Control method of friction stirring tool and friction stirring device

Abstract

To accurately control the press-in quantity of a tool into a work-piece without using a sensor and the like.SOLUTION: A control method of a friction stirring control tool is given in which: required driving current is supplied to a driving source of a tool 1 press-fitted into an overlapping part 30 with a work-piece to perform friction stirring so that behavior of the tool 1 is controlled. Change ratio of applied pressure Dp1, Dp2 for each stage of friction stirring behavior is obtained in advance based on comparing a set applied pressure Pa defined as applied pressure at the time of press-fitting of the tool 1 into the overlapping part 30 with actually applied pressure Pb when actually press-fitting into the overlapping part 30 by supplying the driving source with the driving current to generate the set applied pressure Pa. The driving current is corrected according to the change ratio of applied pressure Dp1, Dp2 to make the actually applied pressure Pb close to the set applied pressure Pa, and then drives the driving source.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a tool that is pressed into a workpiece to perform friction stirring, and a friction stirring apparatus equipped with the tool. [Background technology]

[0002] Metal members, resin members, thermoplastic resin members mixed with fiber reinforced materials, etc. are used as components of structures such as aircraft, railway vehicles, and automobiles. When manufacturing such structures, it is sometimes necessary to join two or more members together. Friction stir welding is known as a joining method for this purpose. Friction stir welding uses a tool that is pressed into a workpiece while rotating at high speed. A backup member is positioned opposite the tool. The tool is pressed into a workpiece whose back surface is supported by the backup member. The tool is attached to the tip of a robot arm, for example. The backup member is also attached to the tip of the robot arm, for example, using a C-frame.

[0003] In friction stir welding, it is essential to press the tool into the workpiece to a predetermined press-in depth (push-in amount) and perform the friction stir operation. Patent Document 1 discloses a friction stir welding device equipped with a sensor that detects the push-in amount of the tool into the workpiece. This device corrects the friction stir welding time based on the detection result of the sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-187778 Summary of the Invention [Problem to be solved by the invention]

[0005] If the tool is pressed into the workpiece according to the preset pressure set in advance for the type of workpiece, the tool can be pressed into the workpiece by the required amount to perform friction stir welding. However, the actual pressure applied by the tool to the workpiece may differ from the set pressure due to various factors. Such factors include, for example, deflection of the C-frame and resistance to pressing into the workpiece. If there is a discrepancy between the set pressure and the actual pressure, accurate friction stir welding may not be performed.

[0006] The actual applied pressure can be detected, for example, by placing a load cell on the backup member side. Then, by performing feedback control of the tool based on the detected value of the load cell, it is possible to eliminate the discrepancy. However, the use of a sensor such as a load cell not only increases the cost of the friction stir welding apparatus, but also poses the problem of malfunction due to the influence of noise.

[0007] The present invention aims to provide a method for controlling a friction stir tool that can accurately control the amount of pressure that the tool is pressed into the workpiece without using sensors, and a friction stir tool apparatus to which this method is applied. [Means for solving the problem]

[0008] A control method for a friction stir tool according to one aspect of the present invention is a control method for a friction stir apparatus including a tool for performing friction stirring, a casing portion accommodating the tool, a C-frame having a base end portion connected to the casing portion and a tip end portion extending from the base end to below the tool, and a backup member disposed opposite to the lower end surface of the tool and held by the tip end of the C-frame, the control method controlling operation of the tool by applying a required drive current to a drive source of the tool, the control method comprising: comparing a set pressurizing force determined as a pressurizing force when the tool is pressed into a workpiece with an actual pressurizing force when a drive current for generating the set pressurizing force is applied to the drive source and the tool is actually pressed into the workpiece; The method is characterized in that a pressure force change ratio is determined, a table showing the relationship between the drive current and the pressure force is determined, a first drive current is calculated from the set pressure force based on the table, a second drive current is determined by correcting the first drive current based on the pressure force change ratio, the drive source is operated using the second drive current to act on the workpiece with the tool, a third drive current actually flowing through the drive source is determined, the third drive current is inversely corrected based on the pressure force change ratio to determine a fourth drive current, a calculated pressure force converted from the inversely corrected fourth drive current is determined by referring to the table, and the drive current is corrected according to the deflection of the C-frame based on the calculated pressure force.

[0009] A friction stir welding apparatus according to another aspect of the present invention comprises: a tool for performing friction stirring; a housing for accommodating the tool; a C-frame having a base end connected to the housing; and a tip end extending from the base end to below the tool; a backup member disposed opposite a lower end surface of the tool and held by the tip end of the C-frame; a drive source for driving the tool when a required drive current is applied; a control unit for controlling the drive source; and a memory unit for storing a pressure change ratio determined by comparing a set pressure force determined as a pressure force when the tool is pressed into a workpiece with an actual pressure force when a drive current for generating the set pressure force is applied to the drive source and the tool is actually pressed into the workpiece. The memory unit stores a table showing the relationship between the drive current and the pressing force, and the control unit calculates a first drive current from the set pressing force based on the table, determines a second drive current by correcting the first drive current based on the pressing force change ratio, operates the drive source using the second drive current to act on the tool against the workpiece, determines a third drive current that actually flowed through the drive source, inversely corrects the third drive current based on the pressing force change ratio to determine a fourth drive current, refers to the table to determine a calculated pressing force converted from the inversely corrected fourth drive current, and corrects the drive current according to the calculated pressing force.

