Patent Application
20080029581
The above and other objects, features, advantages and technical and industrial significance of the present invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which:
Hereinafter, there will be described in detail preferred embodiments of the present invention by reference to the drawings.
Referring first to
The upper metal plate 2 of the two metal plates 2, 4 is a first member formed of a relatively soft material among various metal materials. Examples of the material of the metal plate 2 include aluminum materials including aluminum alloys and copper materials including copper alloys. Meanwhile, the lower metal plate 4 is a second member formed of a hard metal material. Examples of the material of the metal plate 4 include iron or steel materials, which are made of an iron or an alloy thereof. Among the above-mentioned plates, there is preferably used the aluminum plate as the upper metal plate 2, and there is preferably used the iron or steel plate as the lower metal plate 4. The method of the present invention is advantageously adopted to join together the metal plates formed of the above-mentioned materials.
Over the upper one of the superposed two metal plates 2, 4, i.e., over the metal plate 2, there is positioned a known double-acting rotary tool 10. The rotary tool 10 comprises the followings: a shoulder member 14, which is a cylindrical main body of the rotary tool 10 and the bottom thereof is formed as a shoulder surface 12; and a rod (column)-shaped probe 16, which is inserted in a center hole of the shoulder member 14. The shoulder member 14 and the probe 16 can be rotated on their axes at a high speed, and can be independently moved in the axial direction. In this way, the shoulder member 14 and the probe 16 can be moved based on various known double-acting structures. The shoulder member 14 and the probe 16 are made of a steel material. At least parts of the shoulder member 14 and the probe 16, which are to be caused to contact with, pushed to, or inserted into the upper metal plate 2, are formed of a material harder than the metal plate 2, so that the shoulder member 14 and the probe 16 are prevented from being worn off.
In joining together these two metal plates 2, 4 by the method of the friction stir welding according to the present invention, the rotary tool 10 is initially rotated at a high speed, while the probe 16 of the rotary tool is inserted into the upper metal plate 2, which is the first member formed of the soft metal. The shoulder member 14 and the probe 16, which are components of the rotary tool 10, may be rotated together or independently. The probe 16 is pulled into the shoulder member 14, so that the tip of the probe 16 is roughly flush with the shoulder surface 12, when the rotary tool 10, in particular, the shoulder surface 12 of the lower surface of the shoulder member 14 is lightly pushed to the surface of the metal plate 2. Accordingly, the shoulder surface 12 comes into contact with the metal plate 2, and the surface of the metal plate 2 is heated by the friction. Then, the probe 16 is projected out of the shoulder member 14 and inserted into the metal plate 2, in a way that the tip of the probe 16 reaches right above the lower metal plate 4, which is the second member formed of the hard metal.
As described above, the tip of the probe 16 is flush with the shoulder surface 12 when the tip of the probe 16 is butted together with the surface of the metal plate 2, and then the friction stir welding operation is started. According to this arrangement, there can be enjoyed an advantage of effectively restraining or preventing a generation of a burr. However, the method of the present invention is not limited to the above. Instead, there may be suitably adopted various known methods of operating a double-acting rotary tool. For instance, the probe 16 can be projected out of the shoulder member 14 and inserted into the metal plate 2, before the shoulder surface 12 comes into contact with the metal plate 2.
As described above, the shoulder surface 12 is in abutting contact with the surface of the metal plate, and the probe 16 is inserted into the metal plate while the rotary tool 10 is rotated at the high speed, whereby a stirring action is proceeded. As a result of the stirring action, there is formed the friction stir zone 18 under the shoulder surface 12 and around the probe 16 as shown in
In the friction stir welding operation, if the rotary tool 10, in particular the probe 16, is inserted too deep into the superposed parts of the two metal plates 2, 4, there is an anxiety that the tip of the probe 16 is caused to contact with the lower metal plate 4, which is the second member formed of the hard metal, so that the tip of the probe 16 would be worn off. On the other hand, if the depth of a portion of the probe inserted into the first member is too little, an interface between the two metal plates 2 and 4 would not be sufficiently stirred, so that it may be difficult to obtain a sufficient strength of a junction (joint strength). Therefore, it is desirable that a distance “d” between the tip of the probe 16 and the surface of the lower metal plate 4 is generally not less than 10 μm and is not more than 20% of a thickness of the metal plate 2.
