GB2588619A

GB2588619A - Bushing installation

Info

Publication number: GB2588619A
Application number: GB1915662.9A
Authority: GB
Inventors: Huxley Keith
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-10-29
Filing date: 2019-10-29
Publication date: 2021-05-05
Also published as: GB201915662D0

Abstract

A method and tool for installing a bushing 2 with a non-circular aperture (8, Figure 1) into a work piece 50 by expansion fitting. The tool comprises a mandrel puller with mounted nosecap 20, coupled to a circular expansion mandrel. The nosecap comprises a nosecap hole (26, Figure 3a) that the mandrel 10 fits into, and a tip (28, Figure 3a) having a non-circular outer diameter corresponding to the bushing aperture. The nosecap hole interior may comprise a protrusion forming split sleeve retention means, and the exterior may comprise a protrusion for exerting a force on the bushing towards the work piece. The nosecap may have at least one longitudinal split allowing expansion, and the tip may have an oval cross section. The split sleeve may be provided around the mandrel and inside the nosecap. The expansion mandrel may be pulled all the way through the bushing to expand the bushing. The nosecap and expansion mandrel may then be pulled out of the bushing. The expansion mandrel may be pushed back into the work piece such that the expansion end is no longer inside the nosecap before pulling the nosecap and expansion mandrel out of the bushing.

Description

BUSHING INSTALLATION

TECHNICAL FIELD

[00011 The present invention relates to a nosecap for the installation of bushings into work pieces, and a method of doing the same.

BACKGROUND

[0002] Bushings are a type of simple bearing that. may be used to receive a shaft or pin within a work piece. They may be a separate component that can be inserted into a hole in a work piece. Being a separate component means that the bushing may be formed of a different material more suited for acting as a bearing surface than the work piece, or constructed in a different way that gives more desirable properties e.g. machined rather than cast.

[0003] A normal method for inserting bushings into a work piece is cold expansion.

During cold expansion, a round bushing sized to fit inside a hole is placed on a lubricated mandrel which has an expansion end that is wider than the aperture in the bushing. The mandrel is placed in a pulling tool having a nosecap. In use, the mandrel is inserted through the hole in which the bushing is to be installed until the bushing is in the hole and snug against the nosecap. The pulling tool pulls on the mandrel, the wider end of which expands the bushing to form an interference fit in the hole. The nosecap presses against the face of the bushing and provides a reaction force to keep the bushing within the hole during pulling.

[0004] Although cold expansion is a very simple and reliable method for the installation of bushings with a circular aperture, it is not suitable for use with bushing having a non-circular aperture within them because the mandrel would distort the non-circular aperture during expansion. Such bushings may be used when the shaft to be received within the bushing is to be offered a degree of freedom e.g. for sliding motion in a direction transverse to the axis of the shaft. Accordingly, such a bushing is usually installed by cryogenically cooling it using liquid nitrogen to contract the bushing and enable it to be fitted inside a hole.

As the bushing warms back to room temperature, it expands creating an interference fit between the bushing and the hole.

[0005] There are a number of prohlems with using cryogenic cooling for the installation of such bushings, for example: * Liquid nitrogen requires special handling equipment and operator training; * The amount of shrinkage achievable is limited by the temperature of the liquid nitrogen and the co-efficient of expansion of the bushing; * The hushing forms a layer of frost before insertion into the work piece which is then trapped between the bushing and the hole it is inserted into, potentially accelerating corrosion; and * The installation must he completed quickly to avoid damage to protective treatments on the hole or on the bushing.

[0006] Accordingly it is desirable to find a way to install a bushing having a non-circular aperture in a work piece that does not involve the use of liquid nitrogen.

SUMMARY

[0007] A first aspect of the present disclosure provides a nosecap for use with a mandrel puller to expansion-fit a bushing into a work piece, the bushing having a non-circular hole; the nosecap comprising: a nosecap hole for receiving a circular expansion mandrel; and a tip having a corresponding non-circular outer diameter for fitting within the hushing.

[0008] Such a nosecap provides a mechanism for cold expansion of a bushing having a non-circular aperture. It provides this whilst using existing circular expansion mandrels. Accordingly the amount of additional tooling required for installing this different bushing type is minimised which is desirable since expansion mandrels are very precisely calibrated devices.

[0009] Preferably, the nosecap comprises split sleeve retention means. This permits a dry film lubricated split sleeve to be used to lubricate an expansion mandrel being pulled through the nosecap.

[0010] Optionally, the split sleeve retention means is a protrusion on the inside of the nosecap hole. This provides a simple and reliable way to mechanically retain the split sleeve within the nosecap hole.

