Joined structure and joining method

Abstract

To provide a fastening body which may easily deform into a desired shape when press-fitting into a friction stirring part to improve joint strength of a joint structure using the fastening body.SOLUTION: A fastening body (1) is press-fitted from the first member 41 side into a friction stirring part 50 formed at an overlapping part 45 between a first member 41 and a second member 42. The fastening body (1) includes: a head part 11 disposed on a surface of the friction stirring part 50; and a cylindrical shaft part 42 extending from the head part 11 to the second member 42 side. The shaft part 12 has a facilitation part (15) which facilitates expansion of a diameter of a tip part 12a of the shaft part 12 during the press-fitting.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fastener that is press-fitted into a friction stir portion of a first member and a second member that are joined together via the friction stir portion from the first member side, and to a welded structure and a joining method that use the fastener. [Background technology]

[0002] In the manufacture of structures such as aircraft, railroad cars, and automobiles, it is sometimes necessary to overlap and join two or more members made of metal, resin, etc. Joining using rivets (fasteners) is known as one method of such joining.

[0003] For example, the following Patent Document 1 discloses joining two or more resin members using a method that combines the use of rivets and thermal melting. Specifically, Patent Document 1 discloses that the two resin members are joined by a method including the steps of stacking two thermoplastic resin members one above the other and arranging a conductive metal plate between them, passing electricity through and heating the arranged metal plate to fuse the resin members and the metal plate, and driving (pressing) a rivet so as to penetrate the upper resin member and the metal plate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-002505 A Summary of the Invention [Problem to be solved by the invention]

[0005] The joining method of Patent Document 1 requires a conductive metal plate to be separately placed between the resin members, which has the problem of easily increasing weight and manufacturing costs. Therefore, it is proposed to adopt friction stir welding as an alternative method that can solve the problem. Note that friction stir welding is a method of joining two or more members by friction stirring in which a rotating tool is pressed into the objects to be joined. According to this joining method that combines friction stir welding and rivets, the conductive metal plate is no longer an essential element, making it possible to reduce weight and manufacturing costs.

[0006] In the above-mentioned joining method, the rivet is pressed into the friction stir portion, which is the friction-stirred region. However, in this case, the tip of the rivet does not expand as expected during the press-in, and there is a possibility that the required joining strength cannot be obtained.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a fastener that can be easily deformed into a desired shape when pressed into a friction stir part, thereby improving the joining strength of a joined structure using the fastener. [Means for solving the problem]

[0008] In order to solve the above problems, one aspect of the present invention is bonded structure teeth, A first member and a second member stacked in a thickness direction, The first member and The above A friction stir portion formed by pressing a rotary tool into an overlapping portion with a second member from the first member side. and , To the friction stirring section A fastener press-fitted from the first member side Equipped with , The fastening body is The friction stir part is provided with a head portion disposed on the surface thereof and a cylindrical shaft portion extending from the head portion toward the second member, the shaft portion having a promoting portion which promotes the expansion of the diameter of the tip portion of the shaft portion during press-fitting. The bottom surface of the friction stir part, which is the surface opposite to the surface of the friction stir part, is formed at a position midway in the thickness direction of the second member, and the tip of the shaft part protrudes to the outside of the friction stir part and is disposed within the second member. It is something.

[0010] The present invention Other The joining method according to the aspect of the present invention comprises the steps of: a preparation step of preparing a fastener to be press-fitted from the first member side into a friction stir part formed at an overlapping portion between a first member and a second member, the fastener including a head portion disposed on a surface of the friction stir part and a cylindrical shank portion extending from the head portion toward the second member, and forming a promotion portion on the shank portion that promotes the expansion of the diameter of the tip portion of the shank portion during press-fitting; A portion of the first member and the second member overlaps with the first member. ra rounda friction stirring step of forming the friction stir portion in the overlapping portion by performing friction stirring by pressing a rolling tool into the overlapping portion; and a fastening step of pressing the fastened body into the friction stir portion from the first member side. a determination step of estimating a tip diameter of the shank portion after the fastening step based on the dimension of the fastened body before press-fitting, the friction stir depth in the friction stir step, and the protrusion amount of the head from the upper surface of the friction stir part after the fastening step, and determining that a good joining has been performed when the estimated tip diameter is larger than a predetermined threshold value; It includes. Effect of the Invention

[0011] As described above, according to the present invention, it is possible to provide a fastener that can be easily deformed into a desired shape when pressed into a friction stir portion, and to improve the joining strength of a joined structure using the fastener. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view showing a single rivet according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the state in which the rivet has been driven (press-fitted) into the objects to be joined, and is a cross-sectional view showing the structure of a joined structure obtained by driving the rivet. [Diagram 3] 2 is a schematic diagram showing an overall configuration of a friction stir welding apparatus used in manufacturing the welded structure. FIG. [Figure 4] 4 is a cross-sectional view showing a first step (preparation step) of producing the joined structure. FIG. [Diagram 5] 5 is a cross-sectional view showing a second step (positioning step) of manufacturing the joined structure. FIG. [Figure 6] FIG. 4 is a cross-sectional view showing a third process (friction stirring step) for producing the joint structure. [Figure 7] FIG. 11 is a cross-sectional view showing a fourth process (casting step) for manufacturing the joint structure. [Figure 8] 10 is a flowchart showing a procedure for determining whether or not the joining quality is acceptable. [Figure 9] FIG. 2 is a view corresponding to FIG. 1 and showing a modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] [Rivet structure] Fig. 1 is a cross-sectional view showing a single rivet 1 according to one embodiment of the present invention. As shown in this figure, rivet 1 is a fastener including a disk-shaped head 11 and a cylindrical shank 12 extending concentrically from head 11. In this embodiment, rivet 1 is a self-piercing rivet that is driven non-through into a material that does not have a pilot hole. In the following, the head 11 side of rivet 1 in the axial direction will be referred to as "upper" and the shank 12 side as "lower", but this is for convenience of explanation and is not intended to limit the position in which rivet 1 is used.

