BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing one example of fiber-reinforced composites produced by the method of the present invention.
FIG. 2A is an exploded schematic view showing one example of molds for forming the fiber-reinforced composite of FIG. 1.
FIG. 2B-1 is a plan view showing an upper die in FIG. 2A.
FIG. 2B-2 is a transverse side view showing an upper die in FIG. 2A.
FIG. 2B-3 is a longitudinal side view showing an upper die in FIG. 2A.
FIG. 2B-4 is a bottom view showing an upper die in FIG. 2A.
FIG. 2C-1 is a plan view showing a lower die in FIG. 2A.
FIG. 2C-2 is a transverse side view showing a lower die in FIG. 2A.
FIG. 2C-3 is a longitudinal side view showing a lower die in FIG. 2A.
FIG. 2C-4 is a bottom view showing a lower die in FIG. 2A.
FIG. 3A is a partial cross-sectional view showing a pin mechanism provided in the upper die.
FIG. 3B is a partial cross-sectional view showing a pin mechanism provided in the lower die.
FIG. 4A is an enlarged perspective view showing a portion A in FIG. 2A.
FIG. 4B is an enlarged perspective view showing a portion B in FIG. 2A.
FIG. 5A is a side view showing a prepreg laminate placed on the upper die.
FIG. 5B is a side view showing a prepreg laminate placed on the lower die.
FIG. 5C is a side view showing the cutting of a transverse excess margin of the prepreg laminate placed on the upper die.
FIG. 5D is a side view showing the cutting of a transverse excess margin of the prepreg laminate placed on the lower die.
FIG. 5E-1 is a plan view showing a prepreg laminate free from excess margins in the lower die cavity.
FIG. 5E-2 is a side view showing a prepreg laminate free from excess margins in the lower die cavity.
FIG. 5F is a side view showing the cutting of a transverse excess margin of a prepreg laminate placed on the upper die, which drapes on a prepreg laminate placed on the lower die.
FIG. 5G is a partial cross-sectional view taken along the line C-C in FIG. 5F.
FIG. 5H is a side view showing a prepreg strip laminated on flanges of the prepreg laminates sandwiched by the upper and lower dies.
FIG. 5J is an enlarged cross-sectional view showing a portion D in FIG. 5H.
FIG. 6 is a side view showing side dies assembled to the closed upper and lower dies of FIG. 5J.
FIG. 7 is a cross-sectional view showing a prepreg molding and a molding die both covered with a bag film and evacuated.
FIG. 8 is a cross-sectional view showing the prepreg molding and the molding die kept in vacuum.
FIG. 9 is an exploded perspective view showing one example of jigs used for boring the cured prepreg molding.
FIG. 10 is a partial cross-sectional view showing a guide plug inserted into each hole of the upper die.
FIG. 11 is a partial cross-sectional view showing the boring of the cured prepreg molding.
FIG. 12 is a partial cross-sectional view showing a bolt screwed into a hole of the upper die to separate the upper die from the lower die.
FIG. 13 is a perspective view showing a flat-tip tool inserted into a groove provided in a flange of the lower die to separate the fiber-reinforced composite member from the lower die.
FIG. 14 is a perspective view showing another example of fiber-reinforced composite members produced by the method of the present invention.
FIG. 15 is a perspective view showing one example of dies for molding the fiber-reinforced composite member of FIG. 14.
FIG. 16 is a cross-sectional view showing the dimensions of the lower die and the fiber-reinforced composite member at a curing temperature.
FIG. 17 is a graph showing the dimensional changes of the fiber-reinforced composite member and the molding die caused by temperature change.
FIG. 18 is a perspective view exemplifying part of an aircraft fuselage structure assembled from the fiber-reinforced composite members.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[1] Production Method of Fiber-Reinforced Composite
FIG. 1 shows one example of fiber-reinforced composites produced by the method of the present invention. This fiber-reinforced composite panel 1, which is produced by curing prepregs of reinforcing fibers impregnated with a matrix resin, comprises a rectangular, flat panel portion 10, flanges 11, 11 projecting from both transverse side edges of the flat panel portion 10 on one side, flanges 12, 12′ projecting from both longitudinal side edges of the flat panel portion 10 on both sides, circular holes 13, 13 provided in the flat panel portion 10 for weight reduction, and circular notches 14 provided at four corners of the flat panel portion 10. The flat panel portion 10, the flanges 11, 11 and the flange 12 of the fiber-reinforced composite panel 1 have holes 15 for connection to other members with connecting means such as rivets, etc. Taking for example the molding of the fiber-reinforced composite panel 1 shown in FIG. 1, the method of the present invention for producing a fiber-reinforced composite will be explained below.
