Process for injection moulding a composite part

Abstract

A method of injection molding a part made of composite material is provided. The method includes placing a preform in a mold; injecting a resin into the mold so as to impregnate the preform; unmolding the part after curing the resin; and subjecting the resin and the preform to pressure inside the mold while the resin is curing.

Claims

1. A method of injection molding a blade comprising a composite material, the method comprising: placing a blade fiber preform in a mold, the blade fiber preform being formed by weaving yarns and including a root portion having a first planar sloping face, a second planar sloping face, and a bottom planar face between the first and second sloping faces in a cross-sectional view, and an airfoil portion having a leading edge and a trailing edge; injecting a resin into the mold so as to impregnate the blade fiber preform; unmolding the blade after curing the resin; and subjecting the resin and the blade fiber preform to pressure inside the mold while the resin is curing, wherein the blade is free of pores, wherein the mold includes a resin injection hole facing the bottom planar face of the root portion and a vent hole facing a tip of the airfoil portion, a first gas injection hole facing the leading edge of the airfoil portion, and a second gas injection hole facing the trailing edge of the airfoil portion, and wherein the pressure is applied to the blade fiber preform by injecting a fluid under pressure into the mold via the first gas injection hole and the second injection hole.

2. The method according to claim 1, wherein the pressure is applied to the blade fiber preform in the mold before a degree of curing of the resin exceeds a value of from 20% to 30%.

3. The method according to claim 1, wherein the pressure applied to the blade fiber preform in the mold is higher than a vapor pressure of a gas generated during curing of the resin.

4. The method according to claim 1, wherein the pressure applied to the blade fiber preform is greater than or equal to 2 bars, relative to atmospheric pressure.

5. The method according to claim 1, wherein the resin is an epoxy resin, a bismaleimide resin, a polyimide resin, or any resin comprising volatile impurities, solvents, or both.

6. The method according claim 1, wherein the mold is evacuated in order to inject the resin.

7. The method according to claim 1, further comprising a plurality of successive stages of injecting resin into the mold and of pressurizing the resin and the mold.

8. The method according to claim 1, wherein the fluid injected under pressure is a gas such as air or nitrogen, or a liquid that is not miscible with the resin.

9. The method according to claim 1, wherein the mold includes recesses corresponding to the first and second sloping faces of the root portion.

10. The method according to claim 1, wherein the pressure is further applied to the blade fiber preform by injecting the fluid under pressure into the mold via the resin injection hole and the vent hole.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention can be better understood and other details, characteristics, and advantages invention appear on reading the following description made by way of nonlimiting example and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a perspective view of a turbine engine blade made of composite material and having marked thereon points for injecting material and fluid under pressure;

(3) FIG. 2 is a fragmentary section view relating to a variant embodiment of the invention in which the pre-form and the resin are compressed in a mold by means of an actuator; and

(4) FIG. 3 is a fragmentary section view relating to another variant embodiment of the invention, in which the preform and the resin are compressed in the mold by an element that is suitable for expanding during molding.

DETAILED DESCRIPTION OF THE INVENTION

(5) A first implementation of a method of injection molding a turbine engine blade made of composite material is described below with reference to FIG. 1.

(6) The method consists initially in placing a blade preform in a mold. The preform may be made by weaving yarns in two or three dimensions.

(7) Resin is then injected into the mold via at least one point 2 shown diagrammatically in FIG. 1, in such a manner as to impregnate the preform, with the mold preferably being evacuated while this injection is taking place. Such a method is known as vacuum assisted resin transfer molding (VARTM). By way of example, the resin used is an epoxy resin, e.g. the type known under the reference PR520N, a bismaleimide resin, a polyimide resin, or any resin including solvents and/or volatile impurities.

(8) By way of example, the pressure of the resin during injection is of the order of 1 bar to 2 bars, and the temperature is of the order of 150 C. to 200 C. The duration of injection is of the order of a few minutes, for example 30 min at most.

(9) While the resin is curing inside the mold, a chemical compound in gaseous form may form inside the resin, or it may already be present therein.

(10) In order to avoid bubbles of gas forming in the part, once the mold has been filled with a resin, a gas under pressure is injected into the mold via one or more distinct points, represented diagrammatically in FIG. 1 by arrows 3. The gas is preferably injected at a pressure higher than atmospheric pressure. By way of example, the gas under pressure is air or nitrogen at a pressure lying in the range 3 bars to 5 bars. The fluid under pressure may also be a liquid that is not miscible with the resin, for example oil.

(11) This injection of fluid under pressure is preferably performed as soon as possible after injecting the resin so as to ensure that the pressure is applied to the part inside the mold before the degree of curing of the resin exceeds a so-called critical value, lying in the range 20% to 30%. This critical value may vary as a function of the nature of the resin and of the fibers.

(12) Below this threshold, the resin is sufficiently fluid to ensure that the resin and the preform are subjected uniformly to the pressure, thereby guaranteeing that there are no pores at any point inside the part.

(13) The temperature and the gas pressure are maintained until the resin has cured completely so as to make a composite blade that has no pores and that comprises a fiber preform embedded in a rigid resin matrix. The part can then be un-molded.

(14) The injection mold (not visible in FIG. 1) conventionally includes at least one resin injection hole 2 and one vent hole 4. These holes 2, 4 may be used for injecting gas under pressure. Other points 5, 6 for injecting gas under pressure may also be provided, e.g. in the leading edge 7 and in the trailing edge 8 of the blade 1.

(15) It is also possible for all of the gas injection points 3 to be separate from the resin injection point 2 and the vent hole 4. In this way, it is possible to begin by injecting the resin in one workstation, and then continue by injecting the gas under pressure in another workstation, so as to avoid occupying the resin injection workstation in a fabrication line for too long a time. This also avoids the points 3 for injecting gas under pressure being obstructed by plugs resulting from the resin gelling at an injection point 2.

(16) The method may also include a plurality of successive stages of injecting resin into the mold and of pressurizing the resin and the mold, in particular when molding parts that are voluminous.

(17) FIG. 2 shows a variant of the invention in which the method of molding the blade consists in placing a preform 9 in a mold 10, in injecting the resin into the mold so as to impregnate the preform 9, in compressing the preform and the resin in the mold by means of an actuator 11, and in unmolding the blade after the resin has cured.

(18) FIG. 3 shows another variant embodiment in which an element 12 suitable for expanding is placed together with the preform 9 in the mold 10. After injecting resin into the mold 10, the resin, the preform, and the element are heated so that the element 12 expands and exerts pressure on the resin and on the preform 9. The part is unmolded after the resin has cured.

(19) By way of example, the element 12 is a spacer made of silicone, of copper, or of aluminum.

(20) In FIGS. 2 and 3, the principle is similar to that described with reference to FIG. 1, in that the resin and the preform are subjected to sufficient pressure to avoid bubbles of gas forming while the resin is curing.