[0010] According to the above-described friction stir tool control method and friction stir welding apparatus, the drive current of the tool drive source is corrected in accordance with the pressure change ratio, thereby bringing the actual pressure closer to the set pressure. Therefore, if the pressure change ratio for the workpiece is determined in advance, it is possible to control the actual pressure so that it approaches the set pressure without actually measuring the actual pressure using sensors during operation of the friction stir welding tool. In other words, it is possible to control the friction stir welding tool sensorlessly, and press the tool into the workpiece as set to perform friction stirring. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a friction stir tool control method that can accurately control the amount of pressure that the tool is pressed into the workpiece without using sensors, and a friction stir tool apparatus to which this method is applied. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view including an enlarged view of a main part of a robot equipped with a friction stirring device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic side view showing the configuration of a friction stir spot welding apparatus equipped with a double-action friction stir spot welding tool, which is an example of a friction stir tool according to the present invention. [Figure 3] FIG. 3 is a block diagram showing the electrical configuration of the friction stir apparatus. [Figure 4] 4(A) to 4(E) are diagrams sequentially showing the welding steps when the double-action friction stir spot welding tool illustrated in FIG. 2 is used in a shoulder-first process. [Figure 5] FIG. 5 is a side view of the friction stir spot welding apparatus, illustrating the deflection of the C-frame. [Figure 6] FIG. 6 is a graph showing the relationship between the set pressure of the tool and the actual pressure applied when the tool is actually pressed into the workpiece. [Figure 7] Figure 7(A) is a graph showing the correction status of the drive current of the shoulder drive unit (7 axes), Figure 7(B) is a table showing an example of a pressure force-drive current table, and Figure 7(C) is a table showing an example of a drive current correction ratio. [Figure 8] FIG. 8 is a flowchart showing the operation when friction stir spot welding is performed using the friction stir spot welding tool of FIG. 2 in a shoulder-first process. [Figure 9] FIG. 9 is a flowchart showing the process of correcting the drive current of the shoulder drive unit (7 axes) in the load cell-less system. [Figure 10] 10(A) to 10(C) are diagrams sequentially showing the welding steps when friction stir welding of workpieces is performed using a single-action friction stir spot welding tool. [Figure 11] FIG. 11(A) is a graph showing the relationship between the set pressure and the actual pressure for a single-action tool, and FIG. 11(B) is a graph showing the drive current. [Figure 12] FIG. 12(A) is a graph showing the relationship between the set pressure and the actual pressure after the drive current for a single-acting tool has been corrected, and FIG. 12(B) is a graph showing the state of correction of the drive current. [Figure 13] FIG. 13 is a flowchart showing the operation when performing friction stir welding using a single-action friction stir spot welding tool. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The friction stir tool and friction stir apparatus that are the subject of control in the control method according to the present invention can be applied to the production of various joined bodies formed by overlapping and spot-joining two or more structural members, such as plates, frames, exterior materials, or pillars, made of metal, thermoplastic resin, thermoplastic composite material, or the like. The thermoplastic composite material is, for example, a composite material containing fiber reinforcement such as carbon fiber. The joined body thus produced becomes a component of a structure such as an aircraft, a railway vehicle, or an automobile.

[0014] [Application examples of friction stirring equipment] FIG. 1 is a perspective view showing an articulated robot 5 equipped with a friction stir welding device according to this embodiment. Here, an example is shown in which a friction stir welding device M equipped with a double-acting friction stir spot welding tool 1 is attached to the articulated robot 5 as the friction stir welding device. FIG. 2 is a schematic side view showing the configuration of the friction stir spot welding device M. Note that although FIG. 1 includes directional indications of "up" and "down," this is for ease of explanation and is not intended to limit the direction in which the tool 1 is actually used.

[0015] The articulated robot 5 includes a robot arm 51 erected on a base. The robot arm 51 has multiple arm segments and six joint axes connecting these arm segments. That is, the robot arm 51 can rotate around each of the first axis AX1, the second axis AX2, the third axis AX3, the fourth axis AX4, the fifth axis AX5, and the sixth axis AX6 shown in FIG. 1.

[0016] A gun 52 is attached to an arm tip 51T of the robot arm 51. The gun 52 can move freely in three dimensions by rotating about axes AX1 to AX6 of the robot arm 51. A friction stir spot welding apparatus M equipped with a tool 1 is attached to this gun 52.

[0017] 1 includes an enlarged view of the gun 52. The gun 52 includes a housing 53 and a C-frame 54. The housing 53 houses the mechanical components of the friction stir spot welding apparatus M. The C-frame 54 includes a base end 541 located on the arm tip 51T side of the housing 53, and a tip end 542 extending from the base end 541 to below the tool 1. The tip end 542 holds a backup member 15, which will be described later.

[0018] The friction stir welding device according to the present invention may be attached to a device other than the articulated robot 5. For example, an embodiment may be one in which the friction stir welding device is attached to a mechanical device that only moves up and down along one axis. Furthermore, the friction stir welding device is not limited to the friction stir spot welding device M equipped with a double-action friction stir spot welding tool 1. Instead of this, a friction stir linear welding tool, a single-action friction stir spot welding tool (as exemplified in FIG. 10), a friction stir welding tool used for purposes other than welding, or the like may be used as the tool.

[0019] [Configuration of friction stir spot welding equipment] An example of the mechanical configuration of the friction stir spot welding apparatus M will be described with reference to Fig. 2. The friction stir spot welding apparatus M includes a double-acting friction stir spot welding tool 1, a tool drive unit 2 that drives the tool 1 to rotate and move up and down, and a tool fixing unit 55 that fixes the tool 1 to a workpiece. In this embodiment, the workpiece is an overlapping portion 30 formed by overlapping a first member 31 and a second member 32 in the vertical direction, and a welded body 3 is finally formed by friction stir spot welding.

[0020] The tool 1 includes a pin member 11, a shoulder member 12, a clamp member 13, and a spring 14. The pin member 11 is a cylindrical member and is arranged so that its axis extends in the vertical direction. The pin member 11 is rotatable about the axis R as a rotation axis, and is also movable back and forth in the vertical direction indicated by the arrow Z1 along the rotation axis R. When the tool 1 is in use, the tool 1 is fixed to the overlapping portion 30 so that the rotation axis R is aligned with the spot joining position W in the overlapping portion 30.

[0021] The shoulder member 12 is positioned so as to cover the outer periphery of the pin member 11. The shoulder member 12 is a cylindrical member having a hollow portion into which the pin member 11 is inserted. The axis of the shoulder member 12 is coaxial with the axis line (rotation axis R) of the pin member 11. The shoulder member 12 can rotate around the same rotation axis R as the pin member 11, and can move back and forth in the up-down direction indicated by arrow Z2 along the rotation axis R. The shoulder member 12 and the pin member 11 inserted in the hollow portion can both rotate around the rotation axis R and move relatively in the direction of the rotation axis R. In other words, the pin member 11 and the shoulder member 12 can not only move up and down simultaneously along the rotation axis R, but also independently move, with one descending while the other ascends.

[0022] The clamp member 13 is a cylindrical member having a hollow portion into which the shoulder member 12 is inserted. The axis of the clamp member 13 is also coaxial with the rotation axis R. The clamp member 13 does not rotate around its axis, but can move back and forth in the up and down directions indicated by arrow Z3 along the rotation axis R. The clamp member 13 serves to surround the outer periphery of the pin member 11 or the shoulder member 12 when they perform friction stirring. The enclosure provided by the clamp member 13 prevents the friction stir material from scattering, enabling the friction stir spot welded portion to be finished smoothly.

[0023] The spring 14 is attached to the upper end 131 of the clamp member 13 so as to extend upward. The spring 14 biases the clamp member 13 in a direction toward the overlapping portion 30 (downward).

[0024] The tool fixing unit 55 includes a rotary tool fixing device 551 and a clamp fixing device 552. The rotary tool fixing device 551 is disposed above the shoulder member 12 into which the pin member 11 is inserted, and supports the pin member 11 and the shoulder member 12. The clamp fixing device 552 supports the clamp member 13 via a spring 14. In addition, the clamp fixing device 552 supports the rotary tool fixing device 551 via a rotation drive unit 23, which will be described later.

