Mold assembly for manufacturing composite part and related method

Abstract

The present disclosure relates to a mold assembly (200) for manufacturing a composite portion comprising fibers (202) and a resin, the mold assembly (200) comprising: a mold surface (201) extending in a longitudinal direction and in a transverse direction; and a mold (220) defining lateral end walls (203) defining a mold surface (201) in a transverse direction; a flexible sheet (210) configured to be connected to the mold surface (201) between the lateral end walls (203), where the flexible sheet (210) is configured to be partially open and closed such that fibers (202) can be laid in the mold, and where the flexible sheet (210) is further configured to constrain movement of the laid fibers (202). The present disclosure further relates to a method for manufacturing a composite part.

Description

[0001] This application claims priority from European patent application EP 22161769.9 “Mold assembly for infusing wing spar caps and related methods” filed on March 14, 2023. Technical Field

[0002] The present disclosure relates to a method and system for manufacturing a composite part.Furthermore, the present disclosure also relates to a placement head for manufacturing a composite part. Background Art

[0003] Modern wind turbines are commonly used to supply electricity to an electricity grid. Such wind turbines generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set to rotate under the influence of the wind on the blades. The rotation generates a torque, which is usually transmitted to a generator via a rotor shaft, either directly ("directly driven") or by using a gearbox. In this way, the generator produces electricity that can be supplied to an electricity grid.

[0004] In order to extract more energy from the wind, the size of the rotor diameter is increased by increasing the size of the wind turbine blades. Larger size blades introduce higher physical loads into the blades and related components. Wind turbine rotor blades generally include a main body shell formed of two shell halves made of a composite material, such as a glass fiber reinforced composite.

[0005] The main body shell is relatively lightweight and has structural properties that are not designed to withstand the bending moments and other loads acting on the blade during operation. In order to improve the structural properties of the rotor blade, such as stiffness and strength, the blade is generally reinforced with structural members, such as one or more spar caps at the suction and pressure sides of the blade, wherein shear webs connect them. Such spar caps may also be referred to as the "main laminate" or "spar cap laminate" of the wind turbine blade. Throughout this disclosure, these terms may be used interchangeably.

[0006] Spar caps and other composites can be manufactured using several materials such as glass fiber composites and carbon fiber composites. Modern spar caps are generally manufactured using pultruded panels. Pultruded panels are generally bonded together in a resin infusion process to form a composite part such as a spar cap.

[0007] Fiber rovings represent an interesting alternative to pultruded composites due to reduced material costs. Furthermore, the use of fiber rovings allows for a greater degree of customization of fiber placement than when using pultruded sheets.

[0008] In order to achieve a high quality final product, it is important that the fiber stays in its correct position after being placed in the mold. In particular, rovings are less stable than, for example, fiber pultruded boards, i.e., rovings tend to accumulate on parts of the mold surface with a reduced local slope. It is a challenging task to constrain the displacement of the fibers laid in the mold surface. Known ways to limit the displacement of fiber mats or rovings include the use of vacuum systems. These systems generally use vacuum bags that surround the fiber rovings and the mold surface during roving placement. Moreover, these systems require the use of a placement head that works under vacuum conditions to lay the rovings. Vacuum conditions may be difficult to maintain in such a large and multi-component system with a moving part and an opening for supplying rovings. In order to ensure that vacuum is maintained during composite manufacturing, these vacuum systems require frequent maintenance. Moreover, such systems are relatively complex and have poor versatility.

[0009] The present disclosure provides examples of systems and methods that at least partially overcome some of the shortcomings of existing approaches. Summary of the invention

[0010] In a first aspect, a mold assembly for manufacturing a composite part including fibers and resin is provided. The mold assembly includes a mold surface and a flexible sheet. The mold surface extends in a longitudinal direction and in a transverse direction, and the mold defines lateral end walls that bound the mold surface in the transverse direction. The flexible sheet is configured to be connected to the mold surface between the lateral end walls. Moreover, the flexible sheet is configured to be partially open and closed so that fibers can be laid in the mold. In addition, the flexible sheet is also configured to constrain the movement of the laid fibers.

