Friction agitation joining tool and method

Abstract

To provide a friction agitation joining tool and a friction agitation method, capable of suppressing defects, increasing a joining speed, and achieving joining using a general purpose machine tool.SOLUTION: There is provided a friction agitation joining tool 100 comprising: a shoulder 13 formed on a tip of a columnar body 11; and a probe 15 arranged on a center of the shoulder 13 and protruding to an axial direction of the body 11. The shoulder 13 has: a salient shaped shoulder face 17 whose center protrudes to the axial direction; and a groove 19 recessed in the axial direction. The groove 19 has: an inside-groove space which stores a part of a solid phase flowing layer of a joined material which is generated by friction heat caused by rotation of a tool, returns the stored solid phase flowing layer to a facing region of a shoulder face 17 on a rear side of a rotation direction following rotation of the tool, and periodically changes a thickness of the solid phase flowing layer in the facing region.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a friction stir welding tool and a friction stir welding method. [Background technology]

[0002] There has been a demand for improving the safety of passengers in vehicles, and the strength of the vehicle body has been improved for this purpose. On the other hand, against the background of the worsening of the global warming problem, the movement to improve the fuel efficiency of automobiles is accelerating. It is known that reducing the weight of the vehicle body is effective in improving fuel efficiency. Therefore, the use of light metals such as aluminum materials instead of steel materials used in vehicle bodies has been promoted. Incidentally, friction stir welding (FSW) is a technology for joining metal materials together. Friction stir welding is a joining method in which a friction stir welding tool consisting of a pin and shoulder called a probe is inserted into the materials to be joined while rotating, and the joint is joined by solid-phase stirring using the generated frictional heat.

[0003] A typical friction stir welding tool has a shoulder that is concave in the axial direction. However, depending on the shape of the workpieces to be joined and the joining form, friction stir welding tools with a shoulder that protrudes in the axial direction and even friction stir welding tools with concentric or spiral grooves on the tool tip surface have been proposed (Prior Documents 1 to 6). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4450728 [Patent Document 2] JP 2003-245783 A [Patent Document 3] JP 2019-166568 A [Patent Document 4] JP 2000-153374 A [Patent Document 5] Patent Publication No. 2022-79568 [Patent Document 6] Patent Publication No. 2021-112767 Summary of the Invention [Problem to be solved by the invention]

[0005] In general, friction stir welding is performed at a temperature that does not melt the materials being joined, so it is possible to create a joint with little distortion, but it has the disadvantage of a slow joining speed. In addition, the load (weight) on the friction stir welding tool is large, and in order to obtain a certain amount of stirring force, the friction stir welding tool needs to be rotated while tilted at a certain angle relative to the joining line. Therefore, friction stir welding requires dedicated equipment that can withstand the load, which increases the cost of introducing the equipment, etc.

[0006] In addition, the friction stir welding tool with a convex shoulder as in Patent Document 1 is suitable for applications in which the workpieces have curved surfaces and the curved surfaces are friction-stir-welded to each other. However, in applications in which flat plates are joined together, if the shoulder is made convex or if a concentric or spiral groove is provided in the shoulder, the friction between the shoulder and the workpieces is reduced. As a result, the temperature rise associated with stirring the workpieces is reduced, making it difficult to increase the welding speed of the workpieces. In addition, since it is difficult to obtain sufficient frictional heat, the weld becomes unstable and cavity defects are likely to occur.

[0007] Therefore, an object of the present invention is to provide a friction stir welding tool and a friction stir welding method that can increase the welding speed while suppressing the occurrence of defects and enable welding using a general-purpose machine tool. [Means for solving the problem]

[0008] The present invention comprises the following configurations. (1) A friction stir welding tool having a shoulder formed at the tip of a cylindrical main body and a probe disposed at the center of the shoulder and protruding in the axial direction of the main body, The shoulder has a convex shoulder surface whose central portion protrudes in the axial direction, and a groove recessed in the axial direction, the groove has an inner space for storing a part of a solid-phase fluidized layer of the workpieces generated by frictional heat due to rotation of the tool, returning the stored solid-phase fluidized layer to an opposing region of the shoulder surface on the rear side in a rotation direction as the tool rotates, and periodically changing a thickness of the solid-phase fluidized layer in the opposing region. Friction stir welding tools. (2) The tip of the friction stir welding tool described in (1) is pressed against a joint of workpieces and rotated, and the workpieces are joined by moving the friction stir welding tool and the workpieces relative to each other while generating the solid-phase fluidized layer in the workpieces by friction generated between the workpieces and the friction stir welding tool. Friction stir welding method. Effect of the Invention

