Friction stir spot-welding device and friction stir spot-welding method

Abstract

This friction stir spot-welding device comprises: a joining tool including a pin (11) having a central axis (R) and a cylindrical shoulder (12) having a hollow part into which the pin (11) is inserted; a rotation mechanism capable of rotating the joining tool about the central axis (R); and a movement mechanism capable of moving the pin (11) and the shoulder (12) independently in a direction in which the central axis (R) extends. The leading end of the shoulder (12) has an outer circumferential tapered surface where the outer circumferential surface of the shoulder (12) is inclined and becomes tapered. An outer circumferential taper angle formed between a straight line orthogonal to the central axis (R) and the outer circumferential tapered surface in a cross-section including the central axis (R) is set to at least 30 degrees.

Description

Friction stir spot welding device and friction stir spot welding method

[0001] The present disclosure relates to a friction stir spot welding apparatus and a friction stir spot welding method for joining a plurality of metal members.

[0002] A joined body formed by joining a plurality of metal members may be used as a component of a structure such as an aircraft, a railway vehicle, or an automobile. One known method for such joining is friction stir spot joining.

[0003] Patent Document 1 discloses a joining method for forming a joint by friction stir spot welding three metal members using a double-acting rotary tool including a coaxially arranged probe, inner shoulder member, and outer shoulder member. The inner shoulder member has a cylindrical shape that houses a cylindrical probe, and the outer shoulder member has a cylindrical shape that houses the inner shoulder member. In this technique, the probe and inner shoulder member are first pressed into the overlapping portion of the three metal members to be spot-joined, with their tip surfaces flush with each other, up to the vicinity of the interface between the first and second members, to perform friction stir welding. The probe is then protruded from the inner shoulder member and further pressed into the overlapping portion up to the vicinity of the interface between the second and third members, thereby forming a spot stir weld that joins the three metal members at the overlapping portion.

[0004] Japanese Patent Application Laid-Open No. 2006-320924

[0005] In a joint formed by friction stir spot welding, sudden fracture may occur due to excessive input force. Such fractures include interfacial fracture, in which the fracture progresses along the interface between adjacent metal members inside the joint, and plug fracture, in which the fracture progresses toward the outer surface of the joint, crossing the interface. When such fractures occur, it is desirable to precisely control the fracture path to stabilize the joint strength. Therefore, it is desirable to be able to visually confirm the formation state of the joint from the outside during the quality confirmation stage after manufacturing. However, conventional joints such as those described in Patent Document 1 have a problem in that it is difficult to control the occurrence of plug fracture and interfacial fracture in the joint. Furthermore, there is also the problem that attempting to control the joint state of the joint tends to increase the load on the welding tool.

[0006] An object of the present disclosure is to provide a friction stir spot welding apparatus and a friction stir spot welding method that can reduce the occurrence of unstable interfacial fracture in the welded body and make plug fracture easier while suppressing the load on the welding tool.

[0007] A friction stir spot welding apparatus according to one aspect of the present disclosure joins a first member and a second member, each made of metal and having a first front surface and a first back surface, by softening them with frictional heat. The friction stir spot welding apparatus includes a joining tool including a pin having a central axis and a cylindrical shoulder having a hollow portion into which the pin is inserted, a rotation mechanism capable of rotating the joining tool about the central axis, and a movement mechanism capable of independently moving the pin and the shoulder in a direction extending along the central axis. The tip of the shoulder has an outer peripheral tapered surface, where the outer peripheral surface of the shoulder is tapered, and the outer peripheral taper angle, which is the angle between the outer peripheral tapered surface and a line perpendicular to the central axis in a cross section including the central axis, is set to be 30 degrees or greater.

[0008] A friction stir spot joining method according to another aspect of the present disclosure is a method of joining a first member having a first front surface and a first back surface and a second member having a second front surface and a second back surface, each made of metal, by softening them with frictional heat. The friction stir spot welding method includes: preparing a joining tool including a pin having a central axis and a cylindrical shoulder having a hollow portion into which the pin is inserted, wherein a tip portion of the shoulder has an outer peripheral tapered surface where the outer peripheral surface of the shoulder is tapered, and an outer peripheral taper angle, which is an angle between a line perpendicular to the central axis and the outer peripheral tapered surface in a cross section including the central axis, is set to 30 degrees or more; forming an overlapping portion where the first member and the second member overlap each other by abutting at least a portion of the second front surface against the first back surface; retracting the pin from the first front surface and pressing the shoulder into the overlapping portion so that at least a portion of the outer peripheral tapered surface penetrates to a position deeper than the second front surface, thereby forming a joint bottom surface which is an interface between the first member and the second member; and after forming the joint bottom surface, retracting the shoulder and inserting the pin into the overlapping portion.

[0009] FIG. 1 is a schematic diagram showing the configuration of a friction stir spot welding apparatus according to the present disclosure. FIG. 2 is a diagram showing a shoulder-first process in which the shoulder is first pressed into the overlapping portion of the joining members when using a friction stir spot welding tool. FIG. 3 is a diagram showing a process chart of a friction stir spot welding method according to an embodiment of the present disclosure. FIG. 4 is a schematic cross-sectional view illustrating the anchor, hooking, and indent of a joined body according to an embodiment of the present disclosure. FIG. 5 is a schematic cross-sectional view illustrating the arrangement of a pin and a shoulder when forming an indent of a joined body according to an embodiment of the present disclosure. FIG. 6 is a schematic cross-sectional view illustrating a fracture mode of a joined body. FIG. 7 is a schematic cross-sectional view showing the tip of a friction stir spot welding tool. FIG. 8 is a cross-sectional view and an enlarged cross-sectional view of a joined body. FIG. 9 is a cross-sectional view and an enlarged cross-sectional view of a joined body. FIG. 10 is a graph showing the relationship between the hooking height and the difference between the tool plunge amount and the taper height. FIG. 11 is a graph showing the relationship between the hooking height and the difference between the tool plunge amount and the taper height. Fig. 12 is a graph showing the relationship between the taper tip position and the outer peripheral taper angle. Fig. 13 is a graph showing the relationship between the difference between the tool plunge amount and the taper height and the anchor height. Fig. 14 is a graph showing the relationship between the type of steel material and the hooking height. Fig. 15 is a graph showing the relationship between the difference between the tool plunge amount and the taper height and the hooking height.

