JP7247996B2 - Rotary tool for double-sided friction stir welding and double-sided friction stir welding method - Google Patents

Description

The present invention provides a rotating tool for double-sided friction stir welding and a double-sided friction stir welding method used for double-sided friction stir welding in which two steel plates having different thicknesses are joined while rotating a pair of opposing rotating tools in opposite directions. Regarding.

In the friction stir welding method, a rotary tool (e.g., rotating tool) is inserted into both or one side of the unjoined part of the work materials (e.g., steel plates, etc.) that are overlapped or butted together, and the rotating tool is moved while rotating. In this method, the steel sheets are joined by generating frictional heat and softening the steel sheets while agitating the softened portions with a rotating tool to cause plastic flow.

Since the friction stir welding method is a solid-state welding utilizing plastic flow of metal due to frictional heat between a rotating tool and a steel plate, the welding can be performed without melting unbonded portions. Since the steel sheets are not melted, there are few defects in the joint, and since the heating temperature is low, there is little deformation after joining, and there are many advantages such as no need for a filler material for joining.

In this specification, the overlapped portion or the butted portion in which the steel plates are overlapped or butted but not yet joined is referred to as the “unjoined portion”, and the joined and integrated portion is referred to as the “unjoined portion”. Referred to as "junction".

There is a strong demand for weight reduction from the viewpoint of improving fuel efficiency in transportation equipment such as automobiles and ships. In this trend, different types of steel plates, such as two or more types of steel plates with different thicknesses, are butted and joined together to form a material for parts used in transportation machinery, and multiple properties can be obtained from a single material. There is a demand for tailored blank materials with

Laser welding is often used to join tailored blanks in the automotive field. However, laser welding is fusion joining, and when ultra-high-strength steel or high-carbon materials are welded by laser welding, the welded portion becomes a full martensite structure and hardening is remarkable, resulting in a brittle welded portion.

As a method of friction stir welding steel plates having different thicknesses, there are, for example, the techniques of Patent Documents 1 and 2.

Patent Literature 1 describes applying a friction stir welding method to a tailored blank member made of an aluminum material. In Patent Literature 1, the rotational axis of a rotating tool (rotor of a joining tool) is inclined toward the joining member on the lower side, and is inserted into the mating portion of the joining member. That is, the rotary tool is tilted in a direction perpendicular to the joining direction, and is moved in the joining direction along the joining portion, thereby joining the members to be joined from the surface side.

Patent Literature 2 describes applying a friction stir welding method to a tailored blank member to be welded made of aluminum, magnesium, or the like. Patent document 2 uses a bobbin tool having a curved shoulder as a rotary tool. This bobbin tool is configured such that an upper base, an upper shoulder, a lower base, a lower shoulder, and a probe between the shoulders can rotate together.

As described above, the friction stir welding method joins steel sheets by stirring the joining interface with a rotating tool. Since the rotating tool receives a large load during joining, there is a risk that joint failure may occur due to this. Therefore, the rotary tool is required to suppress the occurrence of defective joining at the time of joining.

For example, Patent Documents 3 and 4 disclose techniques for suppressing the occurrence of poor bonding.

Patent Document 3 discloses a technique for suppressing defects caused by variations in the pressing depth of the tool against the workpiece, which occurs when the friction stir welding tool is rotated and pressed into the joint of the workpiece and moved. To do so, techniques are described that provide a constant tool depth. Specifically, in a tool having a shoulder and a pin, the outer peripheral side of the end face of the shoulder that comes into contact with the workpiece when the pin is pressed into the workpiece is formed into an inclined surface. This inclined surface controls the tool pressing depth.

Patent Literature 4 describes a joining technique using a truncated cone-shaped tool having spiral grooves on the shoulder surface. With this tool, it is possible to suppress the sinking of the shoulder portion of the tool during friction stir processing, reduce the generation of burrs and decrease in wall thickness in the processed portion, and make processing traces inconspicuous.

JP-A-2002-35961 Japanese Unexamined Patent Application Publication No. 2013-761 JP 2003-290937 A Japanese Patent Application Laid-Open No. 2007-301579

However, the technique of Patent Document 1 targets aluminum or its alloy as the joining member, and does not take into consideration a highly rigid material such as steel material at all. In Patent Document 1, when joining steel plates with different plate thicknesses, the rotation axis of the rotary tool is inclined toward the joining member on the lower side (perpendicular to the joining direction). It cannot withstand the high loads caused by tilting the rotary tool. As a result, joining is difficult because the rotary tool breaks. Also, in order to withstand this high load, the device mounting the rotary tool must be sufficiently rigid.

The technique of Patent Document 2 joins using a bobbin tool having curved upper and lower shoulders. However, since bobbin tools are used, the upper and lower bobbin tools rotate in the same direction. As a result, the plastic flow moves in the same manner on the upper and lower sides, so when joining thin plates with a short distance between the upper and lower bobbin tools, or when joining at high speed, the welding direction and the rotation direction of the bobbin tool are different. On the retreating side in the opposite direction, there is a problem that voids are generated by plastic flow when the bobbin tool passes through, and linear defects tend to occur in the joint.

In the technique of Patent Document 3, the device requires a mechanism for controlling the pressing depth of the tool. Further, Patent Document 3 uses an aluminum alloy as a workpiece, but Patent Document 3 does not particularly mention the strength characteristics of the tool. Therefore, when another metal, especially a high-melting-point material or a high-hardness material, is used as the work piece, there is a problem that the strength of the tool is insufficient and the welding cannot be performed well.

In the technique of Patent Document 4, in order to prevent the generation of burrs due to the biting of the softened material, the material to be processed that is softened during processing is bitten into the spiral grooves, and is held appropriately on the shoulder surface. Therefore, Patent Literature 4 describes that the groove should be deeper as it approaches the center from the outer periphery of the tool. However, if the amount of metal involved in the tool increases, the tool may break and joining becomes difficult when a highly rigid material such as steel is used.

In addition, compared to low-melting-point metal materials such as aluminum alloys and magnesium alloys, steel materials with high high-temperature strength are sufficiently welded in the unwelded area when friction stir welding is performed under the welding conditions of low heat input and high welding speed. Plastic flow is often not obtained. Therefore, even when steel materials are used as joining members, it is required to suppress the occurrence of defects during joining and to increase the joining speed.