[0009] According to the present invention, it is possible to increase the joining speed while suppressing the occurrence of defects, and further, it becomes possible to perform joining using a general-purpose machine tool. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing the appearance of a friction stir welding tool. [Diagram 2] FIG. 2 is a plan view of the friction stir welding tool as viewed from the tip. [Diagram 3] FIG. 3 is an enlarged perspective view of the shoulder and probe at the tip of the friction stir welding tool. [Figure 4] FIG. 4 is an explanatory diagram showing how two workpieces are friction stir welded together by a friction stir welding tool at a position where the ends of the workpieces are butted against each other. [Diagram 5] FIG. 5 is a cross-sectional perspective view showing a part of the friction stir welding tool. [Figure 6] FIG. 6 is an explanatory diagram that illustrates a solid-phase fluidized layer generated by the rotation of a friction stir welding tool. [Figure 7]FIG. 7 is an explanatory diagram that illustrates the flow of a solid-phase fluidized layer stirred by a friction stir welding tool, in a plan view of the tip of the friction stir welding tool. [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII shown in FIG. [Figure 9] FIG. 9 is a side view of the tip of a friction stir welding tool. [Figure 10] FIG. 10 is a perspective view showing a first modified example of the friction stir welding tool. [Figure 11] FIG. 11 is a perspective view showing a second modified example of the friction stir welding tool. [Figure 12] FIG. 12 is a perspective view showing a third modified example of the friction stir welding tool. [Figure 13] FIG. 13 is a perspective view showing a fourth modified example of the friction stir welding tool. [Figure 14] FIG. 14 is a perspective view showing a fifth modified example of the friction stir welding tool. [Figure 15] FIG. 15 is a perspective view showing a sixth modified example of the friction stir welding tool. [Figure 16] FIG. 16 is a perspective view showing a seventh modified example of the friction stir welding tool. [Figure 17] FIG. 17 is an explanatory diagram that illustrates a state in which friction stir welding is performed by mounting a friction stir welding tool on the spindle of a machining center. [Figure 18] FIG. 18 is an explanatory diagram that illustrates a moving path of the friction stir welding tool controlled by the control unit. [Figure 19] FIG. 19 is a perspective view of a structure 47 in which side surfaces of a pair of extruded panels along the extrusion direction are joined to each other. [Figure 20] FIG. 20 is a cross-sectional view of the extruded panel shown in FIG. [Figure 21] FIG. 21 is an enlarged cross-sectional view of a pair of extruded panels at a joining position where their ends are butted together before joining. [Figure 22] FIG. 22 is a perspective view of the friction stir welding tool used for the joining. [Figure 23]FIG. 23 is a perspective view of the friction stir welding tool used for the joining. [Figure 24] FIG. 24 is a perspective view of the friction stir welding tool used for the joining. [Diagram 25] FIG. 25 is a perspective view of the friction stir welding tool used for the joining. [Figure 26] FIG. 26 is a cross-sectional photograph of the joint in Test Example 8. [Figure 27] FIG. 27 is a cross-sectional photograph of the joint in Test Example 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. 1 is a perspective view showing the appearance of a friction stir welding tool. The friction stir welding tool 100 has a shoulder 13 formed at the tip of a cylindrical main body 11, and a probe 15 disposed at the center of the shoulder 13 and protruding in the axial direction (rotation axis Ax) of the main body 11. The shoulder 13 has a convex shoulder surface 17 whose central portion protrudes in the axial direction, and a groove 19 recessed in the axial direction.

[0012] FIG. 2 is a plan view of the friction stir welding tool 100 as viewed from the tip. The shoulder 13 of the friction stir welding tool 100 of this configuration is provided with four grooves 19 formed linearly from the radial inner side to the radial outer side of the shoulder 13. The four grooves 19 are formed in the radial direction of the shoulder 13, and are arranged radially at equal central angles (90°). Here, the extension direction of each groove 19 is set to two orthogonal axes (X-axis and Y-axis) perpendicular to the rotation axis Ax, but the number of grooves 19 can be appropriately increased or decreased. The number of grooves 19 may be one, but is preferably three or more, and more preferably four or more. If the number of grooves is too large, the stirring effect decreases, so it is preferably eight or less, and more preferably six or less. In addition, the arrangement of the grooves 19 is preferably point-symmetric about the rotation axis Ax, and more preferably line-symmetric about a diametric line passing through the rotation axis Ax. When two or more grooves 19 are provided, they are preferably disposed at equal intervals in the circumferential direction so that the central angles are equal.

[0013] FIG. 3 is an enlarged perspective view of the shoulder 13 and the probe 15 at the tip of the friction stir welding tool 100. The grooves 19 provided in the shoulder 13 divide the shoulder surface 17 protruding in the axial direction into four equal-spaced portions in the circumferential direction. The groove bottoms 19a of the grooves 19 are formed to the same depth in the axial direction, and the inner periphery groove end 19b of each groove 19 on the inner periphery closest to the probe 15 is the deepest, and the outer periphery groove end 19c located on the outer periphery of the shoulder surface 17 is the shallowest, but the groove depth is not limited to this. The cross-sectional shape of the groove 19 along the circumferential direction is V-shaped, and an in-groove space S is formed within the groove 19. The cross-sectional shape of the groove 19 is not limited to this, and may be other shapes such as a rectangle, a semicircle, or an ellipse. A screw groove (not shown) is formed on the outer periphery of the probe 15.

