TWIST ADJUSTMENT TO OPTIMIZE SHAPES AND FORMING OF TEXTILE ARCHITECTURES

Description

Technical Field

[0001] The present invention relates to the general field of compacting woven preforms and more particularly to compacting preforms comprising woven strands having a variable twist. Prior art

[0002] In the field of composite material parts with woven fiber reinforcement, the strands used for weaving are usually oriented in preferred directions in order to obtain the desired strength properties.

[0003] If the aim is to give the part shear strength, it is then necessary to orient the strands of the fiber preform forming the fiber reinforcement of the part differently. To do this, the strands are twisted with a value of 10 to 30 turns, which amounts to applying an angle of between 5° and 15° relative to the main direction of the strand.

[0004] However, this results in a greater compaction effort to crush the strands and therefore the entire fiber preform. In addition, the preform can have different twist angles of the strands in order to adapt, for example, to the radius of curvature of the part.

[0005] It has been found that currently, in order to compact the preform, a mold is used that is sized to withstand the greatest compaction force regardless of the level of twisting of the strands. For example, molds are traditionally sized with twisted strands with a value of 20 turns per meter.

[0006] EP2902179 A2 discloses an installation for compacting strands or a preform comprising strands and a method for compacting strands or a preform comprising strands. Statement of the invention

[0007] The aim of the present invention is to propose a compacting solution which makes it possible to adapt to the variable twisting levels of the strands and thus avoid oversizing the molds when compacting the strands.

[0008] For this purpose, the invention relates to an installation for compacting strands or a preform comprising strands according to claim 1.

[0009] As explained below, the inventors found after study that the molds were oversized to be able to withstand the greatest compaction force applied to the strands. They also found that depending on the twisting of the strands, the thickness of the mold containing the strands could be adapted according to the compaction force applied.

[0010] Therefore, according to the invention, the mold of the compacting installation has a variable thickness which depends on the level of twisting or the twist angle of the strands. Thus, the areas of the mold receiving strands having a large twist angle are thicker than the areas of the mold receiving untwisted or weakly twisted strands.

[0011] The mold according to the invention therefore has several parts of variable thickness, the thickness of each part depending on the twist angle of the strands placed in each part.

[0012] This allows the mold not to be oversized, i.e. not to size the mold based solely on the greatest compaction force applied.

[0013] According to the invention, the first angle is less than the second angle and the first thickness is less than the second thickness. According to another particular characteristic of the invention, the installation also comprises means for applying at least a first pressure on the first part of the mold and a second pressure, different from the first pressure, on the second part of the mold.

[0014] The means for applying the first and second pressures make it possible to apply a compaction force to the strands and the preform. The pressures applied depend on the twist angles and the thicknesses of the mold. Thus, the smaller the thickness of the mold, the lower the pressure applied to the mold. According to another particular characteristic of the invention, the first pressure is lower than the second pressure.

[0015] Another object of the invention is a method of compacting strands or a preform comprising strands according to claim 4.

[0016] According to the invention, the first and second pressure values ​​are determined according to the first and second angle and / or the first and second thicknesses.

[0017] According to another particular characteristic of the invention, the first angle is less than the second angle, the first pressure is less than the second pressure and the first thickness is less than the second thickness. Brief description of the drawings

[0018] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof which are not limiting in nature. [ Fig. 1 ] There figure 1 represents, schematically and partially, an example of a preform which is compacted with an installation or a method according to the invention. Fig. 2A ] There figure 2A represents, schematically and partially, a compacting installation according to one embodiment of the invention. Fig. 2B ] There figure 2B represents, schematically and partially, a compacting installation according to one embodiment of the invention. Fig. 3 ] There figure 3 represents the strand thickness as a function of compaction pressure for strands with different twist levels. Description of the embodiments

[0019] There figure 1 represents, schematically and partially, a preform 100 which can be compacted with a compacting installation and / or a compacting method according to the invention.

