DE102006056353B3 - Lightweight honeycomb panel core for manufacture of e.g. interior cabin panels in large commercial aircraft - Google Patents

Abstract

Claimed is a process to manufacture the honeycomb core of a lightweight panel that is subsequently sandwiched between two outer layers. In a first stage a web of material is prepared that is rigid at room temperature and softens to facilitate bending at a pre-determined temperature. The web incorporates lines of wire that heat when connected to an electrical current and facilitate folding to e.g. a zigzag profile that is retained upon subsequent cooling.

Description

The The present invention relates to a method for producing a Fold honeycomb structure for a core composite and a foldable sheet material.

Even though Applicable to any folding structures, the present invention as well as the underlying problem with respect to folded Core structures for Core associations in aircraft construction closer explained.

by virtue of their good relationship from stiffness and strength to density find in the field of aircraft construction Composite materials and in particular so-called core composites one wide scope.

core composites generally have an upper and a lower cover layer, between those to increase the stiffness, for example, a vertically extending cells is located with hexagonal cross-section core structure.

A others, especially for the application in double-shell aircraft fuselages suitable core structure variant are core structures folded from flat semi-finished products. A special The advantage of these structures is that they are made of all flat foldable materials with low energy consumption and repetitive patterns also a light, bulge-free, drainage-capable, sound-insulating and endless folding the core adapted to the mechanical loads for a core composite leaves.

Of the Manufacturing process of honeycomb structures must be sufficient Accuracy to allow for easy later processing. In addition to the required precision Economical production is a second important criterion. In different conventional Procedure is a sheet to be folded with punches or by embedding between with formative struts provided Membranes in the desired Convolution form brought. Other methods see a pretreatment to weaken of the sheet material along the desired Folding lines. A common feature of these methods is that the Faltwabenstrukturen after the folding process is not sufficient inherent stability so it is necessary to have the folded honeycomb structures during further Procedural steps such as stabilization by coating or impregnating with resin and subsequent heat treatment for curing through mechanical fits, mounts and the like. This leads to high Production costs and in particular makes the production of Folding honeycomb in a continuous process.

It is therefore an object of the present invention, a production method for folded honeycomb structures to create that with a high dimensional accuracy of the folded honeycomb structure low production costs, and in particular a continuous production of the folded honeycomb structures allows.

According to the invention this Task by a method for producing a folded honeycomb structure for one Core composite with the features of claim 1, and by a foldable sheet material solved with the features of claim 12.

The The idea underlying the present invention is that a flat sheet material to be folded along predetermined fold lines locally in the area of fold lines is heated to this way along the desired Folded edges create locally softened zones that are in the manner of hinges between the non-softened areas bounded by the fold lines thus allowing the folded honeycomb structure to have minimal impact mechanical guidance in the desired shape to fold. For this purpose, a sheet material is provided, having a softening temperature, i. a material that softens when it is at or above a certain temperature, the softening temperature of the material is heated. Local heating takes place such that while the folding process, the local temperature of the surface material in the Folding lines equal to or higher as the softening temperature of the sheet is the local Temperature of the sheet material in the limited by the fold lines surface areas but below the softening temperature of the sheet material lies.

Under In another aspect, the invention provides a foldable surface material with a fiber material ready, in particular for use in the method provided, wherein at or below a surface of the surface material electrical conductor tracks run. The tracks are like that arranged that when folding the sheet material along the conductor tracks one from the two-dimensional initial shape of the sheet material results in a third dimension extending honeycomb structure.

In the dependent claims find advantageous embodiments and improvements of Invention.

According to a preferred embodiment, it is further provided to cool the folded honeycomb structure folded from the locally heated sheet material below the softening temperature. As a result, the softening in the area of the folded edges resulting from the folding lines of the fold Undone honeycomb structure, so that the Faltwabenstruktur is stabilized. In particular, it is possible to dispense with a further processing of the folded honeycomb structure on a mechanical support or to remove an optionally used for folding mechanical guide after cooling. This thus considerably simplified further processing makes it possible to reduce the manufacturing costs of the core structure.