(1) MOLDING DIE
(a) Shape
FIGS. 2-4 show one example of molds for forming the fiber-reinforced composite panel 1 shown in FIG. 1. This mold comprises upper and lower molds 2, 3 having cavities 20, 30 for forming the flat panel portion 10 and flanges 11, 11, 12, 12 of the fiber-reinforced composite 1, and side molds 4, 4, 5, 5 clamped to the upper and lower molds 2, 3.
The upper mold 2 has a cavity 20 comprising a horizontal portion 20a for forming the flat panel portion 10 of the fiber-reinforced composite panel 1, and vertical portions 20b, 20b for forming the flanges 12, 12. The upper mold 2 has fan-shaped projections 23a, 23a, 23a, 23a with their circular sides inside at four corners of the horizontal portion 20a, and flat sides of each fan-shaped projection 23a extend slightly outward from the vertical portions 20b, 20b. Because each vertical portion 20b extends to a certain vertical position of the upper mold 2, the root portions (upper portions) of the adjacent fan-shaped projections 23a are connected through a horizontal projection 23c extending along the upper surface of the upper mold 2. Because a groove 21a for receiving a resin-leak-preventing seal 66 extends along the peripheral edge of the cavity 20, a flange 22a is provided between the peripheral edge of the cavity 20 and the groove 21a.
The horizontal portion 20a has a pair of circular projections 23b, 23b in its center portions, to form circular holes 13, 13 in the fiber-reinforced composite member 1. Each circular projection 23b has a hole 25 in its center, into which a pin 65 described later is inserted. There is an annular groove 21b for receiving a resin-leak-preventing seal 66 between each circular projection 23b and an annular flange 22b of the same height provided around the circular projection 23b.
The upper die 2 has holes 24, into which a drill is inserted to form holes 15 in the fiber-reinforced composite member 1. As shown in FIG. 3A, each hole 24 has a large-diameter, threaded portion 24a, and a small-diameter portion 24b without a threaded portion from above. A resin-leak-preventing plug 62 for the upper die 2 has a complementary shape to the hole 24, with a threaded head 62a threadably engageable with the large-diameter, threaded portion 24a. A tip-end portion 62b inserted into the small-diameter hole portion 24b is provided with an O-ring 62c made of, for instance, silicone rubbers, fluororubbers, etc., to prevent resin leak. When the plug 62 is screwed into the hole 24, a tip-end surface of the small-diameter hole portion 24b is on the same plane as the horizontal portion 20a of the cavity 20.
As shown in FIG. 4A, to pry the resultant fiber-reinforced composite member 1 out of the upper die 2, the upper die 2 properly has a shallow groove 26 on an inner surface of the flange 22a (end surface 20c of the cavity 20), into which a flat-tip tool such as a minus driver, etc. is inserted.
The lower die 3 has a shape corresponding to that of the upper die 2. A cavity 30 of the lower die 3 has a horizontal portion 30a for forming the flat panel portion 10 of the fiber-reinforced composite member 1, vertical portions 30b, 30b for forming the transverse flanges 11, 11 of the fiber-reinforced composite member 1, and vertical portions 30c, 30c for forming the longitudinal flanges 12, 12 of the fiber-reinforced composite member 1. There are fan-shaped projections 33a, 33a, 33a, 33a having the same shape as that of the fan-shaped projections 23a, 23a, 23a, 23a of the upper die 2 at four corners of the horizontal portion 30a, with flat side surfaces of each fan-shaped projection 33a slightly projecting from the vertical portions 30b, 30b, 30c, 30c. Because each vertical portion 30b, 30c reaches a certain vertical position of the lower die 2, the root portions (lower portions) of the adjacent fan-shaped projections 33a are connected by a horizontal projection 33c extending along the lower surface of the lower die 3. Because a groove 31a for receiving a resin-leak-preventing seal 66 is formed around the periphery of the cavity 30, a flange 32a is formed between the peripheral edge of the cavity 30 and the groove 31a.
The horizontal portion 30a has a pair of circular projections 33b, 33b in its center portions, to form circular holes 13, 13 in the fiber-reinforced composite member 1. There is an annular groove 31b for receiving a resin-leak-preventing seal 66 between each circular projection 33b and an annular flange 32b of the same height provided around the circular projection 33b. Each circular projection 33b has a hole 37 at center, into which a pin 65 is inserted. Because the pin 65 has a head 65a having a larger diameter than that of the hole 37, the head 65a of each pin 65 inserted into the hole 37 does not enter into the hole 37 but is received in the hole 25 of the upper die 2, resulting in the positing of the lower die 3 relative to the upper die 2.
