JP7019161B2 - Friction stir welding tool - Google Patents

Description

The present invention relates to a friction stir welding tool, and more specifically, to a reverse friction stir welding tool for friction stir welding the material to be joined from the back surface side.

Friction stir welding (FSW) is known as a typical solid phase bonding method for metal materials. In friction stir welding, the metal material to be joined is opposed at the joint, the probe provided at the tip of the rotation tool is inserted into the joint, and the rotation tool is rotated and moved along the interface to be joined. The two metal materials are joined by causing the metal material to flow by frictional heat and the stirring force of the rotary tool.

However, in general friction stir welding, the probe of the rotation tool is inserted into the joint only from the front side of the facing metal material, so a kissing bond, which is an unbonded part between the metal materials, is formed on the back side of the metal material. There is a drawback that it will occur.

In order to improve this defect, for example, as disclosed in Patent Document 1 (Japanese Unexamined Patent Publication No. 2003-181654), friction stir welding is performed from both the front surface and the back surface side of the metal material by a rotation tool called a bobbin tool. A method of joining has been proposed.

However, when using a bobbin tool, a pair of upper and lower shoulder parts connected by a probe is rotated, so if one of the upper and lower shoulder parts is tilted toward the moving direction of the rotation tool, the other shoulder part will be the rotation tool. It tilts to the side opposite to the direction of movement. Therefore, the bobbin tool cannot be tilted in either direction with respect to the metal material, and it is necessary to make the bobbin tool perpendicular to the normal of the surface of the metal material. Therefore, in friction stir welding using a bobbin tool, the tool advance angle cannot be set, and there is a drawback that the range of joining conditions for obtaining a good joint portion is narrow.

On the other hand, the inventor of the present application has proposed a friction stir welding method capable of joining from the back surface of the material to be joined and providing a tool advance angle. Specifically, in Patent Document 2 (Japanese Unexamined Patent Publication No. 2014-61542), a stirring shaft (probe portion) is inserted into a bonded portion of a metal material, and a shoulder portion at the tip of the stirring shaft is brought into contact with the back surface thereof. Friction stir welding method in which the front plate is brought into contact with the metal material, the metal material is sandwiched between the shoulder plate and the surface plate, and the metal material is joined by moving along the interface to be joined while rotating the shoulder portion and the stirring shaft. (Hereinafter referred to as reverse friction stir welding) is disclosed.

In the reverse friction stir welding method described in Patent Document 2, since friction stir welding can be performed from the back surface of the bonded portion in a state where the tool is provided with a forward angle, an unbonded portion such as a kissing bond is formed in the bonded portion. It is possible to expand the range of joining conditions in which a good joining portion can be obtained without causing the above.

Japanese Patent Application Laid-Open No. 2003-181654 Japanese Unexamined Patent Publication No. 2014-61542

However, in the reversal friction stir welding method disclosed in Patent Document 2, in addition to applying a large tensile stress to the tool, a large torque is generated particularly at the base of the probe (the boundary between the probe and the shoulder). Therefore, when joining a thick plate or a metal plate having high strength, the tool is easily broken.

In view of the above problems in the prior art, an object of the present invention is a tool capable of performing inversion friction stir welding even on a thick plate or a high-strength metal plate, and during inversion friction stir welding. It is an object of the present invention to provide a tool for reverse friction stir welding that can effectively suppress the formation of defects in a stirring portion in addition to being difficult to break.

As a result of intensive research on the shape of the tool for reverse friction stir welding in order to achieve the above object, the present inventor eliminates the stress concentration portion in the probe and has a concave curved surface on the shoulder surface that abuts on the material to be welded. We have found that it is extremely effective to provide the above, and have reached the present invention.

That is, the present invention
It is a tool for performing friction stir welding from the back side of the material to be welded.
The tool has a disk-shaped shoulder portion and a probe portion coaxially projecting from the substantially center of the surface of the shoulder portion.
At the tip of the probe portion, a fastening portion for fixing the tool to the rotating portion of the friction stir welding device is provided.
In the friction stir welding, the surface of the probe portion that comes into contact with the material to be welded is not screwed.
Provided is a tool for reversing friction stir welding, which is characterized by.
In the specification of the present application, the "back surface of the material to be joined" means the inner surface of the joint structure manufactured by friction stir welding.

