GB2084066A - Improvements in or relating to punches - Google Patents

Abstract

A punch for machine tools comprises a punch head holder having at one end thereof a tapered bore 11 extending for part of the length of the holder and at its other end with an axial bore 12 extending from the apex of said tapered bore through the remainder of the holder. Punch heads of different shapes can be mounted in the bore 11, each punch head 13 having a shank 15 which is a close fit in the tapered bore 11, the shank 15 being adapted to be secured to the holder by means of a bolt 17 extending through the axial bore from said other end of the holder. <IMAGE>

Description

SPECIFICATION Improvements in or relating to punches The present invention concerns punches which are used in association with presses to punch holes in sheets of metal and in particular sheets of metal.

In the past such punches have been formed by machining the punch head on a solid, normally cylindrical, metal body. In order to mount the punch so formed the end of the metal body remote from the punch is provided with an internally screwthreaded bore. A stepped retaining washer is firmly located on the punch by means of a suitable bolt passing through the washer and into the bore. It is this stepped washer which cooperates with the machine tool so as to mount the punch.

This well known arrangement has a number of disadvantages. In particular it is frequently the case that the actual punch head machined on the punch is relatively small when compared to the remainder of the metal body. As it is possible to use a very wide range of different punches in a single machine tool the result of this is that the storage of these punches takes up a considerable amount of space. Furth ermorethe manufacture of the punches needs not only a considerable degree of accurate machining but also a considerable amount of high quality metal.

The present invention has for an object to alleviate these disadvantages.

Accordingly the present invention consists in a punch for machine tools comprising a punch head holder having at one end thereof a tapered bore extending for part of the length of the holder and at its other end with a central bore extending from the apex of said tapered bore through the remainder of the holder. This holder is intended to cooperate with a punch head having a tapered shank which is a close fit in the tapered bore, the shank being secured to the holder by means of a bolt extending through the axial bore from said other end of the holder.

Preferably the bolt will also be used to secure a stepped retaining washer to the holder so that the combination of the holder and punch head can be mounted in a machine tool in the normal manner.

In order that the present invention may be more readily understood, an embodiment of a prior art punch will now be described together with an embodiment of a punch constructed in accordance with the present invention.

Thus Figure 1 of the accompanying drawings shows an exploded perspective view of a known punch, Figure 2 of the accompanying drawings is an exploded axial section through one embodiment of a punch constructed in accordance with the present invention, Figure 3 is a perspective view of one embodiment of a punch head, and Figure 4 is an end view of a punch head holder intended to cooperate with the punch head of Figure 3.

Referring now to Figure 1 of the drawings a known punch is generally indicated at land comprises main body 2 of circular cross-section having machined in one end thereof a rectangular punch head 3. So that the orientation of the punch head can be accurately set with regard to the machine tool in which the punch is to be mounted and to the die with which the punch is to cooperate the body 2 is provided with a pair of accurately machined flats 4.

The punch 1 is mounted in a machine tool by a stepped retaining washer 5 which is secured to the main body by a screw-threaded bolt 6 which extends through a central bore in the washer 5 into a coaxial bore 7 formed in the main body 2.

Referring now to Figures 2 to 4 of the accompanying drawings these show a punch comprising a punch head holder 10 which in the present embodiment is manufactured from a cylindrical block of metal. The punch holder 10 has machined in one end thereof a tapered recess 11 which extends coaxially for part of the length of the holder body 10. A bore 12 extends between the apex of the recess 11 and the other end of the holder body 10.

The punch head is shown at 13 and comprises at 14 the operative portion of the punch which actually pierces the material being punched. This portion is circular in cross-section. The punch head also has a tapered shank 15, the shank 15 having blind internally screw-threaded bore 16 therein. The shank 15 is a close fit in the tapered recess 11 of the punch head holder 2. A bolt 17 is used both to secure a stepped retaining washer 18 identical to the washer described with regard to the embodiment of Figure 1 to the punch holder 2 and to secure the punch head 13.

In the embodiment shown in Figure 2 the punch itself has a circular cross-section so that the orientation of the punch within the holder body is unimportant. However many punches are non-circular and such a punch is shown in Figures 3 and 4 of the accompanying drawings. In this embodiment the punch head 13' has a rectangular operative portion 20. It is thus essential to ensure that the punch head 13' can be oritentated exactly with respect to the punch holder 2 and that the punch holder 10 in turn can be orientated with respect to the machine tool in which it is to be mounted.

For this purpose the tapered portion of the punch shown in Figure 3 is provided with a small radially projecting dowel 21. The dowel 21, when the punch is inserted into the recess 11 engages in an accurately machined slot 22 formed in a side wall defining the recess 11. The holder body 10 is also provided with a pair of flats 23 and the slot 22 is machined so that it lies exactly halfway between the two flats 23.

The combination of the dowel 21, the slot 22 and the flats 23 enable the punch head 13' to be accurately located in the holder body 10 and the holder body 10 to be accurately located with respect to the machine tool in which it is to be mounted. The relationship between the dowel 21, slot 22 and flats 23 can best be understood from Figure 3 of the accompanying drawings, the flats being shown in dotted lines.

It will be appreciated that although a dowel has been described, the punch head could be provided with any other suitable projection or flange provided that the projection or flange can mate with an appropriately shaped recess in the holder body. It will also be appreciated that if the actual punch is of circular cross-section it is immaterial whether the holder body has flats or not. Thus, a holder body with flats can be used with circular punches as well as with non-circular punches.

It will thus be apparent that a single punch holder can be used to hold a wider variety of punches each of the punches intended to cooperate with the punch holder will have only a fraction of the material which was necessary to make a single prior art punch. Thus the use of a single punch holder and a number of smaller punch heads provides a considerable saving both in material, machining and storage space.

Furthermore, fewer limitations are placed on the shape of the metal bodies from which the punches are machined. It will also be appreciated that it is, in machine tool terms, a relatively simple matterto provide the tapered shanks on the punch heads and the tapered recesses in the punch holder.

Claims (7)

1. A punch for machine tools comprising a punch head holder having at one end thereof a tapered bore extending for part of the length of the holder and at its other end with an axial bore extending from the apex of said tapered bore through the remainder of the holder.

2. A punch as claimed in claim 1 and further comprising a punch head having a shank which is a close fit in the tapered bore, the shank being adapted to be secured to the holder by means of a bolt extending through the axial bore from said other end of the holder.

3. A punch as claimed in claim 2 wherein the shank has a regular taper.

4. A punch as claimed in either claim 2 or claim 3 and including a stepped retaining washer adapted to be secured to the holder by said bolt.

5. A punch as claimed in any one of the preceding claims wherein the punch holder is formed with two accurately machined flats to enable its orientation to be correctly set with respect to the machine tool in which it is to be mounted.

6. A punch as claimed in any one of the preceding claims wherein the punch head holder is provided with at least one slot extending into said tapered bore, said slot being adapted to receive a dowel on a punch head so as to enable the orientation of the punch head to be set accurately with respect to the punch head holder.

7. A punch for a machine tool substantially as hereinbefore described with reference to Figures 2,3 and 4 of the accompanying drawings.