Method for producing a profile from composite fiber material

The present invention provides a method for producing a profile from composite fiber material, in particular in the aviation and aerospace field, having the following steps: A preliminary fabric, particularly made of pre-impregnated fiber material, is first packed in a vacuum bag. Then support elements are laid on the packed preliminary fabric to support the latter. The vacuum bag is then supplied with a vacuum. Next, the preliminary fabric is hardened to the profile under the action of heat, in particularly in an autoclave. With the claimed method the support elements can be formed advantageously from favorable material, in particular aluminum, instead of highly expensive nickel-36 steel, since the support elements are uncoupled mechanically from the preliminary fabric in a longitudinal direction by means of the vacuum bag, enabling movement of the support elements in the longitudinal direction relative to the preliminary fabric.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Section 371 National Stage Application of International Application No. PCT/PCT/EP2008/065114, filed Nov. 7, 2008 and published as WO 2009/083318 on Jul. 9, 2009, in English, which claims the benefit of German Patent Application No. 10 2007 062 872.4, filed Dec. 28, 2007, the entire disclosure of which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a method for the production of a profile from fibre composite material.

Although the present invention and the problem on which it is based are suitable for the production of any profiles, they will be described in detail in respect of stringers of an aircraft.

According to a method known to the Applicant for the production of profiles, for example stringers, a preliminary fabric consisting of fibre composite material is initially deposited on a laminating device. Support elements are then positioned on the preliminary fabric which support said preliminary fabric and thus hold it in the desired shape of the stringer to be produced. Thereafter, the preliminary fabric together with the support elements are wrapped in a vacuum bag and said vacuum bag is subjected to a vacuum. Finally, the arrangement comprising the vacuum bag with the preliminary fabric arranged therein and the support elements is cured in an autoclave with the application of pressure and heat.

Fibre composite materials, particularly with carbon fibres, have a very low thermal expansion coefficient. Consequently, the support elements which are supporting the preliminary fabric and which are in direct contact with the preliminary fabric, must also be formed from a material which has a very low thermal expansion coefficient, as otherwise the preliminary fabric will undergo an undesirable distortion due to the interaction between the preliminary fabric and the support elements. Materials which have a very low thermal expansion coefficient, for example nickel-36 steel, are very expensive. Furthermore, the support elements must have a very specific shape depending on the shape of the profile to be produced. In the case of support elements consisting of nickel-36 steel, this in turn requires a very complex mechanical processing, because nickel-36 steel is very hard. Particularly in the production of streamlined profiles, which are profiles of this type which bend in their longitudinal direction, the expenditure for the mechanical processing of the support elements is very high.

SUMMARY OF THE INVENTION

Therefore, it is the object of the present invention to provide an improved method for the production of a profile from fibre composite material which manages in particular without the very expensive support elements described above.

This object is achieved by a method which has the features of claim1.

According thereto, a method is provided for the production of a profile from fibre composite material, in particular in the aerospace sector, comprising the following steps: First of all, a preliminary fabric is wrapped in a vacuum bag. Then at least one support element is positioned on the wrapped preliminary fabric to support it. The vacuum bag is then subjected to a vacuum. Furthermore, the preliminary fabric is then cured to form the profile.

The idea on which the invention is based lies in the understanding that the vacuum bag allows a movement of the at least one support element relative to the preliminary fabric when the at least one support element and the preliminary fabric are arranged on opposite sides of the vacuum bag. Therefore, this avoids a mechanical interaction between the preliminary fabric and the at least one support element which could result in a distortion of the preliminary fabric. Consequently, economical materials, for example aluminium sheets and steel sheets which can also be easily brought mechanically into the desired shape can be used as the material for the support elements. Alternatively, support elements made of plastics materials, in particular extruded profiles consisting of plastics materials, are also conceivable. Thus, a method for producing a profile from fibre composite material is provided which is very much more economical than the known method. In particular, streamlined profiles can thus be advantageously produced.

