Patent Application
20220024153
The present invention relates to a structural body manufacturing method and a structural body.
From the viewpoint of component weight reduction, there have been attempts to replace metallic structural bodies with structural bodies made of Fiber Reinforced Plastics (FRP), in which reinforcing fibers such as carbon fibers are strengthened by resins. Here, as an example of a FRP-made structural body, the hollow cylindrical members already used for bicycle frames or the like are known.
However, since the frames of bicycles are originally made of metal round pipes joined together, it is relatively easy to replace them with FRP-made hollow cylindrical members, with the exception of difficulties at the join portions or the like. On the other hand, with regard to the structural bodies used in vehicles, since the installation space is limited, there is a problem in that it is difficult to use hollow cylindrical members as-is. Accordingly, in order to allow for a wider range of use as structural bodies, there is demand to form FRP-made structural bodies into plate-shaped or non-circular hollow cross-sectional shapes (for example, rectangular cylindrical shapes).
As one proposal for forming a plate-shaped FRP-made structural body, there is a method of laminating a plurality of prepregs on a mold die, and completely curing them. A prepreg is a sheet-shaped reinforced plastic molded article in which a thermosetting resin such as epoxy is uniformly impregnated into a reinforcing fiber and heated or dried to a semi-cured state.
However, in a FRP-made structural body formed in this way, there are problems in that distortion is likely to occur in the curing process, and an accurate, flat plate shape cannot be obtained.
In addition, if torsional deformation is repeatedly applied to both ends of a plate-shaped FRP-made structural body formed by laminating as described above, relative movement occurs between the upper surface side sheet and the lower surface side sheet. For this reason, there is a problem that the adhesive of the sheets peels off at both edges in the central width direction of the structural body, the fibers tend to peel off, and the strength is decreased.
On the other hand, as one proposal for forming an FRP-made structural body having a non-circular hollow cross-sectional shape, there is a method in which a flexible hollow core having a laminated prepreg or the like disposed around its outer circumference is disposed within the mold, and the hollow core is expanded by pressurization while being heated, by which the outer surface of the prepreg is formed to conform to the mold. However, when molding is performed by such a manufacturing method, there is a risk that wrinkles, voids, and resin rich caused by reinforcing fibers that cannot conform to the shape change in accordance with the mold may occur when the wall thickness of the prepreg changes during the pressurizing and heating process at the time of molding. As a result, the product quality and the product strength of the FRP-made structural bodies is decreased.
With respect to this problem, Patent Document 1 discloses a technique for forming an FRP-made structural body having a non-circular hollow cross-sectional shape. According to the technique disclosed in Patent Document 1, a hollow core having a reinforcing fiber base material disposed on its outer circumference is disposed in a cavity of a molding die, and after the mold is clamped, a resin is injected into the molding die while pressurizing the inside of the core, whereby an FRP hollow structural body can be molded.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-159457
According to the technique of Patent Document 1, by injecting a resin into a molding die while pressurizing a hollow core disposed in the molding die, it is ostensibly possible to prevent problems such as wrinkles or voids from occurring in an FRP hollow structural body. However, such a technique has a problem in that large-scale equipment such as a resin flow path for injecting resin into the molding die is required, resulting in a high cost.
It is therefore an object of the present invention to provide a structural body manufacturing method and a structural body that offer high accuracy of form and strength despite being low cost.
In order to achieve the above object, a structural body manufacturing method according to the present invention includes first step of forming a cylindrical laminate body by winding a plurality of sheets and/or tapes including reinforcing fibers and an uncured thermosetting resin around a mandrel, a second step of compressing an entire circumference of the laminate body with a tape or a film; a third step of heating the laminate body to a state prior to when the thermosetting resin is completely cured; a fourth step of extracting the mandrel from the laminate body; and a fifth step of placing the laminate body around which the tape or film is wound in a molding die, pressurizing the laminate body, and heating the laminate body until the thermosetting resin is completely cured.
The structural body according to the present invention is formed from a thermosetting resin impregnated with reinforcing fibers that has a first plane and a second plane on its outer surface, wherein a normal line extending outward from the first plane and a normal line extending outward from the second plane are oriented in different directions in a cross section orthogonal to an axis of the structural body, and an intersection portion of the first plane and the second plane has a curved surface with a constant curvature or a gradual change, and the reinforcing fiber passing through the intersection portion is continuous without being broken.
The structural body according to the present invention i s formed from a thermosetting resin impregnated with reinforcing fibers and formed in a polygonal shape or a flat plate shape including at least two flat surface portions bent at an intersection portion, wherein: the intersection portion includes a curved outer surface; and the reinforcing fibers extend from one of the flat surface portions through the intersection portion to another flat portion.