[0025] A backup member 15 is disposed opposite the lower end surface of the tool 1. The backup member 15 has a support plane 151 that abuts against the lower surface of the workpiece (overlapping portion 30) to be joined. The backup member 15 is a backing member that supports the overlapping portion 30 when the pin member 11 or the shoulder member 12 is press-fitted into the overlapping portion 30. The backup member 15 is held by the tip portion 542 of the C-frame 54. The clamp member 13, biased by the spring 14, presses the overlapping portion 30 against the backup member 15. This fixes the tool 1 to the overlapping portion 30.

[0026] As described above, the axis of advance / retract movement of the pin member 11 and the axis of advance / retract movement of the shoulder member 12 are both axes along the rotation axis R. Furthermore, the pin member 11 and the shoulder member 12 rotate around the rotation axis R. In this embodiment, since the robot arm 51 has axes 1 AX1 to 6 AX6, as shown in the enlarged view of the main part in FIG. 1, the axis of advance / retract movement of the shoulder member 12 is treated as axis 7 AX7, the rotation axis of the pin member 11 and the shoulder member 12 is treated as axis 8 AX8, and the axis of advance / retract movement of the pin member 11 is treated as axis 9 AX9.

[0027] The tool driving unit 2 includes a pin driving unit 21, a shoulder driving unit 22, and a rotation driving unit 23. The pin driving unit 21 is a mechanism for moving the pin member 11 back and forth (raising and lowering) along the rotation axis R. The pin driving unit 21 drives the lower end 11T of the pin member 11 to descend toward the overlapping portion 30, or to ascend relative to the overlapping portion 30. For example, a linear actuator can be used as the pin driving unit 21. As the linear actuator, an actuator constituted by a servo motor and a rack / pinion, or an actuator constituted by a servo motor and a ball screw, can be used.

[0028] The shoulder drive unit 22 is a mechanism for moving the shoulder member 12 back and forth (raising and lowering) along the rotation axis R. The shoulder drive unit 22 drives the lower end 12T of the shoulder member 12 to press-fit into and retract from the overlapping portion 30. A linear actuator similar to that described above can be used as the shoulder drive unit 22. The shoulder drive unit 22 of this embodiment is a mechanism for raising and lowering the tool fixing portion 55 itself, which supports the pin member 11, shoulder member 12, and clamp member 13. Therefore, the movements of the pin member 11, shoulder member 12, and clamp member 13 in the directions of arrows Z1, Z2, and Z3 shown in FIG. 2 can all be achieved by driving the shoulder drive unit 22.

[0029] However, the pin member 11 can be driven by the pin driver 21 to move forward and backward independently of the shoulder member 12 and the clamp member 13. For example, even when the shoulder driver 22 is driving the shoulder member 12 downward, the pin driver 21 can drive the pin member 11 upward. Furthermore, when the clamp member 13 is lowered by the shoulder driver 22 and its lower end 13T abuts against the overlapping portion 30, the biasing force of the spring 14 also acts on the clamp member 13. Due to this biasing force, the clamp member 13 presses the overlapping portion 30 against the backup member 15, fixing the tool 1 to the overlapping portion 30.

[0030] The rotation drive unit 23 includes a servo motor, a drive gear, etc., and is held by the clamp fixator 552. The rotation drive unit 23 rotationally drives the rotary tool fixator 551. By this rotational drive, the pin member 11 and the shoulder member 12 supported by the rotary tool fixator 551 rotate around the rotation axis R.

[0031] [Control configuration of friction stir spot welding equipment] 3 is a block diagram showing the control configuration of the friction stir spot welding apparatus M. The friction stir spot welding apparatus M includes, as its control configuration, a controller 61, an input unit 62, and a storage unit 63. The controller 61 is made up of a microcomputer or the like, and controls the operation of each unit of the tool driving unit 2 and the robot driving unit 51M by executing a predetermined control program. The robot driving unit 51M includes actuators that drive the first axis AX1 to the sixth axis AX6 of the robot arm 51.

[0032] Specifically, the controller 61 controls the pin driver 21 to independently move the pin members 11 forward and backward. The controller 61 also controls the shoulder driver 22 to cause the pin members 11, shoulder member 12, and clamp member 13 to perform the required forward and backward movements. These forward and backward movements perform operations such as fixing the tool 1 to the overlapping portion 30 and press-fitting the pin members 11 or shoulder member 12 into the overlapping portion 30. Furthermore, the controller 61 controls the rotation driver 23 to rotate the pin members 11 and shoulder member 12 around the rotation axis R during an appropriate period of the forward and backward movements, thereby performing friction stir welding at the spot welding position W of the overlapping portion 30. In addition, the controller 61 controls the robot driver 51M to position the tool 1 at the spot welding position W.

[0033] The double-action friction stir spot welding tool 1 described above can be used in a pin-first process or a shoulder-first process. When friction stir welding is performed in the pin-first process, the controller 61 first presses the pin member 11 of the tool 1 into the overlapping portion 30 to perform friction stir welding, while raising (retracting) the shoulder member 12. In the subsequent backfilling process, the pin member 11 is raised and retracted, while the shoulder member 12 is lowered.

[0034] On the other hand, when friction stir welding is performed using the shoulder-first process, the controller 61 first presses the shoulder member 12 of the tool 1 into the overlapping portion 30 to perform friction stir welding, while raising (retracting) the pin member 11. In the subsequent backfilling process, the shoulder member 12 is raised and retracted, while the pin member 11 is lowered. This embodiment shows an example in which the shoulder-first process is adopted. This shoulder-first process will be described in detail below with reference to FIG. 4.

[0035] The input unit 62 is composed of a keyboard, a touch panel, etc., and receives required data input to the controller 61. The input data includes, for example, various parameters related to the control of friction stir welding, the thickness and material of the workpiece, the press-fit depth of the tool 1, and coordinate data of the spot welding position W.

[0036] The memory unit 63 stores the control program for the friction stir spot welding apparatus M, various basic setting data, data input from the input unit 62, etc. The memory unit 63 in this embodiment includes a table memory unit 64 and a correction ratio memory unit 65. The table memory unit 64 stores a pressure-driving current table indicating the relationship between the pressure when the tool 1 is pressed into the workpiece and the driving current of the driving unit (shoulder driving unit 22 in this embodiment) that presses the tool 1. An example of the table is shown in Figure 7(B) below. The correction ratio memory unit 65 stores a correction ratio table indicating the relationship between the friction stir welding stage and the correction ratio of the driving current. An example of the correction ratio table is shown in Figure 7(C) below.

