GB2586034A

GB2586034A - Floating nut assembly

Info

Publication number: GB2586034A
Application number: GB1910837.2A
Authority: GB
Inventors: Brakes David
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-07-30
Filing date: 2019-07-30
Publication date: 2021-02-03
Anticipated expiration: 2039-07-30
Also published as: GB201910837D0; GB2586034B

Abstract

A floating nut assembly configured to receive a fastener comprises a nut 4 and a nut plate 2 having a fastener aperture 7 and tangs 5 arranged to delimit movement of the nut 4. The floating nut assembly also comprises a plastically deformable spacer 9 arranged to hold the nut 4 in spaced relationship from the nut plate 2. The plastically deformable spacer 9 may be wax.

Description

FLOATING NUT ASSEMBLY

FIELD OF TECHNOLOGY

[0001] This invention relates to a floating nut assembly installable on a workpiece such as part of the wing of an aircraft. The invention also relates to an installation comprising a workpiccc and a floating nut assembly, and to a method of installing a workpiccc by utilizing a floating nut assembly.

BACKGROUND

[0002] An aircraft wing is an example of a workpiccc that is becoming increasingly complex and sophisticated to manufacture and assemble. For safety and quality reasons, it is preferable not. to have assembly line operators working from inside the confined spaces of the wing itself. Various proposals have been made to set up one-way assembly and installation processes in order to fasten components together, which processes are usually computer controlled. A problem which has been encountered with such processes is that. of locating tools with respect to the parts of the fasteners attached to the remote, or blind side, of the workpiccc. Misalignment or over travel of the tool can cause damage to the fastener parts on the blind side and hence hold up the installation process. It has been proposed to use sensors or probes to detect the location of parts on the blind side of the workpiece. However, use of such equipment slows the assembly process and adds to its cost.

BRIEF SUMMARY OF THE TECHNOLOGY

[0003] The invention provides a floating nut assembly configured to receive a fastener, the assembly comprising a nut; a nut plate having a fastener aperture and tangs arranged to delimit movement of the nut; and further comprising a plastically deformable spacer arranged to hold the nut in spaced relationship from the nut plate. The floating nut allows for misalignment of the tool during an installation process. The provision of a spacer separating the nut from the nut plate allows for over travel of the tool without damage being caused to the nut.

[0004] Preferably, the floating nut assembly includes a nut retainer having a first portion arranged to fit over the nut and a second portion arranged to sit between the tangs of the nut plate. The nut retainer usefully provides a reactive force when a fastener is introduced and tightened and also allows the nut to travel with respect to the nut plate.

[0005] Advantageously, the spacer is arranged to deform by the force of a fastener being tightened on the nut. This deformation causes the spacer to be compressed between the nut, fastener and nut plate. The spacer effectively ceases to exist as a spacer in the floating nut assembly and instead fills the gaps between the nut and nut plate, and the nut and fastener.

[0006] The spacer preferably has an external diameter substantially the same as the internal diameter of the nut retainer. Thus, the spacer is urged to move laterally with the nut retainer and hence follows the movement of the nut.

[0007] The spacer preferably also has an internal diameter larger than the diameter of the fastener aperture. This allows for travel of the nut with respect to the nut plate.

[0008] The spacer may be of a wax material. Such a material is low in cost and easy to mould.

[0009] The invention further provides a fastener assembly installable on a workpiece, comprising a fastener and a floating nut assembly constructed according to the present invention.

[0010] Optionally, the fastener is a bolt, which provides a secure and structurally strong fastening.

[0011] The invention further provides an installation comprising a workpiece and a fastener assembly of the present invention. Such an installation may form part of the wing assembly of an aircraft.

[0012] The invention further provides a process of installing a workpiece by means of the fastener assembly of the present invention, comprising the steps of: attaching the floating nut plate assembly to a surface of the workpiece; locating a tool at the attachment location on the opposite surface of the workpiece; activating the tool to make an aperture in the workpiece; inserting a fastener through the apertures in the workpiece and nut plate and into the nut; and tightening the fastener.

