Method for producing intermediate product made of fiber-reinforced composite

Abstract: A method for producing an intermediate product made of a fiber-reinforced composite composed of a reinforcing fiber impregnated with a thermosetting resin or a thermoplastic resin, comprising: (a) the first process where a plurality of sheets (1a,1b,1c,1d,1e) made of the fiber-reinforced composite are laminated to each other, heated under a pressure, and cooled under a pressure to provide a flat plate-shaped laminate (2a); (b) the second process where the flat plate-shaped laminate is cut into a plate (2b,2c,2d); and (c) the third process where the plate is softened by heating, placed on a forming tool, and formed by cooling under a pressure.

Description: The present invention relates to a method for producing an intermediate product made of a fiber-reinforced composite. Stiffened panels made of fiber-reinforced composites (prepregs) are light in weight and high in strength, to have been widely used for automobiles, ships, aircrafts, etc. The stiffened panels are generally produced by placing members for a skin and stiffeners (stringers and frames) each made of a fiber-reinforced composite on a forming tool to prepare an assembly, and by forming the assembly by heating under a pressure while using a pressure bag, etc. To produce a stiffened panel having a reduced weight and improved dimensional and positional accuracy with excellent formability, it is preferred that members composing the stiffeners are preformed to obtain intermediate products beforehand, and the intermediate products are arranged on a skin and then integrated therewith to produce a final product. Conventionally, the above-mentioned intermediate products have been produced by a method comprising the steps of: cutting fiber-reinforced composites many times to obtain desired lamination structures, respectively; laminating the fiber-reinforced composites on a forming tool to provide a laminate; and forming the laminate. However, this method necessitates complicated works, in particular, lamination of the fiber-reinforced composites on the forming tool is achieved by handwork, thereby requiring much effort. It would be desirable to simplify this method of producing an intermediate product by reducing the number of processing steps required. It is known from European Patent Application No. 0775561 to provide stampable sheets by laminating thermoplastic resin together with long and short fibres, the long fibres being greater than or equal to 10 mm and the short fibres being less than 10 mm. As a result of intensive research in view of the above object, the inventor has found that an intermediate product made of a fiber-reinforced composite can be easily produced by reduced processes if a flat plate-shaped laminate of a plurality of fiber-reinforced composite sheets is provided beforehand and appropriately formed. The present invention has been accomplished by the finding. Thus, a method of producing a semi-hardened intermediate product with a hardening degree of 1-50% made of a fiber reinforced composite composed of a reinforcing fiber impregnated with a thermosetting resin according to the present invention comprises: (a) the first process where a plurality of sheets made of fiber-reinforced composite are laminated to each other, heated under a pressure, and cooled under a pressure to provide a flat plate-shaped laminate; (b) the second process where the flat plateshaped laminate is cut into a plate; and (c) the third process where the plate is softened by heating, placed on a forming tool, and formed by cooling under a pressure. Certain preferred embodiments will now be described by way of example only and with reference to the accompanying drawings, in which: Fig. 1 is a perspective view showing production of a flat plate-shaped laminate used in the present invention; Fig. 2 is a perspective view showing flat plates obtained by cutting the flat plate-shaped laminate shown in Fig. 1; Fig. 3 is a perspective view showing a flat plate and L-shaped plates formed from the flat plates shown in Fig. 2; Fig. 4 is a side view showing formation of the L-shaped plates shown in Fig. 3; Fig. 5 is a perspective view showing formation of a T-shaped intermediate product from the flat plate and the L-shaped plates shown in Fig. 3; Fig. 6 is a perspective view showing an example of intermediate products produced by the method according to the present invention; and Fig. 7 is a perspective view showing production of a final product where the intermediate product shown in Fig. 6 is integrated with a skin. A method for producing an intermediate product made of a fiber-reinforced composite according to the present invention comprises: (a) the first process where a plurality of sheets made of the fiber-reinforced composite are laminated to each other, heated under a pressure, and cooled under a pressure to provide a flat plate-shaped laminate; (b) the second process where the flat plate-shaped laminate is cut into a plate; and (c) the third process where the plate is softened by heating, placed on a forming