Sandwich panel with a honeycomb core and method for manufacturing thereof

Abstract

A method for manufacturing an aeronautical sandwich panel with a honeycomb core and results in a core sealed to prevent infused resin from entering into the honeycomb core open cells while improving its mechanical properties, especially for curved or highly curved panels. In further embodiments, the invention proposes the automation of this process.

Claims

1. A method for manufacturing a honeycomb sandwich panel comprising: laying-up an ensemble including a honeycomb core having honeycomb cells, a curable adhesive layer and an amorphous thermoplastic film, wherein the curable adhesive layer and the amorphous thermoplastic film cover entirely at least an upper or lower outer surface of the honeycomb core; laying-up dry fiber on the ensemble; arranging the dry fiber and the ensemble on a one-sided mold; covering the dry fiber and the ensemble on the one-sided mold with a vacuum sheet layer to form a gas-tight space within which is the dry fiber and the ensemble; forming a vacuum in the gas-tight space to at least partially evacuate gas from the honeycomb cells; infusing resin into the at least one fiber layer and the ensemble while in the vacuum, and curing the resin with heat while the at least one fiber layer and the ensemble are subjected to the vacuum, wherein the amorphous thermoplastic film has a degree of crystallinity in a range of zero crystallinity to five percent crystallinity.

2. The method according to claim 1, further comprising at least partially curing the adhesive before the laying-up of the dry fiber on the ensemble.

3. The method according to claim 1, wherein the amorphous thermoplastic film includes top and bottom amorphous thermoplastic films, and the curable adhesive layer includes top and bottom curable adhesive layers, and step of laying-up the ensemble laying-up the top amorphous thermoplastic film and the top curable adhesive layer on an upper outer surface of the honeycomb core, and laying-up the bottom amorphous thermoplastic film and the bottom curable adhesive layer on a lower outer surface of the honeycomb core.

4. The method according to claim 3, further comprising: wherein the step of laying-up the dry fiber includes laying-up a bottom dry fiber layer to a bottom outer surface of the ensemble, and laying-up a top dry fiber layer to an upper outer surface of the ensemble, and the method further includes: applying a first resin infusion mesh to a bottom surface of the bottom dry fiber layer, and applying a second resin infusion mesh to an upper surface of the top dry fiber layer.

5. The method according to claim 3, further comprising: cutting at least one of the curable adhesive layer, the amorphous thermoplastic film and the dry fiber with a computer numerical control machine; positioning on the honeycomb core, the bottom amorphous thermoplastic film, the bottom curable adhesive layer, the top curable adhesive layer and the top amorphous thermoplastic film using a pick-and-place machine; and arranging dry fiber on top, and optionally any auxiliary infusion material, by the pick-and-place machine.

6. The method according to claim 5, further comprising: cutting an auxiliary infusion ply by the computer numerical control machine, and arranging the auxiliary infusion ply on the one-sided mold by the pick-and-place machine.

7. The method according to claim 1, wherein the step of infusing the resin includes infusing the resin through a substantially central inlet in the one-sided mold.

8. The method according to claim 1, wherein the amorphous thermoplastic film is formed of at least one of: Polyvinyl Fluoride (PVF), Polyetherketoneketone (PEKK), Polyaryletherketone (PAEK), Polyether ether ketone (PEEK), Polyethylenimine (PEI) and Polyphenylene sulfide (PPS).

9. The method according to claim 3, further comprising automatically performing a hot membrane forming step to the top dry fiber layer on the ensemble before curing the adhesive layer.

10. A honeycomb sandwich panel manufactured by the method of claim 1, wherein the honeycomb sandwich panel comprises the honeycomb core having honeycomb cells and the curable adhesive layer and the amorphous thermoplastic film covers an entirety of an upper or lower outer surface of the honeycomb core.

