Manufacturing process by vacuum infusion molding of a composite material part with controlled resin flow.

Abstract

The invention relates to a method for manufacturing by vacuum infusion molding a part made of composite material with a thickness of between 30 and 150 mm. This method comprises a step of controlled injection (35) of a resin at an injection nozzle (19) intended to supply resin to a portion of a stack (13) of dry fabrics, comprising a step of controlling the flow rate of resin injected via said nozzle (19) so that said flow rate of resin expressed in kg / min is between a first predetermined value equal to 2.10-3 × ep × S1 and a second predetermined value equal to 12.10-3 × ep × S1 where ep is the thickness of said part expressed in mm and S1 is the surface area of ​​said portion of the stack (13) supplied by said nozzle (19) expressed in m2. Figure to be published: 1

Description

Title of the invention: Manufacturing process by vacuum infusion molding of a composite material part with control of the resin flow rate. Field of invention

[0001] The invention relates to the field of composite materials.

[0002] More specifically, the invention relates to a method of manufacturing by vacuum infusion molding a part made of composite material and a corresponding device.

[0003] The invention finds an application for the manufacture of composite parts with a thickness of between 30 and 150 mm. Prior art

[0004] Among the various techniques used for the production of composite material parts, the technique known as vacuum infusion molding is known. This technique consists of infusing, under the action of vacuum, resin through a preform formed from a stack of reinforcement plies containing fibers, with a view to its polymerization.

[0005] Usually, the diffusion of the resin is first encouraged over the entire surface of a textile layer having a permeability much higher than that of the folds of the preform and arranged in contact with the preform, so that the resin can then gradually diffuse through the preform into the different layers of reinforcing folds, perpendicular to the planes of these folds.

[0006] In vacuum infusion molding processes using a semi-sealed membrane, also called a vacuum bag, to contain the resin thereunder and compress the ply stacks, the resin injection generally stops by itself when the resin can no longer penetrate into the preform.

[0007] The quantity of resin that can be injected therefore directly influences the mechanical qualities of the part. If the quantity of resin injected is insufficient, the part risks having one or more “dry” zones containing no resin, which constitute zones of fragility.

[0008] For this reason, it is difficult to produce by vacuum infusion molding parts more than 10 to 20 mm thick, and having a high fiber volume rate, which are of suitable quality.

[0009] In order to determine whether the resin has properly diffused into all areas of the preform, it has been proposed to weigh the resin injection pot to check whether the mass of injected resin corresponds to that of the quantity of resin that theoretically needs to be injected to completely fill the preform. A disadvantage of this technique is that measuring the weight accurately is a delicate operation for large volumes of resin. Furthermore, the volume of the resin supply pipes between the resin pot and the injection nozzles is often difficult to determine precisely and finally there can be resin leaks in the circuit and at the mold level which can distort the estimation of the mass of resin which has actually diffused into the preform. In addition, the estimation of a theoretical mass of resin often remains approximate because the real volume of the preform is difficult to evaluate and moreover there are uncertainties on the density or the real coefficient of expansion of the resin.

[0010] In order to overcome these drawbacks, document FR 2 948 600 B1 proposes using one or more sensors for detecting the presence of resin made from a material having an electrical capacitance which varies when it is in contact with resin and mounted on the face of the preform opposite that where the resin is injected. This technique, which makes it possible to discriminate between parts which are of suitable quality and parts having defects, does not, however, offer a guarantee of being able to produce parts of suitable quality with certainty.

[0011] Techniques are also known for manufacturing parts made of composite materials from a stack of fiber plies pre-impregnated with resin, which are draped in a mold, and which are compressed by covering the stack with a vacuum bag under which a vacuum is drawn, then which is brought to temperature in an oven or in a pressurized autoclave.

[0012] These known techniques using pre-impregnated fiber plies make it possible to produce parts with a fiber content of up to 60% and a thickness of more than 10 cm. However, they have the disadvantage that the length of the parts that can be produced is limited by the dimensions of the autoclave. Objectives of the invention

[0013] The invention therefore aims in particular to overcome the drawbacks of the state of the art cited above.

[0014] More specifically, the invention aims to provide a vacuum infusion molding technique which makes it possible to produce parts without defects with a thickness of up to 150 mm.

[0015] Another objective of the invention is to propose a vacuum infusion molding technique, which makes it possible to manufacture parts made of material with a thickness of between 30 and 150 mm and of significant length and / or width, such as parts more than 6 to 8 m long and / or more than 1 to 1.5 m wide for example.