Furthermore, when friction stir welding is performed with a single rotating tool placed on one side of a steel plate, although sufficient plastic flow can be obtained by the rotating tool on one side of the unwelded portion, the temperature rise and shear stress load on the other side. is not sufficient and sufficient plastic flow cannot be obtained in many cases. Therefore, there is a problem that a sufficiently homogeneous plastic flow cannot be obtained in the plate thickness direction of the member to be joined.

The present invention has been made in view of the above problems, and is a double-sided friction stir welding method for joining two steel plates having different thicknesses while rotating a pair of opposing rotating tools in opposite directions. It is an object of the present invention to provide a rotary tool for stir welding and a method for double-sided friction stir welding.

In order to solve the above problems, the present invention has been extensively studied.

A rotating tool, which is a conventional example, will be described with reference to FIG.
FIGS. 13(a) and 13(b) show schematic diagrams of a rotary tool 100, which is a conventional example, and which is composed only of a probe 101 and a shoulder 102. FIG. In addition, FIG. 13(a) shows a rotary tool 100 in which a shoulder 102 has a flat cross-sectional shape as an example of the conventional rotary tool 100. As shown in FIG. FIG. 13(b) shows, as another example of the conventional rotary tool 100, a rotary tool 100 in which the shoulder 102 has a concave cross-sectional shape. 13(a) and 13(b) show cross-sectional views of the rotary tool 100 on the upper side and plan views of the rotary tool 100 on the lower side.

13(a) and 13(b), when friction stir welding is performed by butting steel plates having different thicknesses, the rotary tool 100 is tilted in a direction perpendicular to the welding direction. It is necessary to join them together. Due to the difference in plate thickness, a large load is applied to the tool on the steel plate side with the thick plate. As a result, the rotary tool 100 is likely to be damaged, making it difficult to form an appropriate bead shape at the joint.

Therefore, the present inventors have made intensive studies on means for obtaining an appropriate bead shape at the joint and obtained the following conclusions.

When two steel plates with different thicknesses are to be friction stir welded on both sides, by tapering the outer periphery of the rotary tool, the steps of the steel plates become smooth when passing through the rotary tool, and an appropriate bead can be formed. . That is, it is effective to form the outer peripheral portion of the rotating tool in a tapered shape. Further, in order to friction stir weld high-temperature strength steel plates, it is effective to use a material harder than the steel plate for a specific region of the rotary tool that contacts the steel plate.

From the above, the present inventors found that when two steel plates having different thicknesses are butted and joined together, there is no need to incline the rotation axis of the rotary tool in the direction perpendicular to the joining direction. A rotary tool for stir welding has been found. In addition, the inventors have found a double-sided friction stir welding method in which this rotating tool can be suitably used.

The present invention has been made based on the above findings, and has the following gist.
[1] Double-sided friction stir welding in which a pair of rotating tools arranged on one side and the other side of the unjoined portion of two steel plates with different thicknesses are rotated in opposite directions to join the steel plates together. A rotating tool for double-sided friction stir welding used for
the rotary tool has a tip in the center of the rotary tool and an outer periphery outside the tip;
The outer peripheral portion has a tapered shape,
A rotary tool for double-sided friction stir welding, wherein the tip portion and the outer peripheral portion are made of a material harder than that of the steel plate.
[2] For double-sided friction stir welding according to [1], wherein the angle formed by the tapered surface of the outer peripheral portion and the surface perpendicular to the rotation axis of the rotating tool is 2 to 20 °. rotating tool.
[3] [1] or [2], wherein the outer peripheral portion has spiral recesses and/or protrusions in the tapered portion that are oriented in the same direction as or opposite to the direction of rotation of the rotating tool. 2. A rotating tool for double-sided friction stir welding according to .
[4] The tip portion is formed in one type selected from a circular and flat shape, a circular and convex curved surface shape, and a circular and concave curved surface shape [1] to [3] ], the rotary tool for double-sided friction stir welding according to any one of
[5] The rotary tool for double-sided friction stir welding according to [4], wherein the tip portion has spiral concave portions and/or convex portions facing in a direction opposite to the rotating direction of the tool.
[6] A double-sided friction stir welding method using the rotating tool for double-sided friction stir welding according to any one of [1] to [5],
Two steel plates having different plate thicknesses are butted against each other in a state in which one surface side of the unjoined portion of the steel plates has a step in the plate thickness direction, and the surface side of the unjoined portion having the step, or the unjoined portion. Place the rotating tool on both face sides,
The direction of rotation of the rotating tool disposed on the surface side having the step is opposite to the direction of movement of the rotating tool on the side of the steel plate with a large thickness, and the direction of rotation of the rotating tool on the side of the steel plate with a small thickness. A double-sided friction stir welding method in which the rotating tool is rotated and moved along the unjoined portion so that the steel plates are joined together in the same direction as the moving direction.

According to the present invention, it is possible to provide a rotary tool for double-sided friction stir welding that does not require adjustment of the angle of the rotary shaft even when two steel plates having different thicknesses are butted and joined.
Further, by using the rotary tool for double-sided friction stir welding of the present invention, a double-sided friction stir welding method for joining two steel plates having different plate thicknesses while rotating a pair of opposing rotary tools in opposite directions to each other is provided. can.

