GB2224678A

GB2224678A - Mandrel

Info

Publication number: GB2224678A
Application number: GB8925113A
Authority: GB
Inventors: Terry William Portlock
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-11-10
Filing date: 1989-11-07
Publication date: 1990-05-16
Also published as: GB8925113D0; GB8826294D0

Abstract

The mandrel (1) includes a tubular sleeve (5) which is expanded by fluid pressure to secure a workpiece. The mandrel comprises a central body (2) surrounded by the sleeve (5) such that an annular fluid pressure chamber (23) is located between the sleeve and the body, and end pieces (4) at each end of the body (2) closing the chamber (23) and adapted for mounting of the mandrel. A cylindrical recess (13) at one end of the body (2) houses a self-contained fluid pressurising device (6) e.g. a piston and rod assembly (17, 18) which is fluidly connected to the pressure chamber (23) and the adjacent end piece (4) includes an aperture (4A) to enable insertion of an operating tool for e.g. rotating the piston and rod assembly to move it axially for pressurisation. Closable fluid ducting is preferably provided at the other end of the body (2) to enable bleeding or replenishment of the pressure fluid. The mandrel is economic to manufacture and enables convenient fitting and removal of a workpiece. <IMAGE>

Description

"MANDREL" DESCRIPTION The present invention relates to a mandrel or arbor (both referred to as "mandrels" for convenience) for supporting a workpiece in a machine tool.

In the known form of mandrel, the mandrel simply comprises a cylindrical steel body with end portions adapted to facilitate the fitting of the mandrel to a machine tool, such as for example to the headstock and tailstock respectively of a lathe. The workpiece is positioned on the mandrel prior to the mandrel being fitted on the machine tool, and location of the workpiece is achieved by forcing the workpiece axially onto and along the mandrel using a hammer. There is the disadvantage that this rather crude fitting procedure could damage the workpiece and there is the further disadvantage that, if due to some irregularity, the workpiece has to be removed temporarily from the mandrel then it is extremely difficult to refit the workpiece at exactly the original datum positions on the mandrel, to convenience further work operations on the workpiece.

It is the principal object of the present invention to provide a mandrel wherein the workpiece can be relatively easily fitted or removed.

According to the present invention there is provided a mandrel for supporting a workpiece in a machine tool comprising a central body, a tubular expansion sleeve surrounding the body, said sleeve having a substantially uniform wall thickness or axially spaced support means on which the sleeve is fitted for radial support, an annular fluid-pressure chamber being defined between the sleeve and the periphery of the central body, end pieces at the ends of said central body adapted for mounting the mandrel on a machine tool, fluid pressurizing means located in a housing in said central body said fluid pressurizing means comprising a pump and a pump actuator, and conduit means fluidly connecting the fluid pressurizing means to said annular fluid-pressure chamber, said fluid pressurizing means serving to create pressure fluid reaction on the inner wall of the sleeve to radially expand an annular portion of the sleeve for securement of a workpiece on the mandrel.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing wherein: Fig 1 shows a sectional side elevation of a mandrel/arbor in accordance with the present invention; Fig 3A shows schematically the work piece securing action achieved in the mandrel of Fig 1 for workpieces having a cylindrical bore; Fig 3B shows schematically the work piece securing action achieved in the mandrel of Fig 1 for workpieces having a tapering bore.

Fig 4 shows a sectional side elevation of a mandrel/arbor according to a further embodiment of the present invention.

Referring to Figs 1 and 2 a mandrel 1 (or arbor) serves to carry a workpiece to facilitate machining operations on the workpiece in a machine tool, for example in a lathe. The mandrel 1 comprises a generally cylindrical centre body 2, end pieces 3, 4 adapted for the mounting of the mandrel 1 in a machine tool, an outer tube 5 which is a tight fit on the body 2 and on the end piece 3, and a hydraulic fluid pressurising device 6 actuable to pressurize hydraulic fluid on the inner wall of the tube 3 (by means of conduits 7, 8) so as to radially expand the tube 3 whereby a work piece located on the tube 3 is jammed in position on the tube.

The end pieces 3, 4 include frusto conical openings 3A, 4A to receive support spindles at the headstock and tailstock respectively of a lathe for example, and the end piece a can be especially adapted to be driven frond the headstock.