According to one preferred embodiment of the invention, the local heating in the Realized area of the fold lines by means of electrical conductors, the along the predetermined fold lines in or on the sheet material be formed. This happens as part of the deployment of the sheet material. To initiate the folding process, the desired local softening of the Surface material is brought about electrical current passed through the tracks. As a result of that the printed conductors are formed on the flat sheet material, can be for this inexpensive and precise Apply procedure.

According to one preferred development are the electrical conductors in or on the surface material produced by printing with an electrically conductive substance. Similar Printing processes are used in other fields of technology, such as e.g. of the Production of printed circuit boards in electronics or used by rear window heaters in automotive engineering, so that cost-effective resorted to appropriate techniques can be. This development allows for particularly advantageous Way the formation of printed conductors in sheet materials with a smooth surface. Prefers printing is done with an electrically conductive paste, such as e.g. one Silver paste.

According to one Alternative training will be the electrical conductors by incorporating electrically conductive Threads in formed the sheet material. This training allows in a particularly advantageous manner, the formation of conductor tracks in sheet materials, which contain a loose fiber structure such as a woven fabric or fiber or have no surface suitable for printing. Preferably are the conductive ones Threads around Carbon filaments, because these are very cost effective are and have a suitable electrical resistivity.

According to one preferred embodiment of the invention is the sheet material based on a thin, areally extended fiber semifinished product provided with a Resin, such as e.g. Phenolic resin, impregnated or coated. The resulting fiber matrix material with resin matrix gives the folded honeycomb structure a particularly high stability. simultaneously is enabled the mechanical cohesion of the heated state as hinges to increase effective folding lines, as appropriate way Select fiber material and resin so let only the resin matrix soften, while the Fiber material maintains its tensile strength unchanged.

Preferably In this case, the formation of the electrical conductor tracks takes place in front of the Impregnate or Coating of the fiber semifinished product. This has the advantage that the trace comes to rest inside the resin matrix, so good protected is and the sheet material in the area of the fold lines can heat evenly on both sides. Farther is advantageously possible e.g. when using a paper as a fibrous material of it especially easy printability to use and so especially inexpensive Printing method such as e.g. Apply rotary pressure.

According to one preferred development is also a partial networking of the resin by a heat treatment of the impregnated or coated fiber semi-finished product, whereby the sheet material is provided as a thermoset system in a partially crosslinked state. Increased by networking the stability of the surface material so far that the locally unheated areas during the folding process between the softened fold lines without mechanical support e.g. can erect through a mold. At the same time, the crosslinking ensures that the resin on the surface of the surface material no longer sticky. Both effects allow a particularly simple and cost-effective Production of the folded honeycomb structure.

Thereby, on the other hand, networking only takes place in part possible, the sheet material as a thermoset system in the partially crosslinked state by heating to soften a temperature above a softening temperature again. stability as well as softening temperature hang thereby the degree of crosslinking, which is adjusted according to the requirements of the manufacturing process can be. Preferably, the partial crosslinking of the resin takes place up to a degree of crosslinking of 50% -60%.

According to one preferred development is the folding of the sheet material subjected folded honeycomb structure of a second heat treatment during which the degree of crosslinking of the resin is further increased. Preferably doing a much more complete Crosslinking achieved with a degree of crosslinking close to 100. This is advantageous, since so a maximum stability of the thermoset system is reached.

During the heat treatment increases in typical thermoset systems, in addition to the degree of crosslinking, also the softening temperature characterizing the system. Preferably, in the second heat treatment, the temperature of the folded sheet material is always kept below the actual softening temperature of the folded sheet material.

Thereby prevents the folded honeycomb structure at the fold edges or softened in other areas, which allows a deployment or deformation the folding honeycomb structure during the heat treatment to prevent without a mechanical support of the folded form would be required. This is particularly advantageous because a much simplified manufacturing process is possible.