[0014] Head 11 is formed in a solid disk shape that closes the opening at the upper end of shaft portion 12. If the outer diameter of head 11 is R1 and the outer diameter of shaft portion 12 is R2, outer diameter R1 is set to a value larger than outer diameter R2. As a result, head 11 is formed in a disk shape having a portion that protrudes radially outward from the upper end of shaft portion 12.

[0015] Shank 12 is formed to extend in the up-down direction along the same axis as head 11. Shank 12 is a cylinder that extends in a straight line with a constant outer diameter smaller than head 11, and has a hollow portion inside that is open to the side opposite head 11 (the lower end side). If the overall axial length (total length) of rivet 1 including shank 12 and head 11 is L, this total length L is set to a value sufficiently larger than the thickness (axial length) of head 11.

[0016] The end (lower end) of the shaft portion 12 opposite the head 11, i.e., the tip portion 12a, is formed in a sharp pointed shape. That is, the tip portion 12a of the shaft portion 12 has a tapered inner circumferential surface 12s whose inner diameter becomes larger toward the tip side (the farther away from the head 11). The tip portion 12a including the inner circumferential surface 12s also forms the opening edge of the tip (lower end) of the shaft portion 12.

[0017] A groove 15 is formed in the middle of the outer circumferential surface of shank 12 in the axial direction (up-down direction). Groove 15 is a groove obtained by locally reducing the thickness of the outer circumferential wall of shank 12, and has a predetermined concave shape such as a U-shape or V-shape in cross section. Groove 15 is formed so as to extend continuously in the circumferential direction on the outer circumferential surface of shank 12. If the axial distance from the center of groove 15 to tip end position 12t of shank 12 is G, then this distance G is a parameter that determines the shape of shank 12 after it is expanded when rivet 1 is driven, as described below.

[0018] The material of the rivet 1 may be any material having the strength to be able to drive the rivet into the objects to be joined, and may be selected from appropriate materials. For example, metal materials such as titanium and high tensile steel, or resin materials such as thermoplastic resin and thermoplastic composite materials, may be used as the material of the rivet 1. When using a titanium rivet 1 to join fiber reinforced resin materials as in this embodiment, a rivet made of a titanium alloy such as Ti-6AL-4V is preferable.

[0019] [Structure of joint structure] 2 is a diagram showing the state after rivet 1 has been driven (press-fitted) into objects to be joined, and is a cross-sectional view showing the structure of a joined structure 30 obtained by driving the rivet 1. As shown in the figure, the joined structure 30 comprises a first member 41 and a second member 42 that overlap each other, a friction stir part 50 formed in an overlapping part 45 of both members 41, 42, and the above-mentioned rivet 1 driven into the friction stir part 50. The joined structure 30 can be used in structures such as aircraft, railway cars, and automobiles, for example.

[0020] The first member 41 and the second member 42 are both plate-like members, and are overlapped with each other in the vertical direction with the first member 41 on top (and the second member 42 on the bottom). The overlapping first member 41 and second member 42 form an overlapping portion 45 at a position where the friction stir portion 50 is to be formed.

[0021] The first member 41 and the second member 42 are both made of a thermoplastic composite material. Specifically, the first member 41 and the second member 42 are made of a fiber-reinforced thermoplastic resin including a base material made of a thermoplastic resin and a large number of reinforcing fibers impregnated into the base material. The thickness of the second member 42 may be the same as or different from the thickness of the first member 41.

[0022] Examples of thermoplastic resins that can be used as the base material of the first member 41 and the second member 42 include polypropylene (PP), polyethylene (PE), polyamide (PA), polystyrene (PS), polyaryletherketone (PEAK), polyacetal (POM), polycarbonate (PC), polyethylene terephthalate (PET), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), ABS resin, thermoplastic epoxy resin, etc. Examples of reinforcing fibers impregnated into the base material include carbon fibers, glass fibers, ceramic fibers, metal fibers, and organic fibers.

[0023] The friction stir portion 50 is a joint formed by hardening the frictionally stirred material in the overlapping portion 45. The friction stir portion 50 is formed in a cylindrical shape corresponding to the region where the rotary tool 101 described later is pressed in. That is, the friction stir portion 50 has a circular upper surface 50a and a bottom surface 50b, and a cylindrical side peripheral surface 50c. The upper surface 50a is formed at a height position that is approximately flush with the upper surface 41a of the first member 41. The bottom surface 50b is formed at a position corresponding to the boundary between the friction stir portion 50 and the non-frictionally stirred portion (base material region) below it. The side peripheral surface 50c is formed at a position corresponding to the boundary between the friction stir portion 50 and the non-frictionally stirred portion (base material region) on the outer periphery side. The friction stir portion 50 does not necessarily need to reach the second member 42 below, but in this embodiment, the depth of the friction stir portion 50 is set to a value greater than the thickness of the first member 41 so that the friction stir portion 50 reaches the second member 42.

