GB2520325A

GB2520325A - A clamp for removing a temporary fastener

Info

Publication number: GB2520325A
Application number: GB1320292.4A
Authority: GB
Inventors: John Matthew Davies; Arthur O'mahony
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2013-11-18
Filing date: 2013-11-18
Publication date: 2015-05-20
Also published as: GB201320292D0

Abstract

An aerospace temporary fastener removal device 600 that comprises of compression means (613, 615 fig. 6D) that are arranged to compress one or more tines (323, 325 fig.4) of an aerospace temporary fastener 301 by a predetermined amount so that the tines can conform to the diameter of a hole in an aircraft structure through which the fastener is fitted. Once compressed the fastener is able to be pulled through the compression means and through the hole so as to enable removal of the fastener from the structure. The device can further comprise of abutment means arranged to abut a surface of the structure the surface area of the abutment means can be sized to ensure the force on the structure is kept below a predetermined amount to avoid damaging the workpiece surface. There may also be a predefined compression stop configured to prevent further compression of the tines once the tines have been compressed by the predetermined amount. The device can be used to clamp the temporary fastener even if sealant used to bond the workpiece together has entered the fastener (figures 4 and 5), which will still allow for removal of the fastener.

Description

Intellectual Property Office Applicacion Nc,. (lB 320292.4 RTM Dace: I S Fchruary 2014 The following terms are registered trade marks and should he rcad as such wherever they occur in this document: PPG Aerospace Inlelleclual Properly Office is an operaling name of the Pateni Office www.ipo.gov.uk

A CLAMP FOR REMOVING A TEMPORARY FASTENER

FIELD OF THE INVENTION

The present invention relates to a device for removing temporary fasteners.

BACKGROUND OF THE INVENTION

Temporary fasteners are commonly used when temporary assembly of a number of structural components is required.

In the aerospace inthistiy, for example, temporary fasteners are used to fix structural components together whilst sealant cures at interfaces between the structural components. In such circumstances, temporary fasteners can be exposed to uncured sealant, which migrates from the interface region to the fastening region when the components are brought together. Temporary fasteners comprise locking mechanisms which when exposed to sealant can become jammed.

Sealant exposure can be exacerbated when structural components are clamped together through tightening of the temporary fastener.

Temporary fasteners can be difficult to remove when the locking mechanism is jammed.

Removal in these circumstances is normally achieved by disassembling the temporary fastener in situ or by cutting the locking mechanism from the temporary fastener and withdrawing the remnants of the temporary fastener from the structural components. All methods above are more labour intensive and time consuming and in the case of cutting, unwanted damage can be done to the surrounding structure, which results in the affected components requiring reworking or scrapping.

SUMMARY OF THE INVENTION

A first aspect of the present invention provides a clamp for removing an aerospace temporary fastener, comprising: compression means arranged to compress an expandable end of a temporary fastener so as to conform the expandable end of the temporary fastener to a diameter of a hole in a structure through which the temporary fastener is fitted, wherein the compression means is further arranged to enable the compressed expandable end of the temporary fastener to slide through the compression means and into the hole so as to enable rcmoval of the temporary flistener fl'om the structure; and abutment means arranged to abut a surface of the structure, wherein the surface area of the abutmentmeansissizedsoastoensuretheforceperunitareaimpartedbytheclamponthe structure is kept below a predetermined amount as the compressed expandable end of the temporary fastener slides through the compression means.

The abutment means and the sizing thereof ensures that as the temporary aerospace fastener is withdrawn from the clamp, the force per unit area imparted on the structure by the clamp is kept below a predetermined amount. This ensures that the structure underneath or surrounding the clamp is not damaged by the clamp itselL This is particularly relevant to structures of relatively thin crossection or those made from composite, which are easily damaged by point loading. The clamp further allows for the removal ofajammed fastener to be performed quickly and simply.

The removal operation can be performed by a single operator who can work fivm the opposite side of the structure to withdraw the fastener from the hole once the clamp is installed to the fastener. The use of the device further removes the necessity of using a cutting apparatus to remove the tines of the fastener should disassembly not be possible and it reduces the risk of damage to the adjacent structure when used.

