Friction stir welding tool and friction stir welding method

A friction stir welding tool and method, by which influence on durability of the tool is suppressed even when resistance force generated when the tool moves for joining acts on facing end portions of workpieces which are located close to an attachment side of the tool. The tool includes: a stirring shaft; a first shoulder portion provided to be unrotatable relative to the shaft and configured to rotate together with the shaft when it rotates; a second shoulder portion provided to be unrotatable relative to the shaft and configured to rotate together with the shaft when it rotates; and a third shoulder portion attached around the shaft located between the first and second shoulder portions, and includes an inclination preventing portion to prevent inclination of the shaft by contacting the workpieces to receive reaction force from the workpieces when the shaft is made to move along joining lines.

TECHNICAL FIELD

The present invention relates to a friction stir welding tool and a friction stir welding method which are used when plates are joined to each other by friction stir welding.

BACKGROUND ART

Friction stir welding is conventionally used when end portions of plates are made to face each other and are joined to each other. As the friction stir welding, a technique in which double skin members each formed by coupling two plate-shaped members by a rib-shaped member are coupled to each other by a bobbin tool has been proposed. PTL 1 discloses a tool for use in such friction stir welding.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

PTL 1 discloses a bobbin tool type friction stir welding tool including: a stirring shaft; an upper shoulder arranged around the stirring shaft so as to be located at an upper portion of the stirring shaft; a lower shoulder arranged around the stirring shaft so as to be located at a lower portion of the stirring shaft; and an intermediate shoulder arranged around the stirring shaft so as to be located between the upper shoulder and the lower shoulder. The upper shoulder, the lower shoulder, and the intermediate shoulder are arranged on a straight line and are formed integrally as a whole. When the friction stir welding is performed by using such friction stir welding tool, the friction stir welding tool moves along a line at which workpieces face each other, and performs joining of plates at two positions that are a position between the upper shoulder and the intermediate shoulder and a position between the intermediate shoulder and the lower shoulder. Therefore, according to the friction stir welding tool, the plates are joined to each other simultaneously at two positions that are upper and lower positions.

At this time, resistance force in a direction opposite to a movement direction of the friction stir welding tool which performs the friction stir welding acts on the stirring shaft of the friction stir welding tool at the two positions. Especially, at a position of a portion of the stirring shaft of the friction stir welding tool which portion is attached to an apparatus main body which holds the friction stir welding tool, the resistance force acts, and in addition, a relatively large rotational moment generated by the resistance force acting on a portion opposite to the portion attached to the apparatus main body also acts.

Moreover, when a thickness of the double skin member is large, a length between two gaps that are upper and lower gaps may become large. In this case, a larger rotational moment acts at the position of the portion of the stirring shaft of the friction stir welding tool which portion is attached to the main body. Therefore, the stirring shaft may be bent, and therefore, durability of the friction stir welding tool may be influenced.

The present invention was made under the above circumstances, and an object of the present invention is to provide a friction stir welding tool and a friction stir welding method, each of which suppresses influence on durability of the friction stir welding tool even when resistance force generated by movement of the friction stir welding tool for joining acts on a stirring shaft.

Solution to Problem

A friction stir welding tool of the present invention is a tool configured to perform friction stir welding of first and second facing portions each constituted by making a plurality of end portions of workpieces face each other. The friction stir welding tool includes: a stirring shaft; a first shoulder portion configured to be unrotatable relative to the stirring shaft and rotate together with the stirring shaft when the stirring shaft rotates; a second shoulder portion configured to be unrotatable relative to the stirring shaft and rotate together with the stirring shaft when the stirring shaft rotates; and a third shoulder portion attached around the stirring shaft so as to be located at a position between the first shoulder portion and the second shoulder portion. A first gap portion into which the first facing portion is inserted is formed between the first shoulder portion and the third shoulder portion. A second gap portion into which the second facing portion is inserted is formed between the second shoulder portion and the third shoulder portion. The third shoulder portion includes an inclination preventing portion configured to prevent inclination of the stirring shaft during the friction stir welding by contacting the workpieces to receive reaction force from the workpieces.

According to the friction stir welding tool configured as above, since the inclination of the stirring shaft is prevented by the inclination preventing portion, bending of the stirring shaft can be suppressed. Therefore, the durability of the friction stir welding tool can be improved.

A friction stir welding method of the present invention is a friction stir welding method of performing friction stir welding by using a friction stir welding tool, the friction stir welding tool including: a stirring shaft; a first shoulder portion provided so as to be unrotatable relative to the stirring shaft and configured to rotate together with the stirring shaft when the stirring shaft rotates; a second shoulder portion provided so as to be unrotatable relative to the stirring shaft and configured to rotate together with the stirring shaft when the stirring shaft rotates; and a third shoulder portion attached around the stirring shaft so as to be located at a position between the first shoulder portion and the second shoulder portion. The friction stir welding method includes: sandwiching facing end portions of workpieces in a first gap portion formed between the first shoulder portion and the third shoulder portion; sandwiching facing end portions of the workpieces in a second gap portion formed between the second shoulder portion and the third shoulder portion; and performing the friction stir welding when the stirring shaft rotates and moves along joining lines of the workpieces while preventing inclination of the stirring shaft in such a manner that the third shoulder portion contacts the workpieces to receive reaction force from the workpieces.

According to the friction stir welding method designed as above, in the step of performing the friction stir welding, the friction stir welding is performed while preventing the inclination of the stirring shaft. Therefore, the bending of the stirring shaft can be suppressed. Thus, the durability of the friction stir welding tool can be improved.

Advantageous Effects of Invention

According to the present invention, since the inclination of the stirring shaft is prevented, the bending of the stirring shaft can be suppressed, and the durability of the friction stir welding tool can be improved. Therefore, the friction stir welding tool can be used for a long period of time, and an operating cost of an apparatus which performs the friction stir welding can be reduced.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a friction stir welding tool according to Embodiment 1 of the present invention will be described with reference to the attached drawings.FIG.1Ais a perspective view showing a friction stir welding tool100according to Embodiment 1 when viewed obliquely from above.FIG.1Bis a perspective view showing the friction stir welding tool100according to Embodiment 1 when viewed obliquely from below.FIG.2is a side view showing the friction stir welding tool100.FIG.3is a sectional view showing the friction stir welding tool100.FIG.3is a sectional view taken along line ofFIG.2.

As shown inFIGS.1A to3, the friction stir welding tool100of the present embodiment includes an upper shoulder (first shoulder portion)10, a lower shoulder (second shoulder portion)20, an intermediate shoulder (third shoulder portion)30, and a stirring shaft40. The intermediate shoulder30is arranged at a position between the upper shoulder10and the lower shoulder20.

The stirring shaft40is arranged so as to pass through an inside of the upper shoulder10and an inside of the lower shoulder20. The stirring shaft40has a columnar shape that is relatively long in an axial direction thereof. The upper shoulder10and the lower shoulder20are attached around the stirring shaft40.

Since the stirring shaft40passes through the inside of the upper shoulder10and the inside of the lower shoulder20, and the upper shoulder10and the lower shoulder20are fixed around an axis of the stirring shaft40, the upper shoulder10and the lower shoulder20are unrotatable relative to the stirring shaft40. Therefore, in the friction stir welding tool100, when the stirring shaft40is rotated, the upper shoulder10and the lower shoulder20also rotate together with the stirring shaft40.

