Method for producing a composite material part by oriented needling of a preform

Abstract

A method for producing a composite material part comprising a step of producing a preform formed of unidirectional continuous fibers oriented in at least one fiber orientation, a step of applying non-woven filaments to the preform, and a step of needling the filaments by means of a needling device comprising a plurality of needles, each needle being provided with a notch extending along a notch axis perpendicular to the main longitudinal axis of the needle, or several notches each extending along a notch axis perpendicular to the main longitudinal axis of the needle, the notch axes being parallel to each other, the needles and the preform being arranged so that the notch axes form a non-zero angle with the fiber orientation.

Claims

1. A method for producing a composite material part comprising continuous unidirectional fibers and a polymer matrix, comprising: a step of producing a preform formed of several superimposed plies, each ply being formed by continuous unidirectional fibers oriented along one fiber orientation to present a unidirectional fiber direction for each ply, said preform comprising plies of different fiber orientation such that different plies present different unidirectional fiber directions; a step of applying a non-woven felt comprising non-woven filaments to at least a first main face of the preform, the non-woven felt having a surface mass of between 5 g/m.sup.2 and 100 g/m.sup.2 and the non-woven filaments having a diameter of between 5 m and 50 m; and a step of needling said non-woven filaments by means of a needling device comprising a plurality of forked needles, each forked needle being provided at its distal end with a notch extending along a notch axis perpendicular to the main longitudinal axis of the forked needle, so that the non-woven filaments are captured by the notch and are driven by the forked needles through the preform to intermingle with the unidirectional fibers and are arranged within the preform in a known pattern by the step of needling the captured non-woven filaments in a direction substantially perpendicular in the z direction, wherein the captured non-woven filaments are driven and remain substantially perpendicular in the z direction relative to the plies of continuous fibers of the preform, said forked needles and the preform being arranged so that the notch axes form a non-zero angle with each fiber orientation during needling, wherein the notch axes orientation relative to the continuous unidirectional fibers minimizes driving or damaging the fibers of each superimposed ply layer, wherein each forked needle has a diameter of between 0.30 mm and 0.60 mm, wherein the notch has a width and a depth of between 0.03 mm and 0.1 mm, and wherein a needling density of the needling device is between 150 punches/cm.sup.2 and 350 punches/cm.sup.2; and a step of impregnating the dry preform with an impregnating polymer to form the composite material part, the impregnating polymer constituting the polymer matrix of the composite material part.

2. The method according to claim 1, wherein the notch axes are arranged substantially along a bisector of two adjacent fiber orientations, to within plus or minus 10, preferably to within plus or minus 5, more preferably to within plus or minus 2.5.

3. The method according to claim 1, wherein the fiber orientations are defined between +90 and 90 around a reference axis relative to the notch axis, the notch axes are oriented in an orientation furthest from the reference axis.

4. The method according to claim 1, wherein the notch axes form an angle of at least 15 with each fiber orientation, preferably at least 22.5.

5. The method according to claim 1, wherein the preform is formed of plies with fiber orientations at 0 and 90 relative to a reference axis, the notch axes are arranged at +45 and/or 45, preferably at +45 or 45; or plies with fiber orientations at +30 and 30 relative to a reference axis, the notch axes are arranged at 0 or 90, preferably at 90; or plies with fiber orientations at 0, 90, +45 and 45 relative to a reference axis, the notch axes are arranged at +22.5, 22.5, +67.5 and/or 67.5, preferably at +67.5 and/or 67.5, more preferably at +67.5 or 67.5; or plies with fiber orientations at 0, +60 and 60 relative to a reference axis, the notch axes are arranged at 90, +30, or 30, preferably at 90, or plies with fiber orientations at 0, +30 and 30 relative to a reference axis, the notch axes are arranged at 90.

6. The method according to claim 1, wherein it comprises the production of a dry preform comprising several superimposed plies, said plies being formed from continuous dry fibers provided with a binder, said binder comprising a first polymer.

7. The method according to claim 1, wherein the production of the preform comprises the production of superimposed plies, by application by contact, by means of an application roller, of continuous fibers on a laying up tool, each ply being produced by applying one or several bands along an orientation on the laying up tool or on bands of the preceding ply, each band being formed of one or several continuous fibers.

8. The method according to claim 1, wherein the preform comprises at least 5% by weight of water, preferably from 5 to 40% by weight of water, more preferably from 10 to 40% by weight of water.