[0020] The preform 100 comprises two portions 110 and 120 each comprising strands 111 and 112. The strands 111 and 112 are made up of a plurality of fibers twisted together by a twisting or twisting operation of the fibers. The twisting consists of twisting the plurality of fibers by considering the center of the section of the strand as the axis of rotation. In this way, a twisting angle of the fibers relative to the main direction is obtained which changes depending on the position along the radius of the strand. Thus, there is an angle equivalent to 0° at the center of the strand and maximum at the periphery of the strand. This orientation of the fibers relative to the main direction of the strand makes it possible to give more strength to the strand and thus to limit its fraying during a possible weaving operation of the strands.

[0021] The fibers constituting the strands 111 and 112 are, for example, carbon, glass or Kevlar fibers. The strands 111, 112 can, for example, be made from 48,000 fibers by twisting 4 strands of 12,000 fibers, or be made from 24,000 fibers by twisting 2 strands of 12,000 fibers.

[0022] In the first portion 110, the strands 111 are twisted at a first twist angle, and in the second portion 120, the strands 112 are twisted at a second twist angle greater than the first angle. For example, the strands 111 have a twist of 10 turns per meter, which is equivalent to a twist angle of 5° relative to the main direction of the strand; while the strands 112 have a twist of 30 turns per meter, which is equivalent to a twist angle of 15° relative to the main direction of the strand.

[0023] There figure 2A represents, schematically and partially, a compacting installation 200 according to one embodiment.

[0024] The installation 200 comprises a compacting mold 210 in which a preform 220 comprising strands is placed. As explained with reference to the figure 1 , the preform 220 comprises several portions 221 and 222 in which the strands have different twist angles. In this example, the first portion 221 of the preform 220 comprises strands twisted at a first angle α1 and the second portion 222 comprises strands twisted at a second angle α2. The angle α2 is greater than the angle α1.

[0025] According to the invention, the mold 210 comprises several parts 211, 212 and 213 of variable thickness E1, E2, E3, each part being intended to receive at least a part of one of the portions of the preform 220. The thicknesses E1, E2 and E3 of the mold 210 are defined as a function of the twist angles of the different portions of the preform 220. Thus, the part of the mold 210 intended to receive the portion of the preform 220 having the smallest twist angle is the part having the smallest thickness, and the part of the mold 210 intended to receive the portion of the preform 220 having the highest twist angle is the part having the greatest thickness.Considering that the thickness E1 is less than the thickness E3, and that E2 is a thickness varying between E1 and E3, the first part 211 of the mold 210, of thickness E1, is intended to receive the portion 221 of the preform 220, and the third part 213 of the mold 210, of thickness E3, is intended to receive the portion 222. The second part 212 of the mold 210, of variable thickness E2 makes it possible to make the junction between the two portions 221 and 222 of the preform 220 to adapt the compaction force to the difference in twist angle between the two portions 221 and 222.

[0026] The installation 200 may also comprise means 231, 232 and 233 for applying a pressure P1, P2, P3 to the mold 210, and more particularly to certain parts of the mold 210. The pressures P1, P2 and P3 applied by the different means 231, 232 and 233 depend on the thickness of the mold and the twisting angle of the strands.

[0027] In this example, the pressure P1 is lower than the pressure P2 which is itself lower than the pressure P3. The pressure P1 is applied by the application means 231 to the first part 211 of the mold 210, the part which has the smallest thickness E1. The pressure P3 is applied by the application means 233 to the third part 213 of the mold 210 which has the greatest thickness E3. Finally, the pressure P2 is applied by the application means 232 to the second part 212 of the mold 210. The pressure P2 is an intermediate pressure between P1 and P3, it is therefore adapted to the junction between the two portions 221 and 222 of the preform 220 which have different twist angles.

[0028] Thanks to the installation presented, it is possible, for example, when closing the mold and injecting a resin into the mold, to adapt the pressures P1, P2 and P3 applied locally to obtain a compacted preform having a constant thickness, despite the different twist angles within the preform.

[0029] There figure 2B represents, schematically and partially, a compacting installation 201 according to another embodiment of the invention.

[0030] The installation 201 comprises a compacting mold 260 in which a preform 250 comprising strands is placed. As explained with reference to the figure 1 , the preform 250 comprises several portions 251, 252, 253 and 254 in which the strands have different twist angles. In this example, the first portion 251 of the preform 250 comprises the most weakly twisted strands, while the fourth portion 254 comprises the most strongly twisted strands. The second and third portions 252 and 253 have intermediate twist angles so that the twist angle increases from the first portion 251 to the fourth portion 254.

