Manufacturing methods for aircraft parts

Abstract

The objective is to avoid quality degradation of aircraft parts even when integrally molding FRP aircraft parts using ceramic jigs. [Solution] The method for manufacturing an aircraft part according to the embodiment includes the steps of: placing a laminate of fibers, which is a fiber-reinforced plastic material, on a ceramic jig and impregnating the fibers with an uncured thermosetting resin; and manufacturing the fiber-reinforced plastic aircraft part by heating and curing the thermosetting resin impregnated in the fibers by heat transfer, including heat conduction from the surface of the jig. Before setting the laminate of fibers on the jig, the shape of the jig is determined in advance by analyzing the temperature on the surface of the jig when the thermosetting resin is impregnated into the fibers and heated and cured, so that the calculated value of the temperature distribution on the surface of the jig approaches the target value of the temperature distribution.

Description

Technical Field

[0001] Embodiments of the present invention relate to a method for manufacturing aircraft parts.

Background Art

[0002] When manufacturing aircraft parts, it is desirable to reduce manufacturing costs and manufacturing time. Using expensive metal fixtures for manufacturing aircraft parts not only requires the cost of manufacturing the fixtures but also takes time to manufacture the fixtures themselves. Therefore, attempts have been made to reduce the manufacturing cost and manufacturing time of the fixtures by using ceramic fixtures typified by gypsum (see, for example, Patent Document 1).

[0003] On the other hand, regarding the aircraft parts themselves, if assembly work is carried out after manufacturing a plurality of parts, it will lead to an increase in manufacturing costs and manufacturing time. Therefore, attempts have been made to manufacture by integral molding as much as possible without using a plurality of parts.

[0004] When integrally molding aircraft parts, it is common to manufacture aircraft parts by molding fiber reinforced plastics (FRP), also called composite materials such as glass fiber reinforced plastics (GFRP) and carbon fiber reinforced plastics (CFRP).

[0005] As a method for molding FRP with a thermosetting resin as a matrix, after producing an FRP material called a preform by laminating and shaping a prepreg sheet in which fibers are impregnated with an uncured thermosetting resin, heating and curing the resin contained in the preform, or after producing an FRP material called a dry preform by laminating and shaping the fibers before impregnating them with the resin, impregnating the dry preform with an uncured thermosetting resin and heating and curing it, a method called the RTM (Resin Transfer Molding) method is typical. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2011 / 040602 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, ceramic molding jigs have significantly lower thermal conductivity compared to conventional metal molding jigs, while FRP molding requires heating through heat conduction from the surface of the molding jig to the thermosetting resin.

[0008] Therefore, when FRP is enlarged to integrally mold aircraft parts using ceramic molding jigs, problems arise such as the time required to heat up the surface of the molding jig, uneven resin impregnation into the fibers due to temperature unevenness on the surface of the molding jig, and uneven temperature of the FRP during heat curing. In addition, when FRP is molded using ceramic molding jigs, there is a problem of reduced FRP quality, such as increased deformation of the FRP after heat curing.

[0009] Therefore, the present invention aims to prevent deterioration of the quality of aircraft parts even when integral molding of aircraft parts made of FRP is performed using a ceramic jig. [Means for solving the problem]

[0010] A method for manufacturing an aircraft part according to an embodiment of the present invention comprises the steps of: placing a laminate of fibers, which is a fiber-reinforced plastic material, on a ceramic jig and impregnating the fibers with an uncured thermosetting resin; and manufacturing the fiber-reinforced plastic aircraft part by heating and curing the thermosetting resin impregnated in the fibers by heat transfer, including heat conduction from the surface of the jig. Before setting the laminate of fibers on the jig, the shape of the jig is determined in advance by analyzing the temperature on the surface of the jig when the thermosetting resin is impregnated into the fibers and heated and cured, so that the calculated value of the temperature distribution on the surface of the jig approaches the target value of the temperature distribution. [Brief explanation of the drawing]

