GB2045126A

GB2045126A - Bore machining apparatus

Info

Publication number: GB2045126A
Application number: GB7911398A
Authority: GB
Original assignee: INSITU MACHINING CO Ltd
Current assignee: INSITU MACHINING CO Ltd
Priority date: 1979-04-02
Filing date: 1979-04-02
Publication date: 1980-10-29
Also published as: GB2045126B

Abstract

Bore machining apparatus has a tubular carrier 3 rotatably mounted by bearings 5a, 6a in spiders 5b and 6b within a bore 1 which is to be machined by a pneumatically operated honing or milling unit 19. The unit 19 is carried by a frame 9 which is keyed for rotation with the carrier and is counterbalanced at 26. The frame 9 and unit 19 are displaceable longitudinally relative to the carrier 9 by a lead screw 15 within the bore of the carrier so that when the carrier 9 is rotated by motor 13 and the lead screw 15 is rotated, the unit 19 machines the bore 1 both circumferentially and longitudinally. For machining a small diameter bore 1 the unit 19 can be located partly within the tubular carrier 3 to extend through slot 11 along which it is longitudinally displacable, possibly by draw cable, while the carrier 3 is rotated to effect the circumferential and longitudinal machining of the bore. The machining tool 2D is preferably a honing stone which is pneumatically operated so that it vibrates or oscillates on an air cushion both radially and axially relative to the surface of the bore. <IMAGE>

Description

SPECIFICATION Bore machining apparatus This invention relates to bore machining apparatus.

According to the present invention there is provided bore machining apparatus comprising a longitudinally extending carrier having a longitudinal axis; support means by which the carrier is, or is capable of being, supported at two longitudinally spaced positions and at least partly in the bore to be substantially co-axial therewith and by which the carrier is mounted for rotation about its longitudinal axis; means for rotating the carrier a bout its longitudinal axis; a machining head for machining the bore and which head is carried by the carrier between said spaced positions and for rotation with the carrier, and means for adjusting the machining head longitudinally relative to the carrier so that by rotation and longitudinal adjustment of the machining head the bore can be machined both circumferentially and longitudinally.

The machining head may, for example, provide grinding or milling of the bore. The present invention was primarily developed to provide superfinishing to a bore which had been pre-machined to a normal machine-shop finish and preferably the machining head is in the form of a honing stone unit.

An appropriate superfinishing and pneumatically operated honing stone unit is marketed by Nagel Maschinen- u. Werkzeugfabrik GmbH under the codes SG 50 and SG 75. For convenience the invention will hereinafter be considered in its application to the superfinishing of bores with a honing machining head.

It has previously been proposed to superfinish a pre-machined bore with a honing stone by mounting the honing unit to be rotatable and as a cantilevered extension of a carriage which is displaceable axially of the bore to effect the required machining. Such a cantilevered construction frequently causes inaccurate machining of the bore especially when the latter is disposed with its axis horizontal where the load of an inadequately supported honing unit may overmachine or score part of the lower peripheral wall of the bore (so causing inaccuracy and eccentricity in the finished bore). In an attempt to alleviate this problem the cantilevered machining head has to be firmly supported with the consequence that the apparatus becomes bulky. expensive, heavy and permanently mounted to machine bores which have to be manoeuvred into a machining position.By the present invention however the machining head can be firmly supported on the carrier which latter is firmly supported at least partly within the bore and by two axially spaced support means. The support means conveniently comprises spiders having radially extending legs and within which the carrier is rotatably borne. With the machining head disposed axially between the spaced spiders it will be apparent that the previously proposed cantilevered mounting is avoided and the bore can be accurately machined by rotation and axial displacement of the machining head when the carrier and bore are substantially co-axial. Furthermore the apparatus is readily portable since the mounting for the support means can simply be provided by the workpiece having the bore which is to be machined.On this latter point the aforementioned spiders may be bolted to the workpiece or may have their legs in the form of struts which bear against the surface of the bore to extend radially therefrom. The portable nature of the apparatus is a considerable advantage, particularly in the superfinishing of large bores, say having a diameter in excess of 2 feet (as may be required for the fabrication of a press or engine) where it is impractical to manoeuvre the workpiece and the superfinishing of the bore is effected with the workpiece in situ.