[0013] Preferably, the process further includes the step of clearing swarf from the apertures prior to inserting the fastener. The spacer facilitates this step by providing a harrier to the swarf. Swarf may be cleared by blowing a jet of air into the apertures and/or by brushing the swarf away.

[0014] The tool may be a drill, preferably under machine control. The steps of inserting and tightening the fastener may also be carried out by machine.

[0015] It should be noted that the deformable spacer confers three main advantages: it holds the nut in a spaced relationship with respect to the workpiece and hence prevents it from over travel of the tool; it forms a barrier to swarf cause by the tool cutting into the workpiece; and it compresses and disperses when a fastener is inserted and tightened so as to seal the gaps between the nut, nut plate and fastener.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure la is a plan view of a floating nut assembly constructed according to the invention; Figure lb is a side view of the nut assembly of Figure la; Figure lc is a sectional side view of the nut assembly of Figures la and lb; Figure 2 is a flowchart of the process of installing a workpiece utilizing the floating nut. assembly of Figures la, b and c; Figures 3a to 3e are sectional views showing different stages of the process of Figure 2; Figure 3f is a side view of the floating nut. assembly in an installed configuration; and Figure 4 is a perspective view of an aircraft incorporating floating nut assemblies constructed according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE TECHNOLOGY

[0017] With reference to Figures I a, h and c, a floating nut assembly according to the present invention is shown and indicated generally by the reference numeral 1. The main components of this floating nut assembly 1 arc a nut plate 2, nut retainer 3 and nut 4.

[0018] The nut plate 2 comprises a metallic plate that defines an X-Y plane for movement of the nut. retainer 3 and nut 4. In this embodiment, the nut plate 2 has a substantially square footprint. The nut plate 2 has a plurality of tangs 5 along its edges that retain the nut retainer 3 with respect to the nut plate, such that a limited displacement of the nut 4 and retainer 3 is allowed in the X-Y plane and also in a Z-direction perpendicular to the X-Y plane. Owing to the limited displacement of the nut retainer 3 and nut 4, the nut is said to "float". The industry standard radial float for a nut plate in the X-Y plane is 0.76mm, but of course nut plates may he made having whatever float is required. The nut plate 2 is also provided with a plurality of apertures 6, one at each corner. These apertures 6 may be used as a mechanical key for bonding to a workpiece, or for rivets or other fasteners. The nut plate also includes a central aperture 7. Suitable materials for the nut plate 2 are corrosion-resistant steel (CRES), aluminium alloy and titanium alloy.

[0019] The nut retainer 3 comprises a sleeve part 3a that is arranged to hold the nut 4 and a plate part 3b that sits against, and slides with respect to, the nut plate 2, within the limits of the tangs 5. The nut retainer 3 usefully provides a reaction to the tightening torque employed to tighten the nut. 2 during an installation process (as described later in the specification). The nut retainer 3 may be made of plastics material by means of by an over-moulding process, wherein the retainer is moulded over the nut. 4. The nut 4 has a hexagonal outer surface and a bore 8 that is internally threaded (the threads are not shown in the drawings) and arranged to receive a bolt or other fastener during installation.

[0020] In accordance with the invention, the floating nut assembly 1 includes a plastically deformable spacer 9. In this embodiment, the spacer 9 is formed of wax. The spacer 9 is in the form of a collar, the neck 9a of which is arranged to support the nut 4 in a spaced relationship away from the nut plate 2 prior to installation. The neck 9a comprises a sleeve, the inner surface 9c of which is arranged to form a through-hole between the aperture 7 in the nut plate 2 and the internal bore 8 of the nut 4. The internal diameter of the neck 9a is slightly larger than the diameter of the aperture 7 and the diameter of the internal bore 8 so as to allow for float of the nut 4 with respect to the nut plate 2. The shoulder 9h of the spacer 9 has a diameter substantially the same as the internal diameter of the nut retainer 3 so that, as the nut retainer floats in the X-Y plane, the spacer 9 will move with the nut retainer.

