DE102013226018A1 - Reusable core for fiber composite components of complex geometry - Google Patents

Abstract

The invention relates to a method for producing a reusable core for the production of fiber composite components. To produce the core, a sequence of elastic shell material and a core material which is flowable at low temperatures is applied to a core structure. In the core of the invention thus produced, the core material is completely enclosed by the elastic wrapping material. After removing the core structure, the core further has a hollow shape. With molten core material, the core for the fiber deposit in a complex geometry and urformable and for use as a press bag, the core is designed expandable.

Description

The invention relates to a method for producing a reusable core for fiber composite components of complex geometry and a reusable, ur and formable core. The invention further relates to the use of a reusable, ur- and formable core in the manufacture of fiber composite components, in particular of fiber composite components with complex, in particular undercut, geometry and / or non-circular cross section.

For the production of hollow fiber composite components, two categories of cores, blown cores and rigid cores have been used.

Blaskerne usually fulfill a dual function. On the one hand, they serve the orderly and near net shape deposition of fibers during the preform process, so for example when braiding or winding. On the other hand, the shaping and the compression of the fiber composite component during the consolidation process, for example. To remove air pockets or set a desired fiber-to-matrix ratio. To fulfill the second function, the cores are compellingly pressure and dimensionally stable and preferably designed to be expandable. In order to ensure the dimensional stability of the cores, they themselves have to be hollow and continuously subjected to an increased internal pressure. This requires special fiber deposition and shaping tools. In addition, only fiber composite components with circular cross-section with sufficient cross-section fidelity can be implemented.

Hollow fiber composite components with non-circular cross-section and / or complex geometries are alternatively produced by the use of dimensionally stable, "lost cores". These are produced by milling, foaming or casting as a negative of the fiber composite component to be produced, with the core formation taking place partly directly in the consolidation tool. The consolidated fiber composite component is separated from the core by dissolving it thermally, chemically or mechanically. Thus, the core for the production of further fiber composite components is lost.

For the production of hollow fiber composite components with a circular cross section therefore reusable blown cores are preferably used. These are first converted into a dimensionally stable state by increasing the internal pressure, then covered with near-net-shape fibers, and then consolidated in a closed mold while adjusting the internal pressure. In this case, undercut and non-undercut component shapes can be realized with a circular cross-section. An under elevated internal pressure dimensionally stable Blaskern with several individually fillable and expandable compartments is, for example, from the EP 2 368 685 A1 known.

A method of manufacturing a bubble core is disclosed in U.S. Patent Nos. 4,135,359 WO 2008/086022 A1 disclosed. The inner surface of a closable molding train is sprayed with a fast polymerizing plastic mixture and then polymerized. The resulting vacuum bag is adapted to the inner surface of the tool and can be used as a blow hose for the production of fiber composite components. In a preferred embodiment, the vacuum bag is constructed in multiple layers, wherein between different layers of reinforcing material, for example. In the form of a vacuum connection or fiber material is introduced. A similar manufacturing process is in the US 5,262,121 A and another blow core incorporating reinforcing structures in the US 2011/0277918 A1 disclosed.

For the production of hollow fiber composite components with non-circular cross-sections and / or complex geometries, known blown hoses are not suitable. Although these can be expanded by increasing the Blasschlauchinnendrucks in a dimensionally stable state, but the cross-section fidelity of the core is unsatisfactory. Under increased internal pressure of the bladder tends on all sides a round cross-section as a stable state against, in particular comes to body edges of the core to curves.

Dimensionally stable cores of a solid material are in principle suitable for the production of any geometry, but are inevitably designed as lost cores in undercut geometry. In general, the geometry of non-undercut cores is not changeable. Thus, a separate core must be produced for each individual component, which results in high material and labor costs.

The object of the present invention is to overcome the disadvantages of the prior art and to provide a method for producing a reusable, form and pressure stable core for the production of fiber composite components. The core is thereby intended to enable the production of hollow fiber composite components of any desired, in particular non-circular, cross-section and / or complex geometry, in particular undercut geometry. The core should continue to be demoulding and reusable without damage to the fiber composite component. Furthermore, the core should enable the production of fiber composite components with optimized fiber-matrix ratio and low air entrapment. By using the core, a time-saving and material-saving and thus economical production of hollow fiber composite components should be possible.

This object is achieved by the features of the independent claims 1, 8 and 14. Preferred developments are the subject of the respective dependent claims.

• a. Aufbringen einer Lage eines ersten flexiblen Hüllmaterials der Grenztemperatur T₁ auf eine Kernstruktur,
• b. Aufbringen einer Lage eines Kernmaterials der Erweichungstemperatur T₂ < T₁ auf die Lage des ersten flexiblen Hüllmaterials,
• c. Aufbringen einer weiteren Lage eines zweiten flexiblen Hüllmaterials der Grenztemperatur T₃ > T₂ auf die Lage des Kernmaterials, wobei
• i. die Hüllmateriallagen zumindest einen Querschnitt der Kernstruktur vollständig umschließen und
• ii. das Kernmaterial zwischen den Hüllmateriallagen angeordnet wird.