tool, and formed by cooling under a pressure. In the present invention, the fiber-reinforced composite is composed of such a reinforcing fiber as a carbon fiber, a glass fiber, an aramid fiber, etc. impregnated with a thermosetting resin. The thermosetting resin may be an epoxy resin, a bismaleimide resin, a phenol resin, etc. Preferred as the thermosetting resin is an epoxy resin. Ratio of the thermosetting resin to the reinforcing fiber in the fiber-reinforced composite may be appropriately controlled. Further, size of the fiber-reinforced composite is not particularly limited. The lamination structure of the flat plate-shaped laminate, including the direction of the reinforcing fiber composing each fiber-reinforced composite therein, is also not particularly limited. For example, each fiber-reinforced composite may be laminated in such a direction as (± 45° / 0° / 0° / 0° / 0 to 90°). Additionally, the number of laminated fiber-reinforced composites may be appropriately selected. The fiber-reinforced composite is composed of a reinforcing fiber impregnated with a thermosetting resin, and the intermediate product is in a semi-hardened state. In the present invention, "semi-hardened state" means such that the hardening degree of the fiber-reinforced composite is 1 to 50%. In the case where a semi-hardened stringer intermediate product or a semi-hardened frame intermediate product is produced by the method according to the present invention, the intermediate product is a semi-hardened product having a hardening degree of 1 to 50 %, to obtain such that can be easily handled and stored and that has properties suitable for integration with the skin. The hardening degree is more preferably 5 to 20 %. The method of the present invention is suited for producing such a semi-hardened product. Further, as the fiber-reinforced composite is composed of a reinforcing fiber impregnated with a thermosetting resin, the hardening degree of the flat plate-shaped laminate is equal to or less than that of the intermediate product. In the first process, the sheets are preferably heated at 20 to 100 °C under a pressure by a hot press roll, a hot pressing machine, etc. When the heating temperature is more than 100 °C, fluidity of the resin in the fiber-reinforced composite is excessively increased. On the other hand, the heating temperature of less than 20 °C invites insufficient stacking of the flat plate-shaped laminate. Further, the pressure is preferably 0.1 to 10 kg/cm 2 . The pressure of more than 10 kg/cm 2 results in disordered fiber orientation of the fiber-reinforced composite, and the pressure of less than 0.1 kg/cm 2 invites insufficient stacking of the flat plate-shaped laminate. In the first process, the sheets are preferably cooled at 10 to 30 °C under a pressure by a cold press roll, a cold pressing machine, etc. When the cooling temperature is more than 30 °C, a sheet tends to be peeled off the flat plate-shaped laminate. On the other hand, the cooling temperature of less than 10°C requires much energy for cooling. Further, the pressure is preferably 0.1 to 10 kg/cm 2 . The pressure of more than 10 kg/cm 2 results in disordered fiber orientation of the fiber-reinforced composite, and the pressure of less than 0.1 kg/cm 2 invites insufficient stacking of the flat plate-shaped laminate. In the second process, the flat plate-shaped laminate may be cut into a plate by a cutting machine having a cutting blade, a water jet, etc. The size of the plate may be properly controlled depending on its use. In the third process, the plate may be heated and softened by an oven, a heater, etc. The heating temperature is preferably 60 to 100 °C, more preferably 70 to 90 °C. The plate is heated preferably for 10 to 90 minutes, more preferably for 20 to 50 minutes. In the third process, the softened plate may be cooled under a pressure by a cold press roll, a cold pressing machine, etc. The cooling temperature is preferably 0 to 50 °C, more preferably 20 to 40 °C. When the cooling temperature is more than 50 °C, the formed product is returned into a plate shape by insufficient cooling. On the other hand, when the cooling temperature is less than 0 °C, fluidity of the resin in the fiber-reinforced composite is reduced too much before forming, resulting in insufficient forming. Further, the pressure is preferably 0.1 to 10 kg/cm 2 . The pressure of more than 10 kg/cm 2 results in disordered fiber orientation of the fiber-reinforced composite, and the pressure of less than 0.1 kg/cm2 invites insufficient forming. In the third process, the forming tool may be made of a steel, aluminum, etc. The intermediate products having such various shapes as C-shape, I-shape, T-shape, etc. can be produced by the method according to the present invention. Further, the method of the present invention is suitable for production of the curved-shaped intermediate products. Production of the T-shaped intermediate product 7 shown in Fig. 6 by the method according to the present invention will be described below referring to Figs. 1 to 5 without intention of restricting the scope of the