The structural body according to the present invention is formed by a process including the steps of forming a cylindrical laminate body by winding a plurality of sheets and/or tapes including reinforcing fibers and an uncured thermosetting resin around a mandrel, compressing an entire circumference of the laminate body with a tape or a film, heating the laminate body to a state prior to when the thermosetting resin is completely cured, extracting the mandrel from the laminate body; and placing the laminate body around which the tape or film is wound in a molding die, pressurizing the laminate body, and heating the laminate body until the thermosetting resin is completely cured. It should be noted that, as it is difficult to directly specify the structural body according to the present invention by its structure or characteristics, the structural body itself is specified in terms of a structural body manufacturing method.
According to the present invention, it is possible to provide a structural body manufacturing method and a structural body that offer high accuracy of form and strength despite being low cost.
Hereinafter, the embodiments according to the present invention will be described with reference to the accompanying drawings.
It should be noted that, in the present specification, the “reinforcing fibers” are preferably organic fibers represented by carbon fibers, glass fibers, or aramid fibers, silicon carbide fibers, metal fibers, or the like. In addition, it is preferable that the “thermosetting resin” is an epoxy resins, a polyester resin, a vinyl ester resin, a phenol resin, a urethane resin, a polyimide resin, or the like.
The “cylindrical laminate body” can be formed by using a sheet winding manufacturing method to wind a prepreg sheet in which reinforcing fibers have been impregnated with a thermosetting resin and that has been heated or dried to a semi-cured state, or can be formed by using a tape winding method to wind a prepreg tape.
Alternatively, the cylindrical laminate can be formed by winding using a filament winding method in which a roving fiber is wound while being impregnated with resin. However, the sheet winding method and the tape winding method are more preferable because it is possible to use a stable prepreg in which the ratio of the resin and the reinforcing fiber are controlled.
As the prepreg, Torayca (registered trademark) manufactured by Toray Corporation can be suitably used, for example.
The material of the “mandrel” may be any of a metal, a resin, ceramic, or the like, but from the standpoint of cost and durability, it is preferable to use metal. In addition, the shape of the mandrel is preferably a solid cylinder or a hollow cylinder, and may be a divisible shape instead of a single shape.
In the present specification, the “tape or film” refers to a thin-walled member of any material. However, from the viewpoint of ease of use, it is preferable to use tape. The tape may be made of resin, metal, or any material, but it is preferable to use a resin having good workability. In addition, when a resin tape is used, any of polypropylene, polyethylene, polyester, cellophane, Teflon (registered trademark), or polyimide may be used, but due to its good balance of tape properties, polypropylene and polyester are preferably used.
The structural body manufacturing method according to the first embodiment will be described.
The outer diameter of the mandrel MD is set to be slightly smaller with respect to the outer circumferential length of the structural body to be finally formed, in consideration of the thickness of the laminate wound on the outside. That is, it is desirable that the outer diameter in a state in which a plurality of prepreg sheets are wound around the mandrel MD substantially matches the design value of the outer peripheral length of the structure to be finally formed.
With regard to the prepreg sheets PS1˜PS6, here, sheets in which carbon fibers are impregnated into a raw material of an epoxy resin are used. In each prepreg sheet, the carbon fibers are oriented with regularity, and the solid lines in
A first step of the present manufacturing method will be described. The prepreg sheet PS1 is a single prepreg sheet obtained by laminating a sheet in which the orientation direction of the carbon fibers is +45 degrees with respect to the axis of the mandrel MD and a −45 degree sheet in two layers and bonding them together, and has the effect of resisting the torsional stress received by the structural body. The prepreg sheet PS1 is wound around the outer circumference of a mandrel MD subjected to a releasing treatment on its outer circumference, as necessary.
In each of the prepreg sheets PS2, PS3 and PS4, the orientation directions of the carbon fibers are parallel to the axis of the mandrel MD, which has a function of resisting the tensile stresses received by the structural body. The prepreg sheets PS2, PS3 and PS4 are wound sequentially on the prepreg sheet PS1.
In the prepreg sheet PS5, the orientation directions of the carbon fibers are perpendicular to the axis of the mandrel MD, which has a function of resisting expansion when the structural body is subjected to compressive stress. The prepreg sheet PS5 is wound around the prepreg sheet PS4.
The pair of prepreg sheets PS6 have a trapezoidal shape in which the orientation directions of the carbon fibers are perpendicular to the axes of the mandrels MDs. The prepreg sheet PS6 is wound around both ends of the prepreg sheet PS5.
