JP2024042668A - Rotating tool for friction stir welding and friction stir welding method - Google Patents

Abstract

[Problem] To provide a highly durable friction stir welding rotating tool that is less likely to break even when friction stir welding highly rigid workpieces such as steel plates. [Solution] A rotating tool 1 used for friction stir welding two workpieces is provided, comprising a tip portion 10 having a convex curved surface 11, the curved surface 11 being characterized by having a circular first smooth surface 12 located at the center, an annular undulating surface 13 located on the outer periphery of the first smooth surface 12, and an annular second smooth surface 14 located on the outer periphery of the undulating surface 13. [Selected Figure] Figure 1

Description

The present invention relates to a friction stir welding rotating tool used for friction stir welding to join two steel plates, and a friction stir welding method.

In the friction stir welding method, a rotating tool (e.g., a rotary tool) is inserted into the unwelded part of the materials to be joined (e.g., steel plates, etc.) that are stacked or butted against each other, and the rotating tool is moved while rotating. This is a method of joining steel plates by generating frictional heat to soften the parts, and then stirring the softened parts with a rotating tool to cause plastic flow.

Since the friction stir welding method is a solid-phase welding method that utilizes plastic flow of metal due to frictional heat between a rotating tool and the materials to be welded, it is possible to join the materials without melting the unwelded parts. There are many advantages such as fewer defects in the joint because the materials to be joined are not melted, less deformation after joining because the heating temperature is low, and no filler metal required for joining.

In addition, in this specification, the overlapping part or the butt part where the materials to be joined such as steel plates are overlapped or butted but not yet joined is referred to as the "unjoined part", and it is referred to as the "unjoined part", and it is referred to as the "unjoined part". The converted portion is called a “junction”.

There is a strong demand for weight reduction in transportation machinery such as automobiles and ships from the perspective of improving fuel efficiency. In this trend, spot welding and laser welding are often used for parts used in transportation machines. However, since these are fusion joints, when ultra-high tensile steel or high carbon materials are welded, the welded part becomes a full martensitic structure. As a result, hardening becomes significant, resulting in a weak weld.

Examples of friction stir welding methods include the techniques described in Patent Documents 1 and 2 below.

Patent Document 1 describes applying a friction stir welding method to a tailored blank member made of aluminum material. In the technique described in Patent Document 1, the rotational axis of a rotary tool (rotor of a welding tool) is inclined toward a lower welding member, and the tool is inserted into a mating portion of the welding member. That is, the rotary tool moves in the joining direction along the mating portion in a state perpendicular to the joining direction, thereby joining the joining members from the surface side.

Patent Document 2 describes that a friction stir welding method is applied to a tailored blank member of a material to be welded made of aluminum, magnesium, or the like. In the technique described in Patent Document 2, a bobbin tool having a curved shoulder is used as the rotating tool. This bobbin tool is configured such that an upper base, an upper shoulder, a lower base, a lower shoulder, and a probe between the shoulders are rotatable together.

As described above, in the friction stir welding method, materials to be joined, such as steel plates, are joined by stirring the joining interface using a rotating tool. Since the rotating tool is subjected to a large load during welding, there is a risk that joint failure may occur due to this. Therefore, there is a need for rotary tools to suppress the occurrence of bonding defects during bonding.

As methods for suppressing the occurrence of bonding defects, there are, for example, techniques disclosed in Patent Documents 3 and 4 below.

Patent Document 3 describes a method for suppressing defects caused by fluctuations in the pressing depth of the tool against the workpiece, which occurs when the friction stir welding tool is rotated and pressed into the welding part of the workpiece and moved. In order to achieve this, techniques have been described to maintain a constant tool depth. In the technique described in Patent Document 3, in a tool having a shoulder and a pin, the outer peripheral side of the end surface of the shoulder that contacts the workpiece when the pin is press-inserted into the workpiece is formed into an inclined surface. , the tool pressing depth is controlled by this inclined surface.

