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

Abstract

The invention relates to a method for manufacturing a composite material part with a thickness between 30 and 150 mm by vacuum infusion molding. This method comprises a controlled injection step (35) of resin through an injection nozzle (19) intended to supply resin to a portion of a stack (13) of dry fabric. The method also includes a step for controlling the resin flow rate injected through said nozzle (19) such that said resin flow rate, expressed in kg / min, is between a first predetermined value equal to 2 x 10⁻³ × ep × S1 and a second predetermined value equal to 12 x 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: Method for manufacturing a composite part by vacuum infusion molding with resin flow control. Scope of the invention

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

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

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

[0004] Among the various techniques used for manufacturing parts from composite materials, the so-called vacuum infusion molding technique is well known. This technique consists of infusing resin, under the action of a vacuum, through a preform formed of a stack of reinforcing plies containing fibers, in order to polymerize it.

[0005] Usually, the diffusion of the resin is first promoted over the entire surface of a textile layer having a permeability much greater than that of the preform's folds and placed 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 underneath and compress the stacks of plies, the resin injection generally stops by itself when the resin can no longer penetrate the preform.

[0007] The amount of resin that can be injected therefore directly influences the mechanical properties of the part. If the amount of resin injected is insufficient, the part may have one or more "dry" areas not containing resin, which constitute areas of weakness.

[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 volumetric fiber content, 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 container to verify whether the mass of resin injected corresponds to the quantity of resin that should theoretically be injected to completely fill the preform. A drawback of this technique Accurately measuring the weight of large volumes of resin is a delicate operation. Furthermore, the volume of the resin supply lines between the resin container and the injection nozzles is often difficult to determine precisely, and resin leaks can occur in the circuit and at the mold level, potentially skewing the estimate of the mass of resin actually diffused into the preform. In addition, estimating a theoretical resin mass often remains approximate because the actual volume of the preform is difficult to assess, and there are also uncertainties regarding the density or the actual coefficient of expansion of the resin.

[0010] To overcome these drawbacks, document FR 2 948 600 B1 proposes using one or more resin presence detection sensors made from a material with a variable electrical capacitance when in contact with resin, and mounted on the face of the preform opposite to the face where the resin is injected. While this technique makes it possible to distinguish parts of acceptable quality from defective parts, it does not, however, guarantee the reliable production of parts of acceptable quality.

[0011] Techniques for manufacturing parts from composite materials are also known, starting from a stack of pre-impregnated resin fiber plies, which are draped in a mold and compressed by covering the stack with a vacuum bag under which a vacuum is drawn, and then heated 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 exceeding 10 cm. However, they have the disadvantage that the length of the parts that can be manufactured is limited by the dimensions of the autoclave. Objectives of the invention

[0013] The invention therefore aims in particular to overcome the disadvantages of the prior art mentioned above.

[0014] More specifically, the invention aims to provide a vacuum infusion molding technique that allows for the production of parts without defects of thickness up to 150mm.

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

[0016] Another objective of the invention is to provide such a technique for manufacturing parts in composite material by vacuum infusion molding which is easy and inexpensive to implement and which is reliable. Description 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 thickness defects not exceeding 30mm could be obtained by known vacuum infusion molding techniques.

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

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

[0021] - vacuuming of the volume delimited by said flexible membrane and said mold;

[0022] characterized in that it further comprises a controlled injection step of a resin with a viscosity of 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 and a shear rate of 10 s⁻¹, at the level of an injection nozzle mounted near said stack and intended to supply resin to a portion of said stack with surface area Si, for a sufficient duration to allow impregnation of all the dry tissues of said stack, said injection step comprising a step of controlling the resin flow rate injected via said nozzle such that said resin flow rate, expressed in kg / min, is between a first predetermined value equal to 2.10³ x 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. supplied by said nozzle expressed in m2.

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

[0024] The inventors have indeed found, counterintuitively, that limiting the resin flow rate by controlling its flow rate ensures homogeneous penetration and diffusion of the resin throughout the entire thickness of the stack for parts with thicknesses between 30 and 150 mm. One hypothesis that could explain this phenomenon is that by limiting the resin flow rate, the total amount of heat emitted by exothermic reaction in the stack is controlled, thus delaying the temperature rise and consequently the hardening of the resin. Furthermore, the Inventors have observed that, as a general rule, the greater the thickness of the part, the more the resin flow rate 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 near the underside of said stack.

[0026] According to an advantageous embodiment of the invention, said control step includes a flow measurement step and a control step of a flow control device, such as a valve or a resin injection pump, if the measured flow 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 vinyl ester 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 can be preheated up to 60°C.

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

[0032] The drainage fabric thus allows the resin to be diffused over the entire surface of the stack before it penetrates the plurality of reinforcement folds.

