Friction stir spot welding tool

Abstract

To provide a friction stir spot welding tool adopting a pin preceding process, capable of reducing welding pressure of an overlapping portion of to-be-welded members.SOLUTION: A friction stir spot welding tool includes: a columnar pin 11 that rotates around an axis; a shoulder 12 having a hollow portion into which the pin 11 is inserted; and a driving unit 2 that press-fits the pin 11 into to-be-welded objects while rotating the pin and drives the shoulder 12 so as to retreat from the to-be-welded objects. At least a part of a circular tip surface 5 of the pin 11 is provided with a step-shaped portion 51 forming a step in a direction of rotation of the pin 11.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a friction stir spot welding tool having a pin and a shoulder. [Background technology]

[0002] Friction stir welding is known as a method for overlapping and joining two or more members made of metal members, fiber-reinforced thermoplastic resin members, etc. For friction stir welding, a friction stir spot welding tool equipped with a pin and a shoulder having a hollow portion for accommodating the pin is sometimes used. For example, in a shoulder-first process, the shoulder is protruded and pressed into the overlapping portion of the members to be joined, while the pin is retracted to accommodate the material that overflows due to the press-in (see, for example, Patent Document 1). On the other hand, in a pin-first process, the pin is pressed into the overlapping portion, while the shoulder is retracted. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-186869 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned pin-first process, when a high joining pressure is required for the friction stir spot joining of the overlapping parts, the size and cost of the equipment including the joining tool become a problem. For example, when joining overlapping parts of fiber-reinforced thermoplastic resin members, a large pressure is required to cut the continuous fibers contained therein. In this case, in order to reduce the amount of deflection due to the reaction force of the pressure force, it is necessary to adopt large and highly rigid arms to which the joining tool is attached.

[0005] The present disclosure aims to reduce the welding pressure applied to overlapping portions of members to be joined in a friction stir spot welding tool that employs a pin-first process. [Means for solving the problem]

[0006] A friction stir spot welding tool according to one aspect of the present disclosure comprises a cylindrical pin that rotates about an axis, a shoulder having a hollow portion through which the pin is inserted, and a drive unit that drives the pin to rotate while pressing it into objects to be joined, and drives the shoulder to retract from the objects to be joined, and at least a portion of the tip surface of the pin is provided with a step-shaped portion that forms a step in the rotational direction of the pin. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a friction stir spot welding tool that employs a pin-first process and is capable of reducing the welding pressure applied to the overlapping portions of the members to be joined. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a configuration of a friction stir spot welding apparatus including a friction stir spot welding tool according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram showing the configurations of a first member and a second member to be friction stir spot joined. [Diagram 3] FIG. 3 is a diagram showing a joining procedure by the pin-first process using a friction stir spot welding tool. [Figure 4] FIG. 4 is a perspective view and a side view showing a pin of a friction stir spot welding tool according to an embodiment of the present disclosure and the shape of its tip surface, together with a comparative example. [Diagram 5] FIG. 5 is a graph showing the relationship between the amount of press-in of the pin into the test piece and the joining time for the examples and the comparative examples. [Figure 6] FIG. 6 is a graph showing the relationship between the amount of pressurization and the joining time when the pin of the embodiment is pressed into the test piece by changing the pressure applied thereto. [Figure 7]FIG. 7(A) is a diagram showing the behavior of the stirred material in a shoulder-first process, and FIG. 7(B) is a diagram showing the behavior of the stirred material in a pin-first process. [Figure 8] 8(A) to 8(C) are perspective views showing other examples of the shape of the tip of the pin of the friction stir spot welding tool. [Figure 9] 9(A) to 9(F) are plan views showing modified examples of the shape of the tip surface of the pin shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. A friction stir spot welding apparatus equipped with a friction stir spot welding tool according to the present disclosure can be applied to the manufacture of various joined bodies obtained by spot-joining two or more structural materials, such as plates, frames, exterior materials, or columnar materials made of metal, resin, or thermoplastic resin molded bodies mixed with fiber materials, by overlapping them together. The manufactured joined bodies become components of structures such as aircraft, railway vehicles, and automobiles.

[0010] [Configuration of friction stir spot welding device] Fig. 1 is a schematic diagram showing the configuration of a friction stir spot welding apparatus M according to an embodiment of the present disclosure. The friction stir spot welding apparatus M includes a double-action friction stir spot welding tool 1, a tool drive unit 2 that drives the tool 1 to rotate and elevate, and a controller 20 that controls the operation of each part of the friction stir spot welding apparatus M. Note that, although directional indications of "up" and "down" are added in Fig. 1, this is for the convenience of explanation and is not intended to limit the actual direction in which the tool 1 is used.

