Friction stir spot welding method and friction stir spot welding device

Abstract

This friction stir spot welding device (M) performs friction stir welding on an upper plate (31) and a lower plate (32). In a state in which a pin (11) has been retracted relative to an upper plate surface (31A), a controller (C) uses a first pressure to press a shoulder (12) from the upper plate surface (31A) until the shoulder (12) reaches a predetermined reference position set in reference to a lower plate surface (32A), and then uses a second pressure to press the shoulder (12) from the reference position into a pressed-in position deeper than the lower plate surface (32A). The first pressure is set to be lower than the second pressure if the hardness of the upper plate (31) is lower than the hardness of the lower plate (32), and the first pressure is set to be greater than the second pressure if the hardness of the upper plate (31) is higher than the hardness of the lower plate (32).

Description

Friction stir spot welding method and friction stir spot welding device

[0001] The present disclosure relates to a friction stir spot welding method and a friction stir spot welding apparatus 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 probe is also referred to as a pin, and the inner shoulder member is also referred to as a shoulder. The outer shoulder member is also referred to as a clamp. The shoulder has a cylindrical shape that contains a cylindrical pin, and the clamp has a cylindrical shape that contains the shoulder. In this technique, the pin and shoulder 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 pin is then protruded from the shoulder and further pressed into the vicinity of the interface between the second and third members, 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 conventional friction stir spot welding methods such as that described in Patent Document 1, the metal members can be deformed in the planar direction when the rotary tool enters the metal members, and there is a problem that the ends of the joined body can be deformed, particularly when the spot welding location is located near the ends of the metal members.

[0006] An object of the present disclosure is to provide a friction stir spot welding method and a friction stir spot welding apparatus that are capable of suppressing deformation of a welded body around a spot welded portion.

[0007] A friction stir spot welding method according to one aspect of the present disclosure is a friction stir spot welding 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 friction stir spot welding apparatus including a pin and a cylindrical shoulder having a hollow portion into which the pin is inserted; positioning the first member and the second member so that at least a portion of the second front surface faces the first back surface and forms an overlapping portion where the first member and the second member overlap; positioning the pin and the shoulder opposite the overlapping portion; applying first and second pressures for pressing the shoulder, wherein the first pressure is smaller than the second pressure when the hardness of the first member is lower than the hardness of the second member; The method includes setting the first pressure and the second pressure so that the first pressure is greater than the second pressure when the hardness of the first member is greater than the hardness of the second member; pressing the shoulder with the first pressure from the first surface side until it reaches a predetermined reference position set with the second surface as a reference, while the pin is retracted from the overlapping portion; pressing the shoulder with the second pressure from the reference position to a press-in position deeper than the second surface; and retracting the shoulder from the press-in position and inserting the pin into the overlapping portion.

[0008] According to another aspect of the present disclosure, there is provided a friction stir spot welding apparatus 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 apparatus includes a joining tool including a pin and a cylindrical shoulder having a hollow portion into which the pin is inserted, a rotation mechanism capable of rotating the joining tool, a movement mechanism capable of independently moving the pin and the shoulder in a direction in which the pin extends, and a control unit that controls the rotation mechanism and the movement mechanism. The control unit sets a first pressure and a second pressure for press-fitting the shoulder, the first pressure being smaller than the second pressure when the hardness of the first member is lower than the hardness of the second member, and the first pressure being larger than the second pressure when the hardness of the first member is higher than the hardness of the second member; and the first member and the second member are arranged such that at least a part of the second front surface faces the first back surface and an overlapping portion is formed where the first member and the second member overlap. and with the pin and the shoulder positioned opposite the overlapping portion, the pin is retracted from the overlapping portion, the shoulder is pressed in from the first surface side with the first pressure until it reaches a predetermined reference position set with the second surface as a reference, and the shoulder is further pressed in with the second pressure from the reference position to a press-in position deeper than the second surface, and then the rotation mechanism and the movement mechanism are controlled so as to retract the shoulder from the press-in position and cause the pin to enter 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 for explaining a welded portion of a welded body. FIG. 5A is a diagram for explaining a portion of the shoulder-first process in a friction stir spot welding method according to an embodiment of the present disclosure. FIG. 5B is a diagram for explaining a portion of the shoulder-first process in a friction stir spot welding method according to an embodiment of the present disclosure. FIG. 6 is a graph showing the transition of the shoulder depression amount and the deformation amount of a plate edge, for explaining a friction stir spot welding method according to an embodiment of the present disclosure. FIG. 7 is a graph showing the relationship between the indent amount and the TSS, for explaining an example of a friction stir spot welding method according to the present disclosure. FIG. 8 is a graph showing the relationship between the distance from the plate edge to the outer periphery of the shoulder and the deformation amount of the edge, for explaining an example of a friction stir spot welding method according to the present disclosure. FIG. 9 is a graph showing the relationship between the reference position and the end deformation amount, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 10 is a graph showing the relationship between the P1 / P2 pressure ratio and the end deformation amount, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 11 is a graph showing the relationship between the plate combination of the upper plate and the lower plate and the end deformation amount, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 12A is a perspective view showing types of plate combinations, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 12B is a perspective view showing types of plate combinations, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 12C is a perspective view showing types of plate combinations, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 13 is a graph showing the relationship between the presence or absence of adhesive application and the indent amount, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 14 is a graph showing the relationship between the presence or absence of adhesive application and the TSS, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 15 is a graph showing the relationship between the presence or absence of adhesive application and CTS, for explaining an example of the friction stir spot welding method according to the present disclosure.FIG. 16 is a graph showing the relationship between the distance from the plate end to the outer periphery of the shoulder and the amount of end deformation, for explaining an example of the friction stir spot welding method according to the present disclosure. FIG. 17A is a schematic diagram of a welded body, for explaining a friction stir spot welding method according to a modified embodiment of the present disclosure. FIG. 17B is a schematic diagram of a welded body, for explaining a friction stir spot welding method according to a modified embodiment of the present disclosure. FIG. 18 is a perspective view showing the state in which the end of a plate material is deformed in another friction stir spot welding method compared to the friction stir spot welding method according to the present disclosure. FIG. 19 is a photographic image showing the state in which the end of a plate material is deformed in another friction stir spot welding method compared to the friction stir spot welding method according to the present disclosure. FIG. 20 is a graph showing the progress of the shoulder indentation amount and the amount of deformation of the plate end in another friction stir spot welding method compared to the friction stir spot welding method according to the present disclosure.

[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] FIG. 1 is a schematic diagram showing the configuration of a friction stir spot welding apparatus M according to one embodiment of the present disclosure.

[0012] 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 tool 1 for friction stir spot welding, a tool drive unit 2 that drives the tool 1 to rotate and move up and down, and a controller C that controls the operation of the tool drive unit 2. Note that although the directions "up" and "down" are indicated in Fig. 1 for the convenience of explanation, this is not intended to limit the actual direction in which the tool 1 is used.

[0013] 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.

[0014] 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 as a rotation axis R, and is also movable up and down, i.e., forward and backward, along the rotation axis R. When the tool 1 is in use, the rotation 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.

[0015] 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 rotation axis R. The shoulder 12 rotates around the rotation axis R and moves up and down along the rotation axis R, that is, moves forward and backward.

[0016] The shoulder 12 and the pin 11 inserted in the hollow portion rotate together around the rotation axis R, while moving relatively in the direction of the rotation axis R. That is, the pin 11 and the shoulder 12 not only move up and down simultaneously along the rotation axis R, but also can move independently, with one moving down and the other moving up.

[0017] 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 rotation axis R. The clamp 13 does not rotate around its axis, but moves up and down along the rotation 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 stir material from scattering, and enables the friction stir spot welded portion to be finished smoothly.

[0018] 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.