When we carefully observed the breaking condition of the tool that occurred during reverse friction stir welding, we found that in most cases of reverse friction stir welding, a large tensile stress is applied to the probe part and a large torque is generated at the base of the probe part. It was revealed that the probe part was broken from the processed probe part.

On the other hand, the reverse friction stir welding tool of the present invention is characterized in that the surface of the probe portion that comes into contact with the material to be welded during joining is not screwed, and is characterized by the height of thick plates, steel, etc. A strong material is used as a material to be welded, and even when a large stress is applied to the tool, fracture is suppressed and a good stirring portion can be formed.

Here, in general friction stir welding, since the tool is press-fitted into the material to be welded from the thin probe portion, the stress applied in the axial direction to the probe portion does not increase so much. In addition, since compressive stress is applied in the axial direction, even if the probe portion is screwed for the purpose of promoting material flow, the effect on the fracture of the tool is small. Even in general friction stir welding, stress from the side is applied to the probe part when the tool moves, so when screwed, it is easier to break than when there is no screwed. However, this does not pose a serious problem when a light metal material such as an aluminum material is used as the material to be welded.

Further, in the tool for reverse friction stir welding of the present invention, it is preferable that the surface of the shoulder portion where the probe portion protrudes has a concave curved surface. In the reverse friction stir welding tool of the present invention, since the probe portion is not screwed, defects are likely to be formed in the stirring portion due to insufficient material flow. On the other hand, since the surface of the shoulder portion that comes into contact with the material to be joined during bonding is a concave curved surface, the stirring force is increased, and the insufficient stirring force of the probe portion can be compensated. The shoulder portion can be provided with a shape adopted for improving the stirring force of a general friction stir welding tool. For example, a scroll-shaped groove is formed on the surface of the shoulder portion. The stirring power can be improved.

Some conventional friction stir welding tools also have a concave shoulder portion, but the shape is formed for the purpose of suppressing the generation of burrs, and the increase in stirring force has not been paid attention to. On the other hand, the inventor of the present application used a friction stir welding tool and a friction stir welding device that can separately drive the probe part and the shoulder part, and as a result of diligent research on the influence of the tool part on the formation of the stirring part, the stirring force by the probe part. It was clarified that the insufficient stirring power can be compensated by making the shoulder portion concave when the amount is not sufficient. The curvature of the concave shape is not particularly limited as long as the effect of the present invention is not impaired, and may be appropriately set according to the thickness and strength of the material to be joined, and adjusted so that defects are not formed in the stirring portion. do it.

Further, in the tool for reverse friction stir welding of the present invention, it is preferable that the length of the probe portion is 4 mm or more. When the material to be joined is a thin light metal plate, the stress applied to the tool does not increase so much, but even if the material is a light metal plate, when the plate thickness is 4 mm or more, the tool breaks from the probe portion becomes remarkable. On the other hand, in the reverse friction stir welding tool of the present invention, breakage from the probe portion is effectively suppressed. Therefore, by using the reverse friction stir welding tool having a probe portion having a length of 4 mm or more, it is possible to use the reverse friction stir welding tool. Stable reverse friction stir welding can be applied to thick plates.

Further, in the tool for reverse friction stir welding of the present invention, it is preferable that the ratio (Dp / Ds) of the diameter Dp of the probe portion to the diameter Ds of the shoulder portion is 0.4 to 0.6. When the diameter Dp is increased, the strength of the probe portion can be increased, but since the voids due to the passage of the probe portion are increased, defects are likely to be formed in the stirring portion. Further, the stirring force can be improved by increasing the diameter Ds, but the torque applied to the probe portion becomes large. Here, by balancing these actions and effects and setting the Dp / Ds to 0.4 to 0.6, it is possible to suppress both fracture during joining and formation of defects in the agitated portion. By making the root of the probe portion thick and making the entire probe portion tapered, it is possible to suppress breakage from the root of the probe portion. Further, it is also possible to use a tool (the tip of the probe portion functions as the shoulder portion) in which the taper angle is set large and the shoulder portion is not provided. That is, the thickness of the probe portion does not have to be constant with respect to the length direction of the probe portion.