[0011] The tool 1 is supported by various tool fixing parts. For example, the tool fixing part is the tip of an articulated robot. A backup 15 is arranged facing the lower end surface of the tool 1. A joining object 3 is arranged between the tool 1 and the backup 15. The joining object 3 is formed by overlapping at least two members. FIG. 1 shows an example in which an overlapping portion 30, in which a part of a first member 31 made of a flat plate and a part of a second member 32 also made of a flat plate overlap in the vertical direction, is arranged between the tool 1 and the backup 15 as the joining object 3.

[0012] The tool 1 includes a pin 11, a shoulder 12, a clamp 13, and a spring 14. The pin 11 is a cylindrical member, and is arranged so that its axis extends in the vertical direction. The pin 11 can rotate about the axis as a rotation axis R, and can move forward and backward in the vertical direction along the rotation axis R. When the tool 1 is used, the rotation axis R is aligned with a point joining position W at the overlapping portion 30.

[0013] 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, i.e., the rotation axis R. The shoulder 12 can rotate around the rotation axis R and can move up and down along the rotation axis R. The tool 1 of this embodiment is a double-acting tool in which the pin 11 and the shoulder 12 move independently in the axial direction. That is, the shoulder 12 and the pin 11 inserted in the hollow portion can move relatively in the direction of the rotation axis R while rotating together around the axis of the rotation axis R. Specifically, the pin 11 and the shoulder 12 can not only move up and down simultaneously along the rotation axis R, but also independently move such that one moves down and the other moves up.

[0014] 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 about 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 with the clamp 13 prevents the friction stir material from scattering, and enables the friction stir spot welded portion to be finished smoothly.

[0015] The spring 14 is attached to the upper end side of the clamp 13 and urges the clamp 13 downward toward the overlapping portion 30. The clamp 13 is attached to the tool fixing portion via the spring 14. The backup 15 has a flat surface that abuts against the lower surface side of the overlapping portion 30 to be joined. The backup 15 is a backing member that supports the overlapping portion 30 when the pin 11 or the shoulder 12 is pressed into the overlapping portion 30. The clamp 13, urged by the spring 14, presses the overlapping portion 30 against the backup 15.

[0016] The tool driving unit 2 includes a rotation driving unit 21, a pin driving unit 22, a shoulder driving unit 23, and a clamp driving unit 24. The rotation driving unit 21 includes a motor, a driving gear, etc., and drives the pin 11 and the shoulder 12 to rotate around the rotation axis R. The pin driving unit 22 is a mechanism for moving the pin 11 forward and backward along the rotation axis R. The pin driving unit 22 drives the pin 11 so as to press the pin 11 into the overlapping portion 30 and to retract the pin 11 from the overlapping portion 30. The shoulder driving unit 23 is a mechanism for moving the shoulder 12 forward and backward along the rotation axis R, and causes the shoulder 12 to press into the overlapping portion 30 and to retract the shoulder 12. The clamp driving unit 24 is a mechanism for moving the clamp 13 forward and backward along the rotation axis R. The clamp driving unit 24 moves the clamp 13 toward the overlapping portion 30 and presses the overlapping portion 30 against the backup 15. At this time, the biasing force of the spring 14 acts.

[0017] The controller 20 is composed of a microcomputer or the like, and executes a predetermined control program to control the operation of the tool driving unit 2. Specifically, the controller 20 controls the rotation driving unit 21 to cause the pin 11 and the shoulder 12 to perform a required rotation operation. The controller 20 also controls the pin driving unit 22, the shoulder driving unit 23, and the clamp driving unit 24 to cause the pin 11, the shoulder 12, and the clamp 13 to perform a required forward and backward movement operation.

[0018] 2 is a diagram showing the configuration of a first member 31 and a second member 32 to be friction stir spot welded. Here, an overlapping portion 30 is shown in which a part of a plate-shaped first member 31 and a part of a plate-shaped second member 32 are overlapped vertically. The overlapping portion 30 may be an overlapping portion between a plate and a frame (or a columnar member), or an overlapping portion between frames. The overlapping portion 30 has a mating surface BD where a joint surface 31A on the lower surface of the first member 31 and a joint surface 32A on the upper surface of the second member 32 are in direct contact with each other. One or more other plates may be interposed between the first member 31 and the second member 32.

