A method for moulding a sheet into a component of complex shape having areas with different mechanical properties, particularly a motor-vehicle component, includes a first heating step of the sheet carried out 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 incorporated in the roller-shaped main body, so as to heat the sheets in contact with 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. An additional heating step follows extraction of the sheets from the kiln, wherein the sheets are locally heated only at one area, so as to obtain sheets with areas heated to different temperatures.