The object according to the invention is achieved by a method for producing a reusable core, comprising the following method steps

• a. Applying a layer of a first flexible shell material of the limit temperature T ₁ to a core structure,
• b. Applying a layer of a core material of the softening temperature T ₂ <T ₁ to the layer of the first flexible wrapping material,
• c. Applying a further layer of a second flexible shell material of the boundary temperature T ₃ > T ₂ on the position of the core material, wherein
• i. the Hüllmateriallagen completely enclose at least a cross section of the core structure and
• ii. the core material is placed between the Hüllmateriallagen.

In the process according to the invention for producing a reusable, dimensionally stable and pressure-stable core, a core structure is needed on which the layers constituting the core are applied. This thus serves only the shape of the reusable core, but does not fulfill any function in the subsequent production of a fiber composite component. The core structure is preferably configured as a spatial body, so that a layer surrounding the core structure is advantageously hollow and encloses at least one cross section. Further preferably, the core structure has more than one cross-sectional shape, wherein the transitions between different cross-sectional shapes particularly preferably run continuously. Particularly preferably, the core structure is elongated and / or cylindrical.

At least one layer of a first flexible shell material is applied to the core structure in the first step (a) of the method according to the invention, wherein at least one cross section of the core structure is completely enclosed. In the case of an elongated cylindrical core structure, the lateral surface of the cylinder is preferably at least partially enclosed along the entire circumference by the layer of first flexible shell material. Particularly preferably, the lateral surface is completely enclosed by the first flexible shell material. The first flexible shell material has a limit temperature T ₁ . If the first flexible shell material is a thermoplastic, the limit temperature designates its softening or melting temperature, in particular the temperature at which a lasting change in the shape or the mechanical properties of the material is to be expected. If the first flexible sheath material is thermosetting, the limit temperature is the decomposition temperature.

Below its limit temperature, the layer of first shell material is flexible and tear-resistant and in particular has an elongation at break of more than 150%, preferably of more than 250% and particularly preferably more than 500%.

At least one layer of core material is applied to the layer of the first flexible shell material in the second step (b) of the method, wherein the core material completely covers the layer of a first flexible shell material at least in sections. In the case of an elongated cylindrical core structure, the first layer is preferably completely covered or covered in such a way that the layer of first wrapping material protrudes axially over the core material on both sides. The core material has a softening temperature T ₂ which is less than the limit temperature T _{1 of} the first flexible shell material. The softening temperature refers to the glass transition temperature or the melting temperature of the core material. Below its softening temperature, the core material layer is pressure and dimensionally stable to pressures commonly encountered in the deposition of reinforcing fibers and the inherent weight of the core. The following is under pressure stable, the dimensional stability under forces, as they usually occur in common fiber deposition processes understood. Above its softening temperature, the core material is flowable. The glass transition temperature and melting temperature of the core material are preferably smaller than the limit temperature T ₁ .

At least one layer of a second flexible covering material is applied to the core material layer in the third step (c) of the method. Moreover, this layer is preferably applied in a region of the core structure which is covered by the layer of first shell material but not by the core material. In the case of an elongated cylindrical core structure, the core material and the axial projections on both sides are preferably encased in first shell material. The second flexible shell material has a limit temperature T ₃ which is greater than the softening temperature T _{2 of} the core material, preferably greater than its glass transition temperature and the melting temperature. Below its limit temperature, the layer of second wrapping material is flexible and tear-resistant and in particular has an elongation at break of more than 150%, preferably of more than 250% and particularly preferably more than 500%.

According to the invention, the cladding material layers completely surround at least a portion of the core structure. Between the Hüllmateriallagen the core material is arranged. In a preferred embodiment, the cladding material layers are bonded together such that the core material is completely enclosed by the cladding material layers and can not leave the limited volume thereof.

After the application of the second or last layer of shell material and the solidification of the skin layers, the core structure is removed at a temperature less than T ₁ and smaller than T ₃ . Thus, the previously deposited on the core structure, at least three-layer sequence of sheath and core material remains in a hollow configuration. At least the two layers of flexible shell material are in the removal of the core structure in the solid state. If the core structure has a geometry which is not undercut, it is preferably pulled out of the composite of the hollow or the core according to the invention. For an undercut geometry, a core structure of a chemical, thermal (at a temperature T <T _1.3 ) or mechanically releasable material is preferably used. This core structure is removed from the hollow core in the dissolved state. The removal of the core structure is preferably carried out at a temperature T <T ₂ , in particular if the Hüllmateriallagen are not materially connected to each other.

Advantageously, a reusable core is thus produced which has two solid layers of a flexible and tear-resistant wrapping material at a temperature greater than T ₂ and smaller than T _1.3 , between which a layer of flowable core material is arranged. For securely enclosing the molten core material, the skin layers are preferably bonded together so that the core material is completely enclosed and can not escape. Particularly preferably, the Hüllmateriallagen are materially interconnected.