Patent Document 4 describes a technique for performing joining using a tool formed in a truncated conical shape having a spiral groove on a shoulder surface. In the technology described in Cited Document 4, the above-mentioned tool suppresses the sinking of the shoulder part of the tool during friction stir processing, reduces the occurrence of burrs and decreases in wall thickness in the processed part, and also reduces processing marks. It is possible to make it less noticeable.

Japanese Patent Application Publication No. 2002-35961 Japanese Patent Application Publication No. 2013-761 Japanese Patent Application Publication No. 2003-290937 Japanese Patent Application Publication No. 2007-301579

However, the technique described in Patent Document 1 targets a bonding member made of aluminum or an alloy thereof, and does not take into consideration materials with high rigidity such as steel materials, for example. Further, in the technique described in Patent Document 1, when joining steel plates having different thicknesses, the rotation axis of the rotary tool is tilted toward the lower joining member (in a direction perpendicular to the joining direction). Therefore, when attempting to join highly rigid materials, it is difficult to join because the rotary tool cannot withstand the large load caused by tilting the rotary tool and breaks. Additionally, the equipment in which the rotary tool is installed needs to have sufficient rigidity to withstand the large loads mentioned above.

In the technique described in Patent Document 2, joining is performed using a bobbin tool having a curved upper shoulder and lower shoulder. However, since a bobbin tool is used, the rotation directions of the upper and lower bobbin tools are the same, so that the plastic flow moves in the same way on the upper and lower sides. Therefore, especially when welding thin plates with a short distance between the upper and lower bobbin tools or when welding at high speed, the bobbin tool may pass through the retracting side where the welding direction and the rotation direction of the bobbin tool are opposite. In this case, there is a problem in that pores are generated due to plastic flow, and linear defects are likely to occur in the joint.

The technique described in Patent Document 3 requires a mechanism for controlling the pressing depth of the tool in the device. Further, in the technique described in Patent Document 3, an aluminum alloy is used as a workpiece, but Patent Document 3 does not specifically mention the strength characteristics of the tool. Therefore, when using another metal, particularly a high melting point material or a high hardness material, as the workpiece, there is a problem that the tool cannot be joined due to insufficient strength.

In the technology described in Patent Document 4, in order to prevent burrs from being generated due to the softened material biting into the material, the softened material is forced into a spiral groove during processing, and is appropriately held and retained on the shoulder surface. For this reason, Patent Document 4 describes that the deeper the groove is, the closer it is to the center of the tool from the outer periphery. However, if the amount of metal wrapped around the tool increases, the tool can break and joining becomes difficult when working with highly rigid materials such as steel.

The present invention has been made in view of the above-mentioned problems, and is a highly durable friction stir welding tool that is less likely to cause damage to the rotating tool even when friction stir welding highly rigid workpieces such as steel plates. The purpose is to provide rotating tools.

The present inventors have made extensive studies to solve the above problems. Here, a conventional rotary tool for friction stir welding (hereinafter also simply referred to as a "rotary tool") will be described using FIGS. 3 and 4. FIG. 3 is a diagram illustrating an example of a conventional rotary tool, in which (a) is a side view and (b) is a plan view. The rotary tool 3 shown in FIG. 3 is a rotary tool whose tip 30 is composed of only a probe 31 and shoulders 32 and 33. Moreover, FIG. 4 is a figure explaining another example of the conventional rotary tool, (a) is a side view, (b) is a top view. The rotary tool 4 shown in FIG. 4 is a rotary tool in which a distal end portion 40 has a convex curved surface 41, and the curved surface 41 is formed only of a smooth surface.

When friction stir welding the materials to be welded using the conventional rotary tool 3 shown in FIG. Damage is more likely to occur. Further, when friction stir welding is performed using the conventional rotary tool 4 shown in FIG. 4, the materials to be welded cannot be sufficiently stirred, and welding defects are likely to occur.

Therefore, the inventors of the present invention conducted extensive studies on means for suppressing damage to the rotary tool and achieving sufficient stirring of the materials to be joined, and came to the following conclusion.

