Browsing by Author "Silva, C. M. A."
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- Formability of a wire arc deposited aluminium alloyPublication . Silva, C. M. A.; Bragança, Ivo; Cabrita, A.; Quintino, L.; Martins, P. A. F.This paper is focused on the formability of the aluminium alloy AA5083 deposited by wire arc additive manufacturing (WAAM). The presentation draws from metal deposition with a robotic welding system to mechanical and formability characterization by means of standard test specimens. Finite element analysis using porous metal plasticity is utilized to model strain hardening and the changes in porosity due to plastic deformation. Results show that the deposited aluminium alloy has excellent ductility and that its final stress response can significantly improve as a result of strain hardening. Voids resulting from metal deposition are closed by negative values of stress-triaxiality resulting from compression forming. The investigation is also a step towards understanding the potential of including intermediate forming operations in conventional wire arc additive manufacturing (WAAM), consisting of metal deposition and machining.
- Hybrid metal additive manufacturing: A state–of–the-art reviewPublication . Pragana, J. P. M.; Sampaio, Rui F. V.; Bragança, Ivo; Silva, C. M. A.; Martins, P. A. F.This paper starts from the early developments and working principles of the additive manufacturing of polymers, continues with a glimpse on the extension to metals with identification and characterization of the two most widespread technologies, and ends with an overview of the recent developments in hybrid metal additive manufacturing. Earlier classifications of hybrid manufacturing with roots on the utilization of primarily processed raw materials in the form of ingots, sheets, rods, tubes, profiles, powders and pellets are revisited in the light of the emergence of a new type of hybridization resulting from the combination of additive manufacturing with traditional manufacturing processes. Special emphasis is given to the combination of additive manufacturing with forming processes with the two-fold objective of (i) increasing the applicability domain of metal additive manufacturing and overcoming its limitations related to low productivity, metallurgical defects, rough surface quality and lack of dimensional precision, and (ii) adding flexibility and fostering new applications of traditional forming processes.
- Hybrid wire‑arc additive manufacturing of conformal cooling channels: a feasibility studyPublication . Pragana, João; Bragança, I. M. F; Silva, C. M. A.; Martins, P. A. F.This paper investigates the feasibility of hybridizing wire-arc additive manufacturing with metal forming to create conformal cooling channels in moulds for hot material processing. An axisymmetric mould is used as a prototype test case and plastic deformation by flaring of the additively deposited inner tubular element is utilized to create the overhangs for connecting with the outer tubular element that are needed to fabricate the cooling channels. Finite element modelling of plastic deformation by flaring of the additively deposited material is carried out to identify the different modes of deformation and to determine the maximum allowable radius of the overhangs. Results show that the proposed hybridization of wire-arc additive manufacturing with plastic deformation by flaring adds flexibility to the design and fabrication of conformal channels in the as-built mould by eliminating the use of support structures and avoiding the use of complex deposition strategies. Finishing of the functional surfaces of the as-built mould by turning ensures the required accuracy and surface quality.
- Influence of corrosion on the electrical and mechanical performance of hybrid busbarsPublication . Sampaio, Rui F. V.; Bragança, Ivo; Pragana, J. P. M; Silva, C. M. A.; Fernandes, João C. S.; Martins, Paulo A. F.This paper is focused on the electrical and mechanical performance of aluminum-copper hybrid busbars subjected to corrosion over time. Two different types of hybrid busbars with joints produced by conventional fastening with M8 hexagonal socket head bolt-nut pairs made from medium carbon steel and by a new injection lap riveting process with semi-tubular rivets made from the material of the softer conductor are used and subjected to salt spray and electrochemical tests. Electrical resistance measurements performed on hybrid busbars taken from the corrosion testing cabinet at the end of each exposure period allow concluding that the new injection lap riveted hybrid busbars have a better electrical performance over time due to the elimination of fasteners with a higher electrical resistivity than aluminum and copper and to the elimination of the aluminum-steel and copper-steel galvanic pairs. The capability of the injection lap riveted hybrid busbars to withstand shear forces after corrosion testing also revealed to be adequate and like those of the original (uncorroded) hybrid busbars.
- Invisible mechanical lap joints for metal–polymer laminatesPublication . Batista, R. J. S.; Bragança, I. M. F; Silva, C. M. A.; Pragana, J. P. M; Martins, P. A. F.Joining by compression of metallic inserts has been recently developed by the authors to create invisible lap joints between metal and polymer laminates. This paper revisits the process with the objective of proposing a new type of bi-material (polymer–metal) cylindrical insert for lightweight construction applications that is capable of ensuring complete filling of the joint at the end of stroke without increasing the forming force and the risk of sheet bending. The presentation is built upon a combined experimental and finite element research work focused on the modes of deformation, formability limits, forming forces, and resistance strength that lap joints produced with the new bi-material cylindrical inserts are able to withstand before failing. Results allowed designing a simple and easy to fabricate bi-material cylindrical insert that overcomes the main problems that have been pointed out to the metallic inserts earlier proposed by the authors.
- Joining of sheets by sheet-bulk forming: a numerical and experimental studyPublication . Bragança, Ivo; Loja, Amélia; Silva, C. M. A.; Alves, L. M.; Martins, P. A. F.The authors present a new mechanical joining process that allow to connect two sheets perpendicular to one another, a variant of the traditional ‘mortise-and-tenon’ joint. This investigation is focused on joining similar and dissimilar sheets based on sheet-bulk forming and it is supported by experimental data and numerical simulation with an in-house finite element program, I-form. Results show that is possible to join materials by sheet-bulk forming and is also presented the joinability window as a function of the main operating parameters. The divided flux technique could be a valid option to eliminate the observed small clearance related to the elastic recovery of polymers. Furthermore, this technique could also be applied whether a lower initial punch force is required or even a different head morphology is desired. Destructive tensile tests were performed to determine the maximum force that the joints are capable to withstand without failure and to identify the failure mechanism.
- New self-clinching fasteners for electric conductive connectionsPublication . Sampaio, Rui F. V.; Martins, Paulo; Pragana, J. P. M; Bragança, Ivo; Silva, C. M. A.This paper presents new rotational and longitudinal symmetric self-clinching fasteners to fabricate reliable connections in busbars with low electrical resistance for energy distribution systems. Connections consist of form-closed joints that are hidden inside regions where two busbars overlap. The investigation into the fabrication and performance of the new self-clinched joints involved finite element modelling and experimentation to determine the required forces and to evaluate the electric current flow and the electrical resistance at different service temperatures. The original design of the joints that was proposed in a previous work was modified to account for busbar strips of copper and/or aluminum with similar or dissimilar thicknesses, connected by means of self-clinching fasteners made from the same materials of the busbars, instead of steel. The effectiveness of the new self-clinched joints was compared to that of conventional bolted joints that are included in the paper for reference purposes. The results show that rotational symmetric self-clinching fasteners yield lighter fabrication and more compact joints with a similar electrical resistance to that of bolted joints. They also show that longitudinal symmetric self-clinching fasteners aimed at replicating the resistance-seam-welding contact conditions yield a reduction in electrical resistance to values close to that of ideal joints, consisting of two strips in perfect contact and without contaminant or oxide films along their overlapped surfaces.