The intermediate shoulder30is attached to the stirring shaft40through a bearing50. The stirring shaft40is arranged so as to pass through an inside of the intermediate shoulder30. In the present embodiment, the bearing50is, for example, a radial bearing. The intermediate shoulder30is rotatably attached around the axis of the stirring shaft40through the bearing50. Therefore, even when the stirring shaft40rotates, the intermediate shoulder30does not rotate integrally with the stirring shaft40. To be specific, the intermediate shoulder30is configured to be able to be prevented from performing the same rotation as the stirring shaft40when the stirring shaft40rotates. In the present embodiment, the bearing50is the radial bearing. However, the bearing50may be another bearing, such as a thrust bearing. Moreover, the bearing50may have both the function of a radial bearing and the function of a thrust bearing.

The upper shoulder10includes an end surface10aand a side peripheral surface10b. The end surface10ais a surface opposed to the intermediate shoulder30. The side peripheral surface10bis a side surface formed around the axis of the stirring shaft40. A corner10cbetween the end surface10aand the side peripheral surface10bin the upper shoulder10may be chamfered. Moreover, the lower shoulder20includes an end surface20aand a side peripheral surface20b. The end surface20ais a surface opposed to the intermediate shoulder30. The side peripheral surface20bof the lower shoulder20is a side surface formed around the axis of the stirring shaft40. A corner20cbetween the end surface20aand the side peripheral surface20bin the lower shoulder20may be chamfered.

The intermediate shoulder30is configured such that a length thereof in a direction (joining direction D1) along joining lines at which plates of workpieces are joined to each other is larger than each of a length of the upper shoulder10in the above direction and a length of the lower shoulder20in the above direction. Moreover, the intermediate shoulder30is formed such that a length thereof in a direction (facing direction D2) in which the plates of the workpieces face each other when joining the plates of the workpieces is larger than each of a length of the upper shoulder10in the above direction and a length of the lower shoulder20in the above direction. In the present embodiment, especially, the intermediate shoulder30is configured such that the length thereof in the joining direction D1is large and is formed such that the length thereof in the joining direction D1is larger than the length thereof in the facing direction D2.

The intermediate shoulder30may be configured such that a section thereof along a direction intersecting with the joining direction has a substantially rectangular shape. The intermediate shoulder30includes, for example, an end surface30aopposed to the upper shoulder10, a side peripheral surface30b, and an end surface30copposed to the lower shoulder20. For example, in the intermediate shoulder30, a radially outer portion of the end surface30aopposed to the upper shoulder10is inclined so as to be away from the upper shoulder as the radially outer portion of the end surface30aextends toward the side peripheral surface30b. Moreover, for example, in the intermediate shoulder30, a radially outer portion of the end surface30copposed to the lower shoulder20is inclined so as to be away from the lower shoulder20as the radially outer portion of the end surface30cextends toward the side peripheral surface30b. Furthermore, the intermediate shoulder30includes an intermediate shoulder main body portion29.

The intermediate shoulder30includes supporting members32(FIG.2). The supporting members32are attached to the intermediate shoulder main body portion29. The supporting members32are attached to the side peripheral surface30bof the intermediate shoulder30. In the present embodiment, the supporting members32are attached to portions of the side peripheral surface30bwhich portions are located outside in the joining direction D1in the intermediate shoulder30. Wheels (rolling portions)31are rotatably attached to each of the two supporting members32. For example, a shaft extending in the facing direction D2is attached at a center of each wheel31. The wheel31is, for example, supported by the supporting member32so as to be rotatable about the shaft. Therefore, the wheels31roll in the joining direction D1. In the present embodiment, for example, the wheels31are cylindrical rollers. Since each wheel31is constituted by the cylindrical roller, a region where the wheel31contacts the workpiece has a line shape extending in the facing direction D2. Therefore, the wheel31rolls while being in line-contact with the workpiece. Thus, the wheels31can stably roll on the workpieces in the joining direction D1, and the intermediate shoulder30can move stably. In the present embodiment, for example, the wheels31arranged at two positions along the joining direction D1are arranged symmetrically across a center position of the intermediate shoulder30. Moreover, for example, the wheels31arranged at two positions along the facing direction D2in the intermediate shoulder30are arranged symmetrically across the center position of the intermediate shoulder30.

Moreover, the intermediate shoulder30includes whirl-stop portions33configured to contact the workpieces to perform whirl-stop. Each of the whirl-stop portions33is attached to an upper portion of the supporting member32of the intermediate shoulder30. The whirl-stop portion33is attached at a position above the wheel31. In the present embodiment, the whirl-stop portions33are attached to both end portions of each supporting member32which portions are located outside in the facing direction D2. Two whirl-stop portions33are attached to each supporting member32, and therefore, four whirl-stop portions33are attached to the intermediate shoulder30. The whirl-stop portions33are attached to both end portions of the intermediate shoulder30which portions are located in the facing direction in which the workpieces face each other. The whirl-stop portions33may be constituted by, for example, cylindrical rollers. Moreover, for example, each cylindrical roller is attached so as to be rotatable about a rotating shaft34.

A gap (first gap portion) x1is formed between the upper shoulder10and the intermediate shoulder30. A gap (second gap portion) x2is formed between the lower shoulder and the intermediate shoulder.

The workpieces are joined to each other by friction stir welding at two facing positions that are upper and lower positions. In the present embodiment, each of the workpieces to be joined to each other is constituted as a so-called double skin member formed such that two plates w1and w2that are upper and lower plates are connected to each other by a beam member w3.

The friction stir welding is performed by using the friction stir welding tool100configured as above. When performing the friction stir welding, a facing portion (first facing portion) w4constituted by making end portions of the workpieces face each other is inserted into the gap x1between the upper shoulder10and the intermediate shoulder30. In addition, a facing portion (second facing portions) w5constituted by making end portions of the workpieces face each other is inserted into the gap x2between the intermediate shoulder30and the lower shoulder20. To be specific, the facing portions w4and w5of the workpieces are respectively inserted into the gap x1between the upper shoulder10and the intermediate shoulder30and the gap x2between the intermediate shoulder30and the lower shoulder20.

FIG.4is a perspective view showing partial sections of workpieces W and the friction stir welding tool100in a state where the facing portions w4and w5of the workpieces are respectively arranged in the gap x1between the upper shoulder10and the intermediate shoulder30and the gap x2between the intermediate shoulder30and the lower shoulder20.

As shown inFIG.4, the friction stir welding is performed along the joining direction D1. When performing the friction stir welding along the joining direction D1, the friction stir welding tool moves along the joining direction D1while the wheels31roll along the joining direction D1. Since the friction stir welding tool100moves in the joining direction D1while the wheels31roll, friction generated between the intermediate shoulder30and the workpieces W when the friction stir welding tool100moves can be reduced.

At this time, the friction stir welding is performed in a state where the whirl-stop portions33are in contact with the workpieces W. The whirl-stop portions33are rotatable about the corresponding rotating shafts34while being in contact with the workpieces W. Therefore, when the friction stir welding tool moves along the joining direction D1in order to perform the friction stir welding, contact states between the whirl-stop portions33and the workpieces W are maintained while the whirl-stop portions33roll along the joining direction D1.