(1) In the case of friction stir welding, by making the surface of the tip of the rotary tool a convex and smooth surface, the load on the rotary tool is reduced and it becomes less likely to be damaged.
(2) Plastic fluidity can be improved by making the surface of the peripheral part, which has a smaller stress load than the central part (the most distal part) of the tip, have an undulating shape.

Based on the above conclusion, the present inventors have completed a rotary tool for friction stir welding that places less load on the rotary tool and can sufficiently stir the materials to be welded.

That is, the present invention for solving the above problems is as follows.
[1] A rotary tool used for friction stir welding two pieces of materials to be welded,
Equipped with a tip having a convex curved surface,
The curved surface includes a circular first smooth surface disposed in the center, an annular undulating surface disposed on the outer periphery of the first smooth surface, and a circular undulating surface disposed on the outer periphery of the first smooth surface. A rotary tool for friction stir welding, characterized in that it has an annular second smooth surface.

[2] The rotary tool for friction stir welding according to [1] above, wherein the undulating surface has a spiral shape.

[3] The undulating shaped surface is arranged in a range of 0.20r to 0.90r from the central axis of the rotary tool, where r is the radius of the rotary tool. Rotating tool for friction stir welding.

[4] The rotary tool for friction stir welding according to any one of [1] to [3], wherein the rotary tool is made of a harder material than the materials to be welded.

[5] A pair of rotary tools placed on one side and the other side of the abutting or overlapping portion of the two materials to be welded are rotated in opposite directions to rotate the abutting or overlapping portion of the materials to be welded. The unwelded portion of the welded material is softened by the frictional heat between the rotary tool and the unwelded portion of the welded material, and the softened portion is moved with the rotary tool. In a double-sided friction stir welding method in which the materials to be joined are joined by causing plastic flow by stirring,
A friction stir welding method characterized in that the rotary tool for friction stir welding according to any one of [1] to [4] is used as the rotary tool.

According to the present invention, it is possible to provide a highly durable rotary tool for friction stir welding that is unlikely to be damaged even when friction stir welding highly rigid materials to be welded such as steel plates.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining an example of the rotary tool for friction stir welding by this invention, (a) is a side view, (b) is a top view. It is a figure explaining another example of the rotary tool for friction stir welding by this invention, (a) is a side view, (b) is a top view. It is a figure explaining an example of the conventional rotary tool, (a) is a side view, (b) is a top view. It is a figure explaining another example of the conventional rotary tool, (a) is a side view, (b) is a top view. It is a figure explaining an example of the rotation tool by a comparative example, (a) is a side view, (b) is a top view. It is a figure explaining another example of the rotary tool by a comparative example, (a) is a side view, (b) is a top view. FIG. 2 is a diagram illustrating a friction stir welding method according to the present invention.

(Rotary tool for friction stir welding)
EMBODIMENT OF THE INVENTION Hereinafter, with reference to each figure, embodiment of the rotary tool for friction stir welding by this invention is described. Note that the present invention is not limited to this embodiment. FIG. 1 is a diagram illustrating an example of a rotary tool for friction stir welding according to the present invention, in which (a) is a side view and (b) is a plan view. A rotary tool 1 shown in FIG. 1 is a rotary tool used for friction stir welding two pieces of materials to be welded, and includes a tip portion 10 having a convex curved surface 11. Here, the curved surface 11 includes a circular smooth surface (first smooth surface) 12 arranged in the center, an annular undulating surface 13 arranged on the outer periphery of the first smooth surface 12, and an undulating shape. It is characterized by having an annular smooth surface (second smooth surface) 14 arranged on the outer periphery of the surface 13. As shown in FIG. 1(b), the tip portion 10 of the rotary tool 1 has a circular shape when viewed from above.