[0019] FIG. 2 shows an example in which a molded body formed by laminating multiple layers of prepregs in which a continuous fiber array is impregnated with a thermoplastic resin is used as the first member 31 and the second member 32. FIG. 2 shows a part of the sheet stack 33 constituting the first member 31. The sheet stack 33 includes a first sheet layer 33A, a second sheet layer 33B, and a third sheet layer 33C each made of a sheet in which a continuous fiber array is impregnated with a thermoplastic resin. The first sheet layer 33A is a sheet having a thickness of about 0.1 mm to 0.5 mm in which a large number of continuous fibers 34 are arranged in a predetermined arrangement direction and the arrangement is impregnated with a thermoplastic resin to be integrated. The second sheet layer 33B and the third sheet layer 33C are also sheets similar to those described above, but the arrangement directions of the continuous fibers 34 are mutually different. The second member 32 is also a plate made of a multi-layer laminate of sheets similar to the first member 31.

[0020] During friction stir spot welding of the overlapping portion 30 by the tool 1, the thermoplastic resin of the impregnating material is friction stirred while cutting the continuous fibers 34 by pressing the tool 1 in. The prepreg molded body is an example of a constituent material of the first member 31 and the second member 32. For example, the overlapping portion 30 may be formed using two or more metal plates such as aluminum or steel. As an example, the first member 31 on the side where the tool 1 is first pressed in may be made of aluminum alloy, and the second member 32 may be made of high tensile steel.

[0021] [How to use the tool] Next, a method of using the tool 1 exemplified in this embodiment will be described. The method of using the friction stir spot welding apparatus M is roughly classified into a pin-first process in which the pin 11 of the tool 1 is first pressed into the overlapping portion 30 of the workpieces 3 to be joined, and a shoulder-first process in which the shoulder 12 is first pressed into the overlapping portion 30. In this embodiment, the controller 20 drives the tool 1 to operate in the pin-first process.

[0022] 3 is a diagram showing processes P11 to P14 of the friction stir spot welding method by the pin-first process. Here, the processes for friction stir spot welding of an overlapping portion 30 of a first member 31 and a second member 32 are shown in a simplified manner. Process P11 shows a preheating step of the overlapping portion 30. With the lower end of the tool 1 in contact with the surface of the first member 31, the pin 11 and shoulder 12 are rotated around the axis at a predetermined high speed.

[0023] Process P12 shows a step of pressing in the pin 11. As shown by the outline arrow in the figure, the pin 11 is rotated around its axis while being lowered to be pressed into the overlapping portion 30, while the shoulder 12 is withdrawn upward. This action agitates the material in the press-in region of the pin 11. In addition, the overflowing material OF that overflows from the overlapping portion 30 due to the press-in is released into the annular region between the pin 11 and the clamp 13 that is created by the withdrawal of the shoulder 12 (see arrow a1).

[0024] Process P13 shows a backfilling process of the overflowing material OF. In the backfilling process, the pin 11 is raised and retreated, while the shoulder 12 is lowered. By lowering the shoulder 12, as shown by the arrow a2, the overflowing material OF that has escaped to the annular region is backfilled into the press-fitted region of the pin 11.

[0025] Process P14 shows a smoothing process. With the lower end faces of the pin 11 and the shoulder 12 returned to the same height position as the surface of the first member 31, both are rotated to smooth the spot-joined portion. If the first member 31 is made of a thermoplastic resin, the pin 11 and the shoulder 12 may not be rotated in process P14, and the spot-joined portion may simply be pressed. Through the above process, the stir welded portion 4a is formed, and the first member 31 and the second member 32 are spot-joined at the overlapping portion 30.

[0026] [Embodiment of the tool pin] 4 is a perspective view and a side view showing the shape of the pin 11 and its tip portion 11T of the friction stir spot welding tool 1 according to an embodiment of the present disclosure, together with a comparative example. Conventionally, the tip portion 11T of the pin 11 has a shape having a circular tip surface 50 made of a flat surface, as shown in the <Comparative Example> section. In other words, the tip surface 50 is a flat surface without any steps or the like. When the pin-first process is performed using the tool 1 equipped with the pin 11 having such a tip surface 50, a high welding pressure may be required.

[0027] An example in which a high joining pressure is required is when the joining object 3 is a sheet stack 33 made of a thermoplastic resin prepreg (e.g., thermoplastic CFRP) reinforced with continuous fibers 34, as illustrated in FIG. 2, and at least the first member 31 is configured. In the case of such a first member 31, the pin 11 is pressed in while cutting the continuous fibers 34 during friction stirring. In order to cut the continuous fibers 34, a large pressure force needs to be applied to the tool 1. According to experiments by the present inventors, it was found that about 60% of the total pressure applied to the tool 1 is used to cut the continuous fibers of the thermoplastic CFRP. The remaining about 40% of the total pressure is used exclusively to push the overflow material OF into the annular region on the outer periphery of the pin 11.