Since the friction stir welding is performed in such a manner that the friction stir welding tool100moves in the joining direction D1while the whirl-stop portions33roll along the joining direction D1, friction between the whirl-stop portions33and the workpieces W is reduced. Therefore, while the friction stir welding tool100smoothly moves, the contact states between the whirl-stop portions33and the workpieces W are maintained.

In the present embodiment, the friction stir welding tool100is configured such that when the friction stir welding tool and the workpieces W are set, the intermediate shoulder30is sandwiched by the beam members w3of the workpieces W and contacts both of the beam members w3. Moreover, the intermediate shoulder30is configured such that the whirl-stop portions33contact the beam members w3of the the workpieces W.

Before performing the friction stir welding, the plates w1are sandwiched by the gap x1between the upper shoulder10and the intermediate shoulder30, and the plates w2are sandwiched by the gap x2between the intermediate shoulder30and the lower shoulder20in the friction stir welding tool. In the present embodiment, the friction stir welding tool100is arranged such that: the plates w1are sandwiched by the gap x1; the plates w2are sandwiched by the gap x2; and the whirl-stop portions33of the intermediate shoulder30are brought into contact with the beam members w3. The friction stir welding is performed in a state where the whirl-stop portions33are in contact with the workpieces W. Therefore, when performing the friction stir welding, the intermediate shoulder30is supported by the workpieces W. On this account, it is possible to prevent a case where when the stirring shaft40rotates in order to perform the friction stir welding, the intermediate shoulder30rotates together with the rotation of the stirring shaft40. To be specific, the whirl-stop portions33perform whirl-stop such that even when the stirring shaft40rotates, the intermediate shoulder30does not rotate by the rotation of the stirring shaft40. In the present embodiment, the whirl-stop portions33contacts the workpieces W at both outer sides in the facing direction D2. Therefore, when the stirring shaft40rotates, the whirl-stop portions33perform the whirl-stop at both outer sides in the facing direction D2such that the intermediate shoulder30does not rotate.

When performing the friction stir welding, the stirring shaft40rotates about its axis, and the friction stir welding tool100moves in a direction which intersects with an axial direction of the stirring shaft40and extends along a joining line of the facing portion w4and a joining line of the facing portion w5. When the friction stir welding tool100moves, the upper shoulder10rotates by the rotation of the stirring shaft40, and the upper shoulder10and the facing portion w4of the plates w1arranged between the upper shoulder10and the intermediate shoulder30contact each other. At this time, the intermediate shoulder30and the facing portion w4of the plates w1contact each other at a position of a back side of a contact portion where the upper shoulder10and the facing portion w4of the plates w1contact each other.

Since the rotating upper shoulder10and the facing portion w4of the plates w1contact each other while being supported by the intermediate shoulder30, frictional heat is generated between the upper shoulder10and the facing portion w4. This frictional heat causes plastic flow and softening of portions of the plates w1which portions are to be joined to each other. In a state where the portions of the plates w1which portions are to be joined to each other are softened, the stirring shaft40stirs the portions. With this, the facing portion w4of the plates w1is stirred and joined. Thus, the friction stir welding of the facing portion of the plates w1is performed.

Moreover, when the friction stir welding tool100moves in the joining direction, the lower shoulder20rotates by the rotation of the stirring shaft40, and the facing portion w5of the plates w2and the lower shoulder20contact each other. At this time, the facing portion w5and the intermediate shoulder30contact each other at a position of a back side of a contact portion where the facing portion w5of the plates w2and the lower shoulder20contact each other.

The friction stir welding is performed at the gap x2between the intermediate shoulder30and the lower shoulder20as with at the gap x1between the upper shoulder10and the intermediate shoulder30. In a state where upper sides of the plates w2are supported by the intermediate shoulder30, the rotating lower shoulder20and the facing end portions of the plates w2contact each other. Therefore, frictional heat is generated between the lower shoulder20and the facing portion w5of the plates w2. This frictional heat causes the plastic flow and softening of portions of the plates w2which portions are to be joined to each other. In a state where the portions of the plates w2which portions are to be joined to each other are softened, the stirring shaft40stirs the portions. With this, the facing portion w5of the plates w2is stirred and joined. Thus, the friction stir welding of the facing portion w5of the plates w2is performed.

As above, the friction stir welding is performed in such a manner that: the facing portions w4and w5of the plates w1and w2are made to flow by the frictional heat; and the stirring shaft40stirs the flowing portions of the facing portions w4and w5of the plates w1and w2. In the present embodiment, the friction stir welding is performed simultaneously at both the upper gap portion x1between the upper shoulder10and the intermediate shoulder30and the lower gap portion x2between the intermediate shoulder30and the lower shoulder20. Therefore, the two facing portions of the workpieces W can be joined by performing the friction stir welding once. With this, the workpieces W can be efficiently joined to each other.

Moreover, in the present embodiment, the intermediate shoulder30is configured to be rotatable relative to the stirring shaft40. Therefore, the friction stir welding can be performed in such a manner that when the stirring shaft40rotates about its axis, the upper shoulder10and the lower shoulder20rotates by the rotation of the stirring shaft40, but the intermediate shoulder30does not rotate by the rotation of the stirring shaft40. Therefore, the generation of the heat at the portions to be joined to each other can be made small.

If the intermediate shoulder30also rotates by the rotation of the stirring shaft40about its axis together with the upper shoulder10and the lower shoulder20, a relatively large amount of heat is generated between the friction stir welding tool and the workpieces W during the friction stir welding. When a large amount of frictional heat is generated, the workpieces W easily flow by the heat, and therefore, the friction stir welding is performed in a state where the workpieces W are soft. Therefore, burrs tend to be generated.

However, in the present embodiment, when performing the friction stir welding, the amount of heat generated can be made small. Therefore, the friction stir welding is performed in a state where the workpieces W are relatively hard. Thus, the generation of the burrs on the surfaces of the workpieces W can be made small. With this, the appearance of the workpieces W after the friction stir welding can be made satisfactory, and the design of the workpieces W can be improved.

Moreover, if there are the burrs on the surfaces of the workpieces W when inserting a wire or the like into an inside of the workpieces W, the burrs may contact the wire and interfere with the arrangement of the wire. In the present embodiment, since the generation of the burrs of the workpieces W can be made small, the wire or the like is arranged inside the workpieces W without being interfered by the burrs. Therefore, the quality of the workpieces W can be improved.

Moreover, when the burrs are generated at the workpiece W and come off inside the workpieces W, the burrs move inside the workpieces W and may contact the wire or the like. In the present embodiment, since the generation of the burrs is suppressed, the burrs can be prevented from coming off inside the workpieces W. Therefore, the quality of the workpieces W can be improved.

Moreover, when the burrs are generated at the workpieces W by the friction stir welding, and such workpieces W are provided as structures, stress concentration may occur at the burrs, and this may influence the durability of the workpieces W. In the present embodiment, since the generation of the burrs can be made small, the durability of the joined portions of the workpieces W can be improved.

Moreover, in the present embodiment, for example, the four wheels31are rotatably attached to the supporting members32at positions outside friction stir welding regions R1and R2in the joining direction D1in the intermediate shoulder30. Therefore, the wheels31contact the workpieces W at positions outside the friction stir welding regions R1and R2in the joining direction D1in the intermediate shoulder30. The friction stir welding regions R1and R2are plane regions which contribute to the friction stir welding in the friction stir welding tool100. Moreover, in the illustrated example, the wheels31are attached at positions outside the upper shoulder10and the lower shoulder20in the joining direction D1.

