GB2393927A

GB2393927A - A method of assembling components

Info

Publication number: GB2393927A
Application number: GB0223383A
Authority: GB
Inventors: Paul Edward Jarvis
Original assignee: BAE Systems PLC
Current assignee: BAE Systems PLC
Priority date: 2002-10-09
Filing date: 2002-10-09
Publication date: 2004-04-14
Also published as: GB0223383D0

Abstract

The method of assembling components 10, 16 comprises providing between the components an element 54 having shape memory characteristics. Heat is then applied to said element 54 to cause the element 54 to change its shape or form and thereby lock the components 10, 16 together. The element 54 may be mounted on an interlocking section 44 of diabolo shape in cross-section which is locatable in recesses 12, 20 of dovetail shape in cross section formed in the components 10, 16.

Description

1 2393927

A Method of Assembling Components The invention relates to a method of assembling components and is particularly, but not 5 exclusively, concerned with method of assembling airframe components.

Traditionally, aircraft, ships, and certain civil engineering structures have been constructed using parts which are joined together using simple metal fasteners such as rivets. Such a manner of construction has been well proven over many years and is still lo used widely today.

The use of rivets invariably requires the generation of a multiplicity of high precision holes in the parts to be joined together. In the case of aircraft structures and particularly when constructing flying surfaces such as wings and tail planes, similar numbers of 5 high precision countersinks are needed to receive heads of the rivets to provide an aerodynamically smooth surface.

Although holes to receive rivets can be pre-drilled in certain components before they reach an assembly area, the build up of tolerances makes that impractical where parts of 20 varying shape and geometry need to be joined together. In the latter case, it is necessary to drill fastener holes during the assembly sequence. That makes it necessary to assemble temporarily the parts to be joined, drill the necessary holes, disassemble the parts, remove burrs from the drilled holes, reassemble the parts and finally install the fasteners. It will be appreciated that such a sequence is time consuming, labour 25 intensive and adds to the overall cost of the assembly process. The very nature of such a method of assembly means that the parts have to be placed together progressively to build up the assembly prior to the installation of fasteners, the assembly being held together by temporary fasteners such a skin pegs while the permanent fasteners are finally installed.

An object of the present invention is to provide an improved method of assembling components.

According to a first aspect of the invention a method of assembling components comprises providing between the components an element having a shape memory characteristic, and subjecting at least said element to a thermal change thereby effecting 5 a change of shape or form of the element to lock the components together.

Such a method is particularly advantageous as the components can be made away from the assembly area and supplied as a kit of parts ready for assembly without the need for the labour intensive assembly procedures described above.

According to a second aspect of the invention there is provided a kit of parts comprising a plurality of components and an element having a shape memory characteristic, the element being arranged to change its shape or form when subjected to a thermal change so as to lock together the assembled components of the kit.

In either aspect, the thermal change may be effected by raising the temperature of the element. The method may comprise providing an interlocking section between the components 20 which enables the components to interlock. The method may comprise arranging the element between the interlocking section and a said component. The element may be located by means of a feature formed, for example, in the interlocking section. The feature may take the form of a recess such as a groove.

25 In one embodiment, the method comprises arranging the interlocking section on one of the components so as locate in a complementary shaped undercut recess on another component. In such a case, the interlocking section may be of dovetail shape in cross-

section. 30 In another embodiment, the method comprises forming the interlocking section as an independent member which locates in the components to be connected together. In such a case, the interlocking section may be of diabolo shape or other suitable shape in cross-section.

Preferably, the interlocking section is of such shape to enable it to be slid or slotted into a position where it can hold the components together.

In certain assemblies, both types of interlocking section may be used.

The memory shape of the element may be non-linear, for example of sine wave shape.

