JP2020124739A - Both surface friction agitation joint method and both surface friction agitation joint device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double-sided friction stir welding method for joining at least two or more steel plates and a double-sided friction stir welding apparatus. SOLUTION: A pair of facing rotating tools are arranged on the front surface side and the back surface side of an unjoined portion of at least two or more steel sheets, and the rotating tool is pressed against the unjoined portion to rotate the rotating tools in opposite directions. This is a double-sided friction-stirring joining method in which steel plates are friction-stirred and joined by moving in the joining direction while allowing them to move. When the region on the surface side of the steel sheet heated by the heating device provided in front of one of the joining directions of the rotary tool is used as the heating region, the steel plate surface temperature TP (° C.) and the facing region in the heating region are opposed to each other. The gap G (mm) of the shoulder portion and the thickness t (mm) of the steel sheet are controlled so as to satisfy a predetermined conditional expression, and friction stirring joining is performed. [Selection diagram] Fig. 1

Description

The present invention relates to a double-sided friction stir welding method for joining at least two or more metal plates (for example, steel plates), and a double-sided friction stir welding apparatus for performing the double-sided friction stir welding.

In friction stir welding, a pair of rotary tools facing each other are arranged facing each other on the front surface side and the back surface side of a butt portion or a lap portion that is a joint portion of at least two or more metal plates, and at the butt portion or the lap portion. The pair of rotary tools are moved in the joining direction while being rotated, and the metal plate is softened by frictional heat between the rotary tool and the metal plate, and the softened portion is stirred by the rotary tool. As a result, plastic flow is generated in the region that will be the joint, and the metal plates are joined together.

In the following description, the abutted portion (or the overlapped portion) which is in a state where it is not joined just by butting (or overlapping) metal plates (for example, steel plates) is referred to as “unjoined portion”, and A portion that is joined and integrated by plastic flow due to friction stirring in the portion (or the overlapping portion) is referred to as a "joint portion".

Examples of conventional friction stir welding methods include Patent Documents 1 to 8. In Patent Document 1, by rotating both or one of a pair of metal materials to generate frictional heat in the metal material to soften the metal material, the softened portion is agitated to cause plastic flow, whereby the metal material A technique for joining the two is disclosed. However, since the technique of Patent Document 1 rotates the metal material to be joined, there is a problem that the shape and size of the metal material are limited.

As a solution to the problem of Patent Document 1, for example, Patent Document 2 can be cited. In Patent Document 2, a rotary tool made of a material substantially harder than a metal plate is inserted into an unjoined portion of the metal plate, and the rotary tool is moved while being rotated, so that the rotary tool and the metal plate are separated from each other. There is disclosed a technique for continuously joining metal plates in the longitudinal direction by heat and plastic flow generated in the. The technique of Patent Document 2 joins the metal plates by moving the rotary tool in the joining direction while rotating the rotary tool while the metal plates are fixed. For this reason, according to the technique of Patent Document 2, even a member that is substantially infinitely long in the bonding direction can be continuously solid-phase bonded in the longitudinal direction of the member. Further, since the solid-phase joining utilizes the plastic flow of the metal due to the frictional heat between the rotating tool and the metal plate, it is possible to join without melting the joined portion. Further, since the heating temperature is low due to the use of frictional heat, the deformation after joining is small, and since the joining portion is not melted, there are few defects, and in addition, no filler material is required.

Therefore, the friction stir welding method is widely used as a joining method for low melting point metal plates represented by aluminum alloys and magnesium alloys, for example, in the fields of aircraft, ships, railway vehicles and automobiles. The reason is that it is difficult for these low melting point metal plates to obtain satisfactory properties of the joint by the conventional arc welding method, but by applying the friction stir welding method, productivity is improved and quality is improved. This is because a high joint can be obtained.

Even if the friction stir welding method is applied to structural steel sheets that are mainly applied as a material for structures such as buildings, ships, heavy equipment, pipelines and automobiles, there are problems with conventional fusion welding such as arc welding. It is possible to avoid solidification cracking and hydrogen cracking that occur, and to suppress changes in the structure of the steel sheet, so improvement in joint performance can be expected. In addition, since a clean surface can be created by contacting the bonding interface with a rotating tool and the clean surfaces can be brought into contact with each other, an advantage that a preliminary preparation step such as diffusion bonding is unnecessary can be expected. As described above, the application of the friction stir welding method to the structural steel plate is expected to have many advantages. However, since there were problems of defects during welding and welding workability such as high welding speed (that is, moving speed of rotating tool), comparison with application of friction stir welding method to low melting point metal plate The friction stir welding method for structural steel sheets has not spread.

The main causes of defects caused by applying the friction stir welding method described in Patent Document 2 to a structural steel sheet are differences in temperature and plastic flow occurring in the thickness direction of the metal sheet (structural steel sheet). To be When pressing the rotating tool arranged on one surface side of the joint part of the structural steel plate and moving and joining in the welding direction while rotating the rotating tool, the surface side where the shoulder part of the rotating tool is pressed is By applying a temperature rise due to the rotation of the shoulder portion and a large deformation force at a high temperature due to the load of shear stress, a clean surface is created at the joint interface. Then, by bringing the clean surfaces into contact with each other, sufficient plastic flow for achieving a metallurgical joining state can be obtained. On the other hand, the opposite surface side (the surface side where the shoulder of the rotary tool is not pressed) has relatively low temperature and the shear stress applied becomes small, so that the plastic flow sufficient to achieve the metallurgical joining state is achieved. It is easy to fall into a state where you can not get.

As a technique for solving the above-mentioned problem of joining workability, for example, the friction stir welding method of Patent Document 3, Patent Document 4 and Patent Document 5 can be mentioned. These documents disclose a joining technique in which a heating means is added for the purpose of improving joining workability.

Patent Document 3 discloses a technique that has a heating means using an induction heating device and heats a material to be processed before and after joining to increase the joining speed and improve cracks in the joined portion. Has been done.

Patent Document 4 has a heating means using a laser device, and by partially heating the workpieces immediately before joining, the joining speed can be increased while suppressing the microstructure change around the heating region due to preheating. A technology for achieving the above is disclosed.

Patent Document 5 has a heating means using a high-frequency induction heating device, and when the workpieces are partially heated immediately before joining, the surface temperature and width of the heated region of the workpieces are strictly controlled. Accordingly, a technology is disclosed in which plastic flow failure due to insufficient heating of the work material is improved, and sufficient strength and joint workability are improved.

Further, for example, in Patent Document 6, Patent Document 7 and Patent Document 8, one rotary tool is provided at the top and bottom, and the front surface side and the back surface side of the overlapping portion of the two metal plates face each other vertically. There is disclosed a technique in which the rotating tool arranged in this manner is used to press the rotating tool from above and below while rotating the tool and move it in the joining direction to join. It is disclosed that this technique suppresses defective joining, increases the joining strength, improves the reliability of the joining strength and the life of the rotary tool, and improves the economical efficiency of the rotary tool.

JP 62-183979 A Patent No. 2712838 Patent No. 4235874 Patent No. 4313714 International Publication No. 2015/045420 Patent No. 3261433 Patent No. 4838385 Patent No. 4838388

However, when the technique described in Patent Document 2 is applied to a structural steel sheet, the structural steel sheet has high strength at high temperatures, and therefore, under the joining condition of low heat input and high joining speed, as described above. There is a strong tendency to not obtain sufficient plastic flow. Therefore, it is difficult to realize a high bonding speed while suppressing the occurrence of defects during bonding.

The friction stir welding method causes plastic flow by stirring with a rotating tool while softening the material to be processed by friction heat. When the work material is a structural steel plate, a large load is applied to the pin of the rotary tool when the work material is agitated by the rotary tool. This phenomenon has a great impact on the durability and life of the rotary tool, and is a major issue that limits the weldability. The techniques described in Patent Documents 3 to 5 use heating means other than friction heat, and are considered to be effective for this problem. However, since the heating means and the rotary tool are provided on the same surface side of the work material, the heat source is either the front surface side (one surface side) or the back surface side (the other surface side) of the work material. Exists only on the side. The surface side without the heating means and the rotary tool has a lower temperature than the surface side with the heat source, and a temperature difference occurs between the front surface side and the back surface side in the thickness direction of the workpiece. Since the strength of the structural steel sheet, which is the workpiece, becomes lower as the temperature becomes higher, it is considered that the load of the rotary tool in the friction stir welding method becomes lower as the temperature becomes higher. It is considered that the load applied to the tip of the pin of the rotary tool can be reduced by eliminating the temperature difference formed in the thickness direction of the workpiece, but Patent Documents 3 to 5 pay attention to this. Furthermore, no consideration is given to eliminating the temperature difference in the thickness direction of the workpiece.

In the friction stir welding method, the techniques disclosed in Patent Documents 6 to 8 are considered to be effective as a method of eliminating the temperature difference in the thickness direction of the workpiece. However, the techniques disclosed in Patent Documents 6 to 8 use a preheat treatment process of heating a metal plate to be processed by a heating means provided in front of the rotary tool, thereby reducing the load on the rotary tool and reducing the material. Since it does not realize the promotion of plastic flow, the effects of joining workability, suppressing defects, and improving joint strength are still insufficient.