Further, in the tool for reverse friction stir welding of the present invention, it is preferable that the surface of the probe portion is subjected to multifaceted cutting. By applying a multi-faceted cut process to the surface of the probe portion, it is possible to promote the material flow caused by the probe. The number of planes formed in the probe portion is not particularly limited as long as the effect of the present invention is not impaired, but it is preferably 3 to 8 planes, for example. Further, by twisting the entire probe portion that has been subjected to the multi-faceted cutting process, the material flow can be further promoted.

Further, in the tool for reverse friction stir welding of the present invention, it is preferable that the shoulder portion and the probe portion are made of tool steel. Tool materials include tool steels such as SKD61 steel specified in JIS, super hard alloys made of tungsten carbide (WC), cobalt (Co), and nickel (Ni), and cobalt (Co) -based alloys. It can be made of refractory metal such as tungsten (W) alloy, iridium (Ir) and its alloy, or ceramics such as Si ₃ N ₄ and polycrystalline c-BN, but the shoulder part and probe part are tools. By using steel, both the strength and toughness of the tool can be achieved.

According to the present invention, it is a tool capable of performing reverse friction stir welding even on a thick plate or a high-strength metal plate, and in addition to being difficult to break during reverse friction stir welding, defects in the stirring portion are present. It is possible to provide a tool for reverse friction stir welding that can effectively suppress the formation.

It is a schematic diagram which shows one aspect of reverse friction stir welding. It is a schematic diagram which shows one aspect of the tool for reverse friction stir welding of this invention. It is a schematic diagram which shows one aspect of the reversal friction stir welding using the tool for reversal friction stir welding of this invention. It is a schematic diagram which shows another aspect of the tool for reverse friction stir welding of this invention. It is an overview photograph of the tool for reverse friction stir welding used in Example 1. It is an overview photograph of the front plate used in Example 1. It is an overview photograph of the front surface and the back surface of the joint obtained in Example 1. It is a cross-sectional macro photograph of the joint stirring part obtained in Example 1. FIG. It is a cross-sectional macrophotograph of a stirring part obtained under the joining conditions that a tool is brought into contact with the jointed portion from the side surface of the end portion of the material to be joined. It is an overview photograph of the front surface and the back surface of the joint obtained in Example 2. It is a cross-sectional macro photograph of the joint stirring part obtained in Example 2. FIG. It is an overview photograph of the front surface and the back surface of the joint obtained in Example 3. It is a cross-sectional macro photograph of the joint stirring part obtained in Example 3. FIG. It is an overview photograph of the front surface and the back surface of the joint obtained in Example 4. It is a cross-sectional macro photograph of the joint stirring part obtained in Example 4. FIG. It is an overview photograph from the back surface side of the material to be joined after the probe portion was broken in Comparative Example 1. It is an overview photograph from the back surface side of the material to be joined after the probe portion is broken in Comparative Example 2.

Hereinafter, typical embodiments of the tool for reverse friction stir welding of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these. In the following description, the same or corresponding parts may be designated by the same reference numerals, and duplicate description may be omitted. Further, since the drawings are for conceptually explaining the present invention, the dimensions of each component represented and their ratios may differ from the actual ones.

(1) Inverted Friction Stir Welding FIG. 1 shows a schematic diagram of an inverted friction stir welding. The probe portion 8 is inserted into the bonded portion 6 of the bonded materials 2 and 4, and the shoulder portion 10 is brought into contact with the back surfaces of the bonded materials 2 and 4. Generally, the surface of the probe portion 8 that comes into contact with the materials to be joined 2 and 4 is threaded. The front plate 12 is brought into contact with the surface of the materials to be joined 2 and 4, the materials 2 and 4 to be joined are sandwiched between the shoulder plate 10 and the front plate 12, and the shoulder material 10 and the probe portion 8 are rotated and covered. The materials 2 and 4 to be joined are joined to each other by moving along the joining interface 14. The joining control method is not particularly limited, and various conventionally known control methods can be used. For example, tool position constant control, load constant control, and torque constant control can be used.