[0014] FIG. 4 is an explanatory diagram showing a state where the workpieces 21A and 21B are friction-stir-welded by the friction-stir-welding tool 100 at a position where the ends of the two workpieces 21A and 21B are butted against each other. The friction-stir-welding tool 100 is attached to a spindle of a machine tool (not shown). The machine tool moves the tip of the friction-stir-welding tool 100 to a position where the workpieces 21A and 21B are welded. Then, at the weld position, the friction-stir-welding tool 100 is rotated while being pressed against the workpieces 21A and 21B from the normal direction, and is fed along the planned weld line L. In this way, the workpieces 21A and 21B are friction-stir-welded to each other along the planned weld line L to form a weld 23. At this time, the friction-stir-welding tool 100 is rotated and fed without tilting the rotation axis Ax from the normal direction of the workpieces 21A and 21B.

[0015] Next, the action of forming the weld 23 by plastically flowing the workpieces 21A, 21B using the shoulder 13 and probe 15 of the friction stir welding tool 100 will be described in detail. Fig. 5 is a cross-sectional perspective view partially showing the friction stir welding tool 100. The groove 19 has a dam surface 19d rising from the groove bottom 19a toward the axial tip. Although Fig. 5 shows only the dam surface 19d on one side, which is the rear side in the rotation direction R of the friction stir welding tool 100, the dam surface 19d is formed on both the front side and the rear side in the rotation direction R of the groove 19.

[0016] The dam surface 19d is formed continuously along the radial direction of the main body 11, and is a surface perpendicular or substantially perpendicular to the rotation direction R centered on the rotation axis Ax. A pair of the dam surfaces 19d is formed at the front and rear of the groove 19 in the rotation direction R, making the groove cross section V-shaped. Of the pair of dam surfaces 19d, the dam surface 19d on the rear side in the rotation direction particularly contributes to a scraping action that stirs a solid-phase fluidized layer of the workpieces 21A and 21B, which will be described later.

[0017] FIG. 6 is an explanatory diagram showing a solid-phase fluidized layer Wa generated by the rotation of the friction stir welding tool 100. The friction stir welding tool 100 is rotated while pressing its tip against the workpieces 21A and 21B. Then, around the probe 15, the workpieces 21A and 21B start to plastically flow due to frictional heat generated by contact between the probe 15 and the workpieces 21A and 21B. Then, the probe 15 is pushed into the plastically flowed solid-phase fluidized layer Wa. The shoulder surface 17 also comes into contact with the workpieces 21A and 21B to generate frictional heat, and the workpieces 21A and 21B also plastically flow in the area opposite the shoulder surface 17. The solid-phase fluidized layer Wa of the workpieces 21A and 21B thus generated is stirred by the groove 19.

[0018] FIG. 7 is an explanatory diagram showing the flow Q of the solid-phase fluidized layer Wa stirred by the friction stir welding tool 100 in a plan view of the tip of the friction stir welding tool 100. FIG. 8 is a cross-sectional view taken along the VIII-VIII line shown in FIG. 7. As shown in FIG. 7, during friction stir welding, the solid-phase fluidized layer Wa undergoing plastic flow is present in each of the regions facing the four shoulder surfaces 17 separated by the four grooves 19. The solid-phase fluidized layer Wa is scraped up by the weir surface 19d in the groove 19 as the friction stir welding tool 100 rotates, and is temporarily stored in the groove space S of the groove 19. In the groove space S, the scraped up solid-phase fluidized layer Wa is stirred while being pushed back forward in the rotation direction R. When viewed from the workpiece side, this stirring action occurs repeatedly at the passing position of each groove 19 that continues to move due to the tool rotation.

[0019] At this time, near the weir surface 19d, as shown in FIG. 8, the solid-phase fluidized layer Wa is pushed back forward in the rotation direction R and stored in the groove space S, so that the thickness ha at a position other than the groove 19 increases to a thickness hb. Then, after passing through the groove 19, the thickness becomes ha again. That is, the thickness of the solid-phase fluidized layer Wa in the annular region facing the shoulder surface 17 periodically changes between the thickness ha and the thickness hb. Here, "periodic" means that the thickness of the solid-phase fluidized layer Wa increases and decreases for each predetermined rotation angle (90° in this configuration) of the friction stir welding tool 100. Therefore, the specific position that becomes the joint 23 (FIG. 4) of the workpieces 21A and 21B is stirred while the thickness of the solid-phase fluidized layer Wa repeatedly increases and decreases for each predetermined time.

[0020] This stirring is not performed by continuously receiving a constant force on the solid-phase fluidized bed Wa, but by receiving a force that acts repeatedly at certain intervals, and is performed intermittently. This causes pulsation in the flow of the solid-phase fluidized bed Wa, and a high stirring effect is obtained. This type of stirring operation can reliably suppress the occurrence of defects such as cavities and cracks in the joint.

[0021] According to the friction stir welding tool 100 having the above-mentioned configuration, the solid-phase fluidized layer Wa generated by the frictional heat due to the rotation flows in such a way that it is pushed back forward in the rotation direction R by the weir surface 19d of the groove 19 provided in the shoulder 13, and the stirring effect of the solid-phase fluidized layer Wa is improved. In addition, since the groove 19 is formed linearly from the center of the shoulder 13 toward the radially outer side of the shoulder 13, the area occupied by the groove 19 with respect to the entire shoulder 13 is small, and the area of ​​the shoulder surface 17 can be secured widely. This ensures a large contact area between the shoulder surface 17 and the workpieces 21A, 21B, and promotes the generation of frictional heat. As a result, at the tip of the friction stir welding tool 100, a temperature rise due to frictional heat occurs in a short time, a large amount of heat input can be easily obtained, and the amount of solid-phase fluidized layer Wa required for welding can be generated with high efficiency. The generated solid-phase fluidized layer Wa is sufficiently stirred by passing through the groove 19 in the area facing the shoulder surface 17, and a defect-free homogeneous weld 23 is stably formed.