FIG. 1 is a schematic diagram illustrating an example of the double-sided friction stir welding method of the present invention. FIG. 2 is a view for explaining the first embodiment of the rotating tool for double-sided friction stir welding of the present invention, the upper drawing being a side view and the lower drawing being a plan view. FIGS. 3(a) and 3(b) are diagrams illustrating a second embodiment of the rotary tool for surface friction stir welding of the present invention, the upper diagram being a side view and the lower diagram being a It is a top view. FIGS. 4(a) to 4(c) are diagrams for explaining a third embodiment of the rotary tool for double-sided friction stir welding of the present invention. It is a top view. FIGS. 5(a) to 5(c) are diagrams for explaining a fourth embodiment of the rotating tool for double-sided friction stir welding of the present invention, the upper drawing being a side view and the lower drawing being a It is a top view. FIGS. 6(a) to 6(c) are diagrams for explaining a fifth embodiment of the rotating tool for double-sided friction stir welding of the present invention, the upper drawing being a side view and the lower drawing being a It is a top view. FIGS. 7(a) to 7(c) are diagrams for explaining a sixth embodiment of the rotating tool for double-sided friction stir welding of the present invention, the upper drawing being a side view and the lower drawing being a It is a top view. FIGS. 8(a) to 8(c) are diagrams for explaining a sixth embodiment of the rotating tool for double-sided friction stir welding of the present invention, the upper drawing being a side view and the lower drawing being a It is a top view. FIGS. 9(a) to 9(c) are diagrams for explaining a sixth embodiment of the rotating tool for double-sided friction stir welding of the present invention, the upper drawing being a side view and the lower drawing being a It is a top view. FIGS. 10(a) to 10(c) are diagrams for explaining a seventh embodiment of the rotary tool for double-sided friction stir welding of the present invention, the upper diagram being a side view and the lower diagram being a side view. It is a top view. FIG. 11 is a cross-sectional view during welding for explaining a double-sided friction stir welding method to which the rotary tool for double-sided friction stir welding of the present invention is applied. FIG. 12 is a schematic diagram illustrating another example of the double-sided friction stir welding method of the present invention. FIGS. 13(a) and 13(b) are diagrams for explaining a conventional rotating tool, the upper drawing being a side view and the lower drawing being a plan view.

Hereinafter, the rotating tool for double-sided friction stir welding of the present invention will be described with reference to each drawing. Note that the present invention is not limited to this embodiment.

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

INDUSTRIAL APPLICABILITY The rotary tool for double-sided friction stir welding of the present invention (hereinafter referred to as rotary tool) can be suitably used in a double-sided friction stir welding method for joining two steel plates having different thicknesses.

FIG. 1 shows an example of a case where two-sided friction stir welding is performed on steel plates that are butted against each other with a step provided in the plate thickness direction. As shown in FIG. 1, in this double-sided friction stir welding method, the end faces of two steel plates 3 and 4 having different plate thicknesses are butted against each other to form an unjoined portion 6, and one surface side (upper surface side) of the unjoined portion 6 is formed. And a pair of rotating tools 1 and 2 are arranged on the other side (lower side). The rotating tools 1 and 2 move in the joining direction (direction of arrow F shown in FIG. 1) along the unjoined portion 6 while rotating in opposite directions. At this time, the direction of rotation of the rotating tool arranged on the surface side having a step (in the example shown in FIG. 1, the upper surface side of the unjoined portion 6) is the moving direction of the rotating tool (arrow F direction, joining direction), and the side of the steel plate having a smaller thickness is rotated in the same direction as the moving direction of the rotating tool (direction of arrow F). The rotating tools 1 and 2 come into contact with the steel plate at the unjoined portion 6, the butted portion softens due to frictional heat, and solid-state joining is performed by causing plastic flow with the rotating tool, thereby forming the welded portion 5. .

Of the pair of rotating tools 1 and 2 arranged on the upper surface side and the lower surface side of the unjoined portion 6, the rotating tool of the present invention is applied to the rotating tool arranged on the surface side provided with at least a step. effect is obtained. In the example shown in FIG. 1, a step in the plate thickness direction is provided on the upper surface side (one surface side) of the steel plate. In this case, the present invention may be applied only to the rotary tool 1 arranged on the upper surface side of the unjoined portion 6, or the rotary tools 1 and 2 arranged on the upper surface side and the lower surface side of the unjoined portion 6. You may apply this invention to.

In addition, FIG. 1 shows a case where two-sided friction stir welding is performed on an unjoined portion where two steel plates are butted together. The present invention is naturally applicable not only to this case, but also to the case where two-sided friction stir welding is performed on an unjoined portion in which two steel plates are overlapped.

Each embodiment of the rotary tool of the present invention will be described with reference to FIGS. 2 to 10. FIG.
2 shows a first embodiment of the rotary tool of the present invention, FIGS. 3(a) and 3(b) show a second embodiment of the rotary tool of the present invention, and FIGS. 4(c) shows a third embodiment of the rotary tool of the present invention, FIGS. 5(a) to 5(c) show a fourth embodiment of the rotary tool of the present invention, and FIG. 6(a). 6(c) show a fifth embodiment of the rotary tool of the present invention, and FIGS. 7(a) to 7(c), 8(a) to 8(c) and 9(a). 9(c) show a sixth embodiment of the rotary tool of the present invention, and FIGS. 10(a) to 10(c) show a seventh embodiment of the rotary tool of the present invention.
In each figure, the top view is a side sectional view of the rotary tool, and the bottom view is a top plan view of the rotary tool. Since the rotating tool 1 arranged on the upper surface side of the unjoined portion 6 and the rotating tool 2 arranged on the lower surface side have a point-symmetrical shape centering on the tip, here the rotating tool 1 arranged on the upper surface side only.

The rotary tool of the present invention (in the example shown in FIG. 1, a pair of opposing rotary tools 1 and 2, or one rotary tool 1 (on the upper surface side of the steel plate)) is, as shown in FIGS. 2 to 10, It has a tip 9 in the center of the rotary tool and a peripheral part 10 outside the tip 9 .

Note that the distal end portion 9 may have a probe 9a at its center, as shown in FIGS. In this case, the tip portion 9 consists of a probe 9a and a shoulder portion 9b. That is, in the example shown in FIGS. 2-3, the rotary tool of the present invention has a tip portion 9 consisting of a probe 9a and a shoulder portion 9b, and a peripheral portion 10 outside thereof.

Tip portions 9 and outer peripheral portions 10 of rotary tools 1 and 2 are exposed to high temperature conditions during welding. Therefore, the tip portion 9 and the outer peripheral portion 10 are made of a material harder than the steel plates to be joined. As a result, the rotating tools 1 and 2 can apply deformation to the steel plate while maintaining the shape of the tip portion 9 and the outer peripheral portion 10 during joining. As a result, it is possible to achieve a high agitation performance continuously, and proper joining becomes possible.

When comparing the hardness of the steel plate and the rotary tool, for example, the high-temperature Vickers hardness test method (JIS Z 2252) may be used. The rotary tools 1 and 2 may have the above-described hardness at the tip portion 9 and the peripheral portion 10, or may have the above-described hardness for the entirety of the rotary tools 1 and 2.

