DE102008028864B4 - Adhesive bonding of folded honeycomb cores in sandwich structures, device and use - Google Patents

Abstract

A method of making a sandwich structure (200) having a folded honeycomb core (201), the method comprising the steps of: adding magnetisable particles to an adhesive prior to its application to a honeycomb web (301, 304); Attaching the adhesive in a first region (302) and a second region (309) of the sandwich structure (200); selectively positioning the adhesive in the first region (302) of the sandwich structure (200) about the honeycomb web (301, 304) of the folded honeycomb core (201) such that the adhesive is reduced at the second region (309) of the sandwich structure (200); wherein the targeted positioning of the adhesive in the first region (302) about the honeycomb web (301, 304) is at least partially effected by applying a magnetic field which exerts a force on the magnetizable particles.

Description

The invention relates to sandwich structures. In particular, the invention relates to a method for producing a sandwich structure with a folded honeycomb core, a tool for producing a sandwich structure with a folded honeycomb core, a sandwich structure for an aircraft and an aircraft with a sandwich structure.

Honeycomb cores, honeycomb cores, are currently predominantly used for sandwich structures. These point in the thickness direction, ie in the direction of the cell opening 104 (please refer 1 ), an open structure. Sandwich structures which use honeycomb cores are usually expensive to manufacture and thus expensive.

An alternative offer so-called folding honeycomb. Due to their continuous production process, these folded honeycombs are more economical to manufacture, offer adjustable mechanical properties due to variable folding geometries and have a drainage function running in a sandwich direction.

Although the core material has good tensile properties in the direction of the fiber orientation but less good properties transverse to the fiber orientation (so-called normal stress), the folded honeycomb structure can delaminate at a correspondingly high normal stress. Since an adhesion of folded honeycomb only acts on one side of the core, very high levels of normal forces occur, which often weakens the strength and stability of the connection of the folded honeycomb to the outer laminate layers.

The documents US 7,338,696 B2 . US 3,656,992 A . US 6,099,683 A . US 5,944,935 A describe the production of a sandwich structure by means of an adhesive film for bonding a cover layer to a cell structure.

It is an object of the invention to provide an improved sandwich structure with a folded honeycomb core.

A method for producing a sandwich structure with a folded honeycomb core, a tool for producing a sandwich structure with a folded honeycomb core and use of such a sandwich structure in an aircraft according to the features of the independent claims are given. Further developments of the invention will become apparent from the dependent claims.

The described embodiments relate equally to the manufacturing process, the tool and the use of the sandwich structure.

According to the invention, a method for producing a sandwich structure with a folded honeycomb core according to claim 1 is given. An adhesive is applied in a first area and a second area of the sandwich structure. For example, the adhesive is applied to a honeycomb web of the folded honeycomb core. The adhesive is then positioned in the first region of the sandwich structure about the honeycomb web of the folded honeycomb core so that the adhesive on the second region of the sandwich structure is reduced.

In other words, in a first step, the adhesive is distributed at least on the outer surfaces of the honeycomb webs (which later communicate with the laminate material) and the intervening regions of the folded honeycomb core and then redistributed in a second step, so that the Emphasis collects where it is actually needed most. Of the places where it is not needed, it is deducted or removed.

Also, the adhesive may be applied to the inside of the laminate material prior to bonding the laminate material to the folded honeycomb core.

This can ultimately lead to a weight reduction of the finished sandwich structure, as the use of unnecessary adhesive is avoided.

The accumulation of the adhesive on the webs of the core material increases the strength of the sandwich structure, whereby the amount of adhesive or material used is optimally utilized.

By collecting the adhesive at the junctions between the honeycomb webs and the laminate, undercuts result which result in a positive fit. As a result, the connection of the folded honeycomb core to the cover skin (laminate) can be improved.

According to a further exemplary embodiment of the invention, the first region is a region at which the honeycomb web of the core material adjoins a cover layer of the sandwich structure. The second area is an area on the top layer that lies between two honeycomb webs.