The compression means may comprise a first body provided with a first bore portion, a second body provided with a second bore portion, and hinging means configured to hinge the first and second body relative to on another until the first and second bore portions %r at least one bore of predetermined dimension, A clamp with compression means as such permits the operator to locate the clamp into position with a fastener quickly and more easily. Furthermore it allows the operator to apply the clamp single-handedly to a fastener. This is desired when the fastener is located in difficult to access portion of the structure where only one armed access to the fastener is available.

Thc clamp may fUrther comprise gripping surfaces on the first and second bodies positioned relative to thc hinging means and the bore portions. A grip can be applied to the clamp at the grip surfaces and used to actuate the compression means with a mechanical advantage. This makes it easier to use the clamp on fasteners with relatively stiff expandable cnd or in circumstances where the sealant jamming the fastener is in a relatively cured state.

The clamp may provide a plurality of bores, wherein each bore has a different predetermined dimension so that the clamp can be used with multiple fasteners of differing diameters.

The clamp may provide locking means configured to control the compression being applied by the compression means to the expandable end of the fastener. This reduces the need for a separate device to actuate the compression means and thus reduces the number of tools required to perform the operation. The locking means may be provided by a latch.

Another aspect of the present invention provides a clamp for removing an aerospace temporary fastener, comprising: compression means arranged to compress one or more tines of a fastener by a predetermined amount so as to conform the tines of the fastener to the diameter of a hole in a structure, through which the fastener is fitted, wherein the compression means is further arranged to enable the compressed tines to slide out of the compression means and into the hole so as to enable removal of the fastener from the structure; and a predefined compression stop configured to prevent fUrther compression of the fine(s) once the tines have been compressed by a predetermined amount.

A fUrther aspect of the present invention provides an aerospace temporary fastener removal device, comprising: compression means anifanged to compress one or more tines of an aerospace temporary fastener by a predetermined amount so that the tines can conform to the diameter of a hole in an aircraft structure through which the aircraft temporary fastener is fitted, the compression means being further arranged to enable the compressed tines to slide out of the compression means and into the hole so as to enable removal of the fastener from the stntcture.

BRIEF DESCRiPTION OF THE DRAWINGS

Embodiments of the invention will be described further below with reference to the accompanying figures, in which: Figure 1 is a schematic plan view of an aircraft; Figure 2 is the cross-sectional view taken through sectional lone A-A of the aircraft of figure 1 as viewed in the direction indicated in figure 1; Figure 3 is a cross-sectional view of a temporary single sided fastener installed in a hole of a structural assembly onthe aircraft of figure 2; Figure 4 is a cross-sectional view of the fastener of figure 3, jammed by sealant; Figure 5 is the cross-sectional view taken through sectional line B-B of figure 4 as viewed in the direction indicated in figure 4; Figure 6a is a schematic elevation view of a clamp according to an embodiment of the invention for removing the fastener of figure 4; Figure 6b is a schematic plan view of the clamp of figure 6a; Figure 6c is the schematic bottom view of the clamp of figure 6a Figure 6d is the schematic elevation view of the clamp of figure 6; when opened Figure 7 is an isomeiric view of the clamp of figures 6a to 6d shown installed on the fastener of figure4;and Figures 8a to 8c are cross-sectional views of the clamp of figure 7 corresponding to when the fastener is in an installed, an intermediate and a withdrawn position, respectively.

DETAILED DESCRIPTION OF EMBODIMENT(S)

With reference to figure I, an aircraft 00 comprises a plurality of structural elements attached to a fuselage 101, namely; wings 103 and 105, vertical tail plane 107 and horizontal tail planes 109 and 111. Each structural element comprises a plurality of structural components fastened together as stmctural assemblies using mechanical fasteners.

With reference to figure 2, the major structural components, namely the upper cover 20 I, lower cover 203, front spar 205, rear spar 207, upper cover stringers 209, lower cover stringers 211, ribs 213, leading edge details 215 and trailing edge details 217, are fixedly attached to one another so as to provide a stiffened torsion box. The assembly steps comprise holding the major structural components in positions relative to one another in a jig. Holes 221, indicated by dashed lines in figure 2, are then drilled at the locations shown so that permanent mechanical fasteners can be installed to hold the component together. Prior to the permanent fasteners being installed, the gaps or interfaces between each of the component are normally sealed to ensure that fuel cannot leak from the torsion box and to prevent friction between adjacent components.

