Mechanical forming of composite materials

Abstract

Disclosed herein are methods for molding composite materials (110) that include the use of woven or nonwoven veils (120). Also disclosed herein are molded composite materials formed using such methods that exhibit significant improvements in wrinkling.

Description

[Technical Field]

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 62 / 786,855, filed December 31, 2018, the entire contents of which are expressly incorporated herein by this reference. [Background technology]

[0002] Fiber-reinforced polymer composites are widely used in many industries (including aerospace, automotive, marine, industrial, construction, and a variety of consumer products) and are often chosen because they exhibit high strength and corrosion resistance, especially in harsh environments, while being lightweight. Fiber-reinforced polymer composites are typically manufactured from either pre-impregnated materials or resin infusion processes.

[0003] Pre-impregnated material, or "prepreg," generally refers to fibers (such as carbon fibers) impregnated with a curable matrix resin (such as epoxy). The resin content in prepreg is relatively high, typically 40% to 65% by volume. Multiple plies of prepreg can be cut to size for lamination, then subsequently assembled and molded in a mold. If the prepreg cannot easily be conformed to the shape of the mold, heat may be applied to the prepreg to gradually deform it to the shape of the molding surface.

[0004] Fiber-reinforced polymer composites can also be manufactured by liquid molding processes, including resin infusion techniques. These processes include, for example, resin transfer molding (RTM), liquid resin infusion (LRI), vacuum-assisted resin transfer molding (VARTM), resin infusion with flexible tooling (RIFT), vacuum-assisted resin infusion (VARI), resin film infusion (RFI), controlled atmospheric pressure resin infusion (CAPRI), VAP (vacuum-assisted process), single-line infusion (SLI), and constant pressure infusion (CPI). In resin infusion processes, dry fibers bound with a binder are placed into a mold as a preform, and then a liquid matrix resin is directly infused (or injected) in situ. After injection (or infusion), the resin-infused preform is cured to produce the finished composite article.

[0005] For both types of materials, the process of three-dimensional shaping (or molding) of composites is critical to the appearance, properties, and performance of the final molded product. For example, preforms are often formed into precise shapes using a hand layup process, which is time-consuming and often results in high part-to-part variability. While other, less manual methods for shaping composites exist (e.g., vacuum forming, which may use pins, robots, and / or actuators to assist in part formation), such methods have their own drawbacks and shortcomings. For example, vacuum methods are considered "offline" because forming and curing occur in different processing steps. In addition, such methods are often time-consuming and do not take into account the rheological behavior and curing characteristics of the composite material. And, products from such processes are still prone to wrinkles and other defects. Summary of the Invention

[0006] Disclosed herein is a novel method for molding composite materials that not only addresses the shortcomings of other methods known in the art regarding lack of automation and utilization of existing infrastructure and equipment, but also provides very low part-to-part variability and minimal wrinkling, especially at the inner diameter.

[0007] Thus, in one aspect, the present teachings provide a method for forming a composite material, which generally comprises: (A) placing a composite material system into a press tool including a male mold and a corresponding female mold separated by a gap, the male mold and female mold each having an independently non-planar molding surface; (B) compressing the composite material system between the male and female molds by closing the gap between the male and female molds; and (C) maintaining the male and female dies in a closed position until the viscosity of the composite system reaches a level sufficient to maintain the molded shape; Includes:

[0008] The composite material system includes at least one woven or nonwoven veil having an upper surface and a lower surface, and a substantially planar composite material having an upper surface and a lower surface, the lower surface of the substantially planar composite material being in contact with the upper surface of the first woven or nonwoven veil, and the at least one woven or nonwoven veil being held in place by a structural frame.

[0009] In some embodiments, at least one woven or nonwoven veil is stretched across the structural frame. In some embodiments, the structural frame includes an upper frame and a lower frame, and the at least one woven or nonwoven veil is held between the upper and lower frames.

[0010] In some embodiments, the upper surface of the substantially planar composite material is also in contact with the lower surface of a second woven or nonwoven veil, thus forming a layered structure. In this embodiment, the composite material can be held stationary between the first and second woven or nonwoven veils until heat or force is applied to the layered structure.

[0011] In another embodiment, the upper surface of the substantially planar composite material is also in contact with a diaphragm selected from a film including one or more layers each independently selected from a rubber layer, a silicone layer, and a plastic layer.

[0012] In some embodiments, the woven or nonwoven veil has a thickness of about 5 g / m 2 ~about 50g / m 2 In some embodiments, the woven or nonwoven veil comprises polyester fiber, carbon fiber, glass fiber, or a combination thereof.