[0010] The present disclosure will be described in detail below with reference to the drawings. The friction stir spot welding method according to the present disclosure can be applied to the manufacture of various joined bodies formed by spot-joining two or more overlapping structural materials, such as metal plates, frames, exterior materials, or columnar materials. The joined bodies thus manufactured are components of structures such as aircraft, railcars, and automobiles.

[0011] [Configuration of Friction Stir Spot Welding Apparatus] Figure 1 is a schematic diagram showing the configuration of a friction stir spot welding apparatus M according to one embodiment of the present disclosure. The friction stir spot welding apparatus M joins an upper plate 31 and a lower plate 32 by softening them with frictional heat. The friction stir spot welding apparatus M includes a friction stir spot welding tool 1, a tool driver 2 that drives the tool 1 to rotate and elevate, and a controller C that controls the operation of the tool driver 2. Note that although Figure 1 includes directional indications of "up" and "down," this is for ease of explanation and is not intended to limit the actual direction in which the tool 1 is used.

[0012] The tool 1 is supported by a tool fixing portion. The tool fixing portion can be, for example, the tip of an articulated robot. A backup 15 is arranged facing the lower end surface of the tool 1. At least two metal members to be joined are arranged between the tool 1 and the backup 15. FIG. 1 shows an example in which an overlapping portion 30, in which a portion of an upper plate 31 made of a flat plate and a portion of a lower plate 32 also made of a flat plate overlap in the vertical direction, is arranged between the tool 1 and the backup 15. Note that the tool 1 corresponds to the welding tool of the present disclosure.

[0013] The tool 1 includes a pin 11 having a central axis extending along a predetermined axial direction, a shoulder 12, a clamp 13, and a spring 14. The pin 11 is formed in a cylindrical shape and is disposed so that its central axis extends in the vertical direction. The pin 11 is rotatable about the central axis R, and is also movable up and down, i.e., forward and backward, along the central axis R. When the tool 1 is in use, the central axis R is aligned with a spot joining position W at the overlapping portion 30. The tool 1 is a double-acting tool in which the pin 11 and the shoulder 12 move independently.

[0014] The shoulder 12 is a cylindrical member having a hollow portion into which the pin 11 is inserted. The axis of the shoulder 12 is coaxial with the axis of the pin 11, which is the central axis R. The shoulder 12 rotates around the central axis R and moves up and down along the central axis R, that is, moves forward and backward. The shoulder 12 and the pin 11 inserted in the hollow portion move relatively in the direction of the central axis R while both rotating around the central axis R. In other words, the pin 11 and the shoulder 12 can not only move up and down simultaneously along the central axis R, but also independently move, with one descending while the other ascends.

[0015] The clamp 13 is a cylindrical member having a hollow portion into which the shoulder 12 is inserted. The axis of the clamp 13 is also coaxial with the central axis R. The clamp 13 does not rotate around its axis, but moves up and down along the central axis R, that is, moves forward and backward. The clamp 13 serves to surround the outer periphery of the pin 11 or the shoulder 12 when they perform friction stirring. The enclosure by the clamp 13 prevents the friction stirring material from scattering, and enables the friction stir spot welded portion to be finished smoothly.

[0016] The spring 14 is attached to the upper end side of the clamp 13 and biases the clamp 13 downward, that is, toward the overlapping portion 30. The clamp 13 is attached to the tool fixing portion via the spring 14. As shown in FIG. 1 , the backup 15 has a support surface 15A that supports the underside of the overlapping portion 30, which is the object to be joined. The backup 15 is a backing member that supports the overlapping portion 30 when the pin 11 or shoulder 12 is press-fitted into the overlapping portion 30. The clamp 13, biased by the spring 14, presses the overlapping portion 30 against the backup 15.

[0017] The tool driving unit 2 includes a rotation driving unit 21 and an elevation driving unit 22. The rotation driving unit 21 includes a motor, a drive gear, etc., and drives the pin 11 and the shoulder 12 to rotate about the central axis R. The rotation driving unit 21 corresponds to the rotation mechanism of the present disclosure, which rotates the tool 1. The elevation driving unit 22 is a mechanism for moving the pin 11, the shoulder 12, and the clamp 13 forward and backward, i.e., raising and lowering, along the central axis R. The elevation driving unit 22 drives the pin 11 so as to press the pin 11 into the overlapping portion 30 and retract it from the overlapping portion 30. The elevation driving unit 22 also moves the shoulder 12 forward and backward along the central axis R, thereby pressing the shoulder 12 into and retracting the overlapping portion 30. The elevation driving unit 22 corresponds to the movement mechanism of the present disclosure, which can independently move the pin 11 and the shoulder 12 in the axial direction along which the pin 11 extends. The lifting drive unit 22 also moves the clamp 13 toward the overlapping portion 30, pressing the overlapping portion 30 against the backup 15. At this time, the biasing force of the spring 14 acts. In other words, in this embodiment, the lifting drive unit 22 is made up of three shafts: a first lifting shaft that drives the pin 11, shoulder 12, and clamp 13 together, a second lifting shaft that drives the pin 11 independently, and a central rotation shaft.