[0022] For example, in a friction stir welding tool having a probe and a shoulder with a recess around the probe at its tip, the rotation axis is tilted while the tool is advanced in the feed direction. In this case, the friction stir welding tool is subjected to a large resistance, making it difficult to increase the feed speed. In addition, the friction stir welding tool needs to be rotated using a dedicated machine tool, which increases the equipment cost.

[0023] When the shoulder around the probe is a convex surface that protrudes in the axial direction, the tool resistance can be reduced by rotating the rotation axis without tilting it. However, the contact area between the workpiece and the shoulder is small, making it difficult to obtain the necessary frictional heat. As a result, voids and cracks are likely to occur on the surface of the joint, resulting in an unstable joint.

[0024] In addition, in general, the load on the tool is larger in friction stir welding than in tools such as drills and end mills, so the shape of the shoulder is designed not to cause additional rotational resistance. Therefore, when a groove is provided on the shoulder, the groove is formed along the circumferential direction.

[0025] In contrast to such conventional friction stir welding tools, in the friction stir welding tool 100 of the present configuration, as described above, grooves 19 extending radially from the center are formed on the shoulder 13, the central portion of which protrudes in the axial direction, thereby ensuring a large area for the shoulder surface 17 while enabling reliable stirring of the solid-phase fluidized layer.

[0026] All of the shoulder surfaces 17 of the friction stir welding tool 100 of this configuration are formed continuously from the inner peripheral edge to the outer peripheral edge in the radial direction, and are curved surfaces that are also continuous in the circumferential direction with a central angle of 60° or more. In other words, each shoulder surface 17 is a sector subring that is continuous in the circumferential and radial directions. Therefore, during friction stir welding, the shoulder surface 17 comes into contact with the workpieces continuously in the circumferential direction, which has the effect of facilitating the accumulation of generated frictional heat, and the shoulder surface 17 is continuous in the radial direction, which has the effect of achieving a uniform temperature distribution over a wide range of the workpieces.

[0027] Moreover, the grooves 19 are sandwiched between the convex shoulder surfaces 17 and are formed to be recessed from the shoulder surfaces 17 without protruding from the shoulder surfaces 17. As a result, the grooves 19 do not generate excessively large rotational resistance between the workpieces and have a well-balanced shape suitable for stirring the solid-phase fluidized layer Wa.

[0028] As described above, the friction stir welding tool 100 of this configuration has a convex shoulder surface 17 at its tip that can generate a large amount of heat input while reliably stirring the solid-phase fluidized layer Wa, and can also accommodate high-speed feed operations, so that homogeneous, high-quality friction stir welding can be stably performed at a high feed speed, for example, of 1000 mm / min or more, preferably 1500 mm / min or more, and more preferably 2000 mm / min or more. It can be achieved.

[0029] Furthermore, since the circumferential cross-sectional shape of the groove 19 is a symmetrical V-shape, the rotational resistance is the same whether the rotation direction R of the friction stir welding tool 100 is forward or reverse, and the behavior of the solid-phase fluidized layer Wa is also the same.

[0030] In order to more reliably obtain the above-mentioned operational effects of the friction stir welding tool 100, it is preferable to set the shapes of the respective parts to have the following dimensional relationships. 9 is a side view of the tip of the friction stir welding tool 100. In the friction stir welding tool 100, the ratio d / D of the diameter D of the main body 11 to the diameter d of the probe 15 is preferably 0.2 or more and 0.5 or less, and more preferably 0.3 or more and 0.4 or less. The smaller the ratio d / D, the larger the area of ​​the shoulder surface 17 becomes, and the amount of frictional heat generated can be increased.

[0031] Furthermore, the ratio H / D of the diameter D to the protruding height H of the groove 19 of the probe 15 from the groove bottom is preferably 0.1 or more and 0.4 or less, and more preferably 0.2 or more and 0.3 or less. The smaller the ratio H / D, the smaller the feed resistance during joining, making it easier to increase the joining speed.

[0032] Furthermore, the ratio h / D of the diameter D to the maximum depth h of the groove 19 is preferably 0.03 or more and 1.2 or less, and more preferably 0.05 or more and 0.1 or less. The opening angle θ of the V-shaped groove 19 is preferably 30° or more and 90° or less, and more preferably 45° or more and 75° or less. By setting the ratio h / D and the opening angle θ in the above ranges, the circumferential width of the groove 19 is suppressed to a level that does not excessively increase the rotational resistance, and the solid-phase fluidized layer Wa can be well stirred in the groove 19.