[0011] [Figure 1] A flowchart showing the process for manufacturing an aircraft component according to an embodiment of the present invention. [Figure 2] Figure 1 is a perspective view showing an example of an aircraft part manufactured using the manufacturing method shown. [Figure 3] Figure 2 is a perspective view showing an example of a ceramic molding jig for integrally molding aircraft parts. [Figure 4] Front view of the molding jig shown in Figure 3. [Figure 5] Figure 3 shows a top view of the molding jig. [Figure 6] Figure 3 shows a left side view of the molding jig. [Figure 7] Figure 3 shows a right side view of the molding jig. [Figure 8] Figure 3 shows a rear view of the molding jig. [Figure 9] Figure 3 shows a bottom view of the molding jig. [Figure 10] Figure 3 is a perspective view showing an example in which multiple indentations are formed on the top and side surfaces of the molding jig. [Figure 11] Figure 3 shows a front view of the molding jig, illustrating an example of the tilt angle of the molding jig, which is determined as a parameter value for the optimization calculation that minimizes the impregnation time of the thermosetting resin. [Modes for carrying out the invention]

[0012] A method for manufacturing an aircraft component according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0013] FIG. 1 is a flowchart showing the process of a method for manufacturing an aircraft component according to an embodiment of the present invention.

[0014] The method for manufacturing an aircraft component shown in FIG. 1 is a method of integrally molding an aircraft component made of FRP having a thermosetting resin as a matrix using a ceramic molding jig by the RTM method. Representative examples of FRP used as a material for aircraft components include CFRP and GFRP.

[0015] Therefore, in step S1, a ceramic molding jig is designed and manufactured so as to have a shape suitable for molding FRP by the RTM method. A design example of the ceramic molding jig will be described later.

[0016] Next, in step S2, a dry preform, which is a raw material of FRP, is manufactured. The dry preform is a fiber laminate in which a shape corresponding to the shape of the FRP is imparted to the fibers before being impregnated with the thermosetting resin. The dry preform can be manufactured by a fiber laminating process and a shaping process for imparting a shape to the laminated fibers. If necessary, the fibers may be shaped by heating using a binder made of a thermoplastic resin or the like.

[0017] Next, in step S3, the dry preform is placed on the ceramic molding jig. That is, the dry preform is set in the lower mold. Incidentally, the ceramic molding jig may be used as a fiber laminating jig for manufacturing the dry preform. In that case, the step of step S3 of placing the dry preform on the ceramic molding jig can be omitted.

[0018] Next, in step S4, bagging of the dry preform set in the ceramic molding jig is performed. Specifically, the dry preform is covered with a bagging film having a base for performing vacuum suction and an injection port for injecting an uncured thermosetting resin, and the end of the bagging film is attached to the molding jig with a sealant. Subsequently, the space between the ceramic molding jig forming the lower mold and the bagging film is evacuated by a vacuum device. Thereby, the differential pressure between the pressure in the space covered with the bagging film and the atmospheric pressure can be applied to the dry preform. That is, the dry preform can be pressurized using the atmospheric pressure.

[0019] In addition, instead of bagging, the dry preform may be pressurized by pressing an upper mold made of ceramics having an injection port for injecting an uncured thermosetting resin against the dry preform. That is, the ceramic molding jig may be composed of a lower mold and an upper mold. However, if the dry preform is pressurized using the atmospheric pressure by bagging the dry preform, the design and production target of the ceramic molding jig in step S1 can be limited to the lower mold. Therefore, the production period of the molding jig can be shortened.

[0020] Next, in step S5, an uncured thermosetting resin is injected into the space covered with the bagging film. In order to inject the thermosetting resin, it is necessary to raise the temperature of the thermosetting resin with a heating device and inject the thermosetting resin in a state where fluidity is imparted.

[0021] For this purpose, the ceramic molding jig set with the dry preform is carried into a heating device such as an autoclave device or an oven. Then, the thermosetting resin having fluidity in a state heated by the heating device is injected toward the dry preform covered with the bagging film.