In the structural body of the present embodiment, since a mounting member (to be described later) can be attached to both end portions thereof, by winding the outermost prepreg sheet PS6 around both end portions only, a reinforcing effect can be achieved. The number of prepreg sheets and the orientation direction of the carbon fibers can be appropriately changed in accordance with the desired mechanical strength of the structural body.
In this manner, a cylindrical laminate body LM (
A second step of the present manufacturing method will be described.
From such a state, the mandrel MD is rotated together with the rotary drive body RD, and the tape TP is wound around the outer circumference of the laminate body LM while applying a predetermined tension. The predetermined tension varies depending on conditions such as the outer diameter of the laminate body LM, but is preferably in the range of 1 to 5 kgf. As a result, by compressing and pressurizing the laminated prepreg sheets PS1˜PS6, it is possible to eliminate gaps between the prepreg sheets and the like and to increase the density of the laminate body LM.
Further, by moving the tape TP relatively along the direction of the axis O of the mandrel MD, the tape TP is wound over the entire direction of the axis O of the laminate body LM to form a thin layer having a substantially uniform thickness.
However, the means for pressurizing the laminate body LM wound on the mandrel MD is not limited to tape. For example, a tube made of a heat shrinkable film or the like may be disposed around the laminate body LM, and the heat shrinkable film may be shrunk by heating to compress the laminate body LM.
Alternatively, a rubber tape or a tube made of a rubber film (a rubber tube) may be disposed around the laminate body LM, and the laminate body LM can be compressed by its elastic force. As a result, the rotary drive body for rotating the mandrel MD becomes unnecessary, and the cost of equipment is reduced.
A third step of the present manufacturing method will be described.
Here, the level of curing of the thermosetting resin will be described. For example, when an uncured epoxy resin is heated at a rate of 5° C./min from room temperature to 200° C., and the heat flow (exothermic or endothermic) is measured using differential scanning calorimetry (DSC), it is found that a phenomenon peculiar to thermosetting resins occurs.
Specifically, as in the DSC curve illustrated in
When the epoxy resin is cooled again to room temperature and heated a second time to 200° C. at a rate of 5° C./min, as in the DSC curve illustrated in
On the other hand, if the heating is interrupted before the epoxy resin is completely cured, the exothermic peak becomes X° C., below 110.7° C. (
In
Taking advantage of the thermal characteristics of this thermosetting resin, the present inventors have found that the formability of the laminate body LM is improved by interrupting the heating of the laminate body LM at a curing level of 30-90%, for example, before the thermosetting resin is completely cured. The exothermic peak X° C. corresponding to the curing level of 30 to 90% can be obtained by experiments and by simulation. The effect of improving the formability of the laminate body LM will be described later in connection with the fifth step.
A fourth step of the present manufacturing method will be described.
The unheated laminate body LM needs to be stored in a refrigerator or a freezer in order to prevent degradation of the resin material. On the other hand, with regard to the preform body formed through the fourth step, the level of curing of the resin material has been modified, and there is almost no deterioration of the resin material even when stored at room temperature. Accordingly, by mass-producing preform bodies and storing them, it becomes possible to supply the product in response to sudden demand.
In addition, since a plurality of types of structural bodies can be formed from one type of preform body, manufacturing costs can be reduced.
A fifth step of the present manufacturing method will be described.
Furthermore, as illustrated in
Here, when the width of the trough bottom surface in the lower mold LD is set as W, the height of the trough inner wall is set to H, and the outer diameter of the laminate body LM wound with tape TP is set to D, then πD≈2 (W+H) , the inner circumferential length of the mold, and the outer circumferential length of the final structural body can be made substantially equal to each other, whereby a structural body having a consistent shape can be obtained.
Thereafter, as illustrated in
Furthermore, by heating the inside of the upper mold UD and the lower mold LD using a heater (not illustrated in the Figures), the rubber body GM expands, thereby increasing the internal pressure of the laminate body LM. As a result, the laminate body LM is pressed toward the inner wall surface of the upper mold UD and the lower mold LD, and in particular the gap between the inner wall-shaped corner portion CR of the upper mold UD and the lower mold LD and the laminate body LM is closed, such that it is possible to accurately deform the laminate body LM into a rectangular cylindrical shape. In addition, by heating the laminate body LM, it can be completely cured.
At this time, since a tape TP with a high slidability is wound around the laminate body LM subjected to internal pressure, even in cases in which a relative displacement occurs between the outer surface of the laminate body LM and the inner wall surface of the molding die as the rubber body GM expands, sliding can occur between the two with almost no resistance. As a result, the mold familiarity of the laminate body LM is improved, and a consistent product shape can be obtained. In addition, even if a gap occurs between the laminate body LM and the upper mold UD or the lower mold LD, since the tape TP wound around the outer circumference of the laminate body LM can receive the internal pressure of the rubber body GM, it is possible to effectively suppress defects such as wrinkles, voids and resin rich of the laminate body LM, which often occur particularly in the vicinity of the corner portion CR.
