Laser cutting effects on aluminium sheets mechanical properties
In aeronautic field there is always a continuous research, implementation and application of more and more advanced technologies. This leads to the adoption of lasers in the aluminium sheets cutting to create plane external structures as an alternative at the more consolidate mechanical cutting techniques such as the use of punching machines. There is a lack of specific references about laser cutting technology in literature and in international norms so the aim of this work is to understand if the thermal (laser) and mechanical (punching machine) cutting technique are equivalent in terms of not influencing the mechanical properties of the components after cutting. The tested materials are aluminium sheets of EN AW-6061 [Al, Mg, Si, Cu] and EN AW-6082 [Al, Si, Mg, Mn] alloys with a T6 heat treatment and thickness of 0.8, 1.0, 1.2 e 1.6 mm for 6061 and 3.0 mm for 6082. The study has been performed following three different activities: Static mechanical properties (microhardness, tensile test - figure 1, bearing test - figures 2, 3) on 6061 T6 aluminium alloy sheets Axial fatigue test on 6082 T6 aluminium alloy sheets (figure 4) Morphological analysis of the cutting surfaces (figures 5, 6, 7) About the cutting surfaces morphology it is possible to notice that the laser technology creates a surface characterised by re-melted and rough areas (figures 5 and 6) while the punching machine first produces a smooth surface that becomes rough in the final phase of the fracture (figure 7). The microhardness test puts in evidence a hardness decreasing near the cutting edge created with the laser beam till a distance of about 100 Ìm (figure 8) because of the thermal effects obviously absent in the punching machine cutting surfaces. The tensile (table 3 and figure 9) and bearing tests (figure 10) clarify that the laser technology maintains mechanical properties in the ranges indicated by the international design norms even if all the results are a little bit lower than the ones obtained with the punching machine. Axial fatigue data let to say that in terms of alternate stresses and number of cycles to failure the differences on fatigue behaviour of the two types of cutting are negligible (figure 14). Nevertheless, under a morphologic point of view there is a great difference in the position of the fatigue crack initiation and propagation on the laser cut specimens (figure 11) if compared to the punching machine fractured specimens (figure 13) maybe because of the presence of re-melted areas that could represent the starting and arriving points of the laser beam during the cutting. As a conclusion we can say that the laser cutting could be use for the creation of complex figures on metal sheets for airplane external structures at the condition to properly plan the laser beam path during cutting avoiding to start from the more critical zones of the figure.