[0019] 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 rotation axis R. The rotation driving unit 21 corresponds to the rotation mechanism of the present disclosure. The elevation driving unit 22 is a mechanism that moves the pin 11, the shoulder 12, and the clamp 13 forward and backward, i.e., raises and lowers, along the rotation axis R. The elevation driving unit 22 drives the pin 11 to press-fit 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 rotation 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.

[0020] 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.

[0021] 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 . The upper plate 31 corresponds to the first member of the present disclosure. 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 surface 31A corresponds to the first surface of the present disclosure, and the upper plate back surface 31B corresponds to the first back surface of the present disclosure. As an example, the upper plate 31 is an aluminum alloy. The upper plate 31 may be a wrought material or a cast metal. The upper plate 31 may also be subjected to chemical conversion treatment, electro-deposition coating, or the like.

[0022] 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. The lower plate 32 may also be made of aluminum alloy, mild steel, or hot-stamp steel. The lower plate 32 may also be subjected to a non-plated treatment, a zinc-plated treatment, an Al-Si-plated 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, and the hardness of the upper plate 31 is set lower than the hardness of the lower plate 32.

[0023] [Method of Using the Tool] Next, a method of using the tool 1 exemplified in this embodiment, i.e., a friction stir spot welding method, will be described. Methods of using the friction stir spot welding apparatus M can be roughly divided 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.

[0024] Fig. 2 shows processes P11 to P15 of the friction stir spot welding method using the shoulder-first process. Fig. 3 shows a process chart of the friction stir spot welding method according to this embodiment. Fig. 3 shows a simplified process for friction stir spot welding an overlapping portion 30 between an upper plate 31 and a lower plate 32.

[0025] 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 lower plate surface 32A abuts against a lower plate back surface 31B, and the upper plate 31 and the lower plate 32 are arranged to overlap each other.

[0026] Next, as shown in 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 rotation 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 rotation axis R of the tool 1 is inclined relative to the vertical direction. In this embodiment, with the rotation 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. At this time, the clamp 13 presses the overlapping portion 30 against the backup 15 with the biasing force of the spring 14, as shown in process P11 of FIG. 2 . With the lower end surface of the tool 1 abutting against the upper plate surface 31A of the upper plate 31 in this manner, the controller C controls the rotation drive unit 21 to rotate the pin 11 and the shoulder 12 at a predetermined number of rotations around the rotation axis R. 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.

[0027] Next, as shown in process P12 of FIG. 2 and step S3 of FIG. 3 , a press-fitting process is performed in which the pin 11 retracts from the overlapping portion 30 and the shoulder 12 is press-fitted into the overlapping portion 30. In this process, the controller C controls the elevation drive unit 22 to lower the shoulder 12 and press-fit it into the overlapping portion 30 as shown in process P12 of FIG. 2 while maintaining the rotation of the tool 1, while raising, or retracting, the pin 11. Note that the clamp 13 remains stationary. The shoulder 12 is press-fitted into the overlapping portion 30 from the upper plate surface 31A to a press-fit position deeper than the lower plate surface 32A. This operation also agitates the material in the press-fit region of the shoulder 12, as shown 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 4B shown in Fig. 4, which will be described in detail later, is formed. In the press-fitting step, a pressure force along the axial direction, i.e., a total pressure force, is applied to the entire pin 11, shoulder 12, and clamp 13. Meanwhile, a clamp pressure force is applied to the clamp 13 by the spring 14, pressing the clamp 13 toward the backup 15. As a result, the press-fitting pressure force with which the tool 1 is pressed toward the joined bodies 3 corresponds to a force obtained by subtracting the clamp pressure force from the total pressure force.

[0028] Next, as shown in process P13 in Fig. 2 and step S4 in Fig. 3, while maintaining the rotation of the tool 1, the controller C controls the lifting drive unit 22 to retract the shoulder 12 from the press-fit position and lower the pin 11 so that it enters the overlapping portion 30. This step represents a backfilling step of the overflowed material OF. In this step, the controller C controls the lifting drive unit 22 to lift the shoulder 12 and lower the pin 11.

[0029] As the pin 11 descends, the overflow material OF that has escaped into the hollow space is refilled into the press-fit area of ​​the shoulder 12, as shown by arrow b2.

[0030] Next, as shown in process P14 of FIG. 2 and step S5 of FIG. 3, a smoothing process is performed to smooth the overlapping portion 30. In this process, the controller C controls the lifting drive unit 22 to rotate the lower end surfaces of the pin 11 and the shoulder 12 while positioning them slightly lower than the upper plate surface 31A of the upper plate 31, thereby smoothing the spot welded portion. As a result, an indent 4T (see FIG. 4, which will be described in detail later) is formed. Thereafter, as shown in process P15 of FIG. 2 and step S6 of FIG. 3, the tool 1 is separated from the overlapping portion 30. Through the above process, a stir welded portion 4 is formed in which the upper plate 31 and the lower plate 32 are welded, as shown in FIG. 1. The stir welded portion 4 corresponds to the welded portion in this disclosure.

[0031] [Cross-sectional structure of the welded body] Figure 4 is a schematic cross-sectional view illustrating a stir-friction welded portion 4 of a welded body 3 formed by the above-described friction stir spot welding method. The stir-friction welded portion 4 has a weld bottom surface 4A, an anchor 4B, and an indent 4T. Note that Figure 4 shows the plate thicknesses T1 and T2 of the upper plate 31 and the lower plate 32.

[0032] The weld bottom surface 4A 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 rotation axis R, the weld bottom surface 4A has a ring shape corresponding to the shoulder lower surface portion 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 4A has a substantially ring shape in a plan view.

[0033] The anchor 4B is a raised portion formed by a part of the lower plate 32 rising radially inward of the joint bottom surface 4A to a position higher than the lower plate surface 32A with respect to the joint bottom surface 4A. The anchor 4B 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.

[0034] The indent 4T is disposed opposite the joint bottom surface 4A and the anchor 4B 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 the upper plate surface 31A of the upper plate 31. As described above, the indent 4T can be actively formed in the leveling process by rotating the lower end surface of the pin 11 and the lower end surface of the shoulder 12 while positioning them lower than the upper plate surface 31A of the upper plate 31. In the leveling process, the lower end surface of the pin 11 and the lower end surface of the shoulder 12 may be positioned flush with the upper plate surface 31A of the upper plate 31.

[0035] [Regarding Deformation of Plate Ends] Figures 18 and 19 are perspective views and photographs showing deformation of plate ends in another friction stir spot welding method compared to the friction stir spot welding method of this embodiment. Figure 19 is an image of the stir weld 4 of the joint 3 viewed from above along the rotation axis R, similar to Figure 1 . The present inventors have newly discovered that a portion of the plate may deform in the planar direction around the stir weld 4 formed by the friction stir spot welding method. In particular, as shown in Figures 18 and 19 , when the end 31T of the upper plate 31 forms an overlapping portion 30 along the end 32T of the lower plate 32, and the stir weld 4 is formed close to the ends 31T and 32T, a portion of the joint 3 protrudes outward. Such deformation may impose limitations on the size of the objects that can be joined, such as flange width, and may affect the strength of the joint formed by the stir weld 4.

[0036] Therefore, the present inventors conducted extensive experiments and verifications and discovered that the above-mentioned deformation occurs during the press-fitting process of the shoulder 12. Specifically, Fig. 20 is a graph showing the progress of the shoulder press-in amount and the deformation amount of the plate end in another friction stir spot welding method compared to the friction stir spot welding method according to the present disclosure. Table 1 shows the experimental data corresponding to the graph in Fig. 20. Note that the data numbers in the following tables are assigned for the purpose of organizing the data in each table, and do not mean that data assigned the same numbers in different tables are the same data.