[0033] Next, a modified example of the friction stir welding tool will be described. 10 is a perspective view showing a first modified example of the friction stir welding tool. This friction stir welding tool 100A has one groove 19 formed linearly from the inner peripheral edge of the shoulder 13 that contacts the probe 15 toward the radially outer side of the shoulder 13. By providing only one groove 19 extending in the radial direction, the area of ​​the shoulder surface 17 is increased, and the generation of frictional heat can be promoted.

[0034] 11 is a perspective view showing a second modified example of the friction stir welding tool. This friction stir welding tool 100B has a total of two grooves 19, each groove being spaced 180° apart from the probe 15. In this case, frictional heat is generated by the shoulder surface 17 divided into two, and the above-mentioned stirring of the solid-phase fluidized layer can be performed every half rotation.

[0035] 12 is a perspective view showing a third modified example of the friction stir welding tool. This friction stir welding tool 100C has a total of three grooves 19, each groove being spaced 120° apart from the probe 15. In this case, frictional heat is generated by the shoulder surface 17 divided into three parts, and the above-mentioned solid-phase fluidized layer can be stirred every 1 / 3 rotation.

[0036] 13 is a perspective view showing a fourth modified example of the friction stir welding tool. This friction stir welding tool 100D has a total of six grooves 19, each groove being spaced 60° apart from the probe 15. In this case, frictional heat is generated by the shoulder surface 17 divided into six parts, and the above-mentioned solid-phase fluidized layer can be stirred every 1 / 6 rotation.

[0037] 14 is a perspective view showing a fifth modified example of the friction stir welding tool. The grooves 19 of this friction stir welding tool 100E are formed linearly from the inner periphery side of the shoulder 13 toward the radially outer side of the shoulder 13, and are formed in the tangential direction of the outer periphery circle of the probe 15. A total of four grooves 19 are provided at 90° intervals around the probe 15. The inner periphery side edge of the groove 19 is cut off by other grooves 19 adjacent in the circumferential direction, and the outer periphery side edge extends to the outer periphery of the shoulder 13.

[0038] According to this friction stir welding tool 100E, when rotating in the rotation direction R1, the solid-phase fluidized layer entering the groove 19 is sent radially outward, and when rotating in the rotation direction R2, it is sent radially inward. Furthermore, the rotational resistance in the rotation direction R2 is greater than that in the rotation direction R1, and the amount of frictional heat generated varies depending on the rotation direction. Therefore, the rotation direction can be selected so that an appropriate amount of heat input can be obtained depending on, for example, the material and thickness of the workpieces to be joined.

[0039] FIG. 15 is a perspective view showing a sixth modified example of the friction stir welding tool. The groove 19 of this friction stir welding tool 100F is formed in a curved shape that curves to one side in the circumferential direction on the way from the inner circumferential side of the shoulder 13 toward the radially outer side of the shoulder 13. In this case, when rotating in the rotation direction R1, the solid-phase fluidized layer that enters the groove 19 is sent to the radially outer side, and when rotating in the rotation direction R2, it is sent to the radially inner side. In addition, the rotation resistance in the rotation direction R2 is larger than that in the rotation direction R1, and the amount of frictional heat generated changes depending on the rotation direction. Therefore, similar to the case shown in FIG. 14, the rotation direction can be selected so that an appropriate amount of heat input can be obtained.

[0040] 16 is a perspective view showing a seventh modified example of the friction stir welding tool. The grooves 19A of this friction stir welding tool 100G are arranged in a line from the inner periphery of the shoulder 13 toward the radially outer side of the shoulder 13, which is generally equivalent to a state in which a concave groove is formed in the radial direction. In this way, the groove 19A is not limited to a continuous groove, and may be configured with a plurality of grooves arranged discretely. The conditions of the grooves 19A, such as the size, number, and arrangement direction, can be set appropriately according to the conditions of the friction stir welding.

[0041] The above-described friction stir welding tools 100, 100A to 100G can be attached to the spindle of a machine tool dedicated to friction stir welding, but since there is no need to tilt the rotation axis, they can also be applied to general-purpose machine tools such as machining centers.

[0042] FIG. 17 is an explanatory diagram showing a state where a friction stir welding tool is attached to a spindle 33 of a machining center 31 to perform friction stir welding. The machining center 31 illustrated here can move the spindle 33 in the X direction, Y direction, and Z direction, and various tools 37 such as drills and end mills can be freely attached to the spindle 33 by a tool exchange unit 35. When performing friction stir welding using the machining center 31, the workpiece 21 is fixed to a table 39, and the joining surface is cut by a tool such as an end mill, and then the friction stir welding tool 100 prepared in advance in the tool exchange unit 35 is replaced on the spindle. This allows the workpiece 21 after cutting to be friction stir welded using the friction stir welding tool 100. Then, further machining can be performed on the workpiece 21 after friction stir welding. In this way, continuous processing is possible without removing the workpiece 21 from the table 39, high-speed processing can be performed with high processing accuracy, and task time can be shortened.

[0043] In the above-described machining center 31, the welding path for relatively moving the spindle 33 and the workpiece 21 during friction stir welding is controlled based on commands from the control unit 41. In this case, the control unit 41 can freely set the moving direction of the friction stir welding tool 100 in the same way as other tools.