[0016] Another objective of the invention is to provide such a technique for manufacturing parts made of composite material by vacuum infusion molding which is easy and inexpensive to implement and which is reliable. Statement of the invention

[0017] These objectives, as well as others which will appear subsequently, are achieved using a manufacturing process by vacuum infusion molding of a part made of composite material, such as a plate, of substantially constant thickness between 30 and 150 mm.

[0018] It should be noted that to the inventors' knowledge, only parts free from defects with a thickness not exceeding 30 mm could be obtained by known vacuum infusion molding techniques.

[0019] According to the invention, such a method comprises the following steps:

[0020] - forming a stack of dry fabrics on a mold and covering said stacking of a flexible membrane forming a vacuum bag;

[0021] - placing under vacuum the volume delimited by said flexible membrane and said mold;

[0022] characterized in that it further comprises a step of controlled injection of a resin with a viscosity less than or equal to 250 Cps at 20°C measured using a temperature-controlled cone-plate viscometer whose moving cone has a diameter of 50 mm with a shear rate of 10 s'1, at an injection nozzle mounted near said stack and intended to supply resin to a portion of said stack with surface Si, for a time sufficient to allow all the dry tissues of said stack to be impregnated, said injection step comprising a step of controlling the flow rate of resin injected via said nozzle so that said flow rate of resin expressed in kg / min is between a first predetermined value equal to 2.103x ep x Si and a second predetermined value equal to 12.103 x ep x Si where ep is the thickness of said plate expressed in mm and Si is the surface area of ​​said portion of the stack fed by said nozzle expressed in m2.

[0023] The invention therefore proposes, in a novel manner, to control the flow of resin to manufacture, by vacuum infusion molding, parts made of composite material without defects and with a thickness of up to 150 mm.

[0024] The inventors have in fact found, counter-intuitively, that limiting the flow rate of resin by controlling its flow rate makes it possible to guarantee penetration and homogeneous diffusion of the resin over the entire thickness of the stack for parts with thicknesses between 30 and 150 mm. A hypothesis likely to explain this phenomenon could be that by limiting the flow rate of resin, the total quantity of heat emitted by exothermic reaction in the stack is controlled, which delays the rise in temperature, and consequently the hardening, of the resin. In addition, inventors have found that, as a trend, the greater the thickness of the part, the more the resin flow rate value needs to be reduced to ensure homogeneous and total diffusion of the resin within the stack.

[0025] According to a particular aspect of the invention, said injection nozzle is mounted close to the lower face of said stack.

[0026] According to an advantageous embodiment of the invention, said control step comprises a step of measuring the flow rate and a step of controlling a flow rate control member, such as a valve or a resin injection pump, if the measured flow rate value expressed in kg / min is less than said first predetermined value or greater than said second predetermined value.

[0027] Thus, the flow rate can be finely regulated by acting on the position of a valve or on the speed of a resin injection pump, for example.

[0028] According to a preferred aspect of the invention, the injected resin is an epoxy resin, a vinylester resin or a polyester resin.

[0029] In a particular embodiment of the invention, said injected resin is substantially at room temperature.

[0030] In variations of this embodiment, the resin may be preheated to 60°C.

[0031] According to a particular embodiment of the invention, said stack of dry fabrics comprises a plurality of fiberglass or carbon reinforcing plies and at least one draining fabric.

[0032] The draining fabric thus makes it possible to diffuse the resin over the entire surface of the stack before it penetrates into the plurality of reinforcing plies.

[0033] In an advantageous embodiment of the invention, the draining fabric is a biaxial draining fabric.

[0034] According to a particular aspect of the invention, during said vacuuming step the pressure resulting from the vacuuming of the volume delimited by said flexible membrane and said mold is less than or equal to 5 mbar.

[0035] Advantageously, a method as described above comprises a step of placing a second membrane enveloping said vacuum bag-forming membrane and a step of placing under vacuum the volume comprising said second membrane and said vacuum bag-forming membrane, at a pressure lower than the value of the pressure resulting from placing under vacuum in the volume delimited by said flexible vacuum bag-forming membrane and said mold.

[0036] Thus, by creating a double vacuum, the stack of folds is kept suitably compacted.