Here, by fixing the distance between the shoulder portion 10 and the front plate 12 to be constant, reverse friction stir welding can be performed by position control. Further, by performing friction stir welding while pulling up the shoulder portion 10 and the probe portion 8, it is possible to perform reverse friction stir welding by load control. The reverse friction stir welding by load control can easily follow the change in plate thickness. Although butt joint is shown in FIG. 1, it may be lap joint.

The front plate 12 is provided with a through-hole portion having a through-hole for passing the probe portion 8. In reverse friction stir welding, the probe portion 8 needs to be tilted according to the tool advance angle, so the through hole of the front plate 12 is also shaped to cope with the tilt. For example, the through hole may be larger than the diameter of the probe portion 8, and the through hole may be inclined according to the inclination angle of the probe portion 8. Further, the through hole may have a U-shape having an opening at one end of the front plate 12. The shape of the front plate 12 is not particularly limited, and may be, for example, a quadrangular shape, a disk shape, an elliptical shape, a polygonal shape, or the like.

Since the friction stir welding is performed from the back surface of the materials 2 and 4, the materials 2 and 4 to be welded are joined even if the stirring shaft (probe portion 8) of the tool is not inclined (tool advance angle 0 °). There is no unbonded part like a kissing bond on the back surface. In addition, the stirring shaft (probe portion 8) of the tool can be tilted, and a tool advance angle can be imparted at the time of friction stir welding. Since the material flow proceeds smoothly due to the advance angle, the conditions for joining are expanded, and it is possible to prevent joining defects. The tool advance angle is preferably more than 0 ° and 7 ° or less.

Further, unlike the conventional bobbin tool, the rotating members do not abut on both surfaces of the materials to be joined 2 and 4 around the joint, and the undulations of the front plate 12 are transferred to the surfaces of the materials 2 and 4 to be joined. Therefore, by abutting the front plate 12 having a smooth surface, it is possible to obtain a good joint surface without causing marks after friction stir welding on the surfaces of the materials 2 and 4 to be joined around the joint. It will be possible.

Further, in the reverse friction stir welding, the probe of the rotation tool is inserted into the joint only from the front surface side of the materials 2 and 4, and the backing plate is brought into contact with the back surface side, as in the conventional friction stir welding method. It is not necessary to perform the work from both the front surface and the back surface of the joining materials 2 and 4, and most of the work can be performed only from the front surface side of the joining materials 2 and 4. Therefore, even for a structure having a closed structure such as a device or a chassis of a vehicle, the materials to be joined 2 and 4 can be easily joined only from the outside.

(2) Tool for Inversion Friction Stir Welding A schematic diagram of the tool for inversion friction stir welding of the present invention is shown in FIG. Further, FIG. 3 schematically shows the situation of reverse friction stir welding using the reverse friction stir welding tool of the present invention.

The tool 20 for reverse friction stir welding of the present invention has a disk-shaped shoulder portion 10 and a probe portion 8 coaxially protruding from the substantially center of the surface of the shoulder portion 10. The tip of the probe portion 8 has a fastening portion 22 for fixing the reverse friction stir welding tool 20 to the rotating portion 30 of the friction stir welding device, and the probe portion abuts on the materials 2 and 4 to be welded in the friction stir welding. The surface of No. 8 is not screwed.

By connecting the fastening portion 22 and the rotating portion 30, the reversing friction stir welding tool 20 can be rotated, and the position and pulling load of the reversing friction stir welding tool can be controlled by the friction stir welding device. .. The structure of the fastening portion 22 is not particularly limited, and it is sufficient that the tool 20 for reverse friction stir welding and the rotating portion 30 can be firmly connected. FIG. 2 shows a structure for bolting the fastening portion 22 and the rotating portion 30 in contact with each other.

Further, when the probe portion 8 is not screwed, a high-strength material such as a thick plate or steel is used as the material to be joined 2 and 4, and a large tensile stress and / or torque is applied to the probe portion 8. Even if there is, breakage is suppressed and a good stirring portion can be formed.

Further, it is preferable that the surface of the shoulder portion 10 on which the probe portion 8 protrudes has a concave curved surface. In the reverse friction stir welding tool 20, since the probe portion 8 is not threaded, defects are likely to be formed in the stirring portion due to insufficient material flow. On the other hand, since the surface of the shoulder portion 10 that comes into contact with the materials to be joined 2 and 4 during joining is a concave curved surface, the stirring force is increased, and the insufficient stirring force of the probe portion 8 can be compensated. The curvature of the concave shape is not particularly limited as long as the effect of the present invention is not impaired, and may be appropriately set according to the thickness and strength of the material to be joined and adjusted so that defects are not formed in the stirring portion.

