JP7661085B2 - Joined structure and joining method - Google Patents

Description

The present invention relates to a fastener that is pressed into a friction stir portion of a first member and a second member that are joined through the friction stir portion from the first member side, and a joining structure and joining method that use the fastener.

When manufacturing structures such as aircraft, railway cars, or automobiles, it may be necessary to overlap and join two or more members made of metal, resin, etc. One method of joining such structures is known to be the use of rivets (fasteners).

For example, the following Patent Document 1 discloses joining two or more resin members using a method that combines riveting and thermal melting. Specifically, in Patent Document 1, the two resin members are joined by a method that includes the steps of stacking two thermoplastic resin members one above the other and placing a conductive metal plate between them, passing electricity through and heating the placed metal plate to fuse the resin members and the metal plate, and driving (pressing) a rivet so that it penetrates the upper resin member and the metal plate.

JP 2013-002505 A

The joining method of Patent Document 1 requires the separate placement of a conductive metal plate between the resin members, which can lead to an increase in weight and manufacturing costs. Therefore, the adoption of friction stir welding is proposed as an alternative method that can solve this problem. 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. This joining method that combines friction stir welding and rivets makes it possible to reduce weight and manufacturing costs because a conductive metal plate is no longer an essential element.

When using the joining method described above, the rivet is pressed into the friction stir portion, which is the area that has been frictionally stirred. However, in this case, the tip of the rivet does not expand as expected when pressed in, and there is a possibility that the required joining strength will not be obtained.

The present invention was made in consideration of the above 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 joining structure using the fastener.

In order to solve the above problem, one aspect of the present invention provides a joint structure comprising a first member and a second member stacked in the thickness direction, a friction stir portion formed in the overlapping portion between the first member and the second member by pressing a rotary tool from the first member side, and a fastener pressed into the friction stir portion from the first member side, the fastener comprising a head disposed on the surface of the friction stir portion and a cylindrical shank extending from the head toward the second member, the shank having a promoting portion that promotes expansion of the diameter of a tip of the shank when pressed in, a bottom surface which is the surface of the friction stir portion opposite to the surface is formed at a position midway in the thickness direction of the second member, and the tip of the shank protrudes to the outside of the friction stir portion and is disposed within the second member .

A joining method according to another aspect of the present invention includes the steps of: preparing a fastener to be pressed into a friction stir portion formed at an overlapping portion between a first member and a second member from the first member side, the fastener including a head disposed on a surface of the friction stir portion and a cylindrical shank extending from the head toward the second member, and forming a promoting portion on the shank to promote diameter expansion of a tip portion of the shank during pressing; a friction stirring step of performing friction stirring by pressing a rotary tool into the 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 pressing the fastener into the friction stir portion from the first member side ; and a determination step of estimating a tip diameter of the shank after the fastening step based on a dimension of the fastener before pressing in, a friction stirring depth in the friction stirring step, and an amount of protrusion of the head from an upper surface of the friction stir portion after the fastening step, and determining that a good join has been performed if the estimated tip diameter is greater than a predetermined threshold value .

As described above, the present invention provides a fastener that can be easily deformed into a desired shape when pressed into a friction stir part, and can improve the joining strength of a joining structure using the fastener.

FIG. 2 is a cross-sectional view showing a single rivet according to an embodiment of the present invention. 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. 2 is a schematic diagram showing an overall configuration of a friction stir welding apparatus used in manufacturing the welded structure. FIG. 4 is a cross-sectional view showing a first process (preparation step) for manufacturing the joined structure. FIG. 5 is a cross-sectional view showing a second process (positioning step) of manufacturing the joined structure. FIG. 11 is a cross-sectional view showing a third process (friction stirring step) of manufacturing the joined structure. FIG. A cross-sectional view showing the fourth process (casting process) of manufacturing the joint structure. 10 is a flowchart showing a procedure for determining whether or not the joining quality is acceptable. FIG. 2 is a view corresponding to FIG. 1 and showing a modified example of the embodiment.