Further, in the case of high carbon steel containing carbon as an additive element in a range of 0.1% by mass or more and 0.6% by mass or less, there is a possibility that cracking may occur after joining due to hardening and embrittlement due to quenching, and residual stress. The effect of improving the structure of the joint is not sufficient.

INDUSTRIAL APPLICABILITY The present invention is concerned with the above-mentioned problems when the friction stir welding method is applied to the joining of metal plates (steel plates), or when the friction stir welding apparatus is used to join the metal plates (steel plates), that is, at the joining portion. Local plastic flow failure in the joint due to the difference in temperature and plastic flow occurring in the thickness direction of the metal plate, plastic flow failure due to insufficient frictional heat generated between the rotating tool and the metal plate at high speed welding, and It solves the problems of hardening, brittleness, and cracking due to residual stress caused by rapid cooling. In particular, the present invention provides a double-sided friction stir welding method in which the preheat treatment process conditions by a heating device provided in front of the rotating tool in the welding direction are scrutinized, and a double-sided friction stir welding apparatus that realizes this double-sided friction stir welding method. Thereby, it is intended to advantageously eliminate the joint defect, obtain sufficient strength (joint strength), and improve the joint workability, particularly the joint speed.

As described above, the present invention is intended to solve the above problems, and an object thereof is to provide a double-sided friction stir welding method and a double-sided friction stir welding apparatus for joining at least two steel plates.

As a result of intensive studies to solve the above problems, the present inventors have obtained the following findings (a) to (g).

(A) In double-sided friction stir welding, in order to achieve a high joining speed while suppressing the occurrence of defects during joining, a sufficient temperature rise and shear stress to obtain a metallurgically good joining state, In order to uniformly distribute the metal plate (steel plate) in the thickness direction, it is necessary to manage the gap between the shoulder portions of the pair of rotary tools facing each other. In particular, when a tilt angle is given to the pair of rotary tools, it is effective to adjust the diameter and tilt angle of the shoulder portion of the rotary tool in addition to the thickness of the steel plate.

(B) When the rotation directions of the pair of rotary tools facing each other are the same on the front surface side and the back surface side, the relative speed of the other rotary tool to one rotary tool is zero. Therefore, in the gap between the shoulders of the rotary tool, the plastic deformation becomes smaller as the plastic flow of the steel plates approaches a homogeneous state, and heat generation due to the plastic deformation of the steel plates cannot be obtained, so a good welded state cannot be achieved. .. Therefore, in order to obtain a sufficient temperature rise and shear stress that are uniform in the thickness direction of the steel sheet to achieve a good joining state, the rotation directions of the pair of rotary tools are reversed on the front and back sides. Need to be directional.

(C) With the pair of rotary tools facing each other, by controlling the gap between the tips of the pin portions, it becomes possible to uniformly obtain a temperature rise and shear stress in the thickness direction of the steel sheet. It is possible to achieve a high bonding speed while suppressing the occurrence of defects in. Further, the effect is remarkably exhibited by adjusting the thickness of the steel plate and the diameter of the shoulder portion of the rotary tool.

(D) By controlling the diameter of the shoulder portion of the pair of rotating tools facing each other, it becomes possible to uniformly obtain the temperature rise and the shear stress in the thickness direction of the steel sheet, and the occurrence of defects during joining. It is possible to achieve a higher joining speed while suppressing the above. Particularly, by limiting the diameter of the shoulder portion in addition to the thickness of the steel plate, a remarkable effect can be obtained.

(E) By increasing the temperature at the joining start position to a certain temperature, softening of the steel sheets enables high-speed joining. On the other hand, when the temperature is raised too high, the plastic flow, which is the principle of double-sided friction stir welding, decreases conversely, which causes defects.

(F) When the temperature at the welding start position does not reach a certain temperature, heat is mainly generated by the rotary tool, which is the same as the conventional friction stir welding method, and as a result, the joint strength is not improved. On the other hand, if the temperature is too high, the frictional heat of the rotary tool decreases, the temperature distribution of the rotary tool does not change, and the temperature is further quenched, which causes embrittlement.

(G) In the case of high-C steel, since it has high hardenability, cracking may occur due to residual stress generated by embrittlement due to rapid cooling after joining and restraint. Therefore, in order to avoid these problems, it may be possible to reduce the cooling rate and suppress hardening and embrittlement due to tempering. The high C steel referred to in the present invention refers to a steel plate containing carbon as an additive element in the range of 0.1% by mass or more and 0.6% by mass or less.

The gist of the present invention is as follows.
[1] A pair of opposing rotary tools are respectively arranged on the front surface side and the back surface side of the unbonded portion of at least two steel plates, and the rotary tool is pressed against the unbonded portion to rotate the rotary tool. A double-sided friction stir welding method of friction stir welding steel plates by moving in the welding direction while rotating in opposite directions by
The shoulder portion and the pin portion of the rotating tool share a rotating shaft and are made of a material harder than the steel plate,
When the area on the surface side of the steel sheet heated by the heating device provided in the front of one of the joining directions of the rotating tool is a heating area, when heating,
In the heating region, the steel plate surface temperature TP (° C.) satisfies the formulas (1) to (3), and the gap G (mm) between the facing shoulder portions and the thickness t (mm) of the steel plate are represented by the formula (5). The friction stir welding is performed so as to satisfy the above condition, and the friction stir welding is performed.
In the range of -0.5×D≦W<-0.1×D, 40≦TP≦1200 (1)
-0.1×D≦W≦0.1×D, 100≦TP≦1200 (2)
In the range of 0.1×D<W≦0.5×D, 40≦TP≦1200 (3)
0.4×t≦G≦t (5)
Here, W (mm) is a position separated from the joint center line in the width direction of the joint,
D (mm) is the diameter of the shoulder of the rotary tool,
G (mm) is the shoulder gap,
t (mm) indicates the thickness of the steel plate, respectively.
[2] A pair of rotating tools facing each other are respectively arranged on the front surface side and the back surface side of the unbonded portion of at least two steel plates, and the rotary tool is pressed against the unbonded portion to rotate the rotary tool. A double-sided friction stir welding method of friction stir welding steel plates by moving in the welding direction while rotating in opposite directions by
The shoulder portion and the pin portion of the rotating tool share a rotating shaft and are made of a material harder than the steel plate,
The inclination angle α of the rotating shaft inclined from the vertical direction to the joining direction with respect to the steel plate is 0°<α≦3°,
When the area on the surface side of the steel sheet heated by the heating device provided in the front of one of the joining directions of the rotating tool is a heating area, when heating,
In the heating region, the steel plate surface temperature TP (° C.) satisfies the formulas (1) to (3), the gap G (mm) between the facing shoulders, the thickness t (mm) of the steel plate, and the shoulders The double-sided friction stir welding method is characterized in that the diameter D (mm) is controlled so as to satisfy the expression (6), and friction stir welding is performed.
In the range of -0.5×D≦W<-0.1×D, 40≦TP≦1200 (1)
-0.1×D≦W≦0.1×D, 100≦TP≦1200 (2)
In the range of 0.1×D<W≦0.5×D, 40≦TP≦1200 (3)
(0.4×t)−(0.2×D×sin α)≦G≦t−(0.2×D×sin α) (6)
Here, W (mm) is a position separated from the joint center line in the width direction of the joint,
D (mm) is the diameter of the shoulder of the rotary tool,
G (mm) is the shoulder gap,
t (mm) indicates the thickness of the steel plate, respectively.
[3] It is characterized in that any one of treatment 1 to treatment 4 is further performed after the friction stir welding by using a cooling device and/or a rear heating device provided behind the rotating tool in the joining direction. The double-sided friction stir welding method according to [1] or [2].
(Process 1) The joint is cooled.
(Processing 2) The joint is reheated.
(Process 3) After cooling the joint, the joint is reheated.
(Process 4) After reheating the joint, the joint is cooled.
[4] The diameter D (mm) of the shoulder portion satisfies the expression (7) with respect to the thickness t (mm) of the steel sheet. [1] to [3] The double-sided friction stir welding method described.
4×t≦D≦20×t (7)
[5] The gap g (mm) between the facing pin portions satisfies the equation (8) with respect to the thickness t (mm) of the steel plate and the diameter D (mm) of the shoulder portion [ The double-sided friction stir welding method according to any one of 1] to [4].
0<g≦[1-0.9×exp{-0.011×(D/t) ² }]×t (8)
[6] The double-sided friction stirrer according to any one of [1] to [5], wherein the heating device is a high-frequency induction heating device, and the operating frequency of the heating device is 20 kHz or more and 360 kHz or less. Joining method.
[7] A double-sided friction stir welding apparatus for friction stir welding at least two steel plates,
A pair of rotary tools having a shoulder portion and a pin portion that shares a rotation axis with the shoulder portion, the shoulder portion and the pin portion being formed of a material harder than the steel plate;
A rotary drive device for rotating the rotary tool in opposite directions,
A heating device that is provided in front of one of the rotating tools in the joining direction and that heats the surface of the steel plate,
A controller for controlling the heating device and the rotating tool,
The control unit, when the area on the surface side of the steel sheet heated by the heating device is a heating area,
In the heating region, the steel plate surface temperature TP (° C.) satisfies the formulas (1) to (3), and the gap G (mm) between the facing shoulder portions and the thickness t (mm) of the steel plate are represented by the formula (5). (2) Friction stir welding of at least two steel plates is performed by controlling so as to satisfy (1).
In the range of -0.5×D≦W<-0.1×D, 40≦TP≦1200 (1)
-0.1×D≦W≦0.1×D, 100≦TP≦1200 (2)
In the range of 0.1×D<W≦0.5×D, 40≦TP≦1200 (3)
0.4×t≦G≦t (5)
Here, W (mm) is a position separated from the joint center line in the width direction of the joint,
D (mm) is the diameter of the shoulder of the rotary tool,
G (mm) is the shoulder gap,
t (mm) indicates the thickness of the steel plate, respectively.
[8] When the inclination angle α obtained by inclining the rotation axis of the rotary tool with respect to the steel plate from the vertical direction to the joining direction satisfies 0°<α≦3°,
The gap G (mm) between the facing shoulders, the thickness t (mm) of the steel plate, and the diameter D (mm) of the shoulders should be changed to the formula (5) so that the formula (6) is satisfied. The double-sided friction stir welding apparatus according to claim 7, which is controlled.
(0.4×t)−(0.2×D×sin α)≦G≦t−(0.2×D×sin α) (6)
Where D (mm) is the diameter of the shoulder of the rotary tool,
G (mm) is the shoulder gap,
t (mm) indicates the thickness of the steel plate, respectively.
[9] Further, a cooling device and a rear heating device are provided behind the rotating tool in the joining direction, and any one of the processes 1 to 4 is performed using the cooling device and/or the rear heating device. The double-sided friction stir welding apparatus according to [7] or [8].
(Process 1) The joint is cooled.
(Processing 2) The joint is reheated.
(Process 3) After cooling the joint, the joint is reheated.
(Process 4) After reheating the joint, the joint is cooled.
[10] Any of [7] to [9], wherein the rotating tool has a diameter D (mm) of the shoulder portion that satisfies Expression (7) with respect to a thickness t (mm) of the steel plate. The double-sided friction stir welding apparatus as described in 1 above.
4×t≦D≦20×t (7)
[11] In the rotating tool, the gap g (mm) between the facing pin portions satisfies Expression (8) with respect to the thickness t (mm) of the steel plate and the diameter D (mm) of the shoulder portion. The double-sided friction stir welding apparatus according to any one of [7] to [10].
0<g≦[1-0.9×exp{-0.011×(D/t) ² }]×t (8)
[12] The double-sided friction stirrer according to any one of [7] to [11], wherein the heating device is a high-frequency induction heating device, and the operating frequency of the heating device is set to 20 kHz or more and 360 kHz or less. Joining device.

