Method for manufacturing a part made of composite material and having a varying cross section, and part obtained by implementing this method

Abstract

The invention relates to a method for manufacturing a part made of composite material, able to withstand mechanical stresses and which can have a cross-section variation and / or a curvature or torsion variation, and having a preferential direction. The method comprises the following operations, in succession: - laying up at least two unidirectional plies (2, 3) in which the fibres cross at + or - N°; - making a substantially cylindrical tube by winding around a winding axis (R) the group of at least two plies (2, 3); - compacting the tube by mechanical action perpendicular to the winding axis (R) to deform the tube so as to have the shape of a preform for the polymerisation reaction for manufacturing the part.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a part made of composite material and having a variable cross-section, and the part obtained by performing the method.

[0002] The present invention relates to a method for manufacturing composite material parts capable of withstanding mechanical stress, having a cross-sectional variation and optionally also having a curvature or torsional variation, and having a preferred orientation.

[0003] The present invention also relates to parts implemented by the method. Background Technology

[0004] Such parts can include, but are not limited to, beams, automotive leaf springs, connecting rods, lattice rods, and aircraft propulsion blades.

[0005] Most notably, such parts include blades.

[0006] Typically, these parts are obtained by laying multiple unidirectional plies, with the fiber orientation of the unidirectional plies chosen to be most favorable for resisting stress. What makes these parts special is the difficulty in manufacturing the laminated structure, considering their constantly changing shape and the high mechanical stress they endure.

[0007] As is well known, the failure mode that limits the use of composite materials in such parts is the delamination of the fiber layers.

[0008] To combat these phenomena, there are solutions that arrange the fibers in a direction orthogonal to the main direction of fiber stretching, that is, arrange the fibers to pass through multiple layers.

[0009] Therefore, preforms can be fabricated using three-dimensional weaving, such as... Figure 1 The diagram is schematically shown. This figure illustrates a stacked structure of unidirectional sheets, in which fibers of the unidirectional sheets extend alternately in different directions to form stacked layers C, while fibers F are woven to connect the individual layers C.

[0010] This essentially has two drawbacks: it is only applicable to RTM (resin transfer molding) or injection methods, and it excludes the use of prepregs, which results in very high costs for manufacturing preforms.

[0011] Also known in the prior art is a U.S. patent application with application number US 2020 / 039111, which relates to a preform element, a preform using the preform element, and a method for producing the preform, the preform being made of a prepreg containing reinforcing fibers and a thermosetting resin, and being subjected to compression molding such as compression molding.

[0012] Nevertheless, the method described herein cannot produce parts with varying cross-sections.

[0013] A method for manufacturing composite material parts by means of a layup structure is also known from US document US 2022 / 288872.

[0014] More specifically, the method includes the steps of first preparing a mandrel having a circular cross-section and a prepreg sheet. The next step is a first winding step, in which a demolding process is performed on the outer periphery of the mandrel, and then the prepreg sheet is wound around the mandrel. This forms a first cylindrical laminated structure. Next is a first pressing step, in which the mandrel is rotated, causing a thin strip to be wound around the outer periphery of the first laminated structure with a predetermined tension. The prepreg sheet thus laminated is pressed and pressured by moving the thin strip relative to the longitudinal axis of the mandrel, thereby enabling the first strip to be wound around the entire surface of the first laminated structure to form a thin layer of substantially uniform thickness.

[0015] The first heating step then proceeds, in which the first laminated structure, wound with a thin strip, is placed in an oven along with a mandrel and heated for two hours, for example, at 135°C, to fully cure the first laminated structure. The mandrel and the first laminated structure are removed from the oven, and the thin strip wound around the outer periphery of the laminated structure is peeled off. After these operations, the outer peripheral surface of the first laminated structure is rough-machined by grinding or the like, thereby forming a micro-structure with minute irregularities. Alternatively, a sheet of peelable fabric can be wound onto the outermost layer after the last layer of prepreg is wound in the first winding step, and then the peelable layer can be peeled off after removing the thin strip following the first heating step, thus forming minute irregularities on the surface. Furthermore, an adhesive sheet can be wound around the outer periphery of the first laminated structure. This improves the adhesion between the first laminated structure and the second laminated structure subsequently formed in the prior art method.

[0016] The method described herein continues with a second winding step, in which additional prepreg sheets are wound onto the first laminated structure. These additional prepreg sheets are composed of a composite material containing second reinforcing fibers impregnated with a second thermosetting resin and are heated or dried to a semi-cured state. The first sheet, wound around the outer periphery of the mandrel, extends longitudinally from both ends of the first laminated structure. Then, other prepreg sheets of the same length as the first sheet are wound sequentially, these sheets having different fiber orientations to resist expansion when the structure is subjected to compressive stress. Finally, a pair of trapezoidal prepreg sheets can be wound around both ends of the latter sheet, i.e., only around the two end portions on the outermost periphery, to obtain reinforcement at these ends. Thus, a second outer cylindrical laminated structure is formed by winding multiple prepreg sheets around the first laminated structure.