11. A method to form a honeycomb sandwich panel comprising: laying-up a bottom curable adhesive layer and a bottom amorphous thermoplastic film to cover entirely an outer bottom surface of a honeycomb core; laying-up a top curable adhesive layer and a top amorphous thermoplastic film to cover entirely an outer top surface of a honeycomb core; bringing together edges of the top and bottom curable adhesive layers and edges of the top and bottom amorphous thermoplastic films entirely around a perimeter region of the edges to fully enclose the honeycomb core, wherein the laying-up of the top and bottom curable adhesive layers, and the laying-up of the top and bottom amorphous thermoplastic film on the honeycomb core form an ensemble; arranging a bottom dry fiber layer on a bottom outer surface of the ensemble; arranging a top dry fiber layer on an upper outer surface of the ensemble; sealing the top and bottom dry fiber layers and the ensemble in an air-tight space formed between a one-sided mold and a vacuum sheet layer; forming a vacuum in the gas-tight space to at least partially evacuate gas from honeycomb cells in the honeycomb core; infusing resin into the top and bottom fiber layers while the top and bottom fiber layers and the ensemble are in the gas-tight space and in the vacuum, and curing the resin with heat while the top and bottom fiber layers and the ensemble are in the gas-tight space and in the vacuum, wherein the top amorphous top thermoplastic film and the bottom amorphous thermoplastic film have a degree of crystallinity in a range of zero crystallinity to five percent crystallinity.

12. The method of claim 11, further comprising: applying a first resin infusion mesh to a bottom surface of the bottom dry fiber layer, and applying a second resin infusion mesh to an upper surface of the top dry fiber layer, wherein the first and second resin infusion meshes are applied before the infusion of the resin.

13. The method of claim 11, wherein the step of infusion of the resin includes infusing the resin through an inlet positioned substantially at a center of an outer surface of the one-sided mold.

Description

SUMMARY OF THE DRAWINGS

(1) These and other characteristics and advantages of the invention will become clearly understood in view of the detailed description of the invention which becomes apparent from a preferred embodiment of the invention, given just as an example and not being limited thereto, with reference to the drawings.

(2) FIG. 1 is a schematic of an ensemble of the honeycomb core covered by amorphous thermoplastic films and curable adhesive layers.

(3) FIG. 2 is a schematic of a honeycomb sandwich panel according to an embodiment of the present invention.

(4) FIG. 3 shows a schematic of an embodiment of a manufacturing tool to form a honeycomb sandwich panel.

DETAILED DESCRIPTION

(5) As it will be appreciated by one skilled in the art, aspects of the present description may be embodied as a method, as features of the resulting sandwich panel or as a manufacturing tooling.

(6) The invention may be embodied as a method for manufacturing a sandwich panel with a honeycomb core (1). The method may comprise, in a basic configuration, the following steps: (i) laying-up an ensemble formed by a honeycomb core (1) having honeycomb cells and, at least on one side on said honeycomb core a curable adhesive layer (2.1) and an amorphous thermoplastic film (3.1); (ii) laying-up a dry fiber (4.1) over the ensemble; (iii) arranging the dry fiber (4.1) and ensemble on a one-sided mold (12) and covering the dry fiber and ensemble with a vacuum sheet(s) (8, 9, 10) to form a gas-tight space between the vacuum sheet(s) and the one-sided mold, wherein the gas-tight space contains the ensemble and dry fiber; (i) producing a vacuum in said gas-tight space before complete or partial curing of the adhesive layer (2.1), to fully or at least partially evacuate the honeycomb cells in the honeycomb core before they are sealed by the curable adhesive layer (2.1) and the amorphous thermoplastic film (3.1); (iv) infusing the fiber layer (4.1) under vacuum with a resin; and (v) curing the resin under vacuum during a temperature cycle.

(7) FIG. 1 depicts an ensemble formed by a honeycomb core (1) having honeycomb cells and, the honeycomb core is entirely covered by bottom (2.1) and top (2.2) curable adhesive layers, and bottom (3.1) and top (3.1) amorphous thermoplastic films. The covering by the curable adhesive layers and the amorphous thermoplastic films covers the top and bottom outer surfaces of the honeycomb core and the outer sides of the core that are between the top and bottom surfaces.

(8) The amorphous thermoplastic films (3.1, 3.2) may have zero crystallinity or a minimal semi-crystalline, i.e. having less than 5% of crystallinity degree. The amorphous thermoplastic films may be formed of one or more of: Polyvinyl Fluoride (PVF), Polyetherketoneketone (PEKK), Polyaryletherketone (PAEK), Polyether ether ketone (PEEK), Polyethylenimine (PEI) and Polyphenylene sulfide (PPS).