[0033] In an advantageous embodiment of the invention, the draining fabric is a biaxially 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 process as described above includes a step of setting up a second membrane enveloping said vacuum bag membrane and a step of evacuating the volume comprising said second membrane and said vacuum bag membrane, at a pressure lower than the value of the pressure resulting from evacuating the volume delimited by said flexible vacuum bag 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 composite part, 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 evacuating the volume delimited by said flexible membrane and said mold;

[0041] - means for controlled injection of a resin with a viscosity of 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 50mm with a shear rate of 10 s 1, at the level of an injection nozzle mounted near said stack and intended to supply resin to a portion of said stack of surface Si, for a sufficient duration to allow impregnation of all the dry tissues of said stack;

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

[0043] said controlled injection means comprising means for controlling a resin flow control device injected via said nozzle, such as a resin injection valve or pump, configured to maintain the measured flow rate between a first predetermined value and a second predetermined value, said first predetermined value expressed in kg / min being equal to 2.10³ × ep × Si and said second predetermined value expressed in kg / min being equal to 12.10³ × ep × 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. List of figures

[0044] Other features and advantages of the invention will become more apparent upon reading the following description of several embodiments of the invention, given by way of simple illustrative and non-limiting examples, and the accompanying drawings, among which:

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

[0046] [Fig.2] is a vertical cross-sectional view of the device for manufacturing a part in composite material by vacuum infusion molding shown with reference to [Fig.1];

[0047] [Fig.3] illustrates, in block diagram form, the steps of an example embodiment of a process for manufacturing a part in 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, respectively in top view and vertical sectional view, illustrate an example of an embodiment of a vacuum infusion molding device 10 according to the invention, intended to manufacture composite material plates.

[0049] This device includes a mold-forming table 11 on which layers of carbon fiber plies are stacked to give the plate to be manufactured a mechanical resistance conforming to the expectations of 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 two different models of carbon fiber plies measuring 3 m x 0.6 m. More precisely, in this particular embodiment of the invention, the stack 13 is formed of 90% unidirectional carbon fiber plies with a surface weight of 618 g / m² and 10% biaxial carbon fiber plies with a surface weight of 300 g / m².

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

[0052] The stack of fiber plies 13 is covered with a first semi-watertight 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 airtight 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 vacuum-infused molded plate is of suitable flatness.

[0054] In this particular embodiment of the invention, resin injection nozzles 19 are 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 manifold 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 allowing the pump speed to be regulated according to the resin flow rate measured at the resin injection nozzles 19 using gear flow meters (not shown in Figures 1 and 2), thus ensuring a precise control of the flow rate of resin injected into each section of the stack 13 fed 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 level of the injection nozzles 19 in the range of value [1.2.10 3x ep kg / min; 7.2.103 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 of 100mm thickness between 120.103 and 720.10 3kg / 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 according to the resin flow measured at the resin injection nozzles 19, in order to control with precision the flow of resin injected into each section of the stack 13 fed by a nozzle 19.

[0057] In addition, a tube 114 passing through the first semi-sealed membrane 15 is provided to achieve a primary vacuum of 5mbar under the membrane 15. This tube 114 is connected to a vacuum pump 115 via a vacuum chamber 116 forming a resin trap allowing the vacuum pump 115 to be protected from possible resin overflows.

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

[0059] It should 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 50mm with a shear rate of 10 s*.

[0060] The steps of an example embodiment of a manufacturing process according to the invention, using the device 10, of a carbon fiber-based composite material plate of thickness ep equal to 50mm and having a surface fiber density of 52.44 kg / m2, have been synoptically illustrated in [Fig.3] in the form of a block diagram s.

[0061] In a first step 31, a stack 13 of 2.2m x 0.6m carbon fiber fabric layers is formed on the table 11, consisting of 90% unidirectional carbon fiber plies with a surface weight of 618g / m² (UD618) and 10% biaxial carbon fiber plies with a surface weight of 300g / m² distributed periodically between the UD618 plies. A layer of SAERflow biaxial drainage fabric (brand) is added. (registered) marketed by the company Saertex (registered trademark) has also been 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 sealant is applied around the entire periphery of the membrane 16 to ensure vacuum sealing between the membrane 15 and the table 11 (step 321).

[0063] The rigid counter-plate 17 is then placed on the membrane 15 and the whole is covered by the second semi-watertight membrane 18, in a step 33.

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

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

[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 the injection step 35. Furthermore, when the resin injection stops, the inventors found 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 pressurized chamber at room temperature in order to chemically stabilize the plate (step 36).

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

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

[0071] The results of these bending tests established that, on average across the 3 specimens, the bending stress at failure was 500 ± 139 MPa and the shear stress at failure was 12.6 ± 3.3 MPa. Furthermore, the Young's modulus measured on average on each of the faces of The specimen 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

Demands

1. A method for manufacturing by vacuum infusion molding 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) of said stack with a flexible membrane (15) forming a vacuum bag; - vacuuming (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 the level of 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 duration to allow the impregnation of all the dry tissues of said stack (13), said injection step including a step of controlling the flow rate of resin injected via said nozzle (19) such that said resin flow rate 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 fed by said nozzle expressed in 2,

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

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

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

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

6. A 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. A method according to any one of claims 1 to 6, characterized in that it comprises a step of setting up a second membrane (18) enveloping said vacuum bag membrane (15) and a step of vacuuming the volume between said second membrane (18) and said vacuum bag membrane (15) at a pressure lower than the value of the pressure resulting from vacuuming in the volume delimited by said flexible vacuum bag membrane and said mold (11).

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

9. A device (10) for vacuum infusion molding of a composite part, such as a plate, of substantially constant thickness between 30 and 150 mm, comprising: - a mold (11) for receiving a stack (13) of dry fabric; - a flexible membrane (15) forming a vacuum bag for covering said stack (13); - means for evacuating 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 and 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 said surface stack Sb for a sufficient time to allow all dry tissues of said stack to be impregnated (13); - means of measuring resin flow rate; said controlled injection means comprising control means (113) of a control device for the flow rate of resin injected via said nozzle (19), 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 Sb where ep is the thickness of said part expressed in mm and Si is the surface area of ​​said portion of the stack fed by said nozzle expressed in m2.