A method for reducing a total risk due to thinning and thickening when designing a formed sheet metal part formed by deep drawing, performed by a processor of a computing system, by means of a numerical model of a target geometry of the sheet metal part, the numerical model of the target geometry being modified interactively by a user, the method comprising the following steps: • maintaining in computer storage the numerical model of the target geometry of the part being modified; • by the computing system, performing a simulation procedure, ∘ wherein the deformation of the part by a forming process that transforms the part from an initial geometry to the target geometry is computed, ∘ wherein thinning and thickening effects of the forming process on the part are computed as a function of restraining force, wherein thinning effects are effects of a too large restraining force and thickening effects are effects of a too small restraining force, and ∘ wherein the computation steps for the part deformation and the part thinning and thickening effects are repeated for different values of the restraining force; • on the display device, displaying a visual representation of the part subjected to the simulated forming process, including a visual representation of the thickening and thinning effects on the visual representation of regions (11, 12, 13, 14, 15) of the part that are affected by said thickening and thinning effects; • by the computing system, classifying the surface of the part as having several regions, ∘ wherein each region is associated with a particular range of the thickening and thinning effects, and characterized in that the method further comprises: ∘ that for each of these regions, a value that is representative of the area of the region is computed; and • by the computing system, computing and displaying on the display device a diagram displaying the relative size of the values that are representative of the areas of these regions (11, 12, 13, 14, 15), as a function of the restraining force, thereby indicating whether there is a restraining force with which the part can be formed without too much total risk due to thinning and thickening; • by the computing system, according to user input, based on the diagram, terminating the method or performing a further, iterative modification of the target geometry, and a further execution of the method. • maintaining in computer storage the numerical model of the target geometry of the part being modified; • by the computing system, performing a simulation procedure, ∘ wherein the deformation of the part by a forming process that transforms the part from an initial geometry to the target geometry is computed, ∘ wherein thinning and thickening effects of the forming process on the part are computed as a function of restraining force, wherein thinning effects are effects of a too large restraining force and thickening effects are effects of a too small restraining force, and ∘ wherein the computation steps for the part deformation and the part thinning and thickening effects are repeated for different values of the restraining force; ∘ wherein the deformation of the part by a forming process that transforms the part from an initial geometry to the target geometry is computed, ∘ wherein thinning and thickening effects of the forming process on the part are computed as a function of restraining force, wherein thinning effects are effects of a too large restraining force and thickening effects are effects of a too small restraining force, and ∘ wherein the computation steps for the part deformation and the part thinning and thickening effects are repeated for different values of the restraining force; • on the display device, displaying a visual representation of the part subjected to the simulated forming process, including a visual representation of the thickening and thinning effects on the visual representation of regions (11, 12, 13, 14, 15) of the part that are affected by said thickening and thinning effects; • by the computing system, classifying the surface of the part as having several regions, ∘ wherein each region is associated with a particular range of the thickening and thinning effects, and characterized in that the method further comprises: ∘ that for each of these regions, a value that is representative of the area of the region is computed; and • by the computing system, computing and displaying on the display device a diagram displaying the relative size of the values that are representative of the areas of these regions (11, 12, 13, 14, 15), as a function of the restraining force, thereby indicating whether there is a restraining force with which the part can be formed without too much total risk due to thinning and thickening; • by the computing system, according to user input, based on the diagram, terminating the method or performing a further, iterative modification of the target geometry, and a further execution of the method.