Method for joining two fuselage sections by creating a transverse butt joint as well as transverse butt joint connection

The invention relates to a method of connecting two fuselage sections (1, 2, 21, 22) formed by a fiber-reinforced plastics material, in particular wound fuselage sections (1, 2, 21, 22) for aircraft fuselage cells, having a multiplicity of stringers (10, 11, 35, 36) arranged with a uniform distribution at a distance from and parallel to one another on the inner side of an outer skin (3, 4, 25, 26), with the formation of a transverse joint (5, 30). In order to be able in particular to join together wound CFRP fuselage sections so that simple tolerance compensation is made possible in a continuous, industrial production process, the method according to the invention comprises the following steps: aligning a first and a second fuselage section (1, 2, 21, 22) with respect to one another, heating and adapting at least one transverse butt strap (9, 23), formed by a fiber-reinforced thermoplastic material, in such a way that tolerance compensation between differing cross-sectional geometries of the first and second fuselage sections (1, 2, 21, 22) is made possible, or heating at least one end region (27) of a second fuselage section (2, 22) formed by a fiber-reinforced thermoplastic material, and joining together the two fuselage sections (1, 2, 21, 22).

This application is the U.S. national phase of International Application No. PCT/EP2009/051525, filed 11 Feb. 2009 which designated the US and claims priority to German Application No. 10 2008 010 197.4, filed 20 Feb. 2008, and this application claims priority from U.S. Provisional Application No. 61/029,932 filed 20 Feb. 2008; the entire contents of each of the above applications are hereby incorporated by reference.

The invention relates to a method for joining two fuselage sections formed from fibre-reinforced plastics material, more particularly wound fuselage sections for aircraft fuselage cells, with a number of evenly distributed stringers arranged inside on an outer skin parallel to and at a distance from one another to create a transverse butt joint.

Furthermore the invention relates to two embodiments of a transverse butt joint connection between two fuselage sections.

In modern aircraft construction carbon-fibre-reinforced compound component parts (CFRP component parts) are increasingly replacing the standard aluminium alloy materials. Thus by way of example fuselage sections, including the stringers arranged on the inside, are made in one piece in the winding process from carbon fibre reinforced plastics (CFRP). A suitable reinforcing fibre assembly is hereby preferably embedded in the main load direction into a plastics matrix. The plastics matrix can be formed by way of example with thermosetting plastics or mechanically highly stressable thermosoftening plastics. Epoxy resin systems are preferably used as thermosetting plastics whilst polyether ether ketones (PEEK) are used by way of example in the area of the thermosoftening plastics. Carbon fibres, glass fibres, Aramid® fibres, Kevlar® fibres, ceramic fibres or natural fibres are generally used to provide the reinforcing fibre assembly.

One big problem here is combining several CFRP fuselage sections into one fuselage cell because tolerance compensation is no longer possible in the case of solidified CFRP fuselage sections on account of their high inherent rigidity and furthermore the tolerances, particularly with regard to the cross-sectional geometry, during the winding process always turn out as a condition of their functional principle to be considerably greater than in the case of the classic aluminium construction method. These unavoidably higher manufacturing tolerances are a result of inter alia shrinkage processes during the hardening in the autoclave, different reinforcement fibre densities during the laying and winding process, temperature and pressure fluctuations, fluctuations in the quality of the semi-finished fibre products as well as further disturbance variables. Joining together the fuselage sections must however for static reasons in no way take place under mechanical stress.

One possibility for compensating tolerance is to provide additions (so-called “shims”) which are introduced in fluid, hardenable and/or solid form into the joining gap between the fuselage sections. These shims can however have a detrimental effect on the mechanical load bearing capacity of the joined fuselage sections and furthermore considerably increase the assembly costs since by way of example fluid, hardenable “shims” require a long hardening time during which the assembled fuselage sections have to be held together in position. Furthermore the use of shims is not permitted in some highly loaded connecting areas for safety reasons.

The object is therefore concerned with the problem of providing a method for joining more particularly wound carbon fibre reinforced plastics fuselage sections which enables a simple tolerance compensation in one continuous industrial manufacturing process.