The apparatus can be applied to the machining of large or small diameter bores by appropriate sizing of the carrier and machining head. For large diameter bores the machining head can be mounted on a frame which extends radially of the carrier and which is keyed for rotation with the carrier while being longitudinally displaceable along the carrier.

For small diameter bores the machining head may extend through a slot in the wall of a tubular carrier so that such head is rotatable with the carrier while for example, an energising unit part of the machining head is displaceable longitudinally within the bore of the carrier so that the radial extent of the machining head from the axis of the carrier can be minimised. When using the aforementioned extension frame for machining large bores it is preferred that a counterbalance is provided on the frame for the machining head to alleviate flexing of the carrier (especially when machining bores the axes of which are horizontally disposed) and thereby maintain accurate honing.

The machining head is preferably a superfinishing honing unit as previously mentioned which is pneumatically operated so that the stone vibrates or oscillates on an air cushion both radially and axially relative to the surface of the bore which is being machined so that the stone will follow the general profile of the bore while superfinishing. This is particularly advantageous in the finishing of horizontally disposed bores of large press or engine fabrications where the weight of the workpiece may cause temporary deformation of the bore into an oval section and the pneumatically oscillating stone can accommodate and follow the ovality of the bore to provide the required finish without scoring or overmachining.Air supply to the pneumatically operated unit is conveniently, in part, by way of conduits incorporated within the carrier - there being provided suitable rotary couplings between the carrier and the air pressure source.

The carrier may be rotated by any suitable means such as a belt or chain drive from an appropriate motor. Similarly the adjustment of the machining head longitudinally relative to the carrier can be effected by any suitable means such as by lead screw or draw cable; when using a lead screw technique rotation of the lead screw to cause displacement of the machining head can be effected manually or by a motor (conveniently mounted on the carrier).By suitably mounting the apparatus of the present invention relative to the bore (particular ly by locating one of the supports at a position axially remote from the bore so that the carrier extends from the bore and the machining head can be displaced along the carrier from within the bore) it is possible to apply the apparatus to the machining of a face which extends radially from the end of the bore, for example where such face may be intended to receive a gasket of a press or engine to seal a cylinder of which the bore forms part. In such an application it may be necessary to adjust the machining head so that, for example, the stone is angled as appropriate to hone the radially extending face (during which honing the machining head is rotated with the carrier but is not subjected to longitudinal displacement relative thereto).The radially extending faces in a stepped bore may be similarly machined. For machining the different diameter bore parts in a stepped bore the machining head may include the facility for adjustment of its radial extent or, in the case of the previously discussed extension frame, alternative frames may be fitted to the carrier.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings, in which: Figure 1 shows a first embodiment of the apparatus in part axial section and which is primarily intended for the superfinishing of large diameter bores, and Figure 2 shows a second embodiment of the invention in part axial section and which is primarily intended for superfinishing small diameter bores.

In the embodiment of Figure 1 the apparatus of the invention is to superfinish by honing a cylindrical bore 1 in a pre-machined (to normal machine-shop finish) workpiece 2 which may comprise a press or engine body. The workpiece 2 is disposed with the axis of the bore 1 horizontal and mounted within the bore is a tubular carrier 3 having a longitudinally extending axis 4. The carrier 3 is mounted by two axially spaced supports 5 and 6 comprising bearings 5a and 6a respectively within which the carrier 3 is rotatable about its axis 4 and spiders formed by a peripherally spaced array of legs Sb and 6b which extend radially outwardly of the respective bearings 5a and 6a to connect with the workpiece 2.More particularly the legs 5b are bolted to a radially extending end face 7 on the workpiece 2 while the legs 6b comprise struts which abut through pads 8 with the cylindrical surface of the bore 1. The legs Sb and 6b will usually be adjustable in length or are selected of an appropriate length so that the carrier 3 is mounted with its axis 4 substantially co-axial with the bore 1.