[0024] The rivet 1 is driven (pressed) into the friction stir portion 50 so as to mechanically join the first member 41 and the second member 42. That is, after friction stirring of the overlapping portion 45 by a rotary tool 101 described later, the rivet 1 is driven into the overlapping portion 45 (friction stir portion 50) to mechanically join the first member 41 and the second member 42. In this driven state, the head 11 of the rivet 1 abuts against the upper surface 50a (surface) of the friction stir portion 50. Furthermore, the driving causes the shank 12 of the rivet 1 to change into a flared shape with the outer diameter of the tip portion 12a being enlarged. Specifically, the shank 12 after driving is disposed so as to penetrate the first member 41 and extend partway through the thickness direction of the second member 42, and is formed so that the outer diameter is enlarged toward the tip side (the farther away from the head 11). In this state, tip 12a of shaft 12 protrudes to the outside of friction stirring part 50 and functions as an interlock part that fastens first member 41 and second member 42. That is, first member 41 and second member 42 are fixed to each other by being sandwiched between the interlock part consisting of tip 12a that protrudes to the outside of friction stirring part 50 and head 11 that is disposed on upper surface 50a of friction stirring part 50.

[0025] [Friction stir welding equipment] The welded structure 30 including the above-mentioned rivet 1 and friction stir part 50 is manufactured using a friction stir welding apparatus M shown in Fig. 3. As shown in this figure, the friction stir welding apparatus M includes a double-acting rotary tool 101, a tool driving part 102 that drives the rotary tool 101 to rotate and raise and lower, and a controller C that controls the operation of the tool driving part 102. Note that, although Fig. 3 shows directional indications of "up" and "down", this is for the sake of convenience of explanation and is not intended to limit the actual usage posture of the rotary tool 101.

[0026] The rotating tool 101 is supported by a tool fixing part (not shown). This tool fixing part can be, for example, the tip of an articulated robot. A backup member 115 is disposed opposite to the lower end surface of the rotating tool 101. A first member 41 and a second member 42, which are to be joined, are disposed between the rotating tool 101 and the backup member 115.

[0027] The rotating tool 101 includes a pin member 111, a shoulder member 112, a clamp member 113, and a spring 114. The pin member 111 is a member formed in a cylindrical shape, and is disposed so that its axis extends in the vertical direction. The pin member 111 is capable of rotating about the axis as a rotation axis R, and is capable of ascending and descending (moving forward and backward) in the vertical direction along the rotation axis R.

[0028] The shoulder member 112 is disposed so as to cover the outer periphery of the pin member 111. That is, the shoulder member 112 is a cylindrical member having a hollow portion into which the pin member 111 is inserted. The axis of the shoulder member 112 is coaxial with the axis of the pin member 111 (rotation axis R). The shoulder member 112 rotates around the same rotation axis R as the pin member 111, and can move up and down (advance and retreat) along the rotation axis R. In this way, both the shoulder member 112 and the pin member 111 inserted in its hollow portion can rotate around the rotation axis R and move relatively along the rotation axis R. That is, the pin member 111 and the shoulder member 112 can not only simultaneously move up and down along the rotation axis R, but also independently move such that one moves down and the other moves up.

[0029] The clamp member 113 is disposed so as to cover the outer periphery of the shoulder member 112. In other words, the clamp member 113 is a cylindrical member having a hollow portion into which the shoulder member 112 is inserted. The axis of the clamp member 113 is also coaxial with the rotation axis R. The clamp member 113 does not rotate about its axis, but can move up and down (advance and retreat) along the rotation axis R. The clamp member 113 serves to surround the outer periphery of the pin member 111 or the shoulder member 112 when they perform friction stirring. The enclosure by the clamp member 113 prevents the friction stirring material from scattering, and enables the friction stirring portion to be finished smoothly.

[0030] The spring 114 is attached to the upper end side of the clamp member 113, and biases the clamp member 113 in a direction toward the joining object (downward). The clamp member 113 is attached to the tool fixing portion via the spring 114.

[0031] The backup member 115 has an upper surface (support surface) that comes into contact with the lower surface of the joining object. That is, the backup member 115 is a backing member that supports the joining object when the pin member 111 or the shoulder member 112 is pressed into the joining object. The clamp member 113 biased by the spring 114 presses the joining object against the backup member 115.

[0032] The tool driving unit 102 includes a rotation driving unit 121, a pin driving unit 122, a shoulder driving unit 123, and a clamp driving unit 124. The rotation driving unit 121 is a mechanism that rotates the pin member 111 and the shoulder member 112 around the rotation axis R. The pin driving unit 122 is a mechanism that moves the pin member 111 forward and backward (raise and lower) along the rotation axis R. The pin driving unit 122 drives the pin member 111 so as to press the pin member 111 into the joining object and retract it from the joining object. The shoulder driving unit 123 is a mechanism that moves the shoulder member 112 forward and backward along the rotation axis R, and presses the shoulder member 112 into the joining object and retracts it. The clamp driving unit 124 is a mechanism that moves the clamp member 113 forward and backward along the rotation axis R. The clamp driving unit 124 moves the clamp member 113 toward the joining object, and presses the joining object against the backup member 115. At this time, the biasing force of the spring 114 acts. Each of the driving units 121 to 124 includes a servo motor, a transmission gear, etc., and causes the respective driving objects to perform desired operations in response to the rotation of the servo motor.

[0033] The controller C is composed of a microcomputer or the like, and controls the operation of each part of the tool driving unit 102 by executing a predetermined control program. Specifically, the controller C controls the rotation driving unit 121 to cause the pin member 111 and the shoulder member 112 to perform a required rotation operation. The controller C also controls the pin driving unit 122, the shoulder driving unit 123, and the clamp driving unit 124 to cause the pin member 111, the shoulder member 112, and the clamp member 113 to perform a required forward and backward movement operation.

[0034] The friction stir welding apparatus M having the above-mentioned structure is usually used to join two or more members by friction stir welding. Friction stir welding using this friction stir welding apparatus M can be roughly divided into a shoulder-first process joining method and a pin-first process joining method.

