Engenharia Mecânica
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/23
Navegar
2 resultados
Resultados da Pesquisa
- Surface integrity of INCONEL 718 turned under cryogenic conditions at high cutting speeds(2019-06-26) PEREIRA, W. H.; Sergio Delijaicov© 2019, Springer-Verlag London Ltd., part of Springer Nature.Nickel alloys such as Inconel 718 have been widely used in the aerospace, oil and gas, and chemical industries, since they have excellent properties that combine high creep resistance and high mechanical strength, fatigue and corrosion. However, these properties make these alloys extremely difficult to machine, due to a high level of heat generation during material removal, causing rapid wear of cutting tools and a detrimental effect on the surface integrity, reducing the fatigue life of the machined component and lowering the productivity. Looking at the literature, it seemed that there is an opportunity to study the surface integrity of Inconel 718, turned under cryogenic conditions at cutting speeds of 250, 275 and 300 m/min. For these reasons, this work aims to evaluate the influence of the cutting parameters on the surface integrity of Inconel 718 turned under cryogenic conditions using liquid nitrogen (LN2) at high cutting speeds. A whisker-reinforced ceramic tool was used in order to provide wear and shock resistance at high cutting speeds; these are factors that are associated with surface integrity in terms of roughness Ra, residual stresses, microhardness and cutting forces. A central composite design was chosen as factorial planning for the independent variables including cutting speed, feed rate and depth of cut when carrying out the experiments. Cryogenic cooling resulted in an average cutting force of 267 N, where the penetration force was higher. The roughness Ra was 0.52 μm and was influenced by the feed rate and depth of cut. The highest tensile residual stresses in the circumferential direction with LN2 and under dry conditions were 1394 MPa and 1237 MPa, respectively and were influenced by the depth of cut. Small changes in microhardness occurred at a depth of 0.3 mm from beneath machine surface and the presence of a white layer was not observed. Although tensile residual stresses were slightly higher when using LN2 compared to dry machining on the surface, the use of LN2 caused higher compressive residual stresses at the subsurface, which can improve the fatigue life of machined components at high cutting speeds. The results showed that lower cutting parameters tend to give the best results in terms of the cutting force and surface integrity.
- Superficial residual stress, microstructure, and efficiency in similar joints of AA2024-T3 and AA7475-T761 aluminum alloys formed by friction stir welding(2021-09-05) PERANDINI, J. P. B.; Ed Claudio Bordinassi; BATALHA, M. H. F.; CARUNCHIO, A. F.; Sergio Delijaicov© 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.Friction stir welding (FSW) represents a conceptually simple technique that consists of joining either similar or dissimilar solid-state materials through higher plastic deformation rates. FSW is an important technique in the aeronautical and aerospace industries, and its development is vital because of the significant difficulty in joining higher resistance AA 2000 and AA 7000 aluminum alloys with conventional techniques, like fusion welding, due to porosity and mechanical property losses. Thin sheets with a 1.6-mm nominal thickness of AA2024, heat treated to condition T3, and thin sheets with a 1.6-mm nominal thickness of AA7475, heat treated to condition T761, were used to investigate the influence of welding parameters under superficial residual stress and the efficiency of joints by FSW of AA2024-T3 and AA7475-T761 aluminum alloys. A central composite design (CCD) was used as a statistical model in this study (23 factorial points, six stellar points, two central points, and two replicas). Micrographic analysis showed that in the nugget zone of the AA7475-T761 alloy, there was hardness recovery. The fractography images showed that failures occurred mainly due to the joint line remnant defect, evidenced by the presence of cracks. The superficial residual stresses show a maximum value of 81 MPa at the advancing side in run 27 (hot welding) of AA2024-T3, whereas in AA7475-T761, a value of 57 MPa was found in the same run. Finally, tensile strength represents an efficiency of ~92% of the AA2024-T3 base metal value, while for AA7475-T761, this value was ~85%. From a component design perspective, the parameter window of this study is identified as interesting for its evaluation in the possible application in component manufacturing, due to the low values of superficial residual stresses found compared to those in previous work.