Metal fusion bonding – Process – Using dynamic frictional energy
Reexamination Certificate
2001-08-28
2003-04-01
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Using dynamic frictional energy
C228S002100
Reexamination Certificate
active
06540128
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel friction stir welding method and apparatus, as well as a welded structure obtained thereby. Particularly, the invention is concerned with a method and apparatus suitable for joining plural workpieces in a complicated three-dimensional shape.
2. Description of the Prior Art
In Japanese Patent No. 2712838 (WO93/10935) is disclosed a friction stir welding method wherein a metallic rod (hereinafter referred to as “rotating tool”), which is substantially harder than the material of workpieces, is inserted into a joint region of the workpieces and is moved under rotation, and the workpieces are joined together with a frictional heat generated between the rotating tool and the workpieces. This friction stir welding method utilizes a plastic flow phenomenon induced with rotation of the rotating tool in which the workpieces are softened with a frictional heat developed between the workpieces and the rotating tool. It is based on a principle different from a principle of a method (e.g., arc welding) in which workpieces are melted and welded thereby.
As apparatus for practicing the friction stir welding method in question there are known, for example, those disclosed in Japanese Patent Laid-Open Nos. Hei 10-249552 and Hei 10-180467. The apparatus disclosed in Japanese Patent Laid-Open No. Hei 10-249552 is for joining such flat plate-like members as shown in
FIGS. 3 and 4
, and the apparatus disclosed in Japanese Patent Laid-Open No. Hei 10-180467 is for joining such cylindrical members as shown in FIG.
5
.
These prior art apparatus are the same in that the rotating tool and the workpieces move relatively while maintaining a certain geometrical relation during welding, although both are different in that the workpieces used in the former are such flat plate-like ones as shown in
FIGS. 3 and 4
, while the workpieces used in the latter are such cylindrical ones having curvature as shown in FIG.
5
. Thus, no special operation is needed during welding if only a geometrical relation between the rotating tool and the workpieces is set beforehand.
However, with a relative movement between the rotating tool and the workpieces, the geometrical relation between the two may change during welding.
FIG. 6
shows an example of such a change. As illustrated therein, such a change occurs in the case where a joint line is formed by a combination of a straight line and circular arcs. In this case, it is necessary to take some measure for maintaining the geometrical relation between the rotating tool and the workpieces.
On the other hand, in Japanese Patent Laid-Open No. 2000-135575 is disclosed a structure wherein a rotating tool support member with a rotating tool attached thereto in an inclined state is rotatable about an axis which is perpendicular to the surfaces of workpieces. According to this structure, for joining workpieces in such a form as typified by
FIG. 6
, it is possible to maintain a geometrical relation between a rotating tool and workpieces.
In a friction stir welding method, a geometrical relation between a rotating tool and workpieces is important in ensuring the soundness of a joint region. More particularly, as shown in
FIG. 7
, if the rotating tool is tilted at an angle of &thgr; (“attack angle” hereinafter) so that a lower end thereof precedes in a welding direction with respect to the surfaces of the workpieces, it becomes easier to ensure the soundness of the joint region.
A problem found in Japanese Patent Laid-Open No. 2000-135575 is that workpieces can be joined together if they are flat plate-like, i.e., if the surfaces to be joined are flat surfaces, but that arbitrary curved surfaces having a three-dimensional shape cannot be joined.
FIG. 8
is a conceptual diagram of the technique proposed in Japanese Patent Laid-Open No. 2000-135575. In the same figure, a rotating tool
11
is rotated by means of a motor
21
via a rotating tool support member
22
. The rotating tool support member
22
is supported by a rotary cylinder
23
.
FIG. 9
illustrates, in terms of trigonometry, a workpieces joining operation using an apparatus of the configuration shown in
FIG. 8
, in which workpieces are joined counterclockwise from A to B along a joint line which is rectangular. As welding advances from A to B, the welding direction changes 90°.
At this time, if the welding direction alone is changed in a fixed state of a rotational axis of the rotating tool, the relation between the workpieces and the rotating tool attack angle &thgr; changes into a positional relation which is no longer a proper relation. In this case, if the rotary cylinder
23
is rotated 90°, a rotational axis of the rotating tool support member
22
rotates 90° about an axis perpendicular to the workpieces. Since the rotational axis of the rotating tool support member
22
and that of the rotary cylinder
23
define an angle corresponding to the rotating tool attack angle &thgr;, the relation between the workpieces and the attack angle &thgr; is maintained.
Thus, according to the configuration of the apparatus described above, the rotational axis of the rotating tool, which is tilted at a predetermined certain angle relative to an axis perpendicular to the workpieces, is rotated about the axis perpendicular to the workpieces, thereby making it possible to maintain the relation between the workpieces and the attack angle &thgr; of the rotating tool even when the welding direction changes.
Of importance is that the angle of the axis perpendicular to the workpieces is constant and that the rotational axis of the rotary cylinder
23
is coincident with the axis perpendicular to the workpieces. In other words, according to the configuration of the apparatus described above, the inclination of the rotational axis of the rotary cylinder
23
cannot be altered and therefore it is necessary that the angle of the axis perpendicular to the workpieces be constant. The axis perpendicular to the workpieces indicates a normal line with respect to the surfaces to be joined, or the joint surfaces, and it is only the case where the joint surfaces are flat surfaces that the normal line is constant. If the joint surfaces are arbitrary curved surfaces in a three-dimensional shape, the direction of the normal line is not constant. Thus, according to the foregoing prior art structure it is impossible to join curved surfaces of a three-dimensional shape.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a friction stir welding method and apparatus capable of maintaining a geometrical relation between a rotating tool and workpieces for arbitrary curved surfaces having a three-dimensional shape, as well as a jointed structure obtained thereby.
According to the present invention there is provided a friction stir welding method of joining workpieces by pushing a rotating tool into the workpieces under rotation of the rotating tool and moving the rotating tool along a joint line, characterized in that the workpieces are joined together while setting a posture of the rotating tool to be pushed into the workpieces with use of both a member having the same rotational axis as a rotational axis of the rotating tool and capable of rotating independently of the rotation of the rotating tool and a member capable of deflecting the rotational axis of the rotating tool about an axis which intersects or perpendicularly intersects the rotational axis of the rotating tool.
According to the present invention there is provided a friction stir welding method of joining workpieces by pushing a rotating tool into the workpieces under rotation of the rotating tool and moving the rotating tool along a joint line, characterized in that the rotating tool has two rotational axes capable of rotating independently of the rotation of the rotating tool, one of said rotational axes being the same as a rotational axis of the rotating tool and rotatable in both the rotating direction of the rotating tool and the direction opposite thereto, the other r
Aono Yasuhisa
Aota Kinya
Hasshuu Shinichi
Hirano Satoshi
Odakura Tomio
Dunn Tom
Johnson Jonathan
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