This is achieved by the following method steps of the patent claim1:

a) aligning a first and a second fuselage section relative to one another,

b) heating and customizing at least one transverse butt strap formed by a fibre-reinforced thermosoftening plastics material so that a tolerance compensation is possible between deviating cross-sectional geometries of the first and the second fuselage section or heating at least one end area of a second fuselage section which is formed from a fibre-reinforced thermosoftening plastics material, and
c) joining the two fuselage sections together.

According to a first method alternative it is proposed that the two fuselage sections which are to be joined together are preferably formed by a thermosetting carbon fibre reinforced plastics material. The tolerance compensation during joining takes place in this case by heating and in the event of tolerance deviations by the subsequent customizing and remoulding of the transverse butt straps which are used for the final production of the connection and/or stringer couplings which are formed for this purpose by a fibre-reinforced thermosoftening plastics material which is deformable under the influence of heat. The remoulding takes place so that the transverse butt strap contacts the inside of the outer skin of the fuselage section and the stringers at the stringer couplings with the largest possible surface area. The remoulding of the transverse butt straps and/or the stringer couplings takes place as a rule by parallel displacement of at least two rectilinear (end-side) sections in opposite directions to one another, wherein a likewise rectilinear centre section lying between each two relevant sections undergoes a slight incline.

In the case of a second method alternative the two fuselage sections which are to be connected are preferably formed at least at the ends with a wound thermosoftening carbon fibre reinforced plastics material. In order to carry out the method the fuselage sections which are to be joined are aligned relative to one another wherein the tolerance compensation is carried out by heating one of the end sections of the fuselage section which is to joined. After compensation of the where existing deviations has been carried out between the cross sectional geometries of the fuselage sections being joined by at least section-wise compression and/or expansion of the heated end area of the fuselage section which is to be joined on, the connection of the two fuselage sections is carried out in conventional manner by using additional connecting components.

PEEK (polyether ether ketone) by way of example has proved a suitable thermosoftening plastics material for the carbon fibre reinforced plastics components, more particularly the fuselage sections, the transverse butt straps and the stringer couplings, whilst epoxy resin systems are used for forming the resin matrix in the case of thermosetting carbon fibre reinforced plastics components.

According to an advantageous development of the first method version it is proposed that the fuselage sections are connected by means of the at least one transverse butt strap. This makes it possible to retain the long-known conventional connecting technique of using transverse butt straps placed and fixed on the inside in the transverse butt joint area between two fuselage sections. First any possible tolerance deviations, more particularly a vertical stagger, between the assembled fuselage sections being joined in the area of the transverse butt joint are determined by a suitable measuring system which can take place by way of example with a computer-controlled laser measuring system. Then the transverse butt straps formed from the fibre reinforced thermosoftening plastics material are heated in an electrically heatable moulding tool until a problem-free, distortion-free plastics deformation is possible. Where necessary the transverse butt straps are remoulded and customized to compensate the tolerance between the fuselage sections by means of the moulding tools on the basis of the tolerance deviations determined by the laser measuring system and the actual geometry data of the transverse butt joint respectively. After customizing and remoulding the at least one transverse butt strap the cooled transverse butt strap is removed from the moulding tool and fixedly connected in conventional manner on the inside on both sides to the end areas of the fuselage sections to produce a transverse butt joint. If it is necessary to use several transverse butt straps then to simplify the procedure the transverse butt straps can be heated, remoulded and customized immediately one after the other and then mounted for connecting the fuselage sections. The use of a computer-controlled laser measuring system makes it possible to integrate the method into a fully automatic production line. The at least one transverse butt strap is heated for carrying out the customization and remoulding up to a softening temperature of the thermosoftening plastics material used for forming the matrix. In the case of the thermosoftening high performance plastics material polyether ether ketone (PEEK) which is preferably used, the melting temperature is at 330° C.

According to a further development of the method the at least one transverse butt strap is connected to an end area of a fuselage section by rivets, screws, adhesive, welding or any combination thereof.

Through this development the method according to the invention can be integrated without problem into existing production lines whilst retaining the known joining processes.

A further advantageous development proposes that at least one stringer coupling is heated and customized to enable tolerance compensation.