Contact portions (inclination preventing portions)39of the intermediate shoulder30are portions which contact the workpieces W at positions outside the friction stir welding region R1, where the friction stir welding is performed at the upper gap x1, and the friction stir welding region R2, where the friction stir welding is performed at the lower gap portion x2, in the the joining direction D1. In the present embodiment, the contact portions39are the wheels31.

FIG.5is a side view showing the friction stir welding tool during the friction stir welding. When the friction stir welding tool100moves in the joining direction D1to perform the friction stir welding, reaction force acts on the friction stir welding tool100in a direction opposite to the joining direction D1of the friction stir welding tool100. Moreover, the friction stir welding tool100is held by an apparatus main body at a position of an upper portion thereof. When the friction stir welding is performed by the friction stir welding tool100in this state, force Fa which moves the friction stir welding tool100acts on a portion of the friction stir welding tool100which portion is held by the apparatus main body.

In the present embodiment, the friction stir welding is performed in both of the friction stir welding region R1and the friction stir welding region R2. Therefore, the reaction force which acts on the friction stir welding tool100from the workpieces W act in each of the friction stir welding region R1and the friction stir welding region R2.

As shown inFIG.5, the reaction force acting in the friction stir welding region R1of the upper gap x1is represented by F1, and the reaction force acting in the friction stir welding region R2of the lower gap x2is represented by F2. Moreover, a rotational moment acting at a position of the upper gap x1by the reaction force F2at a rotation axis of the stirring shaft is represented by M1. Furthermore, a distance between the upper gap x1and the lower gap x2is represented by H1. The rotational moment M1is represented by a product of the reaction force F2and the distance H1. The rotational moment M1acts in such a direction that the stirring shaft40is inclined by moving a lower portion of the stirring shaft40in a direction opposite to the joining direction D1.

The wheels31of the intermediate shoulder30contact lower portions of the workpieces W. Therefore, the friction stir welding tool100receives the reaction force from the workpiece W at portions where the wheels31contact the workpieces W. Reaction force received from the workpiece W by the wheel31arranged at a front side in the joining direction D1is represented by F3. Moreover, a rotational moment acting on the rotation axis of the stirring shaft by the reaction force F3is represented by M2. Furthermore, a distance between the rotation axis of the stirring shaft and the wheel31is represented by H2. The rotational moment M2is represented by a product of the reaction force F3and the distance H2.

When the rotational moment M1acts on the stirring shaft40at the position of the upper gap x1by the reaction force F2acting on the friction stir welding tool100during the friction stir welding, the stirring shaft40is inclined in a front-rear direction along the joining direction D1. Specifically, the stirring shaft40is inclined such that: a front portion of the intermediate shoulder30in the joining direction D1moves downward; and a rear portion of the intermediate shoulder30in the joining direction D1moves upward.

At this time, at a front side in the joining direction D1, the wheels31contact the workpieces Win regions outside the friction stir welding regions R1and R2in the joining direction D1. When the stirring shaft40is about to be inclined by the rotational moment M1, the reaction force F3from the workpieces W at the positions of the wheels31at the front portion, which moves downward, in the joining direction D1increases. At this time, as the reaction force F3increases, the rotational moment M2generated by the reaction force F3also increases. Therefore, the rotational moment M1which inclines the stirring shaft40is canceled by the rotational moment M2generated by the reaction force F3, and thus, the magnitude of the rotational moment which inclines the stirring shaft40can be suppressed.

Moreover, two wheels31are arranged at each of front and rear positions of the intermediate shoulder30in the joining direction D1so as to be lined up in the facing direction D2. Therefore, the reaction force F3from the workpieces W acts on the intermediate shoulder30at two positions lined up in the facing direction D2. On this account, the reaction force F3acts uniformly in the facing direction D2. Moreover, the rotational moment M2generated by the reaction force F3also acts uniformly in the facing direction D2. Therefore, the reaction force F3and the rotational moment M2acting on the intermediate shoulder30can be balanced in the facing direction D2. On this account, the intermediate shoulder30is more stably arranged on the workpieces W in the facing direction D2.

Moreover, for example, when the movement of the friction stir welding tool100for the friction stir welding is reversed, i.e., the joining direction becomes a direction opposite to the direction D1shown inFIG.5, a direction in which the stirring shaft40is about to be inclined becomes a direction opposite to the direction when the joining direction is the direction D1. The stirring shaft40is inclined such that: the front portion of the friction stir welding tool100in the movement direction moves downward; and the rear portion of the friction stir welding tool100in the movement direction moves upward. In this case, when the stirring shaft40is about to be inclined, the reaction force from the workpieces W increases at the positions of the wheels31located at a front side in the movement direction of the friction stir welding tool100. At this time, as the reaction force from the workpieces W increases, the rotational moment (which acts in a direction opposite to the direction in which the rotational moment M2acts) generated by the reaction force from the workpieces W also increases. Therefore, the rotational moment which inclines the stirring shaft40is canceled by the rotational moment generated by the reaction force from the workpieces W, and thus, the magnitude of the rotational moment which inclines the stirring shaft40can be suppressed.

As above, since parts of the intermediate shoulder30and the workpieces W contact each other at positions outside the intermediate shoulder30in the joining direction D1, the rotational moments which incline the stirring shaft40in the friction stir welding regions R1and R2can be canceled. Therefore, the inclination of the stirring shaft40can be suppressed. With this, the bending of the stirring shaft40can be suppressed. Since the bending of the stirring shaft40can be suppressed, the durability of the friction stir welding tool100can be improved.

Moreover, the rotational moments which incline the stirring shaft40are canceled. Therefore, even when a load acting on the friction stir welding tool100is increased, the friction stir welding tool100can be prevented from being influenced in terms of strength. Therefore, a movement speed in the joining direction D1when performing the friction stir welding can be made high. Since the movement speed during the friction stir welding can be made high, the friction stir welding can be more efficiently performed.

Moreover, in the present embodiment, the wheels31contact the workpiece W, arranged at the lower gap x2, at positions outside the friction stir welding region R1and the friction stir welding region R2in a radial direction of the stirring shaft40. The intermediate shoulder30contacts the workpieces W in regions outside the friction stir welding regions R1and R2. Therefore, when the friction stir welding tool100moves along the joining direction D1, the intermediate shoulder30is arranged on the workpieces W while being stably supported in the joining direction D1.

Therefore, in a state where the rotation axis of the stirring shaft40is stabilized, the friction stir welding tool100moves, and the stirring shaft40can be prevented from being inclined and bent. With this, the durability of the friction stir welding tool100can be improved.

Moreover, two wheels31are arranged at each of front and rear positions of the intermediate shoulder30in the joining direction D1so as to be lined up in the facing direction D2. Therefore, the intermediate shoulder30contacts the workpieces W in regions outside the friction stir welding regions R1and R2in the facing direction D2. Therefore, when the friction stir welding tool100moves along the joining direction D1, the intermediate shoulder30is arranged on the workpieces W while being stabilized in the facing direction D2. On this account, the bending of the stirring shaft40can be suppressed in the facing direction D2.