The seal is achieved by coating the interface between adjacent components with a sealant such as PR1 782-Cl 2 low density aerospace sealant manufactured by PPG Aerospace. The components are then assembled into final position and then temporary fasteners are then installed to hold the components in position while the sealant cures. The sealant work time is typically 20 hours.

With reference to figure 3, a combined collet type temporary fastener 301 is shown installed in a hole 303 defined by the lower cover 203 and rib foot 219. The component interface 304 between the lower cover 203 and rib foot 219 is coated with a sealant material 305, which cures whilst the fastener 301 holds both components in position. The fastener 30! comprises an expandable end 307 and an adjustment head 309. The expandable end is of predetermined diameter and grip length, and it can be inserted into the hole 303 as far as a stopping portion 311 provided by the adjustment head 30S,which abuts a first surface 313 that surrounds the hole 303 at a lower end.

The expandable end 307 is provided with a hollow shaft 315 with an outer surface diameter that has a close tolerance fit to the diameter of the hole 303. The body ofthe shaft 315 is provided with a slot 317 that defines a pair of expandable legs 319 and 321. Both expandable legs are provided with tines 323 and 325, which project radially from the distal ends of the expandable legs 319 and 321. The tines, 323 and 325, are configured to engage a second surthcc 327 that surmunds the opposite end of the hole 303. When the expandable legs 319 and 321, and the tines 323 and 325 are in an engaged configuration, the temporary fastener 301 clamps the lower cover 203 and rib foot 219 together and the temporary fastener cannot be withdrawn from the hole 303.

The expandable legs 319 and 321 are resiliently biased to deform towards a position closer to the axis 329 of the temporary fastener 301. In the defbrmed position, the tines 323 and 325 are disengaged from the second surface 327, and as a result the fastener 301 can be withdrawn from the hole 303. An inner shaft 331 is arranged within the hollow portion of the outer shaft 315 and is configured to translate linearly in opposite directions along the axis 329. One end of the inner shaft 331 is provided with a collet 333, which is provided with a frustoconical portion 335 that is configured to engage the innermost portion of each expandable leg 319 and 321 or each tine 323 and 325. The dimensions of the collect 333 arc such that the collet 333 can fit within the diameter of the hole 303. As the inner shaft 331 and coilet 333 translate linearly towards the adjustment head 309, the collet 333 engages the innermost portion of each expandable leg 319 and 321 or each tine 323 and 325 and urges them radially outwards from the axis 329. This action brings the each expandable leg 319 and 321 into engagement with the hole surface and the tines 323 and 325 into engagement with the second surface 327. Translating the collet 333 in the opposite direction permits the biased expandable Legs 319 and 321 to return to the deformed position and therefore the tines 323 and 325 and the expandable legs 319 and 321, disengage.

With reference to figure 4 and figure 5, a sealant material 305 has migrated in an uneured or partially cured state from the component interface 304 into a cavity 501 between the inner shaft 331 and the expandable legs 319 and 321 ofthe fastener 301, where it has then cured into a semi-solid state. The sealant material 305 in this position biases the expandable legs 319 and 321 in the opposite direction and as a result prevents the expandable legs 319 and 321 and tines 323 and 325 from returning to the deformed position, even when the eollet 333 has translated completely out of engagement, as shown.

With reference to figure 6a, 6b and 64 a fastener removal clamp 600 comprises a first part 601 provided with a tiNt hinge knuckle 603 and a second hinge knuckle 605, which both terminate at a first peripheral edge 606. Both knuckles are spaced apart and configured to enclose a third hinge knuckle 607 that terminates at a conesponding peripheral edge 608 of a second part 609.