Advantageous developments and embodiments of the invention are provided in the subclaims.

The term “preliminary fabric” as used herein is understood as meaning any type of fibre material, in particular fibre-woven fabrics, fibrous tissues or fibre felt. The fibres can be formed, for example, as carbon fibres, glass fibres or aramide fibres. The fibre material is preferably already pre-impregnated with a resin matrix. However, it can likewise be provided that the fibre material is only infiltrated with the resin matrix, for example by an infusion process, after the preliminary fabric has been wrapped and the at least one support element has been positioned, and is then cured to form the profile. The resin matrix is preferably an epoxy resin.

According to a preferred development of the method according to the invention, the at least one support element is formed from aluminium or steel, in particular from an aluminium sheet or steel sheet. Of course, aluminium is to include all aluminium alloys. Aluminium and steel are relatively inexpensive and can also be easily reworked mechanically into the support elements with the desired shape, thereby making it possible to reduce costs further. In particular, support elements made of sheet metal can be easily bent for the production of streamlined profiles.

According to a further preferred development of the method according to the invention, the preliminary fabric is configured with a web, and two support elements which are configured in particular as L-shaped profiles to support the web between them are positioned on the wrapped preliminary fabric. In this respect, the longitudinal axis of the L-shaped profiles extends substantially parallel to the longitudinal axis of the preliminary fabric. The web of the preliminary fabric is dimensionally relatively unstable and therefore the support is needed on opposite sides.

The term “longitudinal axis” of a component as used herein is understood as meaning the axis along which the cross section of the component varies only insignificantly.

According to a further preferred development of the method according to the invention, the two support elements are held relative to one another by a rubber roof profile, two triangular profiles and an adhesive tape connecting them, a clamp and/or a further vacuum bag. The term “rubber roof profile” as used herein is understood as meaning a resilient profile with a support surface and a recess in said support surface, which recess extends in the longitudinal direction of the rubber roof profile. The recess, in particular groove, is configured to resiliently receive the web of the profile together with the portions, supporting the web, of the support elements. The rubber roof profile is particularly suitable for the production of T-profiles. A merely relative mutual fixing of the support elements avoids tensions which arise in elements with a high thermal expansion coefficient when they are respectively fixed at two mutually stationary points. In general, rubber roof profiles, triangular profiles with adhesive tapes, clamps and vacuum bags are very easy to handle compared to the heavy, presently used tools made of nickel-36 steel.

According to a further preferred development, the wrapped preliminary fabric together with the at least one support element are wrapped in a further vacuum bag, in which case the vacuum applied to the further vacuum bag is set to be less than or the same as the vacuum in the vacuum bag. The term “vacuum” as used herein is understood as meaning the value of the difference between atmospheric pressure and the prevailing, absolute pressure. The above development provides that the vacuum bag rests tightly against the preliminary fabric and is not deformed in the direction of the second vacuum bag due to the pressure prevailing therein, which would adversely affect the material characteristics of the cured fibre composite material.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the figures, the same reference numerals denote the same or functionally identical components, unless indicated otherwise.

FIG. 1is a cross-sectional view of an arrangement1for the production of a profile configured as a T-stringer.

The arrangement1has a laminating device2, on which is arranged a preliminary fabric3with a T-shaped cross section, consisting of two parts4,5with in each case an L-shaped cross section and a blade6arranged in between.

According to the present embodiment, the preliminary fabric3consists of a carbon fibre-woven fabric which has been pre-impregnated with an epoxy resin matrix, i.e. the epoxy resin matrix is in the uncured state. The preliminary fabric3extends substantially vertically to the plane of the paper along the longitudinal axis8. The preliminary fabric3can also be configured to be streamlined.

The preliminary fabric is wrapped in a vacuum bag7which is sealed off from the laminating device2by sealing means11,12. Prevailing in the interior13of the vacuum bag7is a vacuum P1, i.e. a low pressure compared to the pressure P0which prevails in the atmosphere14.

