GB2153713A

GB2153713A - Improvements relating to machine tools

Info

Publication number: GB2153713A
Application number: GB08500677A
Authority: GB
Inventors: Christopher Frederick Burleigh
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-01-11
Filing date: 1985-01-11
Publication date: 1985-08-29
Also published as: GB8400605D0; GB8500677D0; GB2153713B

Abstract

There is provided on a machine tool a device for mounting a workpiece and comprising a circular mounting plate 12 carrying a fixed dowel 23 and a dowel 16 which is adjustable towards and away from the fixed dowel. The mounting plate can be rotated about a horizontal axis with roller bearings 13 supporting the weight of the mounting plate and any components mounted thereon. The mounting plate is rotatably mounted on a housing (10, Fig. 2) which is itself pivotable about a vertical axis on base plate 6. <IMAGE>

Description

SPECIFICATION Improvements relating to machine tools This invention is concerned with improvements relating to machines for carrying out operations on workpieces, particularly but not exclusively computer-controlled machines for carrying out machining operations on workpieces such as engine components.

For the mounting of a component of this type on a computer-numerical controlled machine, it is conventional practice to utilise as mountng bores, two bores which it is, or will be, necessary to provide in the component for an additional purpose, such as bolt holes by which the component will ultimately be bolted to another engine component. The machine comprises a base plate rotatable about a vertical axis, on which a mounting device (conventionally termed "a fixture") is mounted, the mounting device comprising a number of operative faces (typically four) to which workpieces may be secured.

Each operative face of the fixture is provided with fixed mounting elements, enabling the workpiece to be mounted on the operative face, and clamping devices are utilised to hold the workpieces in position on the operative faces. To maximise efficiency, it is conventional practice to provide mounting elements for more than one workpiece on some at least of the operative faces of the fixture.

Thus, in a conventional machining operation on (for example) a cylinder head for a car engine, two workpieces will be mounted on a front face of the fixture, one on each of two side faces, and two on a top face of the fixture. The machine will then drill all the necessary holes into the faces presented to the tool of the machine, including (for example) valve guide bores into the workpieces on the front face, manifold holes into the workpieces on the side faces, and end holes into the workpieces on the top face.

On conclusion, the two workpieces on the top face of the fixture are removed (having been completed) and the workpieces on the side faces are removed therefrom and remounted on the top face, the workpieces on the front face are removed therefrom and remounted on the side faces, and two new workpieces are mounted on the front face. This procedure is excessively labour-intensive.

Thus a fixture will in general be capable of carrying only a specific workpiece. Additionally, when a component is re-designed, and/or where the mounting holes are re-positioned, it is necessary to provide a new fixture for the component.

Furthermore, since the fixture is capable of rotation only about a vertical axis, it is not possible to drill compound holes other than in a single plane.

For this purpose, it is necessary to mount the workpiece on a further fixture, having an operative face inclined at an appropriate angle.

According to a first aspect of the invention, there is provided a machine incorporating a mounting device for mounting a workpiece on the machine, the mounting device comprising: (a) a base plate mounted for rotation about a first axis; (b) a mounting plate mounted on the base plate for rotation relative thereto about a second axis which is substantially perpendicular to the first; (c) at least one set comprising two mounting means on the mounting plate; and (d) at least one adjustment means for adjusting the separation between the mounting means.

According to a second aspect of the invention, there is provided a mounting device suitable for use in a machine according to the first aspect of the invention and comprising: (a) a base plate; (b) a mounting plate mounted on the base plate for rotation relative thereto about an axes; (c) at least one set comprising two mounting means on the mounting plate; and (d) at least one adjustment means for adjusting the separation between the mounting means; In use, the mounting device is mounted on a machine in a conventional manner, i.e. for rotation relative to a bed plate of the machine about a vertical axis.

One mounting means of the set is preferably fixed with respect to the mounting plate whilst the other mounting means is adjustable relative to the mounting plate.

The mounting plate may additionally be formed with an array of holes for receiving in selected holes locating elements.

Each mounting means preferably comprises a respective dowel projecting from the mounting plate for engagement in a hole present in a workpiece.

According to a third aspect of the invention, there is provided a method of machining a workpiece wherein the workpiece is releasably secured on a mounting plate, the position of the workpiece relative to the mounting plate being determined by a plurality of locating elements, at least two holes are machined in the workpiece, the workpiece is demounted from the plate, the workpiece is clamped to a rotatable structure having a pair of dowels which are received in said holes to establish a predetermined position of the workpiece relative to the rotatable structure and further machining of the workpiece is then carried out.

The mounting plates may be incorporated in the rotatable structure, the workpiece being releasably secured on the mounting plate for both machining operations.

During the second machining operation, the workpiece may be turned about mutually orthogonal axes.

Preferably, the mounting means comprises releasable (and replaceable) mounting elements. Thus the mounting means may comprise housings provided with threaded bores, and the mounting elements may comprise threaded portions and mounting portions, the mounting portions being of dowel-like form of various diameters and lengths.