[0013] In some embodiments, step (B) includes partially closing the gap between the male and female molds to form a smaller gap between the molds, which is then closed after a specific time or viscosity is reached. In other embodiments, step (B) includes closing the gap between the male and female molds at a speed of about 0.7 mm / sec to about 400 mm / sec while maintaining the male and female molds at a temperature above the softening point of the composite material.

[0014] In some embodiments, the male and female molds are maintained at a temperature above ambient temperature, for example, above 100°C.

[0015] In some embodiments, step (C) is carried out to obtain a composite material having a viscosity of 1.0×10 8 This is continued until the pressure drops below 100 kPa.

[0016] In some embodiments, the method further comprises (D) cooling the composite material system on the tool to a temperature below the softening temperature of the composite material. In other embodiments, the method further comprises (D') removing the composite material system from the tool while the composite material system is above the softening temperature of the composite material.

[0017] In some embodiments, the male and female molds are maintained in the closed position for between about 10 seconds and about 30 minutes.

[0018] In some embodiments, the composite material in the composite material system is machined into a pattern.

[0019] In some embodiments, the method further includes preheating the composite material system in a heating device, such as a contact heater or an IR heater, at a temperature sufficient to reduce the viscosity of the composite material prior to placing the composite material system in the press tool.

[0020] In some embodiments, the composite material comprises structural fibers of a material selected from aramid, high modulus polyethylene (PE), polyester, poly-p-phenylene-benzobisoxazole (PBO), carbon, glass, quartz, alumina, zirconia, silicon carbide, basalt, natural fibers, and combinations thereof.

[0021] In some embodiments, the composite material comprises a binder or matrix material selected from thermoplastic polymers, thermosetting resins, and combinations thereof. In certain embodiments, the binder or matrix material is present in the composite material in an amount of at least about 40%. In certain embodiments, the binder or matrix material is present in the composite material in an amount of at least about 1×10 8 In certain embodiments, the viscosity is (i) the viscosity of the binder or matrix material is 1 × 10 8 mPa, or (ii) the weight of the bale is less than 100 g / m 2 is less than; and - The surface of composite materials contains a lot of resin.

[0022] In some embodiments, the method further comprises applying a release agent to the male mold, the female mold, or both.

[0023] In some embodiments, the composite material system is placed into the optional heating device and press tool by automated means, hi some embodiments, no vacuum pressure is applied to any part of the press tool. [Brief explanation of the drawings]

[0024] [Figure 1] 1 illustrates an exemplary composite material system in accordance with the present teachings. [Figure 2A] 1 illustrates an exemplary molding process in accordance with the present teachings. [Figure 2B] 1 illustrates an exemplary molding process in accordance with the present teachings. [Figure 3] 1 is a photographic comparison of an exemplary part formed using a dual diaphragm mechanical thermoforming process and an exemplary part molded using the methods disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0025] Considering the potential drawbacks of composite material processing, including processing time, part-to-part variability, and cosmetic defects, there remains a need to develop faster, improved, and more reliable assemblies and methods. This is especially true for automotive parts, which must be visually acceptable for reasons such as the inability to paint or cover. While striving for visual perfection, it is also desirable to maximize the use of existing equipment (e.g., metal stamps or presses). However, conventional metal stamping equipment typically results in imperfect, uneven surfaces when used directly on composite materials. The present disclosure provides a method for forming composite materials using a ball-assisted mechanical thermoforming process, which can use metal stamping tools to produce formed parts with unexpectedly excellent surface properties, including, for example, minimal wrinkles on the inner diameter.

[0026] Composite material molding method The present teachings include methods for molding composite materials using the materials described in more detail herein. Thus, in some aspects, the present teachings include: (A) placing a composite material system into a press tool including a male mold and a corresponding female mold separated by a gap, the male mold and female mold each having an independently non-planar molding surface; (B) compressing the composite material system between the male and female molds by closing the gap between the male and female molds; and (C) maintaining the male and female molds in a closed position until the viscosity of the composite material system reaches a level sufficient to maintain the molded shape; The present invention provides a method for forming a composite material, the method generally comprising:

[0027] As used herein, the term "composite material system" refers to an assembly of materials used to form a composite, including at least one woven or nonwoven veil having an upper surface and a lower surface, and a substantially planar composite material having an upper surface and a lower surface, wherein the lower surface of the substantially planar composite material is in contact with the upper surface of a first woven or nonwoven veil, and the at least one woven or nonwoven veil is held in place by a structural frame.