[0018] The controller C is comprised of a microcomputer or the like, and executes a predetermined control program to control the operation of each part of the tool driving unit 2. Specifically, the controller C controls the rotation driving unit 21 to cause the pin 11 and the shoulder 12 to perform a required rotational movement. The controller C also controls the elevation driving unit 22 to cause the pin 11, the shoulder 12, and the clamp 13 to perform a required forward / backward movement movement. The controller C corresponds to the control unit in this disclosure, and sets the rotation, movement amount, movement position, pressure force, etc. of each member described below.

[0019] The upper plate 31 is made of metal and has an upper plate surface 31A and an upper plate back surface 31B as shown in FIG. 1 . The upper plate surface 31A is the surface of the upper plate 31 and corresponds to the upper surface of the upper plate 31 in FIG. 1 . Similarly, the upper plate back surface 31B is the back surface of the upper plate 31 and corresponds to the lower surface of the upper plate 31 in FIG. 1 . The upper plate 31 corresponds to the first member in the present disclosure. The upper plate surface 31A corresponds to the first surface in the present disclosure, and the upper plate back surface 31B corresponds to the first back surface in the present disclosure. Also, as an example, the upper plate 31 is made of an aluminum alloy. Note that the upper plate 31 may be made of a wrought material or a cast metal. Furthermore, the upper plate 31 is subjected to electrocoating. That is, a coating film is formed on the upper plate surface 31A and the upper plate back surface 31B of the upper plate 31. Note that in other embodiments, the upper plate 31 may be subjected to a chemical conversion treatment or the like.

[0020] The lower plate 32 is made of metal and has a lower plate surface 32A and a lower plate back surface 32B as shown in FIG. 1 . The lower plate surface 32A is the surface of the lower plate 32 and corresponds to the upper surface of the lower plate 32 in FIG. 1 . Similarly, the lower plate back surface 32B is the back surface of the lower plate 32 and corresponds to the lower surface of the lower plate 32 in FIG. 1 . The lower plate 32 corresponds to the second member in the present disclosure. The lower plate surface 32A corresponds to the second surface in the present disclosure, and the lower plate back surface 32B corresponds to the second back surface in the present disclosure. As an example, the lower plate 32 is made of high-tensile steel. That is, the upper plate 31 and the lower plate 32 are made of different metals. The lower plate 32 may be made of mild steel or hot-stamped steel. The lower plate 32 may also be subjected to a non-plating treatment, a zinc plating treatment, an Al-Si plating treatment, a chemical conversion treatment, an electro-deposition coating, or the like. An adhesive or sealant may be interposed between the upper plate 31 and the lower plate 32. As described above, when the upper plate 31 is made of an aluminum alloy and the lower plate 32 is made of high-tensile steel, the melting point of the upper plate 31 is set lower than the melting point of the lower plate 32 .

[0021] In this embodiment, examples of combinations in which the upper plate 31 and the lower plate 32 are made of different materials include, in this order, the upper plate 31 and the lower plate 32: Example 1: Al and Fe, Example 2: Resin and Fe, Example 3: Al and Mg, Example 4: Resin and Mg, and Example 5: Resin and Al. In such combinations, the hardness of the lower plate 32 is higher than the hardness of the upper plate 31, and therefore the anchor 4A described below can be stably formed.

[0022] [Method of Using the Tool] Next, a method of using the tool 1 exemplified in this embodiment will be described. Methods of using the friction stir spot welding apparatus M can be roughly classified into a pin-first process in which the pin 11 of the tool 1 is first pressed into the overlapping portion of the joining members, and a shoulder-first process in which the shoulder 12 is first pressed into the overlapping portion of the joining members. Of these, the shoulder-first process is adopted in this embodiment.

[0023] Fig. 2 is a diagram showing processes P11 to P14 of the friction stir spot welding method using the shoulder-first process. Fig. 3 is a diagram showing a process chart of the friction stir spot welding method according to this embodiment. Fig. 3 simply shows the process when friction stir spot welding an overlapping portion 30 of an upper plate 31 and a lower plate 32. Fig. 4 is a schematic cross-sectional view for explaining the anchor, hooking, and indent of a welded body 3 according to this embodiment.

[0024] 3, an overlapping portion 30 is formed by an upper plate 31 and a lower plate 32. In the overlapping portion 30, at least a portion of a surface 32A of the lower plate abuts against a back surface 31B of the upper plate, and the upper plate 31 and the lower plate 32 are arranged so as to overlap each other.

[0025] Next, as shown in step S2 of FIG. 3 , the tool 1 is placed at a predetermined position and rotated. Specifically, the tool 1 is placed facing the overlapping portion 30 so that the central axis R of the tool 1 is parallel to the overlapping direction of the upper plate 31 and the lower plate 32, i.e., the vertical direction. Note that this facing arrangement may also be such that the central axis R of the tool 1 is inclined relative to the vertical direction. In this embodiment, with the central axis R aligned with a predetermined spot joining position W, the lower end surface of the tool 1 abuts against the upper plate surface 31A of the upper plate 31. Also, as shown in FIG. 1 , the clamp 13 presses the overlapping portion 30 against the backup 15 with the biasing force of the spring 14. With the lower end surface of the tool 1 abutting against the upper plate surface 31A of the upper plate 31 in this manner, as shown in process P11 of FIG. 2 , the controller C controls the rotation drive unit 21 to rotate the pin 11 and the shoulder 12 around the central axis R at a predetermined number of rotations. This rotation causes friction to preheat the area of ​​the overlapping portion 30 where the pin 11 and the shoulder 12 are in contact with each other. That is, process P11 in FIG.