[0017] The method described in the prior art further includes the following subsequent steps: Second suppression step; Preheating step; Extraction steps.

[0018] Therefore, it is conceivable that by means of a method that is complex, time-consuming, and therefore expensive to implement, a part with an outer diameter that can be gradually varied can be obtained.

[0019] In this case, in addition to the need to implement complex processes, the final part consists of two cylindrical laminated structures, the first inside and the second outside. The connection between the two laminated structures may not be properly achieved, which in turn causes delamination. Summary of the Invention

[0020] The object of this invention is to provide an alternative method for manufacturing the aforementioned parts, and to overcome the aforementioned disadvantages by allowing the use of industrially available pre-impregnated semi-finished products to achieve out-of-plane fiber bonding and to manufacture variable elongated shapes, while being reasonably cost-effective.

[0021] It is necessary to review some ideas related to manufacturing increasingly complex composite parts in advance, while starting with a basic part.

[0022] In practice, layers of unidirectional prepreg, arranged alternately at + or -N°, are laid and compacted to form a compact preform. As long as the angle N is small (typically less than 30°), the preform exhibits high lateral plasticity. That is, under the pressure of the preform, the angle N can increase, allowing the preform to widen. This characteristic makes it easy to form in a mold through the lateral expansion of the preform thus formed.

[0023] Traditionally, methods for producing parts that withstand tensile or compressive (or bending) stresses involve a layup structure consisting of a layer of 0° unidirectional material (approximately 90% to 80%) and a layer of 90° fibers (approximately 10% to 20%). The 90° fiber layers serve to ensure the lateral cohesion of the part. While this layup method guarantees good lateral strength of the material, it hinders the expansion of the preform during compression molding operations aimed at lateral adaptation in the mold.

[0024] The purpose of this invention is to provide a method for adjusting plastic properties so as to enable the formation of connections in the thickness direction of the preform, together with connections in the longitudinal and transverse directions.

[0025] The method according to the invention for manufacturing composite material parts capable of withstanding mechanical stress, having cross-sectional variations and / or curvature or torsional variations, and having a preferred orientation, comprises the following operations performed sequentially: A layup of at least two unidirectional layers in which the fibers cross each other at + or -N°. A generally cylindrical roll is made by winding a combination of two plies around a winding axis. The blank is pressed by mechanical action perpendicular to the winding axis to deform it into the shape of a preform used in the polymerization reaction to manufacture the part.

[0026] In the method of the present invention, the layup is also cut into appropriate shapes according to a pattern before or after stacking, so as to produce rolls with portions of different diameters after winding.

[0027] It should be noted that, preferably but not limitingly, the winding axis is parallel to the 0° longitudinal axis of the fiber's reference orientation.

[0028] The inclination of the fibers relative to the longitudinal direction, combined with winding and subsequent pressing, gives the preform and the subsequently formed parts fiber connections in both the transverse and thickness directions. These connections bind the composite layers together in the thickness direction, thereby achieving enhanced cohesion and suppressing delamination between layers.

[0029] According to an additional feature of the method of the present invention, the stacked structure of the layup is wound on a mandrel, and a tubular blank can be obtained after the mandrel is removed.

[0030] The tubular or non-tubular composite roll obtained during the first step of the method according to the invention can be deformed by pressing in a die that ensures a constant cross-section along the desired profile.

[0031] The plasticity of the composite roll allows it to be adapted to a variety of shapes while maintaining cohesive properties in three spatial directions.

[0032] According to an additional feature of the method of the present invention, depending on the part to be manufactured, one or more layups with fiber orientations different from the fiber orientations of the layups are incorporated into the layup stack structure before or during the winding operation.

[0033] Furthermore, the plasticity of the composite roll allows for the manufacture of composite parts with a certain curvature. During bending of the composite roll, each fiber extending along the helical path experiences tensile stress in the convex areas and compressive stress in the concave areas; this compensation helps to avoid the risk of wrinkling.

[0034] However, the magnitude of the curvature also depends on the angle value of the fiber and is therefore limited. To mitigate this drawback, the method according to the invention includes a variation.

[0035] Therefore, according to an additional feature of the method of the present invention, each ply is subjected to a cutting operation prior to the ply stacking operation, the cutting operation comprising forming a cutting line in the ply along alternating discontinuities, such that on the one hand each fiber is cut at a constant or non-constant pitch, on the other hand the integrity of the ply is maintained, and furthermore, during stacking, the cutting line of one ply is offset relative to the cutting lines of adjacent plies.

[0036] According to a specific embodiment of the method of the invention, the plies are cut in the same manner and during the layup process, one ply is offset relative to another ply, or offset cuts are made but the plies are fully overlapped.