[0028] As used herein, the term "substantially planar" refers to a material having one plane that is significantly larger (e.g., at least 2, 3, 4, or 5 times larger, or more) than the other two planes. In some embodiments, a substantially planar material has thickness variations along its largest plane. For example, a composite material may include pad-ups (i.e., a localized increase in the amount of plies) or ply drops (i.e., a localized decrease in the amount of plies), material changes, and / or reinforcing materials, such as areas where the composite material transitions to, for example, fabric. In another embodiment, a substantially planar material exhibits minimal thickness variations along an area of ​​the composite material. For example, the term substantially planar may mean that the composite material has an overall thickness variation of no more than + / - 15% over more than 90% of its area. In some embodiments, the thickness variation is no more than ±10% over more than 90% of its area. Substantially planar is not intended to refer to a perfectly flat material, and includes materials with slight concave and / or convex variations.

[0029] Referring now to FIG. 1 , in certain embodiments, a substantially planar composite material (110) is placed on top of a woven or nonwoven veil (120) that is held in place by structural frames (150, 160). For example, the woven or nonwoven veil can be placed on a bed (140) that holds a lower frame (150). The composite material (110) can then be laid on top of the woven or nonwoven veil (120), and the upper frame (160) can be placed on top of the lower frame (150), with the woven or nonwoven veil sandwiched between the two frames. In some cases, for example, if it is desired to minimize waste around the perimeter of the molded part, the composite material can be machined into a pattern before being placed on top of the woven or nonwoven veil. The woven or nonwoven veil can be stretched across the structural frame. Stretching the woven or nonwoven veil across the structural frame serves to support the weight of the composite material. Thus, in some embodiments, a woven or nonwoven veil is stretched across the structural frame such that the woven or nonwoven veil can support the composite material with minimal sag, for example, less than 2.0 cm (from the plane of the structural frame), less than 1.0 cm, less than 0.5 cm, less than 0.25 cm, or even less than 0.1 cm. In some embodiments, an additional woven or nonwoven veil or diaphragm is added to the top surface of the composite material before placing the upper frame. The additional woven or nonwoven veil or diaphragm forms a layered structure with the composite material (i.e., sandwiches the composite material), which in some circumstances can serve to more securely hold the composite material in place. If such an additional woven or nonwoven veil or diaphragm is used, the upper frame (160) is positioned above the lower frame (150) so that the woven or nonwoven veil and the additional woven or nonwoven veil or diaphragm are both sandwiched between the two frames. A center frame can also be utilized if it is advantageous to provide a small gap between the woven or nonwoven veil and the additional woven or nonwoven veil or diaphragm.The upper, (optional) middle, and lower frames maintain the desired woven or nonwoven bale shape by supporting the perimeter, for example, by placing clamps at predetermined intervals around the perimeter. Such frames can be manufactured based on the size and shape of the composite material to be molded. Optionally, pre-fabricated structural support frames are known in the art for use with conventional metal or composite press tools (e.g., from manufacturers such as Langzauner or Schubert).

[0030] In some embodiments, the substantially planar composite material (110) is simply placed on top of the woven or nonwoven veil (120). In other embodiments, this can be done by physically applying pressure (e.g., by hand or mechanical means) to the composite material (or the additional woven or nonwoven veil or diaphragm, if used). Once placed, the composite material is considered indexed. That is, the composite material can be placed (e.g., by automated means) at a specific location along the X and Y axes on the veil. This indexed composite material system can then be placed (e.g., by automated means) at a specific location on a press tool (described in more detail below) so that the press tool consistently engages a predetermined area of ​​the composite material. Thus, the indexed composite material system can be reliably used to manufacture multiple copies of a molded product without the need to individually index each composite material blank.

[0031] If additional woven or nonwoven veils or diaphragms are used, vacuum pressure may be desirable, for example, to extract residual air that could interfere with molding performance, to prevent deformation or wrinkling of the composite (or its components), to help maintain fiber alignment, to support the material during processing and molding, and / or to maintain a desired thickness at elevated temperatures. As used herein, the term "vacuum pressure" refers to a vacuum pressure of less than 1 atmosphere (or less than 1013 mbar). At this point, the composite is held firmly between the veils / diaphragms, whether by vacuum or mechanical means, and thus remains motionless until heat or force is applied. Such a static system may be advantageous, for example, because sufficient tension across its X and Y axes not only keeps the composite stationary in place, but also indexes it (as discussed above).