The first smooth surface 12 is the surface of the most distal portion of the distal end portion 10 of the rotary tool 1 (that is, the portion near the rotation axis of the rotary tool 1). Since the surface of this part is smooth, the load on the rotary tool 1 can be reduced when welding highly rigid materials to be welded such as steel plates, and damage to the rotary tool 1 can be suppressed. . In addition, in this specification, a "smooth surface" means that when the rotary tool 1 is arranged with its rotation axis along the vertical direction, the height position increases as it goes radially outward from the rotation axis of the rotary tool 1. It means a surface that changes continuously and monotonically. Specifically, the first smooth surface 12 is a surface without grooves or steps.

The undulating surface 13 is a surface of a portion disposed on the outer periphery of the first smooth surface 12 (that is, radially outward from the rotation axis of the rotary tool 1). Since the tip portion 10 of the rotary tool 1 has the undulating surface 13, plastic flow of the materials to be welded can be sufficiently generated, and poor joining can be suppressed. In the rotary tool 1 shown in FIG. 1, an undulating surface 13 is formed by providing a groove G in a convex smooth curved surface 11 of the tip portion 10. As shown in FIG. Note that in this specification, the term "undulating surface" refers to a height position that increases from the rotation axis of the rotation tool 1 toward the outside in the radial direction when the rotation tool 1 is arranged with its rotation axis in the vertical direction. It means a surface that has a part where the value changes discontinuously. Specifically, the undulating surface 13 is a surface having grooves, steps, and the like.

The shape of the groove G is not particularly limited, and can be any shape such as a rectangular cross section as shown in FIG. 1, a semicircle, a semiellipse, a V-shape, or a polygonal shape. Among these, a rectangular shape is preferred because it can best induce plastic flow in the materials to be joined.

The width Gw of the groove G is preferably 0.1 mm or more and 5 mm or less. This allows the joined materials to further undergo plastic flow, and joining defects can be further suppressed. The depth Gd of the groove G is preferably 0.1 mm or more and 3 mm or less. This allows the joined materials to further undergo plastic flow, and joining defects can be further suppressed. The width Gw of the groove G preferably satisfies the above range at any position in the extension direction of the groove G. The depth Gd of the groove G preferably satisfies the above range at any position in the center, outer periphery, and inner periphery of the groove G.

It is preferable that the undulating surface 13 has a spiral shape (helical shape). Thereby, plastic flow of the welded materials can be further caused. The materials to be welded, such as metals, softened by frictional heat can be selectively flowed toward the center or normal direction of the rotating shaft of the rotary tool 1, and the stirring of the materials can be better controlled. can.

It is preferable that the vortex constituting the spiral shape be provided in the opposite direction to the rotation direction of the rotary tool 1 (that is, toward the central portion (first smooth surface 12) along the rotation direction). Moreover, it is preferable to provide one or more vortices. The number of vortices depends on the diameter of the tip 10, and it is preferable to increase the number of vortices as the diameter of the tip 10 becomes larger, and to decrease the number as the diameter of the tip 10 becomes smaller. Specifically, when the diameter of the tip 10 is smaller than 6 mm, the number of vortices can be set to 2 or less, and when the diameter of the tip 10 is 6 mm or more, the number of vortices can be set to 3 to 6. preferable. Note that in the rotary tool 1 shown in FIG. 1, the number of vortices is four.

The undulating surface 13 is preferably arranged within a range of 0.20r to 0.90r from the central axis of the rotary tool 1, where r is the radius of the rotary tool 1. More preferably, the undulating surface 13 is arranged only within a range of 0.20r to 0.90r from the central axis of the rotary tool 1, where r is the radius of the rotary tool 1. More preferably, it is arranged only within the range of 0.40r to 0.70r. Thereby, the load on the rotary tool 1 can be reduced, and sufficient compositional fluidity of the materials to be joined can be ensured.

The second smooth surface 14 is a surface disposed on the outer periphery of the undulating surface 13. Since the tip portion 10 of the rotary tool 1 has the second smooth surface 14, similarly to the first smooth surface 12, the load on the rotary tool 1 is reduced when welding highly rigid workpieces such as steel plates. Therefore, damage to the rotary tool 1 can be suppressed. Further, by arranging the second smooth surface 14 on the outer periphery of the undulating surface 13, the plastic fluidity of the welded materials due to the undulating surface 13 can be adjusted.