[0044] 18 is an explanatory diagram that shows a schematic diagram of the movement path PS of the friction stir welding tool 100 by the control unit 41. In a normal machine tool dedicated to friction stir welding, the rotation axis of the friction stir welding tool is tilted, so that the welding path is often limited to a linear path. However, in the case of the friction stir welding tool 100 that performs processing without tilting the rotation axis, by using a machining center 31, movement along arbitrarily curved welding paths PS2 and PS3 is possible, in addition to the linear path PS1. Therefore, the range of application of friction stir welding is expanded, and it is possible to easily handle the joining of workpieces having complex shapes. EXAMPLES

[0045] Next, we will explain the results of friction stir welding of workpieces using various friction stir welding tools with different shapes. The workpieces used here are plate-shaped structures consisting of two extruded panels. (material to be joined) FIG. 19 is a perspective view of a structure 47 in which the side surfaces along the extrusion direction of a pair of extruded panels 45 are joined together. FIG. 20 is a cross-sectional view of the extruded panel 45 shown in FIG. 19. The extruded panels 45 are all plate-shaped extruded materials made of 6000-series aluminum alloys that have been artificially aged and hardened. The extruded panel 45 shown in FIG. 20 has a plate thickness t of 10 mm, a width W of 230 mm, and a longitudinal length of 1000 mm to 1600 mm. The plate thickness ta including the thick-walled portion 49 at the widthwise end is 11.4 mm. At both ends in the widthwise direction of the extruded panel 45, a thin-walled protruding portion 51 is provided protruding along one plate surface 45a, and a recessed portion 53 is provided on the other plate surface with which the tip of the protruding portion 51 can be engaged.

[0046] 21 is an enlarged cross-sectional view of a pair of extruded panels 45 at a joining position where their ends are butted together before joining. The pair of extruded panels 45 were placed upside down in the width direction, and the protrusions 51 and recesses 53 were engaged with each other, and the positions P1 and P2 where the tip surfaces 51a of the protrusions 51 butted against each other were determined as positions for performing friction stir welding. In addition, before friction stir welding, the protruding plate thickness tb of the thick-walled portion 49 was removed by cutting, and the plunge amount Δt for friction stir welding was set based on the machined surface.

[0047] (Friction stir welding tools) 22 to 24 are perspective views of the friction stir welding tool used for welding. The friction stir welding tool 55A (tool A) shown in Fig. 22 has a shoulder 13 formed at the tip of a main body 11, and a probe 15 disposed at the center of the shoulder 13 and protruding in the axial direction of the main body 11. The shoulder 13 is formed with a convex shoulder surface 17 protruding in the axial direction, and no groove is formed therein.

[0048] A friction stir welding tool 55B (tool B) shown in Fig. 23 is similar to the tool A except that one concentric annular groove 57 is provided on the shoulder surface 17 of the above-mentioned tool A. A friction stir welding tool 55C (tool C) shown in Fig. 24 is similar to the tool B except that the annular groove 57 of tool B is changed to two concentric grooves.

[0049] 1 to 3, the results were compared with those of the friction stir welding tool 100 (tool D) having the four radial grooves 19 shown in Fig. 1 to 3 described above, and the tools A to C. The shoulder diameter φD of the tools A to D was 15 mm, the radius of curvature of the tip surface of the probe 15 was 50 mm, and the protruding height H of the probe 15 was 2 mm (see Fig. 9).

[0050] (Test Results) The results of Test Examples 1 to 12, in which the workpieces were friction stir welded under different conditions using the above-mentioned various friction stir welding tools, are summarized in Table 1. The appearance of the joint was evaluated by visually observing the surface and observing the cross section of the joint, and a good appearance was evaluated as "○", a defect such as a cavity or crack was evaluated as "×", and an intermediate result was evaluated as "△".

[0051] [Table 1]

[0052] In test example 1, tool A (Fig. 22) without a groove on the shoulder was used, the tool rotation speed was 200 rpm, and the welding speed was 1000 mm / min. The position where the tip of the friction stir welding tool contacted the surface of the workpieces was set as the reference height, and the tool plunge amount Δt (see Fig. 21) from this reference height was set to 2.6 mm. A cavity defect occurred in the welded part after welding, and it is believed that an insufficient plunge amount was also a cause.

[0053] Test Example 2 was conducted under the same conditions as Test Example 1, except that the plunge depth was increased to 2.8 mm. At a joining speed of 1000 mm / min, the appearance of the joint was good.

[0054] Test example 3 was conducted under the same conditions as test example 2, except that tool B (Figure 23) with one annular groove was used and the plunge depth was set to 3.0 mm. Figure 25 is a cross-sectional photograph of the joint in test example 3. In test example 3, there were some locations where gaps had formed between the plate surfaces of the joined materials, and the appearance of the joint showed that many areas had void defects, with some areas free of defects mixed in.

[0055] In Test Examples 4 to 8, the plunge depth in Test Example 3 was changed to 3.1 mm, and the joining speed was increased from 1200 mm / min to 2000 mm / min. As a result, a dent was formed in the starting portion of the initial joining process in all conditions. Figure 26 is a cross-sectional photograph of the joining process in Test Example 8. When the joining speed was increased to 2000 mm / min, the cavity defect expanded, resulting in an unstable joining state.