[Rivet structure]
Fig. 1 is a cross-sectional view showing a rivet 1 according to one embodiment of the present invention. As shown in this figure, the rivet 1 is a fastener including a disk-shaped head 11 and a cylindrical shank 12 extending concentrically from the head 11. In this embodiment, the rivet 1 is a self-pierce rivet that is driven without penetrating into a material that does not have a pilot hole. In the following, the head 11 side of the 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 the rivet 1 is used.

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

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

The end (lower end) of the shaft 12 opposite the head 11, i.e., the tip 12a, is formed in a sharp point. That is, the tip 12a of the shaft 12 has a tapered inner circumferential surface 12s whose inner diameter increases toward the tip (the further away from the head 11). The tip 12a, including the inner circumferential surface 12s, is also the opening edge of the tip (lower end) of the shaft 12.

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

The material of the rivet 1 may be any suitable material as long as it has the strength to be able to be driven into the objects to be joined. For example, the material of the rivet 1 may be a metal material such as titanium or high tensile steel, or a resin material such as a thermoplastic resin or a thermoplastic composite material. 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.

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

The first member 41 and the second member 42 are both plate-shaped members, and are stacked one on top of the other in the vertical direction with the first member 41 on top (and the second member 42 on the bottom). The stacked first member 41 and second member 42 form an overlapping portion 45 at the position where the friction stirring portion 50 is to be formed.

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 that includes 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.

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, and thermoplastic epoxy resin. Examples of reinforcing fibers that are impregnated into the base material include carbon fibers, glass fibers, ceramic fibers, metal fibers, and organic fibers.

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 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 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.

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 the 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. In addition, the driving causes the shaft portion 12 of the rivet 1 to change into a flared shape with the outer diameter of the tip portion 12a being enlarged. Specifically, the shaft portion 12 after the driving is disposed so as to penetrate the first member 41 and extend halfway in the thickness direction of the second member 42, and is formed so that the outer diameter is enlarged toward the tip side (the further away from the head 11). In this state, the tip 12a of the shaft 12 protrudes to the outside of the friction stirring part 50 and functions as an interlock part that fastens the first member 41 and the second member 42. That is, the first member 41 and the second member 42 are fixed to each other by being sandwiched between the interlock part consisting of the tip 12a that protrudes to the outside of the friction stirring part 50 and the head 11 that is placed on the upper surface 50a of the friction stirring part 50.

[Friction stir welding device]
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 convenience of explanation and is not intended to limit the actual use posture of the rotary tool 101.

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 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.

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 arranged so that its axis extends in the vertical direction. The pin member 111 can rotate about the axis R, and can move up and down (advance and retreat) in the vertical direction along the rotation axis R.

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 can also move independently, with one descending and the other ascending.

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 with 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 around 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 of the clamp member 113 prevents the friction stirring material from scattering, and allows the friction stirring portion to be finished smoothly.

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

The backup member 115 has an upper surface (support surface) that abuts against the lower surface of the joining object. In other words, 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.

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 (raising and lowering) 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 to 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 driver 124 moves the clamp member 113 toward the joining object, pressing the joining object against the backup member 115. At this time, the biasing force of the spring 114 acts. Each of the drivers 121 to 124 includes a servo motor, a transmission gear, etc., and causes the respective driven objects to perform the desired operation in response to the rotation of the servo motor.

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 the required rotational 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 the required forward and backward movement operation.

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 broadly divided into a shoulder-first process joining method and a pin-first process joining method.

In a joining method using the shoulder-first process, the shoulder member 112 of the rotating tool 101 is pressed into the overlapping portion of the two or more components first to perform friction stirring, and the pin member 111 is withdrawn from the overlapping portion. The pin member 111 is then lowered while the shoulder member 112 is withdrawn (raised) to smooth the upper surface of the overlapping portion. In contrast, in a joining method using the pin-first process, the pin member 111 of the rotating tool 101 is pressed into the overlapping portion first to perform friction stirring, and the shoulder member 112 is withdrawn from the overlapping portion. The shoulder member 112 is then lowered while the pin member 111 is withdrawn (raised) to smooth the upper surface of the overlapping portion.

