GB2031780A - Improved shear-proof punch and punching tool including such a punch - Google Patents

Abstract

A shear proof punch of non- circular cross-section has a punch finger slidably received within a groove in each corner of the punch to prevent lateral and angular displacement during punching. The 'corner' may be rounded. The tool for taking the punch includes an adjustable striker member so that its height relative to the ram of a punching machine can be altered to adjust the stroke to a minimum and thereby allow an increased hit rate in automatic punching machines. The punch is releasably secured to the tool so that it may be readily replaced or charged without the need to change the whole tool unit. <IMAGE>

Description

SPECIFICATION 'improved shear-proof punch and punching tool including such a punch this invention relates to an improved punching tool known as a shear-proof punching tool and to an improved shear-proof punch forming part of said tool. Shear-proof tooling is normally used when a hole is to be punched in the edge of a sheet of metal or for nibbling.

For example a square punch may be used to punch out a corner of a sheet of metal, the punch area being greater than the corner being removed. Because the punching is taking place at the corner or edge of the sheet there is a danger of slight lateral displacement of the punch so that a clean cut edge is not always produced. In order to avoid the possibility of lateral displacement the punch is provided with four retractable punch fingers which are slidable in grooves in the punch.

The punch fingers are provided one centrally of each side and normally project beyond the punching surface of the punch. Thus when a corner, for example, is being punched those fingers not engaging the corner of the sheet being punched project into the cooperating die beneath the sheet and locate the punch against lateral displacement.

However, we have now found that whilst the present arrangement satisfactorily prevents lateral displacement there is still a possibility of slight angular displacement which may present a problem in all punches except those of circular cross-section. It is therefore an object of the present invention to provide an improved shear-proof punch of non-circular cross-section and a shear-proof punching tool including such a punch. By the term "noncircular cross-section" it is understood that the punch must have at least two corners the term "corner" being intended to include an gle corners of punches of rectilinear crosssection, and curved corners of punches nonrectilinear cross-section.

According to the present invention we provide a shear-proof punch of non-circular crosssection in which the corner of the punch are each formed by a punch finger slidably re ceived within a groove.

Preferably the punch is of rectangular crosssection and includes a punch finger at each of the four corners. The punch finger may have a cross-section in the form of a segment of a circle.

The invention also includes a shear-proof punching tool comprising a shear-proof punch axially movable relative to a punch body and against resilient means biassing the punch in the opposite direction, the shear-proof punch being of non-circular cross-section and includ ing at each corner a punch finger slidably received within a groove.

Preferably the punch is releasably secured to a punch holder and the ram of a punching machine strikes against an adjustable striker member adjustment of which allows the stroke to be adjusted to a minimum. The punch body may include a replaceable stripper member and the punch fingers are preferably biassed into an extended position as limited by an abutment shoulder which engages a retainer member on the punch.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-sectional side elevation of a shear-proof punching tool in accordance with the invention; Figure 2 is an underneath plan view of the tool of Fig. 1; Figure 3 is a top plan view of the tool of Fig. 1; and Figure 4 is an underneath plan view of an alternative punch.

In the drawings a shear-proof punching tool 1 includes a body 2 which is shown positioned in a punch station of a rotatable turret part of which is diagrammatically shown as 3.

The shear-proof punching tool 1 comprises a punch assembly, a punch holder 5, and a striker member 6. The punch assembly 4 and the punch holders 5 are joined together by a screw 7 and are together axially movable relative to the punch body 2. A spring assembly 8, which comprises a spring retainer 9 secured to the punch holder 5, a spring support 10 secured to the punch body 2 and coil springs 11, serves to bias the movable parts of the tool into the retracted position shown in Fig. 1. The striker member 6 is in screw-threaded engagement with the spring retainer 9 and has a central aperture through which the screw 7 passes.

The punch assembly 4 shown in Figs 1 to 3 consists of a square punch 12 having a groove 13 formed in each corner. Each groove 13 slidably receives a punch finger 14 and the fingers 14 are held in positon by a punch retainer 15. All the fingers 14 have an associated spring 16 which biasses the respective finger into an extended position as shown in Fig. 1 and its extended movement is limited by a shoulder 17 on the finger which engages the punch retainer 15. The lower end of each finger 14 is machined square with the punch 12 so that, as seen in Fig. 2, the fingers 14 have a lower cross-section in the form of a segment of a circle. The punch 12 and associated punch fingers 14 are slidable relative to a stripper plate 18 which is removably secured to the stationary punch body 2 by means of screws 19.

