GB2183511A - Expanding mandril - Google Patents

Abstract

An expanding mandril has a cylindrical body member (10) in whose wall radial pistons (11 to 18) are mounted so that on pressurizing the interior of the member (10) the pistons are moved outwards against the inner face of a tubular workpiece (25). The radial pistons (11 to 18) are placed in at least two radial planes and are spaced out around the axis of the mandril. In order to facilitate preliminary centering of the pistons prior to application of the hydraulic pressure, there is an internal coaxial sleeve with part-spiral cam faces arranged to move at least some of the radial pistons outwards in a centered manner from the mandril axis until they contact the innerface of the workpiece. <IMAGE>

Description

SPECIFICATION An expanding Mandril The invention relates to expanding mandrils and more particularlythough not exclusively to an expandable mandril for mounting a generally cylindrical hollowworkpiece on a machine tool for machining the outerface ofthe workpiece, comprising a cylindrical main body member having radial pistons in it which are able to be hydraulically moved outwards to engage the inner face of the workpiece.

The German gebrauchsmuster patent 7,810,680 describes an expanding mandril of this type in which the radial pistons are jointly acted upon by a fluid under pressure to act on a workpiece, such as a tube, that has been previously centered on the mandril.

Howeverthiscentering operation has to be undertaken with radially adjustable screws, which are settothe diameter oftheworkto be machined.

This centering operation is relatively slow.

One object of the present invention is to devise an expanding mandril ofthetype noted above which makes it possibleforthe centering of the work in the form of a hollow member on the mandril to be undertaken as quickly as possible.

Afurtheraim ofthe invention isto make preliminary centering of the work on the mandril priorto operation of the pistons more rapid than in the prior art.

In order to achieve these or other aims appearing in the course of the present specification and claims, an expanding mandril for mounting a generally cylindrical hollowworkpieceona machinetoolfor machining an face ofthe workpiece, is characterized by comprising a cylindrical main body member having radial pistons in it which are able to be hydraulically moved outwards jointly to engage the innerface of the workpiece, and are arranged in at least two radial planes and are spaced from each otherintheciricumferential direction, and means for mechanically shifting at least some of the radial pistons outwards for centering the workpiece on the mandril priorto hydraulic actuation ofthe pistons.

Such a design makes it possibleforthe respective radial pistonsto be slid into the desired positions, this being preferably done synchronously, i.e. with a ganged operation of the pistons. No independent and consecutive operation of separate screws is called for.

The pistons maybe radiallydisplacedasfarasan adjustable abutment on the mandril so that, after slipping the work over the mandril, all that is required for preliminary centering is a rapid movement of the hand to push out the radial pistons in a radial direction.

In accordance with one possible form ofthe invention,the centering means includes an internal sleeve arranged to be able to be turned concentrically in relation to the axis of the mandril so that cams on the sleeve move the respective pistons radially outwards.

In this case the centering ofthe hollow work takes place simply by turning the internal sleeve sothatthe radial pistons are moved outwards against the inner face ofthe hollow work.

As regardsthenumberandarrangementofthe pistons that are mechanically set for preliminary centering, it is sufficient to set pistons arranged in as few as two planes with three pistons per plane.

Preferably these pistons are atthe ends ofthe mandril.

One embodiment of the present invention will now be described with reference to the accompanying drawings.

Figure lshowstheworking example of the invention in radial-longitudinal section.

Figure 2 is a radial-transverse section thereof taken onthe line Il-Il offigure 1.

The expanding mandril comprises a body member 10 held in a lathewhich is notshown. The body member 10 is bell-shaped and in its wall there are radial holes arranged in groups of three such that eachgroup isalignedwithoneoffour radial-longitudinal planes 11 through 14which are evenly circumferentially spaced about the axis of the mandril, i.e. with an angle of 90 between one radial-longitudinal plane and its neighbors. In the radial holes of each ofthe planes 11 through 14there are radial pistons 1 5 to 18 fitted in afluid-tight mannerso that, on admission of fluid under pressure into the interior of the member 10, the pistons 15 through 1 8 will be urged outwards.

The right-hand end of the main body member is closed by an end cap, not referenced. Inside the body member 10 there is an independently rotatable cam sleeve 20 whose two ends 21 and 22 are bearinged in the member 10. Towards its two ends in planes 11 and 14the inner sleeve 10 has part-spiral cams 151 and 181 foracting on the eight terminal radial pistons 15 and 18 via follower balls in the said planes.

In orderto machine the outer face of a tube 25,the latter is slipped onto the mandril and then by manual turning of the right-hand end of the inner sleeve 20 using a suitable tool the eight radial pistons 15 and 18 are moved outwards by the eight cams 151 and 181 in the two terminal planes 1 1 and 14 so asto engage and center the tube 25.

In terms of figure 2, this turning of the inner sleeve takes place in a clockwise direction and the cams 181 isplace the respective radial pistons outwards via the ball 26, or other anti-friction means into the outer positions marked 18'.

Accordinglythetube 25 will now have been sufficiently centered on the expanding mandril so that the gripping action ofthe expanding mandril on thework may be commenced. Forthisto take place fluid under pressure is admitted into the annular pressure chamber 30 between the inner sleeve and the member 10. The fluid in the form of a liquid is supplied through a coaxial duct32 into the interior of the sleeve 20 which it leaves through holes 31 in the wall ofthe sleeve 20 so that it may act upon the inner ends of the sixteen radial pistons with equal pressure sothattheyengagethe innerface of the tube 25with equal thrusts.

Claims (7)

1. An expandable mandril for mounting a generally cylindrical hollowworkpiece on a machine toolformachining afaceoftheworkpiece, comprising a cylindrical main body member having radial pistons in itwhich are able to be hydraulically moved outwardsjointlyto engagethe innerfaceof theworkpiece, and are arranged in at least two radial-transverse planes and are spaced from each other in the circumferential direction, and means for mechanically shifting at least some of the radial pistons outwards for centering theworkpiece on the mandril priorto hydraulic actuation ofthe pistons.

2. A mandril as claimed in claim 1 wherein said centering means comprises a rotatable sleeve which is concentrically placed within the body member of the mandril and has cams for moving at least some of the radial pistons outwards.

3. Amandrilasclamed in claim2wherein said sleeve cams are adapted to mechanically shift at least three radial pistons in two radial-transverse planes spaced along the axis ofthe mandril.

4. A mandril as claimed in claim 1 wherein the meansforoutwardly mechanically moving the pistons outwards is adapted to produce ganged motion thereof away from the axis of the mandril.

5. A mandril as claimed in claim 1 wherein the pistons are spaced outthrough 360" about the axis of the mandril.

6. An expandable mandril for mounting a generally cylindrical hollowworkpiece on a machine tool, comprising a generally cylindrical main body, meansforcentreing the workpiece on the body, and radially expandable means for gripping the centred workpiece,the centreing means including a plurality of movable centring elements and means for mechanically moving said centring elements outwardly in a centred mannerfrom the madril axis for centring the workpiece on the mandril.

7. A mandril as claimed in claim 1 substantially as described above with reference to and as illustrated in the accompanying drawings hereof.