Method for the preparation of composite material in sandwich form

Abstract

The object of the invention can be a method of manufacturing a product in the form of a sandwich comprising a core and outer layers. The outer layers may be composed of composite material comprising a fiber-reinforced polymeric matrix. The method uses an insert of heat-resistant material, for example silicone. The object of this invention can be to provide a method of manufacturing a sandwich that dissociates the choice of material of the core of the sandwich from the choice of the material of the outer layers.

Claims

1. A method of manufacturing a sandwich-shaped composite material product wherein the sandwich-shaped composite material product comprises two outer layers and a core, the outer layers having a matrix of fiber-reinforced polymeric material, the polymeric material having a melting point below the melting point of the material constituting the fibers; wherein the method is characterized in that it uses an insert consisting of material having a melting point higher than the melting point of the polymeric material, on which the outer layers are consolidated; wherein this insert is subsequently replaced by the core of the sandwich-shaped composite material product to form an assembly, the assembly then undergoing a consolidation treatment for bonding the outer layers to the core; and wherein the method is further characterized in that it comprises the following steps: production of preforms composed of the fiber-reinforced polymeric material intended to become the outer lavers of the sandwich-shaped composite material product, juxtaposition, in a mold, of a first preform of the preforms, of the insert, and of a second preform of the preforms, consolidation of the preforms to obtain the outer layers, by heating and pressurizing, to reach the temperature of the melting point of the polymeric material, without reaching the temperature of the melting point of the reinforcing material or the material of the insert, removal of the insert, separation of the outer layers and insertion of the core of the sandwich-shaped composite material product, heat treatment to adhere the outer layers to the core, cooling of the product thus obtained.

2. The method according to claim 1, characterized in that the preforms are made using pre-impregnated polymer resin fabrics.

3. The method according to claim 1, characterized in that the preforms are made by knitting a yarn comprising the reinforcing material and the polymeric material.

4. The method according to claim 1, characterized in that a peel layer is added between the preforms, at places intended to form a zone without a core.

5. The method according to claim 1, characterized in that the insert is made of silicone.

6. The method according to claim 1, characterized in that the reinforcing material is chosen from glass, carbon and aramid fibers.

7. The method according to claim 1, characterized in that the polymeric material is of the thermoplastic type chosen from polycarbonate (PC), and polyetherimide (PEI), polypropylene (PP), poly(ethylene terephthalate) (PET), and polyether ether ketone (PEEK).

8. The method according to claim 1, characterized in that the polymeric a material is of the thermosetting type chosen from epoxy, cyanate ester, phenolic resins and polyester.

9. The method according to claim 1, characterized in that the core of the sandwich-shaped composite material consists product of cellular honeycomb material.

10. The method according to claim 1, characterized in that the thickness of the core is at least about 2 mm and not greater than about 50 mm.

11. The method according to claim 1, characterized in that the thickness of each of the outer layers is at least about 0.2 mm and not greater than about 5 mm.

Description

EXAMPLES

Example 1

(1) Several “prepreg” cyanate ester impregnated carbon fiber fabrics are draped in a steel mold to form the first skin of the sandwich.

(2) A rigid insert (for example a Teflon® block of a few millimeters) is deposited on the fabrics.

(3) The second skin of the sandwich is made by draping several “prepreg” fabrics on the rigid insert.

(4) Teflon-coated peel ply (PTFE-coated glass fibers) is placed at the junction between the two skins. The junction is the area where the skins join to cover the field of the core.

(5) The mold is closed by a flexible counter-mold.

(6) The skins are consolidated by heat treatment under vacuum at about 180-220° C. for a few hours.

(7) The assembly is allowed to cool and the insert is removed.

(8) A high-temperature-resistant glue is applied to each of the faces intended to be in contact with the core.

(9) A polyimide foam-type core (approximate density of 50 kg/m3) is introduced in place of the insert.

(10) The entire sandwich is then subjected to a final consolidation treatment, under vacuum at a temperature of about 90-120° C., so as to ensure good adhesion of the skins and the core.