The rotary tool 10 is removed from the metal plate, after the friction stir welding, shown in
Specific operations of filling up the hole formed by removing the probe 16 is not limited to the operation of lifting (pulling up) the probe 16, at the same time as bringing down (pressing down) the shoulder member 14. Instead, there may be suitably adopted other operations. For instance, there may be started bringing down the latter a little after starting the lifting of the former. Alternatively, there may be started bringing down the latter, after the former is completely lifted. In addition, the hole can be filled up by flowing the material from another part of the friction stir zone other than the part, from which the probe is removed, by applying an pressing operation to the friction stir zone by using a suitable pressure tool, after the rotary tool 10 is removed from the friction stir zone 18.
As described above, the rotary tool 10 is removed from the joint region (friction stir zone 18) of the two metal plates 2, 4, and the probe hole is filled up, whereby the hole formed by the probe 16 is substantially absent. In this case, the probe hole does not need to be disappeared such that only a trace of the probe hole is left, or even the trace cannot be recognized. Instead, the probe hole may still be existed as a hole having a certain depth, as long as a bottom of the probe hole, which is the deepest portion of the probe hole, is sufficiently covered by the material flown from another part of the friction stir zone 18, other than the part, from which the probe is removed.
In this way, the hole, which is made by removing the probe 16 from the friction stir zone 18, is filled by the material flown from another part of the friction stir zone 18 other than the part, from which the probe is removed. Accordingly, the oxides of the material of the lower metal plate 4 existed on the surface of the lower metal plate 4 and metal components of the metal plate 4 existed in the bottom of the probe hole are covered by the material of the friction stir zone 18, retained inside the friction stir zone, and are not exposed on the surface of the friction stir zone. Therefore, even if some water is existed on the surface of the friction stir zone 18, there can be completely avoided an anxiety of causing a galvanic corrosion phenomenon. Accordingly, there can be advantageously enhanced the soundness of the friction stir zone 18, which leads to an advantageously enhanced reliability of the friction stir zone 18.
In
The present invention may be executed in the above-mentioned embodiments. In addition, the present invention can be advantageously executed in an embodiment as shown in
In a joining step of a method shown in
In the friction stir welding operation, the burr-retaining member 20 is brought down at the same time as or before bringing down the shoulder member 14 and/or probe 16 of the rotary tool 10, whereby the surface of the upper metal plate 2 is pressed down. Subsequently, the rotary tool 10 is brought down, and the friction stir welding operation similar to the above-mentioned operation is conducted. In this case, the burr-restraining member restrains a generation of a burr from a material flown from the friction stir zone 18 formed by the stirring action by the shoulder surface 12 of the shoulder member 14 and the probe 16. In order to allow expansion of the volume of the friction stir zone, caused by restraining the flow of the material which may form the burr, the shoulder member 14 can be slightly moved back (lifted), during the friction stir welding operation. The burr-restraining member 20 is not rotated, and is pressed down with a predetermined pressure, e.g., by a spring, so that the burr is not generated between the burr restraining-member and the upper metal plate 2.
After the friction stir welding operation is completed, the hole formed by removing the probe 16 is filled by the material flown from another part of the friction stir zone other than the part, from which the probe is removed, by pulling up (lifting) the probe 16 and by pressing down the friction stir zone 18 by bringing down the shoulder member 14. Subsequently, the pressure applied to the metal plate 2 from the burr-restraining member 20 is released, and there is realized the intended friction stir welding between the metal plates 2 and 4.
