Patent GB-1259773-A (GB)
Title: Improvements in and relating to the drawing of sheet metal
Inventor: HALL GEORGE ROBERTS
IPC: B21D22/28
Filed: 1968-02-15
Abstract: 1,259,773. Making hollow-ware; cupping. S.T.D. SERVICES Ltd. 14 Feb., 1969 [15 Feb., 1968], No. 7402/68. Headings B3A and B3Q. A container is formed from a sheet metal blank by advancing a plurality of interconnected telescoping punches as a composite unit to draw the blank through a die, advancing the punches to a second die, compressing a fluid to store excess energy converted by relative movement between one of the punches and the innermost punch, and using the stored energy for a further part of the method. One form of apparatus for carrying out the method but in which the energy store is not illustrated, includes three punches 10, 12, 14, Fig. 1, and a hold-down mounted on a mechanically, or hydraulically, operated press-head 18. After the punches 14, 12 complete their drawing stages they co-operate with the succeeding dies 52, 54 and act as hold-downs. Hydraulic cylinders 15, 16, 17 are associated with the punches 12, 14 so that when their supply conduits 25, 29 are closed the punches act as a unit. When the conduits are relieved relative movement occurs between the punches. The dies 50, 52, 54 are spaced apart so that the workpiece is engaged by one or more dies at the same time. In a modification illustrating the energy store, two punches 10, 14, Fig. 2, two dies 50 54 and a hold-down 101 are used. The holddown is applied, against an upward bias, by hydraulic cylinders 102 controlled by a valve 104 which is operated by an abutment 105 on the press-head or by a solenoid. A gas-loaded accumulator 106 and a pressure-control valve 108 are included. The hydraulic cylinder 16 for punch 14 is connected to a free-piston accumulator 38 which is connected to bottles 39, 39A of nitrogen gas. A pre-load is applied to the piston 41 by closing a cock 45 and opening a cock 43 to the high-pressure supply bottle 39A. The punches 10, 14 act in unison until a valve 36 in the hydraulic line 34 is opened by a solenoid or a cam 37 on the presshead when the hydraulic fluid is allowed to pass into the accumulator 38 for compressing the nitrogen. Energy thus stored is used to extend the punch 14 during return stroke of the press. An hydraulic make-up circuit for the punch includes a valve 60 and a pressureresponsive valve 62 for sensing leakage which is made up by the pump 44. If the valve 36 is omitted, the gas pressure in the accumulator 38 determines the drawing pressure at die 50. In this case the hold-down pressure of punch 14 against die 54 may be reduced by abutment of a flange (259), Fig. 18 (not shown), on the punch against an adjustable resilient support (256) in the form of springs or elastomeric material. In another constructor, Fig. 9, dies 50, 52, 54, 56 are arranged at each end of a doubleacting hydraulic press using one or two hydraulic cylinders and including telescopic punches 210, 212, 214 on each side of the press-ram 208. Two separate hydraulic circuits each have an accumulator 238, 239 similar to 38 in Fig. 2, accumulator 238 storing and releasing energy associated with the second die 52 of each set and accumulator 239 serving the third die 54 of each set. A stripper 58 and an hydraulic hold-down 220 are provided for each die set. The gas-capacity of the accumulators is sufficiently large for the increase in pressure due to hydraulic displacement to be a maximum of 3%, the hold-down pressure of the punches thus remaining substantially constant. Hydraulic fluid make-up circuitry may be included. A similar constructor, Fig. 15, uses a common hydraulic circuit connected at 326, 332 to chambers 328, 328A for the punches 312, 312A and at 340 to cylinders 332, 332A for the punches 314, 314A. An accumulator 338, resilient abutments 250 for controlling the hold-down pressure and work-holders 101 are provided. Two punch-and-die sets may be arranged on each side of the press-head 318 so that four containers are formed during each cycle of the press, or two accumulators may be used. The hydraulic energy transfer circuit may be omitted and the nitrogen bottles 39, 39A connected direct to the cylinder 16, Fig. 16, of a single- or double-acting press. A valve 43A between the bottles 39, 39A, is adjustable for controlling the pressure applied to the punch 14, and loss of gas is sensed by a regulating valve 43A which makes up the loss. Strippers.-The end 264, Fig. 17, of the central punch 10 may be movable by an hydraulic cylinder 263 to free the finished container W, which is then removed by a stripping ring 58.