The θ in FIG. 2, which is an angle indicating the concave curvature of the shoulder portion 10, is preferably 5 ° to 15 °, more preferably 8 ° to 12 °. By setting θ to 5 ° or more, the stirring force of the shoulder portion 10 can be effectively increased, and by setting θ to 15 ° or less, the stress applied to the outer edge portion of the shoulder portion 10 becomes too large. Tool breakage can be suppressed. Further, by setting θ to 8 ° or more and 12 ° or less, these effects can be made more remarkable.

Further, the length of the probe portion 8 is preferably 4 mm or more. When the materials 2 and 4 to be joined are thin light metal plates, the stress applied to the probe portion 8 does not increase so much, but even with light metal plates, when the plate thickness is 4 mm or more, the tool breaks from the probe portion 8. It becomes remarkable. On the other hand, in the reverse friction stir welding tool 20, breakage from the probe portion 8 is effectively suppressed, and therefore, by setting the length of the probe portion 8 to 4 mm or more, it is stable even for the thick plate. Inverted friction stir welding can be applied.

Further, in the reverse friction stir welding tool 20, the ratio (Dp / Ds) of the diameter Dp of the probe portion 8 to the diameter Ds of the shoulder portion 10 is preferably 0.4 to 0.6. When the diameter Dp is increased, the strength of the probe portion 8 can be increased, but since the voids due to the passage of the probe portion 8 become large, defects are likely to be formed in the stirring portion. Further, the stirring force can be improved by increasing the diameter Ds, but the torque applied to the probe portion 8 becomes large. Here, by balancing these actions and effects and setting Dp / Ds to 0.4 to 0.6, both fracture and defect formation during joining can be suppressed.

Further, in the reverse friction stir welding tool 20, it is preferable that the surface of the probe portion 8 is subjected to multi-faceted cutting processing. By performing a multi-faceted cut process on the surface of the probe portion 8, it is possible to promote the material flow caused by the probe. FIG. 4 shows an example of a tool in which the probe portion 8 is subjected to multi-faceted cutting. In the tool shown in FIG. 4, the probe portion is cut on three sides, and the presence of the flat surface portion enables a large stirring force to be exhibited. The multi-sided cut process may be a 6-sided cut or an 8-sided cut. When the number of surfaces to be formed is increased, the torque applied to the probe portion 8 during joining can be reduced because the surface becomes closer to a columnar shape, but the stirring force is reduced. Here, in the case of a three-sided cut, it is preferable that the length from the central axis of the probe portion 8 to the plane is 70 to 80% of the length from the central axis to the outermost circumference of the probe portion 8.

The material of the tool 20 for reverse friction stir welding is not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known materials can be used. Tool materials include tool steels such as SKD61 steel specified in JIS, super hard alloys made of tungsten carbide (WC), cobalt (Co), and nickel (Ni), and cobalt (Co) -based alloys. It can be made of refractory metal such as tungsten (W) alloy, iridium (Ir) and its alloy, or ceramics such as Si ₃ N ₄ and polycrystalline c-BN, but the shoulder part and probe part are tools. By using steel, both the strength and toughness of the tool can be achieved.

Although the typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all of these design changes are included in the technical scope of the present invention. Will be.

<< Example 1 >>
A 100 mm × 50 mm × 4 mm A6061-T6 aluminum alloy (Al—Mg—Si alloy) plate was used as the material to be joined, and the aluminum alloy plates were joined by reverse friction stir welding. An overview photograph of the reverse friction stir welding tool and the front plate used is shown in FIGS. 5 and 6, respectively. The diameter of the probe portion is φ6 mm, the length is 15 mm, and the surface is not threaded. Further, the diameter of the shoulder portion is φ15 mm, and the surface having the probe portion is flat (not concave).