The lower die 3 has holes 34 in its horizontal portion 30a, which are vertically aligned with the holes 24 of the upper die 2. One vertical portion 30b and both vertical portions 30c, 30c have holes 34′. The holes 34, 34′ having the same diameter receive a drill for forming holes 15 in the fiber-reinforced composite member 1. As shown in FIG. 3(b), each hole 34 has a small-diameter portion 34a and a large-diameter portion 34b from above. A resin-leak-preventing plug 63 for the lower die 3 comprises a small-diameter portion 63a fit into the small-diameter hole portion 34a, and a large-diameter portion 63b received in the large-diameter hole portion 34b. Though not shown, the large-diameter portion 63b may be threaded to the large-diameter hole portion 34b if necessary, to prevent the plugs 63 from detaching during molding. A tip-end surface of the plug 63 received in the hole 34 or 34′ is on the same plane as the horizontal portion 30a or vertical portion 30b, 30c of the cavity 30. The lower die 3 is provided on its lower surface with a groove 38 for removing the plug 63 from the holes 34′ after curing the matrix resin, along the vertical portions 30b, 30c of the cavity 30.
As shown in FIG. 4B, the lower die 3 is also provided with a shallow groove 36 on an inner surface of the flange 32a (end surface 30d of the cavity 30), into which a flat-tip tool for prying the resultant fiber-reinforced composite member 1 out of the lower die 3 is inserted.
Because the cured fiber-reinforced composite member 1 tends to become thicker by about 0.1 mm after opening the die, a cavity constituted by the cavities 20, 30 of the upper and lower dies 2, 3 is preferably set thinner by about 0.1 mm in advance.
(b) Materials
Materials forming the upper and lower dies 2, 3 may be cast iron, cast steel (for instance, JIS SS400, etc.), carbon steel (for instance, JIS S45C-H, etc.), etc. Cast iron having a low linear thermal expansion coefficient is commercially available under the trademark of “NOBINITE” from Enomoto Chukousho Co., Ltd. Materials forming the side dies 4, 5 may be aluminum, etc.
Materials forming the plugs 62, 63 and the pins 65 may be alloyed steel (for instance, JIS SCM435H, etc.). Materials forming the seal 66 may be rubbers having enough heat resistance to withstand the curing temperature, such as fluororubbers such as polytetrafluoroethylene (PTFE), silicone rubbers, etc. Commercially available PTFE seals include GORE-TEX No. 3300 available from Japan Gore-Tex Inc.
(2) PRODUCTION STEPS
(a) Lamination of Prepregs
The resin-leak-preventing plugs 62, 63 are inserted into the holes 24 of the upper die 2 and the holes 34, 34′ of the lower die 3 in advance. Pluralities of rectangular cloth prepreg sheets notched in a fan shape at four corners are laminated on the upper and lower dies 2, 3. As shown in FIGS. 5A and 5B, the prepreg laminates 1a, 1b on the upper and lower dies 2, 3 respectively have excess margins.
The cloth prepreg sheet is composed of a reinforcing fiber cloth impregnated with a matrix resin. The reinforcing fibers are not particularly restrictive, but may be properly selected from carbon fibers, aramide fibers, glass fibers, boron fibers, etc. depending on applications. The matrix resin is preferably a heat-setting resin, which may be properly selected from epoxy resins, polyurethanes, unsaturated polyesters, bismaleimide resins, phenol resins, etc. depending on applications. When the panel-shaped, fiber-reinforced composite member 1 is used for the aircraft fuselage, the reinforcing fibers are preferably carbon fibers, and the matrix resin is preferably an epoxy resin.
