GB871269A - Method of and means for deep drawing sheet material - Google Patents

Abstract

871,269. Cupping. BUDD CO. Aug. 14, 1959, No. 27812/59. Class 83 (4). A method of forming articles from a sheet metal blank by deep drawing by means of a punch moved transversely to the blank while permitting marginal portions of the blank to move towards the centre of the punch against restraining forces is characterized by the step of keeping the ratio between the size of the instantaneous zone of deformation and the restraining force virtually constant during the entire forming operation so that the stretching of the blank is the same in all successive instantaneous zones of deformation. A draw-press for carrying out the method has a base 10 supporting columns 11 which carry a stationary head 13 and a fixed lower blank holder 12. Slidably mounted on'the columns is a movable head 16 operable by a hand wheel 15 and a screw 14. An upper blank holder is connected with the piston-rods 18 of fluid pressure cylinders 20 secured to the movable head. Fluid pressure is supplied to the cylinders via a camoperated control valve 23. The press punch 28 is operated by a piston 26 in a fluid pressure cylinder 25 controlled by a valve 31. A cam member 35 connected to the piston-rod 27 operates the cam follower 38 of the control valve 23 to supply pressure fluid to the upper work-holder cylinders. In operation, the movable head 16 and the upper blank holder is raised by the screw 14 so that the blank can be placed on the lower blank holder. The punch is in its lowermost position. The movable head is then lowered until the upper blank holder engages the workpiece. As the punch is raised the cam 37 admits pressure fluid to the cylinders 20 to gradually increase the pressure of the blank holders on the margins of the workpiece so as to maintain a constant wall thickness in the drawn workpiece throughout the drawing operation. After removal of the workpiece from the press the marginal portions 45 are trimmed off adjacent the cupped portion. In an example, cupped articles from stainless steel and titanium of diameter 6 inch are formed from blanks of 11 inch diameter and 0.025 inch gauge using an initial pressure of 450 lb. per square inch and increasing to 1050 lb. per square inch.