[0032] Referring now to FIG. 2A, the composite material system (210) may optionally be preheated in a heating device (220). The composite material system may be placed in the heating device manually or by automated means, such as by using an automated shuttle (225). The heating device may be any heater that can be used to form or mold metal or composite products, such as a contact heater or an infrared (IR) heater. In some cases, this preheating softens the composite material, the woven or nonwoven veil, or any optional diaphragm, e.g., so that they are more pliable when forming the final molded product. In some cases, this preheating brings the composite material held within the composite material system to a desired viscosity or temperature. Preheating can be performed in a heating device heated to temperatures greater than about 75°C, 100°C, 125°C, 150°C, 175°C, 200°C, or even higher. This temperature can be adjusted depending on the properties of, for example, the woven or nonwoven veil, the optional diaphragm, and / or the composite components. Such preheating may be advantageous, for example, when it is desired to minimize or eliminate heating of the press tool and / or minimize the time the composite material system is in the press tool.

[0033] To form the final molded product, the composite material system is placed into a press tool. In some embodiments, no vacuum pressure is applied to any portion of the press tool. In other embodiments, a vacuum is applied locally to the tool surface, for example, to remove air trapped between the composite material system and the tool. However, in such embodiments, the vacuum is typically not used as a force to form the shape of the final molded product. The composite material system can be placed into the press tool manually or by automated means, such as by using an automated shuttle (225). The press tool typically includes a male mold (230) and a female mold (240), separated by a gap (250). Each mold has a non-planar molding surface (260 and 270, respectively). Mold release agents can also be added to the male mold, the female mold, or both. Such mold release agents can be useful, for example, to remove molded parts from the mold while at temperatures above ambient temperature. The molding surfaces are fixed; that is, they are not reconfigurable. The molding surfaces are also typically congruent. That is, the male mold is approximately the inverse of the female mold, and in some embodiments can be a perfect match. However, in some embodiments, the male and female molds are such that there is a varying thickness between them when closed. In certain embodiments, the composite material system is disposed in the gap between the male and female molds at a certain predetermined distance.

[0034] Referring to FIG. 2B, the composite material system is then compressed between the male and female dies by closing the gap (280). In some embodiments, this is achieved by partially closing the gap between the male and female dies to form a smaller gap between the dies. This smaller gap is then closed after a specific time or viscosity is reached. "Closing the gap" is understood to mean compressing the dies to achieve a predetermined final cavity thickness along the Z axis (290) between the dies. The final cavity thickness can be adjusted, for example, by controlling where the dies stop relative to each other; the thickness selection can be made by the dies operator and depends on the properties of the final molded product. In some embodiments, the final cavity thickness is substantially uniform. That is, the process produces a double-sided molded final product whose thickness varies by less than 5%. In some embodiments, the process produces a final molded product having a thickness that varies by less than about 4%, e.g., less than about 3%, less than about 2%, or even less than about 1%. In another embodiment, the male and female tools may be configured to provide a cavity thickness that varies intentionally across the X and Y axes.

[0035] In certain embodiments, the male and female dies are maintained at a temperature above ambient temperature. For example, they may be maintained at a temperature above about 75°C, 100°C, 125°C, 150°C, 175°C, 200°C, or higher. This temperature can be adjusted depending on the properties (and viscosity) of the composite components. The mold can be maintained at a temperature above the softening point of, for example, the binder or matrix material used in the composite. In some embodiments, the composite comprises a thermosetting material, and the mold is maintained at a temperature between about 100°C and 200°C. In other embodiments, the composite comprises a thermoplastic material, and the mold is maintained at a temperature above about 200°C. Typically, the composite system is heated at some point, for example, during a preheating step, during the molding process in the press tool, or both, to allow softening of the composite. The binder or matrix material in the composite is in a solid phase at ambient temperatures (20°C to 25°C) but softens upon heating. This softening allows the composite to be molded in the press tool.

[0036] In some embodiments, the male and female molds are maintained in a closed position for a predetermined period of time. For example, in some embodiments, the molds are heated and maintained in a closed position until a desired viscosity or temperature is reached. In some embodiments, the viscosity of the composite material is about 1.0×10 8 The mold is maintained in the closed position until the viscosity of the composite material is below 100 psi. In some embodiments, the mold is heated and maintained in the closed position until crosslinking of the binder or matrix material begins. In other embodiments, the mold is not heated, but is maintained in the closed position for a time sufficient for the material to maintain its molded shape. The mold may be maintained in the closed position for, for example, about 5 seconds to about 60 minutes, e.g., about 10 seconds to about 30 minutes, or about 15 seconds to about 15 minutes. The length of time the mold is maintained in the closed position depends on many factors, including the nature of the composite material and the temperature of the mold.

