Method for manufacturing parts made of composite material and having variations in cross-section, and parts obtained by implementing the method

Abstract

The invention relates to a method for manufacturing parts made of composite material, which are capable of being mechanically stressed, may have variations in cross-section and / or variations in curvature or torsion, and have a preferred direction. The method consists in carrying out the following operations, in succession: • - stacking at least two unidirectional webs (2, 3) of fibres cross-laid at + or -N°; • - producing an essentially cylindrical tube by winding the set of at least two webs (2, 3) around itself about a winding axis (R); • - compressing the tube by a mechanical action perpendicular to the winding axis (R) in order to deform it so that it adopts the shape of the preform used for polymerising the part to be manufactured.

Description

[Description Title of the invention: Method for manufacturing parts made of composite material having variations in cross section, and parts obtained by implementing the method

[0001] The present invention relates to a method for manufacturing parts made of composite material capable of being mechanically stressed, having variations in cross-section and possibly, in addition, variations in curvature or torsion, and having a preferred direction.

[0002] The present invention also relates to parts implemented by said method.

[0003] Such parts may consist, but are not limited to, beams, automotive spring blades, connecting rods, lattice bars, and aircraft propeller blades.

[0004] In particular, such a part consists of a blade.

[0005] Typically, these parts are obtained by draping layers of unidirectional sheets whose fiber orientations are chosen in the directions most favorable to resistance to stresses. The particularity of these parts lies in the difficulty of carrying out the draping given the evolving shapes and the high mechanical stresses supported by these parts.

[0006] It is well known that the failure mode limiting the use of composites for such types of parts is the delamination of the fiber layers.

[0007] In order to combat these phenomena, solutions exist to place fibers in the direction orthogonal to the main direction of the fibering, that is to say crossing the different layers.

[0008] It is thus possible to produce a preform by 3D weaving, as shown schematically in Figure 1. We can see a superposition of unidirectional sheets, the fibers of which extend alternately in directions different, to form superimposed layers C, while fibers F are woven to join the different layers C.

[0009] This has two main disadvantages: it is only suitable for RTM (Resin transfer molding) or infusion methods, and it excludes the use of pre-impregnated materials, which leads to a very high cost of producing preforms.

[0010] Also known in the state of the art is US patent application filed under number US 2020 / 0391 11 and relating to a preform element, a preform using the preform element and a method for producing the preform made from a prepreg comprising reinforcing fibers and a thermosetting resin to be subjected to compression molding such as press forming.

[0011] However, the process described here does not allow for the production of a part with a variation in cross-section.

[0012] Also known from American document US 2022 / 288872 is a method of manufacturing a composite part by superimposing layers.

[0013] More particularly, this method comprises, in a first step, a step of preparing a mandrel having a circular cross-section and prepreg sheets. The next step consists of a first winding step, in which a demolding treatment is carried out on the outer circumference of the mandrel, and then the prepreg sheets are wound around the mandrel. A first cylindrical laminated body is thus produced. This is followed by a first compression step during which the mandrel is rotated, so that a thin strip is wound around the outer circumference of the first laminated body with a predetermined tension.The prepreg sheets thus rolled are compressed and pressurized by relatively moving the thin strip along the direction of the longitudinal axis of the mandrel, so that the first strip can be wound over the entire surface of the first laminated body to form a thin layer of approximately uniform thickness.

[0014] A first heating step is then carried out, in which the first laminated body around which the thin strip is wound is placed with the mandrel in an oven and heated for two hours, at 135°C, for example, to complete curing of the first laminated body. The mandrel and the first laminated body are removed from the furnace, and the thin strip wound around the outer circumference of the laminated body is peeled off. These operations are followed by roughing treatment performed by grinding, or the like, on the surface of the outer circumference of the first laminated body, by which a minute uneven microstructure is formed. Alternatively, a minute unevenness may be formed on the surface by wrapping a thin sheet of peelable fabric on the outermost layer after wrapping the last prepreg sheet in the first wrapping step and peeling off the peelable layer after removing the thin strip after the first heating step. Furthermore, an adhesive sheet may be wrapped around the outer circumference of the first laminated body.In this way, the adhesion of the first laminated body with a second laminated body, subsequently formed in the method of this state of the art, can be improved.