The outer peripheral portions 10 of the rotary tools 1 and 2 are tapered. As compared with the conventional rotary tool 100 shown in FIG. 13, it can be seen that the outer peripheral portion 10 of the rotary tools 1 and 2 of the present invention has a tapered shape. Here, the tapered shape of the outer peripheral portion 10 means that it is formed in a truncated cone shape as shown in FIGS.

By forming the outer peripheral portion 10 in a tapered shape, the following effects can be obtained. Description will be made with reference to FIG. FIG. 11 shows a state in which the rotating tools 1 and 2 have penetrated to the central position in the plate thickness direction at the portion where the steel plates 3 and 4 are softened during joining.

As shown in FIG. 11, the outer peripheral portions 10 of the rotary tools 1, 2 contact the steel plates 3, 4 during joining. By tapering the outer peripheral portion 10, the difference in level between the two steel plates 3 and 4 having different plate thicknesses becomes smooth when the rotary tools 1 and 2 pass through, and a proper bead can be formed. As a result, defect-free joints can be produced. On the other hand, when using a conventional rotary tool such as that disclosed in Patent Document 1, in order to form a proper bead, the rotary axis of the rotary tool must be set in a direction perpendicular to the welding direction (rotary tool It was necessary to incline the rotating shaft of the steel plate to the lower steel plate side). Moreover, when joining high-melting-point materials and high-hardness materials, it is difficult to join because the large load generated by tilting the rotary tool cannot be endured and the rotary tool is damaged. In order to withstand this large load, the device in which the rotary tool is installed must have sufficient rigidity.

However, in the present invention, since the outer peripheral portion 10 of the rotary tool has a tapered shape, a steel plate (thick plate) with a large plate thickness (steel plate 3 in the example shown in FIG. 11) and a steel plate with a small plate thickness (thin plate) ( In the example shown in 11, there is no need to consider the step of the steel plate 4), and the tolerance of the rotation axis angle of the rotary tool for proper bead formation is improved. That is, according to the present invention, the rotation axis of the rotation tool can be tilted in a direction perpendicular to the welding direction (the rotation axis of the rotation tool toward the lower steel plate side) during welding, as in a conventional rotary tool. can move in the joining direction.

In order to obtain this effect, for example, as shown in FIG. portion) is located at the outermost part of the contact portion between the steel plates 3 and 4 and the rotary tool, and the center of the rotary tool is preferably within ±2 mm in the width direction from the butted portion of the steel plates to be joined.
Since the outer peripheral portion 10 of the rotary tool has a tapered shape, even if the tool target position deviates from the joining direction in the normal direction of the steel plate surface, the pressing can be performed according to the taper angle of the tool. You can get the desired bead shape.

The rotary tool of the present invention can obtain the effects of the present invention by having the above-described configuration requirements. For the purpose of further improving the effect, in addition to the above-described constituent elements, the following constituent elements can be provided.

The outer peripheral portions 10 of the rotating tools 1 and 2 are 2° ≤ α ≤ 20° when the angle formed by the tapered surface of the outer peripheral portion and the surface perpendicular to the rotation axis of the rotating tool is α (see FIG. 2). can have a taper with a slope (inclination) of .

If the taper angle (inclination) α is less than 2°, when the rotary tool passes through the gap between the butted portions of two steel plates having different thicknesses, the ability to smooth the stepped portion may decrease. be. In addition, the rotary tool may be damaged due to the large stress applied to the outer peripheral portion 10 of the rotary tool. On the other hand, when the taper angle α is greater than 20°, the contact area between the outer peripheral portion 10 and the two steel plates decreases, resulting in a decrease in bonding capability. Therefore, the taper angle α is preferably 2° or more and 20° or less. It is more preferably 8° or more, and more preferably 15° or less.

As in the example shown in FIG. 2, in the rotary tool of the present invention, the truncated cone-shaped tapered surface is the outer peripheral portion 10, and the inside thereof is the tip portion 9. As shown in FIG. As for the tapered surface, the above-described effects are likely to be obtained if the shape error of the truncated cone shape is within ±0.005 mm with respect to the specified tool dimensions by tool measurement using a displacement meter.

Also, the outer circumference 10 of the rotary tool can have spiral recesses and/or protrusions 11 in the tapered portion. The spiral (helical, spiral) recesses and/or protrusions 11 may be oriented in the same direction (same direction) or in the opposite direction (opposite direction) with respect to the direction of rotation of each rotary tool 1, 2. As the spiral recess and/or protrusion 11, it is preferable to provide, for example, a groove or a step. As the groove, for example, a groove having a square or semicircular cross-sectional shape can be used. As a step, for example, a step-shaped step can be used.

FIGS. 3(a) and 3(b) show a rotary tool 1 having spiral recesses and/or protrusions 11 on its outer peripheral portion 10. The rotary tool 1 in FIG. The rotating tool 1 in FIG. 3B has vortex recesses and/or protrusions 11 in the opposite direction to the direction of rotation. For example. Here, an example in which concave grooves are provided as the concave and/or convex portions 11 is shown.

As shown in FIG. 3( a ), by providing spiral recesses and/or protrusions 11 in the same direction with respect to the rotational direction of the rotating tools 1 and 2 on the tapered surface of the outer peripheral portion 10 , the rotating tools 1 and 2 The softened metal material is made to flow by the frictional heat from the inside to the outside of the rotating tools 1 and 2 generated when the steel plate (thick plate and thin plate) is pressed and stirred by the. As a result, surplus metal material caused by the thickness difference between the thick plate and the thin plate can flow out of the portion pressed by the rotary tools 1 and 2 . As a result, it is possible to reduce the load on the rotating tool.

On the other hand, as shown in FIG. 3( b ), by providing a spiral concave portion and/or convex portion 11 in the outer peripheral portion 10 in the opposite direction to the rotation direction of the rotary tools 1 and 2 , the rotary tools 1 and 2 The softened metal material is made to flow by the frictional heat from the outside to the inside of the rotating tools 1 and 2 generated when the steel plate (thick plate and thin plate) is pressed and stirred. As a result, it is possible to prevent the metal material from flowing out of the portion pressed by the rotary tools 1 and 2 . As a result, the plastic flow of the pressed portion can be promoted. Moreover, it is possible to prevent the thickness of the joint portion from decreasing in proportion to the plate thickness of the base material. Furthermore, a joint surface with less burrs can be formed.

