Fastening method and fastening device

Abstract

Provided is a fastening method for fastening multiple workpieces that each have a through-hole. The fastening method comprises: preparing a group of items to be fastened by stacking multiple workpieces such that the through-holes in the multiple workpieces communicate in a first direction to form a communicating hole and the communicating hole has a first opening and a second opening, the second opening being on the side opposite the first opening in the first direction; heating, outside of the group of items to be fastened, a rod containing reinforcing fibers and a thermoplastic resin; and inserting the heated rod into the communicating hole from the second opening to fasten the group of items to be fastened.

Description

Fastening method and fastening device

[0001] The present disclosure relates to a fastening method and a fastening device for fastening multiple workpieces.

[0002] As a technique for fastening multiple workpieces each having a through hole, for example, Japanese Patent No. 6840410 describes a fastening method in which an intermediate tool made of fiber-reinforced resin consisting of a first head and a shaft portion is prepared, and the shaft portion of the intermediate tool is inserted into the through holes of each workpiece while heating and pressurizing the shaft portion, thereby fastening each workpiece with the intermediate tool.

[0003] In the technology described in Japanese Patent No. 6840410, the intermediate tool is heated in the insertion hole of each workpiece, which may cause thermal damage to each workpiece. Also, because the intermediate tool is heated in the insertion hole, defects may occur between the head and shank of the intermediate tool. This may result in uneven heating of the intermediate tool, which may result in a decrease in fastening strength.

[0004] Therefore, there is a demand for a technique that can improve the fastening strength in the technique for fastening multiple workpieces.

[0005] The present disclosure has been made to solve at least part of the above-mentioned problems, and can be realized, for example, in the following aspects.

[0006] According to a first aspect of the present disclosure, there is provided a fastening method for fastening multiple workpieces, each having a through hole. The fastening method includes the step of preparing a group of workpieces to be fastened, in which the multiple workpieces are stacked, so that a communicating hole is formed in which the through holes in the multiple workpieces communicate with each other in a first direction. The communicating hole has a first opening and a second opening opposite the first opening in the first direction. The fastening method includes the step of heating a rod containing reinforcing fibers and a thermoplastic resin outside the group of workpieces to be fastened. The fastening method includes the step of inserting the heated rod from the second opening into the communicating hole to fasten the group of workpieces.

[0007] According to a second aspect of the present disclosure, there is provided a fastening device for fastening a group of fastening objects having communicating holes in a first direction. The fastening device includes a first molding die, a holder, a heating device, and an insertion jig. The holder faces the first molding die at a distance in the first direction. The holder has a holding through-hole that penetrates in the first direction. The heating device heats the inside of the holding through-hole. The insertion jig is inserted in a direction from the holder toward the first molding die in the first direction.

[0008] 1 is a schematic cross-sectional view of a fastening device; FIG. 2 is a view showing the appearance of a rod; FIG. 3 is a cross-sectional view of a rod; FIG. 4 is a flowchart of a fastening method; FIG. 5 is a view showing step S10 of the fastening method; FIG. 6 is a view showing step S20 of the fastening method; FIG. 7 is a view showing step S30 of the fastening method, illustrating how the rod is heated away from a group of fastening targets; FIG. 8 is a view showing step S40 of the fastening method; FIG. 9 is a view showing step S50 of the fastening method; FIG. 10 is a cross-sectional schematic view of a fastened structure; FIG. 11 is a cross-sectional schematic view of a fastened structure viewed in the +Z-axis direction; FIG. 12 is a cross-sectional schematic view of a part of a fastening device in a second embodiment; FIG. 13 is a view of a first molding die in the second embodiment viewed in the -Z-axis direction; FIG. 14 is a cross-sectional schematic view of a fastened structure formed by the fastening device in the second embodiment; FIG. 15 is a cross-sectional schematic view of a fastened structure formed by the fastening device in the third embodiment; FIG. 16 is a cross-sectional schematic view of a fastened structure formed by the fastening device in the third embodiment; FIG. 17 is a cross-sectional schematic view of a part of a fastening device in a fourth embodiment; FIG. 18 is a cross-sectional schematic view of a fastened structure formed by the fastening device in the fourth embodiment; FIG. 19 is a cross-sectional schematic view of a part of a fastening device in a fifth embodiment. Fig. 10 is a cross-sectional schematic view of a fastening structure formed by a fastening device in a fifth embodiment. Fig. 11 is a cross-sectional schematic view of a part of a fastening device in a sixth embodiment. Fig. 12 is a cross-sectional schematic view of a fastening structure formed by a fastening device in a sixth embodiment. Fig. 13 is a cross-sectional schematic view of a fastening device in a seventh embodiment. Fig. 14 is a diagram showing step S50 in the seventh embodiment. Fig. 15 is a cross-sectional schematic view of a fastening structure in the seventh embodiment. Fig. 16 is a cross-sectional schematic view of a fastening device in another embodiment.

[0009] 1 is a schematic cross-sectional view showing a fastening device 70 according to a first embodiment, and workpieces 81, 85 and a rod 90 arranged on the fastening device 70. The fastening device 70 fastens a plurality of workpieces 81, 85 each having a through hole 82, 86 together using a rod 90 including reinforcing fibers and a thermoplastic resin.

[0010] First, the rod 90 and the plurality of workpieces 81, 85 will be described. FIG. 2 shows the appearance of the rod 90. In this embodiment, the rod 90 is cylindrical. FIG. 3 is a longitudinal cross-sectional view including a central axis AX extending in the longitudinal direction of the rod 90. As shown in FIGS. 2 and 3 , the rod 90 is a fiber-reinforced thermoplastic (FRTP) containing a plurality of reinforcing fibers 93 and a thermoplastic resin 94. The reinforcing fibers 93 are oriented in a predetermined direction. The reinforcing fibers 93 are continuous fibers. In this embodiment, the predetermined direction is the axial direction AX of the rod 90. The axial direction AX is the direction along the axis AX of the rod 90. The reinforcing fibers 93 are continuous in the axial direction AX. In this embodiment, the reinforcing fibers 93 are continuous from one end 901 to the other end 902 of the rod 90. In other words, the length of the reinforcing fiber 93 is approximately the same as the distance from one end 901 to the other end 902 of the rod 90 .

[0011] In this embodiment, the reinforcing fibers 93 included in the rod 90 are, for example, carbon fibers. Examples of the thermoplastic resin 94 included in the rod 90 include polyetheretherketone (PEEK), low-melt polyaryletherketone (LM-PAEK), polyetherketoneketone (PEKK), polyphenylenesulfide (PPS), polyamide (PA), and polypropylene (PP).