For this purpose first the existing tolerance deviations between the relevant opposing stringers in the fuselage sections being joined are determined, which can be carried out by way of example again by means of a contactless laser measuring system. The at least one stringer coupling is then placed in a suitable electrically heatable moulding tool and heated. In the moulding tool in the case where tolerance deviations, more particularly a vertical stagger and/or a lateral stagger, are determined between the stringers being joined, the customization and remoulding takes place on the basis of the actual geometry data determined by the measuring system bearing in mind the preset ideal geometry data for an optimum transverse butt joint between the fuselage sections wherein as a rule an attempt is made to minimize and even out the gap measurement on the circumferential side. It is hereby necessary that the at least one stringer coupling is heated at least to the softening temperature of the thermosoftening plastics material used in the individual case, which is preferably a PEEK.

A further development of the second method version proposes that at least one transverse butt strap is connected to an end area of the first fuselage section, more particularly by rivets, screws, adhesive, welding or any combination thereof, the end area of the second fuselage section is heated by an in particular electrically heatable heating element placed in the end area, more particularly a heating mat, and the end area thus heated of the second fuselage section is pushed onto the end area of the first fuselage section.

As a result of this procedure a simple tolerance compensation is possible between the fuselage sections being joined in the area of the transverse butt joint without any further intermediate steps. The heating mat completely encloses the end area of the fuselage section being joined in the circumferential direction so that the entire end area of the second fuselage section being added on can be uniformly heated at the same time. Heating of the end area must hereby take place until at least into the region of the softening temperature of the thermosoftening plastics material of the fuselage sections being used for forming the matrix. A complex measuring system, as in the case of the first method version is not necessary for the tolerance compensation in this method version. The tolerance compensation takes place in the simplest fashion by sliding the heated and thus ductile deformable end area of the second fuselage section which is being joined onto the transverse butt straps of the first fuselage section which have already been fixed on the end area. The end area of the second fuselage section being joined is hereby expanded and/or compressed where required in sections. The second method version is preferably used when producing transverse butt joints which are only slightly mechanically stressed so that as a rule no stringers being connected run in the fuselage sections in the area of the transverse butt joint. The transverse butt joints produced by means of this method version furthermore have the advantage that the outer skins of the fuselage sections adjoin one another stagger-free, that is practically flush in the area of the transverse butt joint.

An advantageous further development of the second method version provides that the end area of the second fuselage section when cooling down shrink-fits onto the at least one transverse butt strap to produce a slight press-fit engagement.

A particularly close-fitting and equally solid seat of the attached second fuselage sections is hereby achieved.

In the drawings the same structural elements each have the same reference numerals.

FIG. 1shows a perspective sectional view of a transverse butt joint made according to the first method version between two substantially barrel-shaped fuselage sections.

A transverse butt joint5is formed with a gap6between two fuselage sections1,2with outer skins3,4. The two end areas7,8of the fuselage sections1,2are connected by means of a transverse butt strap9. The stringers10,11which have a T-shaped cross-sectional geometry are fixed opposite one another on the insides (not shown) of the outer skins3,4. The stringers10,11are each connected on both sides to a stringer coupling12,13with an L-shaped cross-sectional geometry. The connection of the transverse butt strap9to the two outer skins3,4which run roughly up to a butt join as well as the connection of the stringer couplings12,13to the stringers10,11can be carried out by rivets, screws, clamps, adhesive, welding or any combination thereof. The fuselage sections1,2can have in the end areas7,8a cross-sectional geometry which deviates from the ideal circular geometry and can have by way of example an oval, elliptical cross-sectional geometry or practically any other, preferably constantly curved, cross-sectional geometry.

In order to enable remoulding and customization in the heated state for tolerance compensation both the transverse butt strap9and the stringer coupling12,13are formed from a fibre-reinforced thermosoftening plastics material which is preferably a carbon fibre reinforced polyether ether ketone (PEEK). Alternatively other thermosoftening high performance plastics with comparable mechanical properties can be used. The remaining components of the fuselage sections1,2, more particularly the outer skins3,4as well as the stringers10,11are preferably formed from a fibre reinforced thermosetting plastics material, by way of example from a carbon fibre reinforced epoxy resin system. Alternatively the outer skins3,4and/or the stringers10,11can also be formed from a fibre-reinforced thermosoftening material, such as for example PEEK.