If the enveloping material layers do not completely enclose the core material, the core material can be completely bounded by the enveloping material layers and the inner walls, inlays or side boundaries or clamped side parts of a cavity of a molding tool, in particular mechanically by adhesion. The heating of the core to temperatures higher than T ₂ takes place in this case only in this mold.

The entire hollow core is deformable at temperatures T ₂ <T <T _1.3 and expandable by increasing the internal pressure and collapsible by lowering the internal pressure, whereby the tightness of Hüllmateriallagen is maintained. At temperatures less than T ₂ , the core according to the invention has a layer of solidified and pressure-stable and dimensionally stable core material. The layers of shell material are then largely on the solidified core material.

With solidification of the core material, the core can advantageously be converted into a variety of pressure and dimensionally stable shapes and can advantageously be used in this state as a core for depositing fibers, in particular as a braided core, in the production of fiber composite components. At temperatures above T ₂ , the core can be repeatedly transformed into a complex geometry, in particular into an undercut geometry, and / or be removed from it. By choosing a suitable core structure, the core can already be formed in a complex geometry.

In a particularly preferred embodiment, first and second flexible wrapping material are identical and have a common limit temperature T ₁ = T ₃ . Without limitation, the following only refers to the use of a single flexible wrapping material. The Hüllmateriallagen are preferably made of rubber, latex, polyurethane or silicone and vapor-tight, preferably gasoline and oil-tight and particularly preferably gas-tight and thus have an average leakage rate less than 10 ^-3 Pa · m ³ · s ^-1 , preferably less than 10 ^-5 Pa · m ³ · s ^-1 and more preferably less than 10 ^-7 Pa · m ³ · s ^-1 . The core material used is preferably molding wax, thermoplastic or a low-melting metal alloy, for example Wood's metal or Field's metal.

The flexible shell material is preferably applied in the form of flexible fabrics and / or in the flowable state to the core and / or the core and Hüllmateriallage. With flexible fabrics in particular tear-resistant and flexible films or hoses are referred to. These have an elongation at break of more than 150%, preferably more than 250% and particularly preferably more than 500%. The sheathing of the core structure, the core material and / or the first layer of sheath material is carried out with one or more foil segments, which are materially connected, for example by welding, casting or gluing together.

Alternatively, preferably, the shell material is applied in a flowable state, for example by brushing, spraying, dipping and / or brushing. Particularly preferred is a repeated application of thin layers to produce a Hüllmateriallage. The flowable shell material is solidified by cooling before applying the next core material layer or solidified or polymerized by evaporation of a solvent. The application of flowable shell material is particularly advantageous for core structures of complex geometry. The preferred one Material connection of two successive Hüllmateriallagen is preferably carried out by welding, gluing or by solidification of a flowable shell material on an already solidified shell material (monolithic connection).

The core material layer is preferably applied in the form of at least one solidified element and / or in the flowable state to the underlying flexible Hüllmateriallage. With solidified elements are adapted to the cross-sectional shape of the core adapted or customizable, preferably flat extended elements of core material. These are applied by pressing, whereby preferably an adhesion promoter, for example an adhesive or flowable envelope or core material, is used. Particularly preferably, the application is carried out by brief melting of the elements and pressing until re-solidification. In order to produce a core material layer which completely surrounds at least one cross section, several solidified surface elements must be joined, for example by thermal welding or flowable core material.

Alternatively preferably, the core material is applied in a flowable state, for example by brushing, spraying, dipping and / or brushing. Particularly preferred is a repeated application of thin layers to produce a Kernmateriallage. The flowable core material is solidified before the order of the next Hüllmateriallage. The application of flowable core material is particularly suitable for core structures of complex geometry.

In a preferred embodiment, steps (b) and (c) of the process according to the invention are repeated at least once. Thus, a further layer of core material and a further layer of shell material is applied to the sequence of two layers of casing material and the core material layer arranged therebetween. The further layer of shell material is preferably bonded cohesively to the underlying Hüllmateriallage and closes with this the further layer core material preferably completely, especially if the first two Hüllmateriallagen are cohesively connected to each other. Particularly preferably, the steps (b) and (c) of the method according to the invention are repeated several times, with the layer of second flexible wrapping material alternately followed by further layers of core material and wrapping material. In this case, each core material layer is preferably completely enclosed by the two enveloping material layers which surround it in each case.

Particularly preferably, at least one core material layer in the form of surface elements is applied, which are spaced apart in the axial and / or circumference direction. These surface elements do not complement each other completely to a circumferentially closed core material layer, with at least one completely limited cross section, but have at least one space to each other, more preferably a plurality of intermediate spaces to each other. The spaced-apart surface elements are preferably applied in the form of solidified surface elements made of core material. The intermediate spaces are filled with separating webs, which are formed from a tear-resistant and flexible material of the limit temperature T> T ₂ and close tightly with the Hüllmateriallagen. In particular, the separating webs of wrapping material, which has flowed in the interstices of the surface elements when applying a Hüllmateriallage of flowable wrapping material. The core material is thus available in the molten state from the Hüllmateriallagen and additionally limited by the dividing compartments compartment. Advantageously, this prevents undesired flowing of the molten core material and achieves its uniform distribution within the core material layer. A core with such a segmented core material layer has a uniform pressure stability in the solidified state.

