The inventive crimping tool (1) comprises a pushing head (2) which contact the fold (3) of a sheet (4) and has a front convex contour (5) in a plane view and a guiding seat (6) applicable to the sheet (4), wherein the pushing head (2) and the guiding seat (6) are remote from each other and define therebetween a groove (7) bounded by faces (8, 9) which are opposite in a substantially parallel direction with respect to the pushing head and the seat. The thickness (e) of said groove (7) substantially corresponds to the thickness of parts to be crimped, the front face of the pushing head is convexly connected to said flat face delimiting the groove and the bottom (10) thereof and extends along a convex contour, in particular substantially in a parallel direction with respect to the front face (5) of the pushing head (2).