The Invention will be described below with reference to exemplary embodiments with reference explained in more detail on the accompanying figures of the drawing.

From show the figures:

1A an oblique perspective view of an example of a folded honeycomb structure for a core composite;

1B a cross-sectional view of a core composite with the Faltwabenstruktur from 1A ;

2 a plan view of a foldable sheet material according to an embodiment of the invention, for producing the folded honeycomb structure in 1A ;

3A a cross-sectional view of a section of the sheet material 2 ;

3B a cross-sectional view of a section of a s foldable sheet material according to another embodiment of the invention; and

4 a flow diagram of a method for producing a folded honeycomb structure according to an embodiment of the invention.

In In the figures, the same reference numerals designate the same or the same function Components, unless stated otherwise.

1A shows in perspective perspective view an example of a folded honeycomb structure, as used in the manufacture of core composites. The folded honeycomb structure shown has folded edges 104 . 110 on, which emerge from the fold lines in the folding of a flat starting material along predetermined fold lines. In the illustration at the top of the Faltwabenstruktur seen, extending in zigzag upper fold edges 104 clamp in the folded state an imaginary upper boundary plane of the folded honeycomb structure, while correspondingly extending in zigzag form on the underside of the Faltwabenstruktur lower folding edges 110 span an imaginary lower bounding plane parallel to the upper bounding plane. However, the folded edges of folded honeycomb structures for core composites can also be defined in other, in principle arbitrarily designed boundary surfaces, such as wedge-like inclined planes, curved or irregularly shaped surfaces.

1B shows a cross-sectional view of a core composite 102 who has a honeycomb structure 100 like the in 1A contains shown. The folded honeycomb structure 100 is between an upper 106 and a lower one 108 Covering included. the upper fold edges 104 on the upper cover layer 106 and the lower fold edges 110 attached to the lower cover layer.

2 shows a plan view of a foldable sheet material 200 , which according to an embodiment of the invention for producing a folded honeycomb structure as in 1A shown is used. The sheet lies as one on a roll 204 wound web with defined width w and undefined length, which allows the production of a folded honeycomb structure also defined width and undefined length in a continuous process. Alternatively, it is also possible to use individual sheets of the sheet material 200 with a defined length and width, for example in a discontinuous production process of folded honeycomb structures with likewise defined length and width.

On the surface material 200 you can see a pattern of electrical tracks 202 passing along predetermined fold lines at which it is intended to fold the sheet material to form the folded honeycomb structure.

3A shows a cross-sectional view of a section of the sheet material 2 to explain the composition and structure of the sheet material. The core of the sheet material 200 forms a sheet-like expanded fiber material 304 such as an aramid fiber based paper. On one surface of the paper is an electrically conductive substance 300 such as applied a conductive paste, which is the conductor shown here in cross section 202 forms.

To increase stability, the paper is made with a resin 308 , such as phenolic resin coated or soaked so that the paper is embedded in a matrix of resin. By a subsequent heat treatment, the resin matrix is in a partially crosslinked state, whereby stability and rigidity of the sheet material are further increased. However, since the crosslinking is incomplete, the sheet material has a softening temperature, ie it is possible to bring the sheet material back into a soft, deformable state by deliberately heating to at least the softening temperature.

3B shows a cross-sectional view of a section of a foldable sheet material according to a further alternative embodiment of the invention. As a fiber material is here instead of a paper a scrim or web of fibers 306 For example, aramid fibers or glass fibers used in a partially crosslinked resin matrix 308 are embedded.

The trace shown 202 is here by embedded, electrically conductive fibers such as carbon fibers 202 executed. The different features of the embodiments of 3A and 3B can also be combined differently. For example, the carbon fibers 302 also lie on the surface of the fiber material and / or with the in 3A paper used together.

4 FIG. 12 shows a flowchart of a method for producing a folded honeycomb structure according to an embodiment of the invention. The method shown comprises nine steps 400 - 414 of which the first five steps 400 - 407 providing 416 serve a surface material, as for example in the 2 to 3A shown and explained above.

