GB818886A - Laminated press die cushion - Google Patents

Abstract

818,886. Stamping; bending. BLISS CO., E. W. Aug. 3, 1956 [Aug. 3, 1955], No. 23967/56. Class 83 (4). In a metal working press having upper die means and a die bed a die cushion comprises a lower cup-shaped piston 30 secured to the bolster plate 22 of the die bed, an upper piston 38 fitted within a cup-shaped inner cylinder 32 providing an upper fluid chamber 72, said cylinder being fitted within the lower piston to provide a lower fluid chamber 74 and being secured to a cylinder housing 28 having side portions adapted to telescopically engage the upper and lower pistons, and valve means to control ingress and egress of fluid to and from the upper chamber whilst maintaining the pressure constant therein, the arrangement being such that increase of pressure and volume of fluid in the lower chamber causes egress of fluid from the upper chamber thus raising the cylinder housing, the lower die means and the upper piston. The press comprises a series of vertical steel frame members 12 carrying bolster plates 22. In order to form a long channel member sufficient frame members are fastened together and enough die cushion units 24 (Figs. 6 and 8) are secured to the bolster plates. Each unit comprises three die cushions 26 encased in a common housing. A clamping die 48 is secured to the upper piston 38 of each cushion and a pair of lower dies 50 and 52 are secured to the housing 28. An hydraulic nozzle 54 secured to the lower piston 30 extends through the inner cylinder 32 which is centred by, and slides on, the nozzle. The upper die 66 is secured to a press slide 67 and a pair of strippers 68 and 70 are mounted on opposite sides of the die. In operation, hydraulic fluid is admitted through the nozzle 54 into the upper chamber 72 and also into the lower chamber 74. The upper slide 66 is lowered to its bottom dead centre position and does not contact the workpiece W. The pressure in the lower chamber 74 is increased to raise the inner cylinder and also the housing 28 which permits the upper piston to follow and clamp the workpiece between the dies whereupon fluid is ejected from the chamber 72 through the nozzle 54 into a surge tank (not shown). As the pressure in the lower chamber increases the lower dies 50 and 52 on the housing bend the sides of the blank upwardly around the upper die 66 (Fig. 3). When the fluid pressure in the lower chamber is released the weight of the housing and lower piston returns them to their original positions, the hydraulic fluid being expelled through the connection 62 whilst at the same time fluid is admitted through the nozzle 54 to maintain constant pressure in the upper chamber 72. The upper die is returned to its top dead centre position and the strippers 68 and 70 remove the workpiece from the die. To form irregular-shaped channel members, e.g. the frame members'of truck bodies (Fig. 8), the lower die cushion housing and the forming dies are modified as shown in Fig. 7. The housing 29 is provided with an enlarged table 74 to accommodate the elongated lower die 76. Specification 818,885 is referred to.