[0037]

[0038] In Figure 20, the horizontal axis represents welding time, the left vertical axis represents the shoulder indentation depth, and the right vertical axis represents the end deformation of the sheet material shown in Figure 19. The solid line represents the shoulder indentation depth, and the dashed line represents the end deformation. The zero point on the left vertical axis corresponds to the upper plate surface 31A of the upper plate 31. In this other friction stir spot welding method, the upper plate 31 is a 6000-series aluminum alloy with a thickness of 1.1 mm, and the lower plate 32 is a 1.2 GPa-class steel plate with a thickness of 1.2 mm. The pressure applied by the shoulder 12, i.e., the pressure applied by the tool 1 shown in Figure 1 to the welded body 3, is kept constant, e.g., 7.7 kN, until the predetermined press-fit position is reached. The press-fit position is set 0.15 mm deeper than the boundary between the upper plate rear surface 31B and the lower plate surface 32A. The outer diameter of the shoulder 12 is 5.5 mm, and the outer diameter of the pin 11 is 3.35 mm. The rotation speed is set to 1500 rpm. The distance L between the spot joining position and the end of the upper plate 31 is 3 mm. Table 1 and FIG. 20 are based on a so-called stop action test, and combine the results of visually measuring the end shape of the joined body 3 by stopping the press-fitting of the shoulder 12 at each data position.

[0039] In Table 1, "tool target press-fit depth" refers to the final target press-fit depth of the shoulder 12, based on the lower plate surface 32A of the lower plate 32. The "clamp" pressure input condition is an input condition corresponding to the press force (kN) of the clamp 13, and "ST2-1" and "ST2-2" are input conditions corresponding to the press force applied to the shoulder 12. In the examples described below, "ST2-1" and "ST2-2" are varied, but in this experiment, "ST2-1" and "ST2-2" are constant. As described above, the press-fit pressure of the shoulder 12 against the welded body 3 can be calculated as the difference between the press forces of "ST2-1" and "ST2-2" and "clamp." In Table 1, "end distance" corresponds to the distance L described below, and "tool taper presence / absence" indicates whether the tips of the pin 11 and shoulder 12 are tapered.

[0040] Table 1 also shows information about the target stop position of the shoulder 12 as the "press-in process stop position" and the "backfilling process stop position" (unit: mm). The "press-in process stop position" shown in each data is the stop position during the pressing process, and the "backfilling process stop position" shown in Data 7 and 8 corresponds to the position where the shoulder 12 stopped during backfilling after advancing to the maximum pressing position. Note that both are expressed as distances based on the surface of the upper plate 31. For example, in the case of Data 7, after the shoulder 12 advanced to the maximum pressing amount of 1.21 mm, the test was stopped at a position 0.5 mm from the interface between the upper plate 31 and the lower plate 32 and 0.6 mm from the surface of the upper plate 31.

[0041] 20, it can be seen that after the shoulder 12 is press-fitted from the upper plate surface 31A of the upper plate 31 to the lower plate surface 32A of the lower plate 32, indicated by the dashed line, the amount of deformation at the end increases linearly. Then, after the shoulder 12 comes into contact with the lower plate 32 made of a steel plate, the deformation at the end is limited. From this, the present inventors have inferred that the cause of the deformation at the end is the application of excessive pressure to the upper plate 31 made of a relatively soft aluminum alloy, and have come up with a new idea to improve the above-mentioned press-fitting process.

[0042] [Regarding variable pressure control] Figures 5A and 5B are diagrams for explaining a part of the shoulder-first process in the friction stir spot welding method according to this embodiment. Figure 6 is a graph showing the transition of the shoulder indentation amount and the deformation amount of the plate end, for explaining the friction stir spot welding method according to this embodiment. Table 2 shows the experimental data corresponding to the graph in Figure 6. The meaning of each parameter shown in Table 2 is the same as that in Table 1.

[0043]

[0044] In this embodiment, the press-fitting process of process P12 in FIG. 2 and step S3 in FIG. 3 includes two steps. Specifically, in a first step, process P12A shown in FIG. 5A, the shoulder 12 is pressed into a predetermined reference position at a first pressure. As an example, the reference position is the interface between the upper plate rear surface 31B of the upper plate 31 and the lower plate front surface 32A of the lower plate 32 before press-fitting. Thereafter, in process P12B shown in FIG. 5B, the shoulder 12 is pressed into a predetermined press-fit position at a second pressure. Note that the pressure change from the first pressure to the second pressure and the press-fitting of the shoulder 12 are performed continuously. FIG. 6 is a graph corresponding to FIG. 20, showing the transition of the shoulder press-in amount and the deformation amount of the plate end at this time. In the experiment of Fig. 6 , as in Fig. 20 , the upper plate 31 is a 6000-series aluminum alloy having a thickness of 1.1 mm, and the lower plate 32 is a 1.2 GPa-class steel plate having a thickness of 1.2 mm. In this case, since the hardness of the upper plate 31 is lower than that of the lower plate 32, the first pressure is set to be smaller than the second pressure. As an example, the first pressure is 3 kN and the second pressure is 7.7 kN (see the pressure input conditions in Table 2). The other experimental conditions are the same as those in Fig. 20 .

[0045] As shown in Fig. 6, it was confirmed that the amount of deformation at the end portion was significantly reduced compared to Fig. 20 after the shoulder 12 was pressed into the upper plate surface 31A of the upper plate 31 with a relatively low pressing force until it reached the lower plate surface 32A of the lower plate 32 indicated by the dashed line. Even after the shoulder 12 contacted the lower plate 32 made of a steel plate, the deformation at the end portion remained small. Thus, it was found that by reducing the pressing load of the shoulder 12 in the lower hardness side of the upper plate 31, the flow of material as indicated by the solid arrow in process P12A in Fig. 5A was suppressed, and the deformation of the joined body 3 could be significantly suppressed. 5A and 5B, as an example, the overflowing material is filled up to the tip of the pin 11 when the shoulder 12 is pressed in. However, in order to facilitate the flow of material below the shoulder 12 in the backfilling step of process P13 in FIG. 2, the pin 11 may be raised so that the material does not come into contact with the tip of the pin 11 in FIGS. 5A and 5B.

[0046] Based on the above-described idea, the present inventors have discovered that it is possible to prevent deformation of the ends of the upper plate 31 and the lower plate 32 and the excessive occurrence of the indent 4T. Specifically, when the hardness of the upper plate 31 is lower than the hardness of the lower plate 32, the first pressure is set to be smaller than the second pressure, and when the hardness of the upper plate 31 is higher than the hardness of the lower plate 32, the first pressure is set to be larger than the second pressure.

[0047] 2, with the pin 11 retracted from the upper plate surface 31A, the shoulder 12 is pressed in from the upper plate surface 31A with a first pressure until it reaches a predetermined reference position set with the lower plate surface 32A as a reference.Furthermore, the shoulder 12 is pressed in from the reference position with a second pressure to a press-in position deeper than the lower plate surface 32A.

[0048] In this case, it is desirable to set the reference position within a range from the boundary between the upper plate rear surface 31B and the lower plate front surface 32A to 73% of the thickness of the member with the lower hardness among the upper plate 31 and the lower plate 32. The pressure may be switched on the side of the member with the higher hardness.

[0049] Furthermore, when the upper plate 31 has a lower hardness than the lower plate 32, it is desirable to set the first pressure and the second pressure so that P1 / P2<0.91, where P1 is the first pressure and P2 is the second pressure. It is more desirable to set the first pressure and the second pressure so that P1 / P2<0.7, and it is even more desirable to set the first pressure and the second pressure so that P1 / P2≦0.65.

[0050] Furthermore, when the cross-sectional area of ​​the pin 11 is P and the cross-sectional area of ​​the shoulder 12 is S, it is desirable to set the outer diameters of the pin 11 and the shoulder 12 so that S / P≦2.41.

[0051] It is further desirable to set the outer diameters of the pin 11 and the shoulder 12 so that S / P≦1.8.