[0015] Indeed, the method described herein continues by carrying out a second winding step, on the first laminated body, by means of additional prepreg sheets which consist of a composite material comprising second reinforcing fibers impregnated with a second thermosetting resin, and which are heated or dried to a semi-cured state. The first sheet which is wound around the outer circumference of the mandrel protrudes from both ends of the first laminated body in the longitudinal direction, then other prepreg sheets are wound sequentially and having the same length as the first, the sheets having different fiber orientations so as to resist expansion when the structural body receives a compressive stress.A pair of trapezoidal-shaped prepreg sheets can finally be wound around both ends of the last sheet, that is, on the outermost circumference only around the two end portions, to achieve a reinforcing effect at these ends. A second outer cylindrical laminated body is thus formed by winding a plurality of prepreg sheets around the first laminated body.

[0016] The method described in this state of the art continues with the implementation of the following subsequent steps:

[0017] - a second compression stage;

[0018] - a preheating step;

[0019] - an extraction step.

[0020] It is thus possible, by means of implementing a complex, time-consuming and therefore costly process, to obtain a part with an external diameter capable of varying progressively.

[0021] That being said, in addition to requiring the implementation of a complex process, the part obtained is ultimately made up of two cylindrical laminated bodies, the first internal and the second external, the link between the two bodies being likely not to be carried out correctly and to lead, again, to delamination.

[0022] The aim of the present invention is to propose an alternative method for the manufacture of these aforementioned parts, and remedying the aforementioned drawbacks by allowing the use of industrially available pre-impregnated semi-finished products, to materialize out-of-plane fibrous links, and the production of long, scalable shapes, and for a modest implementation cost.

[0023] It is first appropriate to recall some notions relating to the production of increasingly complex composite parts, while starting from an elementary part.

[0024] In practice, a stack of unidirectional prepreg layers arranged alternately at + or - N° is compacted to form a compact preform. This preform has high transverse plasticity provided that the angle N is small (typically less than 30°). That is to say, under the effect of the compression of the preform, the angle N can increase so as to allow the preform to widen. Such a property allows easy shaping in a mold by transverse expansion of a preform thus formed.

[0025] The method traditionally used for a part supporting tensile or compressive (or bending) stresses consists of making a stack of unidirectional layers at 0° (of the order of 90% to 80%), and layers of fibers at 90° (of the order of 10% to 20%) which have the role of guaranteeing the transverse cohesion of the part. If this method of draping guarantees good health of the material for its transverse hold, it blocks the expansion of the preform in a compression shaping operation aimed at lateral adaptation in the mold.

[0026] The present invention aims to provide a method for adapting the plasticity property to enable the creation of bonds in the direction of the thickness of the preform, together with the bonds in the longitudinal and transverse directions.

[0027] The method of manufacturing parts made of composite material capable of being mechanically stressed, having variations in cross-section and / or variations in curvature or torsion, and having a preferred direction, according to the invention, is characterized in that it consists of successively carrying out the following operations: - stack at least two unidirectional layers of fibers crossed at + or - N°, - produce a generally cylindrical sausage by winding the two layers around a winding axis, - compress said sausage by a mechanical action perpendicular to the winding axis, in order to deform it to make it take the shape of the preform used for the polymerization of the part to be manufactured.

[0028] In the method of the invention, the sheets are further cut, before or after superposition, to a suitable shape from a pattern, so as to lead to the production, after rolling, of a sausage having portions of different diameters.

[0029] It will be noted that preferably but not limited to, the winding axis is parallel to the longitudinal axis 0° of reference for the orientation of the fibers.