According to a further embodiment of the invention, the adhesive is applied as a strapless adhesive film on the Faltwabenkern, wherein the adhesive film is cut after application to the Faltwabenkern at defined locations to allow the targeted positioning of the adhesive in the first region around the honeycomb web.

The adhesive film is applied, for example, by a roller which presses the adhesive film against the honeycomb webs of the folded honeycomb core. By cutting the adhesive film at selected points is achieved that the adhesive film can nestle against the honeycomb webs.

According to a further embodiment of the invention, the cutting of the adhesive film by means of a laser beam or by means of a blade takes place.

Cutting with a laser beam has the advantage that the cutting tool does not have to be ground and that very fine cuts can be carried out. Furthermore, the control of the laser can be programmed so that different cuts, depending on the used honeycomb structure, can be generated.

According to a further embodiment of the invention, the adhesive film is melted after cutting by means of a hot air flow to the honeycomb web. Due to the hot air flow, it is possible to ensure that the areas of the adhesive film which are loose after the incisions are folded over in the desired direction and thus conform to the honeycomb webs. Then, for example, the Faltwabenkern be turned.

According to claim 1, the adhesive is admixed with a powder of magnetizable particles prior to its application to the honeycomb web (or on the laminate). The targeted positioning of the adhesive in the first region around the honeycomb web is then carried out at least partially by applying a magnetic field which exerts a force on the magnetizable particles.

If the adhesive is a flowing adhesive, the flow of the adhesive may be affected by the magnetic field. If the adhesive is an adhesive film, the folding of the loose areas of the adhesive film after being cut by the magnetic field can be controlled. In this case, no hot air flow is required. Rather, heating is sufficient to melt the adhesive film on the webs.

According to a further exemplary embodiment of the invention, the field profile of the applied magnetic field is adjusted to a profile of the honeycomb web such that adhesive collects by the application of force of the magnetic field to the particles in the first region.

This may be, for example, a static magnetic field whose magnetic field lines are designed accordingly, so that the particles (together with the adhesive) migrate to the first region.

The magnetic field may also be a dynamic magnetic field, which is, for example, electrically changed in order to deflect the particles toward the webs.

For example, the magnetic field may also be generated by a magnet or an array of magnets (eg, permanent magnets), the magnet (s) being moved in a direction perpendicular to the honeycomb web.

In this way, the magnet takes the particles and thus the adhesive, so that an adhesive transport takes place towards the honeycomb web.

According to a further embodiment of the invention, the folded honeycomb core is perforated at a kink before applying the adhesive.

This perforation is done for example by means of a milling cutter or a saw blade. Also, the perforation can be done by means of a laser.

Now when the glue is applied to the webs of the folded honeycomb core, it can flow through the resulting holes to collect in selected areas.

In this way, the stability of the finished sandwich structure can be further increased.

According to a further aspect of the invention, there is provided a tool for manufacturing a sandwich structure with a folded honeycomb core according to claim 11, comprising means for generating a magnetic field for selectively positioning an adhesive in a first region of the sandwich structure about a honeycomb web of the folded honeycomb core. The positioning takes place in such a way that the adhesive is reduced in a second area of the sandwich structure; the field profile of the magnetic field generated by the device is adapted to the course of the honeycomb web, so that the adhesive automatically collects in the first region.

According to a further embodiment of the invention, the device has at least one rod-shaped permanent magnet.

According to a further embodiment of the invention, a sandwich structure for an aircraft is specified, wherein the sandwich structure is produced by the method described above.

According to a further aspect of the invention, the use of a sandwich structure produced by the method just described is specified in an aircraft.

In the following, preferred embodiments of the invention will be described with reference to the figures.

1 shows a schematic representation of a sandwich structure with a honeycomb core.

2 shows a schematic representation of a sandwich structure with a folded honeycomb core according to an embodiment of the invention.