In such a case, the element may be deformed into, for example, a linear shape to enable it to be assembled with the components. The thermal change then causes the element to try to revert to its undeformed non- linear memory shape. The method may comprise lo locating the element in a non-linear recess in a said component to enable the element to take up its non-linear memory shape in the recess. Such a non-linear recess may comprise a recess having wide and narrow sections.

The memory shape of the element may be a larger version of its deformed shape.

Preferably, the assembly comprises a sufficient number of components to enable each component to be locked to more than one other component, for example in a box-like or lattice-like configuration. In that way, any risk of components shifting relative to each other as a result of the thermal change is minimised.

Where the assembled components might need to be separated for, say, repair the method may comprise forming the element from a memory shape material which has bi-stable or two way effect characteristics. For example, initial application of heat will cause the element to try to revert to its undeformed memory shape to lock the 25 components together. However subsequent cooling of the element to a particular level, will cause the element to approach its deformed state to enable the components to be separated. According to a third aspect of the invention there is provided an assembly comprising a 30 plurality of components held together by means of an element having a shape memory characteristic and which has been subjected to a thermal change in temperature whereby the element has changed its shape or form so as to lock the components together.

According to a fourth aspect of the invention there is provided an assembly of aircraft components held together by means of an element having a shape memory characteristic and which has been subjected to a thermal change whereby the element 5 has changed its shape or form so as to lock the components together.

In the third or fourth aspect of the invention, the element may have features corresponding to the features of the element referred to in the first or second aspect of the invention or in any of the subsidiary clauses relating thereto.

A method of assembling components will now be described by way of example with reference to the accompanying drawings which illustrate various configurations of components and in which: Fig. 1 is a partial exploded perspective view of various components of an aircraft wing to be assembled in accordance with the invention, Fig. 2 is a perspective view of part of diabolo shaped interlocking member, Fig. 3 is a cross-section through part of spar and stringer assembly somewhat similar to that shown in Fig. 1, 20 Fig. 4 is a cross section of the spar and stringer assembly of Fig. 3 on the line III-III in Fig. 3, Fig. S is a diagrammatic cross- section through an aircraft wing assembled by means of a method in accordance with the invention, and Fig. 6 is plan view of part of the aircraft wing shown in Fig. 4 with a top skin 25 removed. Looking first at Fig. 1, an aircraft wing skin 10 is formed with dovetail cross-section grooves 12 (one only of which is shown) which extends span-wise of the skin 10. The wing skin is also formed with dovetail cross-section grooves 14 which extend chord 30 wise of the skin 10. The spar 16 extends span- wise of the wing skin 10 and is of "I" shaped cross-section. Upper and lower edges of the spar 16 are formed with dovetail cross-section grooves 18, 20. The grooves 18, 20 are of identical form and each one is formed with alternating wide and narrow sections 21, 22 respectively. It will be seen

from Fig. 1 that the recess 18 converges from the wider section 21 to the narrower section 22 and then diverges from the narrower section 22 to the next wider section 21.

Four flanges 24 (three of which are shown in Fig. 1) extend from a web 26 of the spar 5 16 and are formed with respective vertical dovetail crosssection grooves 28.

Stringers 30 are provided between the skin 10 and the spar 16. Each stringer 30 has two vertical edges 32 of dovetail cross-section and a lower edge 34 also of dovetail cross-section. The upper edge of each stringer 30 is formed in a manner similar to the lo upper edge of the spar 16 so as to define a groove 36 of dovetail cross-section having wider and narrower sections 38, 40 respectively. Each stringer 30 is formed with a lightening hole 42.

A diabolo-cross-section element 44 (shown in detail in Fig. 2) has lower and upper 5 sections 46, 48 respectively of complementary shape to the grooves 12, 20. The lower and upper sections 46, 48 have sides 50 formed with identical elongate recesses 52 in which are located respective strips of shape-memory material 54. The strips of material 54 may be held in the recesses 52 by friction. Alternatively, the strips may be held in place by some other feature such as a captive slot or other suitable carrier. The number 20 of strips 54 used will depend on factors such as the magnitude of the frictional grip required between assembled components Similar strips of material 54 may be applied, for example by means of adhesive, to upper and lower surfaces of the element 44.