By means of the present invention, a workpiece comprising two mounting bores in any normal separation may be mounted on the mounting device by the utilisation of mounting elements of the requisite size, and by adjustment of the separation between the mounting means, rotation of the mounting plate about the second axis enabling a workpiece to be brought into a desired alignment relative to the machine. Additionally, by rotation of the mounting device as a whole about the vertical axis, and by rotation of the mounting plate relative to the base plate about a horizontal axis, a greater number of the total machining operations required to be carried out on the workpiece may be effected without demounting the workpiece, than was previously capable of being carried out, including the drilling of compound bores in different planes (i.e.

including both compound bores lying in mutually inclined planes, and compound bores comprising parts lying in mutually inclined planes).

When it is desired to utilise the mounting device for a different workpiece comprising, e.g. mounting bores in different locations, it is necessary simply to adjust the distance of separation of the mounting means, and possibly replacement of the mounting elements.

There will now be given a detailed description, to be read with reference to the accompanying drawings, of a mounting device which is a preferred embodiment of this invention, having been selected for the purpose of illustrating the invention by way of example. In the accompanying drawings: Figure 1 is a diagrammatic representation of a front elevation of the preferred embodiment; Figure 2 is a diagrammatic representation of side elevation of the preferred embodiment, viewed in the direction of the arrow A of Figure 1; Figure 3 is a plan view of the preferred embodiment; and Figure 4 is a front elevation, showing the mounting device having been adjusted.

The mounting device which is the preferred embodiment of this invention has been devised primarily for the machining of workpieces in the form of engine components, by the use of computer numerical-controlled machines. It is however to be understood that the invention has broader applications, and may be used to advantage in the machining of other types of workpiece other than by the use of computer numerical controlled machines.

The device comprises a circular base plate 6, adapted to be mounted in the bed plate 8 of a machine, and to be rotated by operational elements of the machine about a vertical axis. Extending upwardly from the base plate 6 is a housing 10, in which is located a horizontal spindle (not shown) on a front end of which a circular mounting plate 12 is releasably mounted. Also located within the housing there is provided drive means which is operative to rotate the spindle, and hence the mounting plate, by desired, preferably small increments, the drive means advantageously being operated by control elements of the machine as a whole.

Mounted on the base plate 6 are roller bearings (shown schematically at 13) which support the weight of the mounting plate 12 and any components mounted thereon.

A first, rectilinear guideway is formed in the mounting plate 12 at a position offset from the axis of rotation thereof. A housing 20 is slidably mounted in the guideway and is provided with lead screw 21, whereby the housing can be moved along the guideway. A handle 22 is provided at one end of the lead screw for adjusting the position of the housing and the handle may be incorporated in a known device comprising a micrometer scale to facilitate accurate positioning of the housing. There is formed in the housing 20 a threaded bore which is aligned with a rectilinear slot 14 in the mounting plate 12. A dowel 16 is screwed into this bore and projects through the slot 14 and beyond the adjacent face of the mounting plate.

At a position spaced from the slot 14, there is provided in the mounting plate a fixed housing, in which there is screwed a further dowel 23. As shown in the drawings, the fixed dowel preferably lies in a position aligned with the longitudinal centreline of the slot 14.

As shown in Figure 1, there may be provided in the mounting plate, at positions spaced from the axis in directions opposite to those in which the dowels 16 and 23 are spaced, a further fixed dowel 23a and a further adjustable dowel 16a which can be moved along a rectilinear slot 14a by rotation of a handle 22a.

An array of holes 20 is provided in the mounting plate 12 to receive removable location elements (not shown). The location elements may be dowels or elements having more complex shapes. Preferably, there is provided a number of differently shaped location elements, selected ones of which are placed in selected ones of the holes 20 to locate a particular workpiece on the mounting plate.

Alternatively, a number of location elements may be associated with the mounting plate for movement independently of one another between retracted positions, in which they are retracted into respective ones of the holes 20 and projected positions in which they project from the mounting plate in the same direction as do the dowels 16 and 23.

When a workpiece (not shown) is mounted on the mounting plate 12, one or more of the holes 20 may be occupied by a respective clamp for the workpiece.

Additionally or alternatively, there may be formed in the mounting plate one or more "T"-slots for receiving adjustable clamps in a known manner.

A sequence of operations of the machine of which the preferred embodiment forms part will now be described.

Acastworkpiece is mounted in a predetermined position on the mounting plate 12, the workpiece being located by location elements introduced into selected ones of the holes 20 and the workpiece being clamped to the mounting plate by releasable clamps. A first machining operation is then carried out on parts of the workpiece which are accessible whilst the workpiece remains fixed with respect to the mounting plate. This machining operation includes the machining of at least two, parallel bores which are to be used as mounting bores. Usually, the first machining operation will also involve machining at least one face on the workpiece which can be used as a location face, for example being engaged subsequently with the mounting plate 12.