9. The method according to claim 1, wherein it comprises a step of drying the preform after needling.

10. The method according to claim 1, wherein the preform comprises during needling a lubricating agent to reduce friction between the needles and the fibers of the preform, the lubricating agent comprising water, the preform comprising at least 2% by weight of water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood, and other objectives, details, characteristics and advantages will appear more clearly in the following detailed explanatory description of currently preferred embodiments of the invention, with reference to the schematic drawings annexed thereto, in which:

(2) FIG. 1 is a schematic sectional view of an example of a three-dimensional composite material part produced according to the method according to embodiments of the invention;

(3) FIG. 2 is a schematic side view illustrating the laying-up operation of the initial dry preform;

(4) FIG. 3 is a schematic top view of the preform obtained after laying-up the first four plies, on which the plies are partially shown to illustrate the orientation of said plies;

(5) FIG. 4 is a schematic side view illustrating the needling operation of a non-woven fiber felt applied to the preform;

(6) FIG. 5 is a schematic view of a fork needle that can be used in the needling device,

(7) FIG. 6A is a partial enlarged view of FIG. 5 and FIG. 6B is a view along the plane VIB-VIB of FIG. 6A;

(8) FIG. 7 is a partial schematic sectional view of the preform after needling;

(9) FIG. 8 is a schematic view illustrating the orientation of the notches of the needles relative to the orientations of the fiber at 0, +45, 45 and 90 of the plies of the preform;

(10) FIGS. 9 and 10 are sectional views of the press illustrating the forming operation of the preform obtained after needling;

(11) FIG. 11 is a schematic sectional view of the injection mold illustrating the injection operation of the preform obtained after thermoforming;

(12) FIG. 12 is a view similar to that of FIG. 6A illustrating a barbed needle that can be used in the needling device;

(13) FIG. 13 is a view similar to FIG. 8, illustrating the orientation of the notches of the needles relative to the orientations of the fiber at +30 and 30 of another preform; and,

(14) FIG. 14 is a view similar to FIG. 8, illustrating the orientation of the notches of the needles relative to the fiber orientations at 0, +60 and 60 of another preform.

(15) FIG. 1 illustrates an example of a three-dimensional composite material part 1 that can be produced according to a method of the invention, comprising the laying up of continuous fibers to form a flat dry preform, the application of a felt of non-woven fibers to the preform and needling of the felt, the forming of the preform then its impregnation. The part presented here has the shape of a spherical cap 11 with an annular rim 12.

(16) In a first step, such as illustrated in FIG. 2, plies of unidirectional continuous fibers are laid up flat on a laying up tool 2 in different orientations, to form an initial two-dimensional dry panel or preform 101 presenting two main opposing faces 101a, 101b (FIG. 4).

(17) Laying up is carried out by means of a laying up device 3 comprising a fiber placement head 30, known per se, allowing automatic contact laying up of bands formed of one or more fibers. The fibers F enter the head 3 in the form of two layers of fibers, and the head comprises a guiding system 31 for guiding the fibers to the compacting roller 32 in the form of a band of fibers in which the fibers are arranged side by side, for example substantially edge to edge. The head comprises, on either side of the guiding system, cutting means 33 for individually cutting each fiber passing through the guiding system, blocking means 34 for blocking each fiber that has just been cut, and feeding means 35 to individually feed each fiber, in order to be able to stop and resume the application of a fiber at any time, as well as to choose the width of the band. The laying up of a band is achieved by relative movement of the head in relation to the substantially planar layup surface of the layup tool. The head comprises for example a support structure (not shown) on which is mounted the guiding system and by which the head can be assembled to a displacement system, adapted to move the head in at least two directions perpendicular to each other. The head is for example designed to receive eight fibers, and allow the application of bands of 1 to 8 fibers of 6.35 mm ( inch) wide.

(18) The head is here used for the production of a dry preform, from dry fibers provided with a binder, to give a tackiness to the fibers during the laying up and ensure the cohesion of the preform. The binder, consisting of a polymer, may be applied to the fibers prior to laying up, for example in the form of a veil and/or powder, bobbins of fibers pre-provided with the binder being loaded into the fiber placement machine. The binder may be applied on line, during the laying up of the fibers, for example directly on the fibers to be laid, for example in the form of filaments, as described in the French patent application No. 16 70088, filed Mar. 7, 2016 and entitled Process for producing preforms with application of binder on dry fiber, and corresponding machine.

(19) In the particular case of fibers pre-provided with binder, the head 3 is preferably equipped with a heating system (not shown), for example of the IR lamp or laser type, in order to heat the binder during the application of the fibers, and thus allow at least an adhesion of the fibers of the different plies. The heating system heats the fibers before they are applied to the application surface, as well as the application surface or the fibers previously laid, upstream of the roller relative to the direction of the advancement of the head.

(20) The fibers are, for example, continuous flat carbon fibers, of the tows type, comprising a multitude of threads or carbon filaments, with a thermoplastic binder present in an amount of about 2% by weight.

(21) The preform is formed of plies with different fiber orientations, the orientations being conventionally defined relative to a reference axis X, conventionally corresponding to a main axis of the part to be produced, and possibly to the main load axis of the part.