The strips of material 54 may alternatively be located by means of recesses in the walls of the grooves 12, 20 or may be otherwise suitably secured to the walls.

30 The dovetail cross-section edges 32, 34 of the stringers 30 are also formed with recesses similar to recesses 52 which contain strips of deformed shape-memory material 54 as shown in the embodiment illustrated in Fig. 3.

A suitable shape memory material for that is as Nickel-Titanium alloy in an austenetic/martensitic state. One such suitable material is available from Raychem under the name Tynel (Tynel is a registered trade mark). However other kinds of shape memory material are commercially available. The shape memory effect depends on 5 martensitic transformation. From a high temperature austenetic phase, cooling of the material causes martensite to form. If the material is then re-heated the material reverts to its austenetic phase.

If a strip of shape memory material such as strip 54 is of sinusoidal shape and is cooled, 0 martensite forms and the strip retains is sinusoidal shape. If the strip is then mechanically deformed by up to, say, 5% so as to take on a straight condition to enable it to be located in one of the recesses 52 and is then heated, a transformation back to the austenetic phase occurs and the strip takes on its original sinusoidal shape again. As the strip of material 54 cools, martensite is formed but the strip still retains the IS sinusoidal shape. In that way the strip 54 can be used to create a frictional grip as described below.

To assemble to components, the wing skin 10 is suitably supported on a structure of an appropriate shape. The lower edges 34 of the stringers 30 are then slid into the dovetail 20 grooves 14 of the skin 10 and the spar 16 is then lower into position so that the grooves 28 of the flanges 24 slide down the vertical edges 32 of the stringers 30 as shown in the embodiment of Fig. 3. The position of the assembled spar 16 and stringers 32 is then adjusted on the skin 10 so that the grooves 12 and 20 lie precisely opposite each other.

To assist that, alignment ribs 56 may be provided for locating the lower edge of the 25 spar 16 on the skin 10. Alternatively and as shown in Fig. 4, the lower edge ofthe spar 16 may be formed with a rib 58 which locates in a groove 60 on the skin 10 to align the grooves 12, 20. The element 44 is then slid into the groove 12, 20 to lock the spar 16 to the skin 10.

30 As shown in Fig. 5, an upper skin 62 can be placed in position on top of an assembly of spars 16 and stringers 30 similar to that in Fig 1 and can be held in place by further diabolo members 44. As will be appreciated from Fig. 5, a second spar 16a is used in the construction of the wing and is associated with stringers 30 to form the completed

aircraft wing. Leading and trailing edges 64, 66 of the lower and upper skins 10, 62 are also held together by diabolo members 44 which locate in complementary shaped grooves in the leading and trailing edge sections.

5 Once the wing assembly has been completed, the wing is subjected to heat in, say, an autoclave and is raised to a temperature at which the strips of shape memory material 54 will try to revert to their undeformed shape as shown, for example, in broken lines in Fig. 2. The temperature may be from 200 C to 500 C for a period of I to 5 minutes, though temperature and time may depending on a number of factors including the type 0 of shape memory material used and the size of the assembled components. The strips 54 located in the dovetail grooves 12, 14 and 28 create a frictional grip to hold the assembled components together. Those strips 54 in the grooves 18, 20 and 36 move into the wider sections 21, 38 of those grooves in addition to enhance the grip. If desired, the grooves 12, 14 and 28 could be formed with wider and narrower sections.

After heat has been applied for the appropriate length of time, the wing is removed from the autoclave and allowed to cool.

It will be appreciated that the assembly of components is box-like and will resist 20 distortion as the strips 54 adopt their memory shape.