[0022] When uncured thermosetting resin is injected into the bagging film, the injected thermosetting resin spreads along the fibers. This allows the thermosetting resin to impregnate the fibers. At this time, in addition to heat transfer due to the movement of gas in the chamber heated by the heating device, heat transfer including heat conduction from the surface of the ceramic molding jig due to the heating of the surface of the molding jig by the heating device prevents a decrease in the temperature and fluidity of the thermosetting resin.

[0023] Next, in step S6, the thermosetting resin impregnated into the fibers of the dry preform is heat-cured. That is, the temperature of the thermosetting resin is raised to the curing temperature by a heating device. Once the curing of the thermosetting resin is complete, an FRP aircraft part can be manufactured.

[0024] The heat curing of thermosetting resins is carried out not only by heat transfer due to the movement of gas within a heated chamber, but also by heat transfer including heat conduction from the surface of the ceramic molding jig as the surface of the molding jig is heated by the heating device.

[0025] Next, in step S7, the manufactured FRP aircraft parts are removed from the heating device and the ceramic molding jig. This allows the FRP aircraft parts to be obtained as a single molded product and sent to the next process, such as painting or assembly.

[0026] Next, we will explain in detail the design method for ceramic molding jigs.

[0027] Figure 2 is a perspective view showing an example of an aircraft part manufactured using the manufacturing method shown in Figure 1, Figure 3 is a perspective view showing an example of a ceramic molding jig for integrally molding the aircraft part shown in Figure 2, Figure 4 is a front view of the molding jig shown in Figure 3, Figure 5 is a top view of the molding jig shown in Figure 3, Figure 6 is a left side view of the molding jig shown in Figure 3, Figure 7 is a right side view of the molding jig shown in Figure 3, Figure 8 is a rear view of the molding jig shown in Figure 3, and Figure 9 is a bottom view of the molding jig shown in Figure 3.

[0028] For example, if the aircraft part 1 to be molded is an FRP (fiber-reinforced plastic) upper panel for an aircraft fuselage, which has a length of approximately 2 mm in the longitudinal direction and a tapered tip, as shown in Figure 2, then a ceramic molding jig 2 as illustrated in Figures 3 to 9 can be designed and manufactured. That is, prior to the production of the dry preform in step S2 of Figure 1 and the setting of the dry preform into the molding jig 2 in step S3, the shape of the molding jig 2 is determined in advance in step S1, and a molding jig 2 having the determined shape is manufactured.

[0029] The molding jig 2 is manufactured using ceramics, such as gypsum. Therefore, the molding jig 2 can be manufactured in a shorter time and at a lower cost compared to conventional metal molding jigs. However, if the molding jig 2 is made of ceramics, there is a risk of several problems, such as uneven impregnation of the uncured thermosetting resin into the fibers, a longer time required for the thermosetting resin to completely penetrate the fibers, uneven temperature distribution on the surface 3 of the molding jig 2, uneven temperature distribution of the FRP, and excessive deformation of the FRP after heat curing.

[0030] Therefore, the molding jig 2 is designed to avoid various inconveniences that arise from using ceramic material. First, the shape of the molding jig 2 is determined so that the temperature distribution on the surface 3 of the molding jig 2 becomes more uniform.

[0031] Specifically, a temperature analysis is performed on the surface 3 of the molding jig 2 when the thermosetting resin is impregnated into the fibers and then heat-cured. In other words, the temperature change on the surface 3 of the molding jig 2 is simulated using a computer. The shape of the molding jig 2 is then determined so that the calculated temperature distribution on the surface 3 of the molding jig 2 approaches the target temperature distribution.

[0032] The shape of the molding jig 2, based on the results of the temperature analysis on the surface 3 of the molding jig 2, can be determined by an optimization calculation that uses the shape of the molding jig 2 as a parameter and determines the parameter value such that the deviation of the calculated temperature distribution on the surface 3 of the molding jig 2 from the target value is minimized.