[0026] Next, as shown in process P12 of FIG. 2 and step S3 of FIG. 3, a press-fitting process is performed in which the shoulder 12 is press-fitted into the overlapping portion 30 while the pin 11 is retracted from the overlapping portion 30. In this process, while maintaining rotation of the tool 1, the controller C controls the shoulder drive unit 23 to lower the shoulder 12 as indicated by the white arrow in process P12 of FIG. 2 to press-fit the shoulder 12 into the overlapping portion 30, while controlling the elevation drive unit 22 to raise the pin 11 as indicated by the white arrow, i.e., retract the pin 11. Note that the clamp 13 remains stationary. As shown in process P12 of FIG. 2, the shoulder 12 is press-fitted into the overlapping portion 30 to a press-fit position deeper than the lower plate surface 32A relative to the upper plate surface 31A. As a result, the weld bottom surface 4B shown in FIG. 4 is formed. This action also agitates the material in the press-fit region of the shoulder 12, as indicated by arrow b1 in FIG. 2 , and the overflowing material OF that overflows from the overlapping portion 30 due to the press-fitting is released into the hollow space in the shoulder 12 created by the retraction of the pin 11. As a result, a base portion of the anchor 4A shown in FIG. 4 and a hooking 4F, which will be described later, are formed. Note that in the press-fitting process, a pressurizing force, i.e., a pressurizing force, is applied to the entire pin 11, shoulder 12, and clamp 13 along the axial direction. Meanwhile, a pressurizing force is applied to the clamp 13, pressing it against the backup 15. As a result, the pressurizing force with which the tool 1 is pressed against the welded body 3 corresponds to the force obtained by subtracting the clamping force from the press-fitting force.

[0027] Next, as shown in process P13 in FIG. 2 and step S4 in FIG. 3 , while maintaining rotation of the tool 1, the controller C controls the shoulder driver 23 to retract the shoulder 12 from the press-fit position as indicated by the white arrow in process P13 in FIG. 2 , and controls the lift driver 22 to lower the pin 11 so that it enters the overlapping portion 30 as indicated by the white arrow. This step represents a backfilling step of the overflowed material OF. In this step, the controller C controls the shoulder driver 23 to raise the shoulder 12, while controlling the lift driver 22 to lower the pin 11. As the pin 11 lowers, the overflowed material OF that has escaped into the hollow space is backfilled into the press-fit region of the shoulder 12 as indicated by arrow b2.

[0028] Next, as shown in process P14 in FIG. 2 and step S5 in FIG. 3, a smoothing process is performed to smooth the overlapping portion 30. In this process, the controller C controls the lifting / lowering drive unit 22 and the shoulder drive unit 23 to rotate the lower end surfaces of the pin 11 and the shoulder 12 while positioning them lower than the upper plate surface 31A of the upper plate 31, thereby smoothing the spot-welded portion. As a result, an indent 4T shown in FIG. 4 is formed. Through the above process, a stir welded portion 4 is formed, where the upper plate 31 and the lower plate 32 are welded. The stir welded portion 4 corresponds to the welded portion in the present disclosure.

[0029] [Structure of Joint] The stir welded portion 4 of the joint 3 formed by the above-described friction stir spot welding has a joint bottom surface 4B, an anchor 4A, a hooking 4F, and an indent 4T as shown in FIG.

[0030] The weld bottom surface 4B is the interface between the upper plate 31 and the lower plate 32, which is formed at a position deeper than the lower plate surface 32A relative to the upper plate surface 31A when pressed against the shoulder 12. When viewed along the central axis R, the weld bottom surface 4B has a ring shape corresponding to the shoulder lower surface 12S of the shoulder 12. Note that this ring shape is not limited to two perfect circles, and may be an irregular shape depending on the conditions of the friction stir spot welding. In other words, the weld bottom surface 4B has a substantially ring shape in a plan view.

[0031] The anchor 4A is a raised portion formed by a portion of the lower plate 32 rising radially inward of the joint bottom surface 4B to a position higher than the lower plate surface 32A relative to the joint bottom surface 4B. The anchor 4A is formed when the overflow material OF overflows from the overlapping portion 30 into the hollow space of the shoulder 12 during the press-fitting step, and the upper end of the overflow material OF is crushed by the pin 11 during the backfilling step. The anchor 4A corresponds to the inner raised portion of the present disclosure.

[0032] The hooking 4F is a protrusion formed by a portion of the lower plate 32 protruding radially outward from the joining bottom surface 4B to a position higher than the lower plate surface 32A relative to the joining bottom surface 4B. As described above, in the press-fitting process, the overflow material OF of the lower plate 32 overflows into the hollow space of the shoulder 12, and the press-fitting of the shoulder 12 also pushes up a portion of the lower plate 32 radially outward from the shoulder 12, forming the hooking 4F. The hooking 4F corresponds to the outer protrusion in the present disclosure.

[0033] The indent 4T is positioned opposite the joint bottom surface 4B and the anchor 4A in the overlapping direction of the upper plate 31 and the lower plate 32, i.e., in the vertical direction, and corresponds to a recessed portion in which a part of the upper plate surface 31A of the upper plate 31 is recessed.

[0034] 5 is a schematic cross-sectional view showing the arrangement of the pin 11 and the shoulder 12 when forming an indent in the welded body 3 according to this embodiment. In this embodiment, after forming the weld bottom surface 4B, the shoulder 12 is rotated and retracted from the press-fit position. In the leveling process of process P14 in FIG. 2 and step S5 in FIG. 3, the controller C positions the pin lower surface 11S of the pin 11 and the shoulder lower surface 12S of the shoulder 12 closer to the upper plate back surface 31B than the upper plate front surface 31A, as shown in FIG. 5, thereby forming an indent 4T at any position in the stir welded portion 4. The shoulder lower surface 12S corresponds to the tip surface of the shoulder 12.

[0035] As described above, in this embodiment, the controller C of the friction stir spot welding apparatus M joins the upper plate 31 and the lower plate 32 while controlling the tool driving unit 2 so as to form an anchor 4A, a joining bottom surface 4B, a hooking 4F, and an indent 4T in the stir welding portion 4.