[0011] According to this first aspect, the mold assembly allows fibers (e.g., rovings) to be laid in the mold while at the same time the mold assembly constrains the movement of the laid fibers. This is achieved by maintaining a certain tension on the flexible sheet, which can be achieved by partially opening and closing the flexible sheet. Moreover, the mold assembly constrains the displacement of the fibers in a passive manner, that is, the mold assembly does not require activation to constrain the displacement of the fibers. In addition, the fact that the flexible sheet is configured to be partially open and closed allows fibers of different sizes to be introduced into the space defined by the mold and the flexible sheet. In addition, the mold assembly reduces maintenance costs and / or other costs associated with systems based on the use of vacuum.

[0012] In another aspect, a placement head for laying fibers is provided. The placement head is configured to lay fibers on a mold through a flexible sheet. The placement head includes a guide element and a shoe. The guide element is configured to guide the fibers to the mold; and the shoe is configured to contact the flexible sheet. Moreover, the shoe is also configured to partially open and close the flexible sheet. Thus, the shoe defines an open area in the flexible sheet through which the fibers are laid in the mold.

[0013] According to this aspect, the placement head allows the pliable sheet to be opened and closed and provides an open area to lay additional fibers without substantially modifying the overall tension in the pliable sheet. Thus, the placement head promotes an efficient placement process in which the portion of the fiber not under the placement head is substantially unaffected by the addition of material.

[0014] In yet another aspect, a method for making a composite part comprising fibers and resin is provided. The method includes laying fibers in a mold. In addition, the method includes covering the laid fibers and the mold with a flexible sheet to constrain movement of the laid fibers. In addition, the method includes: at least partially revealing the laid fibers or the mold; and laying additional fibers.

[0015] According to this aspect, the method allows laying of fibers in a mold and constraining the movement of the fibers in a simple and still reliable manner. Furthermore, the method allows further laying of fibers without substantially affecting the positioning of previously laid fibers. This can be performed in multiple instances, i.e. providing several layers of fibers at different positions in the mold. The method substantially reduces the complexity of known approaches and makes the manufacturing process more efficient. Moreover, since even rovings can be used efficiently and these can be customized at will, the method facilitates the manufacture of composite parts that are customized to a greater extent.

[0016] Throughout this disclosure, the terms "pultruded composite," "pultruded sheet," "pultrusion," or similar terms are generally used to define a reinforcement material (eg, fibers or braided or woven strands) that is impregnated with a resin and pulled through a heated die such that the resin cures.

[0017] The term "roving" is generally used to define any fibrous or filamentary structure, such as a yarn, i.e., a monofilament yarn or a multifilament yarn, wherein the fiber(s) / filament(s) stretch at least a portion of the entire length of the structure. Moreover, such a fibrous or filamentary structure may be pre-impregnated with a resin, such as a thermoplastic polymer resin. Additionally, the fibrous or filamentary structure may be a woven fiber having filaments oriented in more than one direction, such as a biaxial fiber.

[0018] A "fiber mat" may be considered herein as a piece of cloth or fabric comprising fibers. The fibers may have a variety of different orientations, for example, the fiber mat may be uniaxial, biaxial, multiaxial, or different. The fibers may be woven with different types of weaves or may be non-woven. The fiber mat may include fibers in other arrangements, i.e., stitched fibers, flat strands utilizing adhesives to improve the integrity of the fiber mat, and others. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Non-limiting examples of the present disclosure will be described hereinafter with reference to the accompanying drawings, in which: Figure 1 illustrates a perspective view of a wind turbine according to one example; Figure 2A is a schematic diagram illustrating a wind turbine blade according to one example; Figure 2B schematically illustrates the internal structure of a wind turbine blade; Figure 2C illustrates a molding system that may be used in the manufacture of wind turbine blades; Figure 3 schematically illustrates a mold assembly according to one example; Figure 4 schematically illustrates a cross-sectional view of another example of a mold assembly; Figure 5 schematically illustrates a placement head according to one example; Figure 6 is a flow chart of a method for manufacturing a composite part according to one example. DETAILED DESCRIPTION

[0020] Reference will now be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation only and not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. For example, a feature illustrated or described as part of one embodiment can be used together with another embodiment to produce yet another embodiment. Thus, it is intended that the present disclosure encompasses such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0021] Figure 1 A conventional modern upwind wind turbine 2 according to the so-called "Danish concept" is shown, having a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor axis. The rotor comprises a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 closest to the hub and a blade tip 14 farthest from the hub 8.

