Bending or folding a sheet of material (13; 30; 54, 64) from a flat into a three dimensional form, the sheet having groups of hinge lines 16, by means of two frame members (1, 2; 41,42) movable vertically relative to each other, one frame (1; 42) having sheet supporting parts (11; 21; 61) mounted for movement in the plane of the frame and pivotally attached to one group of hinge lines (16) and the other frame (2; 41) having sheet supporting parts (11a, 11b, 22; 51) mounted for movement in the plane of the frame and pivotally attached to a second group of hinge lines (16) relative vertical movement of the frames (1, 2; 4642) causing the sheet to bend about the hinge lines and assume the three dimensional form. Each frame (41, 42) and one sheet (54, 64) can form the upper and lower platens of a press in which means are provided to bring the sheets (54, 64) adjacent each other and simultaneously assume their three dimensional forms causing a deformable metal sheet sandwiched therebetween to be pressed into an identical shape.