The centre body 2 is in the form of a cylinder with a threaded bore 9 located at one end of the body 2 and co-axial with the axis K-K of the mandrel 1, the end piece 3 having a stepped nose portion 10 which is threadingly fitted to the bore 9 such that an annular groove 11 is provided to hold an annular sealing element 12.

The fluid pressurizing device 6 is located in a cylindrical bore 13 (co-axial with axis K-K) in the body 2 at the end thereof adjacent end piece 4, the body 2 having a threaded neck portion 2A on which the end piece 4 is threadingly received. The end piece 4 has an inner stepped formation which forms an annular groove 14 with the body 2 for the reception of an annular sealing element 15. Referring more especially to Fig. 2, the device 6 comprises a cylindrical housing insert 16 which is pressed into the bore 13. A piston unit 17 is housed in the insert 16 and has a spindle 18 attached at the inner end which spindle 18 is threaded into a bore 19A in.a base part 19 of the insert 16.The piston unit 17 further includes a slot 20 for an annular seal 21, while a cap screw 22 is fitted into a threaded bore at the outer end of the piston unit 17 for rotation of the unit 17, the head of the cap 22 containing an hexagonal indent whereby a key can be inserted into the indent via a central aperture in the end piece 4 to facilitate rotation of the unit 17.

The body 2 includes a shallow annular recess at the periphery forming with the tube 5 an elongate pressurizing chamber 23. The operating fluid for the device 6 can comprise a suitable hydraulic oil. A conduit 25 for example formed by an axial groove at the threading 19A enables oil to be pupped by the piston unit 17.

To assemble the mandrel 1, the seal 12 is firstly fitted on the neck portion of the end piece 3 and, with suitable thread lock substance on the threadings, the end piece 3 is screwed into the adjacent end of the body 2.

The cap screw 22 is similarly locked to the piston unit 17 with a suitable thread locking substance, in both cases sufficient curing time for the lock substance being provided. With end piece 4 temporarily screwed to body 2, the correct sized bearing surfaces for the tube S can now be ground on the assembly, namelv at surface 3B of piece 3, the periphery of body 2 and the surface 4B of piece 4, the end pieces 3, 4 conveniencing mounting of the assembly for this grinding operation. The end piece 4 is then removed to enable the tube 5 to be shrunk fit onto the assembly 2, 3; by for example suitably heating the tube 5 and cooling the assembly 2, 3.The tube 5 is fitted over the assembly and pushed firmly home, ensuring that holes on the tube S are aligned with tapped holes 24 on the end piece 3 (far position setting of the tube by means of grub screws) The insert housing 16 is then pushed into its receiving bore 13 (interference fit) with pressure sealing adhesive present.

The assembly is now ready to be filled with oil, and to this end the assembly is located vertically with the insert 16/bore 13 defining an open-top cup so that the assembly can be filled with oil up to the top edge of the insert 16, allowing air to be displaced before fitting of the piston unit 17. The piston unit 17 is inserted into the bore of the insert 16 so that the spindle 19 engages the threading 19A and the piston unit 17 is then screwed in until only the head of screw 22 protrudes from insert 16, oil consequently being displaced and expelled from around the outside of the central body 2, all excess oil being removed. The seal 15 is then fitted on the end piece 4 and with thread lock substance applied, the end piece 4 is screwed onto the neck 2A until fully home with seal 15 properly positioned. Final machining and grinding of the outer surface of the tube 5 to the correct size can now be carried out.

Various pre-use checks should be carried out on the mandrel 1 to ensure that various dimensions are within their prescribed limits.

These values can include: 1. Tube outside diameter along the length of the tube.

2. Degree of tube radial expansion for given degrees of fluid pressurisation (achieved by screwing in piston unit 17), up to the maximum amount of expansion allowable (determined by the elastic limit of the tube material) - this will also check hydraulic security. Also, contraction of tube to correct size on depressurisation can be checked.

3. Alignment of end piece centres.

Further appropriate tests can be conducted using a test piece e.g. test hob mounted on the mandrel.

