Metal fusion bonding – Process – Using dynamic frictional energy
Reexamination Certificate
2001-09-05
2003-04-08
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Using dynamic frictional energy
C228S002100
Reexamination Certificate
active
06543671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and method for friction stir welding, and, in one aspect, to an apparatus and method for friction stir welding using filler material.
2. Description of the Related Art
Workpieces made of some commercial metallic alloys (e.g., most 2000- and 7000-series aluminum alloys) are difficult to join by conventional welding processes (e.g., arc welding processes). For example, 2000-series aluminum alloys are sensitive in heat-affected zones (HAZs) where the base metal reaches temperatures between liquidus and solidus during welding. In this area, partial melting at grain boundaries forms a network containing brittle intermetallic compounds of CuAl
2
. Thus, weld ductility can be substantially reduced. Further, conventional welding processes can create geometric distortions near the weld joint due to high temperature gradients (non-uniform heating) induced in the workpiece during welding. These distortions can cause warping and other dimensional defects in the workpiece, as well as residual stresses that can lead to premature failure by cracking in the weldment or HAZ (either due to static and/or fatigue stresses), lamellar tearing, or by stress-corrosion cracking in some metals.
In addition, some alloys and types of weld joints are difficult to join except in a flat position. For example, thick weldments are typically made in the flat position unless some way is provided to retain the weld metal in the joint, such as with chilled backing plates and to quickly solidify the weld metal and/or with chilled shoes to hold the weld metal in the joint during solidification. Further, traditional welding processes produce welding fumes, spatter, and a possibility of porosity in the deposited weld metal, due to entrained gases. Yet further, certain metals (e.g., aluminum and aluminum alloys) can have surface oxide layers that are insoluble in the molten weld metal. Thus, these oxide layers can readily become entrained in the weldment, causing defects that can decrease static and fatigue strength of the weldment. Accordingly, the oxide layers are typically removed by pickling, grinding, and/or brushing prior to the workpieces being conventionally welded.
Friction stir welding processes can overcome many of the problems encountered with traditional welding processes in metals. In a typical friction stir welding process, illustrated in
FIG. 1
, a cylindrical tool
102
having a shoulder
104
and a pin
106
is rotated (as indicated by arrow
107
) and plunged (as indicated by arrow
109
) into a joint line
108
between two abutted workpieces
110
,
112
of sheet or plate material. As the pin
106
contacts the workpieces
110
,
112
, friction between the pin
106
and the workpieces
110
,
112
generates heat to plasticize an area of the workpieces
110
,
112
adjacent the joint line
108
. As the pin
106
continues to plunge into the workpieces
110
,
112
, more material is plasticized, thus allowing the pin
106
to plunge further into the workpieces
110
,
112
. Plunging stops when the shoulder
104
comes into contact with and is forced against the workpieces
110
,
112
. Each of the workpieces
110
,
112
is clamped onto an anvil
114
in such a manner as to prevent the abutting joint faces of the workpieces
110
,
112
from being forced apart.
Frictional heat is generated between the shoulder
104
, the pin
106
, and the workpieces
110
,
112
. This heat causes the workpieces
110
,
112
to soften or plasticize without reaching their melting point and allows the tool
102
to traverse (as indicated by arrow
113
) along the joint line
108
. As downward pressure is maintained (as indicated by the arrow
109
) and the tool
102
moves along the joint
108
(as indicated by the arrow
113
), the plasticized material is transferred from the leading edge
116
of the tool
102
to the trailing edge
118
of the tool
102
, and is forged by intimate contact with the shoulder
104
and the pin
106
, and is forced against the anvil
114
. A solid-phase bond
120
is left between the workpieces
110
,
112
.
Process advantages can result from such a friction stir welding process (as in generally all friction welding processes) taking place in a solid phase below melting points of the materials being joined. Thus, since no melting occurs, continuous networks of intermetallic compounds (e.g., intermetallic compounds of CuAl
2
in 2000-series aluminum alloys) have little opportunity to form and generally no fumes or spatter are created. The friction stir welding process also produces lower distortion in the workpieces
110
,
112
, since much less heat is transferred into the workpieces
110
,
112
. Further, the friction stir welding process can be performed in any position, since the material along the joint line
108
is plasticized, not melted, and readily remains in place. Yet further, surface oxide layers are generally swept away during the friction stir welding process due to the friction between the shoulder
104
, the pin
106
and the workpieces
110
,
112
. Thus, pickling, grinding, and/or brushing of the workpieces
110
,
112
are not generally required.
The friction stir welding process has several limitations, however. First, joints between workpieces to be friction stir welded generally must have better fit up than that required for joints between workpieces that are conventionally welded. In general, any gap between the workpieces to be joined must be less than 10 percent of the thickness of the workpieces. For example, if the workpieces to be joined have thicknesses of 12.7 mm (0.5 in), the maximum generally-acceptable gap is 1.27 mm (0.05 in). This requirement is due in large part to the fact that known friction stir welding processes do not employ the use of filler materials, which can be used to fill excessive gaps in weld joints. Such stringent fit up requirements can result in higher workpiece preparation costs and workpiece fixturing costs. These costs can escalate dramatically when large workpieces are joined. Further, traditional friction stir welding processes can generally be used on only a limited number of joint types, e.g., butt joints and edge joints. Joint types requiring a fillet, e.g., corner joints, lap joints, and filleted T-joints, cannot generally be accomplished using traditional friction stir welding processes, as filler metal is required to produce the fillet.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a friction stir welding tool includes a body having passageway therethrough through which a filler material may pass and a pin extending from a bottom of the body capable of creating friction when rotated against a workpiece to weld the workpiece.
According to another aspect of the present invention, an apparatus capable of friction stir welding is provided. The apparatus includes a friction stir welding tool having a body having an upper surface defining an entrance opening and a lower surface, and a pin having a lower surface defining an exit opening, wherein the pin extends from the lower surface of the body. The friction stir welding tool further includes a passageway from the entrance opening to the exit opening and is capable of allowing a filler material to pass therethrough. The apparatus further includes a spindle capable of rotating the friction stir welding tool, wherein the spindle has a passageway therethrough capable of allowing the filler material to pass therethrough and wherein the passageway through the spindle communicates with the passageway through the friction stir welding tool. Further, a filler material feeder is provided that is capable of feeding the filler material, wherein the filler material feeder feeds the filler material into the passageway through the spindle, and a device capable of holding a workpiece.
In another aspect of the present invention, a friction stir welding met
Arbegast William J.
Hatten Timothy E.
Dunn Tom
Edmondson L.
Lockheed Martin Corporation
Williams Morgan & Amerson P.C.
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