Process for manufacturing parts made of composite material, and parts obtained by implementing the process

Abstract

Title: Method for manufacturing parts made of composite material, and parts obtained by implementing the method; 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. It consists of successively carrying out the following operations: stacking at least two unidirectional layers (2, 3) of fibers crossed at + or – No., producing a generally cylindrical shaped rod by winding on itself all of the at least two layers (2, 3) around a winding axis (R), compressing the rod 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 to be manufactured. Figure for the abstract: Fig. 2

Description

Title of the invention: Method for manufacturing parts made of composite material, 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, capable of exhibiting variations in cross-section and / or variations in curvature or torsion, and exhibiting a preferred direction.

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

[0003] Such parts may consist, without limitation, of beams, automobile spring blades, connecting rods, lattice bars, and aircraft propeller blades.

[0004] Usually, 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 taking into account the evolving shapes and the high mechanical stresses supported by these parts.

[0005] It is well known that the mode of failure limiting the use of composites for such types of parts is the delamination of the fiber layers.

[0006] In order to combat these phenomena, solutions exist for placing fibers in the direction orthogonal to the main direction of the fibering, that is to say crossing the different layers.

[0007] It is thus possible to produce a preform by 3D weaving, as shown schematically in [Fig.l]. It shows a superposition of unidirectional sheets, the fibers of which extend alternately in different directions, to form superimposed layers C, while fibers F are woven to join the different layers C.

[0008] This essentially has two 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 the preforms.

[0009] The present invention aims to propose an alternative method for the manufacture of these aforementioned parts, and to overcome 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.

[0010] It is first appropriate to recall some notions relating to the production of increasingly complex composite parts, while starting from an elementary part.

[0011] 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 expand. Such a property allows easy shaping in a mold by transverse expansion of a preform thus formed.

[0012] 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 the good health of the material for its transverse resistance, it blocks the expansion of the preform in a compression forming operation aimed at lateral adaptation in the mold.

[0013] The present invention aims to propose 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.

[0014] The 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, 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 shaped 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.

[0015] It will be noted that preferably but not limitatively, the winding axis is parallel to the longitudinal axis 0° of reference orientation of the fibers.

[0016] The inclination of the fibers relative to the longitudinal direction, associated with the winding and then the compression allows the preform, then the part thus formed, to have 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, preventing delamination problems between layers.

[0017] 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.

[0018] 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.

[0019] The plasticity of the composite sausage allows it to be adapted to numerous shapes while maintaining cohesion properties in the three directions of space.

[0020] 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.

[0021] Depending on the dimensional and / or volume characteristics of the part to be manufactured, the sheets are cut, before or after superposition, to a suitable shape from a pattern, so as to lead to the production, after winding, of a roll having portions of different diameters.

[0022] Furthermore, the plasticity of the composite rod also makes it possible to produce composite parts having 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.

[0023] 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.

[0024] 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.

[0025] According to particular embodiments of the method according to the invention, the sheets are cut in an identical manner, and during stacking, one sheet is offset relative to another, or else offset cuts are made and the sheets are perfectly superimposed.

[0026] Preferably, the winding is carried out around an axis perpendicular to the cutting lines.

[0027] The composite sausage obtained 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.

[0028] According to one variant, the cutouts are advantageously located only in one or more particular zones of the sheets, depending on the part to be produced.

[0029] 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.

[0030] In the attached drawing:

[0031] [Fig-1] represents a schematic perspective view illustrating a process of the state of the technique,

[0032] [Fig.2A], [Fig.2B] and [Fig.2C] represent schematic perspective views of three steps A, B and C of the method according to the invention,

[0033] [Fig.3] represents an elevation view of another step of the same process,

[0034] [Fig.4] represents a schematic sectional view of another step of the same process,

[0035] [Fig.5] represents a partial schematic perspective view with cutaway, of a another step of the same process,

[0036] [Fig.6] represents a schematic perspective view of a composite part manufactured using the process according to the invention,

[0037] [Fig.7A], [Fig.7B] and [Fig.7C] represent views A, B and C, schematic and in perspective, of manufacturing stages of another composite part,

[0038] [Fig.8A] and [Fig.8B] represent schematic plan views, A and B, which illustrate steps of implementing a variant of the method according to the invention.

[0039] [Fig.9] represents a schematic elevation view, illustrating a variant of the same process.

[0040] With reference to figures 2, 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.

[0041] 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 [Fig.3].

[0042] This sausage 4 is therefore made up of the superposition of the two layers 2 and 3 wound in a spiral.

[0043] With reference to [Fig.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.

[0044] With reference to [Fig.5] we can see the preform 6 obtained. The inclination of the fibers 20 and 30 relative to the longitudinal direction X, associated with the winding then the compression allows the preform, and therefore the part thus formed, to have fibrous links in the transverse direction Y as in the direction of the thickness Z.

[0045] These fibrous links which join the composite layers in their thickness allow reinforced cohesion pushing back the problems of delamination between the layers.

[0046] Referring now to [Fig. 6], we can see a rectilinear part 7, of evolving shape and constant sections. 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.

[0047] Figures 7 represent stages of manufacturing a part 8, view C, rectilinear and of evolving shape, but of non-constant section.

[0048] In view A, two unidirectional sheets 2 and 3 are superimposed, then this superposition is cut according to a pattern, or the unidirectional sheets 2 and 3 are cut according to the pattern before superposition.

[0049] Then the winding is carried out around an axis R, so as to obtain a roll 40 of non-constant section, view B, to result in the part 8 after molding and polymerization.

[0050] It will be noted that according to a variant not shown, it is possible to incorporate into the superposition of the plies 2 and 3, parts of plies, of chosen shapes, arranged in particular locations, and by orienting the fibers of these inserts in preferred directions, depending on the composite part to be produced.

[0051] Figures 8 show a variant of the method according to the invention, or more precisely an optional step making it possible to obtain parts of more complex shapes, and in particular, but not limited to, when it is a question of bending the sausage.

[0052] 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.

[0053] In view B we can see the superposition of the two sheets 2 and 3, which is carried out so that the cutting lines 31 are not opposite the cutting lines 21.

[0054] It will be noted that in this case the cuts of the sheets 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.

[0055] It will be understood that after rolling the superimposed and cut plies 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.

[0056] The substantial overlap of the folds makes it possible to limit the harmful influence of the cuts.

[0057] Of course, the cutting lines 21 and 3 may not extend over all of the layers, and may be located in one or more places depending on the shapes of the part to be manufactured.

[0058] Likewise, this variant can be combined with a prior cutting of the sheets or the superposition of sheets, according to a pattern, so as to cover a multitude of possibilities.

[0059] Finally, with reference to [Fig. 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 obtain not a cylindrical rod, but a tubular preform 9 having an interior space 90.

[0060] 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 the 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.

[0061] Furthermore, the plasticity of the preform 9 also allows its deformation by radial compression of the folds. It can be carried out from the inside of the sausage, in a mold by using a mechanical expanding mandrel or by pressurizing a bladder.

[0062] 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 capable of being mechanically stressed.

[0063] Furthermore, the method 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: - stacking at least two unidirectional sheets (2, 3) of fibers crossed at + or - N°, - producing a rod (4; 40; 9) of generally cylindrical shape by winding on itself all of the at least two sheets (2, 3) around a winding axis (R), - compressing said rod (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 plies (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 cutting lines (21, 31) in them along alternating lines discontinuous, 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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