Production method for manufacturing a flat metal plate of a thickness of 6mm or more which is uncoiled from a metal coil, comprising the following steps: - uncoiling the metal plate from the metal coil using an uncoiler; - subsequently cold-rolling the metal plate by means of a skin-pass roller with opposite skin-pass rollers which are configured to achieve a skin-pass elongation of the metal plate along the direction of movement of the metal plate; - subsequently flattening the metal plate by means of a flattening apparatus with alternating flattening rollers which are configured to deform the metal plate according to an alternating curvature with respect to the direction of movement of the metal plate; and - subsequently cutting the metal plate into pieces at right angles to the direction of movement by means of a cutting device, so that a cut flat metal plate of a specific length along the direction of movement is obtained, CHARACTERIZED IN THAT - the alternating curvature is such that it results in a plastification ratio of 55% or more, in which said plastification ratio is determined by the ratio across the thickness of the metal plate between: - the plastic zones (204, 206) of material of the metal plate which is plastically deformed; and - the elastic zone of material of the metal plate which is only elastically deformed at the location of the maximum curvature of the alternating curvature; and - the skin-pass elongation is such that it results in a translation ratio of 15% or more at the location of the alternating curvature, the translation ratio being determined by the ratio across the thickness of the metal plate between: - the translation of the elastic zone at the location of the maximum curvature of the alternating curvature; and - half the thickness of the metal plate. - uncoiling the metal plate from the metal coil using an uncoiler; - subsequently cold-rolling the metal plate by means of a skin-pass roller with opposite skin-pass rollers which are configured to achieve a skin-pass elongation of the metal plate along the direction of movement of the metal plate; - subsequently flattening the metal plate by means of a flattening apparatus with alternating flattening rollers which are configured to deform the metal plate according to an alternating curvature with respect to the direction of movement of the metal plate; and - subsequently cutting the metal plate into pieces at right angles to the direction of movement by means of a cutting device, so that a cut flat metal plate of a specific length along the direction of movement is obtained, - the alternating curvature is such that it results in a plastification ratio of 55% or more, in which said plastification ratio is determined by the ratio across the thickness of the metal plate between: - the plastic zones (204, 206) of material of the metal plate which is plastically deformed; and - the elastic zone of material of the metal plate which is only elastically deformed at the location of the maximum curvature of the alternating curvature; and - the plastic zones (204, 206) of material of the metal plate which is plastically deformed; and - the elastic zone of material of the metal plate which is only elastically deformed at the location of the maximum curvature of the alternating curvature; and - the skin-pass elongation is such that it results in a translation ratio of 15% or more at the location of the alternating curvature, the translation ratio being determined by the ratio across the thickness of the metal plate between: - the translation of the elastic zone at the location of the maximum curvature of the alternating curvature; and - half the thickness of the metal plate. - the translation of the elastic zone at the location of the maximum curvature of the alternating curvature; and - half the thickness of the metal plate.