(9) The amorphous thermoplastic films (3.1, 3.2) may have a surface treatment to improve adhesion with their respective adhesive layers (2.1, 2.2).

(10) The honeycomb core (1) may be a hexagonal-celled polyamide paper with phenolic resin impregnated. The adhesive films (2.1, 2.2) for composite bonding may be structural epoxy with dual curing temperature of for example in a range of 120° C. to 180° C. for curing.

(11) Either compacted or not, during the process of curing the adhesive layer(s), air extraction from honeycomb core cells is done to avoid air being trapped inside the cells. The honeycomb cells may be at least partly evacuated before they are sealed by the curable adhesive layer (2.1, 2.2) and the amorphous thermoplastic film (3.1, 3.2). Accordingly, certain vacuum level is may be applied to the ensemble at room temperature to achieve air extraction and, then, heat is gradually applied while maintaining such vacuum.

(12) This vacuum level may be at a level below a level that might cause the core to collapse. The appropriate vacuum level may depend on the core geometry, chamfer slope of the core and core density. An exemplary vacuum level for a sandwich panel is typically in a range of 200 to 400 mbar.

(13) The process continues by laying-up the dry fibber plies (4.1, 4.2) over the ensemble which may or may not have been compacted.

(14) The dry fiber plies (4.1, 4.2) may be a dry reinforce type such as glass (for Glass Fiber Reinforcement Polymer, ‘GRFP’), carbon (for Carbon Fiber Reinforcement Polymer, ‘CRFP’), fabric (crimped) or non-crimp fabric (also made of carbon or grass fiber) to be placed on top of the ensemble, i.e. the sealed honeycomb core (1).

(15) FIG. 2 depicts an example of the resulting arrangement with dry fiber plies (4.1, 4.2) below and above the ensemble. In FIG. 2, it can be seen that bottom (4.2) and top (4.1) dry fiber plies follow the contours of the outer surfaces of the honeycomb core, extend beyond the edges of the honeycomb core (1) and are brought together beyond the edges.

(16) These bottom (4.2) and top (4.1) dry fiber plies includes glass plies and/or carbon plies.

(17) Once the ensemble and dry fiber plies are arranged on a one-sided mold (12) they are covered by the vacuum sheet(s) (8, 9, 10) to form a gas-tight space between the sheet(s) and the mold that includes the ensemble and dry fiber plies. A vacuum is applied to the gas-tight space to evacuate air and assist resin flow through the dry fiber plies. To help resin flow easily and reach all areas of the dry fiber plies (4.1, 4.2), a particular temperature is applied during this step, such as a temperature of 120° C. or in a range of 110° C. to 130° C.

(18) Once the resin has properly infused the dry fiber plies (4.1, 4.2), the resin is cured by increasing the temperature according to a particular curing cycle.

(19) According to the present invention, there are two main embodiments for performing the method.

(20) In a first example, all the plies of the honeycomb sandwich panel are laid-up on the one-sided mold (12) and confined by the vacuum sheet (8, 9, 10) to a gas-tight space. Thus, the ensemble, the dry fiber plies and any auxiliary infusion plies are in the gas-tight space and a vacuum is applied and maintained at a level that may be in a range of 200 to 400 mbar for 15 min or another period of, for example, up to 120 min. Next, temperature is raised to a level in a range of 80° C. to 105° C. and the plies are hot formed together for a period such as 15 min or for up to 30 min. Then, temperature is further raised to an adhesive curing temperature, such as 120° C., to cure the adhesive for a period such as two (2) hours. Finally, resin is infused and the temperature is further raised, such as to 180° C., and maintained to cure the resin according to a curing cycle.

(21) In a second example, the method comprises: (i) laying-up the ensemble formed by the honeycomb core (1), curable adhesive layers (2.1, 2.2) and amorphous thermoplastic films (3.1, 3.2); (ii) applying a vacuum and heat to cure the adhesive layers such as at an adhesive curing temperature of 120° C. to seal the honey-comb core; (iii) the dry fiber plies (4.1, 4.2) are laid-up over the ensemble; (iv) raising the temperature on the dry fiber plies and ensemble to, for example 90° C., for membrane hot forming; and (v) infusing resin into the dry fibers and raising the temperature further to, for example, 180° C., to cure the resin.

