligar um alumínio a um compósito reforçado com fibras, e verificou-se que ocorre adesão dos materiais, mas alguma degradação do compósito. É necessária mais investigação para minorar essa degradação.