GB1308641A - Presses - Google Patents

Abstract

1308641 Punching SHOREHAM PRECISION TOOLS Ltd 26 April 1971 [27 Jan 1970] 3844/70 Heading B3W A punch press comprises a fixed tool carrier 20, a movable tool carrier 3, a hold down or stripper 41 slidably mounted in one carrier, an ejector 43 slidably mounted in the other carrier and an electric circuit, for starting and stopping the movable carrier, which includes three switches, switches A and B which are actuated by retraction of the hold down/stripper and ejector into their respective tool carriers and switch C which is actuated by the movable tool carrier during a working stroke, the arrangement being such that actuation of switch C either first or last of the three switches during one working stroke stopping the movable tool carrier. The switches are adjustable and before operation of the press the punch 43 is lowered until it first touches a workpiece and the switch C is adjusted until it just operates. It is then adjusted to correspond to the workpiece thickness minus five thousandths of an inch. In operation of the press the hold down 41 engages the workpiece and is pushed into the toolcarrier against the pressure of fluid in a chamber 17, until it actuates the switch A. The switch C is actuated just before, and the switch B just after, the punch reaches the workpiece. If there is no workpiece between the punch 40 and die 42, switch C will operate first and the press will stop. If there are two workpieces or some other abnormal thickness between the punch and die, switch C will operate after both switches A and B and again the press will stop. At the start of a punching stroke a buffer piston 12 is forced away from a piston 11, with which the hold-down is connected, by low pressure fluid supplied to chamber 44; the pressure is reduced to nil during the actual punching and raised to a high level during the return stroke of the punch for returning the hold down. Chamber 45 is used in the same way for the ejector. The die may be mounted on the movable carrier and the punch on the fixed carrier, the roles of the hold down and the ejector being reversed. The switches A and B can be over-ridden to allow the punch to be inched clear of an obstruction. A solenoid valve (35), Fig. 2 not shown, controls hydraulic operation of the ram 1 carrying the tool carrier 3. If the valve spool jams in the ON position, the electric circuits are coupled to the ram stop circuits as a further stop mechanism.