[0012] The workpieces 81, 85 are generally plate-shaped. The workpieces 81, 85 only need to have a plate-shaped portion in at least a portion thereof, and the shapes of the workpieces 81, 85 can be changed as appropriate. The workpieces 81, 85 have through holes 82, 86 in the thickness direction of the plate-shaped portion. In this embodiment, the inner diameter of the through hole 82 and the inner diameter of the through hole 86 are generally equal.

[0013] In this embodiment, the workpieces 81 and 85 are formed from a fiber-reinforced resin material, such as carbon fiber reinforced plastics (CFRP) or glass fiber reinforced plastics (GFRP). Resin materials are lighter and stronger than metal materials, making them suitable for use in large structural components. For example, the workpieces 81 and 85 are used for aircraft fuselage components and spacecraft equipment. For example, fastening the workpieces 81 and 85 made of CFRP using metal fasteners such as rivets may result in electrolytic corrosion depending on the surrounding environment and usage. However, fastening the workpieces 81 and 85 made of CFRP with a rod 90 made of FRTP can prevent electrolytic corrosion.

[0014] The fastening device 70 will be described in detail below. As shown in FIG. 1 , the fastening device 70 includes a first molding die 10, a second molding die 20, a holder 30, an insertion jig 40, and a heating device 50. The first molding die 10, the second molding die 20, and the holder 30 are arranged in this order along the Z-axis direction shown in FIG. 1 . In this embodiment, the first molding die 10, the second molding die 20, the holder 30, and the insertion jig 40 are formed from a metal material such as iron or stainless steel. The material of the fastening device 70 may be any material as long as it has the heat resistance and durability required for the fastening device 70. The Z-axis direction is an example of a first direction in the present disclosure, and is the vertical direction in this embodiment. The +Z-axis direction is the vertically upward direction, and the −Z-axis direction is the vertically downward direction.

[0015] The first molding die 10 is spaced apart from the second molding die 20 and is disposed in the +Z axis direction of the second molding die 20. The first molding die 10 forms the end of the rod 90 in the +Z axis direction when the workpieces 81, 85 are fastened to it. Hereinafter, the rod in the fastened state will also be referred to as the rod in the fastened state. The end of the rod 90 in the +Z axis direction when fastened to it will also be referred to as the first end. In this embodiment, the first molding die 10 has an opening 12 in the -Z axis direction and a recess 11 recessed in the +Z axis direction. A protrusion 13 protruding in the -Z axis direction is provided at the center of the recess 11.

[0016] The second molding die 20 is disposed between the first molding die 10 and the holder 30 in the Z-axis direction. The second molding die 20 has a through hole 23 extending in the Z-axis direction. The through hole 23 is an example of a molding through hole of the present disclosure. In this embodiment, the inner diameter of the through hole 23 is larger than the inner diameters of the through holes 82, 86 of the workpieces 81, 85. In the second molding die 20, an opening 24 in the -Z-axis direction of the through hole 23 is blocked by the holder 30 and the insertion jig 40. As a result, the second molding die 20 forms the end of the rod 90 in the -Z-axis direction in the fastened state. Hereinafter, the end of the rod 90 in the -Z-axis direction in the fastened state will also be referred to as the second end.

[0017] The holder 30 is a jig that temporarily holds the rod 90. The holder 30 is provided with a holding through-hole 33. The holding through-hole 33 has an opening 31 in the +Z-axis direction and an opening 32 in the -Z-axis direction. In this embodiment, the holding through-hole 33 is substantially cylindrical. The inner diameter of the holding through-hole 33 is larger than the outer diameter of the rod 90.

[0018] The insertion jig 40 is a jig formed so as to be insertable into the holding through-hole 33. In this embodiment, the insertion jig 40 is substantially cylindrical. The outer diameter of the insertion jig 40 is smaller than the inner diameter of the holding through-hole 33. The length of the insertion jig 40 in the Z-axis direction is longer than the holding through-hole 33.

[0019] The heating device 50 heats the rod 90 in the holder through-hole 33. In this embodiment, the heating device 50 heats the inside of the holder through-hole 33 via the holder 30. The heating device 50 is, for example, an electric heater that heats the holder 30 when a switch (not shown) is turned on. In this embodiment, a cartridge heater is used as the heating device 50. The heating device 50 may be formed integrally with the holder 30 or may be formed separately. The heating device 50 heats the inside of the holder through-hole 33 from the opening 31 in the +Z-axis direction of the holder 30 to the opening 32 in the −Z-axis direction. In other words, the heating device 50 heats the entire rod 90 placed in the holder through-hole 33.

[0020] The fastening device 70 further includes a control device 60. The control device 60 adjusts the distance L1 between the holder 30 and the second molding die 20 in the Z-axis direction. In this embodiment, the control device 60 includes a first actuator 61, a second actuator 62, and a control circuit 63. The first actuator 61 moves the holder 30 along the Z-axis direction. The second actuator 62 moves the insertion jig 40 along the Z-axis direction. The control circuit 63 drives the first actuator 61 and the second actuator 62 in response to an input operation by an operator. For example, the control circuit 63 adjusts the distance L1 to a desired distance by sending a signal to the first actuator 61. Furthermore, the control circuit 63 moves the insertion jig 40 in the +Z-axis direction by sending a signal to the second actuator 62. Note that the control device 60 is not an essential component of the fastening device 70, and the adjustment of the distance L1 and the movement of the insertion jig 40 in the +Z-axis direction may be performed manually by an operator.

[0021] FIG. 4 is a flowchart of a fastening method using the fastening device 70. First, in step S10, an operator places multiple workpieces 81 and 85 on the fastening device 70 in a stacked manner. As shown in FIG. 5, in this embodiment, the operator places the workpieces 81 and 85 on the end surface 21 of the second mold 20 in the +Z axis direction. The workpieces 81 and 85 are preferably placed relative to the fastening device 70 so that the central axes C of the jigs in the fastening device 70 substantially coincide with the central axes of the through holes 82 and 86. Note that in this embodiment, the central axes C are coaxial with the central axes of the holding through hole 33 and the through hole 23. The central axis C passes through approximately the center of the opening 12 of the first mold 10 and the protrusion 13. Hereinafter, the workpieces 81 and 85 stacked so that the through holes 82 and 86 are connected in the Z axis direction will also be referred to as a fastening target group 100. The group of fastening objects 100 has a first opening 101 in the +Z axis direction and a second opening 102 in the −Z axis direction, and is provided with a communication hole 103 defined by the through holes 82 and 86 .