The rotating tool 1 is preferably made of a material harder than the materials to be joined. This allows frictional heat to be more effectively generated in the materials to be joined, such as steel plates, to be softened, and the softened area can be stirred with the rotating tool to more effectively induce plastic flow and achieve better joining. The above-mentioned hardness of the materials to be joined, such as steel plates, and the rotating tool 1 can be measured, for example, using the high-temperature Vickers hardness test method (JIS Z 2252).

Note that the materials to be joined are not particularly limited, but steel plates such as ultra-high tensile strength steel plates can be suitably joined. Moreover, it is preferable that the plate thickness of the material to be joined is 20 mm or less. When joining two materials to be joined having different thicknesses, the thickness ratio (thickness of thicker steel plate/thickness of smaller steel plate) is preferably 1.6 or less. By setting the thickness and plate thickness ratio of the materials to be joined within the above range, the materials to be joined can be joined more favorably.

When using steel plates as the material to be joined, the applicable steel types are general structural steels and carbon steels, such as JIS (Japanese Industrial Standards) G 3106 rolled steel for welded structures, JIS G 4051 carbon steel for machine structures, etc. It can be suitably used. Further, high-strength structural steel having a tensile strength of 800 MPa or more can also be suitably used. Even when such steel plates are used, a strength of 85% or more of the tensile strength of the steel plate (base material), further 90% or more, more preferably 95% or more of the tensile strength of the steel plate (base material) can be obtained at the joint. be able to.

The rotary tool 1 according to the present invention described above can be suitably used in a double-sided friction stir welding method in which two pieces of materials to be welded are butt-joined.

As described above, the rotary tool 1 according to the present invention has a convex curved surface 11 at its tip 10. Thereby, the load on the rotary tool 1 is reduced when joining the materials to be welded, and damage to the rotary tool 1 can be suppressed. Further, since the tip portion 10 has the convex curved surface 11, it is possible to successfully join not only two materials to be joined with the same thickness but also two materials to be joined with different thicknesses. Furthermore, since the convex curved surface 11 has an annular undulating surface 13 on the outer periphery of the first smooth surface 12, the rotary tool 1 can sufficiently cause plastic flow of the materials to be welded, resulting in poor welding. can be suppressed.

Figure 2 is a diagram illustrating another example of a rotating tool for friction stir welding according to the present invention, where (a) is a side view and (b) is a plan view. The rotating tool 2 shown in Figure 2 has a tip portion 20 having a convex curved surface 21. Here, the curved surface 21 has a circular smooth surface (first smooth surface) 22 located in the center, an annular undulating surface 23 located on the outer periphery of the first smooth surface 22, and an annular smooth surface (second smooth surface) 24 located on the outer periphery of the undulating surface 23. As shown in Figure 2(b), the tip portion 20 of the rotating tool 2 is circular when viewed in a plan view.

In the rotary tool 2 shown in FIG. 2, the undulating surface 23 is formed by providing a step S. As shown in FIG. Similar to the rotary tool 1 shown in FIG. 1, the rotary tool 2 having such an undulating surface 23 can cause plastic flow of the materials to be welded, thereby suppressing joint defects. In addition, since the rotary tool 2 has a convex curved surface 21 at its tip 20, the load on the rotary tool 2 during welding can be reduced and damage to the rotary tool 2 can be suppressed. It is also possible to successfully join two materials to be joined that have different values.

The width Sw of the step S is preferably 0.1 mm or more and 5 mm or less. Thereby, plastic flow of the materials to be joined can be further caused, and joining defects can be further suppressed. Further, the depth Sd of the step S is preferably 0.1 mm or more and 3 mm or less. Thereby, plastic flow of the materials to be joined can be further caused, and joining defects can be further suppressed. It is preferable that the width Sw of the step S satisfies the above range at any position in the extending direction of the step S. Further, it is preferable that the depth Sd of the step S satisfies the above range at any position of the step S at the center, outer periphery, and inner periphery.