One or more spiral recesses and/or protrusions 11 are preferably provided. On the other hand, if more than six spiral recesses and/or protrusions 11 are provided, the effect of improving the flow of the metal material becomes poor. In addition, due to the complicated shape, the spiral concave portion and/or the convex portion 11 of the outer peripheral portion 10 of the rotary tools 1 and 2 may be easily damaged. For this reason, it is preferable to set the number to 6 or less. In the examples shown in FIGS. 3(a) and 3(b), the number of spiral recesses and/or protrusions 11 is four.

Further, the shape of the spiral concave portion and/or the convex portion 11 is not particularly defined as long as the above-described effects can be obtained.

The tips 9 of the rotary tools 1 and 2 are formed in one selected from circular and planar, circular and convex curved (convex), and circular and concave curved (concave). be able to.
FIGS. 4(a) to 4(c) show a rotary tool 1 having a circular and convex shape, that is, the tip portion 9 is circular in plan view and convex in side view. FIGS. 5(a) to 5(c) show a rotary tool 1 which is circular and planar, that is, the tip portion 9 is circular in plan view and planar in side view. FIGS. 6(a) to 6(c) show a rotating tool 1 having a circular and concave shape, that is, a tip portion 9 which is circular in plan view and concave in side view. Each figure (a) is an example in which the outer peripheral portion 10 does not have a spiral concave portion and/or a convex portion, and each figure (b) is an example in which the outer peripheral portion 10 has a spiral concave portion in the same direction with respect to the rotation direction of the rotary tool 1. Each figure (c) is an example in which the outer peripheral portion 10 has spiral recesses and/or protrusions 11 directed in the opposite direction to the rotating direction of the rotary tool 1 .

In addition, as shown in FIG. 4, the convex tip portion 9 means one curved surface (paraboloid, prolate sphere or spherical surface) in which the tip surface in contact with the steel plate bulges toward the center. Further, as shown in FIG. 6, the concave front end portion 9 means one curved surface (paraboloid, prolate sphere or spherical surface) in which the front end surface in contact with the steel plate is depressed toward the center. Further, the planar tip portion 9 means that the tip portion in contact with the steel plate has a flat surface as shown in FIG.

For example, as shown in FIG. 13, with a conventional rotating tool having a probe at the tip, when a high-rigidity material such as a steel plate is to be joined, stress concentrates on the probe, and the durability of the tool tends to decrease. there were. However, when the tip portion 9 is circular and convex, circular and planar, or circular and concave, as in the present invention, stress concentration is relieved by the lack of a probe, and tool durability is improved. We can do even better.

In particular, the higher the height of the convex surface, the greater the ability to generate plastic flow during bonding. In addition, when it is flat, it has the ability to produce a plastic flow that is intermediate between that of a convex surface and that of a concave surface. In this way, the plastic fluidity can be controlled by adjusting the height of the convex surface and the depth of the concave surface of the rotary tool. The shape and size of can be selected as appropriate.

In addition, when the distal end portion 9 of the rotary tool is formed in one selected from the above-described circular and planar shape, circular and convex shape, and circular and concave shape, the distal end portion 9 has a spiral shape (helical shape). , spiral) recesses and/or protrusions 12 . As the shape of the spiral recess and/or protrusion 12, it is preferable to provide, for example, a groove or a step. As the groove, for example, a groove having a square or semicircular cross-sectional shape can be used. As a step, for example, a step-shaped step can be used. The spiral concave portion and/or convex portion 12 provided on the tip portion 9 is formed in the opposite direction (opposite direction) to the rotation direction of each of the rotary tools 1 and 2 .

Preferably, one or more spiral recesses and/or protrusions 12 are provided. On the other hand, if more than six spiral recesses and/or protrusions 12 are provided, the effect of improving the flow of the metal material becomes poor. Moreover, there is a possibility that the distal end portions 9 of the rotary tools 1 and 2 may be easily damaged due to the complicated shape. For this reason, it is preferable to set the number to 6 or less. In the examples shown in FIGS. 7(a) to 7(c), FIGS. 8(a) to 8(c), and FIGS. 9(a) to 9(c), the number of vortices is four. , and provides a “groove” as a spiral recess and/or protrusion 12 .
Although an example of the "groove" is shown here, it may be a "step" as shown in FIGS. 10(a) to 10(c).

As described above, for the outer peripheral portion 10 and the tip portion 9, the presence or absence of spiral recesses and/or protrusions, and the direction in which the spirals and protrusions are formed (the same direction as the direction of rotation or the direction opposite to the direction of rotation) can be selected. Therefore, it is possible to selectively flow the metal material softened by frictional heat in the central direction or the normal direction of the rotating shaft of the rotating tool, so that the stirring of the material can be controlled.

In addition, it is preferable that the material to be joined is a steel plate such as an ultra-high tensile strength steel plate as an object to be joined. However, the materials to be joined are not limited to this example.
The plate thickness of the material to be joined is preferably 20 mm or less, and the plate thickness ratio (thickness of large steel plate/thickness of small steel plate) is preferably 1.6 or less.

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

Next, an embodiment of the double-sided friction stir welding method of the present invention will be described.
The double-sided friction stir welding method of the present invention can suitably use the above-described rotary tool for double-sided friction stir welding (hereinafter referred to as a rotary tool). Here, a case where butt welding is performed as an example of the double-sided friction stir welding method will be described with reference to FIG. 1 described above.

As shown in FIG. 1, the double-sided friction stir welding method comprises a pair of rotating tools 1, 2, a gripping device (not shown), and a control device (not shown) for controlling the operation of the rotating tools 1, 2. Double-sided friction stir welding equipment is used. The controller controls, for example, the inclination angle of the rotary tools 1 and 2, the distance between the tips of the rotary tools 1 and 2, the joining speed, the number of rotations of the rotary tools 1 and 2, and the like. In the gripping device, the steel plates 3 and 4 are fixed to prevent the positions of the steel plates 3 and 4 from changing as the rotary tools 1 and 2 advance. Since it is sufficient to use a gripping device that can prevent this variation, the configuration of the gripping device is not particularly limited in the present invention.