[0021] Figures 2 and 3a to 3c inclusive illustrate an installation method according to the present invention. The first stage 10 comprises a "pre-installation" step of attaching the nut plate assembly 1 to a first component in the form of a substrate 11 in a predetermined location. For simplicity, the installation method is described with reference to one nut plate assembly 1 on the substrate 11. Of course, in real life, particularly in assembling an aircraft structure, many nut plate assemblies 1 will be pre-installed onto the substrate in respective predetermined locations. The nut plate 2 may be attached to the substrate 11 by attaching rivets or other fasteners through the holes 6. Alternatively, the nut plate 2 may be bonded to the substrate 11 by adhesive. The substrate 11 is then offered up to a second component 12. hi the drawings, the second component 12 is depicted as a simple laminar layer, like the substrate 11, for clarity. In the example of assembling an aircraft structure, the second component 12 may be a skin or cover; the first component 11 may also be a skin or may be a spar or a rib, for example, forming part of a skeleton that comprises the wing box of an aircraft.

[0022] To avoid unwanted pre-stresses and to ensure that the completed wing box conforms to the design shape the covers, ribs and spars are not pre-drilled prior to assembly. Furthermore, the covers must be drilled from the side that will form the aerodynamic surface i.e. from the top surface of the skin 12. Therefore, the next step 13 of the installation process comprises locating a computer numerical control (CNC) machine tool in the form of a drill 14, and then activating it to drill and aperture. The tool is typically programmed with locations in three dimensional space. Probes or locating sensors are employed to determine precise locations on the skin 12. The exact method of locating the drill 14 does not form the basis of this patent application and so is not described here in detail. However, as previously mentioned, thermal expansion and manufacturing tolerances make it difficult to locate the drill with the degree of accuracy required in the field of aeronautics.

[0023] With reference to Figures 3a and 3b, the drill 14 is brought into location by programming or detecting or by a combination of methods. The drill 14 is then activated in order to cut an aperture 15 through the workpiece comprising the components 11 and 12. Owing to the aforementioned difficulties in locating CNC tools, the drill 14 may not be in the precise location required. The arrangement of the floating nut assembly 1 allows for small discrepancies in drill location, as the nut 4 is able to slide along the nut plate 2 to occupy the correct position. It is also difficult to control the precise depth of drilling required at a location, with the result that the drill 14 will often travel farther than is strictly necessary through the workpiece, as is shown at point "A" in Figure 3b. The neck 9a of the spacer provides clearance between the nut 4 and the nut plate 2 so that the drill 14 does not come into contact with, and hence damage, the nut in the event of over travel of the drill through the workpiece. It can be seen that a conventional floating nut assembly, in which the nut sits directly on the nut plate, would be damaged by the over travel of the drill shown in Figure 3b. The skilled person can determine the likely worst case of over travel in accordance with the commands programmed into the CNC tool and the manufacturing tolerances of the components 11, 12, and hence specify a spacer 9 having a neck 9a of that length at least.

[0024] Figure 3c shows the workpiece 11, 12 and floating nut assembly 1 with the aperture 15 now drilled. The next stage 16 of the process is that of cleaning the aperture 15 and nut thread 8, to ensure that they are free of dirt and swarf caused by the drilling stage 13. This is effected by blowing air into the aperture. Alternatively, brushes may be used to clear away such debris. The spacer 9 acts as a barrier and prevents dirt and swarf from entering the cavity between the nut 4 and the nut plate 2. Such foreign bodies in the nut assembly 1 could prevent proper tightening of a fastener or even cause the fastener to jam in the internally threaded bore 8.