[0022] In step S10, the worker further moves the first molding die 10 in the direction of arrow A shown in FIG. 5 , i.e., in the −Z-axis direction, to bring it into contact with the group of fastening objects 100. As a result, the worker covers the first opening 101 with the first molding die 10. By performing step S10, the communication hole 103 of the group of fastening objects 100 communicates with the recess 11 of the first molding die 10 and the through-hole 23 of the second molding die 20. Note that in step S10, the first molding die 10, the group of fastening objects 100, and the second molding die 20 may be held by, for example, a clamping device. This prevents the group of fastening objects 100 from shifting in position relative to the fastening device 70. In addition, if the position of the fastening target group 100 in the Z-axis direction can be maintained, in step S10, the first molding die 10 may be moved in the -Z-axis direction relative to the fastening target group 100, and the second molding die 20 may be moved in the +Z-axis direction, thereby sandwiching and fixing the fastening target group 100 between the first molding die 10 and the second molding die 20.

[0023] Next, in step S20, the worker places the rod 90 in the holder 30. In this embodiment, as shown in FIG. 6 , the worker inserts the rod 90 into the holder through-hole 33 of the holder 30. Next, with the rod 90 inserted in the holder through-hole 33, the worker inserts an insertion jig 40 into the holder through-hole 33. In this embodiment, the Z-axis direction is the vertical direction, and the holder through-hole 33 is formed in the Z-axis direction. Therefore, by inserting the insertion jig into the holder through-hole 33 from the opening 32 of the holder through-hole 33, it is possible to prevent the rod 90 from moving in the −Z-axis direction, i.e., the vertically downward direction. Therefore, the insertion jig 40 can also function as a holder that holds the rod 90 in the holder through-hole 33. Note that if the position of the rod 90 can be maintained by the holder 30 alone, it is not necessary to insert the insertion jig 40 into the holder through-hole 33 in step S20. Furthermore, steps S10 and S20 may be performed simultaneously, or their orders may be reversed.

[0024] Next, in step S30, the rod 90 is heated by the heating device 50 outside the group of fastening objects 100. Outside the group of fastening objects 100 refers to a position spaced apart from the group of fastening objects 100 in the Z-axis direction. Outside the group of fastening objects 100 refers to a position not in direct contact with the group of fastening objects 100. In step S30, for example, an operator operates the heating device 50 via an input device. This supplies power to the heating device 50, heating the rod 90 placed in the holding through-hole 33. The heating temperature inside the holding through-hole 33 in step S30 is a temperature equal to or higher than the softening point of the thermoplastic resin 94 contained in the rod 90. The heating temperature may be equal to or higher than the melting point of the thermoplastic resin 94. The heating temperature and heating time by the heating device 50 can be determined in advance through experiments or simulations using the shape of the holder 30, the configuration of the heating device 50, the properties of the thermoplastic resin 94, etc. As shown in FIG. 5 , the holder 30 and the heating device 50 are spaced apart from the second molding die 20 by a distance L1. The distance L1 is a distance at which the thermal influence on the group of objects to be fastened 100 is suppressed when the rod 90 is heated.

[0025] When heating of the rod 90 is completed, in step S40, the worker uses the control device 60 to move the holder 30 toward the group of fastening objects 100. In this embodiment, as shown in FIG. 8 , the worker moves the holder 30 and the insertion jig 40 in the +Z-axis direction until the end face 35 of the holder 30 in the +Z-axis direction abuts the end face 22 of the second molding die 20 in the −Z-axis direction. In other words, the worker moves the holder 30 and the insertion jig 40 relatively toward the group of fastening objects 100 until the distance L1 becomes zero. By performing step S40, the holder through-hole 33 communicates with the communication hole 103 of the group of fastening objects 100. More specifically, the recess 11 of the first molding die 10, the communication hole 103, the through-hole 23 of the second molding die 20, and the holder through-hole 33 communicate with each other.

[0026] In step S50, the worker inserts the heated rod 90 from the second opening 102 of the fastening object group 100 into the communicating hole 103. In this embodiment, the worker uses the control device 60 to move the insertion jig 40 in the +Z axis direction, thereby inserting the heated rod 90 from the holding through hole 33 through the through hole 23 of the second molding die 20 into the communicating hole 103 of the fastening object group 100. In this embodiment, the movement amount of the insertion jig 40 is determined in advance through experiments and simulations. This movement amount is the movement amount required for the heated rod 90 to reach the first molding die 10 and fill the communicating hole 103 and the through hole 23 of the second molding die 20. In this embodiment, the tip of the heated rod 90 reaches the protruding portion 13 of the recess 11 of the first molding die 10 and spreads out approximately radially from the protruding portion 13 toward the outer edge of the recess 11. When step S50 is performed, as shown in FIG. 9 , the heated rod 90 is filled into the communicating hole 103, the recess 11 of the first molding die 10, the communicating hole 103, and the through-hole 23 of the second molding die 20. By performing step S50, the front and rear ends of the heated rod 90 are deformed to form a first end 91 t and a second end 92 t. The first end 91 t is formed by the front end of the heated rod 90 being pressed against the recess 11 of the first molding die 10 and deforming. The second end 92 t is formed by the rear end of the heated rod 90 being deformed within the through-hole 23 of the second molding die 20. In FIG. 9 , for simplicity of illustration, the entire cross section of the rod 90 in the fastened state is shown with cross-hatching; however, in reality, reinforcing fibers 93 appear in the cross section of the rod 90 in the fastened state, as shown in FIG. 10 .

[0027] In step S50, the worker maintains the positional relationship of the holder 30 and the rod 90 with respect to the group of fastening objects 100 until the thermoplastic resin 94 cools and solidifies. In this embodiment, the thermoplastic resin 94 is cooled by room temperature cooling. Once the thermoplastic resin 94 has solidified, the worker removes the group of fastening objects 100 fastened by the rod 90 from the fastening device 70. Hereinafter, the rod 90 and the group of fastening objects 100 fastened by the rod 90 will be collectively referred to as a fastened structure 110. Note that the various processes performed by the worker in the above-described fastening method may be performed by the control device 60 or a robot.

[0028] FIG. 10 is a cross-sectional schematic diagram of a fastening structure 110. FIG. 11 is a view of the fastening structure 110 as viewed from the +Z-axis direction. In this embodiment, a rod 90 including reinforcing fibers 93 is heated and then inserted into the communicating holes 103 of the group of fastening objects 100, thereby fastening the group of fastening objects 100. The orientation direction of the reinforcing fibers 93 is the Z-axis direction, which is the same as the extension direction of the communicating holes 103 and the insertion direction of the insertion jig 40. Therefore, as shown in FIG. 10 , in the fastening structure 110, the continuity of the reinforcing fibers 93 is maintained throughout the first end 91t, the communicating holes 103, and the second end 92t. Maintaining the continuity of the reinforcing fibers 93 includes maintaining a predetermined length of the reinforcing fibers 93 in a predetermined direction. In other words, in the fastening structure 110, the properties of the reinforcing fibers 93 as continuous fibers are maintained. Furthermore, since the first molding die 10 has a protruding portion 13 that protrudes in the -Z axis direction from the center of the recess 11, the heated rod 90 reaches the protruding portion 13 and spreads approximately radially within the recess 11 starting from the protruding portion 13. Therefore, the reinforcing fibers 93 spread within the recess 11 from the protruding portion 13 toward the outer edge at the first end portion 91t. Furthermore, as shown in Figure 11, a recess 95t that is recessed corresponding to the protruding portion 13 of the first molding die 10 is formed at the center of the first end portion 91t. The first end portion 91t has an approximately hemispherical shape with a recessed center.

