Active reconfigurable stretch forming

Abstract

This invention concerns an active reconfigurable stretch forming tool, and in another aspect the invention is a method of stretch forming. The tool comprises an array of extensible shape forming elements which are driven in extension to produce the same force per unit area across a workpiece during shape forming. An array of limit switches are located in front of the array of shape forming elements, such that each shape forming element is driven in extension towards a respective limit switch during shape forming. In use, each limit switch is activated by the workpiece as it is shaped and each switch, upon activation, prevents further extension of the respective driven element. The tool and method are useful in the forming of three dimensional shapes in solid sheet metal or mesh, to produce panels for reflector antennas.

1 . An active reconfigurable stretch forming tool for forming a three dimensional shape in a solid sheet metal or mesh workpiece, to produce a panel for a reflector antenna; the tool comprising:
 an array of extensible shape forming elements which are driven in extension to produce the same force per unit area across a workpiece during shape forming; and,   an array of limit switches located in front of the array of shape forming elements, such that each shape forming element is driven in extension towards a respective limit switch during shape forming;   wherein, in use, each limit switch is activated by the workpiece as the workpiece is shaped and each switch, upon activation, prevents further extension of the respective driven element.   
     
     
         2 . The active reconfigurable stretch forming tool according to  claim 1 , wherein the array of limit switches defines a shape to be imparted to the workpiece. 
     
     
         3 . The active reconfigurable stretch forming tool according to  claim 1 , wherein the tool incorporates shape-control feedback or error correction during shape forming. 
     
     
         4 . The active reconfigurable stretch forming tool according to  claim 1 , wherein the shape forming elements comprise hydraulic cylinders and rams each, of which is powered from a single hydraulic power supply. 
     
     
         5 . The active reconfigurable stretch forming tool according to  claim 4 , wherein each ram is surmounted by a tilting pad and each tilting pad is interlocked with its adjacent pads to form a continuous articulated surface. 
     
     
         6 . The active reconfigurable stretch forming tool according to  claim 5 , wherein the tilting pads are provided with a spherical seat to fit spherical ends on the rams of the hydraulic cylinders. 
     
     
         7 . The active reconfigurable stretch forming tool according to  claim 5 , wherein an interpolator is located on the articulated surface to receive the workpiece. 
     
     
         8 . The active reconfigurable stretch forming tool according to  claim 7 , wherein the rams are arranged below the workpiece to produce concave workpieces. 
     
     
         9 . The active reconfigurable stretch forming tool according to  claim 8 , wherein there is an array of rams both above and below the workpiece. 
     
     
         10 . The active reconfigurable stretch forming tool according to  claim 5 , wherein the limit switches are aligned vertically over respective tilting pads. 
     
     
         11 . The active reconfigurable stretch forming tool according to  claim 1 , wherein each limit switch is connected to a simple solenoid valve in a hydraulic line leading to its respective cylinder such that, as the workpiece is shaped the workpiece will contact one or more of the limit switches, and as soon as the workpiece contacts one or more of the limit switches the switch operates to close the solenoid valve and prevent further movement of the respective tilting pad. 
     
     
         12 . The active reconfigurable stretch forming tool according to  claim 11 , wherein the limit switches are constant-contact analogue devices. 
     
     
         13 . The active reconfigurable stretch forming tool according to  claim 12 , wherein the limit switches are programmed or set to trigger at a predetermined height. 
     
     
         14 . The active reconfigurable stretch forming tool according  claim 13 , wherein the shaping surfaces of the tilting pads are formed with a spherical radius approximating the curvature of a required panel. 
     
     
         15 . The active reconfigurable stretch forming tool according to  claim 14 , wherein a number of sets of tilting pads with a range of spherical radii are provided for the tool. 
     
     
         16 . The active reconfigurable stretch forming tool according to  claim 13 , wherein the top of each tilting pad is flat with provision for clipping inserts of varying spherical radius into place. 
     
     
         17 . A method for forming three dimensional shapes in a solid sheet metal or mesh workpiece, to produce a panel for a large reflector antenna, the method comprising:
 stretching a metal workpiece in a flat state in front of an array of extensible shape forming elements;   driving each shape forming element of the array in extension to produce the same force per unit area across the workpiece, to form a shape in the workpiece;   extending each shape forming element towards a respective limit switch during shape forming until the workpiece activates the limit switch; and,   preventing further extension of a shape forming element upon activation of the respective limit switch.   
     
     
         18 . The method according to  claim 17 , comprising the further step of applying shape-control feedback or error correction as shaping proceeds. 
     
     
         19 . The method according to  claim 18 , wherein each limit switch is connected to a simple solenoid valve in the hydraulic line leading to its respective cylinder such that, as the workpiece is shaped the workpiece will contact one or more of the limit switches, and as soon as the workpiece contacts the one or more of the limit switches the switch operates to close the solenoid valve and prevent further movement of the respective tilting pad. 
     
     
         20 . The method according to  claim 19 , wherein, the limit switches are programmed or set to trigger at a predetermined height.