[0022] Figure 2A A schematic view of an exemplary wind turbine blade 10 is shown. The wind turbine blade 10 has the shape of a conventional wind turbine blade with a root end 17 and a tip end 15, and includes a root region 30 closest to the hub, a profiled or airfoil region 34 farthest from the hub, and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 includes a leading edge 18 that faces in the direction of rotation of the blade 10 when the blade is mounted on the hub, and a trailing edge 20 that faces in the opposite direction of the leading edge 18.

[0023] The airfoil region 34 (also referred to as the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, while the root region 30 has a substantially circular or elliptical cross section due to structural considerations, which, for example, makes it easier and safer to mount the blade 10 to the hub. The diameter (or chord) of the root region 30 can be constant along the entire root region 30. The transition region 32 has a transition profile that gradually changes from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance r from the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

[0024] The shoulder 40 of the blade 10 is defined as the location where the blade 10 has its maximum chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

[0025] It should be noted that the chords of different sections of the blade do not typically lie in a common plane, as the blade may be twisted and / or bent (i.e., pre-bent), thereby providing the chord plane with a correspondingly twisted and / or bent course, which most often occurs in order to compensate for the local velocity of the blade depending on the radius from the hub. The wind turbine blade 10 includes a blade shell, which includes two blade shell parts or half shells, a first blade shell part 24 and a second blade shell part 26, which are typically made of fiber reinforced polymer. The wind turbine blade 10 may include additional shell parts, such as a third shell part and / or a fourth shell part. The first blade shell part 24 is typically a pressure side or upwind blade shell part. The second blade shell part 26 is typically a suction side or downwind blade shell part. The first blade shell part 24 and the second blade shell part 26 are fastened together with an adhesive (such as an adhesive) along a bond line or glue joint 28 extending along the trailing edge 20 and the leading edge 18 of the blade 10. Typically, the root ends of the blade shell portions 24, 26 have a semi-circular or semi-oval outer cross-sectional shape.

[0026] Figure 2B is a schematic diagram illustrating a cross-sectional view of an exemplary wind turbine blade 10, such as a cross-sectional view of an airfoil region of the wind turbine blade 10. The wind turbine blade 10 includes a leading edge 18, a trailing edge 20, a pressure side 24, a suction side 26, a first spar cap 74, and a second spar cap 76. The wind turbine blade 10 includes a chord line 38 between the leading edge 18 and the trailing edge 20. The wind turbine blade 10 includes a shear web 42, such as a leading edge shear web and a trailing edge shear web. The shear web 42 can alternatively be a spar box having a spar side, such as a trailing edge spar side and a leading edge spar side. The spar caps 74, 76 can include carbon fiber, while the remainder of the shell portions 24, 26 can include glass fiber.

[0027] Figure 2C 1 is a schematic diagram illustrating an exemplary mold system for molding a blade shell of a wind turbine blade. The mold system 100 includes a first mold 102 and a second mold 112. The first mold 102 is configured to manufacture a first blade shell portion of a wind turbine blade, such as an upwind shell portion of a wind turbine blade (forming a pressure side). The second mold 112 is configured to manufacture a second blade shell portion of a wind turbine blade, such as a downwind shell portion of a wind turbine blade (forming a suction side). The mold system 100 also includes mold surfaces 104, 114 for depositing fibers.

[0028] Figure 3 A perspective view of a portion of a mold assembly 200 for manufacturing a composite part according to one example is schematically illustrated. The composite part includes fibers 202 and a resin for bonding the fibers 202 together. The mold assembly 200 includes a mold surface 201 and a flexible sheet 210. The mold surface 201 extends in a longitudinal direction and in a transverse direction. Moreover, the mold surface defines a lateral end wall 203 that delimits the mold surface 201 in the transverse direction.

[0029] The flexible sheet 210 is configured to be connected to the mold surface 201 between the lateral end walls 203. The flexible sheet 210 is configured to be partially open and closed so that the fibers 202 can be laid in the mold. In addition, the flexible sheet 210 is also configured to restrict the movement of the laid fibers 202.

[0030] "Partially" open and closed is to be understood herein as only part of the flexible sheet being open at the same time, rather than being open over the entire length of the flexible sheet. For example, at any given moment the partial opening may extend over less than 20% of the total length of the mold, and optionally less than 15%, or less than 10%, or less than 5% of the total length of the mold.

