Method and bending device for bending flat metal workpieces

Abstract

The invention relates to a method and device for bending flat metal workpieces, especially steel sheets, by bending freely over edges along a bending line with a straight, linear movement of the tool, wherein the bending edges are arranged parallel to the longitudinal direction of the sheet and the tool is displaced along the width of the metal sheet, characterized by the steps: inserting a punch between the bending edges of a die, holding the punch at the lowest point of the bend, applying compressive stress in order to level out the stresses in the shaping zone produced by the bending and incrementally superimposing the tensile stress with compressive stress, that is effective along the bending line in the direction of the sheet width of the bent workpiece, wherein the tool producing the compressive stress is moved along the bending line in the direction of the sheet width. In the bending device between the die assemblies below the punch, a carriage is arranged that can be displaced in the direction of the bending axis (i.e. in the sheet width) with a nip roller being effective in the punch axis, which has a groove in the plane of intersection with the punch axis.

1 . Method for bending flat metal workpieces, in particular steel sheets, by bending freely over edges along a bending line with straight linear tool movement, wherein the bending edges are arranged parallel to the longitudinal direction of the sheet and the tool moves along the sheet width, characterised by the following steps
 a) inserting a punch between the bending edges of a forming die,   b) holding the punch at the lowest point of the bend,   c) applying compressive stress to compensate for the stresses in the shaping zone produced by bending   d) incremental superimposition of the tensile stress by compressive stress, which is performed along the bending line in the direction of the sheet width of the bent workpiece, whereby the tool generating the compressive stress is moved along the bending line in the direction of the sheet width.   
     
     
         2 . Method according to  claim 1 , characterised in that the superimposition of the tensile stress in the shaping zone is performed by an incrementally generated compressive stress between the bending edge and bending line, and the bending angle is influenced (adjusted) variably locally over the width of the metal sheet. 
     
     
         3 . Method according to one of the preceding claims, characterised in that the incremental superimposition of the tensile stress with compressive stress is performed by surface pressure, which is in the elastic range i.e. below the yield stress limit R P 0,2  of the respective material. 
     
     
         4 . Method according to one of the preceding claims, characterised in that the compressive stress is generated incrementally with an increasing and decreasing stress peak in the region of the maximum tensile stress between the bending edge and bending line. 
     
     
         5 . Bending device for performing the method according to  claim 1 , consisting of a forming die with two parallel die assemblies and a punch arranged above the die assemblies, which punch can be inserted into the intermediate space between the bending edges, characterised in that between the die assemblies underneath the punch a carriage with a nip roller effective in the punch axis is arranged which can be moved in the direction of the bending axis (i.e. in the sheet width), which nip roller comprises a groove in the section plane with the punch axis. 
     
     
         6 . Bending device according to  claim 5 , characterised in that a bending angle sensor can be inserted at a distance in front of the nip roller between the bending edges and the nip roller is advanced according to the sensor signal measurement. 
     
     
         7 . Bending device for performing the method according to  claim 1 , characterised in that the groove has a V-shape, a radius. 
     
     
         8 . Bending device according to one of the preceding claims, characterised in that the forming die comprises interchangeable and rotatable die assemblies and in this way different die widths can be adjusted. 
     
     
         9 . Bending device according to one of the preceding claims, characterised in that the application of compressive stresses is performed incrementally by means of the nip roller along the bending line. 
     
     
         10 . Bending device according to one of the preceding claims, characterised in that the advancing speed for the movement of the nip roller along the bending line of the bent workpiece is controlled. 
     
     
         11 . Bending device according to one of the preceding claims, characterised in that the depth of the V-groove in the nip roller is measured such that the contact area of the selected groove (V-groove, annular groove) extends with the external wall of the metal sheet into the pulling area of the shaping zone of the metal sheet. 
     
     
         12 . Bending device according to one of the preceding claims, characterised in that the groove width of the V-groove is adjusted to the bending radius of the metal sheet, so that a large contact area is created with the nip roller over the entire width of the shaping zone.