The front plate is provided with a U-shaped through hole, and the probe portion of the reverse friction stir welding tool is inserted into the through hole and connected to the rotating portion of the friction stir welding device. The joining conditions were a tool rotation speed of 500 rpm, a tool movement speed of 250 mm / min, and a tool advance angle of 3 °. Further, the shoulder portion was pulled up so as to sandwich the material to be joined, the gap between the shoulder portion and the front plate was fixed at 3.8 mm, and the joint was performed by constant position control.

Further, a through hole of φ6 mm was provided in the bonded region, and the initial position of the tool was set by inserting the probe portion into the through hole. As a result, the entire surface of the shoulder portion abuts on the material to be joined at the joining start position, and the joining is started in a state where sufficient frictional heat is generated.

FIG. 7 shows an overview photograph of the front surface and the back surface of the obtained joint. The surface of the joint with which the front plate abuts has a smooth shape, and a typical uneven shape of the stirring portion is observed on the back surface of the joint with which the rotating shoulder portion abuts.

FIG. 8 shows a cross-sectional macro photograph of the obtained joint stirring portion. A stirring portion formed by a general friction stir welding and a stirring portion inverted upside down are formed, and a good stirring portion is formed by the inverted friction stir welding. No tunnel-like defects were formed in the stirring portion, and no kissing bond was generated. The width of the stirring portion at a depth of 1 mm from the surface of the material to be joined is 6.3 mm. On the other hand, when the tool is brought into contact with the material to be joined from the side surface of the end of the material to be joined (when the entire surface of the shoulder part is not in contact with the material to be joined at the start of joining), the probe portion is used. The insufficient stirring force could not be compensated by the shoulder part, and a defect was formed near the surface of the stirring part. FIG. 9 shows a cross-sectional macro photograph of the stirring portion obtained under the joining conditions.

<< Example 2 >>
Inversion friction stir welding was performed in the same manner as in Example 1 except that the surface of the shoulder portion having the probe portion had a concave curved surface (θ: 10 ° shown in FIG. 2). FIG. 10 shows an overview photograph of the front surface and the back surface of the obtained joint, and FIG. 11 shows a cross-sectional macro photograph of the stirring portion.

As in the case of the first embodiment, the surface of the joint to which the plate abuts has a smooth shape, and the uneven shape of the typical stirring portion is observed on the back surface of the joint to which the rotating shoulder portion abuts. In addition, a good stirring portion is formed, and no defect is observed. Here, as compared with the joint obtained in Example 1, the width of the stirring portion is wider to the vicinity of the surface of the material to be joined. This result is due to the fact that the surface of the shoulder portion has a concave curved surface, and it can be seen that the stirring force of the shoulder portion is increased.

<< Example 3 >>
The same as in Example 1 except that the surface of the shoulder portion having the probe portion is a concave curved surface (θ: 10 ° shown in FIG. 2) and the probe portion is cut on three surfaces as shown in FIG. Then, reverse friction stir welding was performed. FIG. 12 shows an overview photograph of the front surface and the back surface of the obtained joint, and FIG. 13 shows a cross-sectional macro photograph of the stirring portion.

As in the case of the first embodiment, the surface of the joint to which the plate abuts has a smooth shape, and the uneven shape of the typical stirring portion is observed on the back surface of the joint to which the rotating shoulder portion abuts. In addition, a good stirring portion is formed, and no defect is observed. Here, the width of the stirring portion at a depth of 1 mm from the surface of the material to be joined is 7.3 mm, and the width of the stirring portion is wider to the vicinity of the surface of the material to be joined as compared with the joint obtained in Example 1. It has become. This result is due to the fact that the surface of the shoulder portion has a concave curved surface, and it can be seen that the stirring force of the shoulder portion is increased.

<< Example 4 >>
Inversion friction stir welding was performed in the same manner as in Example 3 except that the tool was brought into contact with the jointed portion from the side surface of the end portion of the material to be joined to start the joining. FIG. 14 shows an overview photograph of the front surface and the back surface of the obtained joint, and FIG. 15 shows a cross-sectional macro photograph of the stirring portion.