[0028] When a high welding pressure is required, measures against the reaction force are necessary. For example, when the tool 1 is mounted on the tip of a robot arm, the rigidity of the robot arm needs to be set high so that bending deformation or the like does not occur due to the reaction force. In order to increase the rigidity, it is necessary to increase the size of the robot arm or use a high-strength arm material, which results in an increase in the size and cost of the friction stir spot welding apparatus M including the tool 1.

[0029] The tip portion 11T of the pin 11 according to the present disclosure has a tip surface 5 shaped to suppress the joining pressure force. As shown in the <Example> section of FIG. 4, the tip surface 5 is circular in axial view, as in the conventional case, but the tip surface 5 is provided with a step-shaped portion 51 that forms a step in the rotation direction F of the pin 11. The step of the step-shaped portion 51 is a radial step extending radially from the center point CP of the circular tip surface 5 to the outer periphery of the circle. A plurality of step-shaped portions 51 are arranged in the circumferential direction of the tip surface 5. FIG. 4 shows an example in which eight radial steps are arranged at equal intervals in the circumferential direction of the tip surface 5.

[0030] The step 51 is shallowest at the center point C of the tip surface 5 and deepest at the outer circumferential edge of the tip surface 5. In other words, the step 51 is shaped such that the step height h gradually increases from the center point C toward the radially outer side of the tip surface 5. As a result of eight such step 51 being formed at equal intervals, eight fan surfaces 52 of the same size are lined up in the circumferential direction on the tip surface 5. These fan surfaces 52 are surfaces with an inclination according to the step height h of the step 51.

[0031] Also referring to the <side view> of FIG. 4, the sector surface 52 has an inclination such that the front end 521 in the rotation direction F of the pin 11 is high and the rear end 522 is low. The "high" front end 521 means that, assuming that the tip surface 5 is the lower end surface of the pin 11, the front end 521 protrudes downward more than the rear end 522. The line Ho added to the <side view> is a horizontal line perpendicular to the axis of the pin 11. The sector surface 52 has an inclination determined by the step height h with respect to this line Ho. The step height h is maximum at the position of the outer periphery of the tip surface 5. The height of the front end 521 and the height of the center point CP are the same height. On the other hand, the height of the rear end 522 is the same height as the center point CP at the position of the center point CP, but is lower by the maximum step height h at the position of the outer periphery of the tip surface 5.

[0032] As can be seen from the shape characteristics described above, the center point CP of the tip surface 5 does not protrude downward. In other words, even though the step shape portion 51 is processed, the tip surface 5 is guaranteed to be flat when viewed macroscopically. This is because, as described above, in process P14 of FIG. 3, there is a process of pressing the tip surface 5 of the pin 11 against the surface of the stir welded portion 4 to finish it, and it is considered that the shape of the tip surface 5 is transferred to the surface of the stir welded portion 4 in this process. In other words, if there is a significant protrusion on the tip surface 5, a recess corresponding to the protrusion is formed on the surface of the stir welded portion 4, so that the flatness of the welded object 3 cannot be guaranteed. To avoid this, it is desirable that there is no significant protrusion on the tip surface 5.

[0033] The stepped portion 51 has a stepped surface based on the height difference between the front end 521 and the rear end 522 of a pair of circumferentially adjacent fan surfaces 52. This stepped surface is a surface extending in a direction perpendicular to the rotation direction F. The stepped surface and the right-angled edge of the front end 521 form a blade shape and play a role in cutting the objects to be joined. Such a blade improves the agitation properties of the objects to be joined and the ability to push the agitation material outward in the radial direction, and also contributes to cutting the continuous fibers 34 described above.

[0034] The step height h of the step shape portion 51 may be set appropriately, but if it is too high, the press-fit resistance will increase, and if it is too low, the effect as a "blade" will be reduced. The step height h can be determined based on the diameter φ of the pin 11. For example, the step height h can be set so that the maximum height difference of the step between the front end 521 and the rear end 522 is in the range of 1% to 10% of the diameter φ of the pin 11, and preferably in the range of 1.5% to 7%.

[0035] The step surface of the step shape portion 51 may be a vertical surface parallel to the axis Zo of the pin 11, or may be a surface having an inclination angle θ with respect to the axis Zo as shown in Fig. 4. The step surface of the step shape portion 51 in the example shown is a surface that intersects at a right angle with a sector surface 52 that is inclined with respect to the line Ho. The inclination angle θ can be selected, for example, within the range of 2 degrees to 7 degrees.