[0035] In the joining method using the shoulder-first process, the shoulder member 112 of the rotary tool 101 is first pressed into the overlapping portion of the two or more components to perform friction stirring, and the pin member 111 is retracted from the overlapping portion. Thereafter, the pin member 111 is lowered while the shoulder member 112 is retracted (raised) to smooth the upper surface of the overlapping portion. In contrast, in the joining method using the pin-first process, the pin member 111 of the rotary tool 101 is first pressed into the overlapping portion to perform friction stirring, and the shoulder member 112 is retracted from the overlapping portion. Thereafter, the shoulder member 112 is lowered while the pin member 111 is retracted (raised) to smooth the upper surface of the overlapping portion.

[0036] [Joining method] Next, a method for joining the first member 41 and the second member 42 using the above-mentioned friction stir welding apparatus M will be described in detail. In this embodiment, when joining the first member 41 and the second member 42, riveting-assisted friction stir welding, which combines the driving of the rivet 1 and friction stir welding, is used. The riveting-assisted friction stir welding is different from normal friction stir welding in that a rivet is added as a joining means, but in this embodiment, by applying the above-mentioned shoulder-first process, it is possible to realize riveting-assisted friction stir welding using only the friction stir welding apparatus M shown in FIG. 3 (without adding another device for driving the rivet 1). That is, when joining the first member 41 and the second member 42, the shoulder member 112 of the rotary tool 101 is pressed into the overlapping portion 45 of both members to perform friction stirring, and the rivet 1 is driven into the overlapping portion 45 (friction stir portion 50) after the friction stirring using the pin member 111. In this way, a joined structure 30 in which the first member 41 and the second member 42 are joined is manufactured. Specifically, the method for joining the first and second members 41 and 42 includes the following four steps P1 to P4.

[0037] 4, step P1 is a preparation step in which the rivet 1 is attached to a rotating tool 101. The rivet 1 attached to the rotating tool 101 in this preparation step P1 is the rivet 1 before it is driven into the overlapping portion 45, and the diameter of the shank 12 has not yet been expanded. In other words, the rivet 1 used in the preparation step P1 has a head 11 and a cylindrical shank 12 that extends straight from the head 11.

[0038] To attach the rivet 1 to the rotary tool 101, the controller C (FIG. 3) drives the pin driver 122 to raise the pin member 111 and create an accommodation space V for the rivet 1 inside the shoulder member 112. That is, the controller C raises the tip (lower end) 111a of the pin member 111 relative to the tip (lower end) 112a of the shoulder member 112 by a stroke equal to or greater than the overall length L (FIG. 1) of the rivet 1, thereby forming an accommodation space V that is continuous with the lower end opening of the shoulder member 112. To enable the rivet 1 to be accommodated in this accommodation space V, a rivet 1 having an outer diameter slightly smaller than the inner diameter of the shoulder member 112 is selected.

[0039] As shown in Fig. 5, step P2 is a positioning step for positioning the rotary tool 101 with the rivet 1 attached to it with respect to an overlapping portion 45 in which the first member 41 and the second member 42 are overlapped from above. In this positioning step P2, the controller C positions the rotary tool 101 so that the rotation axis R (Fig. 3) of the rotary tool 101 coincides with the center of the overlapping portion 45 supported on the backup member 115, and then controls the shoulder driver 123 and the clamp driver 124 so that the respective tips 112a, 113a of the shoulder member 112 and the clamp member 113 abut against the upper surface 41a of the first member 41. The controller C also maintains the relative positional relationship in the axial direction between the pin member 111 and the shoulder member 112 (a state in which the pin tip 111a is retracted a predetermined amount above the shoulder tip 112a) so that the rivet 1 is accommodated between the tip 111a of the pin member 111 and the upper surface 41a of the first member 41.

[0040] As shown in Fig. 6, the process P3 is a friction stirring process in which the shoulder member 112 is pressed in while being rotated. In this friction stirring process P3, the controller C controls the rotation drive unit 121 to rotate the pin member 111 and the shoulder member 112 at high speed, while controlling the shoulder drive unit 123 to lower the shoulder member 112 and press the shoulder member 112 into the overlapping portion 45. The controller C also controls the pin drive unit 122 to raise the pin member 111. This operation frictionally stirs the overlapping portion 45, causing softening and plastic flow of the material, and the softened material Q1 overflows from the press-in region of the shoulder member 112. The overflowing softened material Q1 is released into a hollow space in the shoulder member 112 created by the rise (retraction) of the pin member 111 (see arrow b1). At the start of the friction stirring process P3, the pin members 111 have already retreated upward to such an extent that the accommodation space V (FIG. 4) is formed, and therefore the retreat operation of the pin members 111 may be omitted.

[0041] If the press-fit depth of the shoulder member 112 is h1, the press-fit depth h1 is set to a value such that the shoulder member 112 penetrates at least the upper first member 41. In this embodiment, an example is shown in which the press-fit depth h1 is set to a value such that the shoulder member 112 penetrates the upper first member 41 but does not penetrate the lower second member 42. In other words, the press-fit depth h1 in this embodiment is set to a value that is greater than the thickness t1 of the first member 41 and smaller than the sum (t1+t2) of the thickness t1 and the thickness t2 of the second member 42.

[0042] In this embodiment, the first member 41 and the second member 42 are thermoplastic composite materials, so the material Q1 softened by friction stirring contains reinforcing fibers. However, the reinforcing fibers in the softened material Q1 are cut into small pieces by friction stirring. This makes it easier to drive the rivet 1 in the following process.