If desired, the shape memory material forming the strips 54 may have bistable or two-

way effect characteristics. In that case, the shape memory material can remember both a high temperature shape and a low temperature shape. After cooling the material to 25 form martensite, the cooled material is deformed mechanically into a low temperature shape and to such an extent that, on re-heating, the material does not return fully to its undeformed state. On lowering the temperature sufficiently, the cooling causes the martensite to take the material out of its undeformed state and towards its low-

temperature shape. If the shape memory material is used in an environment where the 30 temperature is well above the temperature at which it takes on its low-temperature shape, the material will still provide the friction grip required. If the temperature is then lowered, the shape memory material will begin to adopt its low temperature shape.

For aircraft use, the temperature at which the low-temperature shape takes effect would

need to be below -30 C. Therefore, with such a material, the initial application of heat will cause the strips of material 54 to move towards their memory shape to lock the components together. By subsequently cooling to a temperature below the anticipated lowest working temperature of the components, for example in an autoclave, the strips 5 will take on a different shape (preferably close to the flat form in the present example) to allow the various interlocked components to be dis-assembled. Dis-assembly may be useful where repair is required.

In the description above, reference has been made to the strip of material moving from

lo a flat deformed state to a sinusoidal memory shape form. As an alternative arrangement, the deformed shape of the strip may simply be a smaller version of the memory shape. When heat is applied, the strip of material 54 enlarges to take on the larger form memory shape to create the frictional grip and provides the necessary interlock between the components. Also, although the term "strip" is used, it will be 5 appreciated that other shapes would be equally effective - rods or wire, for example.

The reader is specifically directed to an article entitled "Fabrication and Properties of Nickel-Titanium Shape Memory Alloy Wires" published in Wire Journal International in April 1989 for technical information on shape memory metals.

Claims

1. A method of assembling components comprising providing between the s components an element having shape memory characteristics, and subjecting at least said element to a thermal change thereby effecting a change of shape or form of the element to lock the components together.

2. A method according to claim 1 comprising raising the temperature of the lo element to effect the thermal change.

3. A method according to claim 1 or 2 comprising providing an interlocking section between the components which enables the components to be interlocked together.

4. A method according to claim 3 comprising arranging the element between the interlocking section and a said component.

5. A method according to claim 4 comprising locating the element by means of a 20 feature such as a recess.

6. A method according to claim S comprising providing the feature on the interlocking section.

25

7. A method according to claim 3, 4, 5 or 6 comprising arranging the interlocking section on one of the components so as locate in a complementary shaped undercut recess on another component.

8. A method according to claim 3, 4, 5 or 6 comprising forming the interlocking 30 section as an independent element which locates in the components to be connected together.

9. A method according to any preceding claim comprising providing a said element which has a non-linear memory shape.

10. A method according to claim 9 comprising deforming the element so as to take s on a shape to enable the components to be assembled, and bringing about the thermal change whereby the element will try to revert to an undeformed memory shape to lock the components together.

11. A method according to claim 9 or 10 comprising locating the element in a non lo linear recess in a said component to enable the element to take up a non-linear memory shape in the recess.

12. A method according to any preceding claim comprising providing a sufficient number of components to enable each component to be locked to more than one other 5 component.

13. A method according to claim 12 comprising assembling the components in a box-like or lattice-like configuration to minimise any risk of components shifting relative to each other as a result of the temperature change.

14. A method according to any preceding claim comprising forming the element from a memory shape material which has a two-way effect.

15. A method according to claim 14 comprising initially subjecting the element to 25 the thermal change to lock the components together and subjecting the element to a further thermal change to enable the components to be separated.

16. A method substantially as described herein with reference to the accompanying drawings.

17. A kit of parts comprising a plurality of components and an interlocking section having a shape memory characteristic for holding the components together as an assembly by the method of any preceding claim.

5

18. An assembly comprising a plurality of components held together by the method of any of claims I to 16.

19. An assembly of aircraft components held together by the method of any of claims I to 16.