[0029] According to the fastening device 70 and the fastening method using the fastening device 70 of the present embodiment described above, the rod 90 is heated outside the group of fastening objects 100, that is, at a position distant from the group of fastening objects 100, and then inserted into the communicating hole 103. This makes it possible to suppress the thermal effect on the group of fastening objects 100 due to the heating of the rod 90. Furthermore, because the rod 90 is heated at a position distant from the group of fastening objects 100, the entire rod 90 can be heated more easily than, for example, a configuration in which a heater is inserted into the communicating hole 103 of the group of fastening objects 100 to heat the rod 90. This prevents uneven heating of the rod 90. This makes it possible to spread the heated rod 90 within the communicating hole 103 of the group of fastening objects 100, thereby enabling the group of fastening objects 100 to be firmly fastened.

[0030] In this embodiment, the reinforcing fibers 93 of the rod 90 are continuous fibers oriented in the same direction as the extension direction of the communicating holes 103 and the insertion direction of the insertion jig 40. This can further increase the strength of the fastening structure 110. Furthermore, the continuity of the reinforcing fibers 93 is maintained even at the first end 91 t and the second end 92 t of the rod 90 in the fastened state. This can effectively increase the strength of the fastening structure 110 in the peel direction.

[0031] In this embodiment, the first end portion 91t can be easily formed by inserting the heated rod 90 from the second opening 102 into the communicating hole 103 and reaching the recess 11 of the first molding die 10. Furthermore, the desired first end portion 91t can be formed by shaping the first molding die 10 into a desired shape.

[0032] Furthermore, in this embodiment, the first molding die 10 has a protruding portion 13 that protrudes in the -Z axis direction from the center of the recess 11. This allows the heated rod 90 to reach the protruding portion 13 and spread within the recess 11. Therefore, the reinforcing fibers 93 can be distributed approximately radially from the protruding portion 13 to the outer edge within the recess 11, and uneven distribution of the reinforcing fibers 93 can be suppressed. This can further improve the strength of the fastening structure 110.

[0033] Furthermore, a protrusion 13 is provided in the center of the recess 11 of the first molding die 10. This allows for a reduction in the amount of rod 90 required to form the first end 91t, compared to a configuration in which the recess 11 does not have the protrusion 13. Therefore, when manufacturing a structure that requires a large number of fastening portions, such as an aircraft fuselage part, the manufacturing cost of the structure can be reduced.

[0034] In this embodiment, the insertion jig 40 is inserted in the +Z axis direction from the opening 32 of the holder 30, and the heated rod 90 is inserted into the communicating hole 103 via the through hole 33 of the holder 30 and the through hole 23 of the second molding die 20. At this time, the heated rod 90 also spreads into the through hole 23 of the second molding die 20, so that the second end 92t of the rod 90 in the fastened state can be formed by the through hole 23. Furthermore, by forming the through hole 23 of the second molding die 20 into a desired shape, the desired second end 92t can be formed.

[0035] Furthermore, in this embodiment, fastening can be performed using a rod 90 that uses the same type of composite material as the group of fastening objects 100. Therefore, for example, when discarding the fastening structure 110 or when crushing the fastening structure 110 to extract and reuse the materials, it is possible to avoid the effort of separating the group of fastening objects 100, i.e., the workpieces 81 and 85, from the rod 90.

[0036] The fastening device 70 described in this embodiment can be modified in various ways. For example, an operator can form the fastened structure 110 into a desired shape by changing the shapes of the first molding die 10 and the second molding die 20. A fastening device using a molding die different from that of the first embodiment and a fastened structure formed by the fastening device will be described below.

[0037] Second Embodiment A fastening device 70a and a fastening structure 110a formed by the fastening device 70a according to a second embodiment will be described with reference to FIGS. 12 to 15 . As shown in FIG. 12 , the first molding die 10a of the second embodiment includes a recess 11a recessed in the +Z axis direction, as in the first embodiment. A protrusion 13a protruding in the −Z axis direction is provided at the center of the recess 11a. As shown in FIG. 13 , the protrusion 13a of the second embodiment differs from the protrusion 13 of the first embodiment in that it includes multiple apexes 14a extending from the center of the recess 11a toward the outer edge. The multiple apexes 14a are arranged radially outward from the center of the recess 11a. In this embodiment, the protrusion 13a includes four apexes 14a. The second molding die 20a of the second embodiment has a similar shape to the second molding die 20 of the first embodiment, except that it is thinner in the +Z axis direction than the second molding die 20 of the first embodiment.

[0038] 14 and 15, the fastening device 70a forms a fastening structure 110a having a recess 95ta in the center of the first end 91ta. The recess 95ta has a shape corresponding to the protrusion 13a of the first molding die 10a. As shown in FIG. 14, the recess 95ta is recessed to correspond to the multiple peaks 14a and has radially arranged grooves 97ta.

[0039] 14 and subsequent figures, the reinforcing fibers 93 are omitted as appropriate, but in this embodiment, the reinforcing fibers 93 are distributed in a substantially radial pattern at the first end 91ta along the apex 14a within the recess 11a. Note that in this embodiment as well, the continuity of the reinforcing fibers 93 is maintained throughout the fastening structure 110a, from the first end 91ta through the communicating hole 103 to the second end 92ta. This also applies to subsequent embodiments.

[0040] Other configurations and fastening methods of the fastening device 70a in the second embodiment are similar to those of the first embodiment. Therefore, the second embodiment also achieves the same effects as the first embodiment. Furthermore, the protruding portion 13a of the first molding die 10a has multiple apexes 14a. This allows the reinforcing fibers 93 to be distributed along the apexes 14a at the first end 91ta. Therefore, a shape and fiber orientation of the first end 91ta that contribute to improving the fastening strength of the workpieces 81 and 85 can be achieved. Furthermore, because the protruding portion 13a has multiple apexes 14a, the weight of the structure including the fastened structure 110a can be reduced compared to a configuration in which the protruding portion 13a does not have apexes 14a. Furthermore, manufacturing costs can be reduced. Therefore, the fastening method using the fastening device 70a of this embodiment is suitable for manufacturing structures requiring multiple fastening parts.