Moreover, in the present embodiment, the wheels31contact the workpieces W in regions outside the friction stir welding regions R1and R2in the facing direction D2. To be specific, the intermediate shoulder30contacts the workpieces W in regions outside the friction stir welding regions R1and R2in the facing direction D2. Since the intermediate shoulder30contacts the workpieces W in regions outside the friction stir welding regions R1and R2in the facing direction D2, the stirring shaft40can be prevented from being inclined and bent in the facing direction D2. With this, the durability of the friction stir welding tool100can be further improved.

Moreover, in the present embodiment, while the wheels31roll in the joining direction D1, the friction stir welding tool100moves in the joining direction D1. Therefore, the wheels31are configured as contact portions (second shoulder portion-side contact portions) which contact the workpieces W at a lower portion (second contact portion side) of the intermediate shoulder30. Since the intermediate shoulder30moves in the joining direction D1while the wheels31roll, friction generated between the intermediate shoulder30and the workpiece W can be made small. On this account, the intermediate shoulder30can be made to move smoothly in the joining direction D1.

Moreover, in the present embodiment, in a state where the workpieces W are supported by the intermediate shoulder30which does not rotate by the rotation of the stirring shaft40, the upper shoulder10and the lower shoulder20rotate by the rotation of the stirring shaft40. The friction stir welding is performed in a state where the workpieces W are supported by the intermediate shoulder30. Therefore, even when the strength of the workpieces W is low, the friction stir welding can be smoothly performed. On this account, for example, when the plates w1and w2of the workpieces W are thin, the friction stir welding can be performed satisfactorily. Thus, ranges of the workpieces W to which ranges the friction stir welding is applied can be made large.

The present embodiment has described a case where the wheels31that are cylindrical rollers roll, and with this, the intermediate shoulder30moves along the joining direction in which the friction stir welding is performed. However, the present invention is not limited to the above embodiment. For example, in the intermediate shoulder30, the contact portions39which contact the workpieces W may be spherical balls which roll in the joining direction. When performing the friction stir welding, the intermediate shoulder30may move along the joining direction D1while the balls roll.

Moreover, a low friction material which reduces friction between the intermediate shoulder30and the workpieces W may be provided at portions of the intermediate shoulder30which portions are located close to the lower shoulder and contact the workpieces W. As the low friction material, DLC (diamond-like carbon) may be used. When the portions of the intermediate shoulder30which portions are located close to the lower shoulder and contact the workpieces W are coated with the DLC, friction coefficients of the portions of the intermediate shoulder30which portions are located close to the lower shoulder and contact the workpieces W can be made made small. Therefore, when the friction stir welding tool100is made to move in the joining direction D1in order to perform the friction stir welding, the intermediate shoulder30can be made to slide smoothly relative to the workpieces W, and resistance generated when the friction stir welding tool100moves can be made small. In this case, in the intermediate shoulder30, the contact portions39which contact the workpieces W may be the intermediate shoulder main body portion29. It should be noted that another low friction material may be used as long as friction between the intermediate shoulder30and the workpieces W can be reduced.

Moreover, the present embodiment has described a case where the whirl-stop portion33that is a cylindrical roller contacts the workpiece W to perform the whirl-stop of the intermediate shoulder30. However, the present invention is not limited to the above embodiment. For example, a whirl-stop portion formed in a ball shape may contact the workpiece W to perform the whirl-stop of the intermediate shoulder30. The whirl-stop portion33may have a shape other than a roller as long as the whirl-stop portion33can contact the workpiece W to perform the whirl-stop. As long as the whirl-stop portion33has such a shape as to be able to roll along the joining direction D1, friction generated between the whirl-stop portion33and the workpiece W when the friction stir welding tool100moves along the joining direction D1can be suppressed, which is preferable.

FIG.6is a flowchart showing steps when the friction stir welding method according to the present embodiment is performed. When performing the friction stir welding, first, the friction stir welding tool100and the workpieces W are set. In the present embodiment, the facing portion w4(FIG.4) constituted by making the end portions of the plates, which are joined to each other, of the workpieces W face each other is sandwiched by and inserted into the gap x1between the upper shoulder10and the intermediate shoulder30(first sandwiching step; S1). Moreover, the facing portion w5(FIG.4) constituted by making the end portions of the plates, which are joined to each other, of the workpieces W face each other is sandwiched by and inserted into the gap x2between the intermediate shoulder30and the lower shoulder20(second sandwiching step; S2). When respectively setting the facing portions w4and w5, each of which is constituted by making the end portions of the workpieces W face each other, in the gaps x1and x2in the friction stir welding tool100, the workpieces W are set such that parts of the intermediate shoulder30contact the workpieces W. In the present embodiment, the wheels31attached to the intermediate shoulder30and the workpieces W contact each other at positions outside the friction stir welding regions R1and R2of the gaps x1and x2of the friction stir welding tool100in the joining direction D1(S3).

A step performed at first may be any of the step of sandwiching the facing portion w4, constituted by making the end portions of the workpieces W face each other, in the gap x1between the upper shoulder10and the intermediate shoulder30, the step of sandwiching the facing portion w5, constituted by making the end portions of the workpieces W face each other, in the gap x2between the intermediate shoulder30and the lower shoulder20, and the step of bringing the wheels31attached to the intermediate shoulder30and the workpieces W into contact with each other. Or, these steps may be performed simultaneously. To be specific, the order of these steps may be any order as long as the facing portion w4of the workpieces W is arranged in the gap x1between the upper shoulder10and the intermediate shoulder30, the facing portion w5of the workpieces W is arranged in the gap x2between the intermediate shoulder30and the lower shoulder20, and the wheels31attached to the intermediate shoulder30and the workpieces are brought into contact with each other.

After the friction stir welding tool100and the workpieces W are set, the stirring shaft40is rotated (S4). Then, the friction stir welding is performed in such a manner that: in a state where the stirring shaft40is rotating, the stirring shaft40is brought into contact with the workpieces W; and the friction stir welding tool100moves in the joining direction D1(S5). When the stirring shaft and the workpieces W are brought into contact with each other in a state where the stirring shaft40is rotating, frictional heat is generated at portions where the stirring shaft40and the workpieces W contact each other. This frictional heat causes the plastic flow and softening of portions of the plates of the workpieces W which portions are to be joined to each other. At this time, the friction stir welding is performed while preventing the stirring shaft40from being inclined (friction stir welding step).

The friction stir welding is performed until the friction stir welding of the entire facing end portions of the workpieces W terminates (S6). After the friction stir welding of the entire facing portions w4and w5of the workpieces W is completed, the friction stir welding terminates.

The present embodiment has described a case where since the intermediate shoulder30contacts the workpieces W at positions outside the friction stir welding regions R1and R2of the gaps x1and x2of the friction stir welding tool100in the facing direction D2, the inclination of the stirring shaft40in the joining direction D2can be suppressed. However, the present invention is not limited to the above embodiment. For example, the intermediate shoulder30may contact the workpieces W at positions outside the friction stir welding regions R1and R2in the joining direction D1and inside the friction stir welding regions R1and R2in the facing direction D2. Even when the intermediate shoulder30contacts the workpieces W at positions inside the friction stir welding regions R1and R2in the facing direction D2, the bending of the stirring shaft40can be suppressed as long as the intermediate shoulder30contacts the workpieces W at positions outside the friction stir welding regions R1and R2in the joining direction D1.