The stiker member 6 is adjustably mounted on the spring retainer 9 by means of a timing screw 20 which is engageable with any one of four arcuate grooves 21 (Fig. 3) in the striker member 6 to lock the member 6 into position at a particular height. This adjustment facility means that the position of the striker member 6 relative to the punch ram (not shown) can be adjusted so as to allow a minimum stroke thereby providing an increased hit rate in automatic punching machines.

In Fig. 4 an alternative punch arrangement is shown for performing slot punching. In this embodiment there are two fingers 22 which are contoured to the curved corners end of the slot punch to simultaneously prevent lateral and angular displacement of the punch during punching.

The tooling of the present invention, in addition to providing improved punching, also provides a unit, the parts of which are interchangeable. Thus the return springs 11 can be changed to alter the pressure for thicker or thinner materials, the stripper plate 18 can be readily removed and replaced, and the punch assembly 4 itself can be replaced without the need to replace the whole unit merely by release of the screw 7.

In operation the desired punch is selected and positioned in the punch holder 5 and secured by the screw 7. A corresponding stripper plate 18 is then secured to the punch body 2 by screw 19. Finally the striker member is adjusted to a desired setting if this is to be altered. Having set up the tool it is placed either in a single punch machine or in a punch station of a turret punch machine.

On engagement of the tool by the ram of the punch machine the punch assembly 4, punch holder 5, spring retainer 9 and striker member 6 are moved axially downwards relative to the punch body 2 and against the coil springs 11. At this stage all the punch fingers 14 project beyond the end of the punch assembly 4 by the action of their associated springs 16. However as the punch assembly 4 continues to move down towards the sheet workpiece those fingers which are aligned with the sheet are forced into their retracted position against the action of the springs 16 whilst those fingers which are not aligned with the sheet remain in their extended position and pass into the cooperating die. Therefore the fingers which pass into the die corners locate the punch against lateral and angular displacement before any punching actually takes place. The fingers which are forceably pushed back are only pushed back flush with the punch surface so that a clean punch is produced.

As soon as pressure from the ram is released the springs 11 withdraw the punch assembly 4 through the stripper plate 18 and all the punch fingers are once again moved into their extended positions by their associated springs 16.

Although the invention has been particularly described with reference to square and substantially rectangular punches it is understood that the invention is applicable to any punch of non-circular cross-section in which angular displacement is undesirable e.g. triangular or elliptical. Also although in accordance witH the invention it is essential to have punch fingers at the corners if desired punch fingers may also be provided intermediate the corners for additional support against lateral displacement.

Claims (13)

1. A shear-proof punch of non-circular cross-section in which the corners of the punch are each formed by a punch finger slidably received within a groove.

2. A shear-proof punch according to claim 1 wherein the punch is of rectangular crosssection.

3. A shear-proof punch according to claim 2 wherein the punch fingers have a crosssection in the form of a segment of a circle.

4. A shear-proof punching tool comprising a shear-proof punch axially movable relative to a punch body and against resilient means biassing the punch in the opposite direction, the shear-proof punch being of non-circular cross-section and including at each corner a punch finger slidably received within a groove.

5. A shear-proof punching tool according to claim 4 wherein the punch is releasably secured to a punch holder for simple replacement.

6. A shear-proof punching tool according to claim 4 or 5 further including an adjustable striker member which in use is struck by the ram of a punching machine, the adjustment permitting the stroke to be adjusted to a minimum.

7. A shear-proof punching tool according to claim 6 wherein the adjustable striker member is externally screw threaded and engaged within a screw-threaded aperture in a retainer for the resilient means, the striker member being selectively lockable in one of a plurality of positions.

8. A shear-proof punching tool according to claim 7 wherein the striker member includes four circumferentially spaced, axial grooves which cooperate with the head of a locking screw to prevent rotation of the striker member once it has been positioned.

9. A shear-proof punching tool according to any one of claims 4 to 8 including a stripper member releasably secured to the punch body.

10. A shear-proof punching tool according to any one of the preceding claims 4 to 9 wherein the punch fingers are biassed into an extended position as limited by an abutment shoulder which engages a retainer member on the punch.

11. A shear-proof punching tool according to any one of claims 4 to 10 wherein the resilient means biassing the punch in the opposite direction comprises a plurality of coil springs.

12. A shear-proof punching tool substan .tally as hereinbefore described with reference to and as illustrated in the accompanying drawings.

13. A shear-proof punch substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.