The spaced-apart surface elements of successive core material layers are preferably applied to each other in a transverse and / or longitudinal section in a brick-like manner. If a core material layer of surface elements spaced apart in the axial direction by separating webs is applied, the following core material layer is applied with separating webs which are not aligned in longitudinal section but offset from one another. The partitions are applied in the longitudinal and / or cross-section particularly preferably centrally to surface elements of the underlying core material layer. Advantageously, this brick-like structure results in a core which, in the solidified state, has uniformly high pressure stability over its entire surface. In particular, such a core has no weak points of low cross-section fidelity in the region of the partitions.

In a preferred embodiment of the method according to the invention, a core structure is used which has an outer surface which corresponds at least approximately to the inner surface of a fiber composite component to be produced. The outer contour of the core structure is preferably smaller by approximately the thickness of the reusable core than the inner surface of a fiber composite component to be produced. With this core structure, a reusable core can advantageously be produced which already largely corresponds to the geometry of the fiber composite component to be produced. A transformation of the reusable core in advance of the first fiber deposit is therefore unnecessary. In addition, reusable cores of complex geometry, in particular undercut geometry, and / or changing Cross-sectional shapes can be generated. Cores with such geometry can be produced only to a limited extent with optimal material distribution within the individual layers by forming a, for example. Cylindrically shaped, reusable core.

• a. eine Lage aus einem ersten flexiblen Hüllmaterial der Grenztemperatur T₁,
• b. eine Lage aus Kernmaterial der Ertweichungstemperatur T₂ < T₁ und
• c. einer Lage aus einem zweiten flexiblen Hüllmaterial der Grenztemperatur T₃ > T₂, wobei i. die Hüllmateriallagen mindestens einen Querschnitt vollständig umschließen, iii. der Kern bei Temperaturen T < T₂ druck- und formstabil und bei Temperaturen T₂ < T < T_1,3 expandier- und kollabierbar ist.

Likewise provided by the invention is a reusable core comprising

• a. a layer of a first flexible shell material of the limit temperature T ₁ ,
• b. a layer of core material of the softening temperature T ₂ <T ₁ and
• c. a layer of a second flexible shell material of the boundary temperature T ₃ > T ₂ , wherein i. the cladding material layers completely enclose at least one cross-section, iii. the core at temperatures T <T ₂ pressure and dimensionally stable and at temperatures T ₂ <T <T _{1.3 is} expandable and collapsible.

The core according to the invention is hollow, encloses at least one cross section completely and has an at least three-layered construction. In the radial direction outward follow a layer of a first flexible shell material of the limit temperature T ₁ , a layer of a core material of the softening temperature T ₂ <T ₁ and a layer of a second flexible shell material of the boundary temperature T ₃ > T ₂ each other. The Hüllmateriallagen each enclose at least one cross section completely. At temperatures below its softening temperature, a core material layer is completely disposed between the skin layers.

Preferably, the Hüllmateriallagen are interconnected so that the core material layer can escape from the volume neither in the solid nor in the liquid state that they form surrounding Hüllmateriallagen. Particularly preferably, the Hüllmateriallagen are materially interconnected. Alternatively preferably, the core material is disposed completely between the skin layers but not completely enclosed by them. For example, in a three-layered hollow cylindrical core, wherein on the front sides alternately sheath and core material enters the surface of the core.

At temperatures below T ₂ , the core is pressure and dimensionally stable due to the solidified core material. At temperatures above T ₂ and below T ₁ and T ₃ flowable core material is disposed between the tear-resistant and flexible Hüllmateriallagen. Are the Hüllmateriallagen cohesively connected to each other, the flowable core material is completely enclosed between these. Such a core is deformable at temperatures T ₂ <T <T _1.3 , in particular expandable with an increase in the internal pressure and collapsible while lowering the internal pressure. Alternatively, the flowable core material is completely enclosed between two skin layers and the inner surfaces of a cavity of a mold. Such a core is deformable at least within the cavity of the mold, in particular expandable with an increase in the internal pressure and collapsible with a reduction in the internal pressure.

The shell materials used have an elongation at break of more than 150%, preferably of more than 250% and particularly preferably of more than 500%. Further preferably, the shell materials are tightly opposite the flowable core material, in particular vapor-tight, preferably gasoline and oil-tight, and particularly preferably gas-tight, and particularly preferably have on average a leakage rate of less than 10 -3 Pa. Pa. M 3 .s-1, preferably less than 10. 5 Pa · m3 · s-1 and more preferably less than 10-7 Pa · m3 · s-1. Particularly preferably, the first and the second wrapping material are identical. As the shell material is preferably rubber, latex, polyurethanes or silicone used. The core material used is preferably molding wax, thermoplastic or a low-melting metal alloy, for example Wood's metal or Field's metal.

