An Experimental Study of the Microformability of Very Thin Materials

This article extends the concept of forming limit curves to very thin (0.1 mm) metallic materials. The forming limit curves for these materials are referred in this paper as microforming limit curves. To study the microformability of such materials, a microdrawing press based on the Marciniak principle, coupled with an image acquisition system, was designed and built in the laboratory. Images of the sample surface were obtained during the microdrawing process and processed using a deformation measurement system based on image correlation. The microformability of aluminium 1050A (99.5 %) and aluminium alloy (Al-3 % Mg) were characterised in tests at three different geometries and then analysed. Besides, a new technique for estimating the strain at the onset of necking was developed and tested against a proven method. This technique is more easily automated because it does not rely on subjective criteria. Thus, it is possible to have the microforming limit curve for very thin sheet by a rapid and objective experimental method.