[0037] In certain embodiments, the male mold is moved through the composite material system while the female mold remains stationary. In other embodiments, the female mold does not remain stationary but moves at a slower speed than the male mold (so that the male mold still functions primarily as the forming surface). In yet other embodiments, both molds move at approximately the same speed to close the gap between them. The molds are moved at a speed and final pressure sufficient to deform / shape the composite material. For example, the molds may be moved at a speed of about 0.4 mm / s to about 500 mm / s, e.g., about 0.7 mm / s to about 400 mm / s, e.g., about 10 mm / s to about 350 mm / s, or about 50 mm / s to 300 mm / s. Furthermore, the molds may be moved to a final pressure of about 100 psi to about 1000 psi, e.g., about 250 psi to about 750 psi. In some embodiments, the molds are moved at a speed and final pressure selected to control the thickness of the final molded product while avoiding wrinkle formation and distortion of the structural fibers. Additionally, the mold may be moved to a selected speed and final pressure to allow for rapid formation of the final molded part. It should be noted that the present teachings are not intended to be limited by the depiction of Figures 2A and 2B of the female mold in contact with the veil surface of the composite material system. Indeed, in some embodiments, the male mold is in contact with the veil surface of the composite material system. While not wishing to be bound by any particular theory, it is believed that this configuration can minimize wrinkling of the inner diameter.

[0038] The composite system is then cooled below the softening temperature of the binder or matrix material. This can occur while the composite system remains in the press tool or after the composite system has been removed from the press tool. At this point, the binder or matrix material returns to a solid phase and the composite retains its newly formed shape. If the composite is a preform, such a preform will retain its desired shape for subsequent resin infusion.

[0039] In addition to superior surface quality, the present method can reduce the need for post-cure machining to achieve the final shape of the structural part. This post-cure process is not only time-consuming, but also very dangerous because the cured structural part cannot be reshaped. Therefore, any damage that occurs during the post-cure process can result in the part becoming scrap. Therefore, in some embodiments, the present method includes machining the composite material before placing it into a woven or non-woven veil. This allows for automated, efficient, and easy machining of the composite material, instead of the complex process of programming, positioning, and cutting the cured three-dimensional composite material.

[0040] The system not only aids in the shaping of composite materials, for example, by maintaining the composite material in a stationary position with sufficient tension across its X and Y axes, but also provides an effective and efficient means for producing complex three-dimensional composite structures with excellent surface properties in an automated fashion. Three-dimensional composite structures can be rapidly and repeatedly manufactured on a large scale. For example, three-dimensional composite structures can be formed from substantially planar composite blanks in cycles of 1 to 10 minutes. Such rapid and repeatable processes are suitable for the production of automotive parts and panels, such as hoods, trunks, door panels, fenders, and wheel wells.

[0041] Woven or nonwoven veils As used herein, the term "veil" refers to a thin mat of continuous or chopped polymer fibers. The fibers may be spun strand yarns or monofilaments. Typically, veils are soluble in resin and can usually be woven (e.g., in a controlled arrangement) or nonwoven (e.g., partially or completely random). Veils have been widely used in composites, for example, to enhance the toughness of composite articles manufactured by liquid resin infusion processes by sandwiching such veils between plies of structural reinforcing fibers.

[0042] The weight of the bales used in connection with the method of the present invention may vary, but is typically about 5 g / m 2 ~about 100g / m 2 In some embodiments, the woven or nonwoven veil has a density of about 75 g / m 2 Less than 60g / m 2 Less than or about 50 g / m 2 In some embodiments, the woven or nonwoven veil has a weight of less than about 5 g / m 2 ~about 50g / m 2 For example, in some embodiments, the woven or nonwoven veil has a weight of about 10 g / m 2 ~about 40g / m 2 In a particular embodiment, the woven or nonwoven veil has a weight of about 15 g / m 2 ~About 30g / m 2 For example, about 15 g / m 2 , about 16g / m 2 , about 17g / m 2 , about 18g / m 2 , about 19g / m 2 , about 20g / m 2 , about 21g / m 2 , about 22g / m 2 , about 23g / m 2 , about 24g / m 2 , about 25g / m 2 and the like weight.