[0036] [Press-fit test example] <Test 1> The tool 1 having the tip surface 5 according to the <Example> in FIG. 4 and the tool 1 having the tip surface 50 according to the <Comparative Example> were used at the tip 11T of the pin 11, and the pressure required to achieve the same pin press-in amount for the same test piece was investigated. As a test piece for the joining object 3, an overlapping portion 30 was prepared in which two thermoplastic CFRP resin sheets having a thickness of 2.5 mm were overlapped. In both the Example and the Comparative Example, the pin 11 had a diameter φ of 9 mm. The maximum height difference of the step height h of the step-shaped portion 51 of the tip surface 5 of the Example was 0.28 mm, and the inclination angle θ of the step surface was 5 degrees. The tip surface 50 of the Comparative Example was a flat horizontal surface.

[0037] The pin 11 was press-fitted into the overlapping portion 30 by using the tools 1 of the example and the comparative example, with the target press-fit value of 3.87 mm. In both the example and the comparative example, the pin 11 was press-fitted to achieve the target press-fit value. However, the pressure required to achieve the target press-fit value was Example = 4 [kN], Comparative Example = 9 [kN] It was confirmed that the tool 1 of the embodiment was capable of performing friction stir spot welding of the overlapping portion 30 with a pressure force significantly lower than that of the comparative example.

[0038] <Test 2> A test was conducted in which the pin 11 was pressed into the same metal sample with the same pressing force using a tool 1 having the same tip surface 5 of the example and a tool 1 having the tip surface 50 of the comparative example as in Test 1. A 1 mm thick sample of A7075 aluminum alloy specified in JIS-H-4040 that had been subjected to T6 treatment was used as the metal sample. The target value of the pin 11 being pressed into the sample was set to 0.5 mm, and the pressing force was set to 5.5 kN, and the pin 11 of the tool 1 of the example and the comparative example was pressed into the metal sample.

[0039] FIG. 5 is a graph showing the relationship between the amount of pressing (mm) of the pin 11 into the metal sample and the joining time (seconds) for the embodiment and the comparative example. Characteristic A1 shows the behavior of pressing the pin 11 by the tool 1 of the embodiment. It can be seen that the pressing of the pin 11 to the target value is completed in about 2.5 seconds from the start of pressing the pin 11 into the metal sample. On the other hand, characteristic B1 shows the behavior of pressing the pin 11 by the tool 1 of the comparative example. As a result, the pin 11 could not be pressed to achieve the target value with the set pressure of 5.5 kN. Characteristic B2 shows the behavior of pressing when the tool 1 of the comparative example is applied with a pressure of 8.7 kN that can be set by the test device used to execute the test 2, and the pin 11 is pressed into the metal sample. As shown in characteristic B2, the tool 1 of the comparative example was only able to press about 0.2 mm even when a pressure force of about 60% more than the set pressure force was applied, and the target value of pressing was not achieved.

[0040] <Test 3> The relationship between the pin press-in amount and joining time was investigated using overlapping portion 30 formed from the thermoplastic CFRP resin sheet used in Test 1 and tool 1 having tip surface 5 of the example. In Test 1, it was confirmed that the press-in target value of 3.87 mm could be achieved with a pressure of 4 kN for tool 1, but an investigation was conducted to see whether press-in was possible with a lower pressure.

[0041] FIG. 6 is a graph showing the relationship between the amount of pin press-in (mm) and the joining time (seconds) when the pin is pressed into the overlapping portion 30 by changing the pressing force applied to the tool 1 of the embodiment. The characteristics A11, A12, A13, and A14 shown in the graph show the pressing behavior when the pressing force is 4 kN, 3.5 kN, 3 kN, and 2 kN, respectively. As can be seen from this graph, it was confirmed that the pressing force can be reduced to 2 kN and the target pressing value can be achieved by reducing the pressing speed of the pin 11 and thereby lengthening the joining time. Incidentally, with the tool 1 of the comparative example, the target pressing value could not be achieved with a pressing force of 4 kN, no matter how much the pressing speed of the pin 11 was reduced.