On the other hand, by improving the mold familiarity of the laminate body LM, since it is possible to reduce the pressure of the molding die while reducing the strength and rigidity of the mold, the degree of freedom in selection of a usable mold material can be expanded. In addition, since the equipment for driving the molding die can also be simplified, a reduction in equipment cost can be achieved.
In addition, due to the shape retaining function of the tape TP, the intersection portion of the side surface (the first surface) and the upper and lower surfaces (a second surface with a normal line having a direction that is different from the first surface) of the laminate body LM formed by being strongly pressed against the right angle corner CR has a curved surface with a curvature that is constant or that gradually changes (that is, no edge is formed at the intersection portion). In addition, since the reinforcing fibers at the intersection portion bend without being broken (the continuity of the fibers is maintained), the strength of the structural body can be secured.
Thereafter, the heating is interrupted, the upper mold UD and the lower mold LD are separated from each other, and each laminate body LM that has been formed into a cylindrical shape is taken out. In addition, by peeling the tapes TP from the laminate body LM, the structural body ST1 illustrated in part in
It should be noted that, instead of the rubber body GM, an air bag which is inflated by injecting air or the like may also be used.
By attaching a mounting member to the structural body ST1 formed as described above, it is possible to connect the structural body ST1 to other components.
The mounting member AT has a shape in which a tapered plate portion PT is integrally joined to a ring-shaped head RG. Grooves GV are formed in the upper and lower surfaces of the plate portions PT, respectively.
Referring to
Thereafter, as illustrated in
In this way, the mounting member AT is prevented from coming out with respect to the laminate body LM. Thereafter, the tape is peeled off in the sixth step, whereby a beam-shaped structural body ST1 as illustrated in
The structural body ST1 illustrated in
A structural body manufacturing method according to a second embodiment will be described.
The laminate body LM, which is a preform body formed in the fourth step and from which the mandrel MD was pulled out, is disposed between the plate-shaped upper mold UD and the plate-shaped lower mold LD as illustrated in
Thereafter, the upper mold UD and the lower mold LD are brought relatively close to each other in a parallel state and mold clamping is performed. Since the interior of the laminate body LM has a cavity, as illustrated in
At this time, since the thermosetting resin of the laminate body LM was heated to a level of curing of 90% or less in the previous third step, a large deformation in which the laminate body LM is crushed into a flat plate shape is permitted.
In addition, due to the shape retaining function of the tape TP, even if the laminate body LM is crushed into a flat plate shape, the outer surface of both edges ED of the laminate body LM, which is the intersection portion of the upper surface (the first surface) and the lower surface (a second surface with a normal line having a direction that is different from the first surface) of the laminate body LM has a curved surface with a curvature that is constant or gradually changing. In other words, a normal line extending outward from the first plane and a normal line extending outward from the second plane are oriented in different directions in a cross section perpendicular to the axis of the laminate body LM. Accordingly, the appearance quality and the strength with respect to bending and twisting of the structural body can be improved. In addition, since the reinforcing fibers that pass through both edges ED can also bend without breaking (such that the continuity of the fibers is maintained), high strength can be further secured.
Thereafter, by separating the upper mold UD and the lower mold LD, taking out the laminate body LM which has been deformed into a plate shape, and further peeling the tape TP from the laminate body LM, a structural body ST2 as partially illustrated in
According to the structural body ST3 according to the present modified example, even in a case when an excessive stress exceeding the allowable stress of the laminate body LM is exerted, since the flat plate FP elastically deforms, the structural body ST3 can be prevented from being immediately broken or the like.
At this time, since the inner diameter of the laminate body LM prior to molding is larger than the outer diameter of the pipe PP, the laminate body LM remains in excess after molding. Accordingly, when the inner circumference of the remaining portion of the laminate body LM is made to adhere closely and a mold is used to locally form a flat plane, the structural body ST4 has a flat portion FL that extends in the radial direction from the pipe PP. According to the present embodiment, when the pipe PP is used as, for example, a pipe through which a fluid passes, it is possible to make a hole in the flat portion FL and fasten it to the structure with bolts.
The present invention is not limited to the above embodiments. For example, in addition to the grooves, the mounting member attached to the structural body can be provided with any concave or convex shape such as holes or dimples, and the structural body can be provided with a concave or convex engaging portion that engages with a concave or convex shape.