(Friction stir welding method)
In the friction stir welding method according to the present invention, a pair of rotary tools, each of which is placed on one side and the other side of an abutting or overlapping part of two pieces of workpieces, are rotated in opposite directions to join the workpieces together. The rotating tool presses against the butt or overlapping part of the material and moves it in the welding direction, softening the unwelded part of the material to be joined by the frictional heat between the rotating tool and the unwelded part of the material to be joined, and then moving the softened part with the rotating tool. This is a friction stir welding method in which materials to be welded are joined together by stirring to create plastic flow. Here, the rotary tool is characterized in that the rotary tool for friction stir welding according to the present invention described above is used as the rotary tool.

As described above, the rotary tool according to the present invention has a convex curved surface at its tip. Therefore, by joining materials to be welded using the rotary tool according to the present invention, the load on the rotary tool can be reduced and damage to the rotary tool can be suppressed. In addition, two materials to be joined having different thicknesses can be joined satisfactorily. Further, in the rotary tool according to the present invention, the convex curved surface has an annular undulating surface on the outer periphery of the first smooth surface. Therefore, by joining the materials to be joined using the rotary tool according to the present invention, it is possible to sufficiently induce plastic flow in the materials to be joined, suppressing joint defects and producing a defect-free joint.

By the friction stir welding method according to the present invention, it is possible to join both the overlapping part where two pieces of workpieces are overlapped and the butt part where two pieces of workpieces are butted, but in particular, the butt part It is possible to perform good bonding.

FIG. 7 is a diagram illustrating an example of the friction stir welding method according to the present invention, and is a diagram relating to the case of joining the butt portions of two steel plates. As shown in FIG. 7, two steel plates are arranged so that their end surfaces (butting surfaces) abut against each other, and are gripped by a gripping device. Next, a pair of rotary tools (for example, rotary tool 1 shown in FIG. 1) placed on one side and the other side of the unjoined portion of the steel plates are rotated in opposite directions, and the rotary tools are aligned on the welding center line. Insert into the unjoined part of the steel plate. Then, the rotary tool is moved in the joining direction along the part to be joined while rotating while pressing the steel plate in the unjoined part. Thereby, the steel plates can be joined by softening both steel plates due to frictional heat between the rotating tool and the steel plate, and stirring the softened portion with the rotating tool to generate plastic flow. The portion where the joining is completed in the abutted portion is a joint portion.

Regarding the welding conditions, when the rotary tool according to the present invention is used in a double-sided friction stir welding method, the rotation speed of the rotary tool is preferably 100 to 5000 r/min, more preferably 300 to 3000 r/min. By controlling the rotational speed within this range, it is possible to maintain a good surface shape while suppressing deterioration of mechanical properties due to excessive input of heat.

Further, the joining speed is preferably 300 mm/min or more, more preferably 500 mm/min or more. Setting the joining speed within this range has the effect of suppressing deterioration of mechanical properties due to input of excessive heat.

Furthermore, the inclination angle of the rotary tool (the angle formed between the rotary axis and the vertical direction when the rotary axis of the rotary tool is tilted backward in the welding direction from the perpendicular line in the vertical direction) is preferably 3 degrees or less.

As described above, by performing friction stir welding of materials to be welded using the rotary tool according to the present invention, it is possible to reduce the load on the rotary tool and to produce a defect-free joint.

Hereinafter, the functions and effects of the present invention will be explained using Examples. Note that the present invention is not limited to the following examples.

(Invention examples 1 to 8)
Two pieces of materials to be joined were joined by the friction stir welding method according to the present invention. At that time, two 1180 MPa class cold rolled steel plates having different thicknesses (1.2 mm and 1.6 mm) were used as the materials to be joined. Note that the average Vickers hardness at 5 points measured on the steel plate base material was 401.