[0036] Referring again to Figure 4, the definitions of the characteristic values ​​of the stir welded portion 4 will be described. In the overlapping direction of the upper plate 31 and the lower plate 32, in other words, in the up-down direction, the thickness of the upper plate 31 is defined as the upper plate thickness T1, and the thickness of the lower plate 32 is defined as the lower plate thickness T2. The distance in the overlapping direction from the lower plate surface 32A to the top of the anchor 4A is defined as the anchor height A. The distance in the overlapping direction from the upper plate back surface 31B to the top of the hooking 4F is defined as the hooking height F.

[0037] In this embodiment, the stir welded portion 4, where the upper plate 31 and the lower plate 32 are joined, has a joint bottom surface 4B, an anchor 4A, a hooking 4F, and an indent 4T. The shoulder 12 forms the joint bottom surface 4B, so that a portion of the upper plate 31 is positioned to penetrate below the upper plate back surface 31B, i.e., the lower plate front surface 32A. Furthermore, on the radially inner side of the joint bottom surface 4B, a portion of the lower plate 32 is positioned to protrude above the upper plate back surface 31B as an anchor 4A. Furthermore, on the radially outer side of the joint bottom surface 4B, a portion of the lower plate 32 is positioned to protrude above the upper plate back surface 31B as a hooking 4F. As a result, the upper plate 31 and the lower plate 32 are interlocked, firmly joining the upper plate 31 and the lower plate 32 and increasing their strength.

[0038] In such a bonded assembly 3, sudden fracture may occur due to an excessive load or the like. FIG. 6 is a schematic cross-sectional view illustrating the fracture mode of the bonded assembly 3. A plug fracture occurs along the overlapping direction of the upper plate 31 and the lower plate 32, while an interfacial fracture occurs along the interface between the upper plate 31 and the lower plate 32. To further stabilize product quality, it is desirable to reduce interfacial fracture and facilitate plug fracture. In this case, the hook 4F can be efficiently formed, and a plug fracture can occur on the surface of the upper plate 31 or between the hook 4F and the hook 4F. However, the present inventors have newly discovered that although the hook 4F can be stably formed by significantly press-fitting the shoulder 12 into the lower plate 32, the load on the welding tool increases. Therefore, after extensive research into the shape of the welding tool, they have discovered a configuration and method that can stably form the hook 4F while reducing the load on the welding tool.

[0039] FIG. 7 is a schematic cross-sectional view showing the tip of the tool 1. Note that in FIG. 7, the tip of the tool 1 is shown facing upward. In this embodiment, the tip of the shoulder 12 has an outer peripheral tapered surface whose outer peripheral surface is tapered. Here, as shown in FIG. 7, the outer peripheral taper angle, which is the angle between a line perpendicular to the central axis R and the outer peripheral tapered surface in a cross section including the central axis R, is set to 30 degrees or more. Note that the tapered shape means that the outer diameter of the shoulder 12 becomes relatively smaller toward the tip. In this case, there may be a portion having the same outer diameter in a predetermined region in the axial direction.

[0040] The tip portion of the shoulder 12 further includes a ring-shaped tip plane that is included in a plane perpendicular to the central axis R and is connected to the outer peripheral tapered surface, and an inner peripheral tapered surface that is inclined from the central axis R toward the tip plane on the inner peripheral side of the tip plane. The tip plane corresponds to the tip surface in this disclosure. If the difference between the distance from a reference intersection point CP, which is the intersection point between the tip plane and the inner peripheral tapered surface in a cross section including the central axis R, to the central axis R and the outer diameter of the shoulder 12 is defined as a taper tip distance, the ratio of the taper tip distance to the thickness of the shoulder 12 is set to 34% or more. Hereinafter, the taper tip distance will be indicated by this ratio and may also be referred to as the taper tip position.

[0041] In addition, in a cross section including the central axis R as shown in Fig. 7, the angle formed by a line perpendicular to the central axis R and the inner tapered surface is defined as the inner taper angle. In Fig. 7, the width of the tip plane is defined as the tip plane width.

[0042] When using the friction stir spot welding apparatus M according to this embodiment, if the height of the outer peripheral tapered surface in the axial direction of the central axis R is set to the tapered height as shown in Figure 7, when forming the joining bottom surface 4B, it is desirable to set the amount of depression by which the outer peripheral tapered surface is depressed to a position deeper than the lower plate surface 32A to no more than three times the tapered height.

[0043] Furthermore, in this embodiment, as an example, the upper plate 31 and the lower plate 32 are each used such that the melting point of the upper plate 31 is lower than the melting point of the lower plate 32. In this case, a portion of the lower plate 32 can be inserted higher into the upper plate 31, which has a relatively low melting point, by friction stir spot welding, and therefore the anchor 4A and the hooking 4F can be formed more stably.

[0044] Next, the welded body, the friction stir spot welding method, and the friction stir spot welding apparatus according to the present disclosure will be described in further detail using examples. Note that the present disclosure is not limited to these examples. Table 1 shows the shapes of 10 different types of tools 1 used in this experiment.

[0045]

[0046] In Table 1, the column marked with "No." indicates the name of each tool 1, and the outer circumferential taper angle and taper tip distance of that tool 1 are written in parentheses after the tool number. Furthermore, the shoulder diameter, pin diameter, taper height, taper tip distance, outer circumferential taper angle, inner circumferential taper angle, and tip flat width are listed in this order, centered on the central axis R. In the following explanation, the name of each tool 1 will be indicated only by the tool number.

[0047] Tables 2 and 3 show the shape evaluation results of the stir welded portion 4 of the welded body 3 formed when friction stir spot welding was performed using the 10 types of tools 1 in Table 1. As shown in Tables 2 and 3, multiple sets of data were obtained for the same tool 1. Each table shows the plunge amount, hooking height, anchor height, and plunge amount-taper height of the shoulder 12 of the tool 1.

