Method and device for the non-cutting production of an outside thread on hollow metal work pieces

Abstract

A method for the non-cutting production of an outer thread on hollow metal work pieces for use as hollow screws, hollow shafts, threaded sleeves or fittings as stable connecting or fastening elements. The method is particularly suited for thin-walled work pieces and a device is provided for carrying out the method. Within a multistage press formed with a displaceable carriage and a stationary work piece carrier unit, a wire or hollow tube section forming the base material is reshaped in one or more reshaping stages I to V into a finished hollow blank. In the multistage press, the pre-fabricated hollow blank is inserted in a further stage VI into a multipart split tool with a cavity having an inside wall that is provided with a negative of the thread to be formed. In the closed state of the split tool, at least one mandrel is inserted into the central opening of the blank and the blank is widened, wherein the contours of the threaded profile is filled by a radial material flow and subsequently the finished work piece is removed.

1 - 21 . (canceled) 
     
     
         22 . A method of producing an outside thread on a hollow metal work piece, the method which comprises:
 providing a multistage press with a displaceable carriage and a stationary work piece carrier unit;   feeding a base material of wire or bar stock within the multistage press and reshaping the base material in stages in one or more reshaping stages by extrusion and upsetting processes into a prefabricated hollow blank with a central opening;   inserting the prefabricated hollow blank in a further stage within the multistage press into a multipart split tool, the split tool having a cavity with an inside wall formed with a negative threaded profile, having a plurality of jaws with closing edges;   with the split tool closed, inserting at least one mandrel into the central opening of the blank and expanding the blank with the mandrel, thereby filling contours of the negative threaded profile by a radial material flow of the hollow blank and thereby forming the outside thread on the hollow blank; and   preventing material of the hollow blank from entering into spaces between said jaws, when said jaws are forced apart during the expanding step, by one or both of the following:
 providing the negative threaded profile in a region of the closing edges of the jaws with a reduced profile depth relative to a remaining region thereof, and thereby producing a relatively reduced threaded profile in those regions of the blank that are located in a region of the closing edges of the jaws; or 
 providing the hollow blank with small recesses in an area thereof intended for shaping the thread, the recesses running in a longitudinal direction of the hollow blank at locations where the jaws of the split tool meet; and 
   subsequently opening the split tool and removing the hollow blank in the form of a finished work piece from the split tool.   
     
     
         23 . The method according to  claim 22 , which comprises securing the blank inserted into the split tool during a movement of the mandrel against elongation in a longitudinal direction. 
     
     
         24 . The method according to  claim 22 , which comprises controlling an opening movement and a closing movement of the jaws of the split tool, and a movement of the mandrel, by a central drive unit of the multistage press. 
     
     
         25 . The method according to  claim 22 , wherein the central opening of the hollow blank has a cross-sectional shape selected from the group consisting of a circular shape, an oval shape, and a trilobular shape. 
     
     
         26 . The method according to  claim 22 , wherein the cavity of the blank is divided into a plurality of cavity sections by at least one partition, and the method comprises introducing a mandrel with a plurality of mandrel sections into the cavity. 
     
     
         27 . The method according to  claim 22 , wherein the limiting wall surrounding the cavity of the blank is interrupted at one or more points. 
     
     
         28 . The method according to  claim 22 , which comprises providing the threaded profile with a plurality of thread sections having mutually different thread geometries, and producing thread sections of different thread geometries during the expanding step. 
     
     
         30 . The method according to  claim 22 , which comprises producing threaded profiles containing other profiles or producing other profiles outside the threaded profile. 
     
     
         31 . The method according to  claim 22 , which comprises providing a mandrel with different form shaping zones for shaping the outside thread, the mandrel having a first section with a polygonal contact surface with rounded corners and the inner wall of the blank being extended radially only in the sphere of action of the corners, and the mandrel subsequently having a second section matched to a cross sectional shape of the cavity of the work piece and assuming a final shaping of the thread during the expanding process. 
     
     
         32 . The method according to  claim 22 , wherein the hollow blank in the area intended for shaping the thread is formed with small recesses running in a longitudinal direction arranged at the locations where the jaws of the split tool meet. 
     
     
         33 . A device for carrying out the method according to  claim 22 , which comprises:
 a multistage press with a displaceable carriage and a stationary work piece carrier unit;   at least one multipart split tool disposed within said multistage press either on said carriage or on said stationary work piece carrier unit, said multipart split tool having jaws and being movable into an opening position and a closing position and having a cavity limited by said jaws with at least one central opening into which a hollow blank can be inserted;   wherein an inner wall of said jaws limiting said cavity is formed with a negative threaded profile, said negative threaded profile of each of said jaws having a depth of thread continuously decreasing on both sides towards a marginal edge thereof, so that a thread profile is produced in a transition area at the adjoining edges of said jaws that is substantially reduced or no thread profile is produced;   at least one expandable mandrel configured for insertion into said hollow blank; and   a drive unit for driving at least one of said mandrel or said multipart split tool.   
     
     
         34 . The device according to  claim 33 , which further comprises, in addition to said split tool, a further swaging tool, at least one reverse extrusion tool and a punching tool disposed within said multistage press, said tools being fitted with dies, with a die positioned on said carriage and the other die opposite positioned on said work piece carrier unit. 
     
     
         35 . The device according to  claim 33 , which comprises at least one stop disposed for securing a position of the blank during an expanding process. 
     
     
         36 . The device according to  claim 33 , wherein said cavity limited by said inner wall of said jaws is so dimensioned that there is only a limited play or contact between a surface area of the insertable blank and said inner wall of said cavity in the closed state of said jaws. 
     
     
         37 . The device according to  claim 33 , wherein the threaded profile of said jaws is interrupted by other profiles. 
     
     
         38 . The device according to  claim 33 , wherein said jaws outside the threaded profile are fitted with other profiles. 
     
     
         39 . The device according to  claim 33 , wherein said expandable mandrel has different form shaping sections, with a first section configured for insertion into said blank having a polygonal construction with corners or edges coming into contact with said blank being rounded. 
     
     
         40 . The device according to  claim 34 , wherein said expandable mandrel comprises a plurality of longitudinally running sections or segments, between which a free space is formed in a radial direction. 
     
     
         41 . In combination with a device for the non-cutting forming of an outside thread on a metal work piece,
 the device including:
 a multipart split tool having jaws being movable into an open position and a closed position in which a cavity is defined by said jaws with a central opening, said jaws defining an inner wall limiting the cavity formed with a negative threaded profile; 
 at least one expandable mandrel and a drive unit for driving the mandrel and/or the multipart split tool; 
   a metal work piece, comprising:
 a hollow blank formed for insertion into the central opening of the multipart split tool and having an interior formed for receiving therein the expandable mandrel; 
 said hollow blank having an outside surface intended for shaping the thread formed with small recesses running in a longitudinal direction of said hollow blank at locations where the jaws of the split tool meet when said hollow blank is inserted into the central opening and the mandrel is being expanded.