Deep drawing requirements are key material characteristics that must be fulfilled from many industrial applications. Due to these requirements, the processes must be strictly controlled, especially in the last steps of the production process such as the skin-pass operation.

The skin-pass is essential for the production of cold rolled steels in order to remove the yield point elongation and obtain the surface quality and flatness required by customers. In this last step, final characteristics are defined with a maximum final reduction percentage to guarantee the drawability. Due to surface and flatness requirements or unexpected problems arisen within the production process, sometimes a higher skin pass percentage is applied, which can influence the mechanical and material properties.

During this case study, FormPlanet applied non-standard tests to measure materials’ drawability providing deep information and knowledge to allow setting the process limits that ensure that the material will fulfil the requested characteristics, avoiding unnecessary rejections or, in the worst case, delivering troublesome material to the final customer.

This use case studied the influence of the skin pass percentage on drawability in three steel grades (16MnCr5, DC05LC and DC04LC), in which deep drawing requirements need to be included in technical specifications.

Axial tensile tests to analyse the normal anisotropy (R) and planar anisotropy (Δr) at different orientations were done by ARANIA. On the other hand, FormPlanet performed drawability tests (Limiting Drawing Ratio – LDR and Earing Tests).

Results indicated that, in the analysed skin-pass ranges studied, there were no significant differences on tensile properties depending on skin pass strain. It was concluded that the skin pass reduction percentage does not have a critical influence in the anisotropy parameters.

This test allows to predict the critical points in real stamping components and can be used for the optimisation of deisgned die, fast acceptance inspection for new sheet/coil, FEM verification and providing a complex view of formability (relation between stress and strain state).