To deploy 416 of the sheet material is first in step 400 a thin, sheet-like semi-finished extended fiber material provided to be adopted in the exemplary embodiment described here as an aramid fiber such as Kevlar ^® / N636 or Kevlar ^® / N637.

With the steps 402 and 404 On the surface of the paper electrical conductor tracks are formed such that they follow the course of predetermined fold lines at which the sheet material is to be folded to form the folded honeycomb structure. This will be done first in step 402 the paper in the area of the intended tracks printed with a conductive paste. Suitable pastes are used, for example, in the manufacture of printed circuit boards and usually contain a metal component and a binder component. The printing can be done by screen printing, rotary printing and other suitable methods.

Since a commonly used conductive pastes Ein Brand is required in step 404 the conductive paste is baked by heating the printed fibrous semifinished product to the required baking temperature. Conveniently, the in step 402 used conductive paste so that the baking temperature is lower than the maximum tolerated by the paper limit temperature, for example, lower than 250 ° C.

In step 406 the paper is coated with phenolic resin, which can be done by dipping or brushing, for example. This increases the stiffness of the paper. In step 407 a partial crosslinking of the phenolic resin takes place by a first heat treatment of the coated paper. This further increases the stiffness of the paper. At the same time, the resin-coated surface of the paper loses its stickiness, which facilitates further processing. The duration and temperature of the heat treatment is chosen so that a degree of crosslinking results with the desired properties (eg 50% -60%), but at the same time it remains possible to soften the surface material by targeted heating to or above its softening temperature again.

This is the provision 416 completed the surface material. The following steps can be immediately followed, eg in the form of a continuous manufacturing process. On the other hand, it is possible to produce the sheet in the manner described in one place and to bring to carry out the following steps to another location, for example as a stack of individual sheets or in the form of rolled tracks of undefined length.

In step 408 electrical current is conducted through the conductive tracks of the sheet material so that it heats up in a limited area on and around the printed conductors. For this purpose, for example, the traces can be contacted at the edge of the paper by metal brushes, staples or needles, which optionally penetrate when running inside the WING chenmaterials interconnects the outer layer of the paper. The strength and time course of the electrical current are expediently chosen such that in the immediate vicinity of the conductor tracks a defined softening of the surface material results by heating to at least the softening temperature.

In step 410 a folding of the sheet material is initiated, for example, by the action of lateral forces. Since the temperature of the sheet material in the sheet-like regions between the strip conductors lies below the softening temperature, the sheet material remains rigid in these regions, while it softens in the line-like regions around the strip conductors. As a result, the areas around the tracks act as hinges, so that the folding geometry is predetermined and the sheet material can easily fold into the Faltwabenstruktur with appropriate guidance.

In step 412 the electric current is switched off while the folded honeycomb structure is held in the folded form by suitable guidance. As a result, the areas around the tracks cool to a temperature below the softening temperature. Thus, the areas around the tracks lose their hinge effect and stabilize the folding honeycomb so far that the guide can be removed.

In step 414 For example, the folded honeycomb structure stabilized in this way is subjected to a second heat treatment as a whole, for example by introducing it into an oven. During the heat treatment, the temperature is always kept below the softening temperature of the material of the folded honeycomb structure in order to prevent the folded honeycomb structure from softening and re-unfolding in the absence of a guide. As a result of the heat treatment, the phenolic resin matrix of the folded honeycomb structure gradually cures, whereby at the same time the softening temperature continuously increases. Therefore, to complete the heat treatment as quickly as possible, it is therefore expedient to always leave the temperature in the oven just below the softening temperature and to increase continuously with this. This can happen, for example, in a tunnel oven with a temperature profile rising toward the exit, through which the folded honeycomb structure is guided.

Even though the present invention with reference to preferred embodiments has been described herein, it is not limited thereto, but on diverse Modifiable way.

For example Is it possible, Printed conductors of the type described on thermoplastic materials to provide, wherein the thermoplastic materials by cooling the locally heated Areas are stabilized.