[0042] From the above Tests 1 to 3, it was confirmed that the step-shaped portion 51 contributes to reducing the joining pressure when the joining objects are joined by pressing the pin 11 in the pin-first process. In the pin-first process in which the pin 11 is pressed in while the shoulder 12 is retracted, as described in the process P12 of FIG. 3, the material immediately below the pin 11 is stirred and fluidized, and is pushed out into the annular space generated by the retraction of the shoulder present on the outer periphery of the pin 11. The step-shaped portion 51 on the tip surface 5 of the pin 11 forms a step in the rotation direction F of the pin 11. Therefore, when the pin 11 is pressed into the joining objects 3 while rotating around the axis, the step-shaped portion 51 actively cuts the material immediately below the pin 11. Even if the joining objects 3 are the sheet stack 33 as exemplified in FIG. 2, the step-shaped portion 51 acts as a blade to cut the continuous fibers 34, so that the joining pressure can be reduced.

[0043] Furthermore, the step-shaped portion 51 also contributes to the active pushing out of the material cut just below the pin 11 into the shoulder retraction space. That is, the step-shaped portion 51 has a step surface extending in a direction perpendicular to the rotation direction F of the pin 11, that is, in the radial direction. As the pin 11 rotates, the step surface functions to push the stirring material outward in the radial direction. This function cannot be achieved by the pin 11 of the comparative example having only the flat tip surface 50. If the step-shaped portion 51 is used in the pin 11 of the embodiment having the functions of actively cutting the material and pushing out the stirring material by the above-mentioned step-shaped portion 51, the stirring of the material just below the pin 11 and the flow of the stirring material toward the radially outward direction of the pin 11 become smooth. Therefore, the pressure of the pin 11 against the workpiece 3 during friction stir spot welding, that is, the welding pressure that must be applied to the tool 1, can be reduced.

[0044] Based on the above confirmation results, it is also possible to adopt a shoulder-first process instead of the pin-first process and provide a step-shaped portion similar to the step-shaped portion 51 of this embodiment on the tip surface of the shoulder 12. However, adopting the pin-first process and providing the step-shaped portion 51 on the tip surface 5 of the pin 11 has more advantages than the shoulder-first process. This point will be explained with reference to FIG. 7.

[0045] FIG. 7(A) shows the behavior of the stirring material in the shoulder-first process, and FIG. 7(B) shows the behavior of the stirring material in the pin-first process. In the tool 100 employing the shoulder-first process, it is assumed that the overflowing material OF escapes into the space in the shoulder 120 created by the rise of the pin 110, as shown by the arrow a3. However, if a step-shaped portion is provided on the tip surface of the shoulder 120, which increases the flow of the stirring material, the overflowing material OF will have no escape route, and as shown by the arrow a4, a flow in which the material flows out radially outward of the shoulder 120 below the clamp 130 may occur. As a result of such material outflow, dents are likely to occur in the friction stir spot welded portion. In contrast, in the pin-first process, as shown by the arrow a5, the overflowing material OF is originally set to escape radially outward of the pin 11. Therefore, even if the flow of the stirring material increases due to the provision of the stepped portion 51, the overflowing material OF easily returns to the stirring area, and no dents are formed in the friction stir spot welded portion.

[0046] In addition, when the joint diameter Ws in the shoulder-first process and the joint diameter Wp in the pin-first process are the same, the pin-first process produces a larger volume of overflowing material OF. For example, when the diameter φ of the pin 11 is 9 mm, the overflowing material OF in the pin-first process is 1.8 times that in the shoulder-first process. Thus, in the pin-first process, in which more material needs to be pushed out during mixing, the significance of forming the stepped portion 51 on the tip surface 5 of the pin 11 to increase the pushing force is greater than in the shoulder-first process.

[0047] [Other examples of pin tip shapes] 8(A) to (C) are perspective views showing other examples of the shape of the tip portion 11T of the pin 11 of the friction stir spot welding tool 1. In Fig. 8(A) to (C), examples are shown in which the steps of the stepped portion are steps formed by cutting out parts of the outer circumferential edges of the pin tip surfaces 5A, 5B, and 5C. These steps are formed by groove-shaped cutouts.

[0048] A plurality of oblique grooves 53 are formed on the tip surface 5A of the tip portion 11T shown in FIG. 8(A). The oblique grooves 53 are recessed grooves formed on the tip surface 5A, and extend linearly from the outer periphery of the tip surface 5A to the radially inward direction of the tip surface 5A. The oblique grooves 53 are grooves that have an inclination in a direction approaching the outer periphery with respect to a virtual line corresponding to the diameter of the circular tip surface 5A. The inclination is an inclination that directs the oblique grooves 53 in a direction following the rotation direction F of the pin 11. By forming such oblique grooves 53, a step shape exists near the outer periphery of the tip surface 5A. FIG. 8(A) shows an example in which eight short oblique grooves 53 are arranged at equal intervals along the outer periphery of the tip surface 5A. The length, radius, depth, arrangement pitch, inclination, etc. of the oblique grooves 53 can be changed as appropriate.

