A method for molding a sheet into a motor-vehicle component includes heating the sheet by a kiln, prior to forming the component. The kiln has a main body with a roller shape, having a plurality of sectors extending along a radial direction with respect to a longitudinal axis of the roller body. The sectors are configured to each receive a sheet, so that the main body with a roller shape is arranged to simultaneously carry a plurality of sheets. The kiln includes a plurality of heating elements in said main body with a roller shape and configured to heat only the first portion of the roller body, so that the roller shaped main body is designed to heat the sheets in a differentiated way, particularly at their areas in contact with said first portion of the roller body. The kiln includes at least one electronically-controlled drive motor, arranged to rotate the roller-shaped main body around the longitudinal axis of the kiln, so as to vary the position of the sectors with respect to the inlet and outlet ports.