[0056] Test Example 9 was conducted under the same conditions as Test Example 3, except that tool C (FIG. 24) with two annular grooves was used and the plunge depth was set to 2.7 mm. The appearance of the joint in this case showed that there were more areas without void defects than in Test Example 3, but the occurrence of defects was not improved as in the case of the single annular groove.

[0057] Test Example 10 was conducted under the same conditions as Test Example 9, except that the push-in amount was reduced to 2.6 mm. As a result, the appearance of the joint was good.

[0058] Test Example 11 used tool D (Figs. 1 to 3) with four radial grooves, and was under the same conditions as Test Examples 1 and 10, except that the welding speed was 1600 mm / min. Test Example 12 was under the same conditions as Test Example 11, except that the welding speed was further increased to 2000 mm / min. Figure 27 is a cross-sectional photograph of the joint in Test Example 12. According to Test Examples 11 and 12, even when the welding speed was increased to 2000 mm / min, no defects occurred in the joint, and a good appearance was maintained. In this way, it was confirmed that Tool D was more effective at improving defects than Tools A, B, and C.

[0059] The present invention is not limited to the above-described embodiments, and the present invention also contemplates the mutual combination of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the description in the specification and well-known techniques, and these are included in the scope of protection sought.

[0060] As described above, the present specification discloses the following: (1) A friction stir welding tool having a shoulder formed at the tip of a cylindrical main body and a probe disposed at the center of the shoulder and protruding in the axial direction of the main body, The shoulder has a convex shoulder surface whose central portion protrudes in the axial direction, and a groove recessed in the axial direction, the groove has an inner space for storing a part of a solid-phase fluidized layer of the workpieces generated by frictional heat due to rotation of the tool, returning the stored solid-phase fluidized layer to an opposing region of the shoulder surface on the rear side in a rotation direction as the tool rotates, and periodically changing a thickness of the solid-phase fluidized layer in the opposing region. Friction stir welding tools. With this friction stir welding tool, the convex shoulder surface suppresses an increase in the feed resistance of the workpieces, and part of the solid-phase fluidized layer generated by frictional heat caused by the rotation of the shoulder surface and the workpieces is stored in the groove space and returned to the opposing area of ​​the shoulder surface behind in the rotation direction, thereby periodically changing the thickness of the solid-phase fluidized layer. This stirring of the solid-phase fluidized layer suppresses the occurrence of defects such as cavities in the welded portion, and a good welded state of the workpieces is maintained even when the welding speed is increased.

[0061] (2) The friction stir welding tool according to (1), wherein the groove is formed linearly from the radially inner side to the radially outer side of the shoulder. According to this friction stir welding tool, the grooves are formed linearly, so that the solid-phase fluidized layer can be stirred uniformly along the longitudinal direction of the grooves.

[0062] (3) The friction stir welding tool according to (2), wherein the groove is formed in a radial direction of the shoulder from an inner circumferential edge of the shoulder close to the probe. According to this friction stir welding tool, the grooves formed in the radial direction stir the solid-phase fluidized layer from a direction perpendicular to the direction of rotation, thereby improving the stirring efficiency of the solid-phase fluidized layer.

[0063] (4) The friction stir welding tool according to (2), wherein the groove is formed in a tangential direction of an outer circumferential circle of the probe. This friction stir welding tool can simultaneously stir the solid-phase fluidized layer in the circumferential and radial directions, improving the stirring efficiency. In addition, depending on the rotation direction, the solid-phase fluidized layer can be selectively discharged radially outward or moved radially inward. Furthermore, when the amount of frictional heat generated differs depending on the rotation direction, the amount of heat input can be adjusted by selecting the rotation direction according to the joining conditions of the workpieces.

[0064] (5) The friction stir welding tool according to (1), wherein the groove is formed in a curved shape from the radially inner side to the radially outer side of the shoulder. According to this friction stir welding tool, the curved grooves allow the solid-phase fluidized layer to be stirred while moving it in the radial direction. Also, depending on the direction of rotation, the solid-phase fluidized layer can be selectively discharged radially outward or moved radially inward. Furthermore, when the amount of frictional heat generated differs depending on the direction of rotation, the amount of heat input can be adjusted by selecting the direction of rotation according to the joining conditions of the workpieces.

[0065] (6) The friction stir welding tool according to any one of (1) to (5), wherein a plurality of the grooves are formed on the shoulder surface. According to this friction stir welding tool, a plurality of grooves are formed, so that the stirring frequency of the solid-phase fluidized layer during one rotation can be increased, and the stirring efficiency can be improved.

[0066] (7) The friction stir welding tool according to (6), wherein four or more grooves are formed. This friction stir welding tool can stir the solid-phase fluidized bed four or more times in one rotation.

[0067] (8) The friction stir welding tool according to any one of (1) to (7), wherein a cross-sectional shape of the groove along a circumferential direction is V-shaped. With this friction stir welding tool, a solid-phase fluidized layer enters the inner space of the V-shape, promoting stirring.