[0037] The invention also relates to a device for vacuum infusion molding of a part made of composite material, such as a plate, of substantially constant thickness between 30 and 150 mm comprising:

[0038] - a mold intended to receive a stack of dry fabrics;

[0039] - a flexible membrane forming a vacuum bag intended to cover said stack;

[0040] - means for creating a vacuum in the volume delimited by said flexible membrane and said mold;

[0041] - means for controlled injection of a resin with a viscosity less than or equal to 250 Cps at 20°C measured using a temperature-controlled cone-plate viscometer whose moving cone has a diameter of 50 mm with a shear rate of 10 s 1 , at an injection nozzle mounted near said stack and intended to supply resin to a portion of said stack of surface Si, for a time sufficient to allow all the dry tissues of said stack to be impregnated;

[0042] - means for measuring the resin flow rate;

[0043] said controlled injection means comprising means for controlling a member for controlling the flow rate of resin injected via said nozzle, such as a valve or a resin injection pump, configured so as to maintain the measured flow rate value between a first predetermined value and a second predetermined value, said first predetermined value expressed in kg / min being equal to 2.10 3x ep x Si and said second predetermined value expressed in kg / min being equal to 12.103 x ep x Si, where ep is the thickness of said plate expressed in mm and Si is the surface area of ​​said portion of the stack supplied by said nozzle expressed in m2. List of figures

[0044] Other characteristics and advantages of the invention will appear more clearly on reading the following description of several embodiments of the invention, given as simple illustrative and non-limiting examples, and the appended drawings among which:

[0045] [Fig-1] is a detailed top view of an exemplary embodiment of a device for manufacturing a part made of composite material by vacuum infusion molding according to the invention;

[0046] [Fig.2] is a vertical sectional view of the device for manufacturing a part of composite material by vacuum infusion molding shown with reference to [Fig.l];

[0047] [Fig.3] illustrates, in block diagram form, the steps of an exemplary embodiment of a method for manufacturing a part made of composite material by vacuum infusion molding according to the invention using the device shown with reference to Figures 1 and 2; Detailed description of the invention

[0048] Figures 1 and 2 illustrate, respectively in top view and in vertical sectional view, an exemplary embodiment of a vacuum infusion molding device 10 according to the invention, intended to manufacture plates of composite material.

[0049] This device comprises a table 11 forming a mold on which layers of carbon fiber plies are stacked, intended to give the plate to be manufactured a mechanical resistance in accordance with the specifications, resting on a draining textile layer 12 having a permeability much higher than that of the carbon fiber plies.

[0050] This stack 13 is formed by successively unrolling on top of each other two different models of carbon fiber plies of dimensions 3 mx 0.6 m. More precisely, the stack 13 is formed, in this particular embodiment of the invention, of 90% of unidirectional carbon fiber plies with a surface weight equal to 618 g / m2 and 10% of biaxial carbon fiber plies with a surface weight equal to 300 g / m2.

[0051] A layer of biaxial draining fabric + / -45° in fiberglass has also been inserted into the stack 13 substantially at the level of the theoretical position of the neutral fiber 14 of the part, so as not to affect its mechanical properties.

[0052] The stack of fiber plies 13 is covered with a first semi-waterproof membrane 15, also called a vacuum bag, the sealing of which with the mold 11 is ensured by a peripheral seal of sealing mastic 16.

[0053] A rigid counter-plate 17 is placed on the first membrane 16 and covered with a second sealed bag 18 intended to be drawn under vacuum, in order to exert pressure on the first membrane and ensure that the upper surface of the plate molded by vacuum infusion is of suitable flatness.

[0054] Resin injection nozzles 19 are in this particular embodiment of the invention mounted substantially at the base of the stack every one meter, in the longitudinal direction of the stack 13 and connected to a resin injection ramp 110. These nozzles 19 are supplied with resin, via resin supply tubes 117, by a resin injection machine 111 equipped with a container 112, or pot, for loading the resin, and also with variable flow gear pumps (not shown in Figures 1 and 2) controlled by a speed control unit 113 making it possible to regulate the speed of the pumps as a function of the resin flow rate measured at the resin injection nozzles 19 using gear flow meters (not shown in Figures 1 and 2) and thus to ensure a precise control of the flow of resin injected into each section of the stack 13 supplied by each nozzle 19.