FIG. 2illustrates a side view of the transverse butt joint5inFIG. 1.

A vertical stagger14between the outer skins3,4and the stringers10,11has been compensated by remoulding the transverse butt strap9and the two stringer couplings12,13which took place in the plastics state. The remoulding of the said component parts takes place in moulding tools (not shown) close to the assembly line of the fuselage sections based on actual geometry data which was determined with a fully automatic measuring system, more particularly a computer-controlled laser measuring system in the area of the transverse butt joint5and compared with ideal geometry data in the transverse butt joint area between the fuselage sections1,2to determine the position and absolute amount of any possible tolerance deviations.

The remoulding and customization process of the transverse butt strap9and the stringer couplings12,13is to be explained using the example of the front stringer coupling13. For the purpose of remoulding the front stringer coupling13by way of example, a parallel displacement of a rectilinear section15of the stringer coupling profile13takes place in relation to a further rectilinear section16of the stringer coupling13wherein an inclined centre section17is formed. Where necessary the corresponding procedure follows for the stringer coupling12and/or the transverse butt strap9. Remoulding the said components hereby takes place substantially perpendicular to the outer skins3,4, that is in the direction of arrow18in the illustrated embodiment.

FIG. 3shows a plan view of the transverse butt joint5with the transverse butt strap9according toFIG. 1. Between the stringers10,11there is additionally a transverse stagger19between the outer skins3,4which was compensated by remoulding and customizing the stringer couplings12,13. The compensation of the transverse stagger19takes place corresponding to the procedure for compensating the vertical stagger14(seeFIG. 2) by remoulding the two stringer couplings12,13transversely to the running direction (longitudinal direction) of the stringers10,11in the direction of arrow20.

For a description of the method according to the invention according to the first version reference is made toFIGS. 1 to 3.

First the end areas7,8of the fuselage sections1,2which are to be joined are measured by means of a measuring system, preferably by means of a fully automatic computer-controlled laser measuring system in order to determine the actual geometry of the fuselage sections1,2in the area of the transverse butt joint5. This is followed by aligning the two fuselage sections1,2in relation to one another. Alternatively the alignment can be carried out just on the basis of the measured actual geometry data. By aligning the two fuselage sections1,2it is reached that the tolerance deviations are spread as evenly as possible over the circumference and at the same time are minimized. This means that by way of example at (diametrically) opposite circumferential points of the end area7of the fuselage section2a distance (not shown) from the corresponding circumferential points of the end area8of the fuselage section1turns out to be as far as possible the same size in order to make the required tolerance compensation symmetrical over the circumference of the fuselage sections1,2.

At least one transverse butt strap9is then heated and remoulded and customized by means of an electrically heatable moulding tool so that a complete compensation of any possible vertical stagger14between the end areas7,8of the two fuselage sections1,2for tolerance compensation is possible. The control of the moulding tools hereby takes place based on a comparison of the measured actual geometry data with the ideal geometry data of the fuselage sections1,2predetermined by the structural design. The thus remoulded transverse butt strap9is then connected to the two end areas7,8of the fuselage sections1,2. The connection of the transverse butt strap9to the end areas7,8can take place by rivets, screws, clamps, adhesive, welding or any combination of these. The transverse butt joint5and thus the joining of the two fuselage sections1,2can be perfected by repeatedly remoulding and customizing further transverse butt straps which may be present.

Following this the stringers10,11arranged at a distance parallel to one another evenly over the circumference inside in the fuselage sections1,2are then each connected preferably by two stringer couplings12,13disposed either side on the stringers10,11. Customizing the stringers10,11by heating and subsequently remoulding and adjusting them takes place in the same way as customizing the transverse butt strap9. Connecting the stringers10,11and the stringer couplings12,13can in turn be carried out by rivets, screws, clamps, adhesive, welding or any combination of these.

The method according to the invention is in the first version dependent on the fact that both the transverse butt strap9and also the stringer couplings12,13are formed from a suitable fibre-reinforced thermosoftening plastics material. The remaining components of the fuselage sections1,2, particularly the outer skins3,4as well as the stringers10,11fixed therein can also be formed from a fibre-reinforced thermosetting plastics material, such as by way of example a carbon fibre reinforced epoxy resin. The method according to the invention enables a tension-free assembly of large-volumed fuselage sections1,2by providing a possibility for compensation between slightly differing cross-sectional geometries of the fuselage sections1,2in the area of the transverse butt joint.