Also can other composites including carbon fiber reinforced plastics be used. Tracks can with appropriate insulation in or on electrically conductive surface materials be formed.

The local warming along the fold lines can be effected by other means such as. an irradiation with laser light, or a touch contact with a contact surface inhomogeneously heated in a corresponding pattern, e.g. a film or roller, embedded in the electrical conductor tracks are.

100

Faltwabenstruktur

102

sandwich

104

Upper folding

106

Upper topsheet

108

Lower topsheet

110

Lower folding

200

surface material

202

electrical conductor tracks

204

role

300

electrical conductive Substance (conductive paste)

302

electrical conductive Threads (carbon threads)

304

paper

306

fiber fabrics

308

resin

400

Provide a fiber material semi-finished product

402

Form electrical conductors

406

Impregnate or coating

407

First Heat treatment for partial networking

408

local Heat

410

wrinkles

412

cooling down

414

Second Heat treatment to the full network

416

Provide of a sheet material

Claims (12)

Method of producing a folded honeycomb structure ( 100 ) for a core network ( 102 ), with the steps: Deploy ( 416 ) of a sheet material ( 200 ) having a softening temperature; local heating ( 408 ) of the sheet in the range of predetermined fold lines to at least the softening temperature; and wrinkles ( 410 ) of the sheet material along the heated area of the fold lines in the folded honeycomb structure. Method according to claim 1, characterized in that the following further step is provided: cooling ( 412 ) of the folded honeycomb structure ( 100 ) below the softening temperature. Method according to claim 1 or 2, characterized in that the providing ( 416 ) of the sheet material ( 200 ) comprises the following sub-step: training ( 402 ) electrical conductors ( 202 ) in or on the sheet material ( 200 ) along the predetermined fold lines; where local heating ( 408 ) is carried out by passing an electrical current through the conductor tracks. Method according to claim 3, characterized in that the forming ( 402 ) of the electrical Tracks ( 202 ) by printing with an electrically conductive substance ( 300 ), and in particular an electrically conductive paste ( 300 ) he follows. Method according to claim 3, characterized in that the forming ( 402 ) of the electrical conductors ( 202 ) by incorporating electrically conductive threads ( 302 ), and in particular of carbon filaments ( 302 ), into the surface material ( 200 ) he follows. Method according to at least one of claims 3 to 5, characterized in that the providing ( 416 ) of the sheet material ( 200 ) further comprises the following sub-steps: providing ( 400 ) of a thin, sheet-like expanded fiber semifinished product ( 304 . 306 ); and impregnating or coating ( 406 ) of the semifinished fiber material with a resin ( 308 ). A method according to claim 6, characterized in that the formation of the electrical conductor tracks ( 202 ) before impregnation or coating ( 406 ) of the semifinished fiber material ( 304 . 306 ) he follows. Method according to claim 6 or 7, characterized in that the provision of the sheet material ( 200 ) further comprises the following substep: partial crosslinking of the resin ( 308 ) by a first heat treatment ( 407 ) of the impregnated or coated semifinished fiber material. Method according to claim 8, characterized in that the partial crosslinking ( 407 ) of the resin ( 308 ) is carried out to a degree of crosslinking of 50% -60%. A method according to claim 9, characterized in that the following further step is provided: substantially complete crosslinking of the resin ( 308 ) by a second heat treatment ( 414 ) of the folded honeycomb structure ( 100 ). A method according to claim 10, characterized in that in the second heat treatment ( 414 ) the temperature of the folded sheet material is always below a current softening temperature of the folded sheet material. Foldable sheet material ( 200 ), in particular for use in a method of claims 1 to 11, with a fiber material ( 304 . 306 ); and electrical conductors ( 202 ) extending at or below a surface of the sheet material; wherein the conductor tracks are arranged such that when folded ( 410 ) of the sheet material along the strip conductors, a folded honeycomb structure extending from the two-dimensional initial shape of the flat material into a third dimension ( 100 ).