[0041] 16 and 17 , a fastening device 70b according to a third embodiment and a fastening structure 110b formed by the fastening device 70b will be described. As shown in FIG. 16 , in the third embodiment, a first molding die 10b includes a recess 11b recessed in the +Z axis direction. The recess 11b is semicircular in cross section. The first molding die 10b differs from the first molding dies 10 and 10a according to the above-described embodiments in that it does not include a protrusion 13.

[0042] The second molding die 20b has a recess 23b recessed in the -Z axis direction. The recess 23b is approximately semicircular in cross-sectional view. The recess 23b has an opening 24b in the -Z axis direction. The recess 23b also functions as a molding through-hole penetrating in the Z axis direction. As shown in FIG. 17 , the first end 91tb and the second end 92tb of the fastening structure 110b formed by the fastening device 70b are approximately semicircular in cross-sectional view. The other configurations and fastening methods of the fastening device 70b in the third embodiment are the same as those in the first embodiment. Therefore, the third embodiment also achieves the same effects as those in the first embodiment.

[0043] Fourth Embodiment A fastening device 70c and a fastening structure 110c formed by the fastening device 70c according to a fourth embodiment will be described with reference to FIGS. 18 and 19 . As shown in FIG. 18 , the first molding die 10c, like the first embodiment, has a recess 11c recessed in the +Z axis direction. The recess 11c of the first molding die 10c differs from the first molding dies 10 to 10b in the above-described embodiments in that it is rectangular in cross section. The recess 11c of this embodiment has a bottom surface 14c perpendicular to the central axis C. Therefore, as shown in FIG. 19 , the first end 91tc of the fastening structure 110c is rectangular in cross section. The second molding die 20a of the fastening device 70c is the same as that of the second embodiment. The other configurations and fastening methods of the fastening device 70c are the same as those of the first embodiment. Therefore, the fourth embodiment also achieves the same effects as those of the first embodiment.

[0044] Fifth Embodiment A fastening device 70d according to a fifth embodiment and a fastening structure 110d formed by the fastening device 70d will be described using Figures 20 and 21. As shown in Figure 20, in the fifth embodiment, the first molding die 10d includes a recess 11d recessed in the +Z-axis direction. The recess 11d includes a bottom surface 14d perpendicular to the central axis C. In this embodiment, the diameter of the opening 12 is larger than the diameter of the bottom surface 14d. In other words, the cross section of the recess 11d is trapezoidal. The second molding die 20d includes a recess 23d recessed in the -Z-axis direction. The recess 23d also functions as a molding through-hole that penetrates in the Z-axis direction. An opening 25d in the +Z-axis direction of the recess 23d is larger than an opening 24d in the -Z-axis direction. In other words, the cross section of the recess 23d is trapezoidal. 21, the first end 91td and the second end 92td of the fastening structure 110d formed by the fastening device 70d have a trapezoidal shape in cross section. The other configurations and fastening methods of the fastening device 70d in the fifth embodiment are the same as those in the first embodiment. Therefore, the fifth embodiment also achieves the same effects as those in the first embodiment.

[0045] Sixth Embodiment A fastening device 70e and a fastened structure 110e formed by the fastening device 70e according to the sixth embodiment will be described with reference to FIGS. 22 and 23 . Workpieces 81e and 85e according to the present embodiment differ from the workpieces 81 and 85 according to the first embodiment in that the inner diameters of the through holes 82e and 86e are not substantially constant in the Z-axis direction. The workpiece 81e includes a first hole portion 83e having a substantially constant inner diameter and a second hole portion 84e whose inner diameter increases in the +Z-axis direction of the first hole portion 83e. The through hole 82e of the workpiece 81e is defined by the first hole portion 83e and the second hole portion 84e. The workpiece 85e includes a third hole portion 87e having a substantially constant inner diameter and a fourth hole portion 88e whose inner diameter increases in the −Z-axis direction of the third hole portion 87e. The through hole 86e of the workpiece 85e is defined by the third hole portion 87e and the fourth hole portion 88e. As a result, the fastening object group 100e, in which the workpieces 81e and 85e are stacked, has a central portion 104e defined by the first hole portion 83e and the third hole portion 87e of the workpieces 81e and 85e, and enlarged diameter portions 105e and 106e defined by the second hole portion 84e and the fourth hole portion 88e of the workpieces 81e and 85e. The central portion 104e and the enlarged diameter portions 105e and 106e define a communicating hole 103e of the fastening object group 100e. The first opening 101e and the second opening 102e of the communicating hole 103e are larger in inner diameter than the central portion 104e of the communicating hole 103e.

[0046] The first molding die 10e of the sixth embodiment is formed in a generally plate-like shape and covers the first opening 101e of the communicating hole 103e. The second molding die 20e has a through-hole 23e with an inner diameter generally equal to that of the central portion 104e of the communicating hole 103e. Therefore, a portion of the second opening 102e of the communicating hole 103e is covered by the end surface 21 of the second molding die 20e.

[0047] As described above, the first molding die 10e does not have a recess recessed in the +Z axis direction. Therefore, in this embodiment, the heated rod 90 is pressed against the first molding die 10e and expands into the expanded diameter portion 105e. As a result, a first end 91te is formed in a portion of the communicating hole 103e corresponding to the expanded diameter portion 105e. Furthermore, the heated rod 90 is filled into the central portion 104e and the expanded diameter portion 105e of the communicating hole 103e. As a result, a second end 92te is formed in a portion of the communicating hole 103e corresponding to the expanded diameter portion 106e. Therefore, a fastening structure 110e is formed in which the first end 91te and the second end 92te of the rod 90 in the fastened state are arranged within the group of fastening objects 100e. In the fastened structure 110e, the end face of the first end 91te in the +Z axis direction is located substantially flush with the end face of the workpiece 81e in the +Z axis direction, and the end face of the second end 92te in the -Z axis direction is located substantially flush with the end face of the workpiece 85e in the -Z axis direction. The other configurations and fastening methods of the fastening device 70e in the sixth embodiment are similar to those in the first embodiment. Therefore, the sixth embodiment also achieves the same effects as the first embodiment. Furthermore, in the sixth embodiment, a fastened structure 110e can be formed in which the first end 91te and the second end 92te do not protrude from the fastening target group 100e, i.e., the workpieces 81e and 85e. Furthermore, compared to a configuration in which the first end 91te and the second end 92te protrude from the fastening target group 100e, the weight of a structure including the fastened structure 110e can be reduced. Furthermore, manufacturing costs can be reduced. Therefore, the fastening method using the fastening device 70e of this embodiment is suitable for manufacturing structures requiring multiple fastening parts.

[0048] In this embodiment, the second molding die 20e is mainly used to hold the group of fastening objects 100e, and therefore the second molding die 20e may be omitted when a clamping device or the like capable of maintaining the position of the group of fastening objects 100e in the Z-axis direction is used.