[0052] In addition, the pin 11 and shoulder 12 may be positioned opposite the overlapping portion 30 so that the shortest distance L between the outer edge of the shoulder 12 and the end of the upper plate 31 when the shoulder 12 abuts against the upper plate surface 31A during press-fitting is 8 mm or less.

[0053] The present disclosure will be described in further detail below based on examples, but the present disclosure is not limited to the following examples.

[0054] FIG. 7 is a graph showing the relationship between indentation amount and TSS (Tensile Shear Strength) to explain an example of the friction stir spot welding method according to the present disclosure. Table 3 shows experimental data corresponding to the graph in FIG. 7 . Data 1 to 3 in Table 3 are comparative examples, and Data 4 to 6 are examples. Note that "reference position input condition" (mm) refers to a reference position set based on the upper plate surface 31A of the upper plate 31. Also, "adhesive application" refers to the presence or absence of adhesive applied between the upper plate 31 and the lower plate 32.

[0055]

[0056] TSS corresponds to the so-called tensile shear strength, and indicates the load at which fracture occurs in the stir weld 4 when the upper plate 31 and the lower plate 32 of the welded body 3 after the stir weld 4 is formed are pulled in opposite directions parallel to the upper plate surface 31A. In other words, the larger the TSS value, the higher the tensile shear strength.

[0057] In the experiment shown in FIG. 7 , the upper plate 31 is a 6000-series aluminum alloy with a thickness of 1.1 mm, and the lower plate 32 is a 1.2 GPa-class steel plate with a thickness of 1.2 mm. That is, the upper plate 31 and the lower plate 32 are made of metals with different main elements. The rotation speed of the tool 1 is 2000 rpm, the outer diameter of the shoulder 12 is 5.5 mm, and the outer diameter of the pin 11 is 3.35 mm. In the comparative example, the press-fit pressure on the shoulder 12 is 7.7 kN regardless of the position of the shoulder 12. On the other hand, in the example, a depth of 1.06 mm from the upper plate surface 31A is set as the reference position, and the press-fit pressure on the upper plate 31 side from the reference position is set to 5 kN, and the press-fit pressure on the lower plate 32 side from the reference position is set to 7.7 kN. In this case, the reference position substantially corresponds to the interface between the upper plate back surface 31B and the upper plate surface 31A. The press-fit position of the shoulder 12 is set to a depth of 0.15 mm below the lower plate surface 32A. In the leveling process described above, the shoulder lower surface 12S of the shoulder 12 and the pin lower surface 11S of the pin 11 are positioned slightly below the upper plate surface 31A, aiming to form an indent 4T of up to about 0.30 mm.

[0058] As shown in Figure 7, in the comparative example in which the pressure applied to the shoulder 12 during the press-fitting process was constant, an indent 4T was formed with a depth of approximately 0.33 mm to 0.35 mm, which was greater than the target depth. This phenomenon is presumably caused by a portion of the material being pushed outward in the radial direction during press-fitting of the shoulder 12, resulting in insufficient overflow material OF flowing into the hollow space of the shoulder 12 shown in process P12 of Figure 2. If the overflow material OF is insufficient in the hollow space, there will also be insufficient material in the backfilling process, resulting in the formation of an indent 4T deeper than the target depth. Furthermore, as described above, the radial outward pushing of a portion of the material during press-fitting of the shoulder 12 leads to the aforementioned deformation of the joined body 3.

[0059] On the other hand, in the example in which the pressurizing force applied to the relatively soft upper plate 31 was reduced, the indent 4T was distributed near the target of 0.30 mm, and the TSS value was larger than that of the comparative example. If the indent 4T is formed deeper than the target, a crack will develop in the thickness direction between the end of the indent 4T and the lower plate 32, which is a fracture known as a plug fracture. For this reason, as shown in Figure 7, the comparative example had a relatively smaller TSS than the example.

[0060] As described above, it was confirmed that by setting an appropriate pressure according to the hardness of the plate material, the desired indent 4T can be obtained and the strength of the joint portion including the stir welded portion 4 can be improved.

[0061] Fig. 8 is a graph showing the relationship between the distance from the plate end of the welded body 3 to the outer periphery of the shoulder 12 and the amount of end deformation, for explaining an example of the friction stir spot welding method according to the present disclosure. The distance from the plate end to the outer periphery of the shoulder 12 is indicated by distance L in the above-mentioned Fig. 18. Table 4 shows the conditions of each experimental data corresponding to the graph in Fig. 8.

[0062]

[0063] In the experiment shown in Figure 8, the materials and thicknesses of the upper plate 31 and the lower plate 32, and the outer diameters of the pin 11 and the shoulder 12 are the same as in the experiment shown in Figure 7. In the comparative example, the press-fitting pressure of the shoulder 12 is 6 kN regardless of the press-fitting position. Furthermore, in Example A, the outer diameter of the clamp 13 is set to 16 mm, and in the comparative example and Example B, the outer diameter of the clamp 13 is set to 10 mm. In Examples A and B, a depth of 0.8 mm from the upper plate surface 31A is set as the reference position, and the press-fitting pressure on the upper plate 31 side is set to 2.5 kN, and the press-fitting pressure on the lower plate 32 side is set to 6 kN. The other conditions are the same as in the experiment shown in Figure 7.

[0064] 8, it was confirmed that the amount of deformation of the end of the welded body 3 was reduced in Examples A and B compared to the comparative example, regardless of the outer diameter of the clamp 13. In particular, even under the severe condition where the stir welded portion 4 is close to the end of the welded body 3 and the distance L is 8 mm or less, it is possible to significantly reduce the amount of deformation by controlling the pressing force. Therefore, the pin 11 and the shoulder 12 may be arranged opposite the overlapping portion so that the shortest distance L between the outer edge of the shoulder 12 and the end of the upper plate 31 when the shoulder 12 abuts against the upper plate surface 31A during press-fitting is 8 mm or less.

[0065] Figure 9 is a graph showing the relationship between the reference position and the end deformation amount to explain an example of the friction stir spot welding method according to the present disclosure. Table 5 also shows the experimental data corresponding to the graph in Figure 9. Note that the "distance from the upper and lower sheet interface" in Table 5 assumes that the reference position of 1.06 is the upper and lower sheet interface, and the difference in the reference position input conditions relative to this 1.06 is shown as the distance from the upper and lower sheet interface. For example, in the second example from the top, the reference position input condition is 0.96, so the distance from the upper and lower sheet interface is 1.06 - 0.96 = 0.10.

[0066]

[0067] In the experiment shown in FIG. 9 , the materials and thicknesses of the upper plate 31 and the lower plate 32, and the outer diameters of the pin 11 and the shoulder 12 are the same as those in the experiment shown in FIG. 7 . The distance L shown in FIG. 18 is set to 3 mm. The rotation speed of the tool 1 is 1500 rpm, the outer diameter of the shoulder 12 is 5.5 mm, and the outer diameter of the pin 11 is 3.35 mm. In the comparative example, the press-fit pressure on the shoulder 12 is 7.7 kN regardless of the press-fit position. In the example, the press-fit pressure on the upper plate 31 side of the predetermined reference position is set to 3 kN, and the press-fit pressure on the lower plate 32 side is set to 7.7 kN. For the data shown on the far left in FIG. 9 , where the reference position is −0.09, the press-fit pressure on the upper plate 31 side is set to 5 kN, and the press-fit pressure on the lower plate 32 side is set to 7.7 kN. The other conditions are the same as those in the experiment shown in FIG. 7 . In the examples, friction stir spot welding is performed under each condition in which the reference position is sequentially changed within the upper plate 31. The horizontal axis in Fig. 9 represents the distance between the lower plate surface 32A and the reference position divided by the plate thickness of the upper plate 31, i.e., the reference position as a ratio of the upper plate thickness.

