In a method for designing a formed sheet-metal part, a method for displaying a visual representation of the quality of the formed sheet-metal part, the method comprising the steps of: simulating the deformation of the part by a forming process of the part, thereby computing thinning and thickening effects of the forming process on the part, for different values of a restraining force; displaying a visual representation of the part and of the thickening and thinning effects of different regions of the part; classifying the surface of the part as having several regions, each region being associated with a particular range of the thickening and thinning effects; computing and displaying on the display device a diagram displaying, as a function of the restraining force, the relative size of areas of these regions.