[0043] The selection of bale weight can be determined based on the properties of the composite material being molded. For example, a more viscous binder or matrix material may require a heavier bale (or bales), while a less viscous binder can utilize a lighter bale. Similarly, if there is a lot of resin at the surface of the composite material, the bale can be selected to prevent the resin from penetrating too far through the bale. In certain embodiments, (i) the viscosity of the binder or matrix material is 1 × 10 8 mPa, or (ii) the weight of the bale is less than 100 g / m 2 is less than; and - The surface of composite materials contains a lot of resin.

[0044] The material used for the veil is not particularly limited and can be any veil known for use in connection with composite materials. However, in some embodiments, the woven or nonwoven veil comprises polyester fibers, carbon fibers, aramid fibers, glass fibers, or combinations thereof. In another embodiment, the woven or nonwoven veil comprises fibers of a resin-soluble polymer, such as those identified in U.S. Patent Application Publication No. 2006 / 0252334 to LoFaro et al., which is incorporated herein by reference. In some embodiments, the woven or nonwoven veil comprises polyester fibers. In some embodiments, the veil is a nonwoven veil comprising polyester fibers. In some embodiments, the veil is a woven veil comprising polyester fibers. In another embodiment, the woven or nonwoven veil comprises carbon fibers. For example, in some embodiments, the veil is a nonwoven veil comprising carbon fibers. In some embodiments, the veil is a woven veil comprising carbon fibers. In yet another embodiment, the woven or nonwoven veil comprises glass fibers. In some embodiments, the veil is a nonwoven veil comprising glass fibers. In some embodiments, the veil is a woven veil comprising glass fibers.

[0045] composite material As used herein, the term "composite material" refers to an assembly of structural fibers and a binder or matrix material. The structural fibers may be organic fibers, inorganic fibers, or mixtures thereof, including commercially available structural fibers such as carbon fibers, glass fibers, aramid fibers (e.g., Kevlar), high-modulus polyethylene (PE) fibers, polyester fibers, poly-p-phenylene-benzobisoxazole (PBO) fibers, quartz fibers, alumina fibers, zirconia fibers, silicon carbide fibers, other ceramic fibers, basalt, natural fibers, and mixtures thereof. End applications requiring high-strength composite structures typically utilize fibers with high tensile strengths (e.g., ≥ 3500 MPa or ≥ 500 ksi). Such structural fibers may comprise one or more layers of fibrous material in any conventional configuration, including, for example, unidirectional tape (unitape) webs, nonwoven mats or veils, woven fabrics, knitted fabrics, non-crimp fabrics, fiber tows, and combinations thereof. It should be noted that structural fibers may be included as one or more plies throughout all or part of the composite, or in the form of pad-ups or ply drops, with localized thickness increases / decreases.

[0046] The fibrous material is held in place and stabilized by a binder or matrix material, thereby maintaining the alignment of the fibrous material and allowing the stabilized material to be stored, transported, and handled (e.g., molded or otherwise transformed) without fraying, tearing, buckling, wrinkling, or other degradation of the integrity of the fibrous material. Fibrous materials held together by small amounts of binder (e.g., typically less than about 10% by weight) are typically referred to as fibrous preforms. Such preforms may be suitable for resin infusion applications such as RTM. The fibrous material may also be held together by large amounts of matrix material (commonly referred to as "prepreg" when referring to fibers impregnated with a matrix) and thus may be suitable for forming a final product without the addition of additional resin. In certain embodiments, the binder or matrix material is present in the composite in an amount of at least about 30%, at least about 45%, at least about 40%, or at least about 45%.

[0047] The binder or matrix material is typically selected from thermoplastic polymers, thermosetting resins, and combinations thereof. When used to form preforms, such thermoplastic polymers and thermosetting resins can be introduced in a variety of forms, such as powders, sprays, liquids, pastes, films, fibers, and nonwoven veils. The means for utilizing these various forms are generally known in the art.

[0048] Thermoplastic materials include, for example, polyesters, polyamides, polyimides, polycarbonates, poly(methyl methacrylate), polyaromatics, polyesteramides, polyamideimides, polyetherimides, polyaramids, polyarylates, polyaryletherketones, polyetheretherketones, polyetherketoneketones, polyacrylates, poly(ester)carbonates, poly(methyl methacrylate / butyl acrylate), polysulfones, polyarylsulfones, copolymers thereof, and combinations thereof. In some embodiments, the thermoplastic material may also include one or more reactive end groups, such as amine or hydroxyl groups, that are reactive with epoxides or curing agents.