[0043] 7(a) and 7(b), process P4 is a driving process in which the rivet 1 is driven into the overlapping portion 45. In this driving process P4, the controller C controls the rotation drive unit 121 to rotate the pin member 111 and the shoulder member 112 at high speed, while controlling the shoulder drive unit 123 to lift the shoulder member 112. Following this lifting of the shoulder member 112, the controller C controls the pin drive unit 122 to lower the pin member 111. This operation forms a cylindrical friction stir portion 50 in the overlapping portion 45, and the rivet 1 is driven in the region including this friction stir portion 50. The formation of the friction stir portion 50 and the driving of the rivet 1 will be described in detail below.

[0044] First, the formation of the friction stir portion 50 by the casting step P4 will be described. In the casting step P4, the shoulder member 112 rises and the pin member 111 descends, so that the softened material Q1 (FIG. 6) that has escaped into the hollow space moves to the area where the shoulder member 112 was pressed in, and the material is backfilled. The backfilled material forms the friction stir portion 50 in the overlapping portion 45 together with the material that was in the hollow space. The friction stir portion 50 is made of the material that has experienced friction stirring in the overlapping portion 45, and is formed into a cylindrical shape with an outer diameter Sr that is approximately equal to the outer diameter ds (FIG. 7(b)) of the shoulder member 112 and a height Sd that is approximately equal to the press-in depth h1 (FIG. 6) of the shoulder member 112. That is, friction stir part 50 has a cylindrical side surface 50c with height Sd (≈h1) and circular top surface 50a and bottom surface 50b with outer diameter Sr (≈ds). While the material is softened in friction stir part 50, the original hardness of first member 41 and second member 42 is maintained in the base material region around friction stir part 50, and the reinforcement structure by reinforcing fibers is also maintained.

[0045] Next, the driving of the rivet 1 in the driving step P4 will be described. In the driving step P4, the rivet 1 is pressed downward as the pin member 111 descends, and the pressed rivet 1 is forced into the overlapping portion 45. In other words, in the driving step P4, the rivet 1 is driven using an existing part (pin member 111) provided in the rotating tool 101. For this reason, in this embodiment, it is possible to form a joint consisting of a combination of the rivet 1 and the friction stir portion 50 in the overlapping portion 45 without separately preparing a tool for driving the rivet 1.

[0046] Specifically, in the driving step P4, the pin driver 122 lowers the pin member 111 to apply a pressing force to the head 11 of the rivet 1, pushing the rivet 1 into the overlapping portion 45 (see FIG. 7(a)). The rivet 1 is pre-loaded in the accommodation space V (FIG. 4) so ​​that the top surface of the head 11 faces the tip 111a of the pin member 111. Therefore, when the pin member 111 descends, the rivet 1 also descends, and the shank 12 advances from the tip side into the interior of the friction stirring portion 50. As this advancement of the rivet 1 (pushing down the pin member 111) progresses, the tip 12a of the shank 12 eventually reaches the bottom surface 50b of the friction stirring portion 50.

[0047] Here, since the region below the bottom surface 50b is an unsoftened base material region, when the tip portion 12a reaches the bottom surface 50b, the axial resistance acting on the shaft portion 12 increases. Therefore, at least when the tip portion 12a reaches the bottom surface 50b, a force acts on the shaft portion 12 to expand the diameter of the tip portion 12a. The generation of such an expanding force is promoted by the tapered inner peripheral surface 12s formed on the tip portion 12a. That is, due to the synergistic effect of the increase in resistance caused by the tip portion 12a reaching the bottom surface 50b and the tapered shape of the inner peripheral surface 12s of the tip portion 12a, a large force acts to expand the diameter of the tip portion 12a of the shaft portion 12. The shaft portion 12 subjected to this expanding force buckles and deforms from the recessed groove 15 formed on its outer peripheral surface, and as a result, the shaft portion 12 is deformed in a flared shape as shown in FIG. 7(b), and the outer diameter of the tip portion 12a is expanded. In other words, the recessed groove 15 functions as a promoting portion that promotes the expansion of the diameter of the tip portion 12a of the shank 12 when the shank 12 is pressed in (when the rivet 1 is driven).

[0048] FIG. 7(b) shows a state where the head 11 of the rivet 1 has reached the upper surface of the overlapping portion 45 (upper surface 50a of the friction stir portion 50), that is, a state where the driving of the rivet 1 has been completed. As shown in this figure, when the driving of the rivet 1 is completed, the tip 12a of the shank 12 of the rivet 1 not only passes over the bottom surface 50b of the friction stir portion 50 and is pressed into the base material region below it, but also passes over the side peripheral surface 50c of the friction stir portion 50 and is pressed into the base material region on the outside. The tip 12a thus pressed into the outside of the friction stir portion 50 exerts an anchor effect against the force that pulls the first member 41 and the second member 42 apart. That is, the tip 12a functions as an interlocking portion that fastens the first member 41 and the second member 42 together.

[0049] Through the above steps P1 to P4, the friction stir portion 50 is formed in the overlapping portion 45 and the rivet 1 is driven. The combination of the rivet 1 and the friction stir portion 50 joins the first member 41 and the second member 42 at the overlapping portion 45 relatively firmly.

[0050] [Pass / Fail Judgment] Next, a method for checking whether the rivet 1 has been properly driven when joining the first and second members 41, 42 by the joining method described above, in other words, a method for judging the pass / fail of the joining quality by the rivet 1, will be described. FIG. 8 is a flowchart showing a specific procedure for this pass / fail judgment. The control shown in this figure is executed by the controller C in parallel with the main control of the riveting-assisted friction stir welding shown in FIGS. 4 to 7. When the control in FIG. 8 starts, the controller C acquires the dimensions of each part of the rivet 1 (step S1). Specifically, the controller C acquires the total length L of the rivet 1 shown in FIG. 1, the outer diameter R2 of the shank 12, and the distance G representing the axial position of the recessed groove 15. These dimensions are stored in advance in a memory unit built into the controller C.

