Patent GB-675277-A (GB)
Title: Improvements in or relating to apparatus for forming sheet material such as sheet metal
IPC: B21D22/10
Filed: 1949-01-26
Abstract: 675,277. Stamping. MARTIN CO., G. L. Jan. 26, 1949 [June 3, 1948; Dec. 16, 1948], Nos. 2133/49 and 2134/49. Class 83 (iv). [Also in Group XXIX] In apparatus for forming sheet material to composite shape in which a box-like head member 1, Fig. 1, containing a block of resilient material 2 presses the sheet 28 over a forming die 27, a draw-ring 26 surrounding the die to support the edges of the work is yieldingly supported by hydraulic means in which the pressure is regulated in a predetermined manner as the material is progressively formed. The head member 1 comprises a box 31 containing the composite block 2 comprising layers 35 ... 37 of different rubber-like materials and held within the box by a ring 32 defining an opening 33 in the box. A bolster plate 21 supports the forming-die 27 and has holes 22 containing posts 25 to support the draw-ring 26 at selected positions according to its size and shape. Enlarged end portions 23 of any unused holes 22 are filled by plugs 24. A filler member 29 on the bolsterplate 21 surrounds the draw-ring 26 and slidingly engages the aperture 33 in the head member 1 to completely enclose the resilient block 2. Auxiliary filling-pieces 29<SP>1</SP>, Fig. 2, may further be used where the outer contour of the draw-ring 26 differs from the inner contour of the member 29, but if the draw-ring 26 completely fills the aperture 33, the filler members 29, 29<SP>1</SP> are omitted. The posts 25 rest on a ring 19 which is in turn yieldingly supported by four hydraulic pistons 14 in a cylinder block 10 resting on the base 5 of the press. The cylinders 11 are interconnected through passages 12 and are coupled to a hydraulic supply by a pipe 60. The pressure in the system is variable to predetermined values at given positions of the draw-ring 26 by a system of relief valves arranged in parallel and set at predetermined pressures and opened or closed as required by solenoid-operated valves controllable through the movement of the draw-ring 26. For this control a pin 41, Fig. 3, on the ring 19 projecting through the wall 18 of the bolster support moves an arm 44 over micro-switches 46, 48 as the draw-ring 26 moves. The switches are adjustable in position along bars 51, 52 and selectively open or close the solenoid-operated valves. Restrictor valves may be incorporated in the circuit to smooth out the pressure changes. In a modification the parallel system of relief valves is replaced by a single variable pressure relief valve 301, Fig. 15, controlled by a pre-set cam 318 moved with the draw-ring 26. The cam has a series of leaves 317 which may be set and locked by a nut 324. As the head 1 descends the hydraulic supply system 301 is cut off from the cylinders 11 by a valve 309 operated by a push-rod 315 on the head 1 so that as the draw-ring 26 is forced back the only path of escape is through the relief valve 301. When the head 1 is raised the valve 309 is again opened so that the supply system is reconnected to the cylinders 11 and the draw-ring raised to strip the work.