Example 2

(11) The first skin is formed by a stack of several non-impregnated reinforcing fabrics, of carbon fibers, deposited in a steel mold.

(12) A soft insert (silicone plate a few millimeters thick) is deposited on the fabric.

(13) The second skin is formed by a fabric of the same type deposited on the insert.

(14) The mold is closed by the steel counter mold.

(15) Cyanate ester resin is injected by a known RTM-type method, at a temperature between 80 and 120° C. under a pressure of 10 to 15 bar.

(16) The heat treatment is prolonged for 4 hours.

(17) The mold is allowed to cool, then the insert is removed and the skins are separated by removing the peel ply.

(18) A very thin layer of cyanate ester resin is added to the skins (on the faces intended to come into contact with the honeycomb).

(19) A honeycomb core is introduced between the two skins, in place of the insert, to form a sandwich.

(20) The entire sandwich is subjected to heat treatment (180-200° C.), under vacuum, for 4 hours so as to bond the skins and the core.

Example 3

(21) A knit is made using a mixed yarn comprising glass fibers and thermoplastic fibers.

(22) This knit is deposited in a steel mold to form the first skin.

(23) An insert of material expandable under the effect of temperature is deposited on the knit.

(24) A second knit of the same type is deposited on the insert to form the second skin.

(25) Teflon-coated peel ply (PTFE-coated glass fibers) is placed at the junction between the two skins. The junction is the area where the two skins join to cover the field of the core.

(26) Teflon-coated peel ply is placed at the junction between the two skins.

(27) The mold is closed by a steel counter mold.

(28) The skins are consolidated by heat treatment at 200-250° C., under a pressure of 3 to 10 bar for a few dozen minutes.

(29) The mold is allowed to cool, then the insert is removed and the skins are separated by removing the peel ply.

(30) A knit preform of a thermoplastic yarn is deposited on either side of a honeycomb core, so as to form a connecting layer between the core and the skins of the sandwich.

(31) The honeycomb core and the knit preforms are introduced between the two skins, in place of the insert, to form a sandwich.

(32) The entire sandwich is subjected to heat treatment (200-250° C.), under vacuum, for a few hours, so as to bond the skins and the core.

Example 4

(33) A knit is made using a mixed yarn comprising glass fibers and thermoplastic fibers.

(34) This knit is deposited in a steel mold to form the first skin.

(35) A rigid insert of material expandable under the effect of temperature is deposited on the knit.

(36) A second knit of the same type is deposited on the insert to form the second skin.

(37) Teflon-coated peel ply is placed at the junction between the two skins.

(38) The mold is closed by a steel counter mold.

(39) The skins are consolidated by a heat treatment at 200-250° C., under a pressure of 3 to 10 bar for few dozen minutes.

(40) The mold is allowed to cool, then the insert is removed and the skins are separated by removing the peel ply.

(41) An expanded epoxy foam core is injected between the two skins, in place of the insert, to form a sandwich.

(42) The whole sandwich is subjected to heat treatment (65-120° C.), under vacuum, for a few hours so as to bind the skins and the core.

Example 5

(43) A knit is made using a mixed yarn comprising glass fibers and thermoplastic fibers.

(44) A first knit is draped over a silicone bladder and the assembly is deposited in a first steel mold for the consolidation of the outer skin. The mold is closed and a vacuum is drawn. The mold is pressurized (3 to 10 bar) and heated rapidly by induction heating to a temperature of 200 to 250° C. The temperature is maintained for a few minutes. After cooling, the bladder is removed and a first skin is thus produced.

(45) A second skin (inner skin) is made in the same way as the first in a second mold.

(46) In the tooling used to consolidate the outer skin, the following is deposited successively: the external skin previously consolidated, an epoxy or liquid form glue film, a honeycomb structure, the previously consolidated internal skin of the final composite product.

(47) The silicone bladder used to consolidate the inner skin is put in place and the mold is closed. A vacuum is drawn to the maximum and the assembly is heated to a temperature of 65-120° C. for a few hours (oven heating method) so as to bond the skins and the core.