According to the present invention, when performing double-sided friction stir welding, the heating device partially heats the work material (steel plate) immediately before the joining, thereby eliminating plastic flow failure due to insufficient heating of the work material. .. In addition, a sufficient temperature rise due to the rotation of the shoulders of a pair of opposing rotary tools and a large deformation force at high temperature due to shear stress are applied to both sides of the joints of the steel plates, so that they are uniform in the thickness direction of the steel plates. It can promote plastic flow. As a result, sufficient strength (joint strength) can be obtained while suppressing the occurrence of defects during joining, and the joining workability can be improved, resulting in a marked industrial advantage.

FIG. 1 is a perspective view schematically showing an example of a state in which a rotary tool and a steel plate are arranged in a double-sided friction stir welding apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing an example of a state in which a rotary tool and a steel plate are arranged in a double-sided friction stir welding apparatus according to another embodiment of the present invention. FIG. 3A is a plan view showing a part of the rotary tool and the steel plate in FIG. 1 or 2, and FIG. 3B is a sectional view taken along the line AA shown in FIG. 3A. FIG. 4 is a sectional view showing a section of the rotary tool used in the embodiment of the present invention.

Hereinafter, the double-sided friction stir welding method and the double-sided friction stir welding apparatus of the present invention will be described with reference to the drawings. The present invention is not limited to this embodiment.

In the present invention, two metal plates (steel plates) are butted, or two metal plates (steel plates) are superposed, and the front side and the back side of the butted portion or the superposed portion (hereinafter referred to as unbonded portion) Place a pair of rotation tools on the side. After that, the steel plate is preheated by a heating device provided in front of the rotating tool in the joining direction under a predetermined preheat treatment process condition, the rotating tool is pressed into the unjoined portion and inserted, and the rotating tools are joined while rotating in opposite directions. By moving in the direction, double-sided friction stir welding is performed on the steel plates.

The present invention can be applied to both joining of abutting portions and joining of overlapping portions. In the following description, the case of performing double-sided friction stir welding of the abutting portion will be described in detail as an example.

First, the double-sided friction stir welding apparatus of the present invention will be described.

FIG. 1 shows an example of a double-sided friction stir welding apparatus 20 of the present invention. The double-sided friction stir welding method of the present invention described below can be preferably applied to the double-sided friction stir welding apparatus of the present invention. It should be noted that FIG. 1 shows a double-sided friction stir welding apparatus 20 in a state in which welding is performed on a butt portion of two steel plates.

As shown in FIG. 1, the double-sided friction stir welding device 20 includes at least a pair of rotary tools 1 and 8 facing each other, a gripping device (not shown), a heating device 13, a rotary drive device 16, and a control device. It has a part 17.

The rotary tools 1 and 8 are composed of a pair of rotary tools that face each other with the steel plate 3 in between. The rotary tool 1 on the front surface side of the steel plate 3 includes a shoulder portion 5 and a pin portion 6 arranged adjacent to the shoulder portion 5. The shoulder portion 5 and the pin portion 6 share the rotating shaft 2. The rotary tool 8 on the back surface side of the steel plate 3 includes a shoulder portion 9 and a pin portion 10 arranged adjacent to the shoulder portion 9. The shoulder portion 9 and the pin portion 10 share the rotating shaft 11. Here, the shoulders 5 and 9 refer to stepped portions generated by the rotary tools 1 and 8 and the pin portions 6 and 10 provided at the tips of the rotary tools 1 and 8. At least the shoulder portions 5 and 9 and the pin portions 6 and 10 are made of a material harder than the steel plate 3. Examples of the material include tungsten carbide (WC) and the like.

The rotary tools 1 and 8 may tilt the rotary shafts 2 and 11 with respect to the steel plate 3 from the vertical direction by a predetermined angle α (°) (hereinafter, referred to as a tilt angle α (°)) as necessary. Good.

The gripping device is a device that fixes the steel plate 3 while moving the stage in the direction opposite to the joining direction (advancing direction) P to prevent the position of the steel plate 3 from fluctuating as the rotary tools 1 and 8 move. As the gripping device, any device that can prevent this variation may be used, and therefore the present invention is not particularly limited in its configuration.

The heating device 13 is provided in front of either of the rotating tools 1 and 8 in the joining direction. The heating device 13 is a device that heats the surface of the steel plate 3. In the present invention, the heating device 13 is not particularly limited as long as it can be heated to a predetermined temperature. For example, a high-frequency induction heating device using high-frequency induction heating, a heating device using laser light as a heat source, and the like can be given.

The heating device 13 may operate separately from the movement of the rotary tools 1 and 8, or may operate in conjunction with it. For example, in the case of a device that moves on the rotary tool side, the heating device 13 is attached to this device and moves at the same speed as this device. Further, for example, when the joint side is fixed to the stage by the gripping device and the stage moves, the heating device is installed at a position other than this stage.

The rotary drive device 16 is a device that drives the rotary tools 1 and 8 under predetermined joining conditions (for example, the rotation direction of the rotary tools 1 and 8, the gaps such as shoulders, and the rotation conditions such as the inclination angle). The rotary drive 16 allows the rotary tools 1, 8 to rotate in opposite directions or in the same direction. For example, as the welding conditions of the present invention, one can be set to a clockwise rotation direction and the other to a counterclockwise rotation direction, a welding speed of 0 to 6 m/min, and a tool rotation speed of 0 to 3000 rpm.

The control unit 17 controls the gripping device, the heating device 13, and the rotary drive device 16 based on the welding condition information input to the double-sided friction stir welding device 20. For example, the heating device 13 heats the steel sheet under the control of the control unit 17 so that the output is the one input before joining. At this time, the temperature of the steel plate surface can be measured using thermography. The control unit 17 also controls the moving speed of the steel plate stage, the moving direction of the stage, the rotating speed of the rotary tool, the rotating direction of the rotary tool, the vertical position of the rotary tool, the vertical movement timing and moving speed of the rotary tool, and the like. be able to. Further, the timing of heating by the heating device 13, the heating time, the output, etc. can be controlled.

In the present invention, the control unit 17 controls the heating device 13 based on the preheat treatment process conditions described later. Details of each control of the heating device 13 and the rotation driving device 16 by the control unit 17 will be described later.