The rotating tools 1 and 2 of the double-sided friction stir welding apparatus are placed on one side (upper side) and the other side (lower side) of two steel plates (steel plate 3 and steel plate 4) having different plate thicknesses (steel plate 3 and steel plate 4) to be welded. Place each. In the following description, the rotary tool arranged on the upper surface side of the steel plates 3 and 4 is called "upper surface side rotary tool 1", and the rotary tool arranged on the lower surface side of the steel plates 3 and 4 is called "lower surface side rotary tool It is sometimes called 2.

The two steel plates 3 and 4 are arranged so that the end surfaces (butting surfaces) of the steel plates 3 and 4 face each other while having a step in the plate thickness direction, and are gripped by a gripping device (not shown). In the example shown in FIG. 1, the steel plate 3 is arranged on the side where the rotation direction T _S of the upper surface side rotary tool 1 is opposite to the joining direction (the direction of arrow F shown in FIG. 1), The steel plate 4 is arranged on the side where the rotation direction _TS of the upper surface side rotating tool 1 is the same direction (same direction) as the joining direction. The steel plate 3 is thicker than the steel plate 4 . The steel plates 3 and 4 are butted against each other so as to have a step only on one side.

As shown in FIG. 12, the steel plates 3 and 4 may be butted together so as to have steps in the plate thickness direction on both one side and the other side (top side and bottom side). At this time, a step is provided so that the steel plate 3 protrudes from the steel plate 4 on the upper surface side of the butted portion, and a step is provided so that the steel plate 4 protrudes from the steel plate 3 on the lower surface side of the butted portion.

As shown in FIG. 1, the rotary tools 1 and 2 are inserted into the unjoined portion 6 of the steel plates 3 and 4 located on the joining center line 8 . The rotary tools 1 and 2 press the steel plate 3 and the steel plate 4 at the unjoined portion 6 and move in the joining direction along the portion to be joined while rotating. As a result, both the steel plates are softened by frictional heat between the rotating tools 1, 2 and the steel plates 3, 4, and the softened portions are stirred by the rotating tools 1, 2 to generate plastic flow, thereby Join 4. The joined portion 5 is the portion where joining is completed in the butted portion.

The effect of the present invention can be obtained by using the rotating tool of the present invention as a rotating tool arranged at least on the side of the steel plates 3 and 4 having a step in the unjoined portion 6 . Of course, even if the rotating tool of the present invention is used as a rotating tool arranged on both the side of the steel plates 3 and 4 having a stepped surface and the flat side without a stepped surface, the effect of the present invention can be similarly obtained. can be done.

In the example shown in FIG. 1, the above-described rotary tool of the present invention is used as the upper side rotary tool 1 . The rotary tool 1 placed on the stepped surface of the steel plate is rotated so that the direction of rotation _TS is opposite to the moving direction (joining direction) of the rotary tool 1 on the side of the steel plate 3 having a large thickness. In addition, the side of the steel plate 4 having a smaller plate thickness is rotated in the same direction as the moving direction (joining direction) of the rotary tool 1 .

By rotating the rotary tool 1 in the direction opposite to the joining direction on the side of the thick steel plate (thick plate) 3, the metal is plastically flowed backward in the joining direction. The plastic flow backward in the joining direction has a small amount of movement for flow, and sufficient plastic flow can be obtained even on the side of the steel plate (thick plate) 3 having a large amount of metal, and appropriate joining is possible. Further, on the side of the steel plate (thin plate) 4 having a small thickness, by rotating the rotating tool 1 in the same direction as the joining direction, the metal is plastically flowed forward in the joining direction. Plastic flow forward in the joining direction increases the amount of movement due to the flow, but sufficient joining is possible because the amount of metal on the steel plate (thin plate) 4 side is small.

However, if the rotation direction of the rotary tool 1 is opposite to the direction described above, the rotary tool 1 will rotate in the same direction as the joining direction on the side of the steel plate (thick plate) 3 having a large thickness. , plastic flow forward in the joining direction. As a result, the amount of movement for flow increases, and the steel plate (thick plate) 3, which has a large amount of metal, cannot sufficiently undergo plastic flow, and joint defects occur.

In addition, as shown in FIG. 1, the rotation directions T _S and T _b of the rotating tools 1 and 2 facing each other are opposite to each other on the upper surface side and the lower surface side when viewed from the upper surface side (or the lower surface side) of the steel plates 3 and 4. and In the example shown in FIG. 1, the direction of rotation of the upper surface side rotating tool 1 is indicated by arrow _TS , and the direction of rotation of the lower surface side rotating tool 2 is indicated by arrow _Tb . By setting them in opposite directions, the rotational torques applied to the steel plates 3 and 4 from the rotational tools 1 and 2 can be canceled out. As a result, compared to the conventional friction stir welding method in which the unjoined portion is pressed and joined only by one rotating tool arranged on one side of the steel plate, the structure of the jig that restrains the workpieces is improved. can be simplified.

On the other hand, if the rotation directions of the opposing rotating tools 1 and 2 are the same on the upper surface side and the lower surface side, the relative speed of one rotating tool with respect to the other rotating tool approaches zero. As a result, as the plastic flow of the steel plates 3 and 4 approaches a homogeneous state, the plastic deformation becomes smaller, and the heat generated by the plastic deformation of the metal material cannot be obtained. Therefore, it is difficult to achieve a good bonding state. Therefore, in order to uniformly obtain a sufficient temperature rise and shear stress in the thickness direction of the steel plate to achieve a good joining state, the rotation direction of the opposing rotary tools 1 and 2 should be the upper surface side. It is effective to reverse the direction on the lower surface side (one surface side and the other surface side).

Joining conditions other than those described above may be in accordance with conventional methods.
For example, in the double-sided friction stir welding method of the present invention, the rotational speed of the rotary tools 1 and 2 is preferably 100 to 5000 r/min, more preferably 500 to 3000 r/min. By setting the number of revolutions within this range, there is an effect of suppressing deterioration of mechanical properties due to the application of an excessive amount of heat while maintaining a good surface shape.
The joining speed is preferably 1000 mm/min or higher, more preferably 2000 mm/min or higher. By setting the joining speed within this range, there is an effect of suppressing deterioration of mechanical properties due to input of an excessive amount of heat.
The angle of inclination of the rotating tool (the angle between the axis of rotation of the rotating tool and the vertical line of the steel sheet when the axis of rotation of the rotating tool is inclined backward in the joining direction from the vertical line 7 of the steel sheet) must be 3 degrees or less. preferable.