[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, riveted friction stir welding, which combines the driving of the rivet 1 and friction stir welding, is used. The riveted friction stir welding differs 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 riveted 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 stirring portion 50) after the friction stirring using the pin member 111. As a result, a joining 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, 42 includes the following four steps P1 to P4.

As shown in FIG. 4, process P1 is a preparation process in which the rivet 1 is attached to the rotary tool 101. The rivet 1 attached to the rotary tool 101 in this preparation process P1 is the rivet 1 before it is driven into the overlapping portion 45, and the shank 12 has not yet been expanded in diameter. In other words, the rivet 1 used in preparation process P1 has a head 11 and a cylindrical shank 12 that extends in a straight line from the head 11.

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 connected to 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.

As shown in FIG. 5, step P2 is a positioning step in which the rotary tool 101 with the rivet 1 attached is positioned with respect to the 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) coincides with the center of the overlapping portion 45 supported on the backup member 115, and then controls the shoulder drive unit 123 and the clamp drive unit 124 so that the 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 axial positional relationship between the pin member 111 and the shoulder member 112 (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.

As shown in FIG. 6, 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 area of the shoulder member 112. The overflowing softened material Q1 is released into the 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 been retracted upward to the extent that the storage space V (FIG. 4) is formed, so the retraction operation of the pin members 111 may be omitted.

If the press-in depth of the shoulder member 112 is h1, this press-in 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-in 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-in 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.

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

As shown in Fig. 7(a) and (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 raise the shoulder member 112. Following the raising 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 into the area including the friction stir portion 50. The formation of the friction stir portion 50 and the driving of the rivet 1 are described in detail below.

First, the formation of the friction stir portion 50 by the casting process P4 will be described. In the casting process 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 having 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, the friction stir part 50 has a cylindrical side surface 50c with a height Sd (≒h1) and a circular top surface 50a and bottom surface 50b with an outer diameter Sr (≒ds). While the material is softened in the friction stir part 50, the original hardness of the first member 41 and the second member 42 is maintained in the base material region around the friction stir part 50, and the reinforcement structure by the reinforcing fibers is also maintained.

Next, the driving of the rivet 1 in the driving process P4 will be described. In the driving process 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 process P4, the rivet 1 is driven using an existing part (pin member 111) provided in the rotating tool 101. Therefore, 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.

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, forcing the rivet 1 into the overlapping portion 45 (see FIG. 7(a)). The rivet 1 is pre-loaded in the storage 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 its shank 12 advances from the tip side into the interior of the friction stirring portion 50. As the rivet 1 advances in this way (pushing down the pin member 111), the tip 12a of the shank 12 eventually reaches the bottom surface 50b of the friction stirring portion 50.

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 starting from the groove 15 formed on its outer peripheral surface, and as a result, as shown in FIG. 7(b), the shaft portion 12 is deformed in a flared shape, and the outer diameter of the tip portion 12a is expanded. In other words, the groove 15 functions as a promoter that promotes the expansion of the tip 12a of the shank 12 when the shank 12 is pressed in (when the rivet 1 is driven).

7(b) shows the 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 stirring portion 50), i.e., the 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 shaft 12 of the rivet 1 not only passes over the bottom surface 50b of the friction stirring portion 50 and is pressed into the base material area below it, but also passes over the side surface 50c of the friction stirring portion 50 and is pressed into the base material area on the outside. The tip 12a thus pressed into the outside of the friction stirring portion 50 exerts an anchor effect against the force that pulls the first member 41 and the second member 42 apart. In other words, the tip 12a functions as an interlocking portion that fastens the first member 41 and the second member 42 together.

By carrying out 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 relatively firmly joins the first member 41 and the second member 42 at the overlapping portion 45.