A web15of the preliminary fabric3is held in the position shown inFIG. 1by a rubber roof profile16and two support elements17,18.

The support elements17,18are each formed from an aluminium sheet with an L-shaped cross section. The support elements17,18are positioned such that they can be displaced while sliding in the longitudinal direction8with respect to the vacuum bag7, portions22,23of the support elements17and18supporting the stringer web15and portions24,25of the support elements17and18resting on the two foot portions26and27of the preliminary fabric3.

The rubber roof profile16has a recess31which extends in the longitudinal direction8and in which the web15is received with the portions22,23between side surfaces of the recess31. Resting against support surfaces which extend substantially vertically to the side surfaces of the recess31is the rubber roof profile on the portions24and25of the support elements17and18.

The rubber roof profile16is inverted over the web15together with the portions22,23of the support elements17,18, the rubber roof profile16being resiliently widened, and thus fixes these support elements17,18relative to one another, as a result of which the stringer web15is held in shape, as shown inFIG. 1. In this respect, the side surfaces produce a slight resilient pressure against the portions22and23of the support elements17and18.

The arrangement1is then subjected to heat (and possibly pressure), preferably in an autoclave. This cures the preliminary fabric3to produce a T-stringer.

The arrangement40ofFIG. 2only differs from that ofFIG. 1in that the rubber roof profile16is replaced by two triangular profiles41,42and by an adhesive tape43which connects them. The triangular profiles41,42are preferably formed from a rubber material and engage into the support elements17,18to hold them in position in conjunction with the adhesive tape43.

In the arrangement50inFIG. 3, a clamp51is provided instead of the rubber roof profile16according to the embodiment ofFIG. 1, which clamp51presses the portions22,23of the support elements17and18against the web15of the preliminary fabric3with a slight force, for which the bow52of the clamp51is preferably formed from a resilient material.

In the arrangement60inFIG. 4, a further vacuum bag61is provided instead of the rubber roof profile16according to the embodiment ofFIG. 1, which vacuum bag61receives in its interior62the preliminary fabric3together with the vacuum bag7and the support elements17,18. A vacuum P2prevails in the interior62of the further vacuum bag61. The vacuum P1can be applied to the interior13of the vacuum bag7and the vacuum P2can be applied to the interior62of the vacuum bag61by hoses63,64, for example, which are each connected to a vacuum pump (not shown).

The following relationship should apply to the vacuums P1and P2:
P1≧P2

For example, P1=100 kPa and P2=25 kPa, P1and P2being measured relative to the atmospheric pressure P0.

In the embodiment according toFIG. 4, with prevailing vacuums P1and P2, the vacuum bag61presses the support elements17,18against the web15to support it.

Common to the embodiments according toFIGS. 1 to 4is the fact that instead of the pre-impregnated preliminary fabric3, dry fibre material can also be used at any time which can be infiltrated with a resin matrix after the positioning of the support elements17,18and before the application of heat and/or pressure to the arrangements1,40,50and60respectively.

Although the invention has been described on the basis of a plurality of embodiments, it is not restricted thereto, but can be modified in many different ways.

The present invention provides a method for the production of a profile from fibre composite material, in particular in the aerospace sector, comprising the following steps: First of all, a preliminary fabric, in particular of pre-impregnated fibre material, is wrapped in a vacuum bag. Support elements are then positioned on the wrapped preliminary fabric to support it. Thereafter, the vacuum bag is subjected to a vacuum. Furthermore, the preliminary fabric is then cured under the effect of heat, in particular in an autoclave, to produce the profile. In the method according to the invention, the support elements can advantageously be formed from a favourable material, in particular aluminium, instead of very expensive nickel-36 steel, because the support elements are mechanically uncoupled from the preliminary fabric in the longitudinal direction by the vacuum bag, thereby allowing a movement of the support elements in the longitudinal direction relative to the preliminary fabric.

LIST OF REFERENCE NUMERALS