The end surfaces of the two steel plates having different thicknesses were flattened by milling, and the end surfaces were butted together as shown in FIG. Next, the rotary tool 1 shown in FIG. 1 was placed on each of one side and the other side of the unjoined portion of the steel plates. At that time, the rotating tool 1 on the upper side is not tilted in the direction perpendicular to the welding direction (that is, the rotation axis of the rotating tool 1 is perpendicular to the surface of the steel plate), and the rotating tool 1 on the one side of the unwelded part ( A pair of rotating tools were placed on the upper surface side (upper surface side) and the other surface side (lower surface side).

The dimensions of the rotary tool 1 are a diameter D1 of the rotary tool 1: 25 mm, a diameter D2 of the first smooth surface 12: 12 mm, a diameter D3 of the undulating surface 13: 16 mm, and a radius of curvature of the curved surface 11: 20 mm. Further, the depth Gd of the groove G is 0.5 mm, and the width Gw of the groove G is 0.5 mm. Note that the width Gw and depth Gd of the groove G are the values for the central groove G and the central position, and there is an unavoidable difference of ±0.1 mm due to the shape of the rotary tool 1. The same applies to the following examples.

The upper rotating tool 1 arranged as described above was rotated counterclockwise, the lower rotating tool 1 was rotated clockwise, and the pair of rotating tools 1 were rotated in opposite directions. In this state, the rotary tool 1 is pressed against the steel plate from both the upper and lower sides of the steel plate, and the pair of rotary tools 1 are moved in the welding direction to join the steel plates with a welding length of 1 m 50 times. A joining joint with a length of 50 m was produced. The bonding conditions are shown in Table 1.

(Invention Examples 9 to 18)
As in Invention Examples 1 to 8, two pieces of materials to be welded were joined by the friction stir welding method according to the present invention. However, as the rotating tool, the rotating tool 2 shown in FIG. 2 was used. The dimensions of the rotary tool 2 are a diameter D1 of the rotary tool 2: 25 mm, a diameter D2 of the first smooth surface 22: 12 mm, a diameter D3 of the undulating surface 23: 16 mm, and a radius of curvature of the curved surface 21: 20 mm. Further, the depth Sd of the step S is 0.1 mm, and the width Sw of the step S is 0.5 mm. Note that the depth Sd and width Sw of the step S are the values at the center step S and the center position, and there is an unavoidable difference of ±0.03 mm due to the shape of the rotary tool 2. The bonding conditions are shown in Table 1.

(Conventional examples 1 to 18)
As in Invention Examples 1 to 8, two pieces of materials to be welded were joined by the friction stir welding method according to the present invention. However, for the rotary tools of Conventional Examples 1 to 9, the rotary tool 3 shown in FIG. 3 was used. Further, as the rotary tools of Conventional Examples 10 to 18, the rotary tool 4 shown in FIG. 4 was used. The dimensions of the rotary tool 3 are: diameter D1 of the rotary tool 3: 25 mm, diameter D4 of the probe 31: 5 mm, diameter D5 of the shoulder 32: 10 mm, probe length L: 0.5 mm, and concave depth (i.e., Fig. 3). Difference between the height position of the lowest end of the probe 31 and the height position of the connection part between the shoulders 32 and 33 in a): 0.3 mm. Further, the dimensions of the rotary tool 4 are a diameter D1 of the rotary tool 4: 25 mm, and a radius of curvature of the curved surface 41: 20 mm. The bonding conditions are shown in Table 1.