Moreover, the above embodiment has described a case where the wheels31are provided only at the lower portion of the intermediate shoulder30. However, the present invention is not limited to the above embodiment. The wheels31may be provided at not only the lower portion of the intermediate shoulder30but also the upper portion (first contact portion) of the intermediate shoulder30. To be specific, the intermediate shoulder30may include not only contact portions39aconfigured to contact the workpieces W at the lower portion but also contact portions (first shoulder portion-side contact portions)39bconfigured to contact the workpieces W at the upper portion (first shoulder portion side). As above, the intermediate shoulder30may contact the workpieces W by both the contact portions39bat the upper portion and the contact portions39aat the lower portion.

FIG.7is a side view showing a friction stir welding tool100aconfigured such that the wheels31are the contact portions39bconfigured to contact the workpieces W at the upper shoulder side of the intermediate shoulder30and the contact portions39aconfigured to contact the workpieces W at the lower shoulder side of the intermediate shoulder30. The wheels31are provided at the intermediate shoulder30so as to be located positions close to the upper shoulder and positions close to the lower shoulder in the axial direction of the stirring shaft40. The wheels31are provided at front and rear sides in the joining direction D1at the above positions. Moreover, two wheels31are provided along the facing direction D2at each of the above positions.

As above, the wheels31may be provided at the intermediate shoulder30so as to be located at the positions close to the upper shoulder and the positions close to the lower shoulder. With this, the friction can be reduced at the positions close to the lower shoulder in the intermediate shoulder30, and in addition, the friction can be reduced at the positions close to the upper shoulder in the intermediate shoulder30. With this, the intermediate shoulder30can be made to move more smoothly along the joining direction D1.

Moreover, at the upper shoulder side of the intermediate shoulder30, the wheels31and the workpieces W are brought into contact with each other at positions outside the friction stir welding regions R1and R2. Therefore, since the intermediate shoulder30is supported by the workpieces W at the upper side, the intermediate shoulder30contacts larger regions of the workpieces W. With this, when the friction stir welding tool100amoves along the joining direction D1, the intermediate shoulder30is further stably arranged on the workpieces W in the joining direction D1.

Moreover, two wheels31lined up in the facing direction D2are arranged at each of positions away from each other in the joining direction D1of the intermediate shoulder30and the axial direction of the stirring shaft40. Therefore, the intermediate shoulder30contacts large regions of the workpieces W in the facing direction D2at both the upper shoulder side and the lower shoulder side. On this account, when the friction stir welding tool100moves along the joining direction D1, the intermediate shoulder30is arranged on the workpieces W while being stabilized in the facing direction D2.

Moreover, since the wheels31contact the workpieces W at the upper shoulder side, the reaction force generated between the wheels31and the workpieces W can be received by the workpieces W at the upper shoulder side. Reaction force received from the workpiece by the wheel31arranged at a front side in the joining direction D1out of the wheels31provided at the lower shoulder side of the intermediate shoulder30is represented by F4, and reaction force received from the workpiece W by the wheel31arranged at a rear side in the joining direction D1out of the wheels31provided at the upper shoulder side of the intermediate shoulder30is represented by F5.

As described above by usingFIG.5, the reaction force acting in the friction stir welding region R1of the upper gap x1is represented by F1, and the reaction force acting in the friction stir welding region R2of the lower gap x2is represented by F2. Moreover, the rotational moment acting at the position of the upper gap x1by the reaction force F2at the rotation axis of the stirring shaft40is represented by M1. Furthermore, the rotational moment acting on the rotation axis of the stirring shaft by the reaction force F4is represented by M3. A distance between the rotation axis of the stirring shaft and the wheel31located at a front side of the lower portion of the intermediate shoulder30is represented by H3. The rotational moment M3is represented by a product of the reaction force F4and the distance H3. Moreover, the rotational moment acting on the rotation axis of the stirring shaft by the reaction force F5is represented by M4. A distance between the rotation axis of the stirring shaft and the wheel31located at a rear side of the upper portion of the intermediate shoulder30is represented by H4. The rotational moment M4is represented by a product of the reaction force F5and the distance H4.

As with the example shown inFIG.5, when the rotational moment M1acts on the stirring shaft40at the position of the upper gap x1by the reaction force F2acting on the friction stir welding tool100during the friction stir welding, the stirring shaft40is inclined. When the stirring shaft40is about to be inclined by the rotational moment M1, the reaction force F4from the workpiece W at the position of the wheel31located at a front side of the lower portion of the intermediate shoulder30in the joining direction D1increases. At this time, as the reaction force F4increases, the rotational moment M3generated by the reaction force F4also increases. Moreover, when the stirring shaft40is about to be inclined by the rotational moment M1, the reaction force F5from the workpiece W at the wheel31located at a rear side of the upper portion of the intermediate shoulder30in the joining direction D1increases. At this time, as the reaction force F5increases, the rotational moment M4generated by the reaction force F5also increases. Therefore, the rotational moment M1which inclines the stirring shaft40is canceled by both of the rotational moment M3generated by the reaction force F4and the rotational moment M4generated by the reaction force F5, and thus, the magnitude of the rotational moment which inclines the stirring shaft40can be further suppressed.

Moreover, two wheels31lined up in the facing direction D2are arranged at each of positions away from each other in the joining direction D1of the intermediate shoulder30and the axial direction of the stirring shaft40. Therefore, the reaction force F4from the workpieces W acts on the intermediate shoulder30at two portions lined up in the facing direction D2of the workpieces W, and the reaction force F5from the workpieces W acts on the intermediate shoulder30at two portions lined up in the facing direction D2of the workpieces W. Therefore, each of the reaction force F4and the reaction force F5acts uniformly in the facing direction D2of the workpieces W. Moreover, each of the rotational moment M3generated by the reaction force F4and the rotational moment M4generated by the reaction force F5also acts uniformly in the facing direction D2. Therefore, the reaction force F4, the reaction force F5, the rotational moment M3, and the rotational moment M4acting on the intermediate shoulder30can be balanced in the facing direction D2. On this account, the intermediate shoulder30is arranged on the workpieces W while being further stabilized in the facing direction D2.

Moreover, for example, when the movement of the friction stir welding tool100afor the friction stir welding is reversed, i.e., the joining direction becomes a direction opposite to the direction D1shown inFIG.7, a direction in which the stirring shaft40is about to be inclined becomes a direction opposite to the direction when the joining direction is the direction D1. The stirring shaft40is inclined such that: the front portion of the friction stir welding tool100in the movement direction moves downward; and the rear portion of the friction stir welding tool100in the movement direction moves upward. In this case, when the stirring shaft40is about to be inclined, the reaction force from the workpieces W increases at both of the upper and lower portions of the intermediate shoulder30. At this time, as the reaction force from the workpieces W increases at both the upper and lower portions, the rotational moments (which act in directions opposite to the directions in which the rotational moments M3and M4act) generated by the reaction force from the workpieces W also increase. Therefore, the rotational moment which inclines the stirring shaft40is canceled by the two rotational moments generated by the reaction force from the workpieces W, and thus, the magnitude of the rotational moment which inclines the stirring shaft40can be further suppressed.

The present embodiment has described a case where the whirl-stop portions33are brought into contact with the workpieces W to serve as whirl stoppers for the intermediate shoulder30. However, the present invention is not limited to the above embodiment. The rotation of the intermediate shoulder30may be suppressed in such a manner that part of the intermediate shoulder30contacts a portion other than the workpiece W. For example, the rotation of the intermediate shoulder30may be suppressed in such a manner that: a jig is arranged between the plates w1and w2of the workpiece W; and the intermediate shoulder30contacts the jig.