In use, a workpiece is fitted on the mandrel 1 by firstly axially positioning the workpiece on the mandrel then expanding the mandrel by rotating the cap screw 22 (with unit 17) clockwise until workpiece is held firmly (see Fig. 3A) - the mandrel/workpiece unit can then be mounted in the machine tool (e. g. lathe) between centres for machining work. When machining is complete, the unit can be removed from the machine tool and the work piece is then easily removed from the mandrel by turning unit 17 anticlockwise to depressurise the tube 5 which returns to its original size. Consequently, the mandrel is quickly prepared to receive the next workpiece.

Fig. 3A shows the situation where the workpiece has a straight cylindrical bore, but the same mandrel can satisfactorily secure workpieces with tapered bores as shown in Fig. 3B, provided the degree of taper is compatible with the expansion performance of the tube 5.

A wide variety of different sized mandrels could be provided, for example with diameters from 1 in (2.54 om) to 2.5 in (6.25 cm). The degree of diameter expansion possible will depend on the sizing of the tube 5 (in particular the tube wall thickness), but a figure of 0.0005 in (0.0127 itin) for example should be satisfactory. The parts of the mandrel will be made from suitable grades of steel.

The above. mandrel of the present invention has the following advantages: 1. The mandrel uses hydraulic power to expand the mandrel tube with no external oil or pressure supply, making the mandrel totally self contained. Only one tool is required to operate the mandrel and that is a hexagon key, which can be supplied with each mandrel.

2. The mandrel tube will always expand symmetrical about the centre line along the length of the mandrel.

3. The mandrel expands to fit a tapered bore within its designed degree of expansion.

4. All machining work will be true to the bore of a workpiece and the centre line of the mandrel.

5. The workpiece can be removed from the mandrel, then replaced and the earlier machining of the workpiece will still be true to the centre line of the mandrel, as though it had never been removed ie; same as the original setup.

The mandrel 1 can be made dismanteable for servicing and repair or replacement of parts.

The above mandrel (arbor) in accordance with the present invention could be used in a wide variety of machine tools. Thus, in addition to lathes, the mandrel could be used for example in cylindrical grinder machines or in milling machines. The mandrel can carry a tool rather than a workpiece, and this tool may take the form of a cutter, including milling cutters, or a grinder.

Modifications are possible. For example the fluid pressurizing unit could take some other form from that shown.

The further embodiment of the invention shown in Fig 4 is generally similar to that of Figs 1 and 2 and like parts carry like reference numerals. However, a significant additional feature in Fig 4 is the provision of additional ducting 31, 32 at the end of the mandrel remote from the fluid pressurizing device 6, and extending from the chamber 23, said ducting 31, 32 passing through the end piece 3 so that the ducting opens externally of the mandrel.

The additional ducting 31, 32 facilitates oil replenishment in the mandrel and oil bleeding, and indeed initial oil filling of the mandrel could be achieved by means of the ducting 31, 32 in contrast to the filling arrangement described for the Figs 1 and 2 embodiment. To place the mandrel in the in-use condition, the ducting 31, 32 is suitably closed, for example by the placement of a ball 33 on a shoulder in the ducting and fitting a grub screw 34 to hold the ball in place. Preferably the toolreceiving recess of the grub screw 34 is filled (eg with wax) to prevent subsequent inadvertent removal of the grub screw. In this example the end piece 3 is integral with the body 2.

Also, the fluid pressurizing device 6 is of slightly different form from that in the previous embodiment. In particular, the cylindrical insert 16 is dispensed with and the body 2 now carries the threading l9A for the spindle 18 of the pump unit. The spindle 18 has a large diameter head portion 17A representing the pump piston carrying the cap screw 22: again an operating tool can be fitted on the cap screw 22 by inserting the tool through the opening 4A in the end piece 4. Suitable ducting is again provided to enable oil to be pumped from the cylindrical bore 13 (now representing the housing for the device 6) to the conduits 7, 8 whense to the chamber 23. For example this ducting can be formed by a suitable geometrical arrangement of the threading between the thread 19A and the spindle.The sealing ring 21 of the pump unit is held in place by a suitable clip 21A on the spindle 18.

Further, the annular sealing element 15 is located in an annular recess 15A in the body 2 and this enables the end piece 4 to be removed without disturbing either sealing element 12, 15. A bearing ring 35 of P.T.F.E material is carried by the body 2 and facilitates sliding of the tube (or sleeve) 5 onto the body 2. The tube 5 which has a uniform wall thickness can again be shrunk fit onto the shoulder 3B.