[0051] Next, the controller C performs friction stirring by pressing the rotary tool 101 into the overlapping portion 45 (step S2). That is, the controller C presses the shoulder member 112 into the overlapping portion 45 while rotating it at high speed (see FIG. 6), and then raises (retreats) the shoulder member 112 to form the friction stirring portion 50 (FIG. 7(a)) in the overlapping portion 45.

[0052] Next, the controller C acquires the outer diameter Sr (FIG. 7(b)) of the friction stirring unit 50 (step S3). Hereinafter, the outer diameter Sr of the friction stirring unit 50 will be abbreviated as the friction stirring diameter Sr. The friction stirring diameter Sr is stored in advance in the storage unit as a value that approximately corresponds to the outer diameter ds of the shoulder member 112.

[0053] Next, the controller C calculates the height Sd of the friction stirring portion 50 (step S4). Hereinafter, the height Sd of the friction stirring portion 50 is abbreviated as the friction stirring depth Sd. The friction stirring depth Sd can be calculated, for example, based on the output value from an encoder built into the servo motor of the shoulder drive unit 123. That is, the controller C specifies the axial value (vertical coordinate) of the shoulder member 112 when friction stirring begins and the axial value when the shoulder member 112 is at the lowest position during friction stirring from the output value of the encoder, and calculates the difference between the specified axial values, that is, the press-fit depth of the shoulder member 112 into the overlapping portion 45, as the friction stirring depth Sd.

[0054] Next, the controller C drives the rivet 1 into the friction stirring part 50 (step S5). That is, the controller C lowers the pin member 111 to press down the rivet 1, thereby press-fitting the shank 12 of the rivet 1 into the friction stirring part 50 (see FIG. 7(b)).

[0055] Next, the controller C calculates the amount of protrusion H of the head 11 from the upper surface 50a of the friction stirring unit 50 (step S6). For example, the controller C specifies the axial value of the pin member 111 and the axial value of the shoulder member 112 at the time when the descent of the pin member 111 is completed as shown in FIG. 7(b) from the output values ​​from the encoders built into the pin driving unit 122 and the shoulder driving unit 123, and calculates the difference between the specified axial values ​​as the amount of protrusion H of the head 11.

[0056] Next, the controller C estimates the tip diameter Rd, which is the outside diameter of the tip 12a of the shank 12 (step S7). Specifically, the controller C estimates the tip diameter Rd of the shank 12 based on the dimensions of the rivet 1 acquired in step S1 (total length L of the rivet 1, outside diameter R2 of the shank 12, and distance G representing the axial position of the groove 15), the friction stir depth Sd calculated in step S4, and the protrusion amount H of the head 11 calculated in step S6. That is, the tip diameter Rd of the shank 12 after the rivet 1 is driven is a dimension caused by the expansion of the shank 12 that occurs in the process of the shank 12 being pressed into the friction stir part 50, particularly the expansion that occurs when the shank 12 buckles from the groove 15, and therefore such tip diameter Rd varies depending on the size of the rivet 1 (total length L and outside diameter R2), the axial position of the groove 15 (distance G), and the friction stir depth Sd. Furthermore, the amount of protrusion H of the head 11 varies depending on whether the rivet 1 has been properly driven, and if the rivet has not been properly driven, the amount of protrusion H will be greater than the thickness of the head 11. Insufficient driving will also distort the tip diameter Rd described above, and in that sense the tip diameter Rd also varies depending on the amount of protrusion H. For these reasons, in step S7 the tip diameter Rd is estimated based on the parameters L, R2, G, Sd and H described above. For this estimation, for example, a model calculation formula determined in advance by experiments or the like can be used.

[0057] Next, the controller C determines whether or not the tip diameter Rd of the shaft portion 12 estimated in the step S7 is larger than the friction stirring diameter Sr acquired in the step S3 (step S8).

[0058] If the determination in step S8 is YES and it is confirmed that the tip diameter Rd is larger than the friction stir diameter Sr, the controller C determines that the rivet 1 has been properly driven (pressed in), and performs a predetermined process, such as providing the result of this determination (OK determination) to the worker (step S9). In other words, the tip diameter Rd being larger than the friction stir diameter Sr (Rd>Sr) means that the tip 12a of the shank 12 has penetrated into the base material region outside the friction stir portion 50, that is, that an interlock portion has been properly formed. The formation of such an interlock portion suggests that the joining quality of the rivet 1 is good. Therefore, the controller C presents an OK determination in step S9.

[0059] On the other hand, if the result of the judgment in step S8 is NO and it is confirmed that the tip diameter Rd is equal to or less than the friction stir diameter Sr, the controller C judges that the driving (press-in) of the rivet 1 was not performed properly, and performs a predetermined process such as providing the result of the judgment (NG judgment) to the worker (step S10). In other words, the tip diameter Rd being equal to or less than the friction stir diameter Sr (Rd≦Sr) means that the tip 12a of the shank 12 has not penetrated into the base material region outside the friction stir portion 50, that is, the formation of an interlock portion has not been achieved. Such non-formation of an interlock portion suggests that the joining quality of the rivet 1 is poor. Therefore, the controller C presents an NG judgment in step S10.

