GB2128115A - Expanding mandrels - Google Patents

Abstract

An expanding mandrel comprises a generally cylindrical body 21 for attachment to a rotation device, the body having an integral abutment portion 27a. A draw bar 22 passes axially through the body 21 and has at its outer end an expander 24. Resilient and flexible means comprising a generally cylindrical sleeve 23 and two resilient and flexible rings 25 are located around the body 21 between the abutment portion 27a and the expander 24. On movement of the expander towards the abutment portion 27a the sleeve, abutment portion and expander cooperate to deform the rings 25 outwardly to grip the inside diameter of a generally tubular work piece, which is to be machined, without distorting the work piece. <IMAGE>

Description

SPECIFICATION Improvements in expanding mandrels The present invention relates to improvements in expanding mandrels for machine tools.

Mandrels are part of a machine tool on which a component is held for machining. Expanding mandrel is a name used by us to describe a mandrel which holds its component by gripping it internally by expanding outwardly.

One existing such expanding mandrel is illustrated in Figure 1 and comprises a body 11 which is bored to receive a draw bar 12. A sleeve 13 mounted on the body 11 is expandable after it has been inserted into the component to be machined by operation of the draw bar hydraulically or pneumatically. On movement of the draw bar to the left in the drawing, the expander 1 2a of the draw bar pushes the sleeve 13 to the left. As the sleeve climbs the ramps 11 a and 1it; on the body lithe sleeve expands to grip the component 14. The mandrel is turned to rotate the component 14 for machining by a tool which is not illustrated.

This type of mandrel is very successful when the component has a perfectly circular bore and when it has sufficient thickness not to be distorted by the expanding sleeve. Unfortunately the bore can be not quite round. Thin components with an imperfectly round bore have been found to be distorted by the expanding sleeve 13 to a truly cylindrical shape.

After machining the outer diameter will be round.

However when the component is removed from the mandrel it returns to its original shape, leaving the outer diameter imperfectly cylindrical.

At present this is overcome by a preliminary boring or re-boring of the component, which is costly both in time and money. It is the object of the present invention to find an alternative solution to the problem.

According to the present invention there is provided an expanding mandrel comprising a body for attachment to a rotation device, resilient and flexible means disposed around the body, and means for deforming the resilient and flexible means so that it engages and grips the inside of the tube to be machined.

Preferably the body includes an abutment portion adjacent one side of the resilient and flexible means, and the means for deforming the resilient and flexible means comprises an expander slideably mounted with respect to the body and engageable with the other side of the flexible and resilient means, whereby relative movement of the expander towards the abutment portion deforms the resilient and flexible means outwardly of the body.

The resilient and flexible means may include a member the shape of which changes with the said movement of the expander to create an increased diameter area for gripping the component. Alternatively the said means may be in the form of one or more circles or cylinders, the diameter of which is increased by stretching when the expander moves towards the abutment portion.

In one embodiment there is provided an expanding mandrel comprising a body, a draw bar slideably mounted within the body and having an expander at the free end thereof, and a sleeve mounted on the body characterised in that there is provided flexible and resilient gripping means mounted on the sleeve and cooperable with the expander so that it can produce an expanded diameter for gripping a component on movement of the expander.

Advantageously the sleeve comprises a rigid member which is slideably mounted on the body and two flexible rings each mounted in a tapered seating one side of which is formed on a rigid member and the other on the body or expander respectively" whereby operation to pull the expander towards the abutment moves the tapered sides towards one another to expand the flexible rings to a greater diameter to grip the component.

The present invention will now be described, by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-section of an expanding mandrel and component of a known kind, and Figure 2 is a cross-section of an expanding mandrel according to the invention.

The mandrel of Figure 1 has already been described in the introduction to the specification.

The mandrel of Figure 2 is similar in operation and comprises a generally cylindrical body 21 with a head 21a by means of which the mandrel is mounted on a work holding machine. The body 21 has a central bore in which is accommodated a draw bar 22 slideably mounted therein. The draw bar 22 has at its outer end an integral disc-shaped expander 24 which has a tapered return flange 24a. The taper on the flange 24a forms one side of a seating for one of two resilient and flexible rings 25. The expander may be constructed separately from the draw bar and subsequently fixed thereto; or alternatively the expander and draw bar can be formed in one piece.

A sleeve 23 is a rigid member slideably mounted on a cylindrical portion of the body 21 and has a central portion 23a of a larger diameter which tapers outwardly on each side to shorter, smaller diameter portions 236. The body 21 has an integral flange 27 with tapered axial lip or abutment 27a, which lip forms with the body a recess 28 for the portion 23b of the sleeve 23 to slide into. Two seatings are formed for the two resilient and flexible rings 25.

One is formed by the lip 27a and one sleeve portion 23b, and the other is formed by the other sleeve portion 23b and the expander 24a. The two tapers of each seating are opposed so that on retraction of the draw bar, the expander 24 and the lip 27a become nearer to the respective sides of the sleeve portion 23a which lifts both the rings outwardly which deforms the wings by expansion to grip a component 26. To release the component the draw bar is returned to its original position and the rings 25 relax into their enlarged and reduced diameter seatings.

It will be appreciated that use of this expanding mandrel will leave even a thin walled component undistorted. Thus it will be possible to machine a truly cylindrical external diameter without a preliminary boring operation.

Claims (6)

1. An expanding mandrel comprising a body for attachment to a rotation device, resilient and flexible means disposed around the body, and means for deforming the resilient and flexible means to engage and grip the inside of a tube to be machined.

2. An expanding mandrel according to claim 1 wherein the body includes an abutment portion located on one side of the resilient and flexible means, and the means for deforming the resilient and flexible means comprises an expander slideably mounted with respect to the body and engageable with the other side of the resilient and flexible means, whereby relative movement of the expander towards the abutment portion deforms the resilient and flexible means outwardly of the body.

3. An expanding mandrel according to claim 2 including a draw bar slideably mounted through the body, which draw bar carries the expander on one end thereof outside the body; and a sleeve mounted on the body between the abutment portion and the expander, the abutment portion, sleeve and expander cooperating together, on sliding movement of the draw bar towards the abutment portion, to deform the said resilient and flexible means to grip a component for machining.

4. An expanding mandrel according to claim 3 wherein the sleeve comprises a rigid member which is slideably mounted on the body and at least one flexible ring mounted in a tapered seating one side of which is formed on the rigid member and the other on one of the expander or the abutment portion, whereby operation of the draw bar towards the abutment member moves the tapered sides towards one another to expand the or each flexible ring to a greater diameter to grip the component.

5. An expanding mandrel acording to claim 4 including a second flexible ring, the flexibles rings being seated in respective seatings, one of which is formed by the rigid member and the expander and the other of which is formed by the rigid member and the abutment portion.

6. An expanding mandrel substantially as herein described with reference to Figure 2 of the accompanying drawings.