GB2058924A

GB2058924A - Pressure fluid assembly

Info

Publication number: GB2058924A
Application number: GB7932150A
Authority: GB
Original assignee: Mercer Nairne & Co Ltd
Current assignee: Mercer Nairne & Co Ltd
Priority date: 1979-09-17
Filing date: 1979-09-17
Publication date: 1981-04-15

Abstract

A pressure fluid assembly, primarily for reciprocating the ram of a punching machine is arranged so as to be selectively variable between a plurality of different maximum punching capacities. The assembly has a cylinder (4), a first piston (1), and a second piston (10) concentric with the first piston. The first piston is axially movable relative to the second piston to provide a first pressure capacity, and movement of the first piston together with the second piston provides a second pressure capacity. <IMAGE>

Description

SPECIFICATION Pressure fluid assembly This invention relates to a pressure fluid assembly.

In punching machines, where the ram of the machine is powered by hydraulic pressure to drive a punch through the workpiece, it is necessary to provide a high punching capacity in order to accommodate various thicknesses of metal workpiece on the same machine.

However, this means, that on many occasions when only thin material is being punched, a much greater pressure is applied than is really necessary.

An object of the present invention therefore is to provide an improved pressure fluid assembly which is of variable capacity particularly suitable for punching machines.

According to the present invention there is provided an assembly comprising a cylinder, an axially movable piston assembly within the cylinder, and means for selectively applying pressure fluid to the piston assembly so as to vary the pressure capacity of the assembly.

Preferably the piston assembly comprises a first piston and a second piston concentric with the first piston, the first piston being axially movable relative to the second piston to give a first pressure capacity, movement of the first piston together with second piston providing a second pressure capacity. If desired the second piston may be axially movable relative to the first piston to provide a third pressure capacity.

The invention also includes a punching machine the ram of which is reciprocated by means of pressure fluid supplied to a cylinder assembly, said cylinder assembly being arranged so as to be selectively variable between a plurality of different maximum punching capacities. With this arrangement the hit rate of say a 25 ton capacity punching machine can be increased when punching thin material by selectively varying the cylinder assembly to lower the maximum capacity to say 10 ton capacity.

Although the preferred pressure fluid is hydraulic fluid, compressed air or other gas may be used if desired.

The invention will now be described by way of example with reference to the accompanying drawing which is a partially sectioned side elevation of a hydraulic assembly particularly designed for use in a punching machine.

In the drawing a hydraulic assembly comprises a first piston 1 movable in axial direction by means of hydraulic fluid supplied through a first port 2. The piston 1 is provided with piston rings 3 which cooperate with the inner wall of the associated cylinder 4 and has an axially extending piston rod 5. A top plate 6 through which port 2 passes is arranged to overlie the piston at 7 so that only part of the piston surface is exposed at the beginning of the stroke. In this way the piston is more responsive to the hydraulic fluid and moves axially at the outset of the stroke more quickly than if the whole piston surface were exposed. Also the overlying surface 7 provides a stop for the piston on the return stroke and a register for the top plate 6.

Below the piston 1, in the retracted position shown in the drawing, is a chamber 8 full of hydraulic fluid and in communication with a second port 9. The first and second ports 2 and 9 are part of a first closed fluid circuit and are arranged to supply hydraulic fluid in conventional manner.

Concentric with the piston rod 5 is a second piston 10 and piston rod 11 axially movable within a cylinder 1 7 which abuts cylinder 4 to form a composite cylinder assembly. For the downward stroke fluid is supplied through a third port 1 2 and an annular wall member 1 3 overlies the piston 10 in its retracted position shown, in the same way as portion 7 of top plate 6, so that only part of the piston surface is exposed at the beginning of the stroke to speed up the axial take-up of the piston and also to provide a stop for the piston on the return stroke.

Below the piston 10 is a chamber 14 in communication with a fourth port 5. The third and fourth ports 1 2 and 5 are part of a second closed fluid circuit and are arranged to supply hydraulic fluid in conventional manner.

In use the first piston 1 is movable axially relative to the piston 10, by supply of hydraulic fluid above the piston 1 through the first port 2: the small exposed surface area of the piston at the outset of the stroke accelerating the piston. At the end of the stroke the piston 1 is returned by hydraulic fluid supplied to chamber 8 through the second port 9: the piston being stopped at the end of the stroke by the overlying portion of top plate 6.

The second piston 10 is axially movable, together with piston 1 in view of the piston rod 11 acting on a flange 1 6 secured to the first piston rod 5, by means of hydraulic fluid supplied above the pistons 1 and 1 0. The two pistons are returned by supply of hydraulic fluid to respective chambers 8 and 1 4 below the pistons.

With the arrangement of the present invention the piston 1 can be arranged to provide a punching capacity of say 1 0+ ton, and the piston 10 and 1 together can be arranged to provide a punching capacity of say 25 ton: the return stroke can suitably be provided by 1 + ton pressure applied under the respective pistons. In this way, when thin sheet material is being punched, only the piston 1 need be used so that a faster stroke can be achieved giving a higher hit rate.

The supply of hydraulic fluid and selection of the 1 0+ ton or 25 ton capacity is suitably controlied by numerical control apparatus.

Although the present invention is particularly desired for use with hydraulically operated punching machines it will be understood that it may be applied to other machines where variable capacity is desired. Also although hydraulic fluid is preferred the pressure fluid may be compressed air or other gas.

Also, although the invention is particularly described in connection with a cylinder assembly providing only two different pressure capacities, the second piston may be arranged to move axially relative to the first piston so as to provide a third pressure capacity if desired.

Claims

1. A pressure fluid assembly comprising a cylinder, axially movable piston means within the cylinder, and means for selectively applying pressure fluid to the piston means so as to vary the pressure capacity of the assembly.

2. A pressure fluid assembly according to claim 1 wherein the axially movable piston means comprises a first piston and a second piston concentric with the first piston, the first piston being axially movable relative to the second piston to give a first pressure capacity, and movement of the first piston together with the second piston providing a second pressure capacity.

3. A pressure fluid assembly according to claim 2 wherein the second piston is axially movable relative to the first piston to provide a third pressure capacity.

4. A pressure fluid assembly according to any one of the preceding claims wherein the pressure fluid is hydraulic fluid.

5. A punching machine including a ram which is reciprocated by means of a pressure fluid supplied to a cylinder assembly, said cylinder assembly being arranged so as to be selectively variable between a plurality of different maximum punching capacities.

6. A pressure fluid assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.