GB2038690A

GB2038690A - Improved punch assembly

Info

Publication number: GB2038690A
Application number: GB7845265A
Authority: GB
Original assignee: Mercer Nairne & Co Ltd
Current assignee: Mercer Nairne & Co Ltd
Priority date: 1978-11-20
Filing date: 1978-11-20
Publication date: 1980-07-30

Abstract

A punch assembly has a punch guide, an axially movable punch unit slidably received in the punch guide and including a punch, a punch cap and a punch head, and coil spring return means for retracting the punch after punching, the punch head and punch cap being releasably secured together by a screw-threaded engagement between a tubular extension on the punch head and a projecting portion of the punch cap. The punch head includes a striker which is adjustable by screwing and is selectively lockable in a plurality of regularly spaced positions so as to vary the length of the punch unit and thereby reduce the stroke of the ram of a punch machine to a minimum for various materials of different thicknesses. <IMAGE>

Description

SPECIFICATION Improved punch assembly This invention relates to a punch assembly.

At present a punch assembly comprises a punch guide, a punch slidably received in the punch guide, a punch head which is hit by the ram of the punch machine, and a resilient return means between the striker and the punch guide. The punch head may either be formed by the head of the punch itself or may be a separate element to which the punch is connected so as to be movable therewith. The resilient return means for stripping the punch may be a single coil spring or, in respect of a heavy duty punching unit, a plurality of spring elements such as polyurathene springs.

An object of the present invention is to provide an improved punch assembly which has greater versa tilitythan known punch assemblies.

According to the present invention there is provided a punch assembly comprising a punch guide, an axially movable punch unit slidably received in the punch guide and including punch means and a punch head which in use is hit by the ram of the punch machine, and resilient return means for retracting the punch unit after punching, the punch head and the punch means being releasably secured together by means of interengagement between a tubular portion on one of the punch head or punch means and a projecting portion on the other.

Preferably the punch means includes a punch and a punch cap to which the punch is releasably secured by a screw.

The punch head preferably includes a striker member which is adjustable by screwing within the punch head and preferably is selectably lockable within one of a number of angular spaced positions by means of a grub screw.

The punch of the punch unit may be changed by access to the screw securing the punch to the punch cap through an axial bore in the striker member. The resilient return means is preferably a plurality of coil springs.

The invention will now be described by way of example with reference to the accompanying draw ings in which: Figure 1 is a cross-section of one embodiment of a heavy duty punching assembly; and Figure 2 is a cross-section of a second embodi ment.

In Figure 1 of the drawings a punching assembly 1 comprises a punch 2 slidably received in a punch guide 3. The punch 2 has an axial screw-threaded bore 4 which receives a screw 5 releasably securing the punch 2 to a punch cap 6. The punch cap 6 has an externally screw-threaded portion 7 which is releas ably secured to a punch head by engagement in an enternally screw-threaded cylindrical extension of a return spring retainer 9. The return-spring retainer 9 has a central opening 10 which receives a striker 11 and both the spring retainer 9 and the striker 11 have an axial bore 12 therethrough to allow the screw 5 to be released when the punch is to be changed. The punch 2, and the punch head formed by spring retainer 9, punch cap 6 and striker 11 together form an axially moveable punch unit of the assembly.The punch guide 3 supports on its upper end an annular spring support 13 which rests on the punch guide 3 and which receives the bottom of a plurality of return coil springs 14 for stripping the punch from material after punching; a suitable number of springs is eight.

The other end of the springs 14 are held in the spring retainer 9. The cylindrical extension 8 of the spring retainer 9 has a portion of smaller cross-section at its free end and this portion is joined to a wider part of the extension 8 by a sloping surface 15. The portion of smaller cross-section acts as a guide during punching by cooperating with the spring support 13 and the wider part provides improved strength.

During punching the wider part of the extension 8 is received within an annular rebate 16 in the spring support 13 so as not to limit the axial movement of the punch unit which is determined by the abutment of the bottom face of the spring retainer 9 with the top face of the spring support 13. The fully retracted position of the punch unit is limited by an annular shoulder 17 on the punch cap 6 which engages under the spring support 13.