[0031] like Figure 3 As illustrated in , the flexible sheet 210 may be connected to the mold surface 201 at or near the top portion of the mold surface 201 or in the lower portion of the mold surface 201, depending on the specifications of the composite part. Figure 3 In FIG. 2 , the connection between the flexible sheet 210 and the mold surface 201 has been illustrated by a dotted line.

[0032] In the illustrated example, roving 202 is used as the fiber material. The roving 202 is easier to move than other fiber materials after it is placed in the mold. With the examples of the present disclosure, the roving 202 can be used effectively. The roving used in this way can provide significant cost reduction and give the possibility of customizing strength and stiffness to a large extent.

[0033] In this example, when the height of the layer of rovings 202 exceeds the height at which the flexible sheet 210 is connected to the mold surface 201, the flexible sheet 210 will apply pressure on the laid rovings 202 towards the mold surface 201. This pressure promotes the stable placement of the rovings 202 and reduces the risk of fiber misalignment or movement during manufacturing. Moreover, since the flexible sheet 210 can be partially opened, additional rovings 202 can be laid without substantially reducing the total pressure acting on most of the rovings 202. When the flexible sheet is partially opened, significant movement of the rovings along the full length of the mold or nearly the full length of the mold can still be avoided.

[0034] In an example, the flexible sheet 210 at least partially seals the mold surface 201. This can allow the flexible sheet 210 to be used as an interface to a vacuum system to infuse the rovings 202 with resin, particularly after all rovings have been positioned in the mold. Moreover, the flexible sheet 210 can be made of an elastic material. More specifically, the flexible sheet can include synthetic rubber, and more specifically, the flexible sheet can include ethylene and / or propylene.

[0035] In addition, the flexible sheet 210 may include a mechanism that allows the flexible sheet to be partially opened and closed, such as, for example, a zipper lock 225, a hook and loop fastener 227 (e.g., Velcro TM ) or a zipper 220 extending in the longitudinal direction of the mold surface. Figure 3 As schematically illustrated in , a combination of the aforementioned elements is also possible. In some examples, the flexible sheet 210 may include a plurality of the elements or a combination thereof, such as, for example, 3 or more zippers, specifically 5 or more zippers, and more specifically 8 or more zippers.

[0036] In some examples, the pliable sheet 210 may include at least one opening 211 configured to introduce resin into the space defined by the pliable sheet 210 and the mold surface 201. In an example, the opening 211 may be configured to be connected to a vacuum system to infuse resin, for example, in a VARTM process (vacuum assisted resin transfer molding).

[0037] In other examples, a vacuum bag may be used to infuse the resin into the rovings 202. In this case, the vacuum bag may be laid on top of the pliable sheet (if it is sufficiently permeable), or the vacuum bag may be laid directly on top of the rovings 202.

[0038] Figure 4 A cross-section of another example of a mold assembly 200 according to the present disclosure is shown. Note that Figure 4The mold assembly 200 in the figure has been illustrated as having a round mold surface 201, but other types of mold surfaces 201 can also be used. Similarly, the flexible sheet 210 can be connected to the mold surface at different heights. In fact, in the example, the connector between the flexible sheet 210 and the mold surface 201 can be configured to be displaced along the surface of the mold surface, that is, using a guide or other connecting member to shift. This can achieve a certain level of pressure acting on the fiber 202 during the manufacturing process, such as when the height of the roving increases, the connection point between the flexible sheet 210 and the mold surface 201 can be shifted to compensate for the increase in the height of the fiber 202. Note that for illustrative purposes, the fiber 202 does not reach the height of the flexible sheet 210 in the figure. Moreover, the fiber 202 in this example is a woven fiber extending in a 2D plane, that is, a uniaxial or biaxial fiber mat. Other types of fibers can also be used, such as, for example, fiber yarns or fiber pultrusions that extend essentially only in one dimension.

[0039] As shown, the flexible sheet 210 may include a zipper 220 to partially open and close the flexible sheet 210. Depending on the specifications of the composite part to be manufactured, the zipper 220 may be oriented at an angle relative to the longitudinal direction of the mold surface 201. Thus, the fibers 202 may be laid at an angle, and the mechanical properties of the composite part may be customized. The fibers 202 may include glass fibers, carbon fibers, aramid fibers, and other suitable fibers. Moreover, the fibers 202 may include fibers that have been pre-impregnated with resin, such as prepregs including fibers impregnated with epoxy resins, polyester resins, vinyl ester resins, or other suitable resins.