[0055] In this particular embodiment of the invention, the control unit 113 is configured so as to maintain the resin flow rate, expressed in kg / min, at the injection nozzles 19 in the value range [1.2.10 3 x ep kg / min; 7.2.10 3 x ep kg / min], where ep is the thickness of the plate to be manufactured expressed in mm, i.e. for example for a plate 100 mm thick between 120.10 3 and 720.10 3 kg / min.

[0056] In a variant of this particular embodiment of the invention, it may be provided to implement a resin injection pump with substantially constant differential pressure and a valve downstream thereof, controlled in opening / closing as a function of the resin flow rate measured at the resin injection nozzles 19, in order to precisely control the flow rate of resin injected into each section of the stack 13 supplied by a nozzle 19.

[0057] Furthermore, a tube 114 passing through the first semi-sealed membrane 15 is provided to create a primary vacuum at 5 mbar under the membrane 15. This tube 114 is connected to a vacuum pump 115 via a vacuum chamber 116 forming a resin trap making it possible to protect the vacuum pump 115 from possible resin overflows.

[0058] In this particular embodiment of the invention, SR Infugreen (registered trademark) 810 epoxy resin mixed with a hardener SD4771 marketed by the company Sicomin (registered trademark) was poured into the resin pot 112. In variants of this particular embodiment of the invention, it may be envisaged to use any other known epoxy, vinylester or polyester resin having a viscosity less than or equal to 250 mPa.s at 20°C.

[0059] It will be noted that in the present patent application, the viscosity values ​​of the resins indicated are values ​​measured using a temperature-controlled cone-plate viscometer whose moving cone has a diameter of 50 mm with a shear rate of 10 s *.

[0060] [Fig. 3] illustrates in a synoptic manner the steps of an exemplary embodiment of a manufacturing method according to the invention, using the device 10, of a plate made of carbon fiber-based composite material with a thickness ep equal to 50 mm and having a fiber surface density of 52.44 kg / m2, in the form of a block diagram s.

[0061] In a first step 31, a stack 13 is formed on the table 11 of layers of carbon fiber fabrics of 2.2m*0.6m, from 90% of unidirectional carbon fiber plies with a surface weight equal to 618g / m2 (UD618) and 10% of biaxial carbon fiber plies with a surface weight equal to 300g / m2 distributed periodically between the UD618 plies. A layer of SAERflow biaxial draining fabric (brand registered trademark) marketed by the company Saertex (registered trademark) was also inserted into the stack 13 substantially at the level of the theoretical position of the neutral fiber 14.

[0062] In a step 32, the stack 13 is then covered with the first semi-waterproof membrane 15 and a bead of sealing mastic is deposited over the entire periphery of the membrane 16 in order to ensure vacuum sealing between the membrane 15 and the table 11 (step 321).

[0063] The rigid counterplate 17 is then placed on the membrane 15 and the assembly is covered by the second semi-waterproof membrane 18, in a step 33.

[0064] A vacuum of 5 mbar is then created under the first membrane 16 and between the first membrane 15 and the second membrane 18 (step 34).

[0065] In a following step 35, resin mixed with a hardener is injected for a period of approximately one hour, sufficient to allow all the dry fabrics of the stack to be impregnated, through the injection nozzles 19 using the machine 111, each of the nozzles supplying resin to a portion of the stack 13 with a length of 0.7 m, of the epoxy resin. During step 35, the flow rate of resin injected at the nozzles 19 is controlled by the control unit 113 integrated into the machine 111, in order to maintain the flow rate between two predetermined values ​​VD1 and VD2, these values ​​having been respectively calculated by the following formulas: - VD1= 2.10 3x ep x Si = 44.103 kg / mn; and VD2=12.10 3 x ep x Si = 264.10 3 kg / mn,

[0066] with ep=50 is the thickness of the plate expressed in mm and Si=0.733*0.6=0.44m2 the surface area of ​​the portion of the stack fed by each nozzle 19 expressed in m2.

[0067] The inventors observed that the temperature in the stack does not rise above 47°C during injection step 35. Furthermore, when the resin injection stops, the inventors observed that approximately 33 kg of resin had been injected into the stack 13.

[0068] The plate is then placed in an oven or in a pressure chamber at room temperature in order to chemically stabilize the plate (step 36).

[0069] Bending tests according to ASTM D7264 were carried out on three specimens cut from a 50mm plate obtained in step 35.

[0070] For this, each test piece was equipped on each of its faces with a unidirectional strain gauge glued to the center of the test piece.