[0048]

[0049]

[0050] In this experiment, a 6000 series aluminum alloy was used as the upper plate 31, and 1.5 GPa-class hot stamp steel plated with Al—Si was used as the lower plate 32. The thickness of the upper plate 31 was 1.1 mm, and the thickness of the lower plate 32 was 1.4 mm.

[0051] Figure 8 is a cross-sectional view of a bonded body 3 formed using tool 1 No. 1 in Table 1, and an enlarged cross-sectional view thereof. Figure 9 is a cross-sectional view of a bonded body 3 formed using tool 1 No. 9 in Table 1, and an enlarged cross-sectional view thereof. As shown in Figure 8, with tool 1 No. 1, the hooking height was 0 and the anchor height was 0.53 mm. On the other hand, with tool 1 No. 9, the hooking height was 0.23 mm and the anchor height was 0.27 mm, confirming that hooking 4F was stably formed.

[0052] FIG. 10 is a graph showing the relationship between the difference between the tool plunge amount and the taper height and the hooking height, based on the results of Tables 2 and 3. Here, the reason why the difference between the tool plunge amount and the taper height is used on the horizontal axis of FIG. 10 will be explained. To minimize the load on the tool 1, it is desirable to reduce the plunge amount of the tool 1. Therefore, by using the degree to which the outer peripheral tapered surface formed at the tip of the shoulder 12 is pressed into the lower plate 32 as the characteristic value on the horizontal axis, the plunge amount of the shoulder 12 and the degree of formation of the hooking 4F can be evaluated. In other words, when the horizontal axis in FIG. 10 is 0, it means that the base end of the outer peripheral tapered surface is positioned at the same position as the lower plate surface 32A of the lower plate 32, and the outer peripheral tapered surface is pressed into the lower plate 32.

[0053] Referring to Figure 10, it is desirable to increase the hook height when the tool plunge amount minus the taper height is small. In this experiment, when the hooking was low, especially in the region near 0 mm, the hook 4F was difficult to form, it was evaluated as "inappropriate dimensions." When a hook 4F with a height of 0.1 mm or more but less than 0.2 mm was formed with a similarly small plunge amount, it was evaluated as "effective." When a hook 4F with a height of 0.2 mm or more but less than 0.3 mm was formed with a similarly small plunge amount, it was evaluated as "more preferable." As a result, as shown in Figure 10, it was newly discovered that the height of the hook 4F varies depending on the shape of the taper formed at the tip of the shoulder 12. In Table 1 above, Nos. 1 to 4 correspond to "inappropriate dimensions," Nos. 5 to 7 correspond to "effectiveness," and Nos. 8 to 10 correspond to "more preferable."

[0054] In particular, the "effect" is achieved when the outer peripheral taper angle is 30 degrees or more. Furthermore, from Table 1, it can be said that the "effect" is also achieved when the taper tip distance is 34% or more. Furthermore, when the outer peripheral taper angle is 37.6 degrees or more and the taper tip distance is 20% or less, the evaluation is stably "more preferable." Furthermore, when the outer peripheral taper angle is 30 degrees or more and the taper tip distance is 22% or more, the evaluation is stably "more preferable." Note that, from the viewpoint of suppressing adhesion, it is desirable to set the upper limit of the outer peripheral taper angle to less than 45 degrees. As described above, the range of the taper tip distance is not necessarily a required configuration, but it has been found that a more stable effect can be obtained by setting the distance within a predetermined range.

[0055] Like FIG. 10 , FIG. 11 is a graph showing the relationship between the difference between the tool plunge amount and the taper height and the hooking height, and shows the intersection of the regression lines under each condition. The three regression lines shown in FIGS. 10 and 11 are obtained by individually regressing the data groups Nos. 1 to 4, Nos. 5 to 7, and Nos. 8 to 10 in Table 1. Here, the regression lines for Nos. 5 to 7 and Nos. 8 to 10 intersect near 0.27 on the horizontal axis. In other words, the significant difference between the two lines decreases in the region above 0.27 on the horizontal axis. Therefore, to effectively realize the effects of the tapered shape, it is desirable to use the tapered shape in a range of 0.27 or less on the horizontal axis. Similarly, the regression lines for Nos. 1 to 4 and Nos. 5 to 7 intersect near 0.23 on the horizontal axis. Therefore, to effectively realize the effects of the tapered shape, the tapered shape may be used in a range of 0.23 or less on the horizontal axis.

[0056] Furthermore, the present inventors conducted extensive experiments and found that the regression lines intersect in the region where the tool plunge amount - taper height is 0.25 mm or more and 0.30 mm or less, particularly around 0.285 mm. Here, this region corresponds to 5.7 times the taper height when the taper height is 0.05 mm, 2.85 times the taper height when the taper height is 0.10 mm, 1.9 times the taper height when the taper height is 0.15 mm, and 1.425 times the taper height when the taper height is 0.20 mm. As a result, it was newly confirmed that it is desirable to set the taper height to approximately 0.10 mm and set the plunge amount of the tool 1 to 3 times or less the taper height. In this case, as the tapered portion is plunged, a portion of the lower plate 32 smoothly flows radially outward, enabling the stable formation of the hooking 4F.

