Loading...
4 results
Search Results
Now showing 1 - 4 of 4
- Integration of forming operations on hybrid additive manufacturing systems based on fusion weldingPublication . Pragana, João; Cristino, Valentino A. M.; Bragança, Ivo; Silva, Carlos; Martins, PauloThis paper is focused on the integration of metal forming operations in hybrid systems that combine additive manufacturing (AM) by gas metal wire arc and subtractive manufacturing by machining. The investigation is carried out in AISI 316L stainless steel wire and draws from tensile testing to incremental sheet forming of truncated conical shapes. Commercial sheets from the same material are utilized for comparison purposes. Thickness measurements, digital image correlation (DIC), circle grid analysis (CGA) and microstructural and scanning electron microscopy (SEM) observations are carried out to understand how different is the mechanical behaviour of the deposited metal from that of commercial metal sheets and how significant is the influence of the deposited metal microstructure on its overall formability. Results confirm that integration of metal forming operations in hybrid AM routes is feasible despite the formability of deposited metal being smaller than that of the commercial metal sheets due to the strong anisotropy induced by the dendritic based microstructure of the deposited metal. Incremental forming of two deposited parts also allows concluding that integration of metal forming operations in hybrid AM systems is a step towards green and sustainable manufacturing by extending their field of applicability to the fabrication of complex ready-to-use parts requiring combination of different processes.
- Joining by forming of additive manufactured 'mortise-and-tenon' jointsPublication . Silva, Diogo F. M.; Bragança, Ivo; Silva, Carlos; Alves, Luís; Martins, PauloThis article is aimed at extending the 'mortise-and-tenon' joining concept commonly utilized in corner or tee joints to lap joints in which one sheet is partially placed over another without any change in their shape. The approach makes use of wire arc additive manufacturing to fabricate the tenons and allows various shapes and thicknesses to be made from a wide range of metallic materials. Upset compression of the tenons is utilized to mechanically lock the two sheets being joined. Experimental and finite element simulation works performed with monolithic (aluminium-aluminium) and hybrid (aluminium-polymer) 'unit cells' consisting of a single lap joint are utilized to investigate the deformation mechanics and the feasibility of the new proposed joining process. Tensile-shear loading tests were carried out to determine the maximum force that the new proposed joints are capable to withstand without failure. Pull-out forces of approximately 8 and 6 kN for the monolithic and hybrid joints allow concluding on the potential of additive manufactured 'mortise-and-tenon' lap joints to connect sheets made from similar and dissimilar materials.
- Coin minting by additive manufacturing and formingPublication . Pragana, João; Rosenthal, Stephan; Alexandrino, Paulo; Araújo, Andreia; Bragança, Ivo; Silva, Carlos; Leitão, Paulo J.; Tekkaya, A. Erman; Martins, PauloAdditive manufacturing is proposed as a novel alternative to coin blank's production routes based on rolling, blanking and edge rimming. The presentation draws from laser powder bed fusion of cylinders, slicing into individual coin blanks by electro discharge machining and surface preparation by polishing, to coin minting in a laboratory press-tool system. Special emphasis is given to material deposition and coin minting due to the originality of producing coin blanks with complex intricate contoured holes and to the necessity of subjecting the additive manufactured coin blanks to extreme compressive stresses that are typical of coin minting. Numerical and experimental results confirm the excellent performance of the additive manufactured coin blanks. The new design layouts included in the additive manufactured coin blanks open the way to produce high value-added singular collector coins, which are disruptively different from those available in the market nowadays.
- Hybrid additive manufacturing of collector coinsPublication . Pragana, João; Rosenthal, Stephan; Bragança, Ivo; Silva, Carlos; Tekkaya, A. Erman; Martins, PauloThe objective of this paper is to present a new hybrid additive manufacturing route for fabricating collector coins with complex, intricate contoured holes. The new manufacturing route combines metal deposition by additive manufacturing with metal cutting and forming, and its application is illustrated with an example consisting of a prototype coin made from stainless steel AISI 316L. Experimentation and finite element analysis of the coin minting operation with the in-house computer program i-form show that the blanks produced by additive manufacturing and metal cutting can withstand the high compressive pressures that are attained during the embossing and impressing of lettering and other reliefs on the coin surfaces. The presentation allows concluding that hybrid additive manufacturing opens the way to the production of innovative collector coins with geometric features that are radically different from those that are currently available in the market.