Moreover, the present embodiment has described a case where four or eight wheels31are attached to the intermediate shoulder30. However, the present invention is not limited to the above embodiment. The number of wheels31may be different from the above. For example, the number of wheels31may be nine or more or three or less, such as two. The number of wheels31may be any number as long as the intermediate shoulder30smoothly moves in the joining direction D1during the friction stir welding.

Moreover, a roller or a ball which reduces friction between the intermediate shoulder30and the workpiece W may be provided on the surface of the intermediate shoulder30so as to be located at positions outside the friction stir welding regions R1and R2of the intermediate shoulder30in the radial direction. Furthermore, a surface of a portion of the intermediate shoulder30which portion contacts the workpiece W may be coated with a low friction material. For example, coating using DLC may be performed. With this, when performing the friction stir welding, friction between the intermediate shoulder30and the workpiece W can be further reduced. Therefore, the friction stir welding can be performed smoothly.

Next, a friction stir welding tool100baccording to Embodiment 2 of the present invention will be described. It should be noted that explanations of the same components as Embodiment 1 are omitted, and only different components will be described.

Embodiment 2 is different from Embodiment 1 in that: an opposing portion (first opposing portion)35aof the intermediate shoulder30which portion is opposed to the upper shoulder10through the upper gap x1and an opposing portion (second opposing portion)35bof the intermediate shoulder30which portion is opposed to the lower shoulder20through the lower gap x2are configured to be movable relative to each other in the axial direction of the stirring shaft40; and an elastic body is arranged between these opposing portions.

FIGS.8A and8Bare side views showing the friction stir welding tool100bof Embodiment 2.FIG.8Ais a side view showing the friction stir welding tool100bin which the opposing portion35aopposed to the upper shoulder10and the opposing portion35bopposed to the lower shoulder20are located relatively away in distance from each other in the intermediate shoulder30. Moreover,FIG.8Bis a side view showing the friction stir welding tool100bin which the opposing portion35aopposed to the upper shoulder10and the opposing portion35bopposed to the lower shoulder20are located relatively close in distance to each other in the intermediate shoulder30.

As shown inFIGS.8A and8B, the workpiece W may not have stable quality as a whole. The dimensional accuracy of such workpiece W may not be high depending on portions thereof. For example, the plate of such workpiece W may be configured to undulate or wave. In such a case, the intermediate shoulder30may contact a portion of the plate which portion is convex upward as shown inFIG.8A, or the intermediate shoulder30may contact a portion of the plate which portion is convex downward as shown inFIG.8B.

When the plate is formed so as to wave as above, a distance between a contact position where the intermediate shoulder30contacts the plate at the upper shoulder side and a contact position where the intermediate shoulder30contacts the plate at the lower shoulder side varies depending on positions along the joining direction D1. In such a case, if the distance between the contact position where the intermediate shoulder30contacts the plate at the upper shoulder side and the contact position where the intermediate shoulder30contacts the plate at the lower shoulder side is constant, the friction stir welding is performed with a gap between the intermediate shoulder30and the plate at a certain position in the joining direction D1, and therefore, the friction stir welding may not be performed accurately.

The friction stir welding tool100bof the present embodiment is configured such that the opposing portion35aof the intermediate shoulder30which portion is opposed to the upper shoulder10through the upper gap x1and the opposing portion35bof the intermediate shoulder30which portion is opposed to the lower shoulder20through the lower gap x2are movable relative to each other in the axial direction of the stirring shaft40. Moreover, the elastic body is arranged at a position between the opposing portion35aof the intermediate shoulder30which portion is opposed to the upper shoulder10and the opposing portion35bof the intermediate shoulder30which portion is opposed to the lower shoulder20. In the present embodiment, for example, a spring36is provided as the elastic body.

Since the spring36is arranged between the opposing portion35aof the intermediate shoulder30which portion is opposed to the upper shoulder10and the opposing portion35bof the intermediate shoulder30which portion is opposed to the lower shoulder20, the opposing portion35aof the intermediate shoulder30which portion is opposed to the upper shoulder10and the opposing portion35bof the intermediate shoulder30which portion is opposed to the lower shoulder20can be biased in respective directions away from each other. The intermediate shoulder30moves along the joining direction D1in a state where the opposing portion35aof the intermediate shoulder30which portion is opposed to the upper shoulder10and the opposing portion35bof the intermediate shoulder30which portion is opposed to the lower shoulder20are biased in respective directions away from each other. Therefore, even when the plate is formed so as to wave, the intermediate shoulder30can follow changes in shape of the plate and move while contacting both of the upper plate and the lower plate. On this account, the friction stir welding tool100bcan perform the friction stir welding in a state where the opposing portion35aof the intermediate shoulder30which portion is opposed to the upper shoulder10and the opposing portion35bof the intermediate shoulder30which portion is opposed to the lower shoulder20are surely in contact with the workpieces W. Thus, the friction stir welding can be performed accurately.

In the present embodiment, the spring36is used as the elastic body. However, the present invention is not limited to this. A component other than the spring may be used as the elastic body. For example, rubber may be used.

Next, a friction stir welding tool100caccording to Embodiment 3 of the present invention will be described. It should be noted that explanations of the same components as Embodiments 1 and 2 are omitted, and only different components will be described.

Embodiment 3 is different from Embodiments 1 and 2 regarding the positions of the beam members w3of the workpieces W subjected to the friction stir welding. Therefore, the shape of the intermediate shoulder30in a front view is different from those of Embodiments 1 and 2.

As shown inFIG.4, each of Embodiments 1 and 2 has described an example in which in a front view of the friction stir welding tool, a section of the intermediate shoulder30along the facing direction D2has a rectangular shape that is long in the direction D2. On the other hand, for example, as shown inFIG.9, Embodiment 3 is configured such that in a front view of the intermediate shoulder30, a portion of the intermediate shoulder30which portion is opposed to the upper shoulder10curves so as to taper toward an upper side.

In Embodiment 3, an interval between the beam members w3of the workpieces W facing each other is formed to be smaller than each of those in Embodiments 1 and 2. When the interval between the beam members w3is made narrow, the rigidity of the workpieces W joined to each other by the friction stir welding can be improved. Therefore, when the interval between the beam members w3is made narrow in order to improve the rigidity of the workpieces W, the length of the intermediate shoulder30in the facing direction D2is made small in accordance with the interval between the beam members w3of the workpieces W such that the intermediate shoulder30contacts both of the beam members w3. Moreover, the upper portion of the intermediate shoulder30is formed in a tapered shape in accordance with the shapes of the beam members w3such that the length thereof in the facing direction D2decreases toward an upper side.

The intermediate shoulder30is formed as above. Therefore, even when the interval between the beam members w3of the workpieces W is narrow, the friction stir welding can be performed in a state where the intermediate shoulder30contacts both of the beam members w3. On this account, the positioning of the intermediate shoulder30can be performed by the beam members w3. Thus, the friction stir welding can be performed accurately. Moreover, since the intermediate shoulder30contacts the beam members w3, the beam members w3serve as whirl stoppers for the intermediate shoulder30. Therefore, the friction stir welding can be performed in a state where the intermediate shoulder30is pressed by the beam members w3so as not to rotate by the rotation of the stirring shaft40. On this account, the friction stir welding can be performed while maintaining a state where the intermediate shoulder30does not rotate. Thus, the amount of heat generated when performing the friction stir welding can be made small.