[0057] Here, we will add a note on the relationship between the tapered shape and the hooking height. In Figure 7, the outer peripheral tapered surface formed at the tip of the shoulder 12 satisfies certain conditions, allowing a portion of the lower plate 32 to be pushed radially outward as the shoulder 12 is pressed into place. As a result, the hooking 4F can be efficiently formed. Furthermore, when the inner peripheral tapered surface is formed, a portion of the lower plate 32 is split into the radially inward and radially outward flows, thereby promoting each flow. Considering the case where a tip flat surface exists between the outer peripheral tapered surface and the inner peripheral tapered surface, the radially inner portion of the shoulder 12 has a limited volume capable of accommodating the material of the lower plate 32, while the radially outer portion of the shoulder 12 has a relatively large volume capable of accommodating the material of the lower plate 32, making it easier for the lower plate 32 to flow. Therefore, since the tip flat surface can function as part of the outer peripheral tapered surface, it is inferred that the flow of material from the lower plate 32 is split mainly at the reference intersection CP. Therefore, as described above, by controlling the taper tip distance in FIG. 7, the amount of press-fitting of the shoulder 12 can be kept small, and the hooking 4F can be formed efficiently.

[0058] 12 is a graph showing the relationship between the taper tip position and the outer peripheral taper angle, and shows the latitude indicating the region where the effect is manifested and the more preferable region. Based on the above experiment, as shown in FIG. 12, when the outer peripheral taper angle of the shoulder 12 is 30 degrees or more, the effect of effectively forming the hook 4F with a small plunge amount can be manifested. Furthermore, when the outer peripheral taper angle is 37 degrees or more and the taper tip distance is 20% or less, more preferable results can be obtained.

[0059] Fig. 13 is a graph showing the relationship between the anchor height and the difference between the tool plunge amount and the taper height. As shown in Fig. 13, the shapes of each tool 1 in Table 1 have no correlation with the anchor height, and it can be confirmed that the anchor height increases as the plunge amount increases.

[0060] Figure 14 is a graph showing the relationship between the type of steel and the hooking height. Table 4 shows the data corresponding to the graph in Figure 14.

[0061]

[0062] In the experiments shown in Table 4 and Fig. 14, a 1.1 mm thick 6000 series aluminum alloy was used as the upper plate 31, while various steel plates each having a thickness of 1.2 mm were used as the lower plate 32. Specifically, three types of steel plates were used: 590 MPa-class unplated steel, 980 MPa-class unplated steel, and 1180 MPa-class unplated steel. In all experiments, the shape of the tip of the shoulder 12 corresponded to No. 7 in Table 1.

[0063] The results of this experiment confirmed that, regardless of the type of steel sheet, the hooking 4F can be stably formed while suppressing the amount of depression by providing the shoulder 12 with the aforementioned tapered shape. It was also confirmed that the presence or absence of a plating layer on the sheet material used does not adversely affect the effect.

[0064] 15 is a graph showing the relationship between the difference between the tool plunge amount and the taper height and the hooking height. Table 5 shows the data corresponding to the graph in FIG.

[0065]

[0066] In the experiments shown in Table 5 and Fig. 15, a 1.1 mm thick 6000 series aluminum alloy was used as the upper plate 31, while a 1.2 mm thick 1180 MPa class unplated steel was used as the lower plate 32. In this experiment, the shape of the tip of the shoulder 12 also corresponds to No. 7 in Table 1. The depression amount of the shoulder 12 into the lower plate 32 was set to three levels: 0.20 mm, 0.23 mm, and 0.34 mm.

[0067] In addition to the experiment shown in Table 4 and FIG. 14 , the results of this experiment confirmed that, for the same 1180 MPa-class unplated steel, even if the depression amount of the shoulder 12 is changed, the hooking 4F can be stably formed in the same manner.

[0068] The present inventors have also confirmed the effects of the above experiments under the following conditions: Plate thickness of the upper plate 31 and the lower plate 32: 0.5 mm or more and 5 mm or less, more preferably 1 mm or more and 3 mm or less Tool rotation speed: 500 rpm or more and 3000 rpm or less, more preferably 1000 rpm or more and 2000 rpm or less Although the friction stir spot welding method and friction stir spot welding apparatus M according to the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. For example, the above-described welded body 3 and the like can be modified as follows.

[0069] In the above description, the upper plate 31 and the lower plate 32 are each described as being made of a single plate material, but the present disclosure is not limited to this. At least one of the upper plate 31 and the lower plate 32 may be made of multiple members arranged to overlap in the overlapping direction. The multiple members may be connected with an adhesive or the like. Even with such a configuration, the upper plate 31 and the lower plate 32 can be firmly bonded, the occurrence of interfacial fracture can be reduced, and even if fracture does occur, plug fracture can be more likely to occur.

[0070] 7, the inner circumferential tapered surface and the tip flat surface are not essential components. Furthermore, the tip flat surface does not necessarily have to be flat. In this case, it is sufficient if a portion of the tip surface is included in a plane perpendicular to the central axis R.

[0071] [Summary of the Disclosure] The specific embodiments described above include disclosures having the following configurations.

[0072] A friction stir spot welding apparatus according to a first aspect of the present disclosure joins a first member having a first front surface and a first back surface and a second member having a second front surface and a second back surface, each made of metal, by softening them with frictional heat. The friction stir spot welding apparatus includes a joining tool including a pin having a central axis and a cylindrical shoulder having a hollow portion into which the pin is inserted, a rotation mechanism capable of rotating the joining tool about the central axis, and a movement mechanism capable of independently moving the pin and the shoulder in a direction extending along the central axis. The tip of the shoulder has an outer peripheral tapered surface inclined toward the tip, and the outer peripheral taper angle, which is the angle between the outer peripheral tapered surface and a line perpendicular to the central axis in a cross section including the central axis, is set to be 30 degrees or greater.

[0073] A friction stir spot welding apparatus according to a second aspect of the present disclosure is the friction stir spot welding apparatus according to the first aspect described above, wherein the tip of the shoulder further has a ring-shaped tip surface that is included in a plane perpendicular to the central axis and is connected to the outer peripheral tapered surface, and an inner peripheral tapered surface that is inclined from the central axis side toward the tip surface on the inner peripheral side of the tip surface, and when the difference between the distance from the intersection of the tip surface and the inner peripheral tapered surface in a cross section including the central axis to the central axis and the outer diameter of the shoulder is defined as a taper tip distance, the ratio of the taper tip distance to the thickness of the shoulder is set to 34% or more.