[0049] Seventh Embodiment In the seventh embodiment, a fastening device and a fastening method are described that are capable of forming a recess similar to that at the first end 91t in the first embodiment also in the center of the second end of the rod 90 in the fastened state.

[0050] FIG. 24 is a diagram showing a fastening device 70f according to the seventh embodiment. The first molding die 10 in the fastening device 70f is the same as that in the first embodiment. The second molding die 20f has a recess 23f recessed in the -Z axis direction. The recess 23f has an opening 24f in the -Z axis direction. The recess 23f also functions as a molding through-hole that penetrates in the Z axis direction. The insertion jig 40f in the fastening device 70f differs from that in the first embodiment in that the end in the +Z axis direction is conical in shape and protrudes in the +Z axis direction. The end of the insertion jig 40 in the +Z axis direction is also referred to as the protruding end 41f.

[0051] FIG. 25 is a diagram illustrating step S50 of the fastening method according to the seventh embodiment. In step S50, the operator moves the insertion jig 40f in the +Z-axis direction. This causes the heated rod 90 to be inserted from the holding through-hole 33 through the opening 24f and recess 23f of the second molding die 20f into the communicating hole 103 of the fastening target group 100. The leading end of the heated rod 90 reaches the protruding portion 13 of the recess 11 of the first molding die 10 and spreads radially from the protruding portion 13 into the recess 11. The rear end of the heated rod 90 is pushed in the +Z-axis direction by the protruding end portion 41f of the insertion jig 40f. Therefore, the heated rod 90 spreads radially from the protruding end portion 41f toward the outer edge of the recess 23f. More specifically, the heated rod 90 spreads radially from the protruding end portion 41f toward the outer edge of the recess 23f.

[0052] FIG. 26 is a cross-sectional schematic diagram of a fastening structure 110f formed by the fastening device 70f. FIG. 26 corresponds to FIG. 10 of the first embodiment. In the fastening structure 110f, a recess 95t is formed in the center of the first end 91t, corresponding to the protruding portion 13 of the first molding die 10. Furthermore, a recess 96tf is formed in the center of the second end 92tf, corresponding to the protruding end 41f. The first end 91t and the second end 92tf have an overall substantially hemispherical shape with a recessed center. In the fastening structure 110f, continuity of the reinforcing fibers 93 is maintained throughout the first end 91t, the communicating hole 103, and the second end 92tf. The reinforcing fibers 93 are distributed substantially radially within the recess 11 at the first end 91t, and substantially radially within the recess 23f at the second end 92tf.

[0053] According to the seventh embodiment, the reinforcing fibers 93 can be distributed substantially radially within the second end 92tf as well as the first end 91t, thereby further suppressing uneven distribution of the reinforcing fibers 93. This further improves the strength of the fastening structure 110f. Furthermore, when manufacturing a structure requiring multiple fastening portions, manufacturing costs can be more effectively reduced.

[0054] Other Embodiments The number of workpieces fastened by the fastening device of the present disclosure may be more than one, and may be three or more. The inner diameters of the through holes in the workpieces may be different. The workpieces may be made of a metal material, not limited to a fiber-reinforced resin composite material. The workpieces may be made of different materials. The shape of the rod 90 may be a rectangular column or a box-like shape. In the above embodiment, the reinforcing fibers 93 included in the rod 90 are oriented in the axial direction AX. However, the orientation direction of the reinforcing fibers 93 may be a direction intersecting the axial direction AX. The rod 90 may also include short fibers as the reinforcing fibers 93. When the rod 90 includes continuous fibers, the continuous fibers do not need to be continuous from one end 901 to the other end 902 of the rod 90, as long as they have a predetermined length. For example, the predetermined length may be approximately 80% of the length of the rod 90. Alternatively, the predetermined length may be half or one-third of the length of the rod 90 in the direction of the axis AX.

[0055] The workpieces 81, 85, 81e, and 85e that form the fastening target groups 100 and 100e only need to have through holes 82, 86, 82e, and 86e, respectively, and the inner diameters of the through holes may be different. Also, in step S10, as long as the workpieces 81, 85, 81e, and 85e are stacked to form a communicating hole 103 in the Z-axis direction, the central axis C of the fastening device 70 and the central axis C of the through holes 82 and 86 do not need to be completely aligned.

[0056] The shape of the molds in the fastening devices 70 to 70g is not limited to the above-described embodiment. For example, the shape of the recesses 11 to 11d, 23b, 23d, and 23f in the molds, the arrangement and number of the protrusions 13 and 13a, and the arrangement and number of the peaks 14a can be changed as appropriate. Furthermore, the holder 30 only needs to be able to temporarily hold the rod 90 while the rod 90 is being heated, and the shape of the insertion jigs 40 and 40f can be changed as appropriate as long as the heated rod 90 can be pushed from the through-hole 33 of the holder 30 into the communicating holes 103 and 103e.

[0057] In the fastening devices 70 to 70g, a heat insulating member may be disposed between the holder 30 and the second molding die 20 to 20e. FIG. 27 shows a fastening device 70g using a heat insulating member 68. The heat insulating member 68 has a through-hole 69 penetrating in the Z-axis direction. An end face 681 of the heat insulating member 68 in the +Z-axis direction abuts against an end face 22 of the second molding die 20 in the −Z-axis direction. In this fastening device 70g, an operator heats the rod 90 via the holder 30, and then inserts the insertion jig 40 into the through-hole 33 of the holder 30 without moving the holder 30. In this configuration, the operator moves the insertion jig 40 in the +Z-axis direction until the upper end of the insertion jig 40 in the +Z-axis direction reaches the same plane as the end face 22 of the second molding die 20. This allows the operator to insert the heated rod 90 from the through hole 33, through the through hole 69 of the heat insulating member 68, and through the through hole 23 of the second molding die 20 into the communication hole 103. In this embodiment, the opening 24 of the second molding die 20 is blocked by the end face 681 of the heat insulating member 68 and the insertion jig 40, and the second end of the rod 90 in the fastened state is formed. This embodiment also makes it possible to prevent the thermal influence of heating the rod 90 from being exerted on the group of objects to be fastened 100. In this embodiment and other embodiments, the amount of movement of the insertion jig 40 in the +Z-axis direction may be adjusted as appropriate depending on the shape of the second molding dies 20-20e, the shape of the second end, etc.

[0058] In step S50 of the fastening method in the above embodiment, the insertion jig 40, 40f moves in the +Z-axis direction according to a predetermined movement amount. This movement amount is the movement amount required for the heated rod 90 to reach the first molding die 10-10e and fill the communicating hole 103 and the through-holes 23, 23e of the second molding die 20-20f. Alternatively, the operator may provide a sensor in the fastening device 70-70g that detects the load applied to the insertion jig 40, 40f, and in step S50, push the insertion jig 40, 40f in the +Z-axis direction until the load applied to the insertion jig 40, 40f reaches a predetermined threshold. This threshold may be determined based on the load required for the heated rod 90 to reach the first molding die 10-10e and fill the communicating hole 103 and the through-holes 23, 23e of the second molding die 20-20f.