[0049] In the tip portion 11T shown in FIG. 8(B), a plurality of helical grooves 54 are formed starting from the tip surface 5B and extending in the axial direction of the pin 11. The helical grooves 54 are recessed grooves formed in the side peripheral surface of the tip portion 11T, and extend in a spiral shape from the outer periphery of the tip surface 5B to the upstream side in the rotation direction F. A step shape is formed near the outer periphery of the tip surface 5B by cutting out the helical grooves 54 radially inward. The helical grooves 54 in FIG. 8(B) are only an example, and the length, radius, depth, arrangement pitch, helical angle, etc. of the helical grooves 54 can be changed as appropriate.

[0050] The tip portion 11T shown in FIG. 8(C) is formed with an axial groove 55 that extends linearly in the axial direction of the pin 11, starting from the tip surface 5C. The axial groove 55 is a recessed groove formed on the side peripheral surface of the tip portion 11T, and extends a predetermined length in the axial direction of the pin 11 from the outer circumferential edge of the tip surface 5B. In the pin 11 equipped with the tip portion 11T having the axial groove 55, both the clockwise direction and the counterclockwise direction can be set as the rotation direction FA. A step shape is formed near the outer circumferential edge of the tip surface 5C by cutting out the axial groove 55 toward the inside in the radial direction. The axial groove 55 in FIG. 8(C) is an example, and the length, radius, depth, arrangement pitch, etc. of the axial groove 55 can be changed as appropriate.

[0051] As illustrated above, a step can be formed by cutting out a part of the outer periphery of the pin tip surface by forming the oblique groove 53, the spiral groove 54, and the axial groove 55. This step can also promote the cutting out of the material directly below the pin 11 and the extrusion of the material into the shoulder retreat space, thereby reducing the joining pressure of the tool 1.

[0052] Figures 9(A) to (F) show various modified examples of forming the stepped portion 51 shown in Figure 4 on the tip surface of the pin 11. Figure 9(A) shows a tip surface 5D having only one stepped portion 51. Similar to the example in Figure 4, the stepped portion 51 extends linearly from the center point C toward the outer circumferential edge of the tip surface 5D, and has a shape in which the step height gradually increases toward the radially outward direction.

[0053] FIG. 9(B) shows a tip surface 5E having two step-shaped portions 51. The two step-shaped portions 51 are arranged in a straight line with the center point C in between. As a result, the tip surface 5E has two semicircular surfaces. These semicircular surfaces are surfaces that have an inclination according to the step of the step-shaped portion 51. FIG. 9(C) shows a tip surface 5F having four step-shaped portions 51. The four step-shaped portions 51 are arranged at equal intervals of 90 degrees in the circumferential direction. The tip surface 5F has four fan surfaces of the same size arranged in the circumferential direction. FIG. 9(D) shows a tip surface 5G in which the four step-shaped portions 51 are arranged at random intervals in the circumferential direction. As in the example of FIG. 9(D), the step-shaped portions 51 do not have to be arranged at equal intervals in the circumferential direction.

[0054] FIG. 9(E) shows a tip surface 5H having four step-shaped portions 51 each having a curved portion 51A. In the above example, the step-shaped portion 51 extending linearly in the radial direction is illustrated, but the tip surface 5H may have a curved portion 51A as in the example of FIG. 9(E). The curved portion 51A is a portion in which the step-shaped portion 51 near the outer periphery of the tip surface 5H is curved to follow the rotation direction F. FIG. 9(F) also shows a tip surface 5I having four step-shaped portions 51 each having a curved portion 51B. The curved portion 51B here is a portion in which the step-shaped portion 51 near the outer periphery of the tip surface 5H is curved in the opposite direction to the rotation direction F. By providing the tip surfaces 5D to 5I shown above on the pin 11, the joining pressure force of the tool 1 can also be reduced.

[0055] [Summary of this disclosure] The specific embodiments described above include disclosures having the following configurations.

[0056] A friction stir spot welding tool according to a first aspect of the present disclosure comprises a cylindrical pin that rotates about an axis, a shoulder having a hollow portion through which the pin is inserted, and a drive unit that drives the pin to rotate while pressing it into objects to be joined, and drives the shoulder to retract relative to the objects to be joined, and at least a portion of the circular tip surface of the pin is provided with a step-shaped portion that forms a step in the rotational direction of the pin.