(b) Cutting of Excess Margins
As shown in FIGS. 5C and 5D, using a trimming tool 72 such as a cutter, etc., the excess margin 12a of the prepreg laminate 1a is cut off or trimmed along the end surface 20c of the cavity 20 of the upper die 2, and the excess margins 11b, 12b of the prepreg laminate 1b are cut off along the end surface 30d of the cavity 30 of the lower die 3. Seals 66 are fit into the grooves 21a, 21b of the upper die 2 and the grooves 31a, 31b of the lower die 3. Silicone sheets are inserted into the groove 26 of the upper die 2 and the groove 36 of the lower die 3. With the pins 65 inserted into the holes 37 of the lower die 3 and their heads 65a received in the holes 25 of the upper die 2, the upper die 2 is combined with the lower die 3 such that the prepreg laminates 1a, 1b come into contact with each other, as shown in FIG. 5F. In a state where the prepreg laminate 1a placed on the upper die 2 is draped on the prepreg laminate 1b placed on the lower die 3, the longitudinal excess margin 11a of the prepreg laminate 1a is cut off along the end surface 30d of the cavity 30 of the lower die 3, as shown in FIGS. 5F and 5G The trimming is usually conducted at room temperature.
Because excess margins are cut off from the easily trimmable uncured prepreg laminates 1a, 1b, the method of the present invention can easily produce fiber-reinforced composite members with better cut surfaces than conventional methods of trimming cured prepreg moldings.
(c) Lamination of Prepregs for Flanges
As shown in FIGS. 5H and 5J, a prepreg strip 1c is laminated on the flanges 12a, 12b of the prepreg laminates 1a, 1b via a filler 1d made of reinforcing fibers and a matrix resin, to strengthen the flanges 12, 12. Thus obtained is a prepreg assembly 1″ integrally comprising the prepreg laminates 1a, 1b, the prepreg strip 1c, and the filler 1d.
(d) Curing Step
As shown in FIG. 6, side dies 4, 4, 5, 5 are clamped to side surfaces of the combined upper and lower dies 2, 3, to support the flanges of the prepreg assembly 1″. The overall die is placed on a base plate 80 and covered with a bag film 81 as shown in FIG. 7. The bag film 81 is evacuated through a pipe 82 connected to a vacuum pump. To keep a vacuum state, the bag film 81 is adhered to an upper surface of the base plate 80 by an adhesive tape.
Heating is conducted while keeping the bag film 81 in a vacuum state (see FIG. 8), to cure the matrix resin. Heating may be conducted in an oven, etc., but it is preferably conducted while pressurizing in an autoclave, etc. The heating temperature is preferably 120-180° C., though slightly different depending on the type of the heat-setting resin. When an autoclave is used, pressurization is preferably conducted at about 3-6 MPa.
(e) Boring
After cooled to room temperature, the side dies 4, 4, 5, 5 are detached. As shown in FIG. 9, boring planar jigs 6, 6, 7, 7 are fixed to the lower die 3, with shouldered bolts 64 screwed into the holes 35 through the holes 61, 71 of the boring planar jigs 6, 6, 7, 7. Each boring jig 6, 7 has holes 60, 70, into which a boring tool is inserted to form holes 15 in the fiber-reinforced composite member 1 in the die. The boring jigs 6, 7 may be made of aluminum, etc. The shouldered bolts 64 may be made of alloyed steel such as JIS SCM435H, etc.
The resin-leak-preventing plugs 62, 63 are detached from the holes 24, 34, 34′ of the dies 2, 3. As shown in FIG. 9, tubular guide plugs 67 each having a hole 67a are inserted into the holes 24, 60, 70 of the upper die 2 and the boring jigs 6, 7. As shown in FIG. 10, each guide plug 67 comprises a large-diameter portion 67b fit into the large-diameter portion 24a of the hole 24, and a small-diameter portion 67c fit into the small-diameter hole portion 24b of the hole 24. Because the holes 60, 70 of the jigs 6, 7 have the same shape as that of the holes 24 except for having no threaded portions, they are engageable with the guide plugs 67.
As shown in FIG. 11, a boring tool 73 such as an NC drill, etc. is inserted into each hole 67a of the guide plug 67, to bore a cured prepreg molding 1′ obtained by curing the prepreg assembly 1″. To improve the accuracy of holes 15 in the fiber-reinforced composite member 1 obtained by boring, the hole 67a of the guide plug 67 preferably has a diameter more than the diameter D of the boring tool 73 and D+50 μm or less. With the guide plugs 67 fit into the holes 24, 60, 70, the cured prepreg molding 1′ is vertically bored. Because the cured prepreg molding 1′ held in the dies 2, 3 are bored using the boring jigs 6, 7 having holes 24, 34, 34′, 60, 70, the connecting holes 15 can be formed accurately and efficiently.