The double-sided friction stir welding apparatus 20 of the present invention can further include a cooling device 14 and a rear heating device 15 in addition to the above-described configuration, from the viewpoint of further improving the strength of the welded joint. FIG. 2 shows an example of a double-sided friction stir welding apparatus 20 that also has a cooling device 14 and a rear heating device 15. It should be noted that here, only parts different from the double-sided friction stir welding apparatus of FIG.

As shown in FIG. 2, the cooling device 14 can be provided behind the rotary tool 1 on the surface side that moves in the joining direction P. The cooling device 14 is a device that cools the joint portion 4 of the steel plate 3 under predetermined cooling conditions (for example, cooling conditions such as a cooling rate and a cooling temperature range) and improves the joint strength by quenching. For example, as the cooling condition, the average cooling rate in the temperature range of 800 to 500° C. at the steel plate surface temperature can be set to 30 to 300° C./S. In the present invention, as the cooling device 14, for example, a cooling device that ejects an inert gas is preferably used. As the inert gas, for example, argon gas, helium gas or the like can be used.

The rear heating device 15 is a device that reheats the joint portion 4 of the steel sheet 3 under predetermined heating conditions (for example, heating conditions such as a heating rate and a heating temperature range). For example, as a heating condition, the reheating temperature range can be set to 550 to 650° C. at the steel plate surface temperature. In the present invention, as the rear heating device 15, for example, a high frequency induction heating device or a heating device using a laser as a heat source is preferably used.

In the present invention, the following processing (processing 1 to processing 4 described below) may be performed by using the cooling device 14 and/or the rear heating device 15. For example, the joint portion 4 of the steel plate 3 is cooled using only the cooling device 14. Further, for example, only the rear heating device 15 is used to reheat the joint portion 4 of the steel plate 3.

Further, for example, as shown in FIG. 2, the rear heating device 15 is provided behind the rotary tool 1 on the surface side that moves in the joining direction P and behind the cooling device 14 in the joining direction. By arranging in this manner, when the quenching is excessively hardened by cooling by the cooling device 14, the rear heating device 15 reheats and tempers the joining part 4 to suppress the hardness of the joining part 4. .. As a result, joint characteristics having both strength and toughness can be obtained.

Further, for example, although not shown, the rear heating device 15 is behind the rotary tool 1 on the surface side that moves in the joining direction P and in front of the cooling device 14 in the joining direction (that is, the rotary tool 1 and the cooling device). 14)). With such an arrangement, immediately after joining, the joint portion 4 of the steel sheet 3 is heated by the rear heating device 15 to control the cooling rate, and then the cooling device 14 performs rapid cooling to heat the joint portion 4. The microstructure around the area can be compounded. As a result, joint characteristics having both strength and ductility can be obtained.

Similarly to the above, the control unit 17 also controls the cooling device 14 and the rear heating device 15 based on the welding condition information input to the double-sided friction stir welding device 20.

Next, the double-sided friction stir welding method of the present invention will be described with reference to FIGS. Here, a case where the joining method of the present invention is applied to the double-sided friction stir welding apparatus 20 having the above-described configuration will be described. FIG. 1 and FIG. 2 show an example of a state in which double-sided friction stir welding apparatus 20 performs double-sided friction stir welding of the butted portion of steel sheet 3. FIG. 3(A) shows a plan view of the peripheral part of the rotary tool 1 on the front surface side of the steel plate 3 shown in FIGS. 1 and 2, and FIG. 3(B) shows the plan view of FIG. 3(A). The sectional view on the AA line is shown.

In the double-sided friction stir welding method of the present invention, as shown in FIGS. 1 and 2, first, a pair of rotary tools 1 and 8 are arranged facing each other on the front surface side and the back surface side of two steel plates 3 that are butted. Then, the heating device 13 is arranged in front of the joining direction P of the rotary tool. In the example shown in FIGS. 1 and 2, for example, a high frequency induction heating device is used as the heating device 13.

Next, the rotary tools 1 and 8 are inserted into the unbonded portion 12 from both the front surface side and the back surface side of the steel plate 3, and the rotary tools 1 and 8 are rotated in opposite directions by the rotation drive device 16 under predetermined rotation conditions. While moving, it is moved in the joining direction P. At this time, the steel plate 3 is heated under a predetermined preheat treatment process condition by the heating device 13 arranged in front of the rotating tools 1 and 8 in the joining direction. The heating device 13 and the rotation drive means 16 are controlled by the control unit 17 based on the welding condition information input to the double-sided friction stir welding device 20. Details of control contents such as preheat treatment process conditions will be described later.

In addition, the arrow P shown in FIG. 1 and FIG. 2 shows the advancing direction (namely, joining direction) of the rotary tools 1 and 8 and the heating apparatus 13, and the arrow Q shows rotation of the rotary tool 1 arranged on the front surface side of the steel plate 3. The arrow R indicates the direction of rotation of the rotary tool 8 arranged on the back surface side of the steel plate 3.

By heating the steel plate 3 by the heating device 13, the steel plate 3 is softened, and the pair of rotating tools 1 and 8 facing each other are rotated in opposite directions to generate frictional heat. Stir with tools 1 and 8. As a result, plastic flow is caused to join the two steel plates 3. The joint portion 4 thus obtained is formed in a linear shape along the traveling direction of the rotary tools 1 and 8. Here, the straight line (the one-dot chain line shown in FIGS. 1 and 2) extending to the central position in the width direction of the unbonded portion 12 and the bonded portion 4 shown in FIG. 1 is referred to as a bonded center line 7. The joining center line 7 coincides with the trajectory of the rotary tools 1 and 8 traveling along the joining direction indicated by the arrow P (see FIG. 3A).

The two steel plates 3 are both gripped by a gripping device (not shown) and fixed at a predetermined position when the rotary tools 1 and 8 move along the joining center line 7.

Next, the rotary tools 1 and 8 in the double-sided friction stir welding method of the present invention will be described.

As described above, in the present invention, the control unit 17 controls the rotation drive device 16 based on the input rotation condition of the joining condition. The rotary drive device 16 rotates the rotary tools 1 and 8 in opposite directions. In the example shown in FIG. 1 and FIG. 2, the rotary tool 8 on the back surface side of the steel plate 3 is in the opposite direction (arrow direction) to the rotation direction of the rotary tool 1 on the front surface side of the steel plate 3 (rotation direction indicated by arrow Q). Rotate in the direction indicated by R). That is, as shown in FIG. 3(A), when the rotary tool 1 is rotated clockwise in the plan view seen from the front surface side of the steel plate 3, the rotary tool 8 on the rear surface side of the steel plate 3 not shown is reversed. Rotate clockwise. Although illustration is omitted, when the rotary tool 1 is rotated counterclockwise, the rotary tool 8 is rotated clockwise.

As shown in FIG. 3(B), the rotary tools 1 and 8 have a tip of the pin portion 6 of the rotary tool 1 on the front surface side and a tip of the pin portion 10 of the rotary tool 8 on the back surface side with respect to the steel plate 3. A gap g (mm) is provided between the tips of the pin portions 6 and 10 without abutting. As a result, a gap G (mm) is formed between the shoulder portions 5 and 9 of the rotary tools 1 and 8. Here, the shoulder means the steps 5 and 9 caused by the difference between the diameter D (mm) of the rotary tools 1 and 8 and the diameter a (mm) of the pin portions 6 and 10.

Thus, a gap g is provided between the tip of the pin 6 of the rotary tool 1 and the tip of the pin 10 of the rotary tool 8, and a gap G is provided between the shoulder 5 of the rotary tool 1 and the shoulder 9 of the rotary tool 8, and The rotating tool 1 and the rotating tool 8 are rotated in opposite directions. As a result, a sufficient temperature rise and shear stress are applied from both sides of the steel sheet 3, the difference in temperature and plastic flow occurring in the thickness direction of the steel sheet 3 at the joint 4 is reduced, and a homogeneous joint state is achieved. be able to. Since the joint defect can be advantageously eliminated by eliminating the plastic flow failure locally generated in the joint portion 4, sufficient strength can be obtained. At the same time, it becomes possible to improve the joining workability, especially the joining speed.

By making the rotating directions Q and R of the rotating tools 1 and 8 facing each other opposite to each other on the front surface side and the back surface side, the rotating torques applied to the metal plate 3 by the rotation of the rotating tools 1 and 8 can be canceled out. .. As a result, the structure of the jig for restraining the steel plate 3 can be simplified as compared with the conventional friction stir welding method in which the rotary tool is pressed and joined only from one side of the steel plate.

However, when the rotation directions of the rotary tools 1 and 8 facing each other are the same on the front surface side and the back surface side, the relative speed of the rotary tool 8 on the back surface side to the rotary tool 1 on the front surface side is zero. As a result, between the shoulders 5 and 9 of the rotating tools 1 and 8, the plastic deformation becomes smaller as the plastic flow of the steel sheet 3 approaches a homogeneous state, and heat generation due to the plastic deformation of the steel sheet 3 cannot be obtained, so that a good welded state Will be unattainable.

Therefore, in order to uniformly obtain a sufficient temperature rise and shear stress in the thickness direction of the work material to achieve a good joining state, the rotation directions Q of the rotating tools 1 and 8 facing each other, Let R be the opposite direction on the front surface side and the back surface side of the steel plate 3.