A workpiece is secured to the mandrel of Fig 4 or removed therefrom in an exactly similar manner to the mandrel of Figs 1 and 2. In particular, where the bore of the workpiece is of pure cylindrical form (Fig 3A) then the tube 5 will be expanded into area contact with the workpiece bore to jam the workpiece for securement on the mandrel, and the surface portion of the tube 5 engaging the workpiece bore will extend substantially parallel to the axis of the body 2.

Claims

1. A mandrel for supporting a workpiece in a machine tool comprising a central body, a tubular expansion sleeve surrounding the body, said sleeve having a substantially uniform wall thickness, axially spaced support means on which the sleeve is fitted for radial support, an annular fluid-pressure chamber being defined between the sleeve and the periphery of the central body, end pieces at the ends of said central body adapted for mounting the mandrel on a machine tool, fluid pressurizing means located in a housing in said central body, said fluid pressurizing means comprising a pump and a pump actuator, and conduit means fluidly connecting the fluid pressurizing means to said annular fluid-pressure chamber, said fluid pressurizing means serving to create pressure fluid reaction on the inner wall of the sleeve to radially expand an annular portion of the sleeve for securement of a workpiece on the mandrel.

2. A mandrel as claimed in claim 1 , wherein one end piece includes an axial aperture for passage of an operating tool to the pump actuator.

3. A mandrel as claimed in claim 1 or 2, wherein at least one of the end pieces is releasably secured to the central body.

4. A mandrel as claimed in any one of the preceding claims, wherein th#e tubular sleeve is a shrink fit on the body and/or end pieces.

5. A mandrel as claimed in any one of the preceding claims, wherein the pump of the fluid pressurizing means comprises a piston device while the pump actuator comprises a head adapted to receive an operating tool.

6. A mandrel as claimed in any one of the preceding claims, wherein said conduit means additionally constitute a reservoir for fluid.

7. A mandrel as claimed in claim 5, wherein said piston device includes a piston unit screw threaded to a fixture in the mandrel whereby an axial fluid-pressure creating movement of the piston unit is created by rotating the piston unit.

8. A mandrel as claimed in any one of the preceding claims, wherein the axially spaced support means are formed on said end pieces.

9. A mandrel as claimed in any one of the preceding claims, wherein the annular fluid-pressure chamber is formed by an annular recess on the periphery of the central body.

10. A mandrel as claimed in any one of the preceding claims, wherein one of said end pieces is adapted to facilitate a driving connection to the mandrel.

11. A mandrel as claimed in any one of the preceding claims, wherein the fluid pressurizing means is located at one end of the body.

12. A mandrel as claimed in any one of the preceding claims, wherein the housing defines an open-top recess located at one end of the body when the axis of the mandrel is orientated vertically, one of said end pieces being releasably secured to the body at said one end.

13. A mandrel as claimed in claim 7, wherein the piston device further comprises a cylindrical casing for the piston unit, said casing being accommodated in said housing, and the piston unit includes a male-threaded spindle in threaded engagement with a female-threaded bore in the casing.

14. A mandrel as claimed in claim 11, wherein additional duct means are provided at the other end of said body whereby fluid can be fed to or discharged from said fluid chamber via said additional duct means.

15. A mandrel as claimed in claim 3, wherein both of the end pieces are releasably secured to the central body.

16. A mandrel as claimed in claim 3, wherein one of the end pieces is integrate with the central body.

17. A mandrel as claimed in any one of the preceding claims, wherein spaced sealing rings are provided adjacent to the end pieces, said sealing rings engaging the tubular sleeve.

18. A mandrel as claimed in claim 17 when dependent on claim 3, wherein the sealing rings are located between the central body and the sleeve, the arrangement being such that said one end piece can be removed without disturbing the sealing rings.

19. A mandrel as claimed in claim 17, wherein an additional annular bearing strip is provided on the central body to facilitate sliding of the sleeve onto the central body.

20. A mandrel for supporting a workpiece substantially as hereinbefore described with reference to and as illustrated in Figs 1 and 2 or Fig 4 of the accompanying drawings.