[0060] [Effects] As described above, in this embodiment, when the first member 41 and the second member 42 are joined, the overlapping portion 45 of both members is friction-stirred by the rotating tool 101, and the rivet 1 is further pressed into the friction-stir portion 50 formed thereby. Therefore, the combination of the friction-stir portion 50 and the rivet 1 can join the first member 41 and the second member 42 with sufficient strength.

[0061] In particular, the rivet 1 used in this embodiment includes a shank 12 having a circumferentially extending groove 15 formed on the outer circumferential surface, so that when the rivet 1 is pressed into the friction stir part 50, the shank 12 is buckled starting from the groove 15, and the tip 12a of the shank 12 can be easily enlarged in diameter. This makes it possible to obtain a state in which the tip 12a of the shank 12 is embedded into the base material region outside the friction stir part 50 with a high probability, and the first member 41 and the second member 42 can be mechanically and appropriately joined by the function of the interlock part consisting of the tip 12a embedded in the base material region. This, in combination with the joining by the friction stir part 50, makes it possible to join the first member 41 and the second member 42 with sufficient strength, improving the joining quality.

[0062] In this embodiment, the groove 15 formed by locally thinning the outer peripheral wall of the shank 12 is used as a means (promoting portion) for promoting the expansion of the shank 12, and depending on the depth of the groove 15, the load-bearing capacity of the rivet 1 itself may be significantly reduced. In other words, if the depth of the groove 15 is made too large, even if the interlock portion is reliably obtained, the improvement in the joint strength may be limited. For this reason, it is desirable to make the depth of the groove 15 as small as possible within a range that provides the effect of promoting the expansion to the extent necessary for the formation of the interlock portion. In other words, it is desirable to determine the depth of the groove 15 to a value that can achieve a good balance between the promotion of the expansion of the shank 12 and the load-bearing capacity (or joint strength) of the rivet 1.

[0063] Furthermore, in this embodiment, a tapered inner circumferential surface 12s (with the inner diameter increasing toward the tip) is formed at the tip 12a of the shank 12, so that the resistance force acting on the shank 12 when the rivet 1 is pressed in can be converted into a diameter-expansion force via the tapered inner circumferential surface 12s. This, combined with the action of the groove 15 described above, sufficiently promotes the diameter expansion of the tip 12a. This can further increase the probability that the interlock portion is formed, and can sufficiently improve the joining quality.

[0064] Furthermore, in this embodiment, the tip diameter Rd of the shank 12 after press-fitting is estimated based on the dimensions of the rivet 1 before press-fitting (L, R2, G in FIG. 1), the friction stir depth Sd, which is the depth of the friction stir portion 50, and the protrusion amount H of the head 11 of the rivet 1 relative to the upper surface 50a of the friction stir portion 50, and the pass / fail of the joining quality is judged based on a comparison of the estimated tip diameter Rd with a predetermined threshold value (here, the friction stir diameter Sr, which is the outer diameter of the friction stir portion 50). With this configuration, the joining quality of the rivet 1 can be guaranteed by a simple method that does not require special inspection equipment (for example, inspection equipment using X-rays, thermography, etc.).

[0065] In particular, in this embodiment, the distance G (FIG. 1) indicating the axial position of the groove 15 is used as one of the dimensional parameters for estimating the tip diameter Rd of the shaft portion 12, so that an appropriate estimate of the tip diameter Rd can be obtained that takes into account the phenomenon in which the shaft portion 12 buckles starting from the groove 15, thereby improving the accuracy of the estimation of the tip diameter Rd.

[0066] [Variations] In the above embodiment, the groove 15 is formed on the outer peripheral surface of the shank 12 as a means for promoting the expansion of the tip 12a of the shank 12 of the rivet 1, that is, as a promoting portion. However, the promoting portion is not limited to the groove 15 as long as it can promote the expansion of the tip 12a. For example, as shown in FIG. 9, it is possible to provide a thinned portion 65 formed by thinning both the inner peripheral wall and the outer peripheral wall in the middle of the shank 12, and to make the thinned portion 65 function as a promoting portion. In addition, although not shown, the shank 12 may be divided into a first portion and a second portion arranged in the axial direction, and the first portion and the second portion may be coaxially joined using a relatively low-strength weld metal or the like. In this way, the joint (welded portion) between the first portion and the second portion can function as a promoting portion.

[0067] In the above embodiment, the first member 41 and the second member 42 are directly overlapped and joined, but the first member 41 and the second member 42 may also be joined with one or more other members interposed between the first member 41 and the second member 42.

[0068] In the above embodiment, both the first member 41 and the second member 42 are made of a thermoplastic composite material including a base material made of a thermoplastic resin and a large number of reinforcing fibers impregnated into the base material, but the materials of the first member 41 and the second member 42 may be different from each other. For example, one of the first member 41 and the second member 42 may be a molded body of a thermoplastic resin, and the other may be a molded body of a fiber-reinforced composite material. Alternatively, one of the first member 41 and the second member 42 may be a molded body of a metal, and the other may be a molded body of a metal or a thermoplastic resin of a different nature.

[0069] [summary] The above-described embodiment and its modified examples mainly include the following inventions.

[0070] A fastener according to one aspect of the present invention is a fastener that is pressed from the first member side into a friction stir portion formed by pressing a rotating tool from the first member side into an overlapping portion between a first member and a second member, and the fastener has a head that is arranged on a surface of the friction stir portion and a cylindrical shank that extends from the head toward the second member, the shank having a promoting portion that promotes expansion of the tip of the shank during pressing.