Received on the carrier 3 between the supports 5 and 6 is a frame 9 which extends diametrically relative to the axis 4. The frame 9 is slidable longitudinally over the carrier 3 and has a guide portion 10 which is received within a longitudinally extending slotted aperture 11 in the wall of the tubular carrier 3. Co-operation between the guide portion 10 and slot 11 ensures that the frame 9 is rotatable in unison with the carrier 3 while permitting longitudinal displacement between the frame 9 and the carrier 3. Rotation of the carrier 3 in the bearings 5 and 6 and relative to the workpiece 2 is effected by a chain drive 12 from an electric or air operated motor 13 mounted on a fixed support 14.

The guide portion 10 includes a nut which engages with a lead screw 15 which extends longitudinally within the bore of the tube 3 to be rotatably mounted at one end in a bearing 16 carried by a wall or frame 17 in the tube 3 while the other end 18 of the lead screw is borne in and extends from the tube 3 to facilitate rotation of the lead screw. As will be apparent, when the lead screw 15 is rotated relative to the carrier 3, the frame 9 is displaced longitudinally along the carrier whilst being rotatable with the carrier. The end 18 of the lead screw can be rotated manually or an appropriate motor (not shown) carried for rotation with the carrier 3 can be coupled to the end 18 to control its rotation.

Mounted on the frame 9 at one of its two radially outer ends is a pneumatically operated superfinishing honing unit 19 such as that marketed under the code SG 50 or SG 75 as previously mentioned.

The unit 19 has a superfinishing stone 20 for honing the surface of the bore 1 as that stone is subjected to vibration and oscillation in a radial and circumferential sense relative to the axis 4 and while the frame 9 is rotated about the axis 4 and displaced axially relative to the carrier 3. The oscillatory movement of the stone 20 is effected by air under pressure derived through a flexible conduit 21 which communicates between the unit 19 and an outlet port 22 in the carrier 3. The port 22 communicates through a conduit 23 which extends through the bore of the carrier (conveniently supported on the frame or wall 17) and by way of a rotary coupling 24 with a conduit 25. The conduit 25 is coupled to an appropriate air pressure source.

The radial extension of the frame 9 diametrically opposite to the unit 19 carries a counterweight 26.

The bore 1 may be considered as being of large diameter (say in excess of 2 feet) and upon operation of the motor 13 it will be seen that the carrier 3 together with the unit 19 are rotated for the stone to effect honing of the cylindrical bore surface both circumferentially and, during longitudinal displacement of the frame 9, longitudinally of the bore surface. Such honing may be desired to provide superfinishing of the bore surface to, typically, 8 micro inches or less.

In the embodiment of Figure 2 the bore 1 in the workpiece 2 may be considered as being of small diameter, say in the order of 3 inches and within this bore is mounted a tubular carrier 27 having a cylindrical bore 28 and a longitudinal axis 29. The carrier 27 is mounted with its axis 29 substantially co-axial with the bore 1 by two pairs of axially spaced spider legs 30 and 31 and in bearings 32 and 33 for rotation about the axis 29.

Means (which for convenience has been omitted from Figure 2) is provided for rotating the carrier 27 relative to the workpiece 2, for example a simple chain and motor drive similar to that shown at 12 and 13 in Figure 1.

Mounted within the bore 28 of the tubular carrier 27 is part of a honing unit 34. The unit 34 is of similar construction and operation to the unit 19 in Figure 1 but has a body part 35 to which the air supply is connected of substantially cylindrical shape and which is slidably dislaceable axially within the bore 28 in piston-like manner. The honing stone 36 of the unit 34 is carried on a component part 37 of the unit which extends from the body 35 through a longitudinally extending slotted aperture 38 in the wall of the carrier 27. For convenience the air supply to the unit 34 has been omitted although this can be by way of a flexible conduit and rotary coupling in a similar manner to the arrangement shown in Figure 1.