[0033] The molding jig 2 is brought into a heating device such as an autoclave or oven along with the dry preform. As a result, the molding jig 2 is heated by heat transfer from the atmosphere in the heating device's chamber, and its temperature rises over time. Specifically, after the molding jig 2 is heated to a temperature suitable for maintaining the fluidity of the uncured thermosetting resin injected into the bagging film and impregnating the fibers, the molding jig 2 is further heated to a temperature suitable for curing the thermosetting resin.

[0034] Therefore, the temperature of the molding jig 2 changes over time and gradually becomes hotter. For this reason, by setting a target value for the temperature distribution on the surface 3 of the molding jig 2 for each time point, and setting a target temperature at each position on the surface 3 to a constant temperature, the temperature distribution on the surface 3 of the molding jig 2 can be made uniform. For example, by setting a small tolerance range for the temperature difference between each position on the surface 3 of the molding jig 2, the temperature variation on the surface 3 of the molding jig 2 can be reduced.

[0035] Furthermore, by setting a higher target value for the temperature distribution on the surface 3 of the molding jig 2 at a given time, the heating time on the surface 3 of the molding jig 2 can also be reduced. In other words, by performing an optimization calculation that minimizes the time it takes for the temperature distribution on the surface 3 of the molding jig 2 to reach the target value, the heating rate on the surface 3 of the molding jig 2 can be increased. Note that the optimization calculation, which uses the shape of the molding jig 2 as a parameter, may be performed using topology optimization software.

[0036] The surface 3 of the molding jig 2 has a portion 4 that comes into contact with the thermosetting resin and a portion 5 that does not come into contact with the thermosetting resin. The portion 4 that comes into contact with the thermosetting resin forms the molding surface through which the molten thermosetting resin flows, and is the surface for shaping the surface of the FRP. Therefore, the portion 4 that forms the molding surface in contact with the thermosetting resin has a complex shape, such as a curved shape, that corresponds to the surface of the FRP.

[0037] The temperature analysis on the surface 3 of the molding jig 2 may be performed separately for the part 4 that forms the molding surface and the part 5 that does not form the molding surface. In other words, constraints for the part 4 that forms the molding surface and constraints for the part 5 that does not form the molding surface may be set separately. For example, the shape optimization calculation of the molding jig 2 may be performed to minimize the variation in temperature distribution for the part 4 that forms the molding surface, while the allowable range of variation in temperature distribution may be set to be larger for the part 5 that does not form the molding surface.

[0038] The portion 5 that does not form a molded surface does not need to have a complex shape, and its shape is arbitrary. Therefore, a recess may be formed in the portion 5 of the surface 3 of the molding jig 2 that does not form a molded surface in order to improve the heating rate of the molding jig 2.

[0039] Figure 10 is a perspective view showing an example in which multiple recesses 6A and 6B are formed on the top and side surfaces of the molding jig 2 shown in Figure 3.

[0040] As illustrated in Figure 10, recesses 6A and 6B can be formed in the non-molding surface portion 5 of the molding jig 2. In the example shown in Figure 10, notched recesses 6A are formed at two corners on the upper surface of the molding jig 2. In addition, three recesses 6A are formed on the front and back surfaces of the molding jig 2.

[0041] As illustrated in Figure 10, when recesses 6A and 6B are formed in the non-molding surface portion 5 of the molding jig 2, the overall surface area of ​​the molding jig 2 increases while the volume of the molding jig 2 decreases. As a result, the volume of the molding jig 2 that is heated by a heating device such as an autoclave or oven decreases, and the amount of heat transferred from the heating device to the molding jig 2 increases due to the increase in surface area, thereby improving the heating rate of the molding jig 2.

[0042] In addition, if the temperature analysis of the surface 3 of the molding jig 2 reveals that the uniformity of temperature on the surface 3 of the molding jig 2 can be improved by forming at least one of the recesses 6A and 6B, then the uniformity of temperature on the surface 3 of the molding jig 2 can be improved by forming the corresponding recesses 6A and 6B.