As described above, there is provided the burr-restraining member 20 around the shoulder member 14 of the rotary tool 10, whereby there is restrained the generation of the burr around the peripheral portion of the tip of the shoulder member 14, i.e., the peripheral portion of the shoulder surface 12. According to this arrangement, there are prevented oxides and metal components of the metal plate 4, which are existed on the surface of the lower metal plate 4, from being brought up to the surface of the first member, along the interface between the friction stir zone 18 and the upper metal plate 2, by a plastic flow, whereby the oxides and other metal components are retained in the friction stir zone. Accordingly, there can be effectively removed an anxiety of causing the galvanic corrosion between the metal components of the metal plate 4, existing at the interface between the metal plates 2 and 4, and the metal plate 2.
In the method of joining together the dissimilar metal plates according to the present invention, there is controlled the movement of a probe drive device 32 and/or a shoulder member drive device 34 by the control unit 30, as shown in
In detail, positions of tips or ends of the shoulder member 14 and the probe 16 are controlled by the control unit 30, based on the followings: a load (pressure) applied from the upper metal plate 2 and the friction stir zone 18 to the shoulder surface 12 of the shoulder member 14; and a load (pressure) which is increased as the tip of the probe 16 inserted into the metal plate 2 gets closer to the surface of the lower metal plate 4. Meanwhile, positions of the shoulder member 14 and the probe 16 relative to the two metal plates 2, 4 are controlled by the control unit 30, by inputs of thicknesses etc., of the two metal members 2, 4 to an input device, which is not shown. Accordingly, the shoulder surface 12 of the shoulder member 14 is pressed to the surface of the upper metal plate 2, while the end of the probe 16 is moved and projected until the end of the probe 16 is positioned right above the lower metal plate 4. In this way, the friction stir zone 18 is advantageously formed within the metal plate 2.
By respectively controlling the moving distances of the probe 16 and the shoulder member 14 by the control unit 30, there can be assured a stable quality of the junction, even if the thicknesses of the metal plates 2, 4 to be joined together are varied. In particular, there can be accurately maintained a distance “d” between the tip of the probe 16 and an upper surface of the lower metal plate 4. Therefore, there can be wholly solved problems, which include the followings: a problem that the probe 16 comes into contact with the lower metal plate 4 caused by excessive insertion of the probe 16, which leads to a further problem of wearing the tip of the probe; and a problem of deteriorating the strength of the junction, because of an insufficient stirring of the interface between the metal plates 2 and 4, caused by an insufficient insertion of the probe.
Moving distances of both of the shoulder member 14 and the probe 16 in the axial direction may be controlled based on the positions of the member 14 and the probe 16, respectively, or on the loads applied to the member 14 and the probe 16, respectively. Alternatively, it is also possible to control the moving distance of one of the shoulder member 14 and the probe 16, e.g., the shoulder member 14, in the axial direction, by controlling the position of the shoulder member 14, while the moving distance of the other, i.e., the probe 16, is controlled by the load applied to the probe 16. In addition, it is also possible to control the moving distance of one of the shoulder member 14 and the probe 16, e.g., the shoulder member 14, in the axial direction, by controlling the position of the shoulder member 14 and the load applied to the member 14 in combination. It is especially desirable that the shoulder member 14 is moved in its axial direction based on the position of the shoulder member relative to the position of the upper metal plate 2, while a depth of a portion of the probe 16 inserted into the metal plate 2 is controlled by the load applied to the probe 16. According to this arrangement, the position of the probe 16 can be advantageously controlled, even if the thickness of the upper metal plate 2 is varied. In addition, it is also desirable that the movement of the shoulder member 14 in its axial direction is controlled based on the position of the shoulder member 14 at the beginning of the friction stir welding operation, and is controlled based on the load applied to the shoulder member 14 in the latter half of the operation.
There have been explained embodiments, which represent the present invention. It is to be understood that the present invention may be embodied with various changes, modifications and improvements that may occur to those skilled in the art, without departing from a scope of the invention defined in attached claims.
For example, in the above embodiment, there is adopted the friction stir spot welding, to which the present invention is advantageously adopted. Alternatively, the present invention can also be adopted to a method, in which the rotary tool 10 is moved to some extent relative to the metal plates 2, 4, while the friction stir welding operation is conducted.
