Patent GB-853113-A (GB)
Title: Improvements in or relating to apparatus for forming metal stock
IPC: B21D7/04
Filed: 1958-07-28
Abstract: 853,113. Stretch forming; bending. CYRIL BATH CO. July 28, 1958, No. 24295/58. Class 83 (4). [Also in Group XXXV] In a machine for stretch-forming a metal workpiece against a curved face-die, the tension applied to the workpiece is maintained at desired values by retroactive automatic control. In Fig. 1 a metal workpiece S to be stretchformed about a die 2 is held at one end against the die by hydraulic gripping means 19 and pulled at the other end by a gripping head 18. Forming is effected by rotating about a vertical axis a table 1 on which the die is mounted, while the tension applied to the head 18 is made to follow a predetermined programme. Head 18 is mounted on: a slide 17 which is pulled by an hydraulic ram 10, free to rotate about a vertical axis on a turn-table 13 so that the force applied is always tangential to the face of the die. Turn-table 13 is carried by a slide 14 movable along the frame of the machine by a further hydraulic ram 15 which is introduced automatically to apply tension to the workpiece when ram 10 reaches its limit of travel and operates a switch 131 controlling an hydraulic valve 124. If desired, forming may be assisted by a shoe 3 pressing the workpiece against the die under the influence of another ram 5, the hydraulic pressure applied to which is adjustable by manual operation of a relief valve 134, and the position of which is adjustable by movement of a slide 160. Control of ram 10 to facilitate insertion of the workpiece may be effected by a hand valve 22 controlling hydraulic pressure at the piston end of the ram. The tension applied to the workpiece is controlled by an electric motor 32 adjusting a relief valve associated with hydraulic supply at the piston-rod end of ram 10. A short length of I-section beam 40 appropriately positioned between head 18 and slide 17 carries strain gauges developing electric signals, representative of the tension applied to the workpiece, which are used for indication and control (see Group XXXV). One of these signals operates a voltmeter to indicate the tension. Electric motor 32 is first operated by a manual reversing controller to take up slack in the workpiece before forming commences. The other electric signal is then arranged to control motor 32 so that tension applied to the workpiece is automatically maintained at a value which is increased by a manual controller until a suitably connected voltmeter indicates that the elastic limit of the material has been reached. An electric relay then operates to reduce tension by a fixed amount and a final adjustment of tension is made manually. When forming is commenced by starting a motor to drive table- 1, tension is at first temporarily decreased and then varied, automatically, by cams, controlled by the rotation of table 1, which influence the automatic tension control system. When shoe 3 is also employed, strain gauges, associated with the shoe support, modify the automatic tension control system to compensate for frictional and other effects. Repeated wiping of the workpiece by shoe 3 while tension is maintained by the control system is referred to.