In a preferred embodiment of the core according to the invention, alternate layers of core material and shell material alternately follow the layer of the second flexible shell material. In each case, two successive Hüllmateriallagen in the radial direction are materially connected to each other and closing at least one Kernmateriallage a complete.

The reusable core according to the invention particularly preferably has at least one core material layer which is formed from surface elements which are spaced apart in the axial and / or circumference direction and which are separated from one another by separating webs. Of the core material layers as a whole, no cross-section is completely enclosed in this case. Rather, the core material layers have individual compartments which, together with the separating webs arranged between the compartments, completely limit a cross section. In this embodiment of the core, flowable core material can not propagate along the entire circumference of the core. Thus, a flow of the core material under the influence of gravity is advantageously avoidable; in particular in surface elements which are spaced apart from each other by dividers extending in the axial direction in the circumferential direction. Further advantageous is a flow of the core material between areas of different cross-sectional shapes or sizes avoidable, especially in surface elements which are spaced apart by extending in the circumferential direction separating partitions in the axial direction. Cores with complex, in particular undercut geometry, and / or changing cross-sectional shapes, particularly advantageously have core material layers of surface elements spaced apart in the axial and in the circumferential direction.

The separating webs arranged between the spaced-apart surface elements in the core material layer are preferably formed of wrapping material and particularly preferably connected in a materially bonded manner to the wrapping material layers. Advantageously, the separating webs have the same mechanical properties as the Hüllmateriallagen, whereby the risk of leakage low and the individual compartments of the core material layers remain completely separated even when expanding the core

Particularly preferably, the surface elements of successive core material layers lie in the transverse direction and / or in the longitudinal section in the radial direction one above the other like a brick. The separating webs in the radial direction of successive core material layers are thus not aligned but offset from one another. Particularly preferably, the separating webs in the longitudinal and / or in the cross section are arranged centrally to the surface elements of the radially following core material layer. A core with brick-like surface elements has at temperatures smaller T ₂ over its entire surface uniformly high pressure stability and shape and cross-section fidelity.

The reusable core is preferably adapted at temperatures smaller than T ₂ to an inner cross-sectional shape of a preform of a fiber composite component to be produced. The adaptation of the cross section is achieved by the use of a correspondingly shaped core element in the manufacture of the core. Alternatively, an already generated, possibly already used for fiber deposition core to a limited extent to the inner cross-sectional shape of a preform of a fiber composite component to be produced adaptable. For this purpose, a core with molten core material layer at temperatures T> T _{2 must be introduced} into a mold and solidified in this and at elevated internal pressure.

• a. durch Faserablage auf einem Kern der Temperatur T < T₂ eine Preform erzeugt wird,
• b. der Kern der Temperatur T < T₂ und die Preform in ein offenes Formwerkzeug eingelegt werden,
• c. das Formwerkzeug geschlossen, evakuiert und die Preform mit einem Matrixwerkstoff konsolidiert wird, wobei i. das Kernmaterial durch Erhöhung der Temperatur über T₂ geschmolzen, ii. der Kern bei einer Temperatur T₂ < T < T_1,3 und erhöhtem Innendruck expandiert und iii. Preform und Matrixmaterial im Formwerkzeug verpresst werden,
• d. der konsolidierte Faserverbundbauteil mit dem Kern aus dem Formwerkzeug entformt und
• e. der Kern bei einer Temperatur T > T₂ von dem Faserverbundbauteil getrennt wird.

Likewise provided by the invention is the use of a reusable core for producing a fiber composite component, wherein

• a. by fiber deposition on a core of temperature T <T ₂ a preform is generated
• b. the core of the temperature T <T ₂ and the preform are placed in an open mold,
• c. closed the mold, evacuated and the preform is consolidated with a matrix material, wherein i. the core material is melted by raising the temperature above T ₂ , ii. the core expands at a temperature T ₂ <T <T _1.3 and increased internal pressure, and iii. Preform and matrix material are pressed in the mold,
• d. the consolidated fiber composite component with the core removed from the mold and
• e. the core is separated from the fiber composite component at a temperature T> T ₂ .

An inventive reusable core of temperature T> T ₂ is used for producing a fiber composite component, in particular a fiber composite component with non-circular cross-section or complex geometry, for example. Undercut geometry. At this temperature, the core is due to the solidified core material advantageous pressure and dimensionally stable to pressures that usually occur in the deposition of reinforcing fibers and the self-weight of the core and fibers. Preferably, the outer cross-sectional shape of the core is adapted to an inner cross-sectional shape of a preform of a fiber composite component to be produced.

The fiber deposition on the pressure-stable and dimensionally stable core is preferably carried out by means of winding, braiding, fiber spraying or by depositing textile fabrics, in particular woven, laid, knitted, knitted, braided or prepregs. With the fiber deposition, a near-net shape preform of the fiber composite component to be produced is preferably produced on the core.