[0059] In the above embodiment, the first direction, which is the extension direction of the communicating holes 103, 103e of the fastening target groups 100, 100e and the extension direction of the holding through-holes 33, is the vertical direction. In contrast, the first direction is not limited to the vertical direction and may be a direction intersecting the vertical direction. The first direction may be, for example, the horizontal direction. Furthermore, the insertion direction of the rod 90 into the communicating hole 103 may be any direction from the second openings 102, 102e to the first openings 101, 101e, and may be any other direction, such as a vertically downward direction. In other words, the insertion direction of the rod 90 into the communicating hole 103 is not limited to the vertically upward direction and may be any other direction, as long as it is a direction toward the first molding dies 10-10e.

[0060] The present disclosure is not limited to the above-described embodiments and can be realized in various forms without departing from the spirit thereof. For example, the present disclosure can also be realized in the following aspects. The technical features in the above embodiments corresponding to the technical features in each aspect described below can be appropriately replaced or combined to solve some or all of the problems of the present disclosure or to achieve some or all of the effects of the present disclosure. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0061] (1) According to a first aspect of the present disclosure, a fastening method for fastening multiple workpieces, each having a through hole, is provided. The fastening method includes preparing a group of workpieces stacked on top of each other so that each through hole in the multiple workpieces is a communicating hole communicating in a first direction, the communicating hole having a first opening and a second opening opposite the first opening in the first direction, heating a rod containing reinforcing fibers and a thermoplastic resin outside the group of fastening objects, and inserting the heated rod through the second opening into the communicating hole to fasten the group of fastening objects. According to this aspect, the rod is heated outside the group of fastening objects, i.e., at a position distant from the group of fastening objects, and then inserted into the communicating hole. Therefore, the influence of heating on the group of fastening objects can be suppressed. Furthermore, because the rod is heated at a position distant from the group of fastening objects, the entire rod can be heated. Therefore, inserting the rod into the communicating hole can firmly fasten the group of fastening objects.

[0062] (2) In the above-described embodiment (1), the reinforcing fibers may be oriented in a predetermined direction. According to this embodiment, in a group of fastening objects fastened by the heated rod, the strength in a direction parallel to the predetermined direction (the direction of fiber orientation) can be increased.

[0063] (3) In the above-described configuration (1) or (2), the reinforcing fibers may be continuous fibers. According to this configuration, the strength of the group of objects fastened by the heated rod can be increased.

[0064] (4) In any of the above embodiments (1) to (3), a first molding die may be disposed in contact with the group of fastening objects so as to cover the first opening. Furthermore, the heated rod may be inserted through the second opening into the communicating hole and reach the first molding die, and the first end of the rod in the fastened state may be formed by the first molding die. According to this embodiment, the first end can be easily formed by inserting the heated rod into the communicating hole and reaching the first molding die. In embodiment (4), the first end may be formed by pressing the tip of the inserted rod against the first molding die to deform it.

[0065] (5) In any of the above embodiments (1) to (4), the first mold may have a recess that communicates with the communicating hole when in contact with the group of fastening objects. The fastening method may include inserting the heated rod from the second opening into the communicating hole and reaching the recess, and forming the first end portion using the first mold. According to this embodiment, the heated rod is filled into the recess portion of the first mold by reaching the recess portion. Therefore, a fastening structure in which the first end portion protrudes from the communicating hole can be easily formed.

[0066] (6) In the above-described embodiment (5), the first molding die may have a protrusion at the center of the recess. The fastening method may be a method in which the heated rod is inserted from the second opening into the communicating hole and reaches the protrusion, thereby spreading within the recess, and the first end portion is formed by the first molding die. According to this embodiment, the heated rod inserted into the communicating hole spreads around the protrusion after reaching the protrusion. This can suppress uneven distribution of reinforcing fibers in the recess. This can therefore improve the strength of the fastening structure.

[0067] (7) In any of the above embodiments (1) to (6), a second molding die having a molding through hole penetrating in the first direction may be placed in contact with the group of fastening objects so as to cover the second opening. The heated rod may be inserted through the molding through hole and from the second opening into the communicating hole, and the second end of the rod in the fastened state may be formed by the second molding die. This embodiment allows the second end of the rod in the fastened state to be easily formed.

[0068] (8) In any of the above embodiments (1) to (7), the rod may be held by a holder provided outside the group of fastening objects, and the rod may be heated via the holder. According to this embodiment, the rod is held outside the group of fastening objects, that is, at a position away from the group of fastening objects, and the entire rod can be heated.

[0069] (9) In any of the above embodiments (1) to (8), the reinforcing fibers may be continuous fibers oriented in the longitudinal direction of the rod. In the fastening method, the rod may be heated outside the communicating hole, and the heated rod may be positioned relative to the second opening so that the longitudinal direction coincides with the first direction, and inserted into the communicating hole from the second opening to fasten the group of fastening objects. According to this embodiment, the extension direction of the communicating hole and the orientation direction of the continuous fibers, which are reinforcing fibers contained in the rod, are the same. Therefore, the orientation and continuity of the reinforcing fibers are maintained within the communicating hole. Therefore, a fastened structure in which the reinforcing fibers are oriented in the extension direction of the communicating hole can be formed. As a result, the strength of the fastened structure can be improved.

[0070] (10) In any of the above embodiments (1) to (9), the rod may be heated outside the communicating hole to a temperature equal to or higher than the softening point of the thermoplastic resin, and then inserted into the communicating hole through the second opening. This embodiment allows the rod to sufficiently expand within the communicating hole, thereby improving the strength of the fastening structure. In addition, in embodiment (10), the thermoplastic resin may be heated to a temperature equal to or higher than its melting point.

[0071] (11) According to a second aspect of the present disclosure, there is provided a fastening device for fastening a group of fastening objects having communicating holes in a first direction. The fastening device includes a first mold, a holder facing the first mold at a distance in the first direction and having a holding through hole penetrating in the first direction, a heating device for heating the inside of the holding through hole, and an insertion jig inserted into the holding through hole in a direction from the holder toward the first mold in the first direction. According to this aspect, there can be provided a fastening device in which a group of fastening objects is disposed between the first mold and the holder, a rod held in the holding through hole is heated by the heating device, and the heated rod can be inserted into the communicating holes of the group of fastening objects by the insertion jig. Note that in aspect (11), the heating device can also be referred to as a heating unit.