(22) The fiber orientations at a and (180) are equivalent. Conventionally, the fiber orientations are defined between +90 and 90 relative to the X axis, the fiber orientations at +90 and 90 being equivalent.

(23) For example, the preform is formed of eight plies of fibers, according to the following laminate sequence +45/45/0/90/90/0/45/+45.

(24) FIG. 3 schematically illustrates the fiber orientations of the first four plies laid: a first ply 111 with a first orientation at +45; a second ply 112 with a second fiber orientation at 45; a third ply 113 with a third fiber orientation at 0, and, a fourth ply 114 with a third fiber orientation at 90.

(25) After producing the preform, a felt 4 of nonwoven filaments or fibers 40 is applied to a first main face 101a of the dry preform, and the preform thus equipped with the felt is subjected to a needling operation, such as schematically illustrated in FIG. 4, by passing through a needling device or needler 5.

(26) The needling device 5, known per se for consolidating mats of fibers, comprises a plurality of needles 8 mounted on a support 52 or needle board, able to be driven, by appropriate means 53, with a back and forth movement in a direction parallel to the needles. The needling device comprises a perforated support table 54 arranged facing the needles and intended to support the preform, and a stripper plate or stripper device 55 placed between the support table and the needles, provided with through holes for the passage of the needles. The support table also includes a set of holes to allow for the passage of the needles after they have passed through the preform.

(27) The needling device is here equipped with the forked 8 needles, of longitudinal axis A, such as illustrated in FIGS. 5, 6A and 6B, each needle comprising at the end of its distal portion or working part 81 a notch 82, so that the needle drives the filaments only during the penetration phase, from top to bottom in FIG. 4. The notch 82 is defined between a bottom wall 83 and two side walls 84a, 84b and has an axis B, called notch axis, arranged parallel to said walls 83, 84a, 84b, and perpendicular to the longitudinal axis A of the needle.

(28) During needling, the preform is driven positively in the direction of the arrow referenced F1, and the needles are driven back and forth. When moving the needles downwards, fibers of the felt are positioned in the notches 51b of the needles and are driven through the entire thickness of the preform, the filaments emerging on the second main face 101b, such as schematically illustrated in FIG. 7. The needling density is defined according to the frequency of the back and forth movement of the needles, the number of needles, and the advancement speed of the preform in the needling device.

(29) According to an embodiment of the invention, the needling is carried out so that the notch axes make a non-zero angle with the orientations of the fiber of the plies.

(30) With reference to FIG. 8, the notch axes B are preferably arranged along a bisector of the angle between two adjacent orientations, that is to say along the bisector C1 of the angle between the fiber orientations at 0 and +45, arranged at 22.5 from the X axis; along the bisector C2 of the angle between the fiber orientations at 0 and 45, arranged at 22.5 from the X axis; along the bisector C3 of the angle between the fiber orientations at +45 and 90, arranged at 67.5 from the X axis; and/or along the bisector C3 of the angle between the fiber orientations at 45 and 90, arranged at 67.5 from the X axis.

(31) According to one embodiment, all the needles are identical and are mounted in the same way on the needle board, the notch axes of the needles all having the same orientation.

(32) In the case of a main fiber orientation at 0, corresponding to the main load axis X of the part, the notch axes are oriented at +67.5 or 67.5, for example at 67.5 such as illustrated in FIG. 8, in order to obtain a maximum angle between the notch axes and the fibers oriented at 0, and thus to limit as much as possible the risks of breakage of these fibers oriented at 0.

(33) The orientation of the notch axes relative to the fiber orientations of the preform is for example obtained by appropriately orienting the preform entering a needling device whose position is fixed.

(34) Preferably, before the needling operation, a lubricant, also called a lubricating agent, is applied to the dry preform. The lubricating agent comprises water and is applied by a spray system on the preform.

(35) During needling, the water present in the preform as a lubricating agent reduces the friction between the needles and thus reduces the heating of the preform, which guarantees an efficient transfer of the felt filaments through the preform, this limits the breakage of the fibers, and makes it possible to trap in the preform any possible fibrils resulting from the breakage of fibers. After needling, the preform is advantageously subjected to a drying operation in order to reduce the water content of the preform or remove any trace of water in the preform. This drying operation is for example carried out by placing the preform in an oven.

(36) After needling, the rest of the felt formed by the filaments present on the first face which have not been needled can be kept on the preform or be removed. According to one embodiment, the needling density and the penetration depth of the needles, which is equal to the distance between the end of the needle and the second main face of the preform, are defined so that the preform has a quantity of filaments, preferably similar, on each of its faces, these filaments on the surface increasing the permeability of the preform, and facilitating in addition the forming operation.

(37) According to an alternative embodiment, the filaments are not applied in the form of a felt, but projected in a random manner on the first face of the preform.