[0037] [Friction stir welding using the shoulder-first process] Next, the above-mentioned shoulder-first process will be described in detail. Figures 4(A) to 4(E) are diagrams showing the friction stir spot welding process when the double-action friction stir spot welding tool 1 illustrated in Figure 2 is used in the shoulder-first process, divided into stages ST1 to ST5 that are executed sequentially. Here, the process of friction stir spot welding is shown when the overlapping portion 30 of the first member 31 and the second member 32 is used as the workpiece.

[0038] Stage ST1 in FIG. 4(A) shows a preheating step of the overlapping portion 30. The preheating step is a step of preheating the overlapping portion 30 by frictional force before the tool 1 is press-fitted. The overlapping portion 30 is pressed by the lower end 13T of the clamp member 13 accompanied by the biasing force of the spring 14, and is pressed against the backup member 15. The lower end 11T of the pin member 11 and the lower end 12T of the shoulder member 12 are abutted against the surface of the first member 31. In this state, the pin member 11 and the shoulder member 12 are rotated at high speed around the rotation axis R.

[0039] Stage ST2 in Figure 4(B) shows the press-fitting process of the shoulder member 12. In the press-fitting process, the shoulder member 12 is lowered to press-fit the lower end 12T into the overlapping portion 30, while the pin member 11 is raised (retracted). Focusing on the movement of the pin member 11, this press-fitting process is an upward movement process in which the pin member 11 moves upward relative to the workpiece. Through the above operation, the material in the press-fit region of the shoulder member 12 is stirred, and a friction stir portion 40 is formed in the overlapping portion 30. Furthermore, as the shoulder member 12 is pressed into place, part of the friction stir portion 40 overflows from the overlapping portion 30 and escapes into the hollow space in the shoulder member 12 created by the retraction of the pin member 11.

[0040] Stage ST3 in Figure 4(C) shows the backfilling process of the overflowing friction stir material. In the backfilling process, the shoulder member 12 is raised and retracted from the overlapping portion 30, while the pin member 11 is lowered. Focusing on the operation of the pin member 11, this backfilling process is a lowering process in which the pin member 11 moves downward relative to the workpiece. As the pin member 11 moves downward, the friction stir material that has escaped into the hollow space is pushed by the lower end portion 11T and backfills the press-fit region of the shoulder member 12.

[0041] Stage ST4 in Figure 4(D) shows the leveling process. In the leveling process, the lower end 11T of the pin member 11 and the lower end 12T of the shoulder member 12 are returned to the height position of the surface of the first member 31, and both are rotated around the rotation axis R to smooth the upper surface of the friction stir part 40.

[0042] Stage ST5 in Figure 4(E) shows the state after friction stir welding is completed. The pin member 11 and shoulder member 12 are raised, and the overlapping portion 30 is released from the clamping member 13 and backup member 15. The friction stir welding portion 40 solidifies to become the friction stir welding portion 4, and the first member 31 and the second member 32 are joined to form the joined body 3.

[0043] [Error factors in tool press-fit depth] In friction stir welding, it is essential to press the tool 1 into the workpiece to a predetermined press-in depth (press-in amount) and perform the friction stir welding. For example, in the above-mentioned shoulder-first process, it is required to press the shoulder member 12 into the overlapping portion 30 to a press-in depth set as the depth at which the highest welding strength can be obtained, and then perform the friction stir welding.

[0044] The pressing force of the tool 1 on the workpiece is used to control the pressing depth of the tool 1. The pressing force includes a set pressing force, a calculated pressing force, and an actual pressing force. The set pressing force is preset as the pressing force when the tool 1 is pressed into the workpiece, and is preset according to the type, thickness, etc. of the workpieces to be joined. For example, the set pressing force is the pressing force commanded to the articulated robot 5 equipped with the friction stir spot welding apparatus M to press the shoulder member 12 into the overlapping portion 30 with a pressing force of 10 kN. The drive current (7-axis drive current; for example, the motor current of a servo motor) of the shoulder driver 22 corresponding to this set pressing force is predetermined in table format as a command current. As an example, it is assumed that the command current required to generate a set pressing force of 10 kN is 10 A (amperes).

[0045] The calculated pressure force is a pressure force recognized by the articulated robot 5. Specifically, the calculated pressure force is a pressure force calculated from an actual drive current, which is a current that actually flows through the shoulder drive unit 22 when a command current of 10 A corresponding to the set pressure force is applied to the shoulder drive unit 22. Unless a circuit abnormality or the like occurs, a current the same as the command current flows through the shoulder drive unit 22, so the actual drive current is 10 A. Therefore, the set pressure force and the calculated pressure force are equal.

[0046] The actual pressure is the pressure that the tool 1 actually applies to the overlapping portion 30. In other words, the actual pressure is the pressure that is actually generated when a command current (actual drive current) that generates the set pressure is applied to the shoulder driver 22, specifically when the shoulder driver 22 is driven with an actual drive current of 10 A and the shoulder member 12 is pressed into the overlapping portion 30. If an actual pressure equal to the set pressure is generated, the tool 1 is pressed into the overlapping portion 30 to the required press-in depth, and appropriate friction stir welding is performed. However, due to the following factors, a difference may occur between the set pressure and the actual pressure; for example, even when the actual drive current is 10 A, the actual pressure may be 9 kN.

[0047] One of the factors that causes a discrepancy between the set pressure and the actual pressure is deflection of the C-frame 54. When the friction stir spot welding apparatus M is attached to a gun 52 having a C-frame 54, as in this embodiment, deflection of the C-frame 54 must be taken into consideration when controlling the press-in depth of the tool 1. FIG. 5 is a side view of the friction stir spot welding apparatus M, illustrating the deflection of the C-frame 54. The overlapping portion 30, which is the workpiece, is supported from below by a backup member 15 supported by a tip portion 542, which is the free end of the C-frame 54. When the tool 1 is pressed into the overlapping portion 30 from above, the pressing force deflects the C-frame 54 so that the tip portion 542 moves downward, as shown by the dotted line in FIG. 5. This deflection causes the overlapping portion 30 to move away from the tool 1, resulting in a loss of pressurizing force.

[0048] In addition, according to the study by the inventors, it was found that when the tool 1 is a double-acting friction stir spot welding tool, the movement direction of the pin member 11 (9th axis AX9) is also a factor in fluctuations in the pressing force. Specifically, it was found that the actual pressing force tends to decrease during the ascending process in which the pin member 11 moves upward (away) from the workpiece, and conversely, the actual pressing force tends to increase during the descending process in which the pin member 11 moves downward (approaches) from the workpiece.