[0030] The inclination of the fibers relative to the longitudinal direction, associated with winding and then compression, allows the preform, then the part thus formed, to present fibrous bonds in the transverse direction as well as in the direction of the thickness. These bonds, which bind the composite layers in their thickness, allow for reinforced cohesion, pushing back the problems of delamination between the layers.

[0031] According to an additional characteristic of the method according to the invention, the superposition of sheets is wound onto a mandrel which, after removal, makes it possible to obtain a tubular rod.

[0032] The composite sausage, tubular or not, obtained during the first stage of the process according to the invention can be deformed by compression in a mold guaranteeing a constant section along the profile that one wishes to constitute.

[0033] The plasticity of the composite sausage allows it to adapt to many shapes while maintaining cohesion properties in the three directions of space.

[0034] According to an additional characteristic of the method according to the invention, one or more plies of fibers of an orientation other than those of the fibers of said plies are incorporated into the superposition of sheets, before or during the winding operation, depending on the part to be produced.

[0035] Furthermore, the plasticity of the composite rod also allows the production of composite parts with a certain degree of curvature. When bending the composite rod, each fiber, which follows a helical path, is stressed in extension at the convex zone, and in compression at the concave zone, this compensation makes it possible to avoid a risk of wrinkling.

[0036] However, the degree of curvature, which also depends on the angulation value of the fibers, is limited, and to overcome this drawback, the method according to the invention includes a variant.

[0037] Thus, according to an additional characteristic of the method according to the invention, before the operation of stacking the sheets, each of the latter is subjected to a cutting operation, which consists of making cutting lines in them along alternating discontinuous lines, so that on the one hand each fiber is cut at a pitch, constant or not, on the other hand the integrity of the sheet is preserved, and on the other hand again that in the stacking of the sheets the cutting lines of one sheet are offset relative to those of the adjacent sheet.

[0038] According to particular embodiments of the method according to the invention, the sheets are cut in an identical manner, and during stacking, they are offset one tablecloth in relation to another, or else we make offset cuts and the tablecloths are perfectly superimposed.

[0039] Preferably, the winding is carried out around an axis perpendicular to the cutting lines.

[0040] The resulting composite sausage is mainly made up of fibers oriented at + or - N°, alternately sectioned, promoting local extension by sliding the fibers apart longitudinally from each other. Such a sausage can withstand greater bending than that permitted without cutting.

[0041] According to one variant, the cuts are advantageously located only in one or more particular areas of the sheets, depending on the part to be produced.

[0042] The advantages and characteristics of the method according to the invention will emerge more clearly from the description which follows and which refers to the attached drawing, which represents non-limiting modes of implementation.

[0043] In the attached drawing:

[0044] [Fig.1] represents a schematic perspective view illustrating a state-of-the-art method,

[0045] [Fig.2] represents schematic perspective views of three steps A, B and C of the method according to the invention,

[0046] [Fig.3] represents an elevation view of another stage of the same process,

[0047] [Fig.4] represents a schematic sectional view of another step of the same process,

[0048] [Fig.5] represents a partial schematic perspective view with cutaway, of another stage of the same process,

[0049] [Fig.6] represents a schematic perspective view of a composite part manufactured using the method according to the invention,

[0050] [Fig.7] represents views A, B and C, schematic and in perspective, of stages of manufacturing of another composite part,

[0051] [Fig.8] represents schematic plan views, A and B, which illustrate steps in implementing a variant of the method according to the invention.

[0052] [Fig.9] represents a schematic elevation view, illustrating a variant of the same process.

[0053] [Fig.10] represents a schematic and perspective view of a blade capable of being obtained by implementing the method of the present invention, said blade having a variation in its section along its main longitudinal axis.

[0054] With reference to figures 2A to 2C, it can be seen in view A that two unidirectional sheets 2 and 3 are used, the fibers 20 of one of which are oriented at an angle a relative to the longitudinal axis 0, while the fibers 30 of the other are oriented at an angle [3 relative to the longitudinal axis 0, in this case a is the symmetrical of [3.