[0011] Optionally, the tip of the nosecap has an oval cross section. An oval may be an off-circular round shape or any other form of elongated circle, possibly having some sections of the perimeter that are straight whilst having others that are circular joined by corners.

[0012] Preferably, the nosecap comprises at least one longitudinal split for allowing the nosecap to expand. This may improve the expansion performance of the nosecap or permit its construction from more rigid materials [0013] Advantageously, the nosecap comprises a protrusion on the outside of the nosecap for exerting a force on the bushing towards the work piece. The bushing may need a degree of force to be first inserted into the work piece. Force may be required to react any pulling force on the bushing during its expansion into the work piece.

[0014] A second aspect of the present disclosure provides a tool for installing a bushing into a work piece by cold expansion, the tool comprising: a mandrel puller; a nosecap as described above mounted to the mandrel puller; and a circular expansion mandrel coupled to the mandrel puller and passing through the nosecap hole.

[0015] Such a tool is similar in use to conventional tools for cold expansion of bushings with circular holes and so is simple to learn to use. It allows cold expansion of a bushing with a non-circular aperture into a work piece without use of cryogenics.

[0016] Preferably, the tool comprises a bushing having a non-circular aperture fitted to the tip of the nosecap such that the tip of the nosecap and part of the mandrel is within the aperture of the bushing.

[0017] A third aspect of the present disclosure provides a method for installing a bushing into a work piece, the bushing having a non-circular aperture, comprising: providing a tool comprising a bushing as describe above; inserting the bushing and mandrel and nosecap into the work piece that is to receive the bushing; and pulling the expansion mandrel to expand the bushing and secure it in the work piece.

[0018] This method permits the cold expansion of bushings with a non-circular aperture into a work piece using existing circular mandrels via a mechanism that is simple to learn.

[0019] Preferably the nosecap further comprises split sleeve retention means, and the method further comprises providing a split sleeve around the mandrel and inside the nosecap. Accordingly reliable lubrication can he provided by a dry film lubricated split sleeve.

[0020] Optionally, the expansion mandrel is pulled all the way through the bushing to expand the bushing. This provides a simple and easy to use operation for expanding the bushing.

[0021] Preferably the nosecap and expansion mandrel are then pulled out of the bushing. This is similar to normal practice when cold expanding bushings with circular apertures and therefore reduces the necessary operator training.

[0022] Alternatively, the method may comprise pushing the expansion mandrel back into the work piece such that the expansion end is no longer inside the nosecap before pulling the nosecap and expansion mandrel out of the bushing. This may make pulling the nosecap out of the bushing easier.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the invention will now he described, by way of example only, with reference to the accompanying drawings, in which: [0024] Figure 1 is a perspective view of a bushing with a non-circular aperture; [0025] Figure 2 is a schematic perspective view of a round mandrel; [0026] Figure 3a is a perspective view of a nosecap in accordance with an embodiment

of the present disclosure;

[0027] Figure 3b is a cross-section of a nosecap in accordance with an embodiment. of

the present disclosure;

[0028] Figure 4 is perspective view of a nosecap, mandrel and split sleeve in accordance

with an embodiment of the present disclosure; and

[0029] Figure 5 is a cross-section perspective view of a bushing being inserted into a work piece in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0030] In this document the term 'circular" and "circle" are used to refer to shapes that have a constant diameter around their circumference. "Round" is used to refer to shapes that lack sharp corners and any transitions on the edges are rounded.

[0031] Figure 1 shows a bushing 2 for use in the method described below. It is generally cylindrical with two parallel flat faces. Its outer edge 4 is circular The diameter of outer eke 4 is almost the same size as the hole that is to receive it. The bushing has a clearance fit in the hole i.e. it can be pushed into the hole without having to exert significant force on the bushing. As shown in this figure the bushing 2 has a chamfered edge 6 which may aid aligning the bushing 2 with the hole that is to receive it.

[0032] The bushing 2 has a central aperture 8 which is to receive the shaft or pin which is to be located in the bushing once it has been installed in the work piece. This central aperture is not circular, but is elongated in one direction in order to provide a degree of transverse freedom for the part of the shaft that the bushing is to receive. This freedom may be provided for a number of reasons, such as permitting for thermal expansion in the finished assembly or for enabling a degree of motion in the shaft aside from simply rotating around its axis.