(f) Removal from Die
The dies 2, 3 and the boring jigs 6, 7 are detached from the resultant fiber-reinforced composite member 1. As shown in FIG. 12, each hole 25 of the upper die 2 has a threaded portion. A bolt 74 is screwed into the threaded hole 25 to push the head 65a of the pin 65 with its tip end, thereby easily separating the upper die 2 from the lower die 3. A flat-tip tool 75 such as a minus driver is inserted into the groove 26 provided on the flange 22a of the upper die 2 to pry the fiber-reinforced composite member 1 out of the upper die 2. As shown in FIG. 13, a flat-tip tool 75 is also inserted into the groove 36 provided on the flange 32a of the lower die 3 to pry the fiber-reinforced composite member 1 out of the lower die 3.
(3) OTHER EMBODIMENTS
FIG. 14 shows another example of the fiber-reinforced composite members produced by the method of the present invention. This panel-shaped, fiber-reinforced composite member 1 is the same as the fiber-reinforced composite member 1 shown in FIG. 1, except for having flanges 12, 12 projecting from both longitudinal side edges on one side, without circular holes 13, 13. FIG. 15 shows one example of dies for forming the fiber-reinforced composite member 1 shown in FIG. 14. This molding die is the same as the molding die shown in FIGS. 2-4, except for comprising an upper die 2 having no cavity and a lower die 3 not having circular projections 33b, etc. The molding method using this die is essentially the same as described above, its explanation will be omitted.
(4) SETTING OF DIMENSION OF MOLDING DIE
To prevent decrease in dimensional accuracy due to thermal expansion during the heat curing, the fiber-reinforced composite member 1 (prepreg assembly 1″, cured prepreg molding 1′) and the molding die preferably have as close linear thermal expansion coefficients as possible. Specifically, because CFRP used for the fiber-reinforced composite member 1 has a linear thermal expansion coefficient of about 2.6×10−6/° C., it is preferable to use NOBINITE CS-5 having a linear thermal expansion coefficient of 2.5×10−6/° C. (200° C.), or CN-5 having a linear thermal expansion coefficient of 2.7×10−6/° C. (200° C.). However, when there is a relatively large difference between their linear thermal expansion coefficients, the dimensions of the cavities of the dies 2, 3 at room temperature are preferably set such that they have the same dimension as that of the cured prepreg molding 1′ at a curing temperature.
Because dimensional accuracy is important in the flat panel portion 10 in the fiber-reinforced composite member 1, its length is designed as W1, and the length of the cavity for providing such designed length is set as W2. When heated from room temperature to the curing temperature, as shown in FIGS. 16 and 17, the length W1 of the flat panel portion 10 becomes W1+ΔW1(=α1·W1·ΔT), and the length W2 of the cavity becomes W2+ΔW2(=α2·W2·ΔT). Here, α1 is the linear thermal expansion coefficient of the fiber-reinforced composite member 1, α2 is the linear thermal expansion coefficient of the lower die 3, and ΔT is the difference (° C.) between room temperature and the curing temperature. Because the length of the flat panel portion 10 is equal to that of the cavity at the curing temperature, W1+α1·W1·ΔT=W2+α2·W2·ΔT. Accordingly, W2 is expressed by the following formula (1):
W
2
=W
1×(1+α1·ΔT)/(1+α2·ΔT) (1).
When the fiber-reinforced composite member 1 is taken out of the dies 2, 3, an angle between the flat panel portion 10 and the flange 11 in the fiber-reinforced composite member 1 tends to become slightly smaller. Accordingly, angles between the horizontal portions 20a, 30a and the vertical portions 30a, 30b of the cavities 20, 30 are preferably set larger than those of the final product by the decrement (for instance, about 0.5-1.5°).
[2] Fuselage Structure
The fiber-reinforced composite members thus obtained are light in weight and high in strength, suitable as members for constructing the aircraft fuselage structure. FIG. 18 shows an example of the aircraft fuselage structure constituted by the fiber-reinforced composite members produced by the method of the present invention. The fiber-reinforced composite members 1 are connected by rivets 90. The structure shown in FIG. 18 can be used as a floor structure in the aircraft fuselage. Although the fiber-reinforced composite members 1 are connected to each other in this example, they may be connected to other members as aluminum alloy members. Although the fiber-reinforced composite members 1 of the same shape are connected in the example shown in FIG. 18, this is not restrictive, and fiber-reinforced composite members 1 of different shapes may be combined.
EFFECT OF THE INVENTION
Because excess margins are cut off from the easily trimmable prepregs in the present invention, fiber-reinforced composite members with better cut surfaces can be produced accurately and easily at lower cost than by conventional methods of trimming excess margins from cured prepreg moldings.
Patent Application
20070286955
