Forming Tool and Method for Enlarging an Opening by Means of an Enlarging Device

Abstract

A forming tool for widening an opening includes an expanding device with several expansion elements. The expansion elements are each provided with a curved forming surface extending between two peripheral end edges. The expansion elements are moveable between a first position corresponding to a contracted state where the expansion elements in connection with one another by way of separating surfaces, and a second position corresponding to a widened state where the expansion elements are displaced in radial direction from a center of the expanding device such that the separating surfaces are spaced apart from one another. In the first position the peripheral end edges are spaced further apart from the center than a central region of the forming surfaces so that the fatigue strength of mounting bores can be increased, openings in thick-walled components can expanded more reliably, and/or the formation of cracks is avoided.

1 - 15 . (canceled) 
     
     
         16 . A forming tool for widening an opening, the forming tool comprising:
 an expanding device comprising several expansion elements,   wherein the expansion elements each have a curved forming surface extending between two peripheral end edges,   wherein the expansion elements are moveable from a first position to a second position,   wherein in the first position, which corresponds to a contracted state, the expansion elements are connected with one another by way of separating surfaces,   wherein in the second position, which corresponds to an expanded state, the expansion elements are displaced in a radial direction from a center of the expanding device such that the separating surfaces are spaced apart from one another,   wherein in the first position, the peripheral end edges are spaced further apart from the center than a central region of the forming surfaces.   
     
     
         17 . The forming tool of  claim 16 , wherein the peripheral end edges and the forming surfaces are equidistantly spaced apart from the center in the second position. 
     
     
         18 . The forming tool of  claim 16 , wherein the forming surface of the expansion elements, seen in cross section in the radial direction, have a shape of a circular arc. 
     
     
         19 . The forming tool of  claim 18 , wherein
 in the first position the peripheral end edges are located on a circumscribed circle and the central region of the forming surface is at a distance from the circle, and   the second position, both the peripheral end edges and the forming surfaces are located on a circumscribed circle.   
     
     
         20 . The forming tool of  claim 18 , wherein in the first position, a radius of the forming surfaces is greater than a distance of the end edges from the center of the expanding device. 
     
     
         21 . The forming tool of  claim 18 , wherein in the first position, a radius of the forming surfaces is between 2.5% and 10% greater than a distance of the end edges from the center of the expanding device. 
     
     
         22 . The forming tool of  claim 18 , wherein in the first position, a radius of the forming surfaces is 5% greater than a distance of the end edges from the center of the expanding device. 
     
     
         23 . The forming tool of  claim 16 , further comprising:
 a drive element configured to move the expanding device from the first position to a second position.   
     
     
         24 . The forming tool of  claim 23 , wherein the drive element includes a mandrel configured for insertion into an inner hole of the expanding device. 
     
     
         25 . The forming tool of  claim 24 , wherein at least inner surface of the inner hole or at least one outer surface of the mandrel has a coating. 
     
     
         26 . The forming tool of  claim 25 , wherein the coating is formed of an electrochemically applied nickel layer and/or a diamond-like carbon layer having a thickness of few nanometers and up to several micrometers. 
     
     
         27 . The forming tool of  claim 23 , wherein an angle between a central axis M of the mandrel and an outer surface is between 0.3 degrees and 3 degrees. 
     
     
         28 . An expansion element for use in a forming tool the expansion element comprising:
 several expansion elements,   wherein the expansion elements each have a curved forming surface extending between two peripheral end edges,   wherein the expansion elements are moveable from a first position to a second position,   wherein in the first position, which corresponds to a contracted state, the expansion elements are connected with one another by way of separating surfaces,   wherein in the second position, which corresponds to an expanded state, the expansion elements are displaced in a radial direction from a center of the expanding device such that the separating surfaces are spaced apart from one another,   wherein in the first position, the peripheral end edges are spaced further apart from the center than a central region of the forming surfaces.   
     
     
         29 . The expansion element of  claim 28 , wherein the expansion element has a trapezoidal cross-sectional shape, wherein at least one side extending between the two legs is curved. 
     
     
         30 . A method for widening an opening from a first diameter to a second diameter, the method comprising the following steps:
 a) providing several expansion elements, each having a forming surface and two separating surfaces extending between two end edges, wherein the expansion elements are moveable from a first position, which in an unexpanded state corresponds to the first diameter, to a second position, which corresponds to the second diameter in the desired expanded state, by displacing the expansion elements in a radial direction, wherein the separating surfaces and the forming surfaces are configured such that in the first position, a central region of the forming surfaces, when placed against the non-widened opening, is further apart from the inner wall of the opening than the end edges, and that in the second position, the forming surfaces altogether correspond to the contour of the inner wall of the desired expanded opening;   b) assembling the expansion elements to form an expanding device and moving the expansion elements to the first position;   c) inserting the expanding device into the opening; and   d) continuously expanding the opening by moving the expansion elements into the second position.   
     
     
         31 . The method of  claim 30 , further comprising:
 widening the opening from one side so that with two adjacent workpieces, only one of the two openings is widened.   
     
     
         32 . The method of  claim 30 , wherein the expanded opening has a diameter d in a workpiece having a plate or stack thickness t, wherein t>d.