[0049] Examples of thermosetting materials include epoxy resins, bismaleimide resins, formaldehyde condensation resins (including formaldehyde-phenolic resins), cyanate resins, isocyanate resins, phenolic resins, and mixtures thereof. Epoxy resins may be mono- or polyglycidyl derivatives of one or more compounds selected from the group consisting of aromatic diamines, aromatic primary monoamines, aminophenols, polyhydric phenols, polyhydric alcohols, and polycarboxylic acids. Epoxy resins may be multifunctional (e.g., difunctional, trifunctional, and tetrafunctional epoxies).

[0050] In some embodiments, a combination of a thermoplastic polymer and a thermosetting resin is used in a composite. For example, certain combinations may act synergistically with respect to flow control and flexibility. In such combinations, the thermoplastic polymer provides flow control and flexibility to the blend, dominating the typically low-viscosity, brittle thermosetting resin.

[0051] Optional diaphragm As used herein, a "diaphragm" refers to a flexible barrier that divides or separates two distinct physical regions and is a sheet of material that can be deformed elastically or inelastically. As used herein, the term "flexible" refers to a material that can deform without a significant return force. Flexible materials typically have a flexibility modulus (Young's modulus measured in Pascals multiplied by the overall thickness measured in meters) of about 1,000 N / m to about 2,500,000 N / m. Typically, the thickness of a diaphragm ranges from about 10 microns to about 200 microns, e.g., from about 30 microns to about 100 microns.

[0052] The material used to manufacture the diaphragm can be, for example, rubber, silicone, plastic, thermoplastic, or similar material. However, in certain embodiments, the material used to manufacture the diaphragm comprises a film including one or more layers independently selected from a plastic layer or an elastic layer. In some embodiments, the diaphragm material is selected to be easily released from the final molded part and / or tool. In other embodiments, the diaphragm is designed to be temporarily or permanently adhered to the molded composite material. The diaphragm material can be formed into a film using conventional casting or extrusion procedures. [Example]

[0053] The following examples are for illustrative purposes only and should not be construed as limiting the scope of the appended claims.

[0054] Comparative Example 1: Double Diaphragm Mechanical Thermoforming A lower flexible diaphragm made of plastic film (Solvay, formerly Cytec Industries, EMX045) was placed on a bed holding the lower frame. A composite blank made of carbon fiber reinforced epoxy was placed on top of the lower flexible diaphragm, followed by a central frame with a vacuum port. An upper flexible diaphragm made of the same film as the lower flexible diaphragm was then placed over the central frame and composite blank. The upper, central, and lower frames were clamped together, thereby forming a pocket surrounded by the lower flexible diaphragm, the upper flexible diaphragm, and the central frame. A vacuum was then applied to remove air from between the upper and lower flexible diaphragms.

[0055] The framed device was then shuttled into a contact heating device where it was heated to 110°C. After heating with the contact heater, the framed device was shuttled into a press tool containing conformal male and female molds configured to the shape of an automotive structural component. The male mold was then moved toward the female mold at a speed of approximately 200 mm / sec. The female mold remained stationary, and both molds were held at 140°C until crosslinking began. The molded structure was removed from the press tool while still hot and allowed to cool after removal.

[0056] A portion of the formed structure is shown in Frame A of Figure 3. The double diaphragm method provides an excellent means for rapidly forming composite materials onto existing metal tooling. However, as shown in Frame A of Figure 3, parts formed using this method can be prone to wrinkling, especially on the inner diameter.

[0057] Example 2: Mechanical Thermoforming with Veils A woven polyester veil was placed on the bed while stretching it across the lower frame. An upper structural frame was added on top of the lower frame, holding the polyester veil between the two structural frames. The upper and lower frames were then fastened together, thereby holding the polyester veil in a stretched position. The same carbon fiber-reinforced epoxy composite blank used in Comparative Example 1 was then placed on top of the polyester veil. This framed device was then processed in the same manner as Comparative Example 1.

[0058] A portion of the formed structure is shown in Frame B of Figure 3. As shown in Frame B of Figure 3, the method of the present invention not only provides an exceptional means for rapidly forming composite materials on existing metal tooling, but also unexpectedly enables the formation of parts with significantly and consistently fewer wrinkles, especially at the inner diameter. Note that the portion shown in Frame B of Figure 3 represents the bulk formed part as a whole.

Claims

1. (A) placing a composite material system into a press tool including a male mold and a corresponding female mold separated by a gap, the male mold and female mold each having an independent non-planar molding surface; (B) compressing the composite material system between the male and female molds by closing the gap between the male and female molds; and (C) maintaining the male and female dies in a closed position until the viscosity of the composite material system reaches a level sufficient to maintain the molded shape; A method for molding a composite material, comprising: the composite material system includes at least one woven or nonwoven veil having an upper surface and a lower surface, and a substantially planar composite material having an upper surface and a lower surface; a lower surface of the substantially planar composite material laid over an upper surface of the first woven or nonwoven veil; Rather than a substantially planar composite material, at least one woven or nonwoven veil is held in place by a structural frame and stretched across the structural frame such that the composite material has a sag of less than 2.0 cm from the plane of the structural frame; method.