In the present invention, it is effective to adjust the arrangement of the rotary tools 1 and 8 as follows in order to suppress the occurrence of joining defects and increase the joining speed. It is also effective in improving the life of the rotary tool.

First, the inclination angle α (°) of the rotary tools 1 and 8 on the front surface side and the back surface side of the steel plate 3 will be described.

The rotary shafts 2 and 11 of the rotary tools 1 and 8 are inclined with respect to the steel plate 3 at an angle (inclination angle) α (°) with respect to the vertical direction, and the tips of the pin portions 6 and 10 with respect to the joining direction P. Precede. Accordingly, the load on the rotary tools 1, 8 can be received by the rotary tools 1, 8 as a component force that is compressed in the directions of the rotary shafts 2, 11. Therefore, the pair of rotary tools 1 and 8 need to be formed of a material harder than the steel plate 3. For example, when a material having poor toughness such as ceramics is used for a rotary tool, when a force in the bending direction is applied to the pin portions 6 and 10, the stress concentrates on the local portions and the fracture occurs. Therefore, by inclining the rotary shafts 2 and 11 of the pair of rotary tools 1 and 8 at an angle α, the load applied to the rotary tools 1 and 8 is received as a component force that is compressed in the directions of the rotary shafts 2 and 11, and the pin portion 6 is used. The bending force for 10 is reduced. As a result, damage to the rotary tools 1 and 8 can be avoided.

If the inclination angle α exceeds 0°, the above effect is obtained. However, if the inclination angle α exceeds 3°, the front and back surfaces of the joint will be concave, and the joint strength will be adversely affected, so the upper limit is 3°. That is, the inclination angle is preferably 0°<α≦3°. More preferably, 0.5°≦α≦2.0°.

Even if the inclination angle α is 0°, the joined state of the present invention can be achieved.

Subsequently, the gap G (mm) between the shoulder portions 5 and 9 of the rotating tools 1 and 8 facing each other, which is important in the present invention, will be described.

In the present invention, it is necessary to strictly manage the gap G between the shoulder portions 5 and 9 of the pair of rotary tools 1 and 8 in order to achieve high joining speed while suppressing the occurrence of defects during joining. .. As a result, it is possible to uniformly obtain a temperature rise and shear stress sufficient to achieve the joined state in the thickness direction of the steel sheet 3.

When the inclination angles α of the rotary shafts 2 and 11 of the rotary tools 1 and 8 on the front surface side and the back surface side of the steel plate 3 are 0°, the gap G (mm) between the shoulder portions 5 and 9 in the butt joint Is adjusted so as to satisfy the range of Expression (5) with respect to the thickness t (mm) of the steel plate 3. In the lap joining, the total thickness of the superposed steel plates 3 is set to t (mm), and the gap G (mm) between the shoulders 5 and 9 is expressed by the formula with respect to the total thickness t (mm) of the steel plates 3. Adjust so that the range of (5) is satisfied.
0.4×t≦G≦t (5)
As a result, since the shoulder portions 5 and 9 of the rotary tools 1 and 8 facing each other are pressed against the front surface side and the back surface side of the steel plate 3 with a sufficient load, the friction due to the shoulder portions 5 and 9 of the rotary tools 1 and 8 is reduced. The plastic deformation in the shearing direction promotes heat generation and plastic flow. As a result, the plastic flow is uniformly promoted in the thickness direction of the steel sheet 3, and a good joined state can be achieved.

When the gap G between the shoulders 5 and 9 exceeds the thickness t of the steel plate 3 (note that in the case of lap joining, the total thickness t of the steel plate 3), the shoulders 5 of the rotary tools 1 and 8 9 cannot press against the front surface side and the back surface side of the steel plate 3 with a sufficient load, and the above effect cannot be obtained. On the other hand, when the gap G between the shoulders 5 and 9 is less than 0.4×t, the front surface and the back surface of the joint 4 are concave, which adversely affects the strength of the joint. Therefore, when the inclination angle is α=0°, the gap G between the shoulders needs to be 0.4×t or more and t or less. Preferably, 0.5×t≦G≦t.

When the inclination angles α of the rotary shafts 2 and 11 of the rotary tools 1 and 8 are 0°<α≦3°, the shoulders 5 and 9 of the rotary tools 1 and 8 are wide on the front surface side and the back surface side of the steel plate 3. It is important to make contact within a range. Therefore, when the inclination angle α is 0°<α≦3°, it is necessary to set the gap G between the shoulder portions 5 and 9 of the rotary tools 1 and 8 to be small. Therefore, when the inclination angle α is given to the rotary tools 1 and 8 in the range of 0°<α≦3°, the gap G (mm) between the shoulders 5 and 9 is the thickness of the steel plate 3 in the butt joint. In addition to the height t (mm), the diameters D (mm) of the shoulder portions 5 and 9 of the rotary tools 1 and 8 are adjusted so as to satisfy the range of the expression (6). In the lap joining, the total thickness of the superposed steel plates 3 is set to t (mm), and the gap G (mm) between the shoulders 5 and 9 is added to the total thickness t (mm) of the steel plates 3. The diameters D (mm) of the shoulders 5 and 9 are adjusted so as to satisfy the range of Expression (6).
(0.4×t)−(0.2×D×sin α)≦G≦t−(0.2×D×sin α) (6)
When the gap G between the shoulders 5 and 9 is less than ((0.4×t)−(0.2×D×sin α)), the front surface and the back surface of the joint 4 are concave, which adversely affects the strength of the joint. On the other hand, when the gap G between the shoulders 5 and 9 exceeds (t−(0.2×D×sin α)), the shoulders 5 and 9 of the rotary tools 1 and 8 are sufficiently located on the front surface side and the back surface side of the steel plate 3. Since it cannot be pressed by a load, the above effect cannot be obtained. Therefore, when the inclination angle is 0°<α≦3°, the gap G between the shoulders is ((0.4×t)−(0.2×D×sinα)) or more (t−(0.2×D×sinα) ) Must be: Preferably, (0.5×t)−(0.2×D×sin α)≦G≦t−(0.2×D×sin α).
Similar effects can be obtained in the case of lap joining. In the case of lap joining, t in the formula (6) indicates the total thickness t (mm) of the steel plate 3.

In addition to the above conditions, the rotary tool of the present invention can further adjust the diameter D of the shoulder portion and the gap g of the pin portion as described below.

First, preferable conditions for the diameter D (mm) of the shoulder portions 5 and 9 of the rotary tools 1 and 8 will be described.

In the present invention, by controlling the diameters D of the shoulder portions 5 and 9 of the rotary tools 1 and 8 in addition to the conditions of the gaps G and g already described, the above-mentioned effect, that is, with respect to the thickness direction of the steel plate 3 is obtained. Therefore, it is possible to more effectively obtain the effect of uniformly increasing the temperature and shearing stress and suppressing the generation of defects during joining while achieving a higher joining speed.

In particular, the diameter D (mm) of the shoulder portions 5 and 9 is preferably adjusted so as to satisfy the range of the formula (7) with respect to the thickness t (mm) of the metal plate 3.
4×t≦D≦20×t (7)
The thickness t of the steel plate in the equation (7) indicates the thickness t (mm) of the steel plate 3 in the butt joint, and the total thickness t (mm) of the steel plates 3 in the lap joint. ..

If the diameter D (mm) of the shoulder portions 5 and 9 is less than 4×t, there is a possibility that uniform plastic flow cannot be effectively obtained in the thickness direction of the steel sheet 3. On the other hand, if the diameter D (mm) of the shoulder portions 5 and 9 exceeds 20×t, there is a possibility that the area where plastic flow is unnecessarily widened. Therefore, an excessive load is applied to the device, which is not preferable. More preferably, the diameter D of the shoulders 5 and 9 is 5×t≦D≦18×t.

Next, a preferable condition of the gap g (mm) between the tips of the pin portions 6 and 10 of the rotary tools 1 and 8 will be described.

In the present invention, in addition to the above-mentioned conditions, by controlling the gap g between the tips of the pin portions 6 and 10, the above-described effect, that is, the temperature rise and the shear stress are uniformly applied in the thickness direction of the steel sheet 3. As a result, it is possible to more effectively obtain the effect of increasing the joining speed while suppressing the occurrence of defects during joining.

In particular, when the ratio of the diameter D (mm) of the shoulder portions 5 and 9 of the rotary tools 1 and 8 and the thickness t (mm) of the steel plate 3 (that is, D/t) is small, the thickness direction of the steel plate 3 is increased. On the other hand, it becomes difficult for homogeneous plastic flow to occur. Therefore, it is preferable to adjust the gap g between the tips of the pin portions 6 and 10 so as to satisfy the range of Expression (8).
0<g≦[1-0.9×exp{-0.011×(D/t) ² }]×t (8)
The thickness t of the steel plate in the equation (8) indicates the thickness of the steel plate 3 in the case of butt joining, and indicates the total plate thickness of the steel plate 3 in the case of lap joining.