[0033] If bushing 2 was to be inserted into a work piece by cryogenic cooling then it would be larger so that at room temperature it would form an interference fit in thc hole that is to receive the bushing 2. Accordingly, it would not be insertable under normal conditions and instead would have to be reduced in size by cryogenic cooling before inserting it into the hole and holding it in place until it has sufficiently warmed and expanded to he self-supporting.

[0034] The aperture 8 is shown as being an truncated circle but any appropriate non-circle shape could be used. This might be an oval shape, such as a stadium shape, cassini oval, superellipse, cartesian oval or similar. Non-oval shapes may also be used in some applications, such as squares, triangles or hexagons. Furthermore complex shapes such as crosses may be used in some circumstances. In each case the apertures may have rounded edges or be square-edged. hi some circumstances it might be desirable to chamfer the rim of the aperture 8 on one or both sides to promote easier insertion/removal of a mandrel.

[0035] Similarly to the aperture 8 the outer edge 4 of the bushing 2 could be circular, a round but non-circular shape or even any other shape. In general however a round shape, especially a circle, is preferred due to the improved fatigue characteristics. The bushing 2 could be used for a variety of purposes apart from just receiving a shaft and so be made of different materials for different applications depending on the desired characteristics.

[0036] Figure 2 shows an expansion mandrel 10 having a circular cross-section. The mandrel 10 has a shaft 12 and a coupling end 14 for reception in a mandrel puller. The mandrel 10 further has an expansion section 16 in which the diameter of the mandrel increases to a widest diameter section 18 before tapering back down at the end of the mandrel 10 opposite to the coupling end 14..

[0037] In use with a prior art bushing, the shaft 12 will fit easily in the circular aperture of the bushing. The expansion section 16 will not fit within the aperture so a bushing is placed on the mandrel 10 from the coupling end 14 and slid along the shaft 12. The mandrel 10 is then coupled to a mandrel puller by coupling end 14. The mandrel puller is fitted with a nosecap through which the mandrel 10 passes. The bushing rests against the end of the nosecap, such that the nosecap can be used to hold the bushing in place when the mandrel 10 is pulled by the mandrel puller.

[0038] The mandrel and bushing are then inserted into a work piece and the bushing is located in the hole that is to receive it. The mandrel puller then pulls the expansion section 16 through the bushing, expanding it into the work piece. The nosecap is held against the bushing during pulling so that the bushing is not pulled out of the work piece. There can be significant friction between the mandrel 10 and a bushing during pulling so lubrication is normally supplied by a dry film lubricated split sleeve between the bushing and mandrel 10. A dry film lubricated split sleeve is a thin metal cylinder or sleeve with a single lengthways split. The split permits easy expansion of the sleeve to fit over expansion section 16. The sleeve is coated with a dry lubricant in a thin film, such as graphite.

[0039] The aperture of the bushing after expansion is widened by the passage of the expansion section 16 of the mandrel. Accordingly if such a mandrel 10 was used with a bushing having an aperture that was not circular, the aperture of the bushing would be distorted by the passage of expansion section 16 to be more circular. Since the non-circular shape is desired for certain applications this makes such an approach unsuitable for use with a bushing having a non-circular aperture.

[0040] Figures 3a and 3b show a nosecap 20 in accordance with an embodiment of the present disclosure. The nosecap has the conventional features of a mounting section 22 for mounting to a mandrel puller, a shaft 24 and a circular axial nosecap hole 26. The nosecap 20 has a modified tip section, 28, which has a non-circular outer profile. As shown in this embodiment the tip has two flat sides to match the flat sides of the aperture in bushing 2. The tip 28 is sized to fit in the aperture 8 of bushing 2 by a clearance fit so that the bushing 2 can be placed over the tip 28.

[0041] In use, the nosecap 20 can be combined with a mandrel 10 and mandrel puller in the usual fashion. However, instead of resting against, the end of the nosecap 20, bushing 2 fits over the nosecap tip 28. Accordingly there is no contact between the bushing 2 and mandrel 10 once the bushing 2 is in place on tip 28. As mandrel 10 is pulled by the mandrel puller, the expansion force caused by expansion section 16 is relayed to the bushing by the nosecap tip 28. In this embodiment, expanding the bushing requires the tip of the nosecap to stretch. Some nosecap materials do not readily expand and return to their previous size. To address this problem, a series of radial splits 30 is cut into the tip 28 (and extend beyond the tip 28 a short way into the rest of the shaft 24) to allow the nosecap to expand at the tip.