As in the case of the first embodiment, the surface of the joint with which the plate abuts has a smooth shape, and the uneven shape of the typical stirring portion is observed on the back surface of the joint with which the rotating shoulder portion abuts. Further, even in a situation where the entire shoulder portion is not brought into contact with the material to be joined at the start of joining, a good stirring portion is formed and no defect is observed. It can be seen that the result is due to the fact that the surface of the shoulder portion has a concave curved surface and that a flat region is formed on the surface of the probe portion, and that the stirring force of the shoulder portion and the probe portion is increased.

<< Comparative Example 1 >>
Inversion friction stir welding was performed in the same manner as in Example 1 except that the surface of the probe portion was threaded (screw thread angle: 30 °, pitch: 0.5 mm, screw thread height: 0.25 mm). However, while the shoulder portion was brought into contact with the surface of the material to be joined and held, the probe portion broke and a joint could not be obtained. The threading applied to the surface of the probe portion has the minimum dimensions and shape that can clearly promote the material flow behavior during the reverse friction stir welding.

FIG. 16 shows an overview photograph from the back surface side of the material to be joined after the probe portion is broken. It can be confirmed that the probe portion is broken before the reverse friction stir welding tool is moved in the joining direction, and the shoulder portion remains on the material to be welded.

<< Comparative Example 2 >>
Inversion friction stir welding was performed in the same manner as in Comparative Example 1 except that the tool was brought into contact with the jointed portion from the side surface of the end portion of the material to be joined to start the joining. At the start of joining, the entire surface of the shoulder part was not brought into contact with the material to be joined, and an attempt was made to suppress the breakage of the probe part by reducing the torque applied to the probe part. I couldn't.

FIG. 17 shows an overview photograph from the back surface side of the material to be joined after the probe portion is broken. As in the case of Comparative Example 2, it can be confirmed that the probe portion is broken before the reverse friction stir welding tool is moved in the joining direction, and the shoulder portion remains on the material to be welded.

As described above, from the results of Examples 1 to 4, by using the reverse friction stir welding tool in which the probe portion is not screwed, the reverse friction stir welding can be performed without breaking the tool during the joining. It can be seen that a good joint without defects can be obtained for an A6061-T6 aluminum alloy plate having a plate thickness of 4 mm. In addition, by making the surface of the shoulder part having the probe part a concave curved surface, it is possible to compensate for the lack of stirring force of the probe part that has not been screwed, and by applying multi-faceted cutting processing to the probe surface, the probe can be used. It can be seen that the stirring power of the portion can be improved.

Further, from the results of Comparative Example 1 and Comparative Example 2, even when the probe portion is subjected to the minimum screw processing, reverse friction stir welding is performed on the A6061-T6 aluminum alloy plate having a plate thickness of 4 mm. It is confirmed that the probe part breaks at the initial stage of joining.

2,4 ... Material to be joined,
6 ... Jointed part,
8 ... Probe part,
10 ... Shoulder club,
12 ... Front plate,
14 ... Interface to be joined,
20 ... Inverted friction stir welding tool,
22 ... Fastening part,
30 ... Rotating part.

Claims (6)

With the tool provided with a forward angle, the shoulder portion of the tool is brought into contact with the back surface side of the material to be welded, and while the shoulder portion and probe portion of the tool are pulled up, friction stir welding is performed from the back surface side of the material to be welded. It is a tool for joining and
The tool has a disk- shaped shoulder portion and a probe portion coaxially projecting from the substantially center of the surface of the shoulder portion.
At the tip of the probe portion, a fastening portion for fixing the tool to the rotating portion of the friction stir welding device is provided.
In the friction stir welding, the surface of the probe portion that comes into contact with the material to be welded is not screwed.
A tool for reversing friction stir welding. The surface of the shoulder portion on which the probe portion protrudes has a concave curved surface.
The tool for reverse friction stir welding according to claim 1. The length of the probe portion is 4 mm or more.
The tool for reverse friction stir welding according to claim 1 or 2. The ratio (Dp / Ds) of the diameter Dp of the probe portion to the diameter Ds of the shoulder portion is 0.4 to 0.6.
The tool for reverse friction stir welding according to any one of claims 1 to 3. The surface of the probe portion must be multi-faceted cut.
The tool for reverse friction stir welding according to any one of claims 1 to 4. The shoulder part and the probe part are made of tool steel.
The tool for reverse friction stir welding according to any one of claims 1 to 5.

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