When the gap g between the tips of the pin portions 6 and 10 is 0 or less, the tips of the pin portions 6 and 10 of the rotary tools 1 and 8 facing each other come into contact with each other and are damaged, which is not desirable. On the other hand, when the gap g between the tips of the pin portions 6 and 10 exceeds [1−0.9×exp{−0.011×(D/t) ² }]×t, the steel plate 3 is uniform in the thickness direction. Plastic flow may not be obtained effectively. More preferably, [0.01-0.009×exp{-0.011×(D/t) ² }]×t≦g≦[1-0.9×exp{-0.011×(D/t) ² }]×t.

The length b of the pin portions 6 and 10 of the rotary tools 1 and 8 is appropriately set according to the inclination angle α, the gap G between the shoulder portions, the gap g at the tip of the pin portion, the diameter D of the shoulder portion, and the thickness t. Just decide.

Next, the preheat treatment process in the double-sided friction stir welding method of the present invention will be described. In the present invention, it is important to have a preheat treatment process of heating the steel sheet 3 by the heating device 13 provided in front of the joining direction P of either one of the rotary tools 1 and 8. In the example shown in FIGS. 1 and 2, the heating device 13 is provided in front of the rotary tool 1 on the surface side of the steel plate 3. The heating device 13 may be provided in front of the rotary tool 8 on the back surface side of the steel plate. In this case, the same effect can be obtained.

The heating conditions in the preheat treatment process of the present invention will be described with reference to FIG. FIG. 3(A) is a diagram showing an example of a heating region by the preheat treatment process, and FIG. 3(B) shows a region in which the workpiece (steel plate 3) is subjected to double-sided friction stirring by the pair of rotary tools 1, 8. It is a figure which shows an example. In addition, in FIG. 3(A), the joining center line 7 is shown as a straight line passing through the rotation axis 2 of the rotary tool 1 on the front surface side of the steel plate 3 and parallel to the joining direction P. Further, the regions indicated by H, I, and J are heating regions, and the heating region means a region on the steel sheet heated by the heating device 13. 3A and 3B, a is the maximum diameter (mm) of the pin portions 6 and 10, D is the diameter (mm) of the shoulder portions 5 and 9, and t is the thickness of the steel plate 3. (Mm), G is the clearance (mm) between the shoulders 5 and 9, g is the clearance (mm) at the tips of the pins 6 and 10, and b is the clearance between the pins 6 and 10 of the rotary tools 1 and 8. The length (mm) is shown respectively.

When the inclination angles α of the rotary shafts 2 and 11 of the rotary tools 1 and 8 are 0°<α≦3°, the above-mentioned gap G (mm) between the facing shoulder portions, the thickness t (mm) of the steel plate, and In addition to the fact that the diameter D (mm) of the shoulder portion satisfies the expression (6), on the other hand, when the inclination angles α of the rotary shafts 2 and 11 of the rotary tools 1 and 8 are 0°, the opposing shoulders described above are used. The gap G (mm) of the portion, the thickness t (mm) of the steel plate, and the diameter D (mm) of the shoulder portion satisfy not only the expression (5) but also the following condition. That is, in the preheat treatment process of the present invention, when the steel plate surface temperature in the heating region is TP (°C), the steel plate surface temperature TP at the position in contact with the rotary tool 1 in the front in the joining direction is represented by the formulas (1) to (3). ) Is controlled so that it satisfies.
In the range of -0.5×D≦W<-0.1×D, 40≦TP≦1200 (1)
-0.1×D≦W≦0.1×D, 100≦TP≦1200 (2)
In the range of 0.1×D<W≦0.5×D, 40≦TP≦1200 (3)
Here, W (mm) indicates a position separated from the joining center line in the width direction of the joining portion.

The above range of 0.5×D≦W<−0.1×D is the heating region H shown in FIG. 3(A), and the range of −0.1×D≦W≦0.1×D is shown in FIG. 3(A). The heating region I shown in FIG. 3 and the range of 0.1×D<W≦0.5×D corresponds to the heating region J shown in FIG. That is, in the example shown in FIG. 3(A), the area separated from the joining center line 7 to the upper side on the paper surface is the minus area, and the area separated from the joining center line 7 to the upper and lower sides of the paper surface is the plus area.

Surface temperature TP of the steel sheet in the range of -0.5 x D ≤ W <-0.1 x D (heating region H): 40 ≤ TP ≤ 1200 (1)
-Surface temperature TP of the steel sheet in the range of 0.1×D≦W≦0.1×D (heating region I): 100≦TP≦1200 (2)
Surface temperature TP of steel sheet in the range of 0.1×D<W≦0.5×D (heating region J): 40≦TP≦1200 (3)
As described above, the strength of the steel sheet 3 tends to decrease as the temperature rises. Therefore, it is necessary to adjust the surface temperature TP of the steel plate 3 in the heating regions H, I, J so that it does not rise excessively. Specifically, in order to secure the heating region in the thickness direction of the steel plate 3, the effect of the present invention can be obtained even if there is a temperature gradient (temperature variation on the surface) on the steel plate surface in the heating region. In that case, the highest surface temperature of the steel sheet 3 in the heating region is 1200° C. or lower. As a result, it is possible to prevent the pair of rotary tools 1 and 8 from being damaged and the microstructure around the heating region from being deteriorated due to the temperature of the joint portion 4 excessively rising.
On the other hand, the lowest surface temperature of the steel plate 3 in the heating region is 40° C. or higher. Thereby, good plastic flow can be secured.

In double-sided friction stir welding (double-sided FSW), it is important to soften the material by frictional heat generated between the shoulder of the rotating tool and the material to be welded and to obtain plastic flow of the material generated by the probe of the rotating tool. .. In the present invention, in order to obtain a more advantageous effect, the steel plate surface temperature TP in each of the heating regions H, I, and J is controlled so as to satisfy all of the expressions (1) to (3). If the range of the expression (1) is not satisfied, the softening of the material around the shoulder cannot be sufficiently compensated, and the plastic flow promoting effect by preheating cannot be obtained. Outside the range of the formula (2), the softening of the material around the tool where the most plastic flow occurs cannot be sufficiently compensated, and the plastic flow promotion effect by preheating cannot be obtained. If the range of the expression (3) is not satisfied, the softening of the material around the shoulder cannot be sufficiently compensated and the effect of promoting plastic flow due to preheating cannot be obtained.

As described above, the heating device 13 is not particularly limited in the present invention. For example, when high frequency induction heating is used as the heating device 13, it is preferable to set the operating frequency to 20 kHz or more and 360 kHz or less in consideration of the heating efficiency and the heating range. By using the heating device having this frequency, it is possible to easily control the temperature range.

In the present invention, the positional relationship between the rotary tools 1 and 8 and the heating device 13 and the temperature control of the heating range of the heating device 13 before joining are important. Therefore, as long as the heating device is arranged in front of the traveling direction (welding direction) of the rotary tool, the distance between the heating device and the rotary tool and the heating range of the heating device do not matter. However, if the distance between the heating device and the rotary tool becomes too small, the rotary tool may be damaged by the heat of the heating device. Therefore, in the example shown in FIG. 1, the positional relationship between the rotary tool 1 on the front surface side of the steel plate 3 and the heating device 13 arranged forward in the traveling direction is determined in consideration of the heating efficiency and the influence on the steel plate. It is preferable. For example, the arrangement position of the heating device 13 is preferably arranged within the range of 1 mm or more and 100 mm in front of the rotary tool 1. In this example, as the heating device 13, a high frequency induction heating device whose operating frequency is 50 to 110 kHz or less is used.

Regarding the bonding conditions other than the above, a conventional method may be used. For example, the number of rotations of the rotary tools 1 and 8 can be set in the range of 100 to 5000 times/minute, and the welding conditions can be adjusted so that the welding speed can be increased to 1000 mm/minute or more.

The double-sided friction stir welding method of the present invention can further include a cooling process by the cooling device 14 and a reheating process by the rear heating device 15 from the viewpoint of further improving the strength of the bonded joint.

Usually, after the joining is completed, the joining portion 4 is naturally cooled. For this reason, when the hardenability of the steel plate 3 that is the workpiece is low, the strength of the bonded joint may not be sufficiently obtained. In order to avoid this, in the present invention, as shown in FIG. 2, a cooling device 14 provided behind the rotary tool 1 moving in the welding direction P in the welding direction is used. By appropriately controlling the cooling rate when cooling the joint portion 4 of the steel sheet 3 with the cooling device 14, it is possible to improve the strength by quenching.

On the other hand, when the steel plate 3 that is the work material has high hardenability, it may be excessively hardened, which may reduce the toughness of the joint. In order to avoid this, in the present invention, as shown in FIG. 2, a rear heating device 15 that heats a rear portion in the joining direction P that is close to the rotary tool 1 is used. By reheating the joint 4 of the steel sheet 3 by the rear heating device 15 and appropriately controlling the cooling rate, it is possible to prevent deterioration in toughness.

In the present invention, the following effects can be obtained by performing any one of the following processes 1 to 4 by the cooling device 14 and/or the back heating device 15.