As described above, by using the rotary tool for double-sided friction stir welding of the present invention, a defect-free joint can be produced for two steel plates having different thicknesses without the need to adjust the angle of the rotation axis according to the applied thickness. It becomes possible. Furthermore, by providing spiral recesses and/or protrusions on either or both of the outer peripheral portion and the tip portion of the rotating tool, the plastic flow of the stirring portion can be controlled more effectively. As a result, for example, burrs can be discharged or suppressed.

Further, as described above, by considering the shape of the rotating tool, it is possible to suppress the occurrence of defects in the weld even at high welding speeds, and to reduce the load on the rotating tool.

Hereinafter, the action and effects of the present invention will be described using examples. In addition, the present invention is not limited to the following examples.

Two types of steel plates with the thickness, chemical composition, tensile strength, and Vickers hardness shown in Table 1 were selected, and double-sided friction stir welding was performed under the welding conditions shown in Tables 2-1 to 2-5. was made.

The end faces of two steel plates having different plate thicknesses were flattened by milling, and the end faces were butted together as shown in FIG. After that, the rotating tool on the upper surface side is moved to one side (upper surface A pair of rotating tools were placed on one side (side) and the other side (bottom side). The rotary tool was pressed from both the upper surface side and the lower surface side of the steel plate and moved in the joining direction to perform joining.

When performing the joining according to the present invention, the upper rotating tool was rotated counterclockwise, and the lower rotating tool was rotated clockwise. In addition, a steel plate having a large thickness was arranged on the side where the rotation direction of the upper surface side rotary tool was opposite to the joining direction. This steel plate having a large thickness is referred to as “test steel plate A” in Tables 2-1 to 2-3. On the other hand, a steel plate with a small thickness was arranged on the side where the rotation direction of the upper side rotary tool is the same as the joining direction. This steel plate with a small thickness is referred to as “test steel plate B” in Tables 2-1 to 2-3. In the example shown in FIG. 1, the steel plate 3 is the test steel plate A, and the steel plate 4 is the test steel plate B.

In this embodiment, nine types of books shown in FIGS. Inventive rotary tools and one type of conventional rotary tool shown in FIG. 13(b) were used.

The dimensions of each rotary tool are as follows.
The dimensions of each rotary tool having a probe 9a at the tip 9 shown in FIGS. 2 and 3(a) to 3(b) are tool diameter D ₁ : 25 mm, probe diameter D ₃ : 7 mm, shoulder diameter D ₄ : 12 mm, probe length: 0.5 mm. 4(a) to 4(c) and FIGS. 7(a) to 7(c), the tip portion 9 of which is formed in a circular and convex shape has a diameter of D ₁ : 25 mm, tip diameter D ₂ : 12 mm, convex height: 0.5 mm. In addition, the groove depth is 0.5 mm and the groove width is 0.5 mm in all figures having grooves.
The dimensions of the conventional rotary _tool with a concave shoulder _shown in FIG. 3 mm.

These rotating tools used tungsten carbide (WC) with a Vickers hardness of 1090 as the material.

3(a) to 3(b), FIGS. 4(b) to 4(c), and FIGS. A spiral recess and/or protrusion 11 was provided. The number of spiral recesses and/or protrusions 11 on the outer peripheral portion 10 is four. The rotary tool shown in FIGS. 7(a) to 7(c) further has a spiral concave portion and/or convex portion 12 on the tip portion 9 as well. The number of spiral recesses and/or protrusions 12 in the tip 9 is each four.

Using the obtained welded joint, the following evaluations were carried out.

(1) Presence or Absence of Surface Defects in Observation of Appearance of Joints For observation, the parts of the obtained welded joints where the welding speed TS was the value shown in Tables 2-1 to 2-5 were used. The presence or absence of surface defects is determined by visual inspection as to whether or not there is a groove-like unbonded state due to insufficient plastic flow or whether or not a bonded portion is concave. For the presence or absence of surface defects, if a groove-shaped unbonded state or a concave-shaped state of the joint is observed, measure the depth D _d (mm) of the groove-shaped or concave-shaped shape using a laser displacement meter. and evaluated according to the following criteria.
<Criteria>
- None: None of the above surface defects are observed.
- Good: Any of the above surface defects are observed. However, the ratio (D _{d /} t ) was 0.1 or less.
- Presence: Any of the above surface defects are observed. Furthermore, the ratio (D _d /t) between the depth D _d (mm) and the average plate thickness t (mm) of the steel plate exceeded 0.1.
Alternatively, the groove-like unbonded state penetrated from the front surface to the back surface of the steel plate. However, if it penetrates, it is considered that the joint is not established, and internal defects and joint strength are not evaluated.

(2) Presence or Absence of Internal Defects in Joint Cross-Section Observation For the observation, the parts of the obtained welded joint where the welding speed TS was the value shown in Tables 2-1 to 2-5 were used. From this part, the position 20 mm from the end on the joining start side, the position 20 mm from the end on the joining end side, and the position intermediate between both ends (the end on the start side and the end on the end side). Cross sections at three locations were cut to obtain test pieces. The presence or absence of internal defects was evaluated based on the following criteria using an optical microscope (magnification: 10 times) to see whether or not an unbonded state formed inside the bonded portion due to insufficient plastic flow was observed.
<Criteria>
- None: No unbonded state formed in a tunnel shape is observed at any of the three positions described above.
- Good: One unbonded state formed inside the bonded portion was observed at the three positions described above.
- Presence: Two or more unbonded states formed inside the bonded portion were observed at the three positions described above.