2. 10. The method of claim 1, wherein the upper surface of the substantially planar composite material is also in contact with the lower surface of a second woven or nonwoven veil, thus forming a layered structure.

3. 3. The method of claim 2, wherein the composite material is held stationary between a first woven or nonwoven veil and a second woven or nonwoven veil until heat or force is applied to the layered structure.

4. 10. The method of claim 1, wherein the upper surface of the substantially planar composite material is also in contact with a diaphragm selected from a film including one or more layers each independently selected from a rubber layer, a silicone layer, and a plastic layer.

5. The method of any one of claims 1 to 4, wherein the structural frame comprises an upper frame and a lower frame, and at least one veil of woven or nonwoven fabric is held between the upper and lower frames.

6. Woven or nonwoven veil 5g / m ２ ~50g / m ２ The method according to any one of claims 1 to 5, wherein the weight of the mixture is

7. The method of any one of claims 1 to 6, wherein the woven or nonwoven veil comprises polyester fibers, carbon fibers, glass fibers, or combinations thereof.

8. 8. The method according to any one of claims 1 to 7, wherein step (B) comprises partially closing the gap between the male and female moulds so that a smaller gap is formed between the male and female moulds, which smaller gap is subsequently closed after a predetermined time or after viscosity is reached.

9. 9. The method according to any one of claims 1 to 8, wherein step (B) comprises closing the gap between the male and female dies at a speed of 0.7 mm / sec to 400 mm / sec while maintaining the male and female dies at a temperature higher than the softening point of the composite material.

10. 10. The method of any one of claims 1 to 9, wherein the male and female moulds are maintained at a temperature higher than ambient temperature.

11. 11. The method of claim 10, wherein the male and female molds are maintained at a temperature greater than 100°C.

12. Step (C) is carried out to determine whether the viscosity of the composite material is 1.0 × 10 ８ The method according to any one of claims 1 to 11, wherein the pressure is less than 100 kPa.

13. The method of any one of claims 1 to 12, further comprising: (D) cooling the composite material system on the tool to a temperature below the softening temperature of the composite material.

14. The method of any one of claims 1 to 13, further comprising: (D') removing the composite system from the tool while the composite system is above the softening temperature of the composite.

15. 15. The method of any one of claims 1 to 14, wherein the male and female molds are maintained in a closed position for a period of from 10 seconds to 30 minutes.

16. A method according to any one of the preceding claims, wherein the composite material in the composite material system is machined into a pattern.

17. 17. The method of any one of claims 1 to 16, further comprising preheating the composite material system in a heating device at a temperature sufficient to reduce the viscosity of the composite material prior to placing the composite material system in the press tool.

18. 18. The method of claim 17, wherein the heating device is a contact heater or an IR heater.

19. 19. The method of any one of claims 1 to 18, wherein the composite material comprises structural fibers of a material selected from aramid, high modulus polyethylene (PE), polyester, poly-p-phenylene-benzobisoxazole (PBO), carbon, glass, quartz, alumina, zirconia, silicon carbide, basalt, natural fibers, and combinations thereof.

20. The method of any one of claims 1 to 19, wherein the composite material comprises a binder or matrix material selected from thermoplastic polymers, thermosetting resins, and combinations thereof.

21. 21. The method of claim 20, wherein the binder or matrix material is present in the composite in an amount of at least 40%.

22. The binder or matrix material is at least 1×10 ８ 22. The method of claim 20 or 21, wherein the composition has a viscosity of 0.05 to 0.15 mPa.

23. (i) the viscosity of the binder or matrix material is 1 x 10 ８ mPa, or (ii) the weight of the bale is less than 100 g / m ２ is less than; and - the composite surface is resin-rich, 21. The method of claim 20.

24. The method of any one of claims 1 to 23, further comprising applying a release agent to the male mold, the female mold, or both.

25. A method according to any one of the preceding claims, wherein the composite material system is placed in the optional heating device and press tool by automated means.

26. A method according to any preceding claim, wherein no vacuum pressure is applied to any part of the press tool.

27. The method according to any one of the preceding claims, wherein at least one woven or nonwoven veil is a woven veil.

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