(Process 1) Cooling the bonded portion For example, in the example shown in FIG. 2, the bonded portion 4 is cooled by the cooling device 14 provided behind the rotary tool 1 in the bonding direction P. In this case, for example, the average cooling rate in the temperature range of 800 to 500° C. is preferably 30 to 300° C./s. If the average cooling rate is less than 30° C./s, strength improvement due to quenching cannot be expected, and the strength of the bonded joint may not be sufficiently obtained. On the other hand, if the average cooling rate exceeds 300° C./s, a hard structure may be formed and the toughness may decrease.

(Processing 2) Reheating the bonded part For example, in the example shown in FIG. 2, the bonded part 4 is reheated by the rear heating device 15 provided behind the rotary tool 1 in the bonding direction P. In this case, for example, by controlling the reheating of the rear heating device 15, it is preferable to set the average cooling rate in the temperature range of 800 to 500° C. to 10 to 30° C./s. In the temperature range deviating from 800 to 500° C., the improvement of the structure cannot be sufficiently obtained by appropriately controlling the cooling rate. If the average cooling rate is less than 10°C/s, the strength of the bonded joint may not be improved. On the other hand, if the average cooling rate exceeds 30° C./s, a hard structure may be formed and the toughness may decrease.

(Process 3) After cooling the joint portion, the joint portion is reheated. For example, in the example shown in FIG. 2, after cooling the joint portion 4 by the cooling device 14 provided in the rear of the joint direction P of the rotary tool 1. The joining portion 4 is reheated by the rear heating device 15 provided behind the cooling device 14 in the joining direction P. As a result, even if the joint portion 4 is hardened by being cooled by the cooling device 14 and excessively hardened, it can be tempered by the rear heating device 15 to suppress the altitude and obtain joint characteristics having both strength and toughness. In this case, for example, the cooling device 14 preferably sets the average cooling rate in the temperature range of 800 to 500° C. to 30 to 300° C./s, and the rear heating device 15 sets the reheating temperature range to 550 to 650° C. It is preferable that

(Processing 4) After reheating the joint, the joint is cooled. For example, although not shown, behind the joint direction P of the rotary tool 1 and in front of the joint direction P of the cooling device 14 (that is, rotation). The rear heating device 15 provided between the tool 1 and the cooling device 14 reheats the bonding part 4, and then the cooling device 14 cools the bonding part 4. In this way, immediately after joining, the joining portion 4 is reheated by the rear heating device 15 to appropriately control the cooling rate and then cooled by the cooling device 14, whereby the microstructure can be composited and the strength can be improved. It is possible to obtain joint characteristics that also have ductility. In this case, for example, by reheating the rear heating device 15, the average cooling rate in the temperature range of 800 to 600° C. is set to 0 to 30° C./s, and then the cooling device 14 averages in the temperature range of 600 to 400° C. The cooling rate is preferably 30 to 300° C./s.

Regarding the joining conditions other than the above, a conventional method may be used. For example, the number of rotations of the rotary tools 1 and 8 can be set in the range of 100 to 5000 rpm, and the welding conditions can be adjusted so that the welding speed can be increased to 1000 mm/min or more.

Further, the metal plate 3 targeted by the present invention can be suitably applied to a general structural steel or a carbon steel plate, for example, a steel plate corresponding to JIS G 3106 or JIS G 4051. Further, it can be advantageously applied to a high strength structural steel sheet having a tensile strength of 800 MPa or more. Even in this case, a strength of 85% or more of the tensile strength of the steel sheet can be obtained at the joint.

Next, FIG. 4 shows an example of a cross section of the rotary tool 1. In the present invention, the shape of the pin portion of the rotary tool is not particularly limited.

The maximum diameter of the pin portion 6 of the rotary tool 1 on the front surface side of the steel plate 3 is, for example, 2 to 50 mm. The maximum diameter of the pin portion 6 in the present invention refers to the maximum diameter among the diameters obtained on the cut surface when one pin portion is cut in a cross section perpendicular to the axial direction.

For example, in the example shown in FIG. 4, since the diameter of the pin portion 6 of the rotary tool 1 on the surface side does not change along the axial direction, the diameter a of the upper surface of the pin portion (5.5 mm in the example of FIG. 4) is pinned. The maximum diameter of the part may be used. Although not shown, when the pin portion 6 of the rotary tool 1 has a tapered shape or the like and the pin diameter differs depending on the axial position, the largest diameter may be set as the maximum diameter of the pin portion.

As described above, according to the present invention, when performing double-sided friction stir welding, the heating device partially heats the work material (steel plate) immediately before joining, so that plastic flow failure due to insufficient heating of the work material. Can be resolved. Further, the shoulders of the pair of rotating tools facing each other are pressed against the front surface and the back surface of the joint portion of the steel plates, and a sufficient temperature rise due to the rotation of the shoulder portions and a large deformation force at high temperature due to shear stress are generated. By adding to both surfaces of the steel sheet, plastic flow is uniformly promoted in the thickness direction of the steel sheet, and a good joined state can be achieved. As a result, sufficient strength (joint strength) is obtained in order to increase the joining speed while suppressing the occurrence of defects during joining. Also, the joining workability can be improved.

Using the steel plates with the thickness, chemical composition and tensile strength shown in Table 1, double-sided friction stir welding was performed on the butt portion or the overlapped portion to obtain a joint (joint joint). In this embodiment, the double-sided friction stir welding apparatus 20 shown in FIG. 1 or 2 was used to perform the welding under the double-sided friction stir welding conditions shown in Table 2-1, Table 2-2 and Table 3. Table 3 shows the maximum temperature of the steel sheet surface heated by using the high frequency induction heating device as the heating device. The temperature was measured by thermography.

When the joint type is "butt", the joint butting surface is a so-called I-shaped groove with no angle and has a surface condition of about milling, and the rotary tool is used from both the front side and the back side of the steel plate butting part. Bonding was performed by pressing. On the other hand, when the joint type was "overlap", the front surface of the steel plate was used as the superimposing surface, and the rotary tool was pressed from both the front surface side and the rear surface side of the steel plate superposing portion to perform the joining.

The rotation direction of the rotary tool is that the pair of facing rotary tools arranged on the front and back sides of the steel plate rotate the front side rotary tool clockwise and the back side rotary tool counter when viewed from the front side of the steel plate. The rotation condition was set to be clockwise, or the rotation tools for both the front side and the back side were set to be clockwise. Here, one type of rotary tool having the cross-sectional shape of FIG. 4 was used, and tungsten carbide (WC) was used as the material of the rotary tool.

Using the obtained bonded joint, presence/absence of surface defects, presence/absence of internal defects in joint cross-section observation, tensile test, and workability were evaluated. Table 4 shows each result. In the examples of the present invention, the evaluation of surface defects and internal defects and the evaluation of workability were performed by the following evaluation methods. The tensile test shows the tensile strength (MPa) when a tensile test piece having a size of No. 5 test piece specified in JIS Z 3121 is sampled from the obtained joint and the tensile test is performed.

<Evaluation of surface defects>
The surface defects were evaluated by observing the appearance of the joined joints. For the observation, a portion was used in which the joining speed of the obtained joined joint was the value described in “Joining speed” in Table 2-1 and Table 2-2. The presence or absence of surface defects is determined by visually observing whether groove-like unbonded state due to insufficient plastic flow or occurrence of burrs due to excessive plastic flow is observed. The evaluation was performed according to the following criteria. In addition, here, the presence or absence of the surface defect is visually observed by visually observing the appearance of the obtained joint, and it is determined that there is any unbonded portion.
-None: None of the surface defects described above are observed.
-Yes: Any of the surface defects described above was found.

<Evaluation of internal defects>
The internal defects were evaluated by observing the cross section of the joined joint. For the observation, a test piece was obtained by cutting each of the cross sections at the portions where the joining speed of the obtained joined joint was the value described in “Joining speed” in Table 2-1 and Table 2-2. The invention examples 1 to 18, the comparative examples 10 to 14, the comparative example 18, the comparative example 22, and the comparative example 24 are 220 mm apart from the end on the joining start side in the joining direction (traveling direction) and the end on the joining end side. A cross section at a position 60 mm away from the part in the direction opposite to the joining direction (traveling direction) was cut into test pieces. Further, in Comparative Examples 1 to 9, Comparative Examples 15 to 17, Comparative Examples 19 to 21, and Comparative Example 23, a position 65 mm away from the end on the joining start side in the joining direction (traveling direction) and the end on the joining end side A cross section at a position 70 mm away from the portion in the direction opposite to the joining direction (traveling direction) was cut into test pieces. The presence or absence of internal defects was evaluated by using an optical microscope (magnification: 5 times) according to the following criteria to determine whether or not an unbonded state formed inside the bonded part due to insufficient plastic flow was observed.
-None: The unbonded state formed in a tunnel shape is not seen at any of the two positions described above.
-Good: At the two positions described above, one unbonded state formed inside the bonded part was observed.
-Yes: At two positions described above, two or more unbonded states formed inside the bonded portion were observed.