[0068] 9, the deformation amount of the end portion of the joined body 3 in the comparative example was in the range of 0.89 mm to 1.02 mm. On the other hand, the deformation amount in the example was smaller than that in the comparative example in the region where the reference position was 0.73 or less in terms of the plate thickness ratio of the upper plate 31 (to the left of the dashed line in FIG. 9).

[0069] Thus, the deformation of the end of the joined body 3 can be suppressed not only by setting the pressure of the shoulder 12 low in the entire region of the relatively soft upper plate 31, but also by increasing the pressure during press-fitting into the upper plate 31. However, to more reliably suppress deformation, it is desirable to set a reference position in the region from the lower plate surface 32A to an upper plate thickness ratio of 0.4, more preferably in the region up to an upper plate thickness ratio of 0.35, and press-fit the upper plate 31 with a relatively low first pressure. Note that, if it is desired to suppress the deformation to some extent, the reference position may be set in a range up to 73% of the thickness of the lower hardness member of the upper plate 31 and the lower plate 32, based on the contact point between the upper plate rear surface 31B and the lower plate surface 32A. Note that the pressure may be switched on the side of the higher hardness member.

[0070] 9, in this experiment, it was confirmed that the amount of end deformation was suppressed to 0.46 mm even when the pressure was changed to the second pressure at a reference position where the upper plate thickness ratio was −0.09, in other words, at a depth of 0.10 mm below the lower plate surface 32A of the lower plate 32. Here, a negative value for the upper plate thickness ratio means that the reference position is set within the lower plate 32. In this way, the pressure force control according to the present invention can achieve a robust effect of suppressing the amount of end deformation even if the reference position is positioned on either side of the upper plate 31 and the lower plate 32 with a predetermined degree of variation with respect to the contact portion between the upper plate 31 and the lower plate 32.

[0071] 10 is a graph showing the relationship between the pressure ratio P1 / P2 and the deformation amount of the end portion for explaining an example of the friction stir spot welding method according to the present disclosure. Table 6 shows the experimental data corresponding to the graph in FIG.

[0072]

[0073] The experiment shown in Figure 10 was conducted under the same experimental conditions as the example shown in Figure 7, except that the magnitude of the pressing force of the shoulder 12 and the rotational speed in the example were 1500 rpm. In the example shown in Figure 10, the experiment was conducted under different conditions, with the magnitude of the first pressure P1 ranging from 2 kN to 7 kN. The magnitude of the second pressure P2 was 7.7 kN. As a result, the P1 / P2 ratio in the comparative example was 1.0, and the pressure ratio P1 / P2 in the example was 0.26 to 0.91.

[0074] As shown in Fig. 10, if the first pressure P1 applied to the shoulder 12 in the upper plate 31 is even slightly smaller than the second pressure P2, the effect of suppressing the amount of end deformation can be obtained. Furthermore, the smaller the ratio P1 / P2, the smaller the amount of end deformation can be maintained. For example, if the hardness of the upper plate 31 is lower than the hardness of the lower plate 32, it is desirable to set the first pressure P1 and the second pressure P2 so that P1 / P2 < 0.91 is satisfied, as shown by the arrow in Fig. 10.

[0075] Furthermore, as shown by the arrows in Figure 10, it is more desirable to set the first pressure and the second pressure so that P1 / P2 < 0.7, as this significantly reduces the amount of end deformation, and it is even more desirable to set the first pressure and the second pressure so that P1 / P2 ≦ 0.65, as this more reliably reduces the amount of end deformation.

[0076] 11 is a graph showing the relationship between the plate combination of the upper plate 31 and the lower plate 32 and the end deformation amount, for explaining an example of the friction stir spot welding method according to the present disclosure. Experimental data corresponding to the graph in FIG. 11 are shown in Table 7.

[0077]

[0078] Furthermore, FIGS. 12A, 12B, and 12C are see-through perspective views showing types of plate combinations for explaining an embodiment of the friction stir spot welding method according to the present disclosure.

[0079] 12A, 12B, and 12C, plate sets 1, 2, and 3 were used in this experiment. In plate set 1, the upper plate 31 was made of a 6000 series aluminum alloy with a plate thickness of 1.0 mm, and the lower plate 32 was made of a 5000 series aluminum alloy with a plate thickness of 2.0 mm. Relatively speaking, the hardness of the upper plate 31 was lower than the hardness of the lower plate 32. In plate set 2, the upper plate 31 was made of a 5000 series aluminum alloy with a plate thickness of 1.2 mm, and the lower plate 32 was made of a 6000 series aluminum alloy with a plate thickness of 3.0 mm.

[0080] Relatively, the hardness of the upper plate 31 is higher than the hardness of the lower plate 32. Furthermore, in the plate set 3, the upper plate 31 is made of a 6000 series aluminum alloy with a plate thickness of 3.0 mm, and the lower plate 32 is made of a 5000 series aluminum alloy with a plate thickness of 2.0 mm. Relatively, the hardness of the upper plate 31 is lower than the hardness of the lower plate 32.

[0081] In the experiments for plate sets 1 and 2, the rotation speed of tool 1 was 2000 rpm, the outer diameter of shoulder 12 was 6.0 mm, and the outer diameter of pin 11 was 3.25 mm. In the experiment for plate set 3, the rotation speed of tool 1 was 2000 rpm, the outer diameter of shoulder 12 was 9.0 mm, and the outer diameter of pin 11 was 6.0 mm. In both experiments, the distance L shown in FIG. 18 was set to 3 mm. The press-fit position of shoulder 12 was 0.3 mm from the lower plate surface 32A in plate set 1, 1.1 mm from the lower plate surface 32A in plate set 2, and 0.5 mm from the lower plate surface 32A in plate set 3. In Example I, the reference position was set at the boundary between the upper plate back surface 31B and the lower plate surface 32A. In Example II, the reference position was set at a position 0.2 mm deeper than the lower plate surface 32A. In other words, in Example II, the pressure of the shoulder 12 is set to the second pressure in the region from a position 0.2 mm deeper than the lower plate surface 32A to 0.3 mm, which is the final press-fit position.

[0082] Regarding the pressure, in the comparative example of plate group 1, the press-fit pressure on the shoulder 12 is set to 8 kN, and in Examples I and II, the first pressure P1 is set to 4 kN and the second pressure P2 is set to 8 kN. In the comparative example of plate group 2, the press-fit pressure on the shoulder 12 is set to 9 kN, and in Example I, the first pressure P1 is set to 9 kN and the second pressure P2 is set to 7 kN. In the comparative example of plate group 3, the press-fit pressure on the shoulder 12 is set to 9.7 kN, and in Example I, the first pressure P1 is set to 7 kN and the second pressure P2 is set to 9.7 kN.

[0083] 11 , in all plate combinations, the example in which the press-fit pressure was set lower for relatively soft plate materials was confirmed to be able to suppress the amount of edge deformation compared to the comparative example in which the press-fit pressure of the shoulder 12 was not changed. In particular, this tendency was confirmed to be applicable even when the upper plate 31 and the lower plate 32 are dissimilar metals with the same main element, for example, two aluminum alloys with different constituent elements other than aluminum. Furthermore, when the lower plate 32 is relatively softer than the upper plate 31, as in plate combination 2, the amount of edge deformation can be similarly suppressed by setting the second pressure P2 lower than the first pressure P1.

[0084] 11, it can be seen that the reference position for changing the applied pressure from the first pressure P1 to the second pressure P2 may be closer to the lower plate 32 than the lower plate surface 32A, as shown in Example II of plate assembly 1. This result also coincides with the result of the reference position (upper plate thickness ratio) of −0.09 in FIG.

[0085] 13 is a graph showing the relationship between the amount of indentation and the presence or absence of adhesive application, for explaining an example of the friction stir spot welding method according to the present disclosure. Table 8 shows the experimental data corresponding to the graph in FIG.