The pressure-stable and dimensionally stable core with the preform deposited thereon is then placed in an open mold. In this case, the molding tool preferably has a cavity with an inner surface which at least approximately corresponds to the outer surface of the preform and particularly preferably connects flush to the open sides of the hollow-shaped core.

The mold is closed, evacuated and the preform consolidated with a suitable matrix material, preferably a thermoplastic or thermosetting plastic or resin. For this purpose, the matrix material is infiltrated into the mold and into the preform. Alternatively, the preform consists of hybrid rovings, fiber-reinforced thermoplastic tapes or organic sheets and the preform contained, preferably thermoplastic, matrix material is softened in the mold, at temperatures T ₂ <T <T _1.3 . During consolidation, the temperature in the mold is increased above T ₂ and below T _1.3 and the internal pressure of the core. Due to the temperature increase, the core material of the core material layer becomes flowable. Due to the increased internal pressure of the core is expanded and acts as an inner pressure bag, the matrix material and preform pressed in the mold. Alternatively, the Expansion of the bubble core by creating a negative pressure in the cavity of the mold. The consolidation temperature of the matrix material used is preferably above T ₂ and below T _1.3 .

By pressing or pressing the matrix material impregnated preform to the inner wall of the mold, the fiber / resin ratio can be adjusted and gas inclusions are removed from the fiber composite. By pressing thus the quality of the fiber composite component to be produced is improved. In addition, the fibers deposited on the core are possibly brought into their final position in the fiber composite component by its widening.

The consolidated fiber composite component is demolded and removed from the mold together with the core. In order to separate the core from the fiber composite component, the internal pressure is lowered while the temperature remains high (T> T ₂ ). Due to lack of stability of the core material layer, the core collapses and can be removed immediately or later from the fiber composite component.

After removal of the core from the fiber composite component and, if appropriate, a cleaning, the core is available for reshaping at elevated temperature, solidification in the pressure-stable state, and for renewed fiber deposition.

The shaping of a core according to the invention takes place with the aid of a molding tool, preferably with the aid of the molding tool used for the consolidation of the fiber composite component.

If the mold used for the consolidation of the fiber composite component is also used for the shaping of the core, its cavity, which is a negative of the fiber composite component to be produced, is reduced by means of inserts. These inserts are at least attached to parts of the inside of the cavity and have a thickness comparable to the thickness of the fiber composite component to be produced. A reusable core is then inserted into the cavity of the mold used for shaping and heated to a temperature greater than T ₂ . Alternatively, a core already heated to such a temperature is placed in the mold. Due to the high temperature, the core material becomes flowable and the core is expandable by increasing the internal pressure of the core. In the expanded state, the core attaches to the inside of the cavity, in the preferred embodiment to the inside of the cavity prepared with the inserts, and receives an outer shape corresponding to its inner shape.

By lowering the temperature below T ₂ , the core is solidified at unchanged high internal pressure in the expanded state and can be easily removed from the mold. The pressure-stable core thus forms a positive of the cavity, in the preferred embodiment of the reduced cavity, and has an outer surface which is adapted to an inner surface of a preform of a fiber composite component to be produced.

Advantageously, with the core according to the invention complex fiber composite components with undercut or non-undercut and circular or non-circular geometry can be produced so that no regular production of a new core is required, in particular no lost cores are needed, but can be used with reusable structures. In addition, it is advantageously achievable with the core to compress the impregnated fibers in the mold by increasing the internal pressure. Thus, high fiber volume content and a reduced pore content in the fiber composite component can be achieved. In addition, the core can be used both as a braided core and as an inner pressure bag for the subsequent resin infiltration.

Advantageously, it is no longer necessary to distinguish which core concept must be followed depending on the geometry of the fiber composite component. Furthermore, cost and production costs can be saved by eliminating the lost cores. In addition, there is the possibility of pressing the fiber structure during consolidation in the mold.

In the following the invention will be explained in more detail with reference to an embodiment and figures, without being limited thereto. Showing:

1 : A schematic representation of the process sequence in the production of a reusable core according to the invention;

2 : The winding core used in the production of the reusable core in a side view and three cross sections along the winding core;

3 : A schematic representation of the process sequence during the shaping of a reusable core according to the invention;

4 : A schematic representation of the process sequence when using a core according to the invention for producing a fiber composite component.

Production of the reusable core

An implementation of the inventive method for producing a reusable pressure and dimensionally stable core according to the invention is in 1 shown. This will be a, in 1 (A) and 2 shown, elongated winding core 1 used, which is rotatable about its longitudinal axis by means of a drive device (M). On the rotating hub 1 becomes a first layer of flexible latex material 2 applied by brush, 1 (B) , Applying the latex 2 takes place at temperatures below its decomposition temperature. After the latex 2 is tied, he forms a gas-tight envelope 2 on the winding core 1 , the lateral surface thereof or at least a circular cross-section of the winding core 1 completely encloses.

