Estudo do processo de expansão de furos em aço avançado de alta resistência por estampagem incremental

Abstract

Advanced high-strength steels (AHSS) are increasingly being used by the automotive industry as these materials make it possible to reduce vehicle weight at competitive costs while increasing passenger safety in the event of a collision. However, one of the major challenges for fabricating parts from these new materials relates to the low conformability of edges. The conformability of sheet edges is conventionally evaluated by the Hole Expansion test, where a central hole is expanded with a tapered punch. The objective of this work is the evaluation of the behavioral performance of the formability by an innovative technique of incremental stamping in the expansion of hole in pre-drilled plates of martensitic AHSS steel. For, the incremental stamping is being researched and used to the most diverse objectives, because, it, has the characteristic of deformation locally, and progressively, of the sheet. The fabrication of a fastening matrix, to include square and disk profile sheets, tools and a conical spiral path, for the incremental stamping by single point of contact (SPIF), made it possible to carry out the tests. In the first strategy, solid lubricant of the graphite powder type was used, and a cylindrical geometry tool with stepped diameters, in which the fracture occurred, before the expansion caused rupture of the edge. In this way, it was possible to estimate the force at the moment of fracture, with the momentary conditions. In the second strategy, with the use of pasty lubricant, graffititype grease, and with a tool of constant cylindrical profile, the holes in the plates were obtained. Thus, it is possible to compare the results with the data obtained by researchers who used the conventional method, governed by ISO 16630. Obtaining a ratio of the expansion of holes (REF) by the SPIF method, with the parameters used in the test, was of 47.2%. The obtained REF, for the same material by the conventional technique is 54%. Therefore, it is observed that the technique used, in martensitic AHSS steel plate, generated cracks at the edges before the conventional technique. This slightly lower result for REF through SPIF can be attributed to the fact that the edge of the bore is not in contact with the tool, which contributes to the onset of localized necking.