[0071] According to the present invention, when the fastener is pressed into the friction stir part, the shaft of the fastener can be buckled starting from the promoting part to easily expand the diameter of the tip of the shaft. This makes it highly likely that the tip of the shaft will penetrate into the base material region outside the friction stir part, and the interlocking part, which is made up of the tip that penetrates into the base material region, can mechanically join the objects to be joined properly. In combination with joining by the friction stir part, this makes it possible to join the objects to be joined with sufficient strength, improving the joining quality.

[0072] The promoting portion may be, for example, a recessed groove that is formed on an outer circumferential surface of the shaft portion and extends in a circumferential direction.

[0073] According to this configuration, the radial expansion of the tip of the shaft can be promoted by a simple configuration of providing a groove on the outer peripheral surface of the shaft. In addition, by adjusting the depth of the groove, it is possible to achieve a good balance between the promotion of radial expansion of the shaft and the load resistance (or joint strength) of the fastened body.

[0074] Preferably, the tip of the shaft portion has a tapered inner circumferential surface whose inside diameter increases toward the tip side.

[0075] According to this configuration, the resistance force acting on the shaft when the fastener is pressed in is converted into a diameter-expansion force via the tapered inner circumferential surface, and the expansion of the tip portion can be sufficiently promoted by a synergistic effect with the action of the promoting portion described above. This can further increase the probability of the interlock portion being formed, and can sufficiently improve the joining quality.

[0076] A joint structure according to another aspect of the present invention includes the first member and the second member, the friction stir portion formed in the overlapping portion between the first member and the second member, and the fastener pressed into the friction stir portion.

[0077] The joint structure of the present invention has sufficient joint strength based on the combination of the fastener and the friction stir portion.

[0078] A joining method according to yet another aspect of the present invention is a method for joining the first member and the second member using the fastener, the method including: a friction stirring step of forming the friction stir portion in the overlapping portion between the first member and the second member by friction stirring in which the rotating tool is pressed into the overlapping portion from the first member side; and a fastening step of pressing the fastener into the friction stir portion from the first member side.

[0079] According to the joining method of the present invention, a joined structure having sufficient joining strength based on the combination of the fastened body and the friction stir portion can be obtained.

[0080] The joining method preferably further includes a determination step of estimating a tip diameter of the shank after the fastening step based on the dimensions of the fastener before pressing in, the friction stirring depth in the friction stirring step, and the amount of protrusion of the head from the upper surface of the friction stirring part after the fastening step, and determining that a good join has been performed if the estimated tip diameter is larger than a predetermined threshold value.

[0081] According to this configuration, the joining quality of the fastened body can be ensured by a simple method that does not require a special inspection device (for example, an inspection device using X-rays or thermography).

[0082] The pre-press fit dimensions may include, for example, the axial length of the fastener, the outer diameter of the shank, and a distance representing the axial position of the promotion portion.

[0083] According to this configuration, an appropriate tip diameter estimate can be obtained that takes into account the phenomenon of the shaft portion buckling starting from the promoting portion, thereby improving the accuracy of the tip diameter estimate. [Explanation of symbols]

[0084] 1: Rivet (fastener) 11:Head 12: Shaft 12a: Tip (of shaft) 12s: (tapered) inner surface 15: Concave groove (promotion part) 30:Joint structure 41: First member 42: Second member 45: Overlap 50: Friction stirring section 50a: Upper surface (of the friction stir part) 65:Thickness reduction part (promotion part) L: (rivet) total length R2: Outer diameter (of shaft) G: Distance (representing the axial position of the groove) H: (Head) protrusion amount Sd: Friction stirring depth Sr: Friction stirring diameter (threshold) Rd: Tip diameter (of shaft)

Claims

1. A first member and a second member stacked in a thickness direction, a friction stir portion formed by pressing a rotary tool into an overlapping portion between the first member and the second member from the first member side; a fastening body press-fitted into the friction stir portion from the first member side, The fastening body is A head portion disposed on the surface of the friction stir part; a cylindrical shaft portion extending from the head portion toward the second member, The shaft portion has a promoting portion that promotes expansion of a diameter of a tip portion of the shaft portion during press-fitting, A bottom surface, which is a surface opposite to the front surface of the friction stirring portion, is formed at a position midway in the thickness direction of the second member, A welded structure, wherein a tip portion of the shaft portion protrudes to the outside of the friction stir portion and is disposed within the second member.

2. The joint structure according to claim 1 , A joint structure, wherein the promotion portion is a circumferentially extending groove formed on the outer circumferential surface of the shaft portion.

3. The joined structure according to claim 1 or 2, A joint structure, wherein the tip of the shaft portion has a tapered inner circumferential surface whose inner diameter increases toward the tip.

4. A preparatory step of preparing a fastener to be pressed from the first member side into a friction stirring portion formed at an overlapping portion between a first member and a second member, the fastener including a head disposed on a surface of the friction stirring portion and a cylindrical shaft portion extending from the head toward the second member, and forming a promotion portion on the shaft portion that promotes the expansion of the tip end of the shaft portion during pressing; a friction stirring step of performing friction stirring by pressing a rotary tool into an overlapping portion between the first member and the second member from the first member side to form the friction stir portion in the overlapping portion; a fastening step of press-fitting the fastening body into the friction stir portion from the first member side; a determination step of estimating a tip diameter of the shaft portion after the fastening step based on the dimensions of the fastener before pressing, the friction stirring depth in the friction stirring step, and the amount of protrusion of the head from the surface of the friction stirring part after the fastening step, and determining that a good join has been performed if the estimated tip diameter is larger than a predetermined threshold.

5. The joining method according to claim 4, A joining method, wherein the dimensions before press-fitting include an axial length of the fastener, an outer diameter of the shaft portion, and a distance representing the axial position of the promotion portion.

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