Patent GB-597632-A (GB)
Title: Improvements in or relating to stamping and drawing presses
IPC: B21D24/08
Filed: 1944-03-20
Abstract: 597,632. Cupping. GENERAL MACHINERY CORPORATION. March 20, 1944, No. 6160. Convention date, March 27,1943. [Class 83 (iv)] A stamping and drawing press having two relatively 'movable die carrying members including a bolster plate has an air cushion mechanism operable by pins extending through the bolster plate and comprising a cylinder and a co-operating piston movable in one direction by pressure air and in the other direction under the pressure exerted by the dies during the working stroke, adjusting means for limiting the extent of relative movement of the piston and cylinder to a stroke slightly in excess of the travel caused by the working movement of the dies and less than the maximum distance obtainable, one member of the cushion mechanism being spaced slightly from the opposite wall of the pressure space to leave a predetermined slight clearance at lower dead centre. The press comprises a bed member 20, Fig. 3, upright outside frame members and a cross web 22<1> which support a bolster plate 30 carrying the lower die 23, Fig. 2. An upper die 24 is carried by a slide 22 adapted to be reciprocated vertically between the uprights. For a bending or drawing operation, the edges of the metal sheet 26 are held between side members of the die 24 and a ring or plate 25 surrounding the lower die 23 and supported by rods 36 extending through holes 35 in the bolster plate and mounted in a plate 40. The bolster plate is formed with a comparatively large number of holes and a selected number are used according to the ring 25 required for the particular operation to be performed. The plate 40 is bolted to the top of the piston which comprises an upper annular wall, a depending outer cylindrical skirt 43 and an inner cylindrical depending wall 42 with a base 51 and which co-operates with a hollow walled cylinder 45 bolted to a supporting flange 47 formed on the bed member 20. Packing members 54, 56 between the piston and cylinder serve to seal an upper annular air space 61 and a lower air space 60 adapted to be separately connected to a pipe 75 which may be opened to atmosphere through a three-way solenoid operated valve 70 or connected to a surge tank by way of valve 70, pipe 69 and a two-way solenoid operated valve 68. If desired; the space 61 may be cut-off from the tank and connected to atmosphere by a manually operated valve 85. The upward movement of the piston under air pressure is limited by a stop 97 on a rod 96 which extends through the piston wall 51, air space 60 and lower cylinder wall and has a screw-threaded lower end cooperating with a nut 100 adapted to be rotated through worm gearing from a motor 110. Movement of the nut 100 is normally prevented by brake shoes 120, Fig. 18, acting on a brake drum 116 under the action of a spring 117 but adapted to be released by the action of a solenoid 118 when the motor 110 is switched on. The operation of the press is normally automatic and is first set by manually-operated switches according to the manner of operation required and then controlled by switches operated by cam drums on a shaft driven by the mechanism, not shown, by which the slide 22 is reciprocated by a self-contained electric motor. For a stamping operation, the space 61 is shut-off from the surge tank and opened to atmosphere by the manual valve 85 and at the beginning of the down-stroke of the slide 22, the space 60 is connected to atmosphere through the three-way valve 70. On the completion of the stamping operation and on the upward movement of the slide 22, the space 60 is connected to the tank 65 through valves 68, 70 and air enters to raise the piston and the ring 25 which in this operation serves only as a lift-off device for the work. For drawing, the operation begins with the parts in the position shown in Fig. 2, both air spaces 60 and 61 being connected to the surge tank 65. As the die 24 descends, the edges of the metal sheet 26 are held by the air pressure between the die and the ring 25. The ring is pushed downwards, air moving back from the cylinder to the tank 65, and the edges of the sheet are drawn out over the side of the lower die 23. At the bottom of the stroke of the die 24, the piston is preferably about one eighth of an inch from the bottom of the cylinder and the valves 68, 70 are then operated to exhaust the spaces 60, 61 and the piston descends the final small amount by gravity. This obviates the need for a mechanical locking or holding down device. The slide 22 then rises and air is again admitted to the cylinder to raise the ring 25 which now acts as a lift-off device for the work. A gauge 203 connected to the piston indicates the position thereof and a further gauge 213 is connected to the rod 96 to indicate the limit of upper movement of the piston. A number of piston and cylinder cushioning devices may be included in the press, the number used at any time depending on the size and nature of the work.