[Pass/Fail Judgment]
Next, a method for checking whether the rivet 1 has been properly placed when joining the first and second members 41, 42 by the joining method described above, that is, a method for judging the pass/fail of the joining quality by the rivet 1, will be described. FIG. 8 is a flow chart 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.

Next, the controller C performs friction stirring by pressing the rotating 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.

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

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 identifies the axial value (vertical coordinate) of the shoulder member 112 when friction stirring is started and the axial value when the shoulder member 112 is at its lowest point during friction stirring from the output value of the encoder, and calculates the difference between the identified axial values, that is, the press-in depth of the shoulder member 112 into the overlapping portion 45, as the friction stirring depth Sd.

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 pressing the shaft 12 of the rivet 1 into the friction stirring part 50 (see FIG. 7(b)).

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 determines 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 (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 determined axial values as the amount of protrusion H of the head 11.

Next, the controller C estimates the tip diameter Rd, which is the outer 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 (the total length L of the rivet 1, the outer diameter R2 of the shank 12, and the 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 caused by the shank 12 buckling from the groove 15, so such tip diameter Rd varies depending on the size of the rivet 1 (total length L and outer 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 is properly driven, and if the rivet is not driven properly, 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, so 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 previously determined by experiments or the like can be used.

Next, the controller C determines whether the tip diameter Rd of the shaft portion 12 estimated in step S7 is greater than the friction stirring diameter Sr obtained in step S3 (step S8).

If the answer to step S8 is YES and it is confirmed that the tip diameter Rd is larger than the friction stir diameter Sr, the controller C judges that the rivet 1 has been properly driven (pressed in) and performs a predetermined process, such as providing the operator with the result of this judgment (OK judgment) (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 shaft 12 has penetrated into the base material region outside the friction stir portion 50, that is, the 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 judgment in step S9.

On the other hand, if the result of 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 determines that the rivet 1 was not properly driven (pressed in) and performs a predetermined process, such as providing the result of this determination (NG determination) 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 shaft 12 has not penetrated into the base material region outside the friction stir portion 50, that is, the formation of the interlock portion has not been achieved. Such non-formation of the interlock portion suggests that the joining quality of the rivet 1 is poor. Therefore, the controller C presents an NG determination in step S10.

[Action and Effect]
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-stirring portion 50 formed thereby. Therefore, the combination of the friction-stirring portion 50 and the rivet 1 can join the first member 41 and the second member 42 with sufficient strength.

In particular, the rivet 1 used in this embodiment includes a shaft portion 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 portion 50, the shaft portion 12 can be buckled starting from the groove 15, and the tip portion 12a of the shaft portion 12 can be easily enlarged in diameter. This makes it possible to obtain a state in which the tip portion 12a of the shaft portion 12 is embedded into the base material region outside the friction stir portion 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 portion consisting of the tip portion 12a embedded in the base material region. This, in combination with the joining by the friction stir portion 50, makes it possible to join the first member 41 and the second member 42 with sufficient strength, improving the joining quality.

In this embodiment, the groove 15 formed by locally thinning the outer wall of the shank 12 is used as a means (promotion 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 can achieve 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.

In addition, 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 an expansion force via the tapered inner circumferential surface 12s. This, in combination with the action of the groove 15 described above, sufficiently promotes the expansion of the tip 12a. This further increases the probability that the interlock portion is formed, and sufficiently improves the joining quality.

In addition, in this embodiment, the tip diameter Rd of the shank 12 after pressing is estimated based on the dimensions of the rivet 1 before pressing (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 quality of the joint is judged to be acceptable or unacceptable based on a comparison between the estimated tip diameter Rd and 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 quality of the joint by the rivet 1 can be guaranteed by a simple method that does not require special inspection equipment (e.g., inspection equipment using X-rays or thermography).

In particular, in this embodiment, the distance G (FIG. 1) representing 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.

[Modification]
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 1 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, a thinned portion 65 formed by thinning both the inner peripheral wall and the outer peripheral wall can be provided in the middle of the shank 12, and the thinned portion 65 can function as a promoting portion. In addition, although not shown, the shank 12 can be divided into a first portion and a second portion arranged in the axial direction, and the first portion and the second portion can 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.