[0043] When forming recesses 6A and 6B in the non-forming portion 5 of the molding jig 2, forming recesses 6A and 6B consisting of multiple planes whose normal directions are mutually orthogonal in three axial directions, as illustrated in Figure 10, makes the processing for forming recesses 6A and 6B easier. Specifically, it is possible to create a laminate of gypsum boards by stacking multiple plate-shaped gypsum boards of unit thickness, and then form recesses 6A and 6B by cutting a part of the gypsum board and peeling it off from the laminate of gypsum boards.

[0044] For example, when manufacturing a molding jig 2 with a height of approximately 450mm to 500mm, a gypsum board called RT board with a thickness of 50mm is standardized and commercially available as a material for CFRP molds. Therefore, if the surfaces that form the recesses 6A and 6B are not curved or inclined surfaces, the recesses 6A and 6B can be easily formed on the molding jig 2 by stacking gypsum boards to create a laminate such as a rectangular parallelepiped, and then simply by cutting the gypsum board and peeling off the cut pieces of gypsum board along the boundaries of the layers of the gypsum board laminate. On the other hand, the part 4 that forms the molding surface including curved surfaces can be formed by carving from the gypsum board laminate.

[0045] The time required to impregnate the fibers with thermosetting resin and the uniformity of the thermosetting resin vary depending not only on the heating rate of the molding jig 2, but also on the injection position of the thermosetting resin, the number of injection positions, and the tilt angle of the molding jig 2. Therefore, by simulating the flow of the uncured thermosetting resin through computer-based analysis of the impregnation of the thermosetting resin into the fibers, optimization calculations can be performed to optimize the injection position of the thermosetting resin, the number of injection positions, and the tilt angle of the molding jig 2 so as to shorten the impregnation time of the thermosetting resin.

[0046] The impregnation time for thermosetting resin is the time it takes for the thermosetting resin to completely impregnate the fibers. For example, the time from the start of thermosetting resin injection until the resin impregnation rate at all locations in the dry preform reaches a threshold can be defined as the impregnation time for thermosetting resin.

[0047] Furthermore, by simulating the time-dependent changes in the impregnation state of the uncured thermosetting resin into the fibers, an optimization calculation can be performed using a computer to determine the values ​​of each parameter so that the time required for the impregnation of the uncured thermosetting resin into the fibers to be minimized.

[0048] Figure 11 is a front view of the molding jig 2, showing an example of the inclination angle θ of the molding jig 2, which is determined as a parameter value for the optimization calculation that minimizes the impregnation time of the thermosetting resin for the molding jig 2 shown in Figure 3.

[0049] The tilt angle θ of the molding jig 2, which is a parameter in the optimization calculation, can be defined, for example, as the angle between the horizontal plane and the top surface of the molding jig 2, as shown in Figure 11. Once the tilt angle θ of the molding jig 2 is determined by the optimization calculation, the bagging film attached to the top surface of the molding jig 2 with sealant will also be tilted, allowing the thermosetting resin to flow in roughly one direction using gravity.

[0050] On the other hand, Figure 5 illustrates an example of the position and number of resin injection ports 7 determined by optimization calculations. The resin injection ports 7 can be attached to the bagging film and connected to the thermosetting resin injection device with tubes or the like. Alternatively, the resin injection ports 7 may be opened on the surface 3 of the molding jig 2.

[0051] Regarding the remaining problem that may arise when the molding jig 2 is made of ceramics, namely the increased deformation of the FRP after molding, the shape of the molding jig 2 can be determined by computer-aided deformation analysis of the FRP to reduce the deformation of the FRP after molding. Specifically, the shape of the part 4 that forms the molding surface of the molding jig 2 can be determined in anticipation of the deformation of the FRP after molding so that the shape of the FRP after deformation becomes an ideal shape. As a more specific example, the shape of the surface 3 of the molding jig 2 can be optimized by performing an optimization calculation that minimizes the error from the nominal value of the FRP shape after molding and deformation, using the shape of the molding surface of the molding jig 2 as a parameter.

