GB754232A - Auxiliary arrangement for equalising the drawing pressure for deep drawing tools, more particularly for eccentric and friction presses - Google Patents

Abstract

754,232. Cupping. GLASER, J., and GANAL, M. Feb. 19, 1954 [Feb. 25, 1953; Jan. 9, 1954], No. 4980/54. Class 83 (4). [Also in Group XXIX] An auxiliary arrangement for deep drawing presses more particularly for eccentric and friction presses, for the hydraulic equalization of the working pressure is characterised by the provision of a pressure cylinder and of a control cylinder, the control cylinder being' fixed to the plunger guide of the press and the pressure spaces of the two cylinders being hydraulically connected with one another. The press comprises a die 3 carried by a plunger 2 slidable in guides 1. An annular holder plate 4 is guided in a yoke piece 6 carrying a ram 8 and supported by pins 5 which abut the top surface of a hydraulic pressure piston 11 in a cylinder 10. The pressure cylinder 10 is connected via an adjustable throttle valve 31 to a control cylinder 15 attached to the plunger guide 1. The piston-rod 17 of the control piston 16 has a roller 18 which co-operates with a cam disc 19 pivoted and spring-loaded on an arm 20 attached to the plunger 2. A longitudinally adjustable stop 25 on the cylinder 15 co-operates with a tappet 24 connected to the cam 19. On the control cylinder 15 is mounted a pressure fluid reservoir 35 which communicates with the cylinder 15 by way of an adjustable double valve comprising an outlet safety valve 37 and an inlet valve 36 for compensating oil losses. On the commencement of the drawing operation downward movement of the piston 11 forces fluid through the adjustable valve 31 into the control cylinder 15 and pushes the piston 16 downwards so that the roller 18 follows the cam means attached to the plunger. The valve 31 ensure's that the drawing pressure remains constant so that uniformity of the drawing operation is obtained. On reversal of the plunger the control piston is raised by the cam means and pressure fluid is returned to the cylinder 10 to impart a follow-up motion to the piston 11 and holder 4 without any lag and the formed workpiece is withdrawn from the ram 8. When the control piston reaches its uppermost position the stop 25 presses against the tapper 24 to rotate the cam and allow the roller to move along the cam surface and the plunger to complete its upward travel. On the downward movement of the plunger the stop releases the tapper 24 and the spring 22 returns the cam to its initial position. The-pressure piston 11 and its rod 12 may be hollow to accommodate a lettered punch. In an embodiment the hollow control piston-rod 51 (Fig. 3) contains a valve assembly (Fig. 2) comprising a lightly spring-loaded valve 54 containing a further strongly spring-loaded valve 56 provided with a throttle bore 58. Below this valve assembly in the rod is a follow-up piston 60, the piston-rod 61 of which engages the arm 20 on the press plunger. In operation, during the forming stroke of the plunger the piston 11 forces fluid into the cylinder 15 to depress the control piston 52 and the fluid pressure also opens the valve 54 in the piston-rod and passes into the space 59 above the follow-up piston 60 so that it is always in engagement with the arm 20. On the upward movement of the plunger the arm raises the piston 60 and the valve 54 is closed to imprison fluid in the space 59. Thus, motion of the plunger 2 is transmitted to the control piston 52 which .forces fluid back into the cylinder 10. The throttle bore 58 on the relief valve 56, however, allows gradual metering of the imprisoned fluid into the cylinder 15 which equalizes the speeds of the pistons 52 and 11. As the plunger approaches the upper limit of its stroke any excess of fluid in the cylinder 15 may escape into the container 35 through the valve 37.