[0055] In view B it can be seen that the next step consists of superimposing and applying against each other the plies 2 and 3, while in view C it can be seen that the next step consists of winding the superposition of the plies 2 and 3 around a winding axis R, so as to obtain a sausage 4, as shown in figure 3.

[0056] This sausage 4 is therefore made up of the superposition of the two layers 2 and 3 wound in a spiral.

[0057] With reference to figure 4 it can be seen that the sausage 4 has been placed in a mold 5 where it is compressed by a mechanical action P, perpendicular to the winding axis, so as to obtain a preform 6 used for the polymerization of the part to be manufactured.

[0058] With reference to Figure 5, the preform 6 obtained can be seen. The inclination of the fibers 20 and 30 relative to the longitudinal direction X, associated with the winding and then the compression, allows the preform, and therefore the part thus formed, to have fibrous links in the transverse direction Y as well as in the thickness direction Z.

[0059] These fibrous bonds which unite the composite layers in their thickness allow for reinforced cohesion, repelling problems of delamination between the layers.

[0060] Referring now to Figure 6, we can see a rectilinear part 7, of evolving shape and constant section. It comes from a sausage 4 after molding, and it has portions 70, 71 and 72, of different shapes, the cross sections of which, respectively 700, 710 and 720, are also shown, and showing a distribution of the fibers in all directions.

[0061] Figures 7 represent stages in the manufacture of a part 8, view C, rectilinear and of evolving shape, but of non-constant section.

[0062] In view A, we make the superposition of two unidirectional sheets 2 and 3, then we make the cutting of this superposition according to a pattern, or we cut the unidirectional sheets 2 and 3 according to the pattern before superposition.

[0063] Then the winding is carried out around an axis R, so as to obtain a strand 40 of non-constant section, view B, to end up with the part 8 after molding and polymerization.

[0064] Thus, it is possible, by means of implementing the method of the invention, including a step according to which the unidirectional sheets 2, 3 are cut, before or after superposition, to an appropriate shape according to a pattern, to obtain a roll 40, then a part 8, of portions of different diameters and evolving along the longitudinal axis of said final part.

[0065] The present invention then makes it possible to maintain reinforced cohesion in the thickness of the unidirectional fiber layers, even if the section of the final part is evolving and not constant along its longitudinal axis, while proposing a simple, rapid, and inexpensive process to implement.

[0066] It will be noted that according to a variant not shown, it is possible to incorporate into the superposition of the sheets 2 and 3, parts of sheets, of chosen shapes, arranged in particular locations, and by orienting the fibers of these pieces in preferred directions, depending on the composite part to be produced.

[0067] Figures 8 show a variant of the method according to the invention, or more precisely an optional step making it possible to obtain parts with more complex shapes, and in particular, but not limited to, when it is a question of bending the sausage.

[0068] In view A we can see the sheets 2 and 3, in which cuts are made, perpendicular to the longitudinal axis 0, in the form of the cutting lines, respectively 21 and 31, along alternating discontinuous lines, so as to cut the fibers 20 and 30.

[0069] In view B we can see the superposition of the two layers 2 and 3, which is carried out so that the cutting lines 31 are not opposite the cutting lines 21.

[0070] It should be noted that in this case the cuts of layers 2 and 3 are made according to identical patterns, which requires that their superposition be carried out with an offset in the longitudinal direction. Of course, it is possible to carry out the cuts according to offset patterns, allowing for perfect superposition.

[0071] It will be understood that after rolling the superimposed and cut sheets 2 and 3, a more malleable sausage is obtained, and more capable of taking curved shapes, since the partially cut fibers are more likely by sliding to adapt to non-developable shapes. Preferably, as shown, the winding is carried out around an axis R perpendicular to the cutting lines 21 and 31.

[0072] The substantial overlap of the folds helps to limit the harmful influence of the cuts.

[0073] Of course, the cutting lines 21 and 3 may not extend over all the layers, and may be located in one or more places depending on the shapes of the part to be manufactured.