Both parts 601 and 609 am formed of ENO8 (080M40) grade stainless steel or equivalent that is machined from one or more billets. Alternatively, both parts 601, 609 can be formed by any other suitable process e.g. casting. Both parts may be formed of any other suitable metaffie, ceramic, plastic or composite material or combinations thereof A hinge pin 611 is inserted in a hole 614 formed by the first, second and third binge knuckles 603,605,607. The binge pin 611 enablesbothparts6oland6O9tomtatcrelativctoeachotheraboutaflxedaxisofrotati on defined by the axis 612 of the hinge pin 611. Both parts 601,609 abut one another at a predetermined stop position provided by contact of the first and second planar contact futces 613, 615. The hinge pin 611 may be formed from the same material as the first part 601 and second part 609 and is retained in the hole 614 using a drive fit.

A first bore portion and a second bore portion are defined by the bodies of the first and second parts 601 and 609, respectively. The bore portions substantially form two bores 617 and 618, each of predetermined dimensions when both parts 601 and 609 am rotated into abutment at the predetermined stop position as shown in figure 6b. In this position, coplanar surfaces 619 and 621 define a first opening 627 for the first bore 617. Similarly, as shown in figure 6c, coplanar surfaces 623 and 625 define a second opening 629 for the second bore 618. When both parts 601 and 609 are rotated into abutment at the predetermined stop position, the predetermined diameter of the second bore 618 matches substantially the diameter of the hole 303 in the structure.

Similarly, the diameter of the first bore 617 is smaller than the secondbore 618 and so it is configured to substantially match a hole of smaller diameter than the hole 303. With reference to figures 6b & 6c, both the first part 601 and second pail 609 are further provided with planar gripping surfaces 631 and 633 in proximity to third and fourth peripheral edges 635 and 637, respectively. It will be appreciated that any number of bore portions and bores with different diameters can be provided by the device.

With reference to figure?, to install the clamp 600, it is opened by an operatoç then biought into position around the fastener 301 so that the expandable legs 319,321 and tines 323, 325 are aligned with at least one of the bore portions of the bore 618 (not shown), The first part 60! and second part 609 are rotated relative to each other about the pin axis 612 until that thc contact surthces 613 and 615 abut one another at the predetermined stop position, This provides compression means where by the bore 618 compresses the expandable legs 319,321 and tines 323,325 to a predetermined diameter of the bore, which at the second opening 629 is at least equal to the diameter of the hole 303. As the compression means is applied, the cured sealant 305 within the cavity 501 deforms between the compressed expandable legs 319 and 321, and the inner shaft 331.

The expandable legs 319,321 and tines 323, 325 tend to be strongly biased against the compression means. This can be because of the cured state of the sealant or the stiffliess of the material that the expandable legs are made from or because the collet 333 is stuck against expandable Legs even though it has been released. In the case of the later, sufficient compression of the expandable legs against the collet would force it to eject. The first part 60! and second part 609 that form the bores 617 and 618 therefore have to be formed from a suitably stiff material to resist defbrmation or damage from the expandable legs 319,321 or tines 323, 325.

A clamp 701 is applied at the gripping surface 631 and the corresponding surface 633 (not shown) during relative rotation of the first and second parts to overcome the biasing of the expandable legs 319,321 and maintain the position of both parts 601 and 609 once they are in abutment at the predetermined stop position. The position of the gripping surface to which the clamp 701 is applied, further provides mechanical advantage that assists bringing both parts 601 and 609 together because the clamp force is applied at a distance A' relative to the rotation axis 612 ofthe hinge pin 611. With the first part 601 and second part 609 in abutment, the expandable legs 319,321 and the tines 323, 325 are in the deformed position i,e, they cannot engage the second surface 327.

With reference to figures 8a to 8c, the temporary fastener 301 can be withdrawn by the operator once the compression means has been applied i.e. the expandable legs 319 and 32! and tines 323 and 325 are compressed into the deformed position by the bore 618 of the device 600, by continuously pulling from the adjustment head 309 side of the fastener 301 i.e. from the lower side of the assembly. The surfaces 623 and 625 are designed to conform to the surface of the component surface 327 and to not contact the interior surface of the hole 303, which is prone to damage. By design the surfaces arc sized with a sufficient area so as to ensure that force transferred from the device to the component during withdrawal of the fastener 301 remains below a predetermined limit so that the likelihood of the structure surrounding the hole 303 being damaged or deformed beyond allowable limits is reduced or prevented entirely. For composite components this is particularly important where such material is susceptible to delamination or damage when sufficiently high point loads are applied at the surface. Damage in these instances may not be visible and so additional non-destructive testing would otherwise need to be applied.

