Patent GB-790622-A (GB)
Title: Improvements in or relating to presses for drawing sheet metal
IPC: B21D22/00
Filed: 1954-01-26
Abstract: 790,622. Cupping. WATSON, F. J. and QUADRANT ENGINEERING CO., Ltd. April 25, 1955 [Jan. 26, 1954], No. 2407/54. Class 83 (4). A cupping press in which the punch and die are moved by tool carriers relatively towards one another and a pressure plate and abutment grip the margins of the blank so that during the draw part of the metal is drawn from between the pressure plate and abutment, the pressure plate being supported by fluid pressure in a pressure cushion, includes in combination, an over pressure valve operable automatically to permit fluid to escape from the cushion cylinder when above a datum pressure, datum varying means and an operative connection between the datum varying means and at least one of the tool carriers so as to vary the datum pressure in a predetermined manner in timed relationship with the tool carriers the variation of the datum pressure during at least part of the draw being such that the pressure exerted on the metal blank by the pressure plate decreases as the draw proceeds. The regulator unit 11 comprises a housing' 15 having two chambers 16, 17 each divided into two sub-chambers 18, 19 and 21, 22 by flexible spring-loaded diaphragms 23, 24 respectively. An air passage 28 connects the sub-chambers 19, 22 to the pressure cushion cylinder 32. The sub-chamber 19 has an air outlet tube 33 which houses an adjustable tapered over-pressure valve 36. The inner end of the tube is normally closed by a spring-loaded mushroom valve 38 having a stem 39 slidable within the valve 36. The stem 39 has a tapered portion 41. The valve 38 is urged to its closed position by a stud 43 on the diaphragm 23. The sub-chamber 22 is provided with an inlet tube 44 normally closed by an under-pressure valve 46 supported by spring- loaded metal bellows 47. The bellows spring is adjustable by a screw member 49 and the valve is opened by a rod 53 actuated by a stud 55 on the diaphragm 24. Compressed air is supplied from an inlet 56 to the sub-chamber 22 when the valve is open. Each diaphragm is guided by a hollow stem 57. The sub-chambers 18, 21 are filled with oil and connect respectively with chambers 71, 72 of the accumulator unit 12. Associated with spring-loaded diaphragms 75, 76 in the chambers 71, 72 respectively are two springs 82, 83 held in position by projections 84, 85 on diaphragm plates 78, 81 and plates 86, 87, guided by pillars 88 and sleeves 89. The plates 86, 87 are engaged by rollers 93 mounted on pivoted beams 94 actuated by cams 97 on the.press crankshaft 98. In operation, the degree of compression of the springs 82, 83 is varied by the cams 97 as the shaft 98 rotates and the varying spring pressures are transmitted to the sub-chambers 18, 21 of the regulator unit thereby determining the datum pressures for the under-pressure and over-pressure valves. The difference between these datum pressures is adjustable by means of screws 99 on the roller blocks 100. In an embodiment, the tool carrier 101 supporting the pummel 103 is stationary and the die 104 is supported by the movable tool carrier 102. The pressure plate 105 is carried on pins attached to a cushion plate 107 supported by a piston 109 working in the pressure cushion cylinder 32. The cams are shaped so that the pressure applied by the pressure plate gradually decreases as the draw proceeds the initial pressure being sufficiently high to prevent wrinkling of the blanks and the gradual decrease adjusted to prevent tearing of the partly drawn blank. The die 104 may be replaced by a confined rubber member and each of the accumulator unit springs 82, 83 may be replaced by two or more springs, of different lengths arranged concentrically to widen the range of spring characteristics. The two cams 97 may have different contours so as to raise the datum of the over-pressure valve more than that of the under-pressure valve to permit the pressure in the cushion cylinder to build up under certain conditions of dwell while permitting the under-pressure valve to open if the pressure in the cushion cylinder falls below the under-pressure valve datum.