[0040] The zipper 220 of the flexible sheet 210 may include a chain and two sliders arranged in a head-to-head configuration (also known as an O-type configuration). This configuration of the sliders allows an open area to be created between the sliders, wherein one of them opens the chain and the other of them closes the chain. Figure 5 This feature is discussed in more detail below. Note that other types of openable connections, such as zip locks and hook and loop fasteners, can also be used to achieve similar effects.

[0041] Figure 5Schematically illustrates a mold assembly 200 including a placement head 300 according to an example of the present disclosure. The placement head 300 is illustrated in combination with a zipper 220 including a chain 221 and two slides 222, 223. The placement head 300 of the mold assembly can be configured to be connected to the two slides 222, 223 so that when the placement head moves, one slide 222 opens the chain 221, and the other slide 223 closes the chain 221. Thus, an open area 224 for approaching a mold or mold surface 201 between the two slides 222, 223 can be defined. In addition, the placement head 300 can also be configured to pass the fiber 202 through the open area 224 and lay it along the longitudinal direction. Note that if the movement of the placement head 300 is reversed, the opening and closing of the chain 221 will be performed by the other slide 222, 223.

[0042] On the other hand, Figure 5 A placement head 300 according to an example of the present disclosure is also disclosed. The placement head 300 is configured to place the fiber 202 in a mold (not shown) through the flexible sheet 210. The placement head 300 includes a guide element 301 and a shoe 302. The guide element 301 is configured to guide the fiber in the mold (not shown). The shoe 302 is configured to contact the flexible sheet 210. Moreover, the shoe 302 is also configured to partially open and close the flexible sheet 210. Thus, the shoe 302 defines an open area 224, and the fiber is placed in the mold through the open area 224. Figure 5 The placement head 300 in FIG. 1 is illustrated with a dotted line so as not to obstruct the observation of the zipper 220 below.

[0043] The fibers 202 may in particular be rovings or fiber mats.

[0044] The boot 302 may include a fastening element for connecting to the sliders 222, 223 of the zipper 220. The fastening element may be configured to connect to the slider of a zipper lock, or the fastening element may include other types of connectors configured to open and close a hook-and-loop fastener. The boot 302 may be sized to allow fibers 202 of different widths (i.e., woven fibers extending in a 2D plane, fiber yarns extending in a longitudinal direction, or other types of fibers) to pass through the open area 224.

[0045] exist Figure 5 In the embodiment of the present invention, the guide element 301 has been illustrated as a closed duct through which the fibers are fed to the mold, but other types of guide elements may be employed for this task. In addition, the guide element 301 may include a drive that controls the amount or quantity of fibers laid in the mold during displacement of the placement head 300 along the mold surface.

[0046] Figure 64 is a flow chart of a method 400 for manufacturing a composite part including fibers 202 and a resin according to the present disclosure. The method 400 includes laying fibers 202 in a mold 201 at box 401. Moreover, the method 400 also includes covering the laid fibers 202 and the mold surface 201 with a flexible sheet 210 at box 402 to constrain the movement of the laid fibers 202. In addition, the method 400 also includes at least partially revealing the laid fibers 202 or the mold surface 201 at box 403 and laying 404 additional fibers 202.

[0047] In some examples, the flexible sheet 210 used in the method 400 can be at least partially openable. Moreover, the step 403 of at least partially revealing the laid fibers 202 or the mold surface 201 can include locally opening at least a portion of the flexible sheet 210 to lay 404 additional fibers 202. In addition, the at least partial opening of the flexible sheet 210 can be performed at least partially automatically (i.e., by using the placement head 300 or other automated system to slide at least one slider 222, 223 of the zipper 220 or the zipper lock 225).

[0048] In the example, laying 401 fibers 202 and covering 402 the laid fibers 202 and mold surface 201 are performed using placement head 300. Moreover, placement head 300 may also perform subsequent opening of portions of pliable or sheet 210 (or revealing 403 the laid fibers 202) and laying 404 additional fibers 202.

[0049] Additionally, the flexible sheet 210 may be made of an elastic material such that the length of the flexible sheet 210 may be modified when the flexible sheet 210 applies pressure to the fibers 202 .

[0050] In another example, the method 400 further includes: at least partially packing the laid fibers 202; and infusing the laid fibers 202 with resin. Packing and infusing can be performed using a flexible sheet 210. This allows pressure to be maintained on the fibers (e.g., rovings) at all times, and greatly reduces the risk of misalignment before resin infusion. Infusion of the resin can include one of resin injection and applying a vacuum (e.g., in a VARTM process (vacuum assisted resin transfer molding)).