[0049] Another factor that can cause a discrepancy between the set pressure and the actual pressure is fluctuations in pressure due to the pressing operation of the tool 1 itself. A difference occurs in the actual pressure when the workpiece is pressed without rotating the tool 1 around the rotation axis R, and when the workpiece is pressed while rotating the tool 1 and performing friction stirring. In the latter case, the tool 1 presses the part of the material that has been softened by friction stirring, so the pressure tends to be lower than in the former case.

[0050] Furthermore, there are factors that make it difficult to match the calculated pressure force with the actual pressure force in terms of control. The actual pressure force can be detected by arranging a pressure force detection sensor, such as a load cell, on the backup member 15 side. For example, if a load cell is installed at the tip 542 of the C-frame 54, the actual pressure force can be feedback-controlled based on the detected value of the load cell, thereby eliminating the discrepancy between the calculated pressure force and the actual pressure force. However, if control is performed without using a load cell due to concerns about cost and malfunction, it is difficult to eliminate the discrepancy between the calculated pressure force and the actual pressure force because the actual pressure force cannot be directly read.

[0051] [Control to match the set pressure and actual pressure] In this embodiment, control is performed to correct the drive current of the drive source of the friction stir tool so that the set pressure and the actual pressure match. When the above-mentioned double-action friction stir spot welding tool 1 is used, the set pressure and the actual pressure when the drive current that generates this set pressure is applied to the shoulder drive unit 22 and the tool is actually pressed into the overlapping portion 30 are compared to determine the pressure force change ratio in advance. Then, the drive current applied to the shoulder drive unit 22 is corrected in accordance with the pressure force change ratio so that the actual pressure approaches the set pressure, preferably so that the two match.

[0052] FIG. 6 is a graph showing the relationship between the set pressure Pa and the actual pressure Pb in friction stir welding in a shoulder-first process using a friction stir spot welding tool 1. In other words, it is a graph showing the change ratio of the set pressure to the actual pressure. The change ratio of the pressure is experimentally derived using a workpiece sample or is derived in advance based on the empirical values ​​of friction stir welding on the workpiece. The regions ST1, ST2, and ST3 indicated at the top of FIG. 6 correspond to the stages ST1, ST2, and ST3 illustrated in FIGS. 4(A) to 4(C). FIG. 6 shows an example in which the set pressure Pa is 10 kN and the actual pressure Pb varies in the range of 9 kN to 11 kN.

[0053] In the preheating process of stage ST1, the set pressure Pa and the actual pressure Pb are the same. This is because the preheating process is a stage where the tool 1 (shoulder member 12) is not pressed into the overlapping portion 30. In contrast, in the press-fitting process of stage ST2, the actual pressure Pb drops to 9 kN. Factors contributing to this drop include the above-mentioned deflection of the C-frame 54 and losses due to the rotational press-fit of the tool 1. Another factor is losses associated with the stage ST2 being an ascending process in which the pin member 11 rises relative to the workpiece. From the pressure difference between the set pressure Pa and the actual pressure Pb in this stage ST2, the first pressure change ratio Dp1 for that stage ST2 can be determined in advance.

[0054] In the backfilling process of stage ST3, the actual pressure Pb increases to 11 kN. In stage ST3, the shoulder member 12 rises, making it difficult for flexure loss to occur in the C-frame 54. On the other hand, since this is the descent process in which the pin member 11 descends relative to the workpiece, the pin member 11 applies a pressing force to the overlapping portion 30. As a result, the actual pressure Pb increases in stage ST3. The second pressure change ratio Dp2 for stage ST3 is determined in advance from the pressure difference between the set pressure Pa and the actual pressure Pb for stage ST3. In this way, the pressure change ratio is determined in advance for each of stages ST1 to ST3 involved in the press-fitting operation of the tool 1.

[0055] When performing friction stir spot welding by controlling an articulated robot 5 equipped with a friction stir spot welding device M, the drive current (7-axis drive current) of the shoulder driver 22 is corrected in stages ST1 and ST2 according to the first and second pressure force change ratios Dp1 and Dp2. Fig. 7(A) is a graph showing the correction status of the 7-axis drive current given to the shoulder driver 22. Fig. 7(A) shows, as the 7-axis drive current, a command current Aa corresponding to the set pressure and a corrected current Ab obtained by correcting this command current Aa according to the first and second pressure force change ratios Dp1 and Dp2.

[0056] In stage ST1, where the set pressure Pa and the actual pressure Pb are the same, no correction is made to the command current Aa. Therefore, the command current Aa = the correction current Ab = 10 A. In contrast, in stage ST2, where the actual pressure Pb decreases, the command current Aa is corrected to increase by a correction amount Da1 corresponding to the first pressure change ratio Dp1. In this example, the correction amount Da1 = +1 A, and the command current Aa is increased from 10 A to 11 A. In stage ST3, where the actual pressure Pb increases, the command current Aa is corrected to decrease by a correction amount Da2 corresponding to the second pressure change ratio Dp2. In this example, the correction amount Da2 = -1 A, and the command current Aa is decreased from 10 A to 9 A.

[0057] Fig. 7(B) is a table showing an example of a pressure force-drive current table. The drive currents A1 to A5... in the right column of this table are command currents for shoulder drive unit 22 that are predetermined for each set pressure force P1 to P5... The table of Fig. 7(B) is, so to speak, a table that converts set pressure forces into drive currents for shoulder drive unit 22. This pressure force-drive current table is stored in advance in table storage unit 64 (Fig. 3) of storage unit 63.

[0058] FIG. 7C is a table showing an example of the correction ratio of the drive current based on the pressure force change ratio. This table shows the correction ratio of the drive current A1 for each of stages ST1 to ST3 when the set pressure force P1 is used. As described above, the drive current is corrected to zero for stage ST1, the correction ratio is positive for stage ST2, and the correction ratio is negative for stage ST3. The numerical value of the correction ratio may differ if the set pressure force is different, but the tendency of plus / minus remains the same. This correction ratio table is stored in advance in the correction ratio storage unit 65 of the storage unit 63.

[0059] The above is an example in which a shoulder-first process is adopted, but the concept of correcting the drive current is similar in a pin-first process. In a pin-first process, it is the pin member 11 that is pressed into the workpiece, so the pin driver 21 is the press-fit drive source of the tool 1. In the press-fit process in which the pin member 11 is pressed into the workpiece, i.e., the lowering process in which the pin member 11 descends relative to the workpiece, the drive current given to the pin driver 21 is corrected to be decreased relative to the command current. On the other hand, in the backfilling process in which the pin member 11 retracts from the workpiece, i.e., the ascending process in which the pin member 11 ascends relative to the workpiece, the drive current given to the pin driver 21 is corrected to be increased relative to the command current.