(38) The preform provided with needled filaments, called reinforced preform 201, is then transferred to a press for the forming operation, also called a stamping operation. Such as illustrated in FIG. 9, the press 6 comprises a female forming tool 61 or matrix, having a recess whose shape corresponds to that of the spherical cap 12 of the preform to be produced, and a male forming tool 62, or punch, comprising a boss of complementary shape. The forming is performed by bringing closer together the male forming tool and the female forming tool, from an open position of the press illustrated in FIG. 9 towards a closed position of the press illustrated in FIG. 10.

(39) The forming is carried with heat, the preform being at a forming temperature between the glass transition temperature and the melting temperature of the polymer constituting the binder, and between the glass transition temperature and the melting temperature of the polymer forming the filaments of the felt. This forming temperature of the preform is obtained by preheating the preform before positioning in the press and/or by heating the two tools 61, 62. This preheating is for example carried out by passing the initial preform between the upper and lower ramps of the infrared lamps of an oven or preheating tunnel. Preferably, during forming, the preform is kept under tension by a tensioning system, for example of the blank holder type, such as shown schematically under the reference 63. The tools 61, 62 are then spaced one from another in the open position to demold the reinforced three-dimensional preform 301 from the press.

(40) The resulting three-dimensional reinforced preform 301 is then subjected to an operation of adding or impregnating a thermosetting or thermoplastic impregnation polymer, by an injection and/or infusion process. With reference to FIG. 11, the three-dimensional reinforced preform is for example placed in an injection mold 7, between the male part and the female part of the mold, an impregnation polymer is injected under pressure into the preform, according to a RTM (Resin Transfer Molding) or Gap-RTM method, such as schematically illustrated by the arrow referenced F2. The composite part 1 obtained at the end of this impregnation step may be subjected to a trimming operation.

(41) Alternatively, the needling device is equipped with forked needles comprising several notches at its end. According to another embodiment, the needling device is equipped with said barbed needles 108, such as illustrated in FIG. 12, comprising along its distal portion or working portion 181 one or more notches, oriented in the direction of the end of the needle, for example two notches 182a, 182b, arranged symmetrically on either side of the longitudinal axis, and whose notch axes are arranged in parallel.

(42) For example, a part is produced according to the following process: Laying up: Laying up of a preform by placement of carbon fibers provided with a binder applied in line, formed of a thermoplastic copolyester having a melting point of around 130 C., and a glass transition temperature of around 15 C., the preform being produced by laying eight plies of fibers in different orientations, according to the following laminate sequence: +45/45/0/90/90/0/45/+45. Humidification: application of water on the preform, the resulting preform comprising 30% by weight of water. Application: Application of a non-woven felt made of filaments or polyester fibers 14 m in diameter, with a length of 40 to 60 mm, and a melting point of about 200 C., said felt, of isotropic orientation, having a surface mass of 50 g/m.sup.2. Needling with forked needles, having a working part of gauge 42 (0.40 mm), having a notch or fork at the end, 0.05 mm in depth and 0.05 mm in width, with a needling density of 200 punches/cm.sup.2 and a penetration depth of 5 mm, the notch axes being oriented at 67.5 from the X axis. drying: drying of the preform by passage in an oven above 100 C. Forming: forming at a forming temperature of 120 C. Injection: injection of the type gap-RTM of a thermosetting epoxy polymer in a three-minute cycle with a first phase of compression and heating to 120 C. for about 2 minutes, and a second injection and polymerization phase at 50 bars, put under vacuum, for about 1 minute.

(43) FIG. 13 illustrates the orientation of the notch axes B during needling in the case of a preform formed of plies with fiber orientations at +30 and 30. According to the invention, the notch axes B are arranged along a bisector of the two adjacent orientations, that is to say along the first bisector C1 between the fiber orientations at 30 and +30, arranged at 0 from the X axis; along the second bisector C2 between the fiber orientations at 30 and +30, positioned at 90 from the X axis.

(44) Such as illustrated in FIG. 13, the notch axes B are preferably arranged so that the angle with the reference axis is the maximum, that is along the second bisector at 90.

(45) FIG. 14 illustrates the orientation of the notch axes B of a preform formed of plies with fiber orientations at 0, +60 and 60. The notch axes B are then arranged along a bisector of two adjacent orientations, that is to say along the bisector C1 between the fiber orientations at 0 and 60, at 30 from the X axis; along the bisector C2 between the fiber orientations at 0 and 60, at 30 from the X axis; and/or along the bisector C3 between the fiber orientations at 60 and +60, at 90 from the X axis.

(46) Such as illustrated in FIG. 14, the notch axes B are preferably arranged so that the angle with the reference axis is the maximum, that is along the bisector C3 at 90.

(47) Although the invention has been described in connection with various particular embodiments, it is obvious that it is not limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if they are within the scope of the invention.