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 and configured to heat a first portion of the roller body, in such a way that the roller-shaped main body is arranged to heat said plurality of sheets in a differentiated form, particularly at their areas in contact with said first portion of the 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 locally heating the sheets to a predetermined temperature by means of said kiln in such a way as to obtain sheets with areas at different temperatures, - removing the locally-heated sheets from the kiln, - 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 and configured to heat a first portion of the roller body, in such a way that the roller-shaped main body is arranged to heat said plurality of sheets in a differentiated form, particularly at their areas in contact with said first portion of the 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 and configured to heat a first portion of the roller body, in such a way that the roller-shaped main body is arranged to heat said plurality of sheets in a differentiated form, particularly at their areas in contact with said first portion of the 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 locally heating the sheets to a predetermined temperature by means of said kiln in such a way as to obtain sheets with areas at different temperatures, - removing the locally-heated sheets from the kiln, - 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.