[0060] [Friction stir welding process flow] Fig. 8 is a flowchart showing the processing of the controller 61 (Fig. 3) when friction stir welding is performed using the friction stir spot welding tool 1 of Fig. 2 in a shoulder-first process. The controller 61 acquires position information and attribute information of the workpieces to be joined from input information from the input unit 62 or information stored in the memory unit 63 (step S1). Specifically, information such as coordinate information of the joining position, type data indicating the material of the workpieces to be joined, the thickness of the workpieces, and the press-fit depth of the tool 1 is acquired.

[0061] Next, the controller 61 acquires information on the set pressure, seven-axis drive current, and their correction ratios for the joining position acquired in step S1 (step S2). At this time, the controller 61 refers to the pressure-drive current table in the table storage unit 64 of the storage unit 63 and the correction ratio table in the correction ratio storage unit 65.

[0062] Next, the controller 61 drives the robot arm 51 to position the tool 1 on the workpieces to be joined. Specifically, the controller 61 controls the robot drive unit 51M to drive the first axis AX1 to the sixth axis AX6 of the robot arm 51 by the required amount (step S3). In the example of Fig. 2, when step S3 is completed, the lower ends 11T and 12T of the tool 1 face the overlapping portion 30 with a predetermined gap between them, and the rotation axis R of the tool 1 is aligned with the spot joining position W.

[0063] Thereafter, the controller 61 causes the tool 1 to perform a friction stirring operation. The controller 61 drives the shoulder driver 22 to lower the entire tool 1 (seven-axis lowering drive), and also drives the rotation driver 23 to rotate the pin member 11 and shoulder member 12 around the rotation axis R (eight-axis rotation drive) (step S4). When the lower end surface of the tool 1 abuts against the upper surface of the overlapping portion 30, the overlapping portion 30 is clamped by the clamp member 13, and the preheating step of the stage ST1 shown in FIG. 4(A) is started (step S5). As described above, in the preheating step, the seven-axis drive current provided to the shoulder driver 22 is not corrected, and the seven-axis drive current obtained in step S2 is applied as is.

[0064] Next, the controller 61 executes the press-fitting process of the stage ST2 shown in FIG. 4(B). Specifically, the controller 61 drives the shoulder driver 22 to further lower the shoulder member 12 (seven-axis downward drive), continues to rotate the tool 1 by the rotation driver 23 (eight-axis rotation), and drives the pin driver 21 to raise the pin member 11 (nine-axis upward drive) (step S6). In this press-fitting process, the pin member 11 moves upward, so the seven-axis drive current is increased. The controller 61 increases the seven-axis drive current based on the correction ratio for the stage ST2 acquired in step S2.

[0065] Next, the controller 61 executes the backfilling process of the stage ST3 shown in FIG. 4(C). Specifically, the controller 61 drives the shoulder driver 22 to raise the shoulder member 12 (seven-axis upward drive), continues the rotational drive of the tool 1 by the rotation driver 23 (eight-axis rotation), and drives the pin driver 21 to lower the pin members 11 (nine-axis downward drive) (step S7). In this backfilling process, the pin members 11 move downward, so the seven-axis drive current is reduced. The controller 61 reduces the seven-axis drive current based on the correction ratio for the stage ST3 acquired in step S2.

[0066] Thereafter, the controller 61 executes a leveling process for the stage ST4 as necessary, and then drives the shoulder drive unit 22 to raise the entire tool 1 so that the tool 1 moves upward away from the overlapping portion 30 (step S8). This raising also releases the clamping of the overlapping portion 30 by the clamp member 13. Thereafter, the controller 61 stops the rotational drive of the tool 1 by the rotation drive unit 23 (step S9), completing the processing at the target joining position.

[0067] [Drive current control using pressure sensorless method] 9 is a flowchart showing the process of correcting the seven-axis drive current of the shoulder driver 22 using a method that does not use a pressure sensor, such as a load cell-less method. This process is executed by the controller 61 in steps S6 and S7, which correct the seven-axis drive current by increasing or decreasing it, in the flow shown in FIG. 8, for example. Note that the specific example enclosed in a dotted line on the right side of the flowchart in FIG. 9 is assumed to be the press-fitting step of the stage ST2 shown in FIG. 6 (step S6 in FIG. 8).

[0068] The controller 61 acquires a preset set pressure for the friction stir spot welding location to be performed on the workpiece (step S11). As an example, it is assumed that the set pressure is 10 kN. Next, the controller 61 refers to a table of 7-axis drive currents calculated from the set pressure, as shown in FIG. 7(B), which is stored in the table storage unit 64 of the storage unit 63. Based on this table, the controller 61 specifies a command current (first drive current) for the shoulder drive unit 22 (7-axis drive unit), which is the 7-axis drive unit, in accordance with the set pressure acquired in step S11 (step S12). As an example, it is assumed that the command current corresponding to the set pressure = 10 kN is 10 A.

[0069] Next, the controller 61 adjusts or corrects the command current determined in step S12 based on the pressing force change ratio shown in FIG. 6. Specifically, the controller 61 refers to a correction ratio table for the 7-axis drive current, as shown in FIG. 7(C), which is stored in the correction ratio storage unit 65. Based on this table, the controller 61 multiplies the command current by a correction ratio set for each stage of the friction stir spot welding process, and sets a drive current command value (second drive current) for the 7-axis drive unit (step S13). In one example, the correction ratio for stage ST2 is +20%, so the drive current command value is 12 A, which is a 20% increase from the command current of 10 A.

[0070] Next, the controller 61 actually supplies a current corresponding to the drive current command value set in step S13 to the seven-axis drive unit (step S14), causing the tool 1 to act on the workpiece. In one example, a drive current command value of 12 A is supplied to the shoulder drive unit 22, causing the shoulder member 12 to press into the overlapping portion 30. If the process is a backfilling process of the stage ST3, the action of the tool 1 on the workpiece is to retract the shoulder member 12 from the overlapping portion 30 and lower the pin member 11.

[0071] Next, the controller 61 detects the actual drive current (third drive current) that actually flows through the seven-axis drive unit when the current of the drive current command value is supplied to the seven-axis drive unit to act on the workpiece with the tool 1 (step S15). As an example, the actual drive current that actually flows through the shoulder drive unit 22 when the drive current command value = 12 A is supplied to the shoulder drive unit 22 to cause the shoulder member 12 to perform a press-fit operation is calculated. Here, it is assumed that the actual drive current = 12 A.

[0072] Thereafter, the controller 61 performs an adjustment correction on the actual drive current that is the reverse of the adjustment correction performed in step S13, based on the adjustment ratio (pressure change ratio) set for each stage. At this time, the controller 61 references the adjustment ratio table in the adjustment ratio storage unit 65. This process determines an inverse adjustment drive current (fourth drive current) (step S17). In one example, the adjustment ratio for stage ST2 is +20%, and the actual drive current of 12 A is divided by 1.2 for the inverse adjustment, resulting in an inverse adjustment drive current of 10 A.