[0025] With reference to Figures 3c and 3d, the next stage 17 of the process is that a fastener, shown here in the form of a bolt 18, is inserted through the drilled aperture 15, the central aperture 7 of the nut plate 2 and into the bore 8; and is then tightened. The arrangement of the floating nut assembly 1 allows the nut 4 to float to a position where it can accept the fastener in the case where there is a discrepancy between the drilled location and the location of the nut plate 2. Figure 3c illustrates an example where there is a small misalignment in the respective centre lines of the drilled aperture 15 and the bore 8 of the nut 4. The bolt 18 may he inserted manually or by machine. A torque is then applied to the head 18a of the bolt, as shown by the large arrow in Figure 3d. The nut retainer 3 provides a reaction to the turning forces experienced by the nut 4 and so the nut slides along the bolt. 18 by virtue of the co-operating helical threads (not shown) on the nut and bolt. As the nut 4 is urged towards the nut plate 2, the spacer 9 is compressed and squeezed between them. The wax flows to fill the gaps between the nut 4, nut plate 2 and bolt 18. In this manner, the spacer ceases to act as a separator between the nut 4 and nut plate 2 and instead fills the gaps in the floating nut assembly 1 and provides a seal between the nut 4, bolt 18 and nut plate 2. The side view of Figure 3f shows the nut and fastener at the completion of this process. The process is then repeated over the entire installation until the components are completely and securely assem [0026] Figure 4 is a perspective view of an aircraft 19 having wings 20, 21 assembled according to the process set out in Figure 2 and incorporating a plurality of arrays of floating nut assemblies 1 constructed according to the invention. The invention may also be utilised in assembling and installing parts of the empennage, such as the vertical stabiliser 22 and/or the horizontal stabilisers 23; or parts of the fuselage 24.

[0027] Variations may be made without departing from the scope of the invention. For example, the spacer may he made of a plastically deformable material other than wax, for example, plastic (such as PTFF or polythene), foam, natural fibres, silicone rubber or other elastomeric materials. The spacer needs to have sufficient structural integrity that it can support the weight of the nut and nut. retainer prior to assembly, but. be easily compressible and deformable during the process of tightening the bolt. The fastener need not be in the form of a bolt: rivets, studs or pins may be employed. Further variations will be apparent to the person skilled in the art. bled.

Claims

[0028] CLAIMS A floating nut assembly configured to receive a fastener, the assembly comprising a nut; a nut plate having a fastener aperture and tangs arranged to delimit movement of the nut; and further comprising a plastically deformable spacer arranged to hold the nut in a spaced relationship from the nut plate.
2. A floating nut assembly as claimed in claim 1, further comprising a nut retainer having a first portion arranged to fit over the nut and a second portion arranged to sit between the tangs of the nut plate.
3. A floating nut assembly as claimed in claim 1 or 2, in which the spacer is arranged to deform by the force of a fastener being tightened on the nut..
4. A floating nut assembly as claimed in any preceding claim, in which the spacer has an external diameter substantially the same as an internal diameter of the nut retainer.
5. A floating nut assembly as claimed in any preceding claim, in which the spacer has an internal diameter larger than the diameter of the fastener aperture.
6. A floating nut. assembly as claimed in any preceding claim, in which the spacer is of a wax-based material.
7. A fastener assembly installable on a workpiece, comprising a fastener and a floating nut assembly as claimed in any preceding claim.
8. A fastener assembly as claimed in claim 7, in which the fastener comprises a bolt.
9. An installation comprising a workpiece and a fastener assembly as claimed in claim 7 or 8.
10. A process of installing a workpiece by means of a floating nut assembly as claimed in any one of claims 1 to 6, comprising the steps of: attaching the floating nut assembly to a predetermined location on a surface of the workpiece; locating a tool at the predetermined location on the opposite surface of the workpiece; activating the tool to make an aperture in the workpiece; inserting a fastener through the apertures in the workpiece and nut plate and into the nut; and tightening the fastener so that the spacer deforms.
11. A process as claimed in claim 10, in which the tool is a drill.
12. A process as claimed in claim 10 or 11, further comprising the step of clearing swarf from the apertures prior to inserting the fastener.
13. A process as claimed in claiml2, in which the step of clearing swarf is effected by blowing air into the apertures.
14. A process as claimed in claim 12 or 13, in which the step of cleaning swarf is effected by brushing.
15. A process as claimed in any one of claims 10 to14, in which at least one of the steps of locating the tool, inserting the fastener and tightening the fastener are carried out by machine.
16. A wing assembly including an installation as claimed in claim 9.
17. An aircraft including a wing assembly as claimed in claim 16.