[0051] Note that some of the technical features described with respect to mold assembly 200 and placement head 300 may be included in method 400 for manufacturing a composite part, and vice versa.

[0052] This written description uses examples to disclose the present teachings (including preferred embodiments) and also enables any person skilled in the art to practice the present teachings (including making and using any device or system and performing any incorporated methods). The scope of patentability is defined by the claims and may include other examples that occur to a person skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims. Aspects from the various embodiments described and other known equivalents for each such aspect can be mixed and matched by a person of ordinary skill in the art to construct additional embodiments and techniques according to the principles of the present application. If reference symbols related to the drawings are placed in brackets in the claims, the reference symbols are used only to attempt to improve the understandability of the claim and should not be interpreted as limiting the scope of the claim.

Claims

1. A method (400) for making a composite part comprising fibers (202) and a resin, the method (400) comprising: Laying (401) the fibers (202) in a mold; covering (402) the laid fibers (202) and the mold surface (201) with a flexible sheet (210) to constrain movement of the laid fibers (202); at least partially revealing (403) the laid fibers (202) in the mold; and Additional fibers (202) are laid (404).

2. The method (400) of claim 1, wherein: The flexible sheet (210) is at least partially openable, and the at least partially revealing (403) comprises locally opening at least a portion of the flexible sheet (210) for the laying (404) of the further fibers (202).

3. The method (400) according to any one of claims 1 and 2, wherein: The method further includes: at least partially isolating the laid fibers (202); and infusing the laid fibers (202) with resin.

4. The method (400) according to any one of claims 1 to 3, wherein: The sealing and the perfusion are performed using the flexible sheet (210).

5. The method (400) according to any one of claims 1 to 4, wherein: The flexible sheet (210) includes a zipper lock (225) and / or a zipper (220).

6. The method (400) according to any one of claims 2 to 5, wherein: The at least partial opening of the flexible sheet (210) is at least partially performed automatically by sliding at least one slider (222, 223) of the zipper lock (225) or zipper (220).

7. The method (400) according to any one of claims 1 to 6, wherein: The fibers (202) are fiber rovings.

8. The method (400) according to any one of claims 1 to 7, wherein: The composite part is a spar cap of a wind turbine blade.

9. A mold assembly (200) for manufacturing a composite part comprising fibers (202) and a resin, the mold assembly (200) comprising: a mold surface (201) extending in a longitudinal direction and in a transverse direction; and a mould (220) defining lateral end walls (203) delimiting said mould surface (201) in said transverse direction, A flexible sheet (210) is configured to be connected to the mold surface (201) between the lateral end walls (203), wherein the flexible sheet (210) is configured to be partially opened and closed so that the fibers (202) can be laid in the mold, and wherein the flexible sheet (210) is also configured to constrain the movement of the laid fibers (202).

10. The mold assembly (200) according to claim 9, wherein: The die assembly (200) further comprises a placement head (300) for laying the fibers (202), and optionally wherein the fibers (202) are rovings.

11. The mold assembly (200) according to any one of claims 9 and 10, wherein: The flexible sheet (210) comprises a zip lock or hook and loop fastener extending along the longitudinal direction of the mould surface (201).

12. The mold assembly (200) according to any one of claims 9 to 11, wherein: The flexible sheet (210) includes at least one zipper (220) extending along the longitudinal direction of the mold surface (201).

13. The mold assembly (200) according to claim 12, wherein: The zipper (220) includes a chain (221) and two sliders (222, 223) arranged in a head-to-head configuration.

14. The mold assembly (200) according to claim 13, wherein: The placement head (300) is configured to be connected to the two slides (222, 223) so that one slide (222) opens the chain (221) and the other slide (223) closes the chain (221), thereby defining an open area (224) for approaching the mold surface (201) between the two slides (222, 223), and wherein the placement head (300) is also configured to pass the fiber (202) through the open area (224) and lay it along the longitudinal direction.

15. The mold assembly (200) according to any one of claims 9 to 14, wherein: The flexible sheet (210) at least partially encloses the mold surface (201), and wherein the flexible sheet (210) includes an opening (211) configured to introduce resin into a space defined by the flexible sheet (210) and the mold surface (201).

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