The process sequence of the second version of the method can be seen fromFIG. 4. First a first and a second fuselage section21,22are aligned relative to one another. At least the second fuselage section22which is to be joined onto the first fuselage section21is formed at least in the end area with a fibre reinforced thermosoftening plastics material. By way of example the fuselage section22can be formed from a polyether ether ketone (PEEK) with a carbon fibre reinforcement.

At least one transverse butt strap23is then fixedly connected to an outer skin25on the inside in an end area24of the first fuselage section21.

Finally an outer skin26is heated in an end area27of the second fuselage section22which is to be joined on, and is hereby made sufficiently plastically deformable to allow a tolerance compensation.

By pushing the second fuselage section22with the softened end area27onto the transverse butt strap23in the direction of the arrow28the assembling of the two fuselage sections21,22together is completed by simultaneously implementing any tolerance compensation which may be required in a further method step.

For the final connection of the two fuselage sections21,22it is necessary as a rule to fixedly connect the transverse butt strap23additionally to the end area27of the joined on fuselage section22by rivets, screws, adhesive, welding or any combination of these.

For heating the end area27a preferably electrically heatable, flexible and circumferential heating mat29or sleeve is mounted on same. The heating mat29preferably remains on the end area27until the second fuselage section22has been pushed completely onto the first fuselage section21. The heating mat29enables a slight longitudinal compensation in the radial direction in order to avoid the creation of stresses and to make it easier to remove the heating mat29or heating sleeve.

After pushing the second fuselage section22onto the first fuselage section21the heating mat29is removed, and where necessary before cooling the top of the transverse butt joint thus formed can be smoothed over. The optional smoothing can take place by way of example with plates whose geometry corresponds with a desired external geometry of the transverse butt joint area and which are pressed with high contact pressure in the area of the transverse butt joint. In the case where the area of the transverse butt joint is substantially cooled down after removing the heating mat29the plates are preferably provided with an integrated electrical heating in order to heat up and smooth the area of the transverse butt joint again at least up to the area of the plasticizing temperature of the thermosoftening fibre reinforced plastics material which is used.

An extensive expensive measuring and precise pre-alignment of the two end areas24,27of the fuselage sections21,22being joined is unlike in the first version of the method no longer required.

In the case where the end area27of the second fuselage section22being joined has a slightly smaller cross-sectional geometry compared with the first fuselage section21, after the end area27has cooled down and as a result of the shrinkage conditioned by the cooling a slight press-fitting engagement is set between the end area27and the transverse butt strap23whereby a particularly close-fitting and simultaneously solid seat is guaranteed.

The transverse butt strap23is preferably formed from a fibre-reinforced thermosetting material, such as by way of example a carbon-fibre reinforced epoxy resin. The method according to the second version is not provided for producing transverse butt joints in mechanically highly stressed areas of the aircraft fuselage cell so that as a rule no stringers are arranged in the area of the transverse butt joint and thus also no stringer couplings need be provided.

FIG. 5shows a cross-sectional illustration through a transverse butt joint formed according to the method according toFIG. 4.

The two outside skins25,26are connected in the end areas24,27by means of the transverse butt strap23by providing a transverse butt joint30. A narrow gap31runs between the two outer skins25,26. Fastening means such as for example rivets, screws or the like are indicated by the four chain-dotted lines. A lower ring frame profile32as well as a clip33are furthermore fixed in the end area27for laterally supporting the ring frame on the transverse butt strap23. The lower ring frame profile32having a roughly L-shaped cross-sectional geometry is connected to an upper inversely L-shaped ring frame profile34by two fastening means, such as rivets, to form an approximately S-shaped cross-sectional geometry. Since the second version of the method is primarily to provide transverse butt joints in weak-load areas of the aircraft fuselage cell the two stringers35,36and stringer couplings are not absolutely necessary nor provided in the area of the transverse butt joint30.

The two ring frame profiles32,34as well as the clip33and the optionally mounted stringers35,36can be formed from any material.

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