[0042] The shaft 24 has a generally circular cross-section as is normal. In order for the tip 28 to fit in the truncated circle aperture 8 of the bushing 2, in this embodiment the tip has been narrowed on two sides. This results in two shoulders 32 where the tip 28 meets the rest of the shaft. These shoulders 32 can serve to prevent the bushing 2 from sliding all the way down the shaft 24. The shoulders 32 may also be used to react any pulling force transmitted to the bushing 2 during expansion that might tend to pull the bushing 2 out of the work piece.

[0043] In variants, instead of shoulders 32 any other appropriate external protrusion on nosecap 20 could be used to react any pulling force on bushing 2 and to hold bushing 2 in place on the tip 28. This may be particularly desirable if the nosecap shaft 24 has the same profile as nosecap tip 28. In this variant the pulling force transmitted to the bushing could be reacted by the end of mounting section 22. In other variants, friction between the bushing 2 and nosecap 20 may be sufficient that no protrusion is necessary on nosecap 20 to keep the bushing in place.

[0044] In this embodiment, since the bushing 2 is located on the tip 28 of the nosecap there is no contact, and therefore no friction, between the mandrel 10 and bushing 2 but instead there will he significant friction between the mandrel 10 and nosecap 20. Accordingly, lubrication should he provided between the two to improve tool life. The axial nosecap hole 26 in this nosecap 20 has a slightly larger diameter at the tip 28 to receive a dry film lubricated split sleeve to provide this lubrication. There is a step 34 to retain a split sleeve and prevent it slipping further down in nosecap 20. This split sleeve retention function could be provided instead by any other suitable feature within the nosecap hole 26 that would catch and prevent a split sleeve slipping, such as a circular ridge in the nosecap hole 26 or one or more protrusions on the inner face of nosecap hole 26.

[0045] Referring now to Figure 4 the mandrel 10, nosecap 20 and a dry film split sleeve are shown assembled as when fitted on a mandrel puller (not shown). The assembly is thus ready to receive a bushing 2 for cold expansion into a work piece. Alter the mandrel 10 has been pulled towards nosecap 20 enough to expand a bushing 2, it can be returned to this starting position shown in Figure 4 and then another bushing 2 placed over the nosecap 20.

[0046] In this embodiment, the bushing 2 fits over the nosecap 20 in which the mandrel is received. Accordingly, the mandrel is smaller than might be expected for the size of the aperture 8 in the bushing 2. As such, the bushing 2 may even fit by clearance fit over the expansion section 16 of mandrel 10. Accordingly this assembly may be used repeatedly without disassembly between expansions since after use a new bushing 2 can be placed over the expansion section 16 of mandrel 10 and on to the nosecap tip 28.

[0047] Repeated use may require periodic replacement of the split sleeve 40 as its lubricating properties may diminish with use. In some applications it may be necessary to replace the split sleeve 40 with every operation of the mandrel puller. It may be possible to do this whilst the mandrel 10 is still mounted in the mandrel puller since the split in split sleeve 40 may permit the split sleeve 40 to fit over expansion section 16 of mandrel 10. In some variants the bushing 2 may not reliably fit over the expansion section 16 of mandrel 10 in the pre-expanded state and therefore the mandrel 10 would be removed from the mandrel puller before bushing 2 is placed on the shaft 12 of mandrel 10.

[0048] Figure 5 shows a cross section of the mandrel 10, nosecap 20 and split sleeve 40 fitted with a hushing 2 which is in a work piece 50 during expansion of the bushing 2. For clarity, the shoulders of 32 of nosecap 20 are not shown. As the mandrel 10 is pulled by the mandrel puller, it slides into the nosecap 20 (being lubricated by split sleeve 40) and the expansion section 16 causes the nosecap tip 28 to expand, thereby expanding bushing 2 into the hole in work piece 50 and securing it in place.

[0049] Sufficient expansion of bushing 2 may he provided by simply pulling the mandrel 10 far enough that expansion section 16 clears the bushing 2 and sits within the shaft 24 of the nosecap 20. In such a case the nosecap tip 28 may then be able to be simply pulled out of the bushing 2. This is the usual order of operations in cold expansion. In other embodiments, after pulling the mandrel 10 to expand the bushing 2, the mandrel 10 could then he pushed back in to the work piece 50 hefore the nosecap 20 and mandrel 10 assernhly is removed from the work piece. This is possible due to the expansion section of the mandrel 16 fitting in the aperture 8 of bushing 2. It may be preferable to push the mandrel 10 back in to the work piece 50 since the expansion section 16 will not be within the nosecap 20 so the nosecap may be easier to remove from the bushing 2.