[0052] Furthermore, in order to reduce the amount of shape deformation of the FRP after molding, the lamination structure of the fibers constituting the FRP may also be optimized. That is, changing the length direction and density of the fibers changes the amount of deformation of the FRP after molding. Therefore, by performing an optimization calculation that minimizes the error from the nominal value of the FRP shape after molding and deformation, using the length direction and density of the fibers as parameters, the optimal fiber length direction and density can be determined.

[0053] The manufacturing method for aircraft component 1 described above optimizes the shape of the molding jig 2 through various computer-based analysis processes so that problems such as uneven temperature distribution do not occur even when FRP is molded by the RTM method using a ceramic molding jig 2, which has significantly lower thermal conductivity compared to a metal molding jig. (effect)

[0054] Therefore, according to the manufacturing method of aircraft part 1, it is possible to use a ceramic molding jig 2 without degrading the quality of aircraft part 1. As a result, the manufacturing cost and time of the molding jig 2 can be reduced compared to the conventional method of molding FRP using a metal molding jig. In addition, the time required to impregnate the fibers with thermosetting resin can also be reduced.

[0055] This makes it possible to reduce the overall manufacturing cost and manufacturing time of aircraft component 1. Furthermore, when aircraft component 1 made of CFRP was actually integrally molded using a ceramic molding jig 2, it was confirmed that the manufacturing cost of aircraft component 1 could be reduced by 57% and the manufacturing time by 72% compared to the conventional manufacturing method in which aircraft components are manufactured by assembling multiple parts each manufactured using a metal molding jig.

[0056] (Other embodiments) Although specific embodiments have been described above, these embodiments are merely examples and do not limit the scope of the invention. The novel methods and apparatus described herein can be embodied in various other forms. Furthermore, various omissions, substitutions, and modifications can be made in the forms of methods and apparatus described herein, without departing from the spirit of the invention. The attached claims and equivalents include such various forms and modifications as being encompassed within the scope and spirit of the invention. [Explanation of Symbols]

[0057] 1. Aircraft parts 2. Molding jig 3 surface 4. Parts that come into contact with thermosetting resin 5. Parts that do not come into contact with the thermosetting resin. 6A, 6B Indentation 7. Resin injection port θ Inclination angle of the molding jig

Claims

1. The process involves placing a laminate of fibers, which is the material for fiber-reinforced plastic, onto a ceramic jig and impregnating the fibers with an uncured thermosetting resin, A step of manufacturing a fiber-reinforced plastic aircraft part by heating and curing the thermosetting resin impregnated in the fibers by heat transfer, including heat conduction from the surface of the jig; It has, A method for manufacturing aircraft parts, in which, before setting the laminate of fibers into the jig, the shape of the jig is determined by determining the shape of the jig such that the calculated value of the temperature distribution on the surface of the jig approaches the target value of the temperature distribution, based on a temperature analysis of the surface of the jig during the process of pre-impregnating the fibers with the thermosetting resin and heat-curing it.

2. A method for manufacturing an aircraft part according to claim 1, wherein the shape of the jig is determined by an optimization calculation in which the value of the parameter is determined such that the deviation of the calculated value of the temperature distribution from the target value is minimized.

3. A method for manufacturing an aircraft part according to claim 1 or 2, wherein a recess consisting of a plurality of planes having three axial directions whose normal directions are mutually orthogonal is formed in the portion of the jig that does not come into contact with the thermosetting resin.

4. A method for manufacturing an aircraft part according to claim 3, comprising stacking multiple plate-shaped gypsum boards having a unit thickness to produce a laminate of gypsum boards, and forming the recess by cutting a part of the gypsum board and peeling it off from the laminate of gypsum boards.

5. A method for manufacturing an aircraft part according to claim 1 or 2, comprising simulating the time change in the impregnation state of the uncured thermosetting resin into the fibers, and determining the inclination angle of the jig by optimization calculation, in which the value of the parameter is determined such that the time until the impregnation of the uncured thermosetting resin into the fibers is minimized.

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