[0073] Next, the controller 61 refers to the pressure-driving current table in the table storage unit 64 to determine the calculated pressure (target actual pressure) converted from the inverse-corrected driving current (step S17). In one example, when the inverse-corrected driving current is 10 A, the calculated pressure is 10 kN. The controller 61 then corrects the driving current command value (second driving current) so that the actual pressure when the 7-axis driving unit is driven by the actual driving current (third driving current) matches the calculated pressure (target actual pressure) (step S18). The 7-axis driving unit is driven by the corrected driving current command value. By this processing, the actual pressure, which cannot be actually measured, can be controlled based on the 7-axis driving current.

[0074] [Embodiment when using a single-action friction stir spot welding tool] While the above describes an example in which the present invention is implemented using a double-action friction stir spot welding tool, the present invention can also be implemented using a single-action friction stir spot welding tool. Figures 10(A) to 10(C) are diagrams sequentially showing the welding process when friction stir welding workpieces using a single-action friction stir spot welding tool.

[0075] The tool used is a single-axis tool 16 formed in a cylindrical shape. The single-axis tool 16 is capable of rotation about an axis (rotation axis R) and of moving forward and backward in a direction along the axis. The single-axis tool 16 is driven to move forward and backward by a drive source (not shown). The single-axis tool 16 is mounted on a gun 52 attached to the tip 51T of a robot arm 51, as shown in FIG. 1. In other words, it is necessary to perform control taking into account the deflection of the C-frame 54.

[0076] 10(A) shows a state in which the tip pin 16T of the single-spindle tool 16 is press-fitted into an overlapping portion 30 between a first member 31 and a second member 32, which are workpieces. The single-spindle tool 16 is rotated at high speed around the rotation axis R and lowered so that the tip pin 16T is pressed into the overlapping portion 30. The back surface of the overlapping portion 30 is supported by a backup member 15.

[0077] FIG. 10(B) shows a state in which the single-axis tool 16 is rotated at high speed around the rotation axis R, with the tip pin 16T pressed into the overlapping portion 30 to a predetermined press-in depth, and friction stir welding is being performed. This friction stirring causes the material of the overlapping portion 30 to melt, forming a friction stir portion 40 around the tip pin 16T. FIG. 10(C) shows a state in which the tip pin 16T of the single-axis tool 16 has been pulled out of the overlapping portion 30. The friction stir portion 40 hardens, forming a stir welded portion 4, and the first member 31 and the second member 32 are joined.

[0078] Fig. 11(A) is a graph showing the relationship between the set pressure Pa and the actual pressure Pb for a single-action friction stir spot welding tool (single-axis tool 16), and Fig. 11(B) is a graph showing the drive current of the unillustrated drive source of the single-axis tool 16. Here, an example is shown in which when the set pressure Pa of the single-axis tool 16 is 10 kN, the command current Aa supplied to the drive source is 10 A. The period when the set pressure Pa is 10 kN is the period in Figs. 10(A) to 10(B) in which the single-axis tool 16 is pressed into the overlapping portion 30.

[0079] Even when a single-axis tool 16 is used, the actual pressure Pb of the single-axis tool 16 decreases due to bending of the C-frame 54 and the press-fitting operation of the single-axis tool 16 itself. Here, an example is shown in which the actual pressure Pb has decreased to 9 kN. In other words, even if a command current Aa of 10 A corresponding to a set pressure Pa of 10 kN is applied to the drive source, only the actual pressure Pb of 9 kN is output. A pressure change ratio Dp1 indicating the degree of decrease in the actual pressure Pb relative to the set pressure Pa is determined in advance experimentally or empirically.

[0080] FIG. 12(A) is a graph showing the relationship between the set pressure Pa and the actual pressure Pb after the drive current is corrected, and FIG. 12(B) is a graph showing the correction status of the drive current. Even if the drive source is driven with a command current Aa corresponding to the set pressure Pa to press the single-axis tool 16 into the overlapping portion 30, only an actual pressure Pb reduced by the pressure force change ratio Dp can be generated. For this reason, when pressing the single-axis tool 16, a corrected drive current A obtained by increasing the command current Aa by a correction amount Da is applied to the drive source, as shown in FIG. 12(B). The correction amount Da is an increase corresponding to the pressure force change ratio Dp. By such correction, the set pressure Pa and the actual pressure Pb can be made closer to or equal to each other, as shown in FIG. 12(A).

[0081] 13 is a flowchart showing the processing of the controller 61 when friction stir welding is performed using a single-action single-axis tool 16 for friction stir spot welding. Here, axis 7 is treated as the lifting axis of the single-axis tool 16, and axis 8 is treated as the rotation axis of the single-axis tool 16. In this embodiment, the electrical configuration is similar to that of the block diagram in FIG. 3, but the pin driver 21 and shoulder driver 22 are changed to drive sources that lift and lower the single-axis tool 16. The rotation driver 23 is a driver that rotates the single-axis tool 16 around the rotation axis R.

[0082] The controller 61 acquires position information and attribute information of the workpieces to be joined (step S21). Specifically, information such as coordinate information of the joining position, type data indicating the material of the workpieces to be joined, the thickness of the workpieces, and the press-fit depth of the tool 1 is acquired. Next, the controller 61 acquires information on the set pressing force, 7-axis drive current, and its correction ratio for the joining position acquired in step S1 (step S22). At this time, the controller 61 refers to a correction ratio table stored in the correction ratio storage unit 65 of the storage unit 63.

[0083] Next, the controller 61 drives the robot arm 51 to position the tool 1 on the workpieces to be joined. Specifically, the controller 61 controls the robot drive unit 51M to drive the first axis AX1 to the sixth axis AX6 of the robot arm 51 by the required amount (step S23). When step S23 is completed, the tip pin 16T of the single-axis tool 16 faces the overlapping portion 30 at a predetermined interval, and the rotation axis R of the single-axis tool 16 is aligned with the spot joining position.

[0084] Thereafter, the controller 61 drives the drive source to start the descent of the single-spindle tool 16 (seven-axis descent drive), and also drives the rotation drive unit 23 to start the rotation of the single-spindle tool 16 (eight-axis rotation drive) (step S24). Eventually, as shown in Fig. 10(A), the tip pin 16T of the single-spindle tool 16 comes into contact with the surface of the overlapping portion 30, and press-fitting begins (step S25).

[0085] Thereafter, the pressing process and the stirring process are executed (step S26). The controller 61 lowers the single-axis tool 16 until the tip pin 16T reaches a predetermined pressing depth relative to the overlapping portion 30. At this time, the seven-axis drive current is increased by a correction amount Da corresponding to the pressing force change ratio Dp, thereby compensating for the decrease in pressing force. The controller 61 also causes the rotation drive unit 23 to continue rotating the single-axis tool 16.