[0086]

[0087] The experimental conditions for the comparative example and example shown in Figure 13 are the same as those shown in Figure 7 . Under the adhesive application condition, adhesive was pre-applied between the upper plate back surface 31B and the lower plate surface 32A before friction stir spot welding of the upper plate 31 and the lower plate 32, i.e., before the shoulder 12 was pressed in. As shown in Figure 13 , regardless of whether adhesive was applied, the example showed a smaller indentation than the comparative example. Note that in the comparative example where adhesive was pre-applied as described above, the indentation was significantly larger, and correspondingly, edge deformation tended to occur more easily. Even in such cases, by setting a low pressure to press the shoulder 12 into the relatively soft upper plate 31, it is possible to reduce the indentation and suppress edge deformation. Note that instead of adhesive, a sealant may be pre-applied between the upper plate back surface 31B and the lower plate surface 32A. The same applies below.

[0088] Fig. 14 is a graph showing the relationship between the presence or absence of adhesive application and the TSS, for explaining an example of the friction stir spot joining method according to the present disclosure. Experimental data corresponding to the graphs in Fig. 14 and Fig. 15 (described later) are shown in Table 9. Table 9 lists the indents in the TSS joint and the CTS joint separately.

[0089]

[0090] As also shown in Figure 14, the four graphs on the left side of the figure, like those in Figure 7, show that the upper plate 31 is a 6000-series aluminum alloy with a thickness of 1.1 mm, and the lower plate 32 is a 1.2 GPa-class steel plate with a thickness of 1.2 mm. Note that the steel plate is not plated. Note that in the comparative example, the press-fit pressure on the shoulder 12 is 7.7 kN regardless of the position of the shoulder 12. In the example, a depth of 1.06 mm from the upper plate surface 31A is set as the reference position, and the press-fit pressure on the upper plate 31 side from the reference position is set to 3 kN, and the press-fit pressure on the lower plate 32 side is set to 7.7 kN. Other conditions are the same as those in Figure 7.

[0091] 14, the upper plate 31 is a 6000 series aluminum alloy having a thickness of 1.1 mm, and the lower plate 32 is an Al-Si plated 1.5 GPa class steel having a thickness of 1.4 mm. The conditions of the press-fit pressure, reference position, and press-fit position are the same as those described above.

[0092] As shown in Figure 14, when no adhesive was applied in the comparative example, the TSS performance was met, but when adhesive was applied, the TSS performance decreased. This phenomenon also corresponds to the increase in the amount of indentation, as mentioned above. On the other hand, as shown in the working example, even when adhesive was applied, it was confirmed that the TSS performance improved when the press-fit pressure of the shoulder 12 of the upper plate 31 was set low. Similar performance was also obtained when a 1.4 mm thick Al-Si plated 1.5 GPa-class steel was used as the lower plate 32.

[0093] In either case, regardless of whether or not an adhesive is used, it is possible to suppress an increase in the amount of indentation, and it is possible to restore the strength of the bonded body 3.

[0094] Fig. 15 is a graph showing the relationship between the presence or absence of adhesive application and CTS (cross tension strength) for explaining an example of a friction stir spot welding method according to the present disclosure. The experimental conditions for each graph in Fig. 15 are the same as those in Fig. 14. The CTS on the vertical axis in Fig. 15 represents cross tensile strength. The upper plate 31 and the lower plate 32 are overlapped in a cross shape in plan view, and the friction stir spot welding portion 4 is formed at the intersection. The CTS corresponds to the load at which fracture occurs when the upper plate 31 and the lower plate 32 are subsequently pulled apart.

[0095] 15, when the lower plate 32 is an unplated 1.2 GPa-class steel plate and no adhesive is applied, it was confirmed that the performance of the CTS in the example is better than that in the comparative example, and the strength of the stir welded portion 4 is improved. Note that it was also confirmed that the performance of the CTS is slightly reduced by the application of adhesive in the example.

[0096] 16 is a graph showing the relationship between the distance L from the plate end to the outer periphery of the shoulder and the amount of deformation of the end, for explaining an example of the friction stir spot welding method according to the present disclosure. Table 10 shows the experimental data corresponding to the graph in FIG.

[0097]

[0098] The graph in Figure 16 shows experimental data obtained by setting a small press-fit pressure on the shoulder 12 with different combinations of the outer diameter of the pin 11 and the outer diameter of the shoulder 12. The symbol φ5-3 in the graph's legend indicates a combination in which the outer diameter of the shoulder 12 is 5 mm and the outer diameter of the pin 11 is 3 mm. The inner diameter of the shoulder 12 is approximately equal to the outer diameter of the pin 11, allowing the two to move and rotate relative to each other. The same applies to the other combinations of outer diameters in the graph. The S / P ratio in Figure 16 indicates the cross-sectional area ratio between the pin 11 and the shoulder 12, where P is the cross-sectional area of ​​the pin 11 and S is the cross-sectional area of ​​the shoulder 12. For each condition shown in the legend in Figure 16, the S / P ratios are 1.78, 2.05, 1.70, 1.33, and 2.41, from top to bottom.

[0099] In all conditions, the rotation speed of the tool 1 was 2000 rpm. The upper plate 31 was made of a 6000 series aluminum alloy with a thickness of 1.0 mm, and the lower plate 32 was made of a 980 MPa class steel with a thickness of 1.2 mm. Other press-fitting conditions were the same as those in FIG. 7.

[0100] 16, it was confirmed that the amount of deformation at the end of the joined body 3 could be suppressed under each condition of the S / P ratio between 0 and 2.41, including the case of φ6-3.25, which had the largest S / P ratio. It was also confirmed that the amount of deformation at the end was particularly effective in suppressing the amount of deformation at the end when the S / P ratio was between 0 and 1.8. Therefore, it is particularly desirable to set the outer diameters of the shoulder 12 and the pin 11 so as to satisfy these conditions.

[0101] Table 11 shows example dimensions of the shoulder 12 and pin 11 according to the above-described examples. Under these conditions, it was confirmed that the deformation of the end portion of the lower plate 32 and the excessive occurrence of the indent 4T could be suppressed by controlling the first pressure and the second pressure. The unit of diameter is mm.

[0102]

[0103] Table 12 shows examples of the dimensions of the shoulder and pin according to each of the comparative examples described above.

[0104]

[0105] Furthermore, the present inventors have confirmed that the effects of the present disclosure are particularly evident in the following ranges, including the above examples: 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 1500 rpm or more and 2000 rpm or less

[0106] <Modified Embodiment> In the above embodiments and examples, the upper plate 31 and the lower plate 32 are joined by softening them with frictional heat, but the present disclosure is not limited to this. Figures 17A and 17B are schematic diagrams of a joined body for explaining a friction stir spot joining method according to a modified embodiment of the present disclosure. The present disclosure is also applicable to joining three or more overlapping plate materials.

[0107] Specifically, as shown in Fig. 17A, the present invention may be applied to a joined body in which only the top two plates are joined and a third plate is placed below them. In Fig. 17A, the top plate 31 and the middle plate 33 are joined by friction stir spot welding to form a joint bottom surface 4A. Meanwhile, the bottom plate 32 is joined to the middle plate 33 by spot welding, adhesive, or the like. In this case, too, the pressure application force can be adjusted according to the relationship in hardness between the top plate 31 and the middle plate 33.

[0108] 17B, ​​two sheets of material corresponding to the upper plate may be joined together with a third sheet of steel. For example, if the upper plate 31 and the middle plate 33 are made of the same material, the pressurization force may be directly applied without changing between them. On the other hand, if the upper plate 31 and the middle plate 33 are made of different materials, it is desirable to press them with varying pressure from the upper plate 31 to the middle plate 33. Furthermore, if the upper plate 31, the middle plate 33, and the lower plate 32 are made of different materials, it is desirable to change the pressurization force in three stages. For example, if the hardness of each member is medium, small, and large from the upper plate 31 side, the pressurization force may also be adjusted to medium, small, and large.