present invention. (a) First Process Fig. 1 shows production of a flat plate-shaped laminate 2a, where five sheets 1a to 1e each made of a fiber-reinforced composite are laminated to each other, heated under a pressure by a hot press roll 3, and cooled under a pressure by a cold press roll 4, automatically. The first process can be carried out automatically, so that the flat plate-shaped laminate can be remarkably easily provided. (b) Second Process Flat plates 2b, 2c and 2d shown in Fig. 2 is obtained by cutting the flat plate-shaped laminate 2a in a predetermined size. In the conventional methods, the fiber-reinforced composites are cut many times and laminated on a forming tool. As compared with this, the above-mentioned flat plate-shaped laminate 2a is cut and formed in the present invention, so that the number of the cutting processes is reduced to [1 / lamination number of fiber-reinforced composites]. (c) Third Process In general, the T-shaped intermediate product is produced by two forming steps. The flat plates 2b and 2c are softened by heating and formed by cooling under a pressure, to prepare L-shaped plates 6a and 6b shown in Fig. 3, respectively. The L-shaped plates 6a and 6b having the same shape can be formed from the flat plates 2b and 2c by simple forming tools 5a and 5b shown in Fig. 4. Then, the flat plate 2d is softened by heating, placed on a forming tool 5c shown in Fig. 5 together with the L-shaped plates 6a and 6b. The plates 2d, 6a and 6b are mounted forming tools 5d to 5f on, and formed by cooling under a pressure to produce the T-shaped intermediate product 7 shown in Fig. 6. In this embodiment, because the plates 2d, 6a and 6b have the same lamination structure, needed is only one flat plate-shaped laminate 2a, thereby reducing the number of the laminating processes. The intermediate products having such a simple shape as C-shape, etc. can be produced by one forming step. The T-shaped intermediate product 7 may be heated under a pressure by a hot pressing machine, an autoclave, etc., integrated with the skin, etc., and completely hardened to produce a final product. For example; as shown in Fig. 7, the T-shaped intermediate product 7 is placed on a skin 8 spread on a forming tool 5g, and integrally formed while mounting forming tools 5h and 5i thereon. A semi-hardened intermediate product obtained by the method according to the present invention may be stored at approximately -20 °C to room temperature, although it may be completely hardened to produce a final product immediately after formation thereof As described in detail above, according to a method of present invention, an intermediate product made of a fiber-reinforced composite can be easily produced by reduced processes without complicated works.

Claims: A method of producing a product made of a fiber-reinforced composite composed of a reinforcing fiber impregnated with a resin, comprising: (a) the first process where a plurality of sheets (1a,1b,1c,1d,1e) are laminated to each other, heated under a pressure, and cooled under a pressure to provide a flat plate-shaped laminate (2a); (b) the second process where said flat plate-shaped laminate is cut into a plate (2b,2c,2d); said method being characterised in that it is a method of producing a semi-hardened intermediate product having a hardening degree of 1-50%, in that said plurality of sheets for said first process are made of reinforcing fibre impregnated with a thermosetting resin and in that the method further comprises (c) the third process where said plate of fibre reinforced thermosetting resin composite is softened by heating, placed on a forming tool, and formed by cooling under a pressure. A method as claimed in claim 1, wherein in said first process (a) said plurality of sheets made of said fibre reinforced composite are heated at a temperature of 20-100°C under a pressure of 0.1 to 10 kg/cm 2 , and cooled at a temperature of 10-30°C under a pressure of 0.1 to 10 kg/cm 2 , and in said third process (c) said plate is softened by heating at a temperature of 60-100°C for 10-90 minutes and formed by cooling at a temperature of 0-50°C under a pressure of 0.1-10kg/cm 2 . A method according to claim 1 or 2, wherein the third process (c) comprises the steps of softening two plates (2b,2c), placing them on a forming tool (5a,5b) and forming two L-shaped plates (6a,6b) by cooling under a pressure; and softening a plate (2d) and placing on a forming tool (5c) together with the L-shaped plates (6a,6b) and cooling under pressure to produce a T-shaped intermediate product (7). A method of producing a stiffened panel using the T-shaped intermediate product (7) made in accordance with the method of claim 3, comprising the steps of placing the T-shaped intermediate product (7) on a skin (8); and heating the T-shaped intermediate product (7) under pressure until completely hardened to produce a final product.

Inventors: SATO KEIICHI, SATO, KEIICHI, Sato, Keiichi, K.K. Honda, Gijutsu Kenkyujo
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 2001
Main classification: B29C70
IPC codes: B29C53, B32B37, B29C70