[0074] A friction stir spot joining method according to a third aspect of the present disclosure is a method for joining a first member having a first front surface and a first back surface and a second member having a second front surface and a second back surface, each made of metal, by softening them with frictional heat. The friction stir spot welding method includes: preparing a joining tool including a pin having a central axis and a cylindrical shoulder having a hollow portion into which the pin is inserted, wherein a tip portion of the shoulder has an outer peripheral tapered surface where the outer peripheral surface of the shoulder is tapered, and an outer peripheral taper angle, which is an angle between a line perpendicular to the central axis and the outer peripheral tapered surface in a cross section including the central axis, is set to 30 degrees or more; forming an overlapping portion where the first member and the second member overlap each other by abutting at least a portion of the second front surface against the first back surface; retracting the pin from the first front surface and pressing the shoulder into the overlapping portion so that at least a portion of the outer peripheral tapered surface penetrates to a position deeper than the second front surface, thereby forming a joint bottom surface which is an interface between the first member and the second member; and after forming the joint bottom surface, retracting the shoulder and inserting the pin into the overlapping portion.

[0075] A friction stir spot welding method according to a fourth aspect of the present disclosure is the friction stir spot welding method according to the third aspect described above, further comprising preparing, as the joining tool, a tool in which a tip portion of the shoulder is included in a plane perpendicular to the central axis and further has a ring-shaped tip surface connected to the outer peripheral tapered surface, and an inner peripheral tapered surface on the inner peripheral side of the tip surface that is inclined from the central axis side toward the tip surface, and wherein, when the difference between the distance from the intersection of the tip surface and the inner peripheral tapered surface in a cross section including the central axis to the central axis and the outer diameter of the shoulder is defined as a taper tip distance, the ratio of the taper tip distance to the thickness of the shoulder is set to 34% or more.

[0076] A friction stir spot welding method according to a fifth aspect of the present disclosure is the friction stir spot welding method according to the third or fourth aspect, further comprising: when forming the weld bottom surface, setting the amount of depression by which the outer peripheral tapered surface is depressed to a position deeper than the second surface to be no more than three times the taper height, where the height of the outer peripheral tapered surface in the axial direction of the central axis is defined as the taper height.

Claims

1. A friction stir spot welding device that joins a first member and a second member, each made of metal and having a first front and a first back surface, and a second member and having a second front and a second back surface, by softening them with frictional heat, comprising: a joining tool including a pin having a central axis and a cylindrical shoulder having a hollow portion into which the pin is inserted; a rotation mechanism capable of rotating the joining tool around the central axis; and a movement mechanism capable of independently moving the pin and the shoulder in the direction of extension of the central axis, wherein the tip of the shoulder has an outer peripheral tapered surface in which the outer peripheral surface of the shoulder is tapered, and the outer peripheral taper angle, which is the angle between the outer peripheral tapered surface and a straight line perpendicular to the central axis in a cross section including the central axis, is set to be 30 degrees or more.

2. A friction stir spot welding device according to claim 1, wherein the tip of the shoulder further comprises: a ring-shaped tip surface that is included in a plane perpendicular to the central axis and is connected to the outer peripheral tapered surface; and an inner peripheral tapered surface that is inclined from the central axis side towards the tip surface on the inner peripheral side of the tip surface, and wherein, when the difference between the distance from the intersection of the tip surface and the inner peripheral tapered surface in a cross section including the central axis to the central axis and the outer diameter of the shoulder is defined as the taper tip distance, the ratio of the taper tip distance to the thickness of the shoulder is set to 34% or more.

3. A friction stir spot welding method for joining a first member and a second member, each made of metal and having a first front surface and a first back surface, and a second member and having a second front surface and a second back surface, by softening them with frictional heat, comprising: preparing a joining tool including a pin having a central axis and a cylindrical shoulder having a hollow portion into which the pin is inserted, the tip of the shoulder having an outer peripheral tapered surface where the outer peripheral surface of the shoulder is tapered, and the outer peripheral taper angle, which is the angle between a line perpendicular to the central axis and the outer peripheral tapered surface in a cross section including the central axis, is set to 30 degrees or more; at least a portion of the second front surface abuts the first back surface, forming an overlapping portion where the first member and the second member overlap; with the pin retracted from the first front surface, press-fitting the shoulder into the overlapping portion, causing at least a portion of the outer peripheral tapered surface to penetrate deeper than the second front surface, to form a weld bottom surface which is the interface between the first member and the second member; After forming the weld bottom surface, the shoulder is retracted and the pin is inserted into the overlapping portion.

4. A friction stir spot welding method as claimed in claim 3, further comprising preparing the joining tool, wherein the tip of the shoulder is included in a plane perpendicular to the central axis and further comprises: a ring-shaped tip surface connected to the outer peripheral tapered surface; and an inner peripheral tapered surface on the inner peripheral side of the tip surface that is inclined from the central axis side towards the tip surface, and wherein, when the taper tip distance is defined as the difference between the distance from the intersection of the tip surface and the inner peripheral tapered surface in a cross section including the central axis to the central axis and the outer diameter of the shoulder, the ratio of the taper tip distance to the thickness of the shoulder is set to 34% or more.

5. A friction stir spot welding method according to claim 3 or 4, further comprising: setting the amount of pressing, when forming the weld bottom surface, by which the outer peripheral tapered surface is pressed to a position deeper than the second surface to no more than three times the taper height, where the height of the outer peripheral tapered surface in the axial direction of the central axis is the taper height.

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