[0037] Preferably, the winding is performed around an axis perpendicular to the cutting line.

[0038] The resulting composite roll is primarily composed of alternately cut fibers oriented at + or -N°, which facilitates localized elongation through the longitudinal sliding of the fibers apart. Such a roll can withstand greater bending than is permissible when uncut.

[0039] According to one variation, the cut is advantageously located only in one or more specific areas of the layup, depending on the part to be manufactured. Attached Figure Description

[0040] The advantages and features of the process according to the invention will become more apparent from the following description, which relates to the accompanying drawings, which illustrate non-limiting embodiments thereof.

[0041] In the attached diagram: Figure 1 A schematic perspective view illustrating a prior art method is shown. Figure 2 shows a schematic perspective view of three steps A, B, and C of the method according to the present invention. Figure 3 A front view of another step of the same method is shown. Figure 4 A schematic cross-sectional view of another step of the same method is shown. Figure 5 A schematic perspective view of a partial cross-section of another step of the same method is shown. Figure 6 A schematic perspective view of a composite material part manufactured by the method according to the present invention is shown. Figure 7 shows schematic perspective views A, B, and C of another step in the manufacture of composite material parts. Figure 8 shows schematic top views A and B, illustrating the steps of implementing a variation of the method according to the invention.

[0042] Figure 9It is a schematic front view illustrating a variation of the same method.

[0043] Figure 10 A schematic perspective view of a blade that can be obtained by implementing the method of the present invention is shown, the blade having a cross-sectional variation along its longitudinal main axis. Detailed Implementation

[0044] Reference Figures 2A to 2C As can be seen in view A, two unidirectional layups 2 and 3 are used. In one unidirectional layup, the fiber 20 is oriented at an angle α relative to the longitudinal axis 0, while in the other unidirectional layup, the fiber 30 is oriented at an angle β relative to the longitudinal axis 0. In this case, α and β are symmetrical.

[0045] As seen in View B, the next step involves stacking and bonding layers 2 and 3 together. In View C, the next step involves winding the stacked structure of layers 2 and 3 around the winding axis R, thereby obtaining the desired result. Figure 3 The blank shown.

[0046] Therefore, the blank 4 is composed of a stacked structure of two spirally wound layers 2 and 3.

[0047] Reference Figure 4 As can be seen, the roll 4 has been placed in the mold 5, and it is pressed in the mold by a mechanical action P perpendicular to the winding axis, thereby obtaining a preform 6 for the polymerization reaction used to manufacture parts.

[0048] Reference Figure 5 As can be seen, the preform 6 obtained. The inclination of fibers 20 and 30 relative to the longitudinal direction X, combined with winding and subsequent pressing, gives the preform and the part thus formed fiber connections in both the transverse direction Y and the thickness direction Z.

[0049] These fiber bonds that connect the composite layers in the thickness direction achieve enhanced cohesion, thereby preventing delamination between layers.

[0050] Now refer to Figure 6 A straight, variable-shape, and constant-section part 7 can be seen. It is obtained from a tubular blank 4 after molding, and it has parts 70, 71, and 72 with different shapes and cross sections of 700, 710, and 720, respectively. These cross sections are also shown, and the distribution of fibers in all directions is shown.

[0051] Figure 7 illustrates the steps involved in manufacturing part 8, which is visible in view C. Part 8 is straight and has a variable shape, but its cross-section is not constant.

[0052] In view A, a stacked structure of two unidirectional plies 2 and 3 is made, and then the stacked structure is cut according to the pattern, or the unidirectional plies 2 and 3 are cut according to the pattern before stacking.

[0053] The blank 40, which has a non-constant cross-section and is visible in view B, is then wound around axis R to obtain part 8 after molding and polymerization.

[0054] Therefore, by means of the method of implementing the present invention, including the step of cutting the unidirectional lay-up 2, 3 into appropriate shapes according to a pattern before or after stacking, a roll 40 can be obtained, and then a part 8 can be obtained, which has portions of different diameters and these portions can vary along the longitudinal axis of the final part.

[0055] Thus, the present invention enables enhanced cohesion to be maintained in the thickness direction of the unidirectional fiber layup, even if the cross-section of the final part varies and is not constant along its longitudinal axis, while providing a simple, fast and inexpensive method for implementation.

[0056] It should be noted that, according to the variant not shown, ply portions of selected shapes can be combined in the stacked structure of ply 2 and 3, arranged in specific locations, and the fibers of these components can be oriented in a preferred direction according to the composite part to be manufactured.

[0057] Figure 8 illustrates a variation of the method according to the invention, or more precisely, an optional step, which enables the production of parts with more complex shapes, particularly but not limitingly, when the roll is to be bent.