3 shows a schematic cross-sectional view of the sandwich structure of 2 ,

4 shows a schematic cross-sectional view of the sandwich structure of 1 ,

5 shows the glue line of a honeycomb core.

6 shows the glue line of a folded honeycomb.

7 shows a micrograph of a glue seam formation on a honeycomb core.

8th shows a working step of a retraction process honeycomb cores.

9 shows a representation of an incised adhesive film before melting with a hot air film according to an embodiment of the invention.

10 shows an adhesive accumulation on the honeycomb webs of a folded honeycomb after curing according to an embodiment of the invention.

11 shows a tool according to an embodiment of the invention.

12a shows an accumulation of adhesive by the tool of the 11 is caused.

12b shows a further accumulation of adhesive by the tool of the 11 is caused.

13 shows a perforation produced by milling on the honeycomb webs according to an embodiment of the invention.

14 shows a flowchart of a method according to an embodiment of the invention.

15 shows an aircraft according to an embodiment of the invention.

The illustrations in the figures are schematic and not to scale.

In the following description of the figures, the same reference numerals are used for the same or similar elements.

1 shows a schematic representation of a sandwich structure 100 with a honeycomb core 101 , Above and below the core 101 are topcoats 103 . 102 arranged. The core structure 101 and also the core structures of the other figures are usually made of aramid fibers (paper) and a phenolic resin impregnation, especially for aerospace applications. The structure leaves by its open in the thickness direction structure 104 no drainage function within the closed sandwich too.

2 shows a sandwich structure 200 with a folding honeycomb 201 , The arrow 204 shows the direction of cell opening. Again, above and below the Faltwabe 201 facings 203 . 202 provided to form the sandwich structure. The closed in the thickness direction structure (drainage function in the direction 204 ) leaves the adhesive on each side only one - sided access to the core material, which in 3 with the reference numerals 302 . 303 . 306 and 307 is designated.

3 shows the bars 301 . 304 a folded honeycomb, which is between the laminate layers 202 and 203 are arranged. The lamiac layers 202 . 203 are on their insides 309 . 310 wetted with adhesive. The folding honeycomb is only wetted with adhesive on its respective outside. So the folding honeycomb at the top is only in the areas 302 . 303 wetted, but not in the area 305 , Accordingly, the Faltwabe on its underside only in the areas 306 . 307 wetted, but not in the area 308 ,

The one-sided load and the associated high proportion of normal forces that can occur in such a sandwich structure, can lead to a failure of the bond between the phenolic resin and the aramid paper.

4 shows a schematic cross-sectional view of a sandwich structure with a Honeycomb honeycomb. The bridges 401 . 404 The honeycomb honeycomb are adhesive on both sides 402 . 403 . 405 . 406 wetted.

5 shows a glue line of a honeycomb honeycomb.

6 shows the glue lines 601 . 602 . 603 a folding honeycomb of comparable cell size.

Compared with a honeycomb core sandwich structure, the surfaces of the existing glue lines in the folding honeycombs are much smaller than those of normal honeycombs (honeycomb honeycombs) with comparable cell width (see 5 and 6 ). Only along the existing glue lines is there any contact between the core material and the cover layers 202 . 203 possible with the adhesive layer.

As from the comparison of 5 and 6 becomes clear, the surface or the length of the glue lines of the folded honeycomb is significantly lower than that of the Honeycomb honeycomb.

In order to increase the stability of the sandwich structure, the fillet weld seam can be made more pronounced, so that the adhesive surface is increased so that the forces can be better introduced into the core.

7 shows a micrograph of fillet weld formation on a honeycomb core. It is the honeycomb bridge 401 to see that in the adhesive film 701 by means of Kehlnat 402 is embedded. In general, an adhesive film 701 provided with a carrier material. The Kehlnat 402 ensures a connection of the honeycomb bridge 401 to the laminate 102 , The reference number 702 shows the investment used to prepare the sample.

