Metal fusion bonding – Process – Using dynamic frictional energy
Patent
1996-09-26
1998-09-29
Heinrich, Samuel M.
Metal fusion bonding
Process
Using dynamic frictional energy
228 21, 156 735, 156580, B23K 2012
Patent
active
058135928
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of friction welding for joining of (metal) members and more particularly to so-called friction stir welding based on a relative rubbing movement between a probe of harder material and members to be joined. The present invention also is directed to an improved tool to be applied in the friction welding process.
Friction welding based on the principle of "rubbing" of articles to be joined together so as to generate a sufficient amount of heat, thus generating plasticised conditions in the adjacent surfaces, has been known and practised for several decades. The frictional heat is generated solely by the two to be joined components. However, the resulting weld seams suffer from a number of disadvantages inherent in the applied processes. The main drawback which considerably limits the applicability of friction welding is that at least one of the components to be welded has to be axis-symmetric. Consequently, such process is not applicable for e.g. structural applications requesting provision of longitudinal continuous welds.
The improved version of this welding so-called friction stir welding, is known from W093/10935. A probe (third body) of a narder material than the treated workpieces is applied in the welding process. Friction stir welding is based on a relative cyclic movement between the probe and the workpieces, urging the probe and workpieces together to create a plasticised region in the workpiece region due to generated frictional heat, stopping the relative cyclic movement and allowing the plasticised material to solidify. Thus no heat is generated due to a relative motion between the workpieces to be joined. The method is illustrated by several examples of different workpiece materials (plastics, metals), applications (reparation of cracks, sealing, joining) and embodiments of the applied probe.
Neither the above disclosed method and apparatus, when applied for joining of extruded shapes into structures for critical applications, can meet the request for high integrity welds free from voids and proper metallurgical bonding of structural parts, nor a demand for provision of welds in a lap configuration.
In order to achieve a proper consolidation of the weld metal the probe bottom part (shoulder) must maintain during the whole welding operation (forward movement) in an intimate contact with surface of the joined members. If the probe shoulder during this forward movement even temporarily "lifts" from the surface a small amount of plasticised welding material will be expelled behind the probe thus causing occurrence of voids in the-weld since there is no available material to fill the vacant space after the expelled material.
Furthermore there is another limitation connected to use of "smooth" welding probe known from the prior art, namely low welding speeds are required in order to achieve a sufficient frictional heating of the material (contact time between the probe and the joined members), and to ensure a sufficient flow of the plasticised welding material.
It is therefore an object of the present invention to provide an improved method of friction stir welding, ensuring high integrity welds free from voids and exhibiting a smooth quality surface.
A further object of the invention is to improve the present known friction stir butt welding method to provide also lap welds and three or more components joint configuration.
Another object of the present invention is to provide a new type of probe ensuring uniform homogenized weld seams exhibiting reduced heat affected zone.
The above and other objects are achieved in accordance with the present invention by provision of a method for friction stir welding and an apparatus (probe) as defined in the accompanying claims 1 and 7, respectively.
Other objects, specific features and advantages of the present invention will be apparent from the following detailed descriptions of preferred embodiments with reference to the accompanying drawings, FIGS. 1-5, where:
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic
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Midling Ole Terje
Morley Edward James
Sandvik Anders
Heinrich Samuel M.
Novack Martin M.
The Welding Institute
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