(22) As mentioned, in this second example, the plies adapt better to the final geometry preventing dry fiber plies from skidding before the resin infusion.

(23) The vacuum may also be applied for a predetermined time between adhesive curing and resin infusion to mitigate the air expansion during the following curing cycle because of the high temperature. The exact time varies depending on core size, density and vacuum level applied previously.

(24) As mentioned, these examples can be automated as follows: cutting all auxiliary infusion plies such as peel ply (5.1, 5.2), perforated release films (6.1, 6.2) and any resin infusion mesh (7.1, 7.2) in a computer numerical control (‘CNC’) machine (15); cutting the dry fiber plies (either CFRP, GFRP, fabrics or Non Crimp Fabrics) (4.1, 4.2), the bottom (2.2) and top (2.1) adhesive films, the bottom (3.2) and top (3.1) amorphous thermoplastic films, and optionally, a copper or bronze foils for lightning strike protection in the CNC machine; using a pick-and-place machine (14) to arrange in the one-sided tool (12), the auxiliary infusion plies underneath the ensemble; using the pick-and-place machine to arrange the bottom dry fiber plies (4.2), and the honeycomb core (1) with both adhesive layers (2.1, 2.2) and both amorphous thermoplastic films (3.1, 3.2); performing a hot membrane forming at 90° C. to adapt these plies, so that the adhesive layers (2.1, 2.2) and thermoplastic films (3.1, 3.2) perfectly adapt to the honeycomb core (1) shape; using the pick-and-place machine to arrange the auxiliary infusion plies on top; curing the adhesive layers at the predetermined adhesive curing temperature in order to seal the honey-comb core; and infusing resin and performing the curing cycle, preferably in an oven.

(25) Otherwise, instead of the oven, the curing cycle can be performed in an autoclave without pressure.

(26) A person of ordinary skill in this art will recognize that the step of sealing the honey-comb core (i.e. curing the adhesive layers as defined by such material) and the step of performing the membrane hot forming may be swapped. Therefore, the basic steps should be: a) hot forming, adhesive curing, resin infusion and curing; or b) adhesive curing, hot forming, resin infusion and curing.

(27) FIG. 3 depicts a schematic embodiment of a manufacturing tool with the resulting arrangement of plies according to an embodiment of the present invention where auxiliary infusion plies are also laid-up.

(28) In the middle of the figure, it is seen the honeycomb core (1) with top (2.1) and bottom (2.2) adhesive layers and top (3.1) and bottom (3.2) amorphous thermoplastic films for the function of sealing and stabilizing the core. For illustrative purposes, it is depicted as a single element with the shape of the honeycomb core (1).

(29) Above and below this sealed honeycomb core, it is seen the dry fiber plies (4.1, 4.2) which extend beyond the edge of the honeycomb core and, thus, are brought together.

(30) Also at both sides, there are auxiliary infusion plies such as, from the inside to the outside: peel plies (5.1, 5.2), perforated release films (6.1, 6.2) and a first (bottom) (7.2) and second (top) (7.1) resin infusion meshes.

(31) Regarding the manufacturing tool for manufacturing a sandwich panel according to the previous embodiments, this manufacturing tool at least comprises: a one-sided mold (12) with a substantially central inlet (12.1) configured to let the resin infuse the dry fiber (4.1, 4.2); and a vacuum sheet (8, 9, 10) configured to be arranged over said one-sided mold (12) for forming a gas-tight space therein.

(32) As known, the vacuum sheet typically comprises a semipermeable membrane (8), an air-weaver (9), and the plastic bag (10).

(33) Also, it has been depicted the sealant tape (11) that let the vacuum sheet (8, 9, 10) form a gas-tight space with the one-sided mold (12). On the left side of FIG. 3, it can be seen the vacuum system (13) to draw the air out of such gas-tight space.

(34) In addition, for exemplary purposes, the expected path of the resin has been drawn by thicker arrows.

(35) While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.