[0071] The results of these bending tests made it possible to establish that on average over the 3 specimens, the bending stress o at rupture of the specimens was 500 ± 139 MPa and that the shear stress r at rupture of the specimens was 12.6 ± 3.3 MPa. Furthermore, the Young's modulus measured on average on each of the faces of the test piece is 106.8 ± 4.5 GPa on the face subjected to tension and 102.6 ± 4.4 GPa on the face subjected to compression.

Claims

Claims

1. Manufacturing method by vacuum infusion molding of a part made of composite material, such as a plate, of substantially constant thickness between 30 and 150 mm comprising the following steps: - formation (31) of a stack (13) of dry fabrics on a mold (11) and covering (32) said stack with a flexible membrane (15) forming a vacuum bag; - placing under vacuum (34) the volume delimited by said flexible membrane and said mold; characterized in that it further comprises a controlled injection step (35) of a resin with a viscosity less than or equal to 250 Cps at 20°C measured using a temperature-controlled cone-plate viscometer whose moving cone has a diameter of 50 mm with a shear rate of 10 s'1, at an injection nozzle (19) mounted near said stack (13) and intended to supply resin to a portion of said stack with surface Si,for a sufficient time to allow all the dry fabrics of said stack (13) to be impregnated, said injection step comprising a step of controlling the flow rate of resin injected via said nozzle (19) so that said flow rate of resin expressed in kg / min is between a first predetermined value equal to 2.10 3x ep x Si and a second predetermined value equal to 12.103 x ep x Si where ep is the thickness of said part expressed in mm and Si is the surface area of ​​said portion of the stack supplied by said nozzle expressed in 2,

2. ni. Method according to claim 1, characterized in that said control step comprises a step of measuring the flow rate and a step of controlling a flow rate control member, such as a valve or a resin injection pump, if the measured flow rate value expressed in kg / min is less than said first predetermined value or greater than said second predetermined value.

3. Method according to any one of claims 1 and 2, characterized in that said injected resin is an epoxy resin, a vinylester resin or a polyester resin.

4. Method according to any one of claims 1 to 3, characterized in that said injected resin is substantially at room temperature.

5. Method according to any one of claims 1 to 4, characterized in that said stack (13) of dry fabrics comprises a plurality of reinforcing plies of fiberglass or carbon and at least one draining fabric (12).

6. Method according to any one of claims 1 to 5, characterized in that during said vacuuming step the pressure resulting from the vacuuming of the volume delimited by said flexible membrane (15) and said mold (11) is less than or equal to 5 mbar.

7. Method according to any one of claims 1 to 6, characterized in that it comprises a step of placing a second membrane (18) enveloping said vacuum bag-forming membrane (15) and a step of placing under vacuum the volume between said second membrane (18) and said vacuum bag-forming membrane (15) at a pressure lower than the value of the pressure resulting from placing under vacuum in the volume delimited by said flexible vacuum bag-forming membrane and said mold (11).

8. Method according to any one of claims 1 to 7, characterized in that it further comprises a step of exposing (36) said part formed in said step of controlled injection of resin to a pressure of a gas in an enclosure substantially at ambient temperature.

9. Device (10) for vacuum infusion molding of a composite material part, such as a plate, of substantially constant thickness between 30 and 150 mm comprising: - a mold (11) intended to receive a stack (13) of dry fabrics; - a flexible membrane (15) forming a vacuum bag intended to cover said stack (13); - means for creating a vacuum in the volume delimited by said flexible membrane (15) and said mold (11); - means for controlled injection of a resin with a viscosity less than or equal to 250 Cps at 20°C measured using a temperature-controlled cone-plate viscometer whose moving cone has a diameter of 50 mm with a shear rate of 10 s1, at an injection nozzle (19) mounted near said stack (13) and intended to supply resin to a portion said Sb surface stack for a sufficient time to allow all of the dry tissues of said stack (13) to be impregnated; - means of measuring the resin flow rate; said controlled injection means comprising control means (113) of a member for controlling the flow rate of resin injected via said nozzle (19), such as a valve or a resin injection pump, configured so as to allow the measured flow rate value to be maintained between a first predetermined value and a second predetermined value, said first predetermined value expressed in kg / min being equal to 2.10 3x ep x Si and said second predetermined value expressed in kg / min being equal to 12.103 x ep x Sb where ep is the thickness of said part expressed in mm and Si is the surface area of ​​said portion of the stack supplied by said nozzle expressed in m2.

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