When the first machining operation has been completed, the workpiece is released from the mounting plate and the location elements are removed. If appropriate dowels 16 and 23 are not already present in the housings, then the required dowels are screwed into the housings. The housing 20 is adjusted to provide a predetermined separation between the dowels 16 and 23. The workpiece is then mounted once more on the mounting plate, the dowels 16 and 23 being received in the locating bores which have already been formed in the workpiece. The workpiece is clamped once more to the mounting plate and a second machining operation is carried out.

It will be noted that the position of the dowel 23 relative to the mounting plate 12 cannot be varied.

Furthermore, the dowel 16 can be reciprocated towards and away from the dowel 23 along a predetermined rectilinear path but cannot undergo movements in other directions relative to the dowel 23. Provided the mounting bores have been formed accurately at predetermined positions in the workpiece, the position of the workpiece during the second machining operation can be predetermined precisely. It will be noted that the mounting plate 12 can rotate about its axis relative to the vertical axis of rotation of the base plate 6 but the relation between these axes is fixed.

Usually, a face of the workpiece which was presented towards the mounting plate 12 during the first machining operation will be accessible during the second machining operation. Accordingly, by rotation of the base plate 6 about the vertical axis and rotation of the mounting plate 12 about its horizontal axis relative to the base plate, bores can be drilled in one or other of the machining operations in all faces of the workpiece and compound bores can be formed.

Whilst the provision of a single, fixed dowel housing for each adjustable dowel housing has been described, it will be understood that there may be provided two or more alternative fixed dowel housings for each adjustable dowel housing. Nevertheless, the position of each fixed dowel relative to the axis of rotation of the mounting plate 12 is precisely known and the angular position of the workpiece about the fixed dowel is precisely determined by the adjustable dowel so that instructions can be given to the machine for machining at precisely predetermined positions without any necessity for ascertaining the position relative to the machine of a datum position on the workpiece. In the machining, at different times, of different workpieces, the position of the dowel 23 engaged in a locating bore of the workpiece will be precisely known.

It will be understood that a second workpiece may be mounted on the mounting plate 12 and located by means of the dowels 16a and 23a.

Whilst the preferred embodiment has been described above in a conventional orientation, in which the base plate is mounted for rotation about a vertical axis, and the mounting plate is mounted for rotation about a horizontal axis, the invention may of course be used in other orientations, such as that in which the base plate is mounted for rotation about a horizontal axis, and the mounting plate mounted for rotation about a vertical axis.

In addition, whilst the use of the preferred embodiment has been described above in relation to the direct mounting of a component on the mounting plate, the invention may be put into practice by the use of an intermediate carrier, which is itself mounted on the mounting plate, and to which the workpiece is itself secured.

By removal of the mounting elements 16,23 and replacement by elements of different sizes, and by adjusting the distance of separation between the mounting elements of the two sets, the mounting plate may readily be adapted to receive a different component, for machining purposes.

The mounting plate 12 can be dismounted from the spindle of the housing 10 and used on known alternative machines, for example, machines commonly referred to as five axis machines.

The invention disclosed in the foregoing description, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process of attaining the disclosed result may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A machine incorporating a mounting device for mounting a workpiece on the machine, the mounting device comprising: (a) a base plate mounted for rotation about a first axis; (b) a mounting plate mounted on the base plate for rotation relative thereto about a second axis which is substantially perpendicular to the first; (c) at least one set comprising two mounting means on the mounting plate; and (d) at least one adjustment means for adjusting the separation between the mounting means.

2. A mounting device suitable for use in a machine comprising: (a) a base plate; (b) a mounting plate mounted on the base plate for rotation relative thereto about a second axis; (c) at least one set comprising two mounting means on the mounting plate; and (d) at least one adjustment means for adjusting the separation between the mounting means.

3. A machine according to claim 1 or a device according to claim 2 wherein one mounting means of each set is fixed with respect to the mounting plate.

4. A machine or device according to claim 3 wherein another mounting means of each set is adjustable along a rectilinear path relative to the mounting plate.

5. A machine or device according to claim 4 wherein the adjustable mounting means is movable towards and away from said one mounting means.

6. A machine according to any one of claims 1 and 3 to 5 or a device according to any one of claims 2 to 5 wherein each mounting means comprising a housing on the mounting plate and a dowel screwed into the housing to project from the mounting plate.

7. A machine according to any one of claims 1 and 3 to 6 or a device according to any one of claims 2 to 6 wherein there is formed in the mounting plate an array of holes.

8. A method of machining a workpiece wherein the workpiece is releasably secured on a mounting plate, the position of the workpiece relative to the mounting plate beng determined by a plurality of locating elements, at least two holes are machined in the workpiece, the workpiece is demounted from the plate, the workpiece is clamped to a rotatable structure having a pair of dowels which are received in said holes to establish a predetermined position of the workpiece relative to the rotatable structure and further machining of the workpiece is then carried out.

9. A mounting device substantially as herein described with reference to the accompanying drawings.

10. Any novel feature or novel combination of features disclosed herein or in the accompanying drawings.