[0074] In other words, this cutting operation by cutting line can be local, limited in the area of the part requiring significant deformations.

[0075] Likewise, this variant can be combined with a preliminary cutting of the tablecloths or the superposition of tablecloths, according to a pattern, in order to cover a multitude of possibilities.

[0076] Finally, with reference to Figure 9, it can be seen that the winding of the superposition of sheets 2 and 3 can be carried out on a mandrel, so as to to obtain not a cylindrical sausage, but a tubular preform 9 having an interior space 90.

[0077] Such a preform 9, after crushing in a mold, makes it possible to obtain a central part which has fibers in the two preferred directions, namely those of fibers of the layers 2 and 3, while the fibrous bonds which pass through the layers in the direction of the thickness are concentrated at the longitudinal edges which are the zones at which delaminations generally appear on the parts of the state of the art.

[0078] Furthermore, the plasticity of the preform 9 also allows its deformation by radial compression of the folds. This can be achieved from the inside of the sausage, in a shaped mold by using a mechanical expanding mandrel or by pressurizing a bladder.

[0079] The method according to the invention, whatever the version used, alone or in combination with one or more other variants, makes it possible to manufacture numerous parts in composite material of all shapes, straight, curved, etc., and likely to be mechanically stressed.

[0080] On the other hand, the process according to the invention makes it possible to produce parts at high speeds, automatically, unlike conventional draping which can be likened to craftsmanship.

Claims

Claims

1. Method for manufacturing parts made of composite material capable of being mechanically stressed, capable of having variations in cross-section and / or variations in curvature or torsion, and having a preferred direction, characterized in that it consists of successively carrying out the following operations: - stack at least two unidirectional layers (2, 3) of fibers crossed at + or - N°, - producing a sausage (4; 40; 9) of generally cylindrical shape by winding the set of at least two layers (2, 3) around a winding axis (R), - compressing said sausage (4; 90; 9) by a mechanical action perpendicular to the winding axis (R), in order to deform it to make it take the shape of the preform used for the polymerization of the part (7; 8) to be manufactured, and in that, said sheets (2, 3) are cut, before or after superposition, to a suitable shape according to a pattern, so as to lead to the production, after winding, of a sausage (40) having portions of different diameters.

2. Method for manufacturing parts made of composite material according to claim 1, characterized in that the superposition of sheets (2, 3) is wound onto a mandrel which, after removal, makes it possible to obtain a tubular rod (9).

3. Method for manufacturing parts made of composite material according to claim 1 or claim 2, characterized in that one or more plies of fibers of an orientation other than those of the fibers (20, 30) of said plies (2, 3) are incorporated into the superposition of sheets (2, 3), before or during the winding operation, depending on the part to be produced.

4. Method for manufacturing parts made of composite material according to any one of claims 1 to 3, characterized in that before the operation of stacking the plies (2, 3), each of the latter is subjected to a cutting operation, which consists of making in them cutting lines (21, 31) along alternating discontinuous lines, so that on the one hand each fiber (20, 30) is cut at a pitch, constant or not, on the other hand the integrity of the sheet (2, 3) is preserved, and on the other hand again that in the stack of sheets (2, 3) the cutting lines of a sheet are offset relative to those of the adjacent sheet.

5. Method for manufacturing parts made of composite material according to claim 4, characterized in that the plies (2, 3) are cut identically, and during stacking one ply is offset relative to another, or else offset cuts are made and the plies (2, 3) are perfectly superimposed.

6. Method for manufacturing parts made of composite material according to claim 4 or claim 5, characterized in that the cuts are located only in one or more particular zones of the layers (2, 3), depending on the part to be produced.

7. Method according to any one of claims 4 to 6, characterized in that the winding is carried out around an axis (R) perpendicular to the cutting lines (21, 31).

8. Part made of composite material characterized in that it is manufactured by the method according to any one of claims 1 to 7.

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