[0068] (9) The friction stir welding tool according to any one of (1) to (8), wherein the convex shape of the shoulder is a curved shape that bulges in the axial direction. According to this friction stir welding tool, the shoulder surface has a convex curved shape that bulges in the axial direction, which reduces the rotational resistance between the workpieces and the shoulder surface and allows the feed speed to be increased, which makes it easier to further improve the welding speed.

[0069] (10) A tip of the friction stir welding tool according to any one of (1) to (9) is pressed against a joint of workpieces and rotated, and the workpieces are joined by moving the friction stir welding tool and the workpieces relative to each other while generating the solid-phase fluidized layer in the workpieces by friction generated between the workpieces and the friction stir welding tool. Friction stir welding method. According to this friction stir welding method, the workpieces can be joined at a high joining speed while suppressing the occurrence of defects.

[0070] (11) The friction stir welding method according to (10), wherein the friction stir welding tool is pressed against the joint from a normal direction of the surfaces of the workpieces and rotated. According to this friction stir welding method, the rotational resistance with the workpieces is suppressed and the feed speed can be increased, which makes it easier to further improve the welding speed.

[0071] (12) The friction stir welding method according to (10) or (11), wherein the friction stir welding tool is attached to a spindle of a machining center and the workpieces are joined. According to this friction stir welding method, friction stir welding can be performed using a highly versatile machining center, so that friction stir welding can be performed in combination with machining using other tools such as cutting and polishing. In this way, since the workpieces to be joined can be continuously machined while being positioned on the table, machining accuracy and efficiency can be improved and tact time can be shortened.

[0072] (13) The friction stir welding method according to (12), wherein the friction stir welding tool and the workpieces are moved relative to each other in a curved line on the surfaces of the workpieces. According to this friction stir welding method, the planned joining line between the workpieces is not limited to a straight line, and it is possible to join even curved lines. Therefore, for example, it is possible to join workpieces having complex shapes, thereby improving design freedom.

[0073] (14) The friction stir welding method according to any one of (10) to (13), wherein the workpieces are aluminum or an aluminum alloy. According to this friction stir welding method, aluminum material, which is lighter than steel material, can be friction-diffusion-welded at high speed, and the range of applications of aluminum material can be expanded, for example, to vehicles. [Explanation of symbols]

[0074] 11 Main body 13 Shoulder 15 Probe 15a Proximal end 17 Shoulder surface 19,19A Groove 19a groove bottom 19b Inner gutter end 19c End of outer periphery gutter 21A,21B Material to be joined 23 Joint 31 Machining Center 33 Main axis 35 Tool Change Unit 37 Tools 39 Table 41 Control section 45 Extrusion Panel 47 Structure 49 Thick wall part 51 Protrusion 51a Tip surface 53 Recess 55A, 55B, 55C Friction stir welding tools 57 Circular groove 100 Friction stir welding tool

Claims

1. A friction stir welding tool having a shoulder formed at a tip of a cylindrical main body and a probe disposed at a center of the shoulder and protruding in an axial direction of the main body, The shoulder has a convex shoulder surface whose central portion protrudes in the axial direction, and a groove recessed in the axial direction, the groove has an inner space for storing a part of a solid-phase fluidized layer of the workpieces generated by frictional heat due to rotation of the tool, returning the stored solid-phase fluidized layer to an opposing region of the shoulder surface on the rear side in a rotation direction as the tool rotates, and periodically changing a thickness of the solid-phase fluidized layer in the opposing region. Friction stir welding tools.

2. The groove is formed linearly from the radially inner side to the radially outer side of the shoulder. The friction stir welding tool of claim 1 .

3. The groove is formed in a radial direction of the shoulder from an inner circumferential edge of the shoulder. The friction stir welding tool according to claim 2.

4. The groove is formed in a tangential direction of an outer circumferential circle of the probe. The friction stir welding tool according to claim 2.

5. The groove is formed in a curved shape from the radially inner side to the radially outer side of the shoulder. The friction stir welding tool of claim 1 .

6. A plurality of the grooves are formed in the shoulder. The friction stir welding tool of claim 1 .

7. The grooves are formed in four or more pieces. The friction stir welding tool according to claim 6.

8. The cross-sectional shape of the groove along the circumferential direction is V-shaped. The friction stir welding tool of claim 1 .

9. The convex shape of the shoulder is a curved shape that bulges in the axial direction. The friction stir welding tool of claim 1 .

10. The tip of the friction stir welding tool according to any one of claims 1 to 9 is pressed against a joint portion of workpieces and rotated, and the friction stir welding tool and the workpieces are moved relative to each other to join the workpieces while the solid-phase fluidized layer is generated in the workpieces by friction generated between the workpieces and the friction stir welding tool. Friction stir welding method.

11. The friction stir welding tool is pressed against the joint from a normal direction of the surface of the workpiece and rotated. The friction stir welding method according to claim 10.

12. The friction stir welding tool is attached to a spindle of a machining center, and the workpieces are joined. The friction stir welding method according to claim 10.

13. The friction stir welding tool and the workpiece are moved relative to each other in a curved line on the surface of the workpiece. The friction stir welding method according to claim 12.

14. The workpiece is aluminum or an aluminum alloy. The friction stir welding method according to claim 10.

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