[0086] When the stirring process is completed, the controller 61 executes a process of pulling out the single-spindle tool 16 (step S27). Specifically, the controller 61 drives the drive source to raise the single-spindle tool 16 (7th-axis lift drive) and stops the rotation of the single-spindle tool 16 by the rotation drive unit 23 (8th-axis stop).

[0087] According to the friction stir tool control method and friction stir welding apparatus of the present embodiment described above, the actual pressure is brought closer to the set pressure by correcting the drive current of the drive source (shoulder drive unit 22) of the double-acting friction stir spot welding tool 1 or the single-acting friction stir spot welding single-axis tool 16 in accordance with the pressure change ratio. Therefore, if the pressure change ratio for the workpiece is determined in advance, it is possible to control the actual pressure to approach the set pressure without actually measuring the actual pressure using sensors during operation of the tool 1 or the single-axis tool 16. In other words, the friction stir spot welding tool can be controlled sensorlessly, and the tool can be pressed into the workpiece as set to perform friction stir welding. [Explanation of symbols]

[0088] 1. Tools 11 Pin member 12 Shoulder member 16 Single-Axis Tools 2 Tool drive unit 21 Pin drive unit 22 Shoulder drive unit (tool drive source) 23 Rotation drive unit 30 Overlapped part (work) 4 Stirring joint 40 Friction stir section 5. Articulated robots 51 Robot Arm 61 Controller (control unit) 63 Storage section 64 Table storage section 65 Correction ratio storage section M Friction stir point welding device (friction stir device) Pa Set pressure Pb Actual pressure

Claims

1. A control method for a friction stir welding apparatus including a tool for friction stirring, a housing for accommodating the tool, a C-shaped frame having a base end connected to the housing and a tip end extending from the base end to below the tool, and a backup member disposed opposite a lower end surface of the tool and held by the tip end of the C-shaped frame, the method comprising: applying a required drive current to a drive source of the tool to control operation of the tool; a pressing force change ratio is calculated by comparing a set pressing force, which is determined as a pressing force when the tool is pressed into the workpiece, with an actual pressing force when a driving current for generating the set pressing force is applied to the driving source and the tool is actually pressed into the workpiece; A table showing the relationship between the driving current and the pressure force is obtained; calculating a first drive current from the set pressure based on the table; determining a second driving current by correcting the first driving current based on the pressure change ratio; The drive source is operated by the second drive current to actuate the tool on the workpiece, and a third drive current actually flowing through the drive source is determined; a fourth driving current is obtained by performing an inverse correction on the third driving current based on the pressure change ratio; A calculated pressure force converted from the inversely corrected fourth driving current is obtained by referring to the table. A method for controlling a friction stir tool, comprising correcting the drive current in accordance with the deflection of the C-frame based on the calculated pressurizing force.

2. The method for controlling a friction stir tool according to claim 1, The tool a cylindrical pin member that rotates around an axis and is movable up and down along the axis; a cylindrical shoulder member positioned to cover the outer periphery of the pin member, rotating around the same axis as the pin member and movable up and down along the axial direction, a first pressure force change ratio obtained from the set pressure force and the actual pressure force during an upward movement of the pin member relative to the workpiece; a second pressure force change ratio obtained from the set pressure force and the actual pressure force during a descending process in which the pin member moves in a direction downward relative to the workpiece is calculated in advance; In the increasing step, the driving current is corrected so as to be increased in accordance with the first pressure force change ratio; In the lowering step, the drive current is corrected so as to decrease in accordance with the second pressing force change ratio.

3. The method for controlling a friction stir tool according to claim 2, Double-action friction stir spot welding tools are a preheating step of preheating the workpiece by bringing the pin member and the shoulder member into contact with the surface of the workpiece and rotating them about an axis; a press-fitting step of lowering the shoulder member to press-fit it into the workpiece while lifting the pin member; a backfilling step of raising the shoulder member and retracting it from the workpiece while lowering the pin member, In the preheating step, the driving current is not corrected, In the press-fitting step, the driving current is increased in accordance with the increasing step; A method for controlling a friction stir tool, wherein in the backfilling step, a reduction correction of the drive current is performed in accordance with the lowering step.

4. The method for controlling a friction stir tool according to claim 1, The tool is a single-action friction stir spot welding tool having a cylindrical shape and a single-axis tool that can rotate around an axis and move back and forth along the axis, a pressure reduction ratio obtained from the set pressure and the actual pressure during a period in which the single-axis tool is pressed into the workpiece is calculated in advance; A method for controlling a friction stir tool, comprising: correcting the drive current so as to increase it in accordance with the pressure force reduction ratio when the single-spindle tool is pressed into the workpiece.

5. A tool for performing friction stirring; a housing portion that houses the tool; a C-shaped frame having a base end portion connected to the housing portion and a tip end portion extending from the base end portion to below the tool; a backup member disposed opposite a lower end surface of the tool and held by a tip end portion of the C-shaped frame; a drive source that receives a required drive current and drives the tool; a control unit that controls the drive source; a storage unit that stores a pressure change ratio calculated by comparing a set pressure that is determined as a pressure when the tool is pressed into the workpiece with an actual pressure when a drive current that generates the set pressure is applied to the drive source and the tool is actually pressed into the workpiece, the storage unit stores a table indicating a relationship between the drive current and the pressure force; The control unit calculating a first drive current from the set pressure based on the table; determining a second driving current by correcting the first driving current based on the pressure change ratio; The drive source is operated by the second drive current to actuate the tool on the workpiece, and a third drive current actually flowing through the drive source is determined; a fourth driving current is obtained by performing an inverse correction on the third driving current based on the pressure change ratio; A calculated pressure force converted from the inversely corrected fourth driving current is obtained by referring to the table. The friction stirring apparatus corrects the drive current according to the deflection of the C-shaped frame based on the calculated pressure force.

6. The friction stirring apparatus according to claim 5, The tool a cylindrical pin member that rotates around an axis and is movable up and down along the axis; a cylindrical shoulder member positioned to cover the outer periphery of the pin member, rotating around the same axis as the pin member and movable up and down along the axial direction, The storage unit a first pressure force change ratio obtained from the set pressure force and the actual pressure force during an upward movement of the pin member relative to the workpiece; a second pressing force change ratio obtained from the set pressing force and the actual pressing force during a descending process in which the pin member moves in a direction downward relative to the workpiece is stored in advance; The control unit In the increasing step, the driving current is corrected so as to be increased in accordance with the first pressure force change ratio; In the lowering step, the drive current is corrected so as to decrease in accordance with the second pressure force change ratio.

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