[0058] In view A, layers 2 and 3 can be seen, in which slits are made in the form of cutting lines 21 and 31 along alternating discontinuous lines perpendicular to the longitudinal axis 0, thereby cutting fibers 20 and 30.

[0059] In view B, you can see the stacked structure of two layers 2 and 3, which is made in such a way that the cutting line 31 is not opposite to the cutting line 21.

[0060] It should be noted that in this case, the cuts of layers 2 and 3 are made according to the same pattern, which requires that their overlap be staggered in the longitudinal direction. Of course, the cuts can also be made according to staggered patterns, thus achieving complete overlap.

[0061] It should be understood that after the stacked and cut layers 2 and 3 are rolled, a more ductile roll is obtained and it is more capable of forming curved shapes because the partially cut fibers are more easily adapted to non-unrollable shapes by sliding. Preferably, as shown, the winding is performed around an axis R perpendicular to the cut lines 21 and 31.

[0062] The resulting coverage of the fold allows for the limitation of the harmful effects of the cut.

[0063] Of course, the cutting lines 21 and 3 may not extend across all layers, but may be located at one or more positions depending on the shape of the part to be manufactured.

[0064] In other words, this cutting operation via the cutting line can be localized, limited to areas within the part that require significant deformation.

[0065] Similarly, this variation can be combined with pre-cutting of plies or stacked plies according to a pattern, thus encompassing a wide range of possibilities.

[0066] Finally, refer to Figure 9 As can be seen, the stacked structure of layers 2 and 3 can be wound onto the mandrel, thus obtaining not a cylindrical roll, but a tubular preform 9 with an internal space of 90.

[0067] After such a preform 9 is pressed in a mold, a central portion is obtained, which presents fibers in two preferred directions, namely the fibers of lay-up 2 and 3, while the fiber connections through each layer in the thickness direction are concentrated at the longitudinal edges, which are areas where delamination usually occurs on prior art parts.

[0068] Furthermore, the plasticity of the preform 9 allows it to be deformed by radial pressing of the layup. This can be done from inside the roll in a forming die using a mechanically expandable mandrel or by pressurizing an air bladder.

[0069] According to the method of the present invention, regardless of which version is used, alone or in combination with one or more other variations, it enables the manufacture of numerous composite material parts of arbitrary straight, curved, or other shapes that can withstand mechanical stress.

[0070] Furthermore, unlike conventional lay-up methods that are comparable to manual work, the method according to the invention enables the automatic manufacture of parts at high speeds.

Claims

1. A method for manufacturing composite material parts, said composite material parts being able to withstand mechanical stress and having variations in cross-section and / or curvature or torsion, and having a preferred orientation, characterized in that, The method includes the following operations performed sequentially: At least two unidirectional layups (2, 3) are stacked, wherein the fibers in the at least two unidirectional layups cross each other at + or -N°. A generally cylindrical roll (4; 40; 9) is made by winding at least two of the said layups (2, 3) as a whole around the winding axis (R). The blank (4; 90; 9) is pressed by mechanical action perpendicular to the winding axis (R) to deform the blank into the shape of a preform used in the polymerization reaction for the part (7; 8) to be manufactured, and wherein the lay-up (2, 3) is cut into appropriate shapes according to a pattern before or after stacking, thereby producing a blank (40) of multiple parts with different diameters after winding.

2. The method for manufacturing composite material parts according to claim 1, characterized in that, The stacked structure of the layups (2, 3) is wound around a mandrel, thereby enabling the formation of a tubular roll (9) after the mandrel is removed.

3. The method for manufacturing composite material parts according to claim 1 or claim 2, characterized in that, Depending on the part to be manufactured, before or during the winding operation, one or more fiber (20, 30) orientations different from those of the layup (2, 3) are incorporated into the stacked structure of the layup (2, 3).

4. The method for manufacturing composite material parts according to any one of claims 1 to 3, characterized in that, Before the operation of laying the plies (2, 3), each ply is subjected to a cutting operation, which includes forming cutting lines (21, 31) in the ply along alternating discontinuous lines, such that, on the one hand, each fiber (20, 30) is cut at a constant or non-constant pitch, on the other hand, the integrity of the ply (2, 3) is maintained, and on the other hand, even after the ply (2, 3) is laid, the cutting line of one ply is offset relative to the cutting line of the adjacent ply.

5. The method for manufacturing composite material parts according to claim 4, characterized in that, The plies (2, 3) are cut in the same manner and during the layup process, one ply is offset relative to another ply, or staggered cuts are made but the plies (2, 3) are fully overlapped.

6. The method for manufacturing composite material parts according to claim 4 or claim 5, characterized in that, Depending on the part to be manufactured, the cuts are located only in one or more specific areas of the (2,3) layup.

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

8. A composite material part, characterized in that, Manufactured by the method according to any one of claims 1 to 7.

Images