The types of adhesives predominantly used for sandwich components are thermosetting films with a carrier material (eg polyamide fabric). Such adhesive films offer the possibility of keeping the amount of adhesive constant over the entire component surface and thus to provide sufficient adhesive everywhere. Wet areas between the bars are often useless additional weight and are not needed. This is particularly important in the case of folding honeycombs, as the areas affected between the bars are even larger here than in honeycomb structures.

To honeycombs, as in 8th shown to achieve a desired distribution of the adhesive on the honeycomb webs, strapless adhesive films can be used, after which a so-called. Retikulationsverfahren is performed. For this purpose, a hot air stream is passed through the honeycomb. The applied adhesive film is liquefied by the heat and is formed by the air flow to a bubble. With increasing warming, the wall thicknesses of the bubble become thinner and thinner until the bubble 801 gets destroyed. Subsequently, the entire adhesive is applied to the honeycomb webs.

One of the steps of a retraction procedure is in 8th shown. A prerequisite for the functioning of this method is, in addition to the open cells of the core material, a strapless adhesive film 801 that can be melted down. Due to its closed structure, however, this method is not applicable to folding honeycomb.

The folding honeycombs used for the sandwich structure according to the invention can be produced by means of a biaxial embossing plotter (X-Y plotter) which produces the bending edges of the honeycombs. This method offers the possibility of being able to flexibly design the folding geometries of the folding honeycomb. The tool costs are low.

The embossing plotter can also be used to impress small pores into the creases (see 13 ). These should later give the adhesive the opportunity to flow at these points through the honeycomb material and form an undercut after curing. Such a form fit has advantages for the mechanical properties of the sandwich structure.

If, however, a rolling technique is involved in the production of the sandwich structure, it may happen that the pores are closed again by the curing of the phenolic resin, which always has to take place after embossing and "placing" the honeycomb.

In the following three methods for the production of an optimized adhesive connection of folded honeycomb cores in sandwich structures are described, with the help of which the sandwich structures can be produced. The methods described below can also be combined with each other.

Retraction method for folded honeycomb:
The sandwich structure with folded honeycomb core can be created by a combination of carrierless adhesive film, specific cutting of the adhesive film and heating of the adhesive film.

In this case, an adhesive film is applied to the Faltwabenstege. However, the adhesive film has no carrier fleece. The adhesive film is, for example, 3 M Scotch-Weld ^™ AF163-2U Wt.06.

After the adhesive film has been applied to the core material and possibly lightly pressed with the aid of heat (for example by means of a laminating roller), the adhesive film is cut in certain places. The cutting takes place, for example, along the valleys of the folded honeycomb (see 9 ). In this way, the adhesive can be forced to contract.

The cutting takes place for example with the aid of a cutting tool (for example a knife) or by means of laser irradiation. For the further procedure, a distinction is made between the upper side of the laminate and the underside of the laminate, so that an upper and lower adhesive joint are formed.

9 shows a representation of a folded honeycomb structure with an attached adhesive film (for the underside of the sandwich structure) before melting with a Heißluftföhn. The adhesive film 901 is for example at the area 903 cut in, leaving loose areas 902 form the adhesive film, which are not yet supported by the webs of Faltwabe.

Due to the effect of gravity, the adhesive film is cut longitudinally and transversely to the honeycomb on the later underside of the sandwich structure and slightly fused with a Heißluftföhn or blower, so that the adhesive can already largely put on the webs. Now, the prepared core is turned over and applied to the lower cover skin (laminate) of the sandwich structure (see, for example, reference numerals 202 of the 3 ).

Now you can start with the upper gluing. For this purpose, the upper side is first again fitted with an adhesive film and pressed. After re-cutting the film (here only the longitudinal cuts are necessary), it is possible in contrast to the bottom directly to the upper cover skin 203 without having to use a hot air blower, as gravity prevents the loose adhesive film from sticking to the upper cover skin. The curing of the adhesive film is then again using standardized methods. As a result, an up to five times higher peel strength compared to the closed standard film adhesive can be achieved.