Next, a friction stir welding tool100daccording to Embodiment 4 of the present invention will be described. It should be noted that explanations of the same components as Embodiments 1 to 3 are omitted, and only different components will be described.

Each of Embodiments 1 to 3 has described an example in which each of the workpieces W to be joined to each other includes: the upper and lower plates w1and w2; and the beam member w3arranged between the plates. On the other hand, Embodiment 4 will describe a case where the workpieces W each having, for example, a U-shaped section are joined to each other by the friction stir welding at upper end portions thereof facing each other and lower end portions thereof facing each other.

As shown inFIG.10, in Embodiment 4, each of workpieces w6and w7is formed in a U shape that is open inward. Edge portions of the inward opening portions are joined to each other by the friction stir welding. With this, a tubular workpiece W is formed such that a section thereof along the facing direction D2is a rectangular closed section.

In the present embodiment, the edge portions of the opening portions of the workpieces W are arranged at the gap x1between the upper shoulder10and the intermediate shoulder30and the gap x2between the intermediate shoulder30and the lower shoulder20in the friction stir welding tool100d.

Moreover, the friction stir welding is performed in such a manner that: the intermediate shoulder30is arranged inside a region surrounded by the U-shaped workpieces w6and w7that are open inward; and the friction stir welding tool100dmoves along the joining direction while rotating the stirring shaft40.

Moreover, in Embodiment 4, the shapes of the workpieces w6and w7are configured such that a length between portions of the workpieces w6and w7which portions are opposed to each other in the facing direction D2is relatively large in a region between the gap x1and the gap x2in the axial direction. The intermediate shoulder30includes projecting portions37projecting outward in the facing direction D2such that the intermediate shoulder30can contact the workpieces w6and w7even when the length between the portions of the workpieces w6and w7which portions are opposed to each other in the facing direction D2is relatively large.

The intermediate shoulder30includes rollers38. Each of the rollers38is rotatably provided at an end portion of the corresponding projecting portion37which portion is located outside in the facing direction D2. Moreover, the roller38is provided at the projecting portion37such that part of an outer peripheral surface38athereof which part is located outside in the facing direction D2protrudes outward in the facing direction D2beyond the projecting portion37. The rollers38are arranged such that rotation axes38bthereof are parallel to the rotation axis of the stirring shaft40. The portions of the outer peripheral surfaces38aof the two rollers38which portions protrude outward beyond the projecting portions37are brought into contact with the respective workpieces w6and w7.

The intermediate shoulder30includes the projecting portions37and the rollers38, and the rollers38are attached to tip end portions, located outside in the facing direction D2, of the projecting portions37. Therefore, even when a distance from the intermediate shoulder30to each workpiece in the facing direction D2is long, the intermediate shoulder30can contact the workpieces w6and w7through the projecting portions37and the rollers38.

When the friction stir welding tool100dmoves in the joining direction D1, the rollers38roll in a direction along the joining direction D1. Therefore, friction generated between the intermediate shoulder30and the workpieces w6and w7can be made small. Thus, the intermediate shoulder30can be made to move smoothly in the joining direction D1.

Since the friction stir welding is performed in a state where the workpieces w6and w7and the intermediate shoulder30are in contact with each other through the projecting portions37and the rollers38, the positioning of the intermediate shoulder30can be performed by the workpieces w6and w7.

Moreover, since the friction stir welding is performed in a state where the workpieces w6and w7and the intermediate shoulder30are in contact with each other through the projecting portions37and the rollers38, the friction stir welding can be performed in a state where the intermediate shoulder30is supported by the workpieces w6and w7. Therefore, the workpieces w6and w7can serve as whirl stoppers for the intermediate shoulder30. With this, the friction stir welding can be performed in a state where the whirl-stop of the intermediate shoulder30is being performed, i.e., in a state where even when the stirring shaft40rotates, the intermediate shoulder30does not rotate by the rotation of the stirring shaft40.

Next, a friction stir welding tool100eaccording to Embodiment 5 of the present invention will be described. It should be noted that explanations of the same components as Embodiments 1 to 4 are omitted, and only different components will be described.

FIG.11is a sectional view showing the friction stir welding tool100eaccording to Embodiment 5. In Embodiments 1 to 4, the entire intermediate shoulder30is arranged around the axis of the stirring shaft40through the bearing50. Therefore, the entire intermediate shoulder30is configured to be able to be prevented from performing the same rotation as the stirring shaft40when the stirring shaft40rotates. On the other hand, in the friction stir welding tool100eof Embodiment 5, the intermediate shoulder30includes: a first opposing portion30dopposed to the upper shoulder10; a second opposing portion30eopposed to the lower shoulder20; and a lateral peripheral wall portion30fincluding the wheels31and the whirl-stop portions33. The peripheral wall portion30fof the intermediate shoulder30is arranged around the axis of the stirring shaft40through a bearing50a. Therefore, the peripheral wall portion30fis attached so as to be rotatable relative to the stirring shaft40. Moreover, the stirring shaft40passes through the inside of the first opposing portion30dand the inside of the second opposing portion30e, and the first opposing portion30dand the second opposing portion30eare fixed around the axis of the stirring shaft40and are unrotatable relative to the stirring shaft40. Therefore, when the stirring shaft40is rotated, the peripheral wall portion30fdoes not rotate, but the first opposing portion30dand the second opposing portion30erotate by the rotation of the stirring shaft40.

The friction stir welding tool100eis configured as above. Thus, the friction stir welding can be performed by using the friction stir welding tool100ewhile the first opposing portion30dand the second opposing portion30erotate by the rotation of the stirring shaft40. Therefore, the friction stir welding can be performed at both of the upper and lower sides of the workpieces contacting the friction stir welding tool100ewhile the friction stir welding tool100erotates relative to the workpieces at both front and back surfaces of the workpieces. On this account, the friction stir welding can be performed while generating high frictional heat between the friction stir welding tool100eand the workpieces. As above, the friction stir welding tool100emay be configured to perform the friction stir welding while the first opposing portion30dand the second opposing portion30ein the intermediate shoulder30rotate by the rotation of the stirring shaft40.

In this case, the peripheral wall portion30fis configured to be rotatable relative to the stirring shaft40. Therefore, when performing the friction stir welding, the wheels31can stably roll on the workpieces in the joining direction D1. On this account, the intermediate shoulder30can move in the joining direction D1. Moreover, in this case, the friction stir welding is performed in a state where the whirl-stop portions33contact the workpieces while rolling in the joining direction D1. Therefore, the whirl-stop portions33perform the whirl-stop of the intermediate shoulder30such that when the stirring shaft40rotates, the intermediate shoulder30does not rotate by the rotation of the stirring shaft40.

As a result, the friction stir welding may be performed while the portion of the intermediate shoulder30which portion is opposed to the upper shoulder10and the portion of the intermediate shoulder30which portion is opposed to the lower shoulder20rotate by the rotation of the stirring shaft40, or the friction stir welding may be performed while the portion of the intermediate shoulder30which portion is opposed to the upper shoulder10and the portion of the intermediate shoulder30which portion is opposed to the lower shoulder20do not rotate by the rotation of the stirring shaft40.

REFERENCE SIGNS LIST