As seen from the drawing the striker 11 is adjustably received in the spring retainer 9 and has a grub screw 18 which is engageable with one of a number of indentations 19 (only one of which is shown) in the bottom surface of the opening 10. This adjustment facility means that the position of the striker member 11 relative to the punch ram (not shown) can be adjusted so as to allow a minimum stroke for varying thicknesses of material to be punched. Alternatively the striker 11 may be locked in position by means of a grub screw which is engageable with one of a number of arcuate grooves in the edge of the striker member.

In use it will be understood that the various parts of the punch assembly of Figure 1 can be changed easily without complete disengagement of the assembly. For example the punch 2 is easily changed by access to the screw 5 through the axial bore 12 and the coil springs 14 may be changed by unscrewing the spring retainer 9 from engagement with the punch cap 6. Alternatively some springs can be removed for softer materials so as to reduce the stripping pressure so that the punch guide 3 does not indentthe material. The adjustable striker 11 allows improved performance particularly in automatic punching machines where the stroke of the ram can be adjusted to a minimum thereby providing a greater hit-rate per minute.

In the embodiment of Figure 2 the punching assembly 1 is similar to that shown in Figure 1 except that the cylindrical extension 8 is replaced by a separate sleeve 20. In this embodiment the punch cap 6 has an externally screw-threaded portion 7 which is secured to a punch head by engagement in an internally screw-threaded sleeve 20 the other end of which receives the striker 11. The striker 11 has an axial bore 21 therethrough aligned with the sleeve 20 to allow the screw 5 to be released when the punch is to be changed. The axial bore 21 is smaller than the axial bore 12 of the first embodiment. The punch 2 punch cap 6 and the punch head formed by the sleeve 20, spring retainer 9 and striker 11 together form an axially movable punch unit of the assembly.

The spring retainer 9 which in this embodiment is separate, is movable with the striker 11 by a shoulder 22 on the sleeve 20 engaging an annular rebate 23 on the spring retainer 9. Other than the shoulder 22, the sleeve is of constant dimension throughout.

Although the invention has been particularly described with reference to a heavy-duty punch assembly it is understood that the invention is also applicable to a light-duty punch assembly in which only a single stripper spring will be provided and in such an arrangement a stripper plate will normally be secured to the bottom of the punch guide 3 to strip the punch from the thinner material being punched. Also although both embodiments show the tubular portion as part of the punch head it is understood that the tubular extension could form part of the punch cap, the spring retainer having an externally threaded extension fitting therein so that the two parts may be separated from one another.

Claims

1. A punch assembly comprising a punch guide, an axially movable punch unit slidably received in the punch guide and including punch means and a punch head which in use is hit by the ram of the punch machine, and resilient return means for retracting the punch unit after punching, the punch head and the punch means being releasably secured together by means of interengagement between a tubular portion on one of the punch head or punch means and a projecting portion on the other.

2. A punch assembly according to claim 1 wherein the punch means includes a punch and a punch cap to which the punch is releasably secured by a screw.

3. A punch assembly according to claims 1 or 2 wherein the punch head includes a striker member which is adjustable so as to vary the length of the punch unit.

4. A punch assembly according to claim 3 wherein the striker member is in screw-threaded engagement with the punch head so as to be adjustable by screwing and is selectively lockable within one of a number of angular spaced positions.

5. A punch assembly according to claim 4 wherein the tubular portion comprises an internally screwthreaded cylindrical extension of the punch head which cooperates with an externally screw-threaded projecting portion of the punch cap.

6. A punch assembly according to claim 4 wherein the punch head includes an internally screwthreaded sleeve which cooperates with an externally screw-threaded projecting portion of the punch cap adapted to fit in one end of the sleeve.

7. A punch assembly according to claim 5 wherein the striker member is aligned with the cylindrical extension and has an axial bore to permit access to the screw securing the punch to the punch cap so that the punch may be changed without disengagement of the parts.

8. A punch assembly according to claim 6 wherein the striker member is received in the other end of the sleeve and has an axial bore to permit access to the screw securing the punch to the punch cap so that the punch may be changed without disengagement of the parts.

9. A punch assembly according to any one of the preceding claims wherein the resilient return means comprises a plurality of circumferentially spaced coil springs acting between a spring support on the punch guide and a spring retainer on the punch head.

10. A punch assembly according to claim 9 wherein the coil springs may be changed by disengagement of the punch head from the punch means alternatively some springs may be removed for use with softer materials to reduce the stripping pressure.

11. A punch assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.