10 shows the glue accumulation on the webs 601 . 602 a folded honeycomb after hardening. How out 10 As can be seen, the adhesive film has on the side edges 1001 . 1002 the webs nestled.

Magnetic adhesive:
Another way to position the adhesive on the honeycomb webs is to use magnetic fields. For this purpose, the adhesive magnetic particles, for example in the form of so-called. Nanoferriten be mixed, which make the adhesive magnetizable. The nanoferrites may be Magsilica particles from Degussa. But there are also other particles from other manufacturers usable.

In order to achieve sufficient magnetizability, the adhesive is mixed with two to fifteen percent by weight. The weight ratio depends, for example, on the viscosity of the adhesive. The thinner a resin (adhesive) is, the fewer nanoferrites are needed to move the adhesive. With increasing ferrite content, the forces acting on the adhesive also increase. In addition, the filler content also has an influence on the viscosity. The viscosity also increases with the proportion of the filler. Depending on the application, other percentages by weight of the particles are admixed in order to set the optimum of increasing force and decreasing mobility (ie increasing viscosity).

The prepared adhesive can now be applied evenly to the cover skin. This can be done by means of rolling or doctoring. After placing the folding honeycomb a special tool for distributing the adhesive is used.

11 shows a schematic representation of the tool according to an embodiment of the invention. The tool 1100 includes magnetic tracks 1101 . 1102 . 1103 , which correspond to the zigzag shape of the folds of the folding honeycomb (see 6 ) are arranged. The magnetic paths are formed, for example, in each case by the poles of a corresponding bar magnet. Now, if the sandwich component is placed on the tool and the tool is aligned so that the magnetic field lines can act on the kinks, the adhesive can be accumulated at the kinks where it is needed. Furthermore, the tool has a frame with a holding area 1104 on, which serves to guide the tool.

In other words, the adhesive is transported through the magnetic field. The magnetic fields can be generated by one or more permanent magnets or by an electromagnet (or a combination of permanent and electromagnets).

In a simple embodiment, the tool has only a single linear magnet or bar magnet, which is pulled along under the sandwich structure. For example, the magnet is parallel to the drainage direction (see arrow 204 of the 2 ) and is moved perpendicular to the drainage direction. By moving the magnet, the adhesive is collected according to the field lines and pulled along. When hitting the continuous honeycomb web, the adhesive remains at the point of impact, so that then forms a fillet weld. On the other side of the bridge, the process begins again.

In this way, for example, an accumulation of adhesive on each side of the webs done. An advantage of this method lies in the production of semi-finished products in a continuous production process.

The 12a and 12b show accumulations of glue 1201 and 1202 , which are caused by the magnetic forces of such a tool.

Perforated honeycomb webs:
In particular, this method can be combined with the two aforementioned methods. It is introduced with a cutter having a diameter of, for example, 0.5 to 1 mm, a perforation in the bending point of the folded honeycomb.

13 shows such a perforation produced by milling at the honeycomb webs 601 , The honeycomb webs 601 have perforation holes on their tops and bottoms 1301 . 1302 or perforation slots.

The same effect can be achieved by a saw blade of appropriate thickness. Depending on the viscosity of the adhesive, the depth and the width of the cut, an undercut forms after the adhesive has set. Such a positive fit, similar to a zipper, can significantly increase the strength of the finished sandwich structure.

14 shows a flowchart of a method according to an embodiment of the invention. In step 1 Adhesive is applied to the honeycomb webs of a folded honeycomb core. In step 2 In the areas where the honeycomb webs contact the laminate cover layers, the adhesive is collected and removed from the areas where it is not needed.

In step 3 the adhesive is then cured.