On the solidified layer of first flexible wrapping material made of latex 2 Subsequently, solidified elements of core material from molded wax 3 applied, 1 (C) , The Elements 3 are spaced in the circumferential direction and at a temperature below the softening temperature of the mold wax 3 applied. The radially inwardly facing boundary surfaces of the solidified elements 3 however, are at a temperature above the softening temperature of the molded wax 3 briefly melted and on the first layer of flexible shell material 2 pressed. By cooling and solidifying the interfaces of the molded wax elements 3 These adhere to the latex layer 2 at.

In the next, in 1 (D) shown, process step is a second layer of latex as a flexible shell material 2 by brushing and at a temperature below the decomposition temperature of the latex 2 applied. The wrapping material 2 is in the flowable state and thus covers the solidified core material 3 and penetrates into the spaces between the spaced, solidified elements of mold wax 3 one. There the latex solidifies 2 to dividers 4 , the material fit with the first layer and the second layer of flexible shell material 2 , the latter by setting the latex 2 is also solidified, is connected.

On the three-ply core is, as in 1 (E) shown at a temperature below the softening temperature of the molding wax 3 another layer of circumferentially spaced, solidified elements of mold wax core material 3 applied. This is done in turn by partial melting of the inwardly facing interfaces of the solidified elements 3 their pressing against the layer of shell material and adhesion by solidification of the interface core material. As in 1 (F) is shown on the adherent, solidified elements of mold wax 3 another layer of flexible wrapping material 2 applied by brush. The wrapping material 2 is in the flowable state and in turn penetrates into the spaces between the spaced, solidified elements of wax form 3 one. There the latex solidifies 2 to dividers 4 the cohesively with the second layer and the third layer of flexible shell material 2 , the latter by setting the latex 2 is also solidified, is connected.

After setting the third layer of flexible wrapping material 2 will, as in 1 (G) shown, the hub 1 in the axial direction from the five-ply core 11 drawn. This is done at a temperature above the softening temperature of the mold wax, so that a hollow core 11 remains in the expanded, pressure and dimensionally stable state of a cavity 5 includes.

Shaping the reusable core

The outer contour or outer cross-sectional shape of, as in the 1 and 2 shown manufactured core 11 is then in a, in 3 Shaped, shaping method to the inner contour or the outer cross-sectional shape of a preform 13 a fiber composite component to be produced 15 customized.

For this, first, the, in 3 (A) shown, open mold 6 , for the production of the fiber composite component 15 one, whose desired final contour corresponding cavity 7 has, prepared. For this, as in 3 (B) shown, depositors 8th from one at the softening temperature of the molded wax 3 Temperature-stable and pressure-stable material in the cavity 7 inserted. The depositors 8th have a thickness which is the thickness of the fiber composite component to be produced 15 at least approximately.

In the open mold is then an inventive core 10 which is at a temperature above the softening temperature of the molded wax 3 is heated or in the cavity 8th heated to this, inserted. By moving together the tool halves of the open mold 6 and by means of suitable cover plates, the tool 6 . 9 closed, 3 (C). In the closed mold 9 becomes the collapsed core 10 at a temperature above the softening temperature of the molded wax 3 expanded. This is done by increasing the internal pressure by introducing air into the cavity 5 of the core 10 , With further increased internal pressure of the expanded core 11 by lowering the temperature below the solidification temperature of the molding wax 3 solidified and thus converted into a, even without increased internal pressure, pressure and dimensionally stable state, 3 (D) ,

The mold 9 . 6 is then opened and the expanded core 11 as well as the depositors 8th removed from the mold. The in 1 (E) shown expanded core has an outer contour or an outer cross-sectional shape, the inner contour or the inner cross-sectional shape of a preform 13 a fiber composite component to be produced 15 equivalent. The inner contour of the expanded core 11 has a thickness which is around the layer thickness of the fiber composite component to be produced 15 smaller than the inner contour of that component 15 , The wrapping material layers 2 of, in 3 (E) shown, expanded core 11 continue to enclose more than one cross-section completely. Thus, they completely surround a square cross-section along the axes of intersection AA and CC. At the cutting axis BB enclose the Hüllmateriallagen 2 a cuboid cross section completely. The inner envelope material situation 2 thus encloses a cavity 5 Completely. The expanded core 11 also has a between the Hüllmateriallagen 2 arranged nuclear material situation 3 on. The core material layer consists of surface elements which are spaced apart from each other in the circumferential direction, and which are separated by separating webs extending in the axial direction 4 are separated from each other.

Use of the core for producing a fiber composite component As in 4 (A) shown, the so on the inner contour of the preform 13 a fiber composite component to be produced 15 adapted, expanded core 11 subsequently for the production of just such a fiber composite component 15 used. This is the expanded as well as pressure and dimensionally stable core 11 initially at a temperature below the solidification temperature of the mold wax 3 in a radial braiding machine 12 braided and thus a preform 13 on the core 11 stored, 4 (B) ,

core 10 and preform 13 are then in the cavity 7 of the mold 6 inserted and in it after the mold 9 closed with a matrix material 14 infiltrated 4 (C) , The consolidation temperature of the matrix material 14 is above the softening temperature of the core material 3 and below the threshold temperature of the shell material 2 , By the consolidation temperature of the matrix material 14 in the mold 9 is set, becomes the core 10 softens and is by increasing the internal pressure, in particular by feeding compressed air into the cavity 5 , expands, 4 (D) , Thus, the core works 11 as a printing bag, the preform 13 and matrix material 14 pressed together and thus improves the quality of the fiber-matrix composite.