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 be joined with one or more other members interposed between them.

In the above embodiment, both the first member 41 and the second member 42 are made of a thermoplastic composite material including a thermoplastic resin base material 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 thermoplastic resin, and the other may be a molded body of fiber-reinforced composite material. Alternatively, one of the first member 41 and the second member 42 may be a molded body of metal, and the other may be a molded body of a different metal or thermoplastic resin.

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

The fastener according to one aspect of the present invention is a fastener that is pressed from the first member into a friction stir section formed by pressing a rotary tool into an overlapping portion between a first member and a second member from the first member side, and has a head that is disposed on the surface of the friction stir section and a cylindrical shaft that extends from the head toward the second member, and the shaft has a promoting portion that promotes the expansion of the tip of the shaft when pressed in.

According to the present invention, when the fastener is pressed into the friction stir section, the shaft of the fastener can be buckled starting from the promotion section, and the tip of the shaft can be easily expanded in diameter. This makes it highly likely that the tip of the shaft will penetrate into the base material region outside the friction stir section, and the interlock section, 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 using the friction stir section, this makes it possible to join the objects to be joined with sufficient strength, improving the joining quality.

The promotion portion can be, for example, a circumferentially extending groove formed on the outer circumferential surface of the shaft portion.

This configuration makes it possible to promote radial expansion of the tip of the shaft with a simple configuration that only requires 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 promoting radial expansion of the shaft and the load capacity (or joint strength) of the fastener.

Preferably, the tip of the shaft has a tapered inner circumferential surface whose inner diameter increases toward the tip.

With this configuration, the resistance force acting on the shaft when the fastener is pressed in is converted into an expansion force via the tapered inner circumferential surface, and the synergistic effect with the action of the promotion part described above can sufficiently promote the expansion of the tip. This can further increase the probability of the interlock part being formed, and can sufficiently improve the joining quality.

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

The joint structure of the present invention has sufficient joint strength based on the combination of the fastener and the friction stir part.

The 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, and includes a friction stirring step of forming the friction stir portion in the overlapping portion between the first member and the second member by performing friction stirring by pressing the rotating tool into the overlapping portion between the first member and the second member from the first member side, and a fastening step of pressing the fastener into the friction stir portion from the first member side.

The joining method of the present invention makes it possible to obtain a joining structure with sufficient joining strength based on the combination of the fastener and the friction stir part.

The joining method preferably further includes a determination step of estimating the 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 upper surface of the friction stirring part after the fastening step, and determining that a good join has been achieved if the estimated tip diameter is greater than a predetermined threshold value.

This configuration makes it possible to ensure the quality of the joint produced by the fastener using a simple method that does not require special inspection equipment (e.g., inspection equipment using X-rays or thermography, etc.).

The dimensions before press-fitting may include, for example, the axial length of the fastener, the outer diameter of the shaft portion, and a distance representing the axial position of the promotion portion.

This configuration makes it possible to obtain an appropriate tip diameter estimate that takes into account the phenomenon in which the shaft portion buckles starting from the promotion portion, thereby improving the accuracy of the tip diameter estimate.

1: Rivet (fastener)
11: Head portion 12: Shaft portion 12a: Tip portion (of shaft portion) 12s: (Tapered) inner peripheral surface 15: Groove (promotion portion)
30: Joint structure 41: First member 42: Second member 45: Overlap portion 50: Friction stir portion 50a: Upper surface (of friction stir portion) 65: Thinning portion (promotion portion)
L: total length (of rivet) R2: outer diameter (of shaft) G: distance (representing axial position of groove) H: protrusion (of head) Sd: friction stirring depth Sr: friction stirring diameter (threshold)
Rd: Tip diameter (of shaft)

Claims (5)

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 . 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. 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. a preparation step of preparing a fastener to be press-fitted from the first member side into a friction stir portion 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 portion 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 a tip portion of the shank portion during press-fitting;
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 . 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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