[0057] According to the first aspect, when the workpieces are joined by pressing the pin, the step-shaped portion contributes to reducing the joining pressure. That is, in the pin-first process in which the pin is pressed in while the shoulder is retracted, the material immediately below the pin is pushed out to the shoulder retraction space present on the outer periphery of the pin. The step-shaped portion forms a step in the rotation direction of the pin. Therefore, when the pin is pressed into the workpieces while rotating around the axis, the step-shaped portion actively pushes out the material immediately below the pin to the shoulder retraction space while scraping it. Therefore, the stirring of the material immediately below the pin and the flow of the stirred material toward the radial outside of the pin become smooth. Therefore, the pressure of the pin on the workpieces during friction stir spot welding, that is, the joining pressure force that must be applied to the tool, can be reduced. Since the reaction force can also be suppressed by reducing the joining pressure, it becomes possible to mount the friction stir spot welding tool on a small robot or a small dedicated device. This makes it possible to avoid the increase in size and cost of equipment including friction stir spot welding tools.

[0058] A friction stir spot welding tool according to a second aspect is the tool of the first aspect, wherein the step of the stepped portion is a radial step extending in the radial direction from the center point of the tip face to the outer circumferential edge.

[0059] According to the second aspect, since the step is a radial step, the material can be efficiently pushed out in the direction of the outer periphery of the pin when stirring by pressing the pin into the material.

[0060] A friction stir spot welding tool according to a third aspect is the tool of the second aspect, wherein a plurality of the radial steps are arranged in the circumferential direction of the tip surface of the pin.

[0061] According to the third aspect, since a plurality of radial steps are arranged in the circumferential direction, the force for pushing out the material toward the outer periphery of the pin can be increased, and the pressure applied by the pin can be reduced.

[0062] A friction stir spot welding tool according to a fourth aspect is the tool of the third aspect, wherein the plurality of radial steps are arranged at equal intervals in the circumferential direction of the tip surface.

[0063] According to the fourth aspect, since a plurality of radial steps are disposed at equal intervals, it is possible to perform the cutting of the material immediately below the pin and the pushing out of the material toward the outer periphery of the pin in a well-balanced manner.

[0064] A friction stir spot welding tool according to a fifth aspect is any of the first to fourth aspects, wherein the maximum height difference of the step of the stepped portion is set in the range of 1% to 10% of the diameter of the pin.

[0065] According to the fifth aspect, the step height of the stepped portion can be optimized.

[0066] A friction stir spot welding tool according to a sixth aspect is the tool of the first aspect, wherein the step of the stepped portion is a step formed by cutting away a part of an outer circumferential edge of the tip surface.

[0067] According to the sixth aspect, even if there is a step due to a partial notch on the outer periphery, it is possible to promote cutting out of the material directly below the pin and pushing out the material into the shoulder retreat space, thereby reducing the joining pressure of the tool. [Explanation of symbols]

[0068] 1 Tool (friction stir spot welding tool) 11-pin 12 Shoulder 13 Clamp 2 Tool drive unit (drive unit) 3 conjugate 3 4 Stirring joint 5, 5A~5I tip surface 51 Stepped section 53 Diagonal groove (stepped section) 54 Spiral groove (stepped section) 55 Axial groove (stepped portion) F Rotation direction M Friction stir spot welding equipment R Rotation axis (axis)

Claims

1. A cylindrical pin that rotates around an axis, a shoulder having a hollow portion through which the pin is inserted; a drive unit that drives the pin to press-fit into the workpieces while rotating it, and drives the shoulder to retract from the workpieces, A friction stir spot welding tool, wherein at least a portion of the tip surface of the pin is provided with a stepped portion that forms a step in the rotation direction of the pin.

2. The friction stir spot welding tool according to claim 1, The friction stir spot welding tool, wherein the step of the stepped portion is a radial step extending in the radial direction from the center point of the tip surface to the outer circumferential edge.

3. The friction stir spot welding tool according to claim 2, A friction stir spot welding tool, wherein a plurality of the radial steps are arranged in the circumferential direction of the tip surface of the pin.

4. The friction stir spot welding tool according to claim 3, A friction stir spot welding tool, wherein the plurality of radial steps are arranged at equal intervals in the circumferential direction of the tip surface.

5. The friction stir spot welding tool according to any one of claims 1 to 4, A friction stir spot welding tool, wherein the maximum height difference of the step of the stepped portion is set in the range of 1% to 10% of the diameter of the pin.

6. The friction stir spot welding tool according to claim 1, A friction stir spot welding tool, wherein the step of the stepped portion is a step formed by cutting out a part of the outer circumferential edge of the tip surface.

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