The surface 801 of the second bore is substantially smooth so as to permit the expandable legs 319 and 321, and the tines, 323 and 325, to slide through the bore 618. As stated above, the dimensions of the borc opening 629 is substantially equal to the diameter of the hole 303 and this permits the expandable end of the fastener to slide along the second bore surface 801 and into the hole 303 without jamming or catching the edge of the hole 303. The hole 303 continues to compress the expandable end until the fastener 301 is completely withdrawn from the hole 303.

In another embodiment of the present invention, the first part 601 and second part 609 of the clamp further comprise locking means. The locking means can be provided by a partially threaded holes defined by the first part 601 and the second part 609 and a fastener configured to be inserted into the hole when the device is being installed. The fastener is configured to engage a threaded portion of the hole 901 provided by the first part 601 or the second part 609. The threading can be loose so as to permit the fastener to be more easily engaged with the threaded portion when the device is brought together around a fastener 301. Preferably, the hole is defined bythe fimtpart6Ol andseeondpart6O9,betweenthe surfaces63l and633. Oncethefasteneris substantially locked in the hole, the compression means is maintained until the fastener is removed. The locking means can alternatively be provided by any other suitable mechanism such as one or more clasps, latches etc. In the case of a latch being used to provide locking means, it may also be arranged so as to provide additional mechanical advantage in order to facilitate closing the device. The latch may be provided with an over-centre action so as to positively hold the latch in a closed position.

While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail.

Additional advantages and modifications will readily appear to those skilled in the art. Therefbre, the invention in its broader aspects is not limited to the specific details of the representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made fivm such details without departure from the scope of applicant's general inventive concept.

Claims

CLAIMS1. A clamp for removing an aerospace temporary fastener, comprising: compression means arranged to compress an expandable end of a temporary fastener so as to conform the expandable end of the temporary fastener to a diameter of a hole in a structure through which the temporary fastener is fitted, wherein the compression means is further arranged to enable the compressed expandable end of the temporary fastener to slide through the compression means and into the hole so as to enable removal of the temporary fastener from the structure; and abutment means arranged to abut a surface of the structure, wherein the surface area of the abutment means is sized so as to ensure the force per unit area imparted by the clamp on the structure is kept below a predetermined amount as the compressed expandable end of the temporary fastener slides through the compression means.
2. A clamp according to claim 1. wherein the compression means comprises: a first body provided with a first bore portion; a second body provided with a corresponding second bore portion; and hinging means configured to hinge the first and the second body relative to one another until the first and second bore portions form at least one bore of predetermined dimension.
3. A clamp according to claim 2, further comprising: gripping surfaces provided by the first and the second body, wherein the gripping surfaces are positioned relative to the hinging means and the bore portions so that when the gripping surfaces are ipped by a grip, a mechanical advantage is provided to assist the compression means.
4. A clamp according to any preceding claim, wherein the first and second bore portions form a plurality of bores.
5. A clamp according to any preceding claim further comprising: locking means configured to lock the compression means applied to the expandable end of the fastener.
6. A clamp according to claim 5 wherein thc locking means is provided by a latch.
7. A clamp for removing an aerospace temporary fastener, comprising: compression means arranged to compress one or more tines of a fastener by a predetermined amount so as to conform the tines of the fastener to the diameter of a hole in a structure through which the fastener is fitted, wherein the compression means is further arranged to enable the compressed tines to slide out of the compression means and into the hole so as to enable removal of the fastener from the structure; and a predefined compression stop configured to prevent further compression of the tine(s) once the tines have been compressed by the predetermined amount.
8. Ai aerospace temporary fastener removal device, comprising: compression means arranged to compress one or more tines of an aerospace temporary fastener by a predetermined amount so that the tines can conform to the diameter of a hole in an aircraft structure through which the aircraft temporary fastener is fitted, the compression means being further arranged to enable the compressed tines to slide out of the compression means and into the hole so as to enable removal of the fastener from the structure.
9. A clamp as described herein with reference to any of figures 6 to 8.