Method, tool and device for the production of threads

Abstract

A method for the production of threads, especially internal threads, by means of a rotationally driven thread former, with which the thread pitches are driven in and out of the surface of the workpiece in a chipless fashion by pressure forming, in particular in and out of the inner surface of a workpiece bore. In order to be able to produce threads of different nominal diameter especially economically and with improved joining quality in the area of the thread, the thread is formed such that a shank tool in the fashion of a thread miller, equipped with at least one profile projection, preferably two profile projections located at a constant distance from one another, where the profile projections at its forming head are constructed as continuous over the circumference and with radial extension varying over the circumference, is driven into the workpiece initially at a circumferential point of the workpiece bore, preferably is brought to the total thread pressing depth, and while substantially retaining the eccentricity set with respect to the axis of the workpiece bore, executes a relative circular movement running through 360° (circular movement) relative to the axis of the tool bore, while the forming head simultaneously executes a constant axial relative feed movement by the extent of the thread pitch to be produced.

1 . A method for the production of threads by means of a rotationally driven thread tool, with which the thread pitches are driven in and out of the surface of the workpiece in a chipless fashion by pressure forming, in particular in and out of the inner surface of a workpiece bore, wherein the thread is formed such that a shank tool in the fashion of a thread miller, equipped with at least one profile projection where each profile projection at its forming head is constructed as continuous over the circumference and polygonal with radial extension varying over the circumference, inserted in a workpiece bore having a larger diameter and moved along the inner surface of the workpiece bore with a pre-determined axial feed while turning, wherein after insertion into the workpiece bore, the shank tool is driven radially into the workpiece initially at a circumferential point of the workpiece bore, and while substantially retaining the eccentricity set with respect to the axis of the workpiece bore, executes a relative circular movement running through 360° relative to the axis of the tool bore, while the forming head synchronously executes a constant axial relative feed movement by the extent of the thread pitch to be produced.  
   
   
       2 . The method according to  claim 1 , wherein the forming head has an axial extension which corresponds to the length of the thread to be produced.  
   
   
       3 . The method according to  claim 1 , wherein the forming head is driven into the workpiece bore substantially centrally to the extent of the thread depth, is then driven radially outward while retaining the axial relative position to the workpiece bore, until a thread ridge is fully formed at a circumferential point between adjacent profile projections, then executes the circular movement extending over 360° with simultaneous axial feed and finally is driven radially inward so that the profile projections of the forming head come out of engagement with the internal thread produced.  
   
   
       4 . The method according to  claim 3 , wherein the radially outwardly directed movement of the forming head takes place along an arc-shaped curve.  
   
   
       5 . The method according to  claim 4 , wherein on entry of the profile projections into the workpiece, the arc-shaped curve has a motion component in the direction of the subsequent circular movement.  
   
   
       6 . The method according to  claim 1 , wherein the profile projections with the radial extension varying over the circumference each form a plurality of pressing lands over the circumference.  
   
   
       7 . The method according to  claim 6 , wherein the processing lands are nonuniformly distributed over the circumference.  
   
   
       8 . The method according to  claim 6 , wherein the pressing lands of adjacent profile projections are offset with respect to one another in the circumferential direction.  
   
   
       9 . The method according to  claim 8 , wherein the axially adjacent pressing lands of the forming head each lie along a helix.  
   
   
       10 . The method according to  claim 1 , wherein the area of engagement with the workpiece the circumferential speed of the forming head is synchronized with the circular movement.  
   
   
       11 . The method according to  claim 1 , wherein the area of engagement with the workpiece the circumferential speed of the forming head is oppositely directed to the circular movement.  
   
   
       12 . A rotationally drivable tool for the production of threads by means of chipless pressure forming of the inner surface of a workpiece bore, comprising a forming head comprising at least two profile projections embodied in the fashion of a thread miller and located at a constant distance from one another, which are constructed as continuous over the circumference and with radial extension varying over the circumference, so that in the area of each profile projection, at least one pressing land is formed over the circumference, wherein the profile projections each form a plurality of pressing lands over the circumference with radially varying axial extension over the circumference, wherein the pressing lands of neighboring profile projections are offset with respect to one another in the circumferential direction.  
   
   
       13 . The tool according to  claim 12 , wherein the profile projections are axially offset with respect to one another by the extent of the thread pitch to be produced.  
   
   
       14 . The tool according to  claim 12 , wherein the forming head has an axial extension which substantially corresponds to the length of the thread to be produced.  
   
   
       15 . The tool according to  claim 12 , wherein the pressing lands are nonuniformly distributed over the circumference.  
   
   
       16 . The tool according to  claim 12 , wherein the axially adjacent pressing lands of the forming head each lie along a helix.  
   
   
       17 . The tool according to  claim 12 , wherein the depth of the grooves between neighboring profile projections varies over the circumference.  
   
   
       18 . The tool according to  claim 12 , wherein the depth of the grooves between neighboring profile projections remains substantially the same over the circumference.  
   
   
       19 . The tool according to  claim 12 , wherein said tool consists of a high-strength material.  
   
   
       20 . The tool according to  claim 12 , further comprising a tool carrier made of a support material which receives at least one tool strip of another material.  
   
   
       21 . The tool according to  claim 12 , wherein at least in the area of the pressing lands, the forming head is provided with a coating.  
   
   
       22 . The tool according to  claim 20 , wherein the coating is a hard material layer which consists of nitrides comprising the metal components Cr, Ti and Al and comprising the component C, wherein the Cr fraction is 30 to 65%, the Al fraction is 15 to 80%, and the Ti fraction is 16 to 40%, each relating to all the metal atoms in the entire layer.  
   
   
       23 . The tool according to  claim 21 , wherein the structure of the entire layer consists of a homogeneous mixed phase.  
   
   
       24 . The tool according to  claim 21 , wherein the structure of the entire layer consist of a plurality of homogeneous individual layers per se, which alternately consist on the one hand of (Ti x Al y Y z )N with x=0.38 to 0.5 and y=0.48 to 0.6 and z=0 to 0.04 and on the other hand consist of CrN wherein the uppermost layer of the wear-protective layer is formed by the CrN layer.  
   
   
       25 . A device for carrying out the method according to  claim 1 , comprising a drive spindle for the rotationally driven thread former and a triaxial control system with which the feed movement along the tool axis, the driving-in and driving-out movements of thread formed into and out of engagement with the workpiece and the circular movement are executed in a synchronized fashion.  
   
   
       26 . The device according to  claim 25 , wherein the triaxial control system is provided by a 3D CNC machine tool.