[0109] In this way, the present disclosure can be applied to setting the pressurization force in two specified members in a bonded structure made up of three or more layers of members, focusing on the hardness of the two specified members.

[0110] [Summary of the Disclosure] The specific embodiments described above include disclosures having the following configurations.

[0111] A friction stir spot welding method according to a first aspect of the present disclosure is a friction stir spot welding 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 method comprising the steps of: preparing a friction stir spot welding apparatus including a pin and a cylindrical shoulder having a hollow portion into which the pin is inserted; arranging the first member and the second member so that at least a portion of the second front surface faces the first back surface and forms an overlapping portion where the first member and the second member overlap; arranging the pin and the shoulder to face the overlapping portion; and applying a first pressure and a second pressure for pressing the shoulder, setting the first pressure and the second pressure so that the first pressure is smaller than the second pressure when the hardness of the first member is lower than the hardness of the second member, and so that the first pressure is larger than the second pressure when the hardness of the first member is higher than the hardness of the second member; pressing the shoulder with the first pressure from the first surface side until it reaches a predetermined reference position set with the second surface as a reference, while the pin is retracted from the overlapping portion; pressing the shoulder with the second pressure from the reference position to a press-in position deeper than the second surface; and retracting the shoulder from the press-in position and entering the overlapping portion.

[0112] According to this configuration, when friction stir spot welding the first and second members, adjusting the pressure when pressing the shoulder in accordance with the hardness of each member prevents excessive outward extrusion of a portion of the members and suppresses deformation of the joined body around the spot welding point. In addition, preventing excessive indentation at the spot welding point reduces unstable fracture of the joined body.

[0113] Furthermore, a friction stir spot welding method according to a second aspect of the present disclosure further comprises, in the friction stir spot welding method according to the first aspect, setting the reference position in a range from the boundary between the first back surface and the second front surface to 73% of the plate thickness of the member having the lower hardness among the first member and the second member.

[0114] According to this configuration, it is possible to further prevent a part of the members from being excessively pushed outward during friction stir spot welding.

[0115] Furthermore, a friction stir spot welding method according to a third aspect of the present disclosure further comprises: in the friction stir spot welding method according to the first aspect, using the first member and the second member with a hardness of the first member lower than a hardness of the second member; and in the friction stir spot welding method according to the first or second aspect, setting the first pressure and the second pressure so as to satisfy P1 / P2<0.91, where P1 is the first pressure and P2 is the second pressure.

[0116] According to this configuration, when a shoulder penetrates from a first member having a relatively low hardness to a second member having a high hardness during friction stir spot welding, it is possible to further prevent a portion of the first member from being pushed outward excessively.

[0117] 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 first aspect, further comprising: using the first member and the second member having a hardness lower than that of the second member; and setting the first pressure and the second pressure so as to satisfy P1 / P2<0.7.

[0118] According to this configuration, when a shoulder penetrates from a first member having a relatively low hardness to a second member having a high hardness during friction stir spot welding, it is possible to further prevent a portion of the first member from being pushed outward excessively.

[0119] 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 first aspect, further comprising: using the first member and the second member having a hardness lower than a hardness of the second member; and setting the first pressure and the second pressure so as to satisfy P1 / P2≦0.65.

[0120] According to this configuration, when a shoulder penetrates from a first member having a relatively low hardness to a second member having a high hardness during friction stir spot welding, it is possible to further prevent a portion of the first member from being pushed outward excessively.

[0121] Furthermore, a friction stir spot welding method according to a sixth aspect of the present disclosure is the friction stir spot welding method according to any one of the first to fifth aspects, further comprising using metals having different main elements for the first member and the second member.

[0122] According to this configuration, even when the first member and the second member are made of metals having different main elements, it is possible to suppress deformation of the bonded body around the spot-bonded portion.

[0123] Furthermore, a friction stir spot welding method according to a seventh aspect of the present disclosure is the friction stir spot welding method according to any one of the first to fifth aspects, further comprising using dissimilar metals having the same main element as the first member and the second member.

[0124] According to this configuration, even when the first member and the second member are made of dissimilar metals having the same main element, it is possible to suppress deformation of the bonded body around the spot-bonded portion.

[0125] Furthermore, a friction stir spot welding method according to an eighth aspect of the present disclosure is the friction stir spot welding method according to any one of the first to seventh aspects, further comprising interposing an adhesive or sealant between the first back surface of the first member and the first front surface of the second member before the shoulder is pressed in.

[0126] According to this configuration, by interposing an adhesive or sealant between the first and second members before friction stir welding, it is possible to maintain adhesion between the two members in areas other than the joint. While this may result in a decrease in TSS at the joint, adjusting the pressure during shoulder press-fitting according to the hardness of each member can improve TSS. It is also possible to prevent excessive indentation.

[0127] Furthermore, a friction stir spot welding method according to a ninth aspect of the present disclosure is the friction stir spot welding method according to any one of the first to eighth aspects, further comprising setting the outer diameters of the pin and the shoulder so that S / P≦2.41, where P is the cross-sectional area of ​​the pin and S is the cross-sectional area of ​​the shoulder.

[0128] According to this configuration, by setting the relative thickness of the shoulder with respect to the pin within a specific range, it is possible to particularly prevent a portion of the member from being excessively pushed outward during friction stir spot welding.

[0129] Furthermore, a friction stir spot welding method according to a tenth aspect of the present disclosure is the friction stir spot welding method according to any one of the first to eighth aspects, further comprising setting the outer diameters of the pin and the shoulder so that S / P≦1.8, where P is the cross-sectional area of ​​the pin and S is the cross-sectional area of ​​the shoulder.

[0130] According to this configuration, by setting the relative thickness of the shoulder with respect to the pin within a specific range, it is possible to particularly prevent a portion of the member from being excessively pushed outward during friction stir spot welding.

[0131] Furthermore, a friction stir spot welding method according to an eleventh aspect of the present disclosure is the friction stir spot welding method according to any one of the first to tenth aspects, further comprising forming the overlapping portion so that the end of the first member is aligned with the end of the second member, and arranging the pin and the shoulder opposite the overlapping portion so that the shortest distance between the outer peripheral edge of the shoulder and the end of the first member when the shoulder abuts against the first surface during the press-fitting is 8 mm or less.

[0132] According to this configuration, even when the distance between the end of the first member and the outer peripheral edge of the shoulder is small, at 8 mm or less, it is possible to prevent a portion of the member from being excessively pushed outward, and to prevent the outer shape of the joined body from being significantly deformed.

[0133] Further, a friction stir spot welding apparatus according to a twelfth aspect of the present disclosure is a friction stir spot welding apparatus that 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 comprising: a welding tool including a pin and a cylindrical shoulder having a hollow portion into which the pin is inserted; a rotation mechanism capable of rotating the welding tool; a movement mechanism capable of independently moving the pin and the shoulder in a direction in which the pin extends; and a control unit that controls the rotation mechanism and the movement mechanism, wherein the control unit controls a first pressure and a second pressure for pressing in the shoulder, the first pressure being smaller than the second pressure when the hardness of the first member is lower than the hardness of the second member, and a second pressure being larger than the second pressure when the hardness of the first member is higher than the hardness of the second member. the first pressure and the second pressure are set so that the first pressure is greater than the second pressure when the second pressure is higher than the first pressure; the first member and the second member are arranged so that at least a portion of the second surface faces the first back surface and an overlapping portion where the first member and the second member overlap is formed, and the pin and the shoulder are arranged facing the overlapping portion; the pin is retracted from the overlapping portion, the shoulder is press-fitted with the first pressure from the first surface side until it reaches a predetermined reference position set with the second surface as a reference, and the shoulder is further press-fitted with the second pressure from the reference position to a press-fit position deeper than the second surface, and then the rotation mechanism and the movement mechanism are controlled so that the shoulder is retracted from the press-fit position and the pin enters the overlapping portion.