Tables 3-1 and 3-2 show the evaluation results of (1) and (2) above, respectively. In addition, we also evaluated the following:

(3) Evaluation of the number of welding times until the rotating tool is damaged In this evaluation, a pair of rotating tools (upper surface side rotating tool and lower surface side rotating tool) were used to perform double-sided friction stir welding with a welding length of 0.5 m multiple times. Tables 3-1 and 3-2 show the number of welding times when the rotary tool was damaged during welding. Note that the maximum number of times of welding was set to 10 times, and the welding conditions under which the rotary tool was not damaged before reaching the maximum number of times of welding were indicated as "none" in Tables 3-1 and 3-2.

(4) Tensile Strength of Welded Joint In the evaluation of (3) above, the tensile strength was evaluated using the welded joint obtained when joining was performed a plurality of times. A tensile test piece having the dimensions of a No. 1 test piece specified in JIS Z 3121 was taken from the obtained welded joint, a tensile test (JIS Z 3121) was performed using this test piece, and the measured tensile strength is shown in Table 3-1. and shown in Table 3-2. In addition, when the rotating tool was damaged in the first welding and a welded joint could not be produced, it was described as "(measured value) none" in Tables 3-1 and 3-2.
In this example, the joint strength was considered to be sound if a tensile strength of 85% or more of the tensile strength of the steel plate having the lower tensile strength among the two types of base metal steel plates was obtained. It can be evaluated as being in a bonded state.

From Tables 3-1 and 3-2, in Invention Examples 1 to 69, even when the joining speed was increased to 1.0 m/min or more, no surface defects were observed in joint appearance observation. In addition, no internal defects were observed by observing the cross section of the joint. From this, it was confirmed that a bonded joint in a sound bonded state was obtained. And the rotating tool did not break even when joining was performed 10 times. Furthermore, the tensile strength of the joint was 95% or more of the tensile strength of the steel sheet having the lowest tensile strength among the two types of steel sheets used as the base materials.

On the other hand, in Comparative Examples 1 to 33, the results are as follows.

In Comparative Examples 1 to 9, the steel plate (test steel plate A) in which the welding direction and the tool rotation direction are opposite directions is thicker than the steel plate (test steel plate B) in which the welding direction and the tool rotation direction are the same direction. Bonding was performed under the bonding conditions with a small On the test steel plate B side, which has a large amount of metal, it was rotated in the same direction as the joining direction, so plastic flow was caused forward in the joining direction. As a result, the amount of metal movement for flow was large, and sufficient plastic flow could not be achieved. As a result, surface defects and internal defects were observed in the resulting bonded joint, and a sound bonded state could not be obtained. Furthermore, the joint strength was 80% or less of the tensile strength of the steel sheet having the lower tensile strength among the two steel sheets of the base material.

In Comparative Examples 10 to 18, since a conventional rotary tool that does not have a predetermined tapered shape in the outer peripheral portion was used as the upper side rotary tool, the ability to smooth the steps in the butted portion was lowered. As a result, surface defects and internal defects were observed in the resulting bonded joint, and a sound bonded state could not be obtained. Furthermore, the joint strength was 80% or less of the tensile strength of the steel sheet having the lowest tensile strength among the two steel sheets of the base material.

In Comparative Examples 19 to 27, since welding was performed with the rotation directions of the upper surface side rotating tool and the lower surface side rotating tool being the same, the relative speed of one rotating tool with respect to the other rotating tool approaches zero. As a result, as the plastic flow of the welded parts approaches a homogeneous state, the plastic deformation becomes smaller, and heat generation due to the plastic deformation of the material is no longer obtained. As a result, surface defects and internal defects were observed in the resulting bonded joint, and a sound bonded state could not be obtained. Furthermore, the joint strength was 80% or less of the tensile strength of the steel sheet having the lowest tensile strength among the two steel sheets of the base material.

In Comparative Examples 28 to 33, since the taper angle α of the upper rotating tool was 30°, the contact area between the rotating tool and the steel plate decreased in the unjoined portion, resulting in lower joining ability. As a result, surface defects and internal defects were observed in the resulting bonded joint, and a sound bonded state could not be obtained. Furthermore, the joint strength was 80% or less of the tensile strength of the steel sheet having the lowest tensile strength among the two steel sheets of the base material.

REFERENCE SIGNS LIST 1, 2 rotary tool 3, 4 steel plate 5 joined portion 6 unjoined portion 7 vertical line perpendicular to steel plate 8 joining center line 9 tip portion 9a probe portion 9b shoulder portion 10 outer peripheral portion 11, 12 spiral recess and/or or convex portion 100 rotary tool 101 probe 102 shoulder

Claims (5)

Both sides used for double-sided friction stir welding in which a pair of rotating tools arranged on one side and the other side of the unjoined portion of two steel plates with different thicknesses are rotated in opposite directions to join the steel plates together. A rotary tool for friction stir welding,
the rotary tool has a probeless tip at the center of the rotary tool and a peripheral portion outside the tip;
The outer peripheral portion has a tapered shape , and the angle formed by the tapered surface of the outer peripheral portion and the surface perpendicular to the rotation axis of the rotary tool is 2 to 20°,
A rotary tool for double-sided friction stir welding, wherein the tip portion and the outer peripheral portion are made of a material harder than that of the steel plate. 2. The rotary tool for double-sided friction stir welding according to claim 1 , wherein the outer peripheral portion has spiral concave portions and/or convex portions in the tapered portion. 3. The double-sided surface according to claim 1 , wherein the tip portion is formed in one selected from a circular and planar shape, a circular and convex curved surface shape, and a circular and concave curved surface shape. Rotary tools for friction stir welding. 4. The rotary tool for double-sided friction stir welding according to claim 3 , wherein the tip portion has spiral recesses and/or protrusions. A double-sided friction stir welding method using the rotating tool for double-sided friction stir welding according to any one of claims 1 to 4 ,
Two steel plates having different plate thicknesses are butted against each other in a state in which one surface side of the unjoined portion of the steel plates has a step in the plate thickness direction, and the surface side of the unjoined portion having the step, or the unjoined portion. Place the rotating tool on both face sides,
The direction of rotation of the rotating tool disposed on the surface side having the step is opposite to the moving direction of the rotating tool on the side of the steel plate with a large thickness, and the direction of rotation of the rotating tool on the side of the steel plate with a small thickness. A double-sided friction stir welding method in which the rotating tool is rotated and moved along the unjoined portion so that the steel plates are joined together in the same direction as the moving direction.

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