(Comparative Examples 1 to 18)
As in Invention Examples 1 to 8, two pieces of materials to be welded were joined by the friction stir welding method according to the present invention. However, as the rotary tool in Comparative Examples 1 to 9, the rotary tool 5 shown in FIG. 5 was used. Further, as the rotary tool in Comparative Examples 10 to 18, the rotary tool 6 shown in FIG. 6 was used. The dimensions of the rotary tool 5 are a diameter D1 of the rotary tool 5: 25 mm, a diameter D2 of the first smooth surface 52: 12 mm, a diameter D3 of the undulating surface 53: 25 mm, a radius of curvature of the curved surface 51: 20 mm, and a groove G. The depth Gd of the groove G is 0.5 mm, and the width Gw of the groove G is 0.5 mm. The dimensions of the rotary tool 6 are: diameter D1 of the rotary tool 6: 25 mm, diameter D2 of the first smooth surface 62: 6 mm, diameter D3 of the undulating surface 63: 25 mm, radius of curvature of the curved surface 61: 20 mm, The depth Gd of the groove G is 0.5 mm, and the width Gw of the groove G is 0.5 mm. The bonding conditions are shown in Table 1.

The rotating tools 1 to 6 were made of tungsten carbide (WC) having a Vickers hardness of 1090.

The following evaluations were performed using the joints obtained for Invention Examples 1 to 18, Conventional Examples 1 to 18, and Comparative Examples 1 to 18.

The above 50 m long welding was performed 10 times using 10 rotary tools, and evaluation was made based on the following criteria in terms of damage to the rotary tools and the appearance of the bead of the bonding material. The results obtained are shown in Table 2.
<Standards>
・◎: There is no damage to the rotating tool, and there is no burr or uneven bead width on the bonding material. ○: There is no damage to the rotating tool, and there is no burr or uneven bead width on the bonding material at least once. Visible・△: No damage to the rotating tool, and linear surface defects are seen on the bonding material one or more times・×: Damage to the rotating tool

As is clear from Table 2, in Invention Examples 1 to 18, welding with a welding length of 50 m was possible without damaging the rotary tool, and no burrs or uneven bead widths were observed. On the other hand, in Conventional Examples 1 to 18 and Comparative Examples 1 to 18, damage to the rotary tool was confirmed, or although no damage to the rotary tool was confirmed, linear surface defects occurred one or more times. confirmed.

According to the present invention, it is possible to provide a highly durable rotary tool for friction stir welding that is unlikely to be damaged even when friction stir welding highly rigid workpieces such as steel plates.

1, 2, 3, 4, 5, 6 Rotary tool 10, 20, 30, 40, 50, 60 Tip portion 11, 21, 41, 51, 61 Convex curved surface 12, 22, 52, 62 First smooth Surfaces 13, 23, 53, 63 Contoured surfaces 14, 24 Second smooth surface 31 Probes 32, 33 Shoulder G Groove Gd Groove depth Gw Groove width S Step Sd Groove depth Sw Groove width

Claims (5)

A rotary tool used for friction stir welding two pieces of materials to be welded,
Equipped with a tip having a convex curved surface,
The curved surface includes a circular first smooth surface disposed in the center, an annular undulating surface disposed on the outer periphery of the first smooth surface, and a circular undulating surface disposed on the outer periphery of the first smooth surface. A rotary tool for friction stir welding, characterized in that it has an annular second smooth surface. The rotary tool for friction stir welding according to claim 1, wherein the undulating surface has a spiral shape. The friction stir welding device according to claim 2, wherein the undulating surface is arranged within a range of 0.20r to 0.90r from the central axis of the rotary tool, where r is the radius of the rotary tool. rotation tool. The rotary tool for friction stir welding according to any one of claims 1 to 3, wherein the rotary tool is made of a harder material than the materials to be welded. A pair of rotary tools placed on one side and the other side of the abutting or overlapping portion of the two materials to be welded, respectively, are pressed against the abutting or overlapping portion of the materials to be joined while rotating in opposite directions. and moving in the welding direction, and while softening the unwelded portion of the welded material due to frictional heat between the rotary tool and the unwelded portion of the welded material, the softened portion is stirred by the rotary tool. In a double-sided friction stir welding method in which the materials to be joined are joined by generating plastic flow,
A friction stir welding method characterized in that the rotary tool for friction stir welding according to any one of claims 1 to 3 is used as the rotary tool.

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