Relative rotation between the unit 34 and carrier 27 can be restrained by engagement of the part 37 in the slot 38 or appropriate co-operating keyways can be provided for such purpose to relieve unnecessary loads on the component part 37.

Longitudinal displacement of the honing unit 34 relative to the carrier 27 is provided by a cable 39 the opposite ends of which are secured to the body 35 and which is reeved over axially spaced pulleys 40 appropriately mounted on frames 41 secured to the carrier 27. Displacement of the unit 34 by the cable 39 can be controlled manually or by an appropriate motor (not shown).

It will be realised that during rotation of the carrier 27 and longitudinal displacement of the stone 36 honing of the cylindrical bore 1 will be effected in a similar manner to the Figure 1 arrangement but, as will be apparent from the drawings, the arrangement in Figure 2 can be very much more radially compacted than that in Figure 1 for use with similar diameter bores 1.

Claims

1. Bore machining apparatus comprising a longitudinally extending carrier having a longitudinal axis; support means by which the carrier is, or is capable of being, supported at two longitudinally spaced positions and at least partly in the bore to be substantially co-axial therewith and by which the carrier is mounted for rotation about its longitudinal axis; means for rotating the carrier about its longitudinal axis; a machining head for machining the bore and which head is carried by the carrier between said spaced positions and for rotation with the carrier, and means for adjusting the machining head longitudinally relative to the carrier so that by rotation and longitudinal adjustment of the machining head the bore can be machined both circumferentially and longitudinally.

2. Apparatus as claimed in claim 1 in which the support means comprises spiders having radially extending legs and within which the carrier is rotatably borne.

3. Apparatus as claimed in either claiin 1 or claim 2 in which at least part of the support means is, or is intended to be, bolted to a workpiece a bore in which is to be machined.

4. Apparatus as claimed in any one of the preceding claims in which at least part of the support means are in the form of struts which abut, or are intended to abut, a workpiece within a bore thereof which is to be machined.

5. Apparatus as claimed in any one of the preceding claims in which the machining head is mounted on a frame which extends radially of the carrier and which frame is keyed for rotation with, and is longitudinally displaceable relative to, the carrier.

6. Apparatus as claimed in claim 5 in which the frame has at least one machining head which is counterbalanced on the frame to alleviate flexing of the carrier during rotation.

7. Apparatus as claimed in claim 6 when appendantto claim Sin which the frame extends diametrically relative to the carrier and the machining head is mounted on a first radially extending part of the frame while the opposed radially extending part of the frame carries means to counterbalance that machining head during its rotation.

8. Apparatus as claimed in any one of claims 1 to 4 in which the machining head is carried partly within a tubular carrier so that such head extends through a longitudinally extending slot in the wall of the tubular carrier, the machining head being longitudinally displaceable within the bore and along the slot of the carrier.

9. Apparatus as claimed in any one of the preceding claims in which displacement of the machining head longitudinally relative to the carrier is effected by a lead screw or draw cable device associated with the carrier.

10. Apparatus as claimed in claim 9 in which the lead screw or draw cable device is adjustable by motor means carried by the carrier.

11. Apparatus as claimed in either claim 9 or claim 10 in which the lead screw or draw cable device extends longitudinally within the bore of a, or the, tubular carrier.

12. Apparatus as claimed in any one of the preceding claims in which the machining head is powered by means supplied thereto through a rotary coupling on the carrier.

13. Apparatus as claimed in any one of the preceding claims in which the carrier is rotated by a motor which is, or is intended to be, secured relative to the bore.

14. Apparatus as claimed in claim 13 in which the motor drives the carrier through a belt or chain drive.

15. Apparatus as claimed in any one of the preceding claims in which the machining head is a pneumatically operated honing stone unit.

16. Bore machining apparatus substantially as herein described with reference to Figure 1 of the accompanying illustrative drawings.

17. Bore machining apparatus substantially as herein described with reference to Figure 2 of the accompanying illustrative drawings.