[0072] (12) In the above-described embodiment (11), the first mold may have a recess recessed in a direction from the holder toward the first mold in the first direction. According to this embodiment, the heated rod can be brought to the recess of the first mold and filled into the recess, thereby easily forming a fastening structure having one end protruding from a communicating hole.

[0073] (13) In the above-described embodiment (12), the recess may have a protrusion provided at the center of the recess, the protrusion protruding in the first direction from the first mold toward the holder. According to this embodiment, the heated rod spreads around the protrusion after reaching the protrusion. Therefore, uneven distribution of the reinforcing fibers in the recess can be suppressed. Therefore, the strength of the fastening structure can be improved.

[0074] (14) In the above-described embodiment (13), the protrusion may have a plurality of apexes radially arranged from the center of the recess as viewed in the direction from the holder toward the first mold in the first direction. According to this embodiment, the reinforcing fibers can be distributed along the apexes. Furthermore, compared to a configuration in which the recess does not have an apex, the weight of the structure including the fastening structure can be reduced. Furthermore, manufacturing costs can be reduced. Note that in embodiment (14), the radial arrangement of the plurality of apexes may mean that the plurality of apexes extend from the center of the protrusion or recess to the outer edge of the recess or outside the recess. The center of the recess may coincide with the center of a communicating hole arranged in the fastening device.

[0075] (15) In any of the above embodiments (11) to (14), the fastening device may include a second mold disposed between the first mold and the holder in the first direction and spaced apart from the first mold. The second mold may have a molding through-hole penetrating in the first direction. According to this embodiment, one end and the other end of the heated rod can be formed by the first mold and the second mold.

[0076] 10, 10a, 10b, 10c, 10d, 10e: first molding die, 11, 11a, 11b, 11c, 11d: recess, 12: opening of first molding die, 13, 13a: protrusion, 14a: top, 14c, 14d: bottom, 20, 20a, 20b, 20c, 20d, 20e, 20f: second molding die, 21: end face of second molding die, 22: end face of second molding die, 23, 23e: through hole, 23b, 23d, 23f: recess, 24, 24b, 24d, 24f: opening, 25d: opening, 30: holder, 31: opening, 32: opening, 33: holding through-hole, 35: end surface, 40, 40f: insertion jig, 41f: protruding end, 50: heating device, 60: control device, 61: actuator, 62: control circuit, 68: heat insulating member, 681:, end surface, 69: through-hole, 70, 70a, 70b, 70c, 70d, 70e, 70f, 70g: fastening device, 81, 85, 81e, 85e: wire 82, 86, 82e, 86e: through holes, 83e: first hole portion, 84e: second hole portion, 87e: third hole portion, 88e: fourth hole portion, 90: rod, 901, 902: end portions of rod, 91t, 91ta, 91tb, 91tc, 91td, 91te, 91t: first end portions of rod in fastened state, 92t, 92ta, 92tb, 92td, 92te, 92tf: second end portions of rod in fastened state, 93: reinforcing fiber , 94: thermoplastic resin, 95t, 95ta: recess, 96tf: recess, 97ta: groove, 100, 100e: fastening object group, 101: first opening, 102, 102e: second opening, 102e: second opening, 103, 103e: communicating hole, 104e: central portion, 105e: enlarged diameter portion, 106e: enlarged diameter portion, 110, 110a, 110b, 110c, 110d, 110e, 110f: fastening structure, AX: axis, C: central axis, L1: distance

Claims

1. A fastening method for fastening a plurality of workpieces, each having a through hole, comprising the steps of: preparing a group of workpieces to be fastened by stacking the plurality of workpieces so that each through hole in the plurality of workpieces is a communicating hole that communicates in a first direction, and a communicating hole having a first opening and a second opening opposite the first opening in the first direction is formed; heating a rod containing reinforcing fibers and a thermoplastic resin outside the group of workpieces to be fastened; and inserting the heated rod into the communicating hole from the second opening to fasten the group of workpieces.

2. A fastening method according to claim 1, wherein the reinforcing fibers are oriented in a predetermined direction.

3. A fastening method according to claim 1, wherein the reinforcing fibers are continuous fibers.

4. A fastening method as claimed in claim 1, comprising: placing a first molding die in contact with the group of objects to be fastened so as to cover the first opening; inserting the heated rod from the second opening into the communicating hole and reaching the first molding die; and forming a first end of the rod in a fastened state by the first molding die.

5. A fastening method as claimed in claim 4, wherein the first molding die has a recess communicating with the communication hole when in contact with the group of objects to be fastened, and the heated rod is inserted from the second opening into the communication hole until it reaches the recess, and the first end portion is formed by the first molding die.

6. A fastening method according to claim 5, wherein the first molding die has a protrusion in the center of the recess, and the heated rod is inserted from the second opening into the communicating hole and reaches the protrusion, thereby spreading the rod within the recess, and the first end portion is formed by the first molding die.

7. A fastening method as claimed in claim 1, comprising: placing a second molding die having a molding through hole penetrating in the first direction in contact with the group of objects to be fastened so as to cover the second opening; inserting the heated rod through the molding through hole and from the second opening into the communicating hole, and forming a second end of the rod in a fastened state by the second molding die.

8. A fastening method according to claim 1, wherein the rod is held by a holder provided outside the group of objects to be fastened, and the rod is heated via the holder.

9. A fastening method as claimed in claim 1, wherein the reinforcing fibres are continuous fibres oriented in the longitudinal direction of the rod, the rod is heated outside the communicating hole, the heated rod is positioned relative to the second opening so that the longitudinal direction coincides with the first direction, and the rod is inserted from the second opening into the communicating hole, thereby fastening the group of objects to be fastened.

10. A fastening method according to claim 1, wherein the rod is heated outside the communicating hole to a temperature equal to or higher than the softening point of the thermoplastic resin, and then inserted into the communicating hole through the second opening.

11. A fastening device for fastening a group of fastening objects having communicating holes in a first direction, comprising: a first molding die; a holder facing and spaced apart from the first molding die in the first direction, the holder having a holding through hole passing through in the first direction; a heating device for heating the inside of the holding through hole; and an insertion jig inserted into the holding through hole in a direction from the holder toward the first molding die in the first direction.

12. A fastening device according to claim 11, wherein the first mold has a recess recessed in a direction from the holder toward the first mold in the first direction.

13. A fastening device according to claim 12, wherein the recess has a protrusion provided in the center of the recess, the protrusion protruding in a direction from the first mold toward the holder in the first direction.

14. A fastening device according to claim 13, wherein the protrusion has a plurality of apexes arranged radially from the center of the recess as viewed in the direction from the holder toward the first mold in the first direction.

15. A fastening device according to claim 11, comprising a second molding die disposed between the first molding die and the retainer in the first direction and spaced apart from the first molding die, the second molding die having a molding through hole penetrating in the first direction.

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