A method for moulding a sheet into a component of complex shape having areas with different mechanical properties, particularly a motor-vehicle component, such as, for example, the central upright of a motor-vehicle body, comprising the following steps: - arranging at least one mould for forming the sheet configured to produce said motor-vehicle component; - arranging at least one kiln to carry out a heating step of the sheet, prior to forming said sheet, said kiln comprising: - a casing (2, 11) of refractory material having at least one inlet port and one outlet port arranged for inserting and extracting a sheet from said kiln, respectively, - a main body with a roller shape arranged inside said casing (2, 11) and having a plurality of sectors extending along a radial direction with respect to a longitudinal axis of the roller body, said sectors being configured to each receive a sheet, in such a way that said roller-shaped main body is designed to simultaneously carry a plurality of sheets, - a plurality of heating elements incorporated in said roller-shaped main body so as to heat said roller body, in such a way that the roller-shaped main body is arranged to heat said plurality of sheets, at their areas in contact with said roller body, - at least one electronically-controlled drive motor, arranged to rotate said roller-shaped main body around said longitudinal axis, so as to vary the position of the sectors with respect to the inlet and outlet ports (6, 7); - inserting a plurality of sheets within said sectors and uniformly heating the sheets to a predetermined temperature by means of said kiln, - removing the thus heated sheets from the kiln, - carrying out an additional heating step following 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. - subjecting the sheets to a forming step within said mould and uniformly cooling the locally-heated sheets, so as to obtain a component of complex shape having areas with different mechanical properties. - arranging at least one mould for forming the sheet configured to produce said motor-vehicle component; - arranging at least one kiln to carry out a heating step of the sheet, prior to forming said sheet, said kiln comprising: - a casing (2, 11) of refractory material having at least one inlet port and one outlet port arranged for inserting and extracting a sheet from said kiln, respectively, - a main body with a roller shape arranged inside said casing (2, 11) and having a plurality of sectors extending along a radial direction with respect to a longitudinal axis of the roller body, said sectors being configured to each receive a sheet, in such a way that said roller-shaped main body is designed to simultaneously carry a plurality of sheets, - a plurality of heating elements incorporated in said roller-shaped main body so as to heat said roller body, in such a way that the roller-shaped main body is arranged to heat said plurality of sheets, at their areas in contact with said roller body, - at least one electronically-controlled drive motor, arranged to rotate said roller-shaped main body around said longitudinal axis, so as to vary the position of the sectors with respect to the inlet and outlet ports (6, 7); - a casing (2, 11) of refractory material having at least one inlet port and one outlet port arranged for inserting and extracting a sheet from said kiln, respectively, - a main body with a roller shape arranged inside said casing (2, 11) and having a plurality of sectors extending along a radial direction with respect to a longitudinal axis of the roller body, said sectors being configured to each receive a sheet, in such a way that said roller-shaped main body is designed to simultaneously carry a plurality of sheets, - a plurality of heating elements incorporated in said roller-shaped main body so as to heat said roller body, in such a way that the roller-shaped main body is arranged to heat said plurality of sheets, at their areas in contact with said roller body, - at least one electronically-controlled drive motor, arranged to rotate said roller-shaped main body around said longitudinal axis, so as to vary the position of the sectors with respect to the inlet and outlet ports (6, 7); - inserting a plurality of sheets within said sectors and uniformly heating the sheets to a predetermined temperature by means of said kiln, - removing the thus heated sheets from the kiln, - carrying out an additional heating step following 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. - subjecting the sheets to a forming step within said mould and uniformly cooling the locally-heated sheets, so as to obtain a component of complex shape having areas with different mechanical properties.