The targeted positioning of the adhesive after application, for example, by a combination of magnetic force exerted on particles contained in adhesive and the guidance of the accumulated adhesive through appropriate perforations.

15 shows an aircraft 1500 with sandwich structures according to an embodiment of the invention. The aircraft is a passenger aircraft. The sandwich structures 1501 For example, they are used to reinforce the hull.

In addition, it should be noted that "comprising" and "having" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. It should also be appreciated that features or steps described with reference to any of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be considered as limitations.

Claims (13)

Process for producing a sandwich structure ( 200 ) with a folded honeycomb core ( 201 ), the method comprising the steps of: admixing magnetisable particles to an adhesive prior to its application to a honeycomb web ( 301 . 304 ); Attaching the adhesive in a first area ( 302 ) and a second area ( 309 ) of the sandwich structure ( 200 ); targeted positioning of the adhesive in the first area ( 302 ) of the sandwich structure ( 200 ) around the honeycomb bridge ( 301 . 304 ) of the folded honeycomb core ( 201 ), so that the adhesive on the second area ( 309 ) of the sandwich structure ( 200 ) is reduced; wherein the targeted positioning of the adhesive in the first area ( 302 ) around the honeycomb bridge ( 301 . 304 ) at least partially by applying a magnetic field which exerts a force on the magnetizable particles. The method of claim 1, wherein the first region ( 302 ) is an area where the honeycomb bridge ( 301 ) of the core material to a cover layer ( 202 . 203 ) of the sandwich structure ( 200 ) connects; where the second area ( 309 ) around an area on the cover layer ( 202 . 203 ) between two honeycomb webs ( 301 . 304 ) lies. The method of claim 1 or 2, wherein the adhesive as a carrier-less adhesive film on the Faltwabenkern ( 201 ) is applied; wherein the adhesive film after application to the Faltwabenkern ( 201 ) at defined locations ( 903 ) is cut to prevent the positioning of the adhesive in the first area ( 302 ) around the honeycomb bridge ( 301 . 304 ). The method of claim 3, wherein the cutting of the adhesive film by means of a laser beam. Method according to one of the preceding claims, wherein the adhesive film after cutting by means of a hot air flow at the honeycomb web ( 301 . 304 ) is melted. Method according to one of the preceding claims; wherein a field profile of the applied magnetic field so on a course of the honeycomb web ( 301 . 304 ) is adapted by the application of force of the magnetic field to the particles in the first area ( 302 ) collects. Method according to one of the preceding claims, wherein the magnetic field is controlled by a magnet ( 1101 . 1102 . 1103 ) which is in a direction perpendicular to the honeycomb web (FIG. 301 . 304 ) is moved. Method according to one of the preceding claims, further comprising the step: perforating the folded honeycomb core ( 201 ) at a kink before applying the adhesive. A method according to claim 8, wherein the perforation is by a mill or a saw blade. Method according to one of the preceding claims, wherein the sandwich structure ( 200 ) is intended for use in an aircraft. Tool ( 1100 ) for producing a sandwich structure ( 200 ) with a folded honeycomb core ( 201 ), the tool comprising: a device ( 1101 . 1102 . 1103 ) for generating a magnetic field for the targeted positioning of an adhesive in a first region ( 302 ) of the sandwich structure ( 200 ) around a honeycomb bridge ( 301 . 304 ) of the folded honeycomb core ( 201 ), so that the adhesive on a second area ( 309 ) of the sandwich structure ( 200 ) is reduced; wherein a field profile of the magnetic field generated by the device so on a course of the honeycomb web ( 301 . 304 ) is adapted by the application of force of the magnetic field to the particles in the first area ( 302 ) collects. Tool according to claim 11, wherein the device comprises a rod-shaped permanent magnet ( 1101 . 1102 . 1103 ) having. Use of a sandwich structure ( 200 ) manufactured by a method according to any one of claims 1 to 10 in an aircraft.

Images