MOW In some embodiments, the radial splits 30 in the nosecap 20 may provide sufficient flexibility to allow the removal of the nosecap 20 whilst the mandrel 10 is still retracted into shaft 24. In embodiments where the mandrel 10 is pushed back in to the work piece 50, it may not be necessary to fully pull mandrel 10 through the bushing 2 in order to sufficiently expand bushing 2 e.g. it may be sufficient that the expansion section 16 partially enters the bushing 2 rather than is pulled completely through.

1-00511 Since the expansion of the bushing 2 is realised by the nosecap 28 being expanded by the mandrel 10, the tip section 28 should be chosen so that when deformed by the expansion section 16 of mandrel 10 the desired shape is imparted to the aperture 8 of the bushing 2. Accordingly the tip section 28 may fit somewhat loosely in the bushing 2 before expansion.

[0052] Since the mandrel 10 is separated from the hushing 2 by the nosecap 20, the force which must he reacted by the nosecap 20 during the pulling of mandrel 10 may he significantly lower than when performing cold expansion of a conventional bushing having a circular aperture. Accordingly, it may be possible to use a nosecap 20 formed of a more flexible material such as plastic or silicone rubber. Such materials may be easier to shape to provide the non-circular tip 28. Furthermore, different material choices for nosecap 20 may provide sufficient inherent flexibility that the radial splits 30 are not required or may be substantially reduced in number, length or size.

[0053] In some variants the nosecap tip 28 may be discontinuous around the central nosecap hole 26 e.g. may comprise one or more fingers which sit around the hole 26. Such a nosecap could be realised by further machining the flat sides of nosecap tip section 28 in Figure 3 so that the nosecap hole 26 is open on those sides. In such an embodiment, part of the expansion force on a bushing would be exerted by the mandrel 10, and the nosecap tip 28 would provide the other part the expansion force against, the bushing 2 [0054] In some variants lubrication may be provided via other means than dry film lubricated split sleeve 40. For example, wet lubrication (with or without a split sleeve) may be desirable in some circumstances as it may allow repeated use of the nosecap 20 mandrel 10 assembly without having to replace the split sleeve 40. Alternatively, dry lubricants may be provided on one or both of the mandrel and nosecap or they may be manufactured from lubricious material that sufficiently reduces friction that a separate lubricant, is not. needed.

[0055] Although the invention has been described above with reference to one or more preferred examples or embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

[0056] Where the term -or" has been used in the preceding description, this term should be understood to mean "and/or", except where explicitly stated otherwise.

Claims

CLAIMS: 1. A nosecap for use with a mandrel puller to expansion-fit a bushing into a work piece, the bushing having a non-circular aperture; die nosecap comprising: a nosecap hole for receiving a circular expansion mandrel; and a tip having a corresponding non-circular outer diameter for fitting within the non-circular aperture.
2. A nosecap according to claim 1, further comprising split sleeve retention means.
3. A nosecap according to claim 2, wherein the split sleeve retention means is a protrusion on the inside of the nosecap hole.
4. A nosecap according to any preceding claim, wherein the tip of the nosecap has an oval cross section.
5. A nosecap according to any preceding claim, further comprising at least one longitudinal split for allowing the nosecap to expand.
6. A nosecap according to any preceding claim, comprising a protrusion on the outside of the nosecap for exerting a force on the bushing towards the work piece.
7. A tool for installing a bushing into a work piece by cold expansion, the tool comprising: a mandrel puller; a nosecap according to any preceding claim mounted to the mandrel puller; and a circular expansion mandrel coupled to the mandrel puller and passing through the nosecap hole.
8. A tool according to claim 7, further comprising: a bushing having a non-circular aperture fitted t.o the tip of the nosecap such that the tip of the nosecap and part of the mandrel is within the aperture of the bushing.
9. A method for installing a bushing into a work piece, the bushing having a non-circular aperture, comprising: providing a tool according to claim 8; inserting the hushing and mandrel and nosecap into the work piece that is to receive the bushing; and pulling the expansion mandrel to expand the bushing and secure it in the work piece.
10. A method according to claim 9, wherein the nosecap further comprises split sleeve retention means, the method further comprising providing a split sleeve around the mandrel and inside the nosecap.
11. A method according to claim 9 or 10, wherein the expansion mandrel is pulled all the way through the bushing to expand the bushing.
12. A method according to claim 9, 10 or 11, wherein the nosecap and expansion mandrel are then pulled out of the hushing.
13. A method according to claim 9, 10 or 11, comprising: pushing the expansion mandrel hack into the work piece such that the expansion end is no longer inside the nosecap before pulling the nosecap and expansion mandrel out of the bushing.