<Evaluation of workability>
The workability was evaluated on the basis of the results of the surface defects, internal defects and the tensile test described above, and the evaluation was carried out according to the criteria shown below, and any one of the symbols ⊚, ◯ and × was given. In this example, the symbols ⊚ and ∘ were accepted, and the symbol x was rejected. The "bonding speed" shown in the following criteria refers to the bonding speeds shown in Table 2-1 and Table 2-2.
-A: No surface defects and internal defects are generated at a bonding speed of 5 m/min or more, and tensile strength is 85% or more of the base metal.-A: No surface defects or internal defects are generated at a bonding speed of less than 5 m/min. , Tensile strength is 85% or more of the base metal x: Surface defects or internal defects occur, or tensile strength is less than 85% of the base metal

As shown in Table 4, in Invention Examples 1 to 18, no surface defect was observed in the joint appearance observation, and no internal defect was observed in the joint cross section observation, and it was confirmed that a sound joint state was obtained. Further, regarding the joint strength, 85% or more of the tensile strength of the steel sheet as the base material was obtained. The workability was evaluated as acceptable.

The "healthy bonding state" means that both the surface defects and the internal defects are evaluated as "good" or "none".

On the other hand, in Comparative Examples 1 to 24, any one or two of surface defects were observed in the joint appearance observation and one or two internal defects were observed in the joint cross section observation, and a sound joint state was not obtained. Regarding the joint strength, it was less than 85% of the tensile strength of the steel sheet as the base material in Comparative Examples 1 to 24. The evaluation of workability was unsuccessful.

1 Surface-side rotating tool 2 Surface-side rotating tool rotating shaft 3 Metal plate 4 Joint 5 Surface-side rotating tool shoulder 6 Pins of surface-side rotating tool 7 Joint center line 8 Rear-side rotating tool 9 Backside rotating tool shoulder 10 Backside rotating tool pin portion 11 Backside rotating tool rotating shaft 12 Unjoined portion 13 Heating device 14 Cooling device 15 Rear heating device 16 Rotation drive device 17 Control unit 20 Double-sided friction Stirrer

Claims (12)

A pair of opposing rotary tools are respectively arranged on the front surface side and the back surface side of the unbonded portion of at least two steel plates, the rotary tool is pressed against the unbonded portion, and the rotary tools are reversed by a rotary drive device. A double-sided friction stir welding method of friction stir welding steel plates by moving in the welding direction while rotating in the direction,
The shoulder portion and the pin portion of the rotating tool share a rotating shaft and are made of a material harder than the steel plate,
When the area on the surface side of the steel sheet heated by a heating device provided in the front of one of the rotating tools in the joining direction is a heating area, when heating,
In the heating region, the steel plate surface temperature TP (° C.) satisfies the formulas (1) to (3), and the gap G (mm) between the facing shoulder portions and the thickness t (mm) of the steel plate are represented by the formula (5). The friction stir welding is performed so as to satisfy the above condition, and the friction stir welding is performed.
In the range of -0.5×D≦W<-0.1×D, 40≦TP≦1200 (1)
-0.1×D≦W≦0.1×D, 100≦TP≦1200 (2)
In the range of 0.1×D<W≦0.5×D, 40≦TP≦1200 (3)
0.4×t≦G≦t (5)
Here, W (mm) is a position separated from the joint center line in the width direction of the joint,
D (mm) is the diameter of the shoulder of the rotary tool,
G (mm) is the shoulder gap,
t (mm) indicates the thickness of the steel plate, respectively. A pair of opposing rotary tools are respectively arranged on the front surface side and the back surface side of the unbonded portion of at least two steel plates, the rotary tool is pressed against the unbonded portion, and the rotary tools are reversed by a rotary drive device. A double-sided friction stir welding method of friction stir welding steel plates by moving in the welding direction while rotating in the direction,
The shoulder portion and the pin portion of the rotating tool share a rotating shaft and are made of a material harder than the steel plate,
The inclination angle α of the rotating shaft inclined from the vertical direction to the joining direction with respect to the steel plate is 0°<α≦3°,
When the area on the surface side of the steel sheet heated by a heating device provided in the front of one of the rotating tools in the joining direction is a heating area, when heating,
In the heating region, the steel plate surface temperature TP (° C.) satisfies the formulas (1) to (3), the gap G (mm) between the facing shoulders, the thickness t (mm) of the steel plate, and the shoulders The double-sided friction stir welding method is characterized in that the diameter D (mm) is controlled so as to satisfy Expression (6), and friction stir welding is performed.
In the range of -0.5×D≦W<-0.1×D, 40≦TP≦1200 (1)
-0.1×D≦W≦0.1×D, 100≦TP≦1200 (2)
In the range of 0.1×D<W≦0.5×D, 40≦TP≦1200 (3)
(0.4×t)−(0.2×D×sin α)≦G≦t−(0.2×D×sin α) (6)
Here, W (mm) is a position separated from the joint center line in the width direction of the joint,
D (mm) is the diameter of the shoulder of the rotary tool,
G (mm) is the shoulder gap,
t (mm) indicates the thickness of the steel plate, respectively. The cooling device and/or the rear heating device provided on the rear side of the rotating tool in the joining direction are used to further perform any one of the processes 1 to 4 after the friction stir welding. Or the double-sided friction stir welding method described in 2.
(Process 1) The joint is cooled.
(Processing 2) The joint is reheated.
(Process 3) After cooling the joint, the joint is reheated.
(Process 4) After reheating the joint, the joint is cooled. The double-sided friction stirrer according to any one of claims 1 to 3, wherein a diameter D (mm) of the shoulder portion satisfies Expression (7) with respect to a thickness t (mm) of the steel plate. Joining method.
4×t≦D≦20×t (7) The gap g (mm) between the pin portions facing each other satisfies the formula (8) with respect to the thickness t (mm) of the steel plate and the diameter D (mm) of the shoulder portion. The double-sided friction stir welding method according to any one of 4 above.
0<g≦[1-0.9×exp{-0.011×(D/t) ² }]×t (8) The double-sided friction stir welding method according to any one of claims 1 to 5, wherein the heating device is a high-frequency induction heating device, and the operating frequency of the heating device is set to 20 kHz or more and 360 kHz or less. A double-sided friction stir welding apparatus for friction stir welding at least two steel plates,
A pair of rotary tools having a shoulder portion and a pin portion that shares a rotation axis with the shoulder portion, the shoulder portion and the pin portion being made of a material harder than the steel plate;
A rotary drive device for rotating the rotary tool in opposite directions,
A heating device that is provided in front of one of the rotating tools in the joining direction and heats the surface of the steel plate,
A controller for controlling the heating device and the rotating tool,
The control unit, when the area on the surface side of the steel sheet heated by the heating device is a heating area,
In the heating region, the steel plate surface temperature TP (° C.) satisfies the formulas (1) to (3), and the gap G (mm) between the facing shoulder portions and the thickness t (mm) of the steel plate are represented by the formula (5). (2) Friction stir welding of at least two steel plates is performed by controlling so as to satisfy (1).
In the range of -0.5×D≦W<-0.1×D, 40≦TP≦1200 (1)
-0.1×D≦W≦0.1×D, 100≦TP≦1200 (2)
In the range of 0.1×D<W≦0.5×D, 40≦TP≦1200 (3)
0.4×t≦G≦t (5)
Here, W (mm) is a position separated from the joint center line in the width direction of the joint,
D (mm) is the diameter of the shoulder of the rotary tool,
G (mm) is the shoulder gap,
t (mm) indicates the thickness of the steel plate, respectively. When the inclination angle α obtained by inclining the rotation axis of the rotating tool with respect to the steel plate from the vertical direction to the joining direction satisfies 0°<α≦3°, the control unit may:
The gap G (mm) between the facing shoulders, the thickness t (mm) of the steel plate, and the diameter D (mm) of the shoulders should be changed to the formula (5) so that the formula (6) is satisfied. The double-sided friction stir welding apparatus according to claim 7, which is controlled.
(0.4×t)−(0.2×D×sin α)≦G≦t−(0.2×D×sin α) (6)
Where D (mm) is the diameter of the shoulder of the rotary tool,
G (mm) is the shoulder gap,
t (mm) indicates the thickness of the steel plate, respectively. Further, a cooling device and a rear heating device are provided behind the rotating tool in the joining direction, and any one of the processes 1 to 4 is performed using the cooling device and/or the rear heating device. Alternatively, the double-sided friction stir welding apparatus according to item 8.
(Process 1) The joint is cooled.
(Processing 2) The joint is reheated.
(Process 3) After cooling the joint, the joint is reheated.
(Process 4) After reheating the joint, the joint is cooled. 10. The rotating tool according to claim 7, wherein a diameter D (mm) of the shoulder portion satisfies a formula (7) with respect to a thickness t (mm) of the steel plate. Double-sided friction stir welding equipment.
4×t≦D≦20×t (7) The rotating tool is characterized in that a gap g (mm) between the facing pin portions satisfies Expression (8) with respect to the thickness t (mm) of the steel plate and the diameter D (mm) of the shoulder portion. The double-sided friction stir welding apparatus according to any one of claims 7 to 10.
0<g≦[1-0.9×exp{-0.011×(D/t) ² }]×t (8) The double-sided friction stir welding apparatus according to any one of claims 7 to 11, wherein the heating device is a high-frequency induction heating device, and the operating frequency of the heating device is set to 20 kHz or more and 360 kHz or less.

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