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- A new joining by forming process to produce lap joints in metal sheetsPublication . Pragana, João; Silva, Carlos; Bragança, Ivo; Alves, Luís; Martins, PauloThis paper proposes a new joining by forming process to produce lap joints in metal sheets. The process combines partial cutting and bending with mechanical interlocking by sheet-bulk compression of tabs in the direction perpendicular to thickness. The lap joints are flat with all the plastically deforming material contained within the thickness of the two sheets partially placed over one another. The design of the lap joints is performed by a simple analytical model and the overall concept is validated by means of numerical modelling and experimentation. Destructive shear tests demonstrate the effectiveness and performance of the new proposed lap joints. (C) 2018 Published by Elsevier Ltd on behalf of CIRP.
- Joining aluminium profiles to composite sheets by additive manufacturing and formingPublication . Baptista, R. J. S.; Pragana, João; Bragança, Ivo; Silva, Carlos; Alves, Luís; Martins, PauloThis paper explores the application of the 'mortise-and-tenon' concept for joining hollow section aluminium profiles to composite strips or sheets. Wire arc additive manufacturing is combined with joining by forming to fabricate the tenons and to obtain the mechanical interlocking with the mortises available in the strips (or sheets). The workability limits are established by means of an analytical model that combines plastic deformation, instability and fracture. Experimental and finite element modelling are utilized to develop the overall joining process and to validate the round 'mortise-and-tenon' design resulting from the analytical model. Pull-out and shear destructive tests are carried out to evaluate the overall strength of the joints and results allow concluding that the new joints can easily and effectively replace existing solutions based on welding, fastening or adhesive bonding. The proposed joining process also circumvents the need to design extra fixing and interlocking features in low cost hollow section aluminium profiles for easy assembling.
- Manufacturing hybrid busbars through joining by formingPublication . Pragana, João; Baptista, R. J. S.; Bragança, Ivo; Silva, Carlos; Alves, Luís; Martins, PauloThis paper focus on the production of hybrid busbars made from copper and aluminium by means of a joining by forming process that was recently developed by the authors. The process involves the combined use of partial cutting and bending with form-fit joining by compression in the direction perpendicular to strip thickness. The resulting joints are flat with the plastic deformed materials enclosed within the thickness of the overlapped strips. Design is performed by means of an analytical model and the overall manufacturing concept is validated through numerical and experimental modelling. Major process parameters are identified and their influence on the overall deformation mechanics and joining feasibility is investigated. The effectiveness and performance of the new joints is analysed by means of tensile-shear loading tests. Results show that joining by forming can be successfully utilized to produce form-fit joints with good shear forces in hybrid busbars for electrical applications.
- Joining by forming of metal-polymer sandwich composite panelsPublication . Pragana, João; Contreiras, Tomás R. M.; Bragança, Ivo; Silva, Carlos; Alves, Luís; Martins, PauloThis article presents new joining-by-forming processes to assemble longitudinally two metal-polymer sandwich composite panels perpendicular to one another. Process design draws from an earlier development of the authors for metal sheets to new concepts based on the combination of sheet-bulk forming with mortise-and-tenon joints. Selected examples obtained from experimentation and finite element modelling give support to the presentation. A new three-stage joining by the forming process is capable of producing mechanically locked joints with larger and stiffer flat-shaped heads than those fabricated by alternative single- or two-stage solutions. Failure in the new three-stage joining by the forming process is found to take place by cracking instead of disassembling after unbending the flat-shaped head of the joint back to its original shape. The required forming forces to produce the new metal-polymer joints are below 15 kN, allowing them to be an effective, easy-to-implement alternative to existing solutions based on adhesive bonding, welding and mechanical fastening.