An assembly for preforming a sheet of reinforcement fabric, said sheet of reinforcement fabric being intended to be subjected to at least one deformation action to make a preformed shell, comprising: - at least one frame; - a plurality of gripping devices adapted to grip the sheet of reinforcement fabric, said plurality of gripping devices being associated either directly or indirectly with said at least one frame; wherein: - each gripping device of said plurality of gripping devices being adapted to grip a margin portion of the sheet of reinforcement fabric; - said assembly further comprises a moving system comprising a plurality of first moving devices; wherein - movement of each first moving device is independent of that of the other first moving devices; - each gripping device of said plurality of gripping devices being associated with a first moving device; - said first moving device being adapted to move each gripping device of said plurality of gripping devices independently of the others, so that when said sheet of reinforcement fabric is gripped by said plurality of gripping devices, each gripping device can move to guide localized deformations of the sheet of reinforcement fabric which occur during the deformation action of the sheet of reinforcement fabric; characterized in that - said assembly comprises a plurality of supports, associated either directly or indirectly with said frame, each support of said plurality of supports being also associated either directly or indirectly with at least one gripping device so as to support at least one gripping device; and wherein - each support is associated with a respective gripping device and with a respective first moving device; and wherein - said first moving device is fixed to said support and each gripping device further comprises a carriage associated with said support and adapted to translate with respect to said support when moved by said first moving device; and wherein - at least one support comprises at least one support joint; and wherein - said support is associated with said frame by means of said support joint which guides the rotation of the support with respect to the frame. - at least one frame; - a plurality of gripping devices adapted to grip the sheet of reinforcement fabric, said plurality of gripping devices being associated either directly or indirectly with said at least one frame; - each gripping device of said plurality of gripping devices being adapted to grip a margin portion of the sheet of reinforcement fabric; - said assembly further comprises a moving system comprising a plurality of first moving devices; - movement of each first moving device is independent of that of the other first moving devices; - each gripping device of said plurality of gripping devices being associated with a first moving device; - said first moving device being adapted to move each gripping device of said plurality of gripping devices independently of the others, so that when said sheet of reinforcement fabric is gripped by said plurality of gripping devices, each gripping device can move to guide localized deformations of the sheet of reinforcement fabric which occur during the deformation action of the sheet of reinforcement fabric; - said assembly comprises a plurality of supports, associated either directly or indirectly with said frame, each support of said plurality of supports being also associated either directly or indirectly with at least one gripping device so as to support at least one gripping device; and wherein - each support is associated with a respective gripping device and with a respective first moving device; and wherein - said first moving device is fixed to said support and each gripping device further comprises a carriage associated with said support and adapted to translate with respect to said support when moved by said first moving device; - at least one support comprises at least one support joint; and wherein - said support is associated with said frame by means of said support joint which guides the rotation of the support with respect to the frame.