GB2223431A - Machining a cylindrical or part-cylindrical work piece - Google Patents

Abstract

Apparatus for such machining comprises a rotable, axially-reciprocable tool carrier 1 for a tool holder 20 equipped with a cutting tool 22 projecting radially of the carrier, the tool holder being radially displaceable in response to drive means rotating with, but independently-operable relative to the tool carrier. The carrier is a hollow bar 1 with a linear motor 9 operated rod 12 with a cam surface 26 at its end engaging a cam surface 25 on the holder 20 to move the tool 22 radially outwardly against a spring 28. <IMAGE>

Description

Improvements in and relating to machine tools The invention relates to apparatus for machining the inner surface of a cylindrical or part cylindrical workpiece. It is sometimes necessary to develop an internally relieved or recessed profile within a cylindrical or part cylindrical workpiece. One method of accomplishing this is to clamp the workpiece in a chuck and then use a boring bar fitted with a mechanism to generate sideways movement.

The sideways movement is synchronised to the speed of rotation of the chuck. This is a relatively slow operation. To form deeper recesses in the workpiece it is also possible to use a milling tool to progessively remove material from the inner surface of the workpiece. The latter is of course held stationary for this type of operation.

Both of the methods just described are principally useful for relatively thick, one-piece workpieces. Relatively thin workpieces are normally split in the axial direction in two separate halves. The required recesses are then generated by milling or by use of a boring bar; the operation is then repeated on the second half of the workpiece. This too is a relatively slow operation and to produce a desired internal profile it may be necessary to both carry out milling and boring operations. It is an object of the present invention to provide improved apparatus for carrying out operations of the kind just described.

According to the present invention, apparatus for machining a cylindrical or part cylindrical workpiece comprises a rotatable, axially reciprocable tool carrier for a tool holder which is in use equipped with a cutting tool projecting radially of said carrier, and is characterized in that the tool holder is radially displaceable in response to drive means rotating with, but independantly operable relative to the tool carrier.

The tool carrier is preferably constituted by a hollow bar, the drive means comprising a cam at one end of a second bar supported inside the hollow bar and axially displaceable relative to it. Preferably the second bar is axially displaceable by means of a linear motor.

Advantageously, the tool holder is biased away from contact with the workpiece and operation of the drive means causes the tool holder and the tool supported thereon to move radially with respect to the axis of rotation of the tool carrier into contact with said workpiece.

Where a linear motor is used, the radial movement of the tool is preferably generated solely by operation of the linear motor.

It will be appreciated that in order to provide a desired finish to the workpiece it may by necessary to make more than one pass. For example where the piece is to have portions of constant internal radius it is advantageous to form these after machining the recesses or other internal profiles. For example a final pass at a higher speed with the tool held stationary may be satisfactory.

For the avoidance of doubt, the expressions "recesses" and "internally relieved profile" both refer to the generation in the workpiece of a controlled internal departure from circularity. Normally such departures do not extend around the full internal circumference or over the full axial length of the workpiece. Whilst the apparatus of this invention might be used to generate an axially extending departure from circularity, such as a groove, it will normally be simpler to produce such grooves by milling or broaching operations, in a conventional manner. The invention is equally applicable to thick and thin-walled workpieces. In the case of a thin workpiece which would normally be machined in separate stages, as two separate portions, it may be clamped up and treated like a solid, thick walled workpiece.

In order that the invention be better understood, a preferred embodiment of it will now be described by way of example with reference to the accompanying drawings, in which; Figure 1 is a purely schematic side view of a machine tool constructed in accordance with the invention and including some details of the control/positioning system, and Figure 2 is a cross-sectional side view of part of the tool of Figure 1, but shown in greater detail.

In both Figures, like parts bear like reference numerals, in the interests of ease of understanding. Referring firstly to Figure 1, a hollow boring bar I is supported between main bearings 2,3 which are carried by a U-shaped saddle 4 rigidly attached to the machine frame 11. (Only one bearing, 2, is seen in Figure 2); At one end of the bar 1, there is a drive motor 5 to rotate the bar, a rotational encoder 6 for monitoring angular displacement of the bar during rotation and a linear encoder 7 for determining the axial position of the bar at any time. An alternative position for the rotary encoder 6 is shown in Figure 2. The purpose and mode of operation is however, exactly the same. There is also a hydraulic actuator 8 for accomplishing axial displacement of the bar 1, as indicated by arrows in Figure 1.

At the opposite end of the bar 1, there is a precision linear motor 9, which is supported from the end of the boring bar 1 by a rigid bracket 10 extending from which is a pin 32 abutting a rod 33 attached to the machine frame 11 second bar 12 (best seen in Figure 2) is mounted inside and rotates with the bar 1, the two bars being rotationally coupled by the location of the rectangular free end of the bar 12 in a rectangular shaped aperture 24 in the shaft 21. The bar 12 is however, free to move axially with respect to the bar 1, under the control of the linear motor 9, a coupling 13 between the latter serving to permit the bar 12 to move axially whilst at the same time rotating with the bar 1, the linear motor remaining rotationally stationary by virtue of pin 32 abutting against rod 33.