[0134] According to this configuration, when friction stir spot welding the first and second members, the pressure applied when the shoulder is pressed into the first and second members is adjusted according to the hardness of each member, thereby preventing excessive outward extrusion of a portion of the members. As a result, deformation of the joined body around the spot welding point can be suppressed. Furthermore, excessive indentation at the spot welding point can be prevented, thereby reducing fracture of the joined body.

[0135] In addition, a friction stir spot welding apparatus according to a thirteenth aspect of the present disclosure is the friction stir spot welding apparatus according to the twelfth aspect, wherein the control unit sets the reference position within a range from the boundary between the first back surface and the second front surface to 73% of the plate thickness of the member having the lower hardness among the first member and the second member.

[0136] According to this configuration, it is possible to further prevent a part of the members from being excessively pushed outward during friction stir spot welding.

[0137] Furthermore, in a friction stir spot welding apparatus according to a fourteenth aspect of the present disclosure, in the friction stir spot welding apparatus according to the twelfth or thirteenth aspect, when the hardness of the first member is lower than the hardness of the second member, the control unit sets the first pressure and the second pressure so as to satisfy P1 / P2<0.91, where P1 is the first pressure and P2 is the second pressure.

[0138] According to this configuration, when a shoulder penetrates from a second member having a relatively low hardness to a second member having a high hardness during friction stir spot welding, it is possible to further prevent a portion of the first member from being pushed outward excessively.

[0139] Furthermore, in a friction stir spot welding apparatus according to a fifteenth aspect of the present disclosure, in the friction stir spot welding apparatus according to the twelfth or thirteenth aspect, when the hardness of the first member is lower than the hardness of the second member, the control unit sets the first pressure and the second pressure so as to satisfy P1 / P2<0.7, where P1 is the first pressure and P2 is the second pressure.

[0140] According to this configuration, when a shoulder penetrates from a second member having a relatively low hardness to a second member having a high hardness during friction stir spot welding, it is possible to further prevent a portion of the first member from being pushed outward excessively.

[0141] Furthermore, in a friction stir spot welding apparatus according to a sixteenth aspect of the present disclosure, in the friction stir spot welding apparatus according to the twelfth or thirteenth aspect, when the hardness of the first member is lower than the hardness of the second member, the control unit sets the first pressure and the second pressure so as to satisfy P1 / P2≦0.65, where P1 is the first pressure and P2 is the second pressure.

[0142] According to this configuration, when a shoulder penetrates from a second member having a relatively low hardness to a second member having a high hardness during friction stir spot welding, it is possible to further prevent a portion of the first member from being pushed outward excessively.

Claims

1. A friction stir spot welding 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, comprising the steps of: preparing a friction stir spot welding device including a pin and a cylindrical shoulder having a hollow portion into which the pin is inserted; positioning the first member and the second member such that at least a portion of the second front surface faces the first back surface to form an overlapping portion where the first member and the second member overlap; positioning the pin and the shoulder opposite the overlapping portion; setting a first pressure and a second pressure for pressing in the shoulder such that the first pressure is smaller than the second pressure when the hardness of the first member is lower than the hardness of the second member, and the first pressure is greater than the second pressure when the hardness of the first member is higher than the hardness of the second member; a first pressure applied to the shoulder from the first surface side until the shoulder reaches a predetermined reference position set with the second surface as a reference while the pin is retracted from the overlapping portion; a second pressure applied to the shoulder from the reference position to a press-in position deeper than the second surface; and a second pressure applied to the shoulder from the press-in position and the pin entering the overlapping portion.

2. The friction stir spot welding method of claim 1, further comprising setting the reference position within a range from the boundary between the first back surface and the second front surface to 73% of the plate thickness of the member having the lower hardness among the first member and the second member.

3. The friction stir spot welding method of claim 1, further comprising: using the first member and the second member having a hardness lower than that of the second member; and setting the first pressure and the second pressure so as to satisfy P1 / P2<0.91, where P1 is the first pressure and P2 is the second pressure.

4. The friction stir spot welding method of claim 1, further comprising: using the first member and the second member having a hardness lower than that of the second member; and setting the first pressure and the second pressure so as to satisfy P1 / P2<0.

7.

5. The friction stir spot welding method according to claim 1, further comprising: using the first member and the second member having a hardness lower than that of the second member; and setting the first pressure and the second pressure so as to satisfy P1 / P2≦0.

65.

6. A friction stir spot welding method according to any one of claims 1 to 5, further comprising using metals having different main elements for the first member and the second member.

7. A friction stir spot welding method according to any one of claims 1 to 5, further comprising using dissimilar metals having the same main element as the first member and the second member.

8. A friction stir spot welding method as described in any one of claims 1 to 7, further comprising interposing an adhesive or sealant between the first back surface of the first member and the first front surface of the second member prior to pressing in the shoulder.

9. A friction stir spot welding method as claimed in any one of claims 1 to 8, further comprising setting the outer diameters of the pin and the shoulder so that S / P≦2.41, where P is the cross-sectional area of ​​the pin and S is the cross-sectional area of ​​the shoulder.

10. A friction stir spot welding method as claimed in any one of claims 1 to 8, further comprising setting the outer diameters of the pin and the shoulder so that S / P≦1.8, where P is the cross-sectional area of ​​the pin and S is the cross-sectional area of ​​the shoulder.

11. A friction stir spot welding method as described in any one of claims 1 to 10, further comprising forming the overlapping portion so that the end of the first member follows the end of the second member, and positioning the pin and the shoulder opposite the overlapping portion so that the shortest distance between the outer peripheral edge of the shoulder and the end of the first member when the shoulder abuts against the first surface during the pressing is 8 mm or less.

12. A friction stir spot welding apparatus 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, comprising: a welding tool including a pin and a cylindrical shoulder having a hollow portion into which the pin is inserted; a rotation mechanism capable of rotating the welding tool; a movement mechanism capable of independently moving the pin and the shoulder in the direction in which the pin extends; and a control unit for controlling the rotation mechanism and the movement mechanism, wherein the control unit sets a first pressure and a second pressure for pressing in the shoulder such that the first pressure is smaller than the second pressure when the hardness of the first member is lower than the hardness of the second member, and the first pressure is larger than the second pressure when the hardness of the first member is higher than the hardness of the second member; a friction stir spot welding apparatus which controls the rotation mechanism and the movement mechanism so that the first member and the second member are arranged so that at least a portion of the second surface faces the first back surface to form an overlapping portion where the first member and the second member overlap, and the pin and the shoulder are arranged facing the overlapping portion, the pin is retracted from the overlapping portion, the shoulder is pressed in with the first pressure from the first surface side until it reaches a predetermined reference position set with the second surface as a reference, and the shoulder is further pressed in with the second pressure from the reference position to a press-in position deeper than the second surface.

13. The friction stir spot welding device described in claim 12, wherein the control unit sets the reference position within a range from the boundary between the first back surface and the second front surface to 73% of the plate thickness of the member having the lower hardness among the first member and the second member.

14. A friction stir spot welding apparatus as described in claim 12 or 13, wherein when the hardness of the first member is lower than the hardness of the second member, the control unit sets the first pressure and the second pressure so as to satisfy P1 / P2<0.91, where P1 is the first pressure and P2 is the second pressure.

15. A friction stir spot welding apparatus as described in claim 12 or 13, wherein when the hardness of the first member is lower than the hardness of the second member, the control unit sets the first pressure and the second pressure so as to satisfy P1 / P2<0.7, where P1 is the first pressure and P2 is the second pressure.

16. A friction stir spot welding apparatus as described in claim 12 or 13, wherein when the hardness of the first member is lower than the hardness of the second member, the control unit sets the first pressure and the second pressure so as to satisfy P1 / P2≦0.65, where P1 is the first pressure and P2 is the second pressure.

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