[0031] According to the invention, the mold 260 comprises several parts of variable thickness. Thus, in this embodiment, the thickness of the mold increases and varies between the thickness E and the thickness E', E' being greater than E. The part of the mold having the smallest thickness, i.e. a thickness E, is intended to receive the portion of the preform 250 having the smallest twist angle, i.e. the portion 251. The part of the mold having the greatest thickness, i.e. the thickness E', is intended to receive the portion of the preform 250 having the highest twist angle, i.e. the portion 254. The increasing thickness of the mold between E and E' also makes it possible to adapt to the increasing twist angles between the four portions 251, 252, 253 and 254.

[0032] The installation 201 may also comprise a means 240 for applying a uniform pressure P to the mold 260. Thanks to the different thicknesses of the mold 260, the compaction force applied to the portions 251 to 254 of the preform 250 is therefore very variable between the portions 251 to 254 thanks to the variation in thickness of the mold 260.

[0033] Thanks to this installation, it is possible, for example, to obtain, when closing the mold and injecting a resin into the mold, a compacted preform having a variable thickness or a constant thickness, depending on the uniform pressure value P applied and the variations in thickness of the mold.

[0034] There figure 3 is a graph representing on the ordinate the thickness of the strand in millimeters (mm) as a function of the compaction pressure applied to the mold in megapascals (MPa). The thickness of the strand is represented for several levels of strand twisting.

[0035] For each curve 301 to 305, the strands are made up of 24,000 fibers. For curve 301, the strands have a twist of 30 turns per meter. For curve 302, the strands have a twist of 25 turns per meter. The strands in curve 303 have a twist of 20 turns per meter, the strands in curve 304 have a twist of 15 turns per meter, and the strands in curve 305 have a twist of 10 turns per meter. Thus, the strands in curve 305 are the most loosely twisted, and those in curve 301 are the most tightly twisted.

[0036] It can be seen that for a given twist, the thicker the strands, the lower the compaction pressure to be applied; whereas for a given strand thickness, the higher the level of twist, the greater the compaction pressure.

[0037] The expression "between ... and ..." must be understood as including the limits.

Claims

1. An installation (200, 200) for compacting strands (111, 112) or a preform (100, 220, 250) comprising strands, the strands or the preform comprising at least a first portion (110, 221, 251) in which the strands are twisted at a first angle and a second portion (120, 222, 254) in which the strands are twisted at a second angle different from the first angle and greater than the first angle, the installation comprising a mould (210, 260) which comprises the strands or the preform comprising strands, and being characterised in that the mould has at least a first part (211) in which the first portion of the strands or of the preform (221, 251) is disposed, the first part having a first thickness (E1, E) and a second part (213) in which the second portion of the strands or of the preform (222, 254) is disposed, the second part having a second thickness (E3, E') different from the first thickness and greater than the first thickness.

2. The installation according to claim 1, also comprising means (231, 233) for applying at least a first pressure (P1) on the first part of the mould (211) and a second pressure (P2), different from the first pressure, on the second part of the mould (213).

3. The installation according to claim 2, in which the first pressure (P1) is less than the second pressure (P2).

4. A method for compacting strands (111, 112) or a preform (100, 220, 250) comprising strands, the strands or the preform comprising at least a first portion (110, 221, 251) in which the strands are twisted at a first angle and a second portion (120, 222, 254) in which the strands are twisted at a second angle different from the first angle, the method being characterised in that it comprises: - placing the strands or the preform in a mould (210) so that the first portion of the strands (111, 112) or of the preform (100, 220, 250) is disposed in a first part of the mould (211) and the second portion of the strands or of the preform is disposed in a second part of the mould (212), the first part of the mould having a first thickness (E1, E) and the second part of the mould having a second thickness (E3, E') different from the first thickness; and - applying a first compacting pressure on the first part of the mould (211) and a second compacting pressure, different from the first pressure, on the second part of the mould (212), the values of first and second pressures being determined according to the first and second angle and / or the first and second thickness.

5. The compacting method according to claim 4, in which the first angle is less than the second angle, the first pressure is less than the second pressure and the first thickness is less than the second thickness.