The axial position of the bar 12 is precisely controlled by control/programming unit 32 in accordance with the information derived from the encoders together with programming instructions, as will be further discussed later.

Referring now primarily to Figure 2, the bar 1 carries a radially-displaceable tool holder 20, (shown only by an arrow in Figure 1). This comprises a shaft portion 21 radially disposed relative to the major axis of the bar 1 and having at one end a cutter 22 and at the other end a boss 23. A helical compression spring 28 trapped between the boss and the bar 1 serves to bias the cutter 22 radially inwardly away from any surrounding workpiece. An aperture 24 in the shaft 21 contains cam surface 25 aligned generally perpendicular to the axis of the shaft, but generally parallel to the axis of the bar 1.

The free end of the second bar 12 is provided with a cam surface 26. When the second bar is displaced axially of the bar 1, the cutter end of the shaft 21 is forced radially outwardly, against the spring 28.

The bar 12 is itself supplied with a return spring 27 trapped between an abutment 29 on the bar and the inside of a housing 30.

In use, the relative position of the first and second cam surfaces 25,26 is critical in determining the precise radial position of the cutter 22. Furthermore, by changing the relative position, the cutter can be arranged to cut, or not cut the inner surface of an associated workpiece (not shown in detail, but indicated at 31).

By correctly programming the linear motor movement in relation to (a) angular position and (b) axial position of the tool relative to the workpiece, the tool can be caused to generate a desired profile in the inner surface of the workpiece. This may take the form of one or more recesses in the workpiece. On the other hand, by fixing the relative movement in one position the tool can be caused to machine the inner surface of the workpiece to a constant diameter. This may be particularly useful as a finishing operation after machining one or more recesses, especially where the non-recessed areas must be accurately cylindrical.

It will be appreciated that the machine tool just described is extremely versatile, since its operation can largely be programmed using the position information provided by the encoders to generate all kinds of internal departures from truly circular in the inner surface of a workpiece.

Claims (7)

1. Apparatus for machining a cylindrical or part cylindrical workpiece comprising a rotatable, axially reciprocable tool carrier for a tool holder which is in use equipped with a cutting tool projecting radially of said carrier, characterised in that the tool holder is radially displaceable in response to drive means rotating with, but independantly operable relative to the tool carrier.

2. Apparatus according to Claim 1 wherein said tool carrier is constituted by a hollow bar, the drive means comprising a cam at one end of a second bar supported inside the tool carrier and axially displaceable relative to it.

3. Apparatus according to Claim 2 characterised in that the second bar is axially displaceable by means of a linear motor.

4. Apparatus according to any of Claims 1 - 3 characterised in that the tool holder is biassed away from contact with a workpiece and that operation of said drive means causes the tool holder and a tool supported thereon to move radially with respect to the axis of rotation of the tool carrier into contact with said workpiece.

5. Apparatus according to claim 3 or claim 4 wherein said radial movement is generated solely by the operation of said linear motor.

6. The use of the apparatus according to any preceding claim characterised in that the drive means is operated to cause the tool to generate in the workpiece a controlled departure from internal circularity.

7. Apparatus for machining a cylindrical workpiece substantially as herein described with reference to and as illustrated by the accompanying drawings.

7. Apparatus for machining a cylindrical workpiece substantially as herein described with reference to and as illustrated by the accompanying drawings.

Amendments to the claims have been filed as follows 1. Apparatus for machining a cylindrical or part cylindrical workpiece comprising a rotatable, axially reciprocable tool carrier for a tool holder which is in use equipped with a cutting tool projecting radially of said carrier, characterised in that the tool holder is radially displaceable in response to drive means rotating with, but independantly operable relative to the tool carrier and that said drive means is operable in conjunction with said axial reciprocation to generate simultaneous departures from circularity and parallelism in the workpiece.

2. Apparatus according to Claim 1 wherein said tool carrier is constituted by a hollow bar, the drive means comprising a cam at one end of a second bar supported inside the tool carrier and axially displaceable relative to it.

3. Apparatus according to Claim 2 characterised in that the second bar is axially displaceable by means of a linear motor.

4. Apparatus according to any of Claims 1 - 3 characterised in that the tool holder is biassed away from contact with a workpiece and that operation of said drive means causes the tool holder and a tool supported thereon to move radially with respect to the axis of rotation of the tool carrier into contact with said workpiece.

5. Apparatus according to claim 3 or claim 4 wherein said radial movement is generated solely by the operation of said linear motor.

6. The use of the apparatus according to any preceding claim characterised in that the drive means is operated to cause the tool to generate in the workpiece a controlled departure from internal circularity.