In the above embodiment, there is explained the present invention by using an example in which the metal plates 2, 4 are used as the first and second members to be joined together. However, the shape of the members to be joined together is not limited to the plate shape. Instead, any members can be adopted to the present invention, as long as each of the superposed parts of the members, to which the friction stir welding operation such as the friction stir spot welding operation is conducted, has a shape similar to that of a plate or a face plate.
As the rotary tool 10, there can be suitably used various known double-acting rotary tools. A shape and a configuration of the probe 16 can also be suitably selected from various known shapes and configurations, such as an upright cylindrical shape, and a conical shape or a truncated cone-shape, of which an end portion is tapered off. In addition, there may be provided projections, protrusions, or grooves, on the surface of the probe. A shape of the shoulder surface 12 of the end portion of the shoulder member 14 is not particularly limited. Instead, there is adopted a known configuration, as the configuration of the shoulder surface 12, such as a flat surface or a concave surface, which surface is gradually curving inward.
It is to be understood that the present invention may be embodied with other changes, modifications, and improvements that may occur to a person skilled in the art, without departing from the scope of the present invention.
Initially, there was prepared, as the first member 2 formed of a soft metal, a plate member formed of 6000 series aluminum material (AA6016-T4) having a thickness of 1 mm. There was also prepared, as the second member 4 formed of a hard metal, a plate member formed of a steel material (SPCC) having a thickness of 1 mm.
Subsequently, the aluminum plate 2 and the steel plate 4 were superposed on each other. The friction stir welding operation according to the present invention was implemented from a side of the aluminum plate 2, by using the rotary tool 10, wherein a cylindrical steel clamp as the burr-restraining member 20 was inserted, so that the cylindrical steel clamp was brought into engagement with a peripheral portion of the rotary tool 10, as shown in
In detail, the backing jig 22 was butted together with a back surface of the lower metal plate 4, and in this way, the plates 2, 4 were supported on each other. The cylindrical steel clamp which had an external diameter of 16 mm and an internal diameter of 10 mm was butted together with an upper surface of the aluminum plate 2 located on the steel plate 4, by using the double-acting rotary tool 10. Subsequently, the shoulder member 14 which had an external diameter of 10 mm and the probe 16 which had an external diameter of 4 mm were rotated in the same direction at a high speed, in a way that a lower surface of the shoulder surface is flushed with that of the probe 16. While the shoulder member 14 and the probe 16 were thus rotated, the lower surfaces of the shoulder member 14 and the probe 16 were butted together with the upper surface of the aluminum plate 2. Subsequently, the probe 16 was inserted into the aluminum plate 2, in a way that the tip of the probe reached right above the steel plate 4 and until the distance between the tip of the probe and the steel plate 4 became 100 μm. Then, the friction stir welding operation was performed, and there was formed a friction stir zone 18 as shown in
After the friction stir welding operation, the probe 16 was removed from the friction stir zone 18, while the shoulder member 14 was moved down, whereby the friction stir zone 18 was pressed down. Subsequently, a hole formed by removing the probe 16 was filled with a material flown from the friction stir zone 18. Accordingly, there was obtained a joined member of the aluminum plate and the steel plate, without substantially leaving a hole formed by removing the probe on the surface of the friction stir zone 18.
In the above friction stir welding operation, the movement of the shoulder member 14 in the axial direction was controlled based on positional information of the surface of the aluminum plate 2 on the backing jig 22. Also, the distance between the tip of the probe 16 and the surface of the steel plate was controlled based on the load which was applied to insert the probe.
In the friction stir welding operation, a generation of a burr to a peripheral portion of the shoulder member 14 was retained by the cylindrical steel cramp as the cylindrical burr-restraining member 20. Accordingly, there was able to be obtained the joined members joined by the friction stir welding, without exposing Fe-component on the surfaces thereof. In this case, heights of bumps on the surface of the joint region were not more than 0.05 mm. There was also recognized that the back surface of the joint region was almost flat and was sound. Moreover, there was conducted a tensile shear test, and the joint region exhibited a breaking strength of 2.5 KN, so that there was confirmed that there was an excellent joint strength.