After the preform 13 with the matrix material 14 to the fiber composite component 15 is consolidated, the internal pressure in the cavity 5 at unchanged high temperature in the mold 9 decreased. As a result, the core collapses 10 due to the flowable core material 3 is not dimensionally stable or pressure stable, 4 (E) , Subsequently, the mold 9 . 6 opened and fiber composite component 15 and collapsed core 10 from the cavity 7 taken and the core 10 from the component 15 removed from the mold, 4 (F) After a reshaping, as in 3 shown, is the core 11 again for fiber deposition and production of a fiber composite component 15 , as in 4 shown available.

LIST OF REFERENCE NUMBERS

1

 winding core

2

 flexible wrapping material

3

 nuclear material

4

 dividers

5

 cavity

6

 open mold

7

 cavity

8th

 depositors

9

 closed mold

10

 Core (collapsed)

11

 Core (expanded)

12

 Radialflechtmaschine

13

 preform

14

 matrix material

15

 Fiber composite component

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2368685 A1 [0005]
• WO 2008/086022 A1 [0006]
• US 5262121 A [0006]
• US 2011/0277918 A1 [0006]

Claims (15)

A method of making a reusable core, comprising the following steps a. Applying a layer of a first flexible shell material of the limit temperature T ₁ to a core structure, b. Applying a layer of core material of softening temperature T ₂ <T ₁ to the layer of the first flexible shell material, c. Applying a further layer of a second flexible shell material of the limit temperature T ₃ > T ₂ on the position of the core material, wherein i. the cladding material layers completely enclose at least one cross section of the core structure and ii. The core material is placed completely between the Hüllmateriallagen. A method according to claim 1, characterized in that the flexible shell material is applied in the form of flexible sheets and / or in the flowable state to the core and / or the core material layer. Method according to one of claims 1 and 2, characterized in that the core material layer is applied from at least one solidified element of core material and / or in the flowable state to a layer of a flexible wrapping material. Method according to one of the preceding claims, characterized in that steps (b) and (c) are repeated at least once. Method according to one of the preceding claims, characterized in that at least one core material layer in the form of spaced in the axial and / or circumference direction and separated by separating webs surface elements is applied. Method according to claim 5, characterized in that the surface elements of successive core material layers are applied in a brick-like manner in transverse and / or longitudinal section. Method according to one of the preceding claims, characterized in that the surface of the core structure at least approximately corresponds to the inner surface of a fiber composite component to be produced. Reusable core for producing a fiber composite component, comprising a. a layer of a first flexible shell material of the limit temperature T ₁ , b. a layer of core material of softening temperature T ₂ <T ₁ and c. a layer of a second flexible shell material of the limit temperature T ₃ <T ₂ , characterized i. the cladding material layers completely enclose at least one cross-section and ii. the core at temperatures T <T ₂ pressure and dimensionally stable and at temperatures T ₂ <T <T _{1.3 is} expandable and collapsible. Reusable core according to claim 8, characterized in that alternate layers of core material and of sheath material alternately follow the layer of the second flexible sheath material. Reusable core according to either of Claims 8 and 9, characterized in that at least one core material layer is formed from surface elements which are spaced apart in the axial and / or circumference direction and which are separated by separating webs. Reusable core according to claim 10, characterized in that the separating webs are formed of flexible wrapping material. Reusable core according to claim 11, characterized in that the surface elements of successive core material layers in the transverse and / or longitudinal section lie in the radial direction one above the other like a brick Reusable core according to claim 8, characterized in that the core is adapted at temperatures T <T ₂ to an inner cross-sectional shape of a preform of a fiber composite component to be produced. Use of a reusable core according to any one of claims 8 to 13 for the manufacture of a fiber composite component, wherein a. by fiber deposition on a core of temperature T <T ₂ a preform is generated, b. the core of the temperature T <T ₂ and the preform are placed in an open mold, c. closed the mold, evacuated and the preform is consolidated with a matrix material, wherein i. the core material is melted by raising the temperature above T ₂ , ii. the core expands at a temperature T ₂ <T <T _1.3 and increased internal pressure, and iii. Preform and matrix material are pressed in the mold, d. the consolidated fiber composite component with the core removed from the mold and e. the core is separated from the fiber composite component at a temperature T> T ₂ . Use according to claim 14, characterized in that a. a core is inserted into the cavity of a mold, heated to a temperature T> T ₂ and expanded by increasing the internal pressure of the core, b. the core material is solidified at elevated internal pressure by lowering the temperature below T ₂ as a positive of the cavity and c. a pressure-stable core according to claim 13 is removed from the mold.

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