Metal fusion bonding – Including means to provide heat by friction between...
Reexamination Certificate
1999-01-22
2001-10-09
Elve, M. Alexandra (Department: 1725)
Metal fusion bonding
Including means to provide heat by friction between...
C228S013000, C228S112100, C228S019000
Reexamination Certificate
active
06299048
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plant for friction stir welding, comprising a welding probe, a drive unit driving the welding probe, a work table supporting the workpiece or workpieces to be welded, and at least one clamping means for clamping the workpieces to one another and/or to the work table or the workpiece to the work table, respectively, during the welding operation.
DESCRIPTION OF THE RELATED ART
The definition friction stir welding designates a welding method according to which the workpieces to be joined together are plasticized along their joint line by supply of frictional heat from a rotating welding probe which is caused to move along the joint between the workpieces while at the same time being pressed against the workpieces. As described in WO93/10935 and WO95/26254 the welding probe should be manufactured from material harder than the workpieces, and during the welding operation the workpieces should be securely fixed relative to one another and to the work table. In this respect this technique differs from that of conventional friction welding according to which the frictional heat is generated by the relative motion of the workpieces as they are being pressed together, i.e. the frictional heat is generated only by the two components to be joined together. This welding technique according to the above-mentioned publications is used for the welding of different materials, such as plastics, metals, etcetera in various fields of application, for example to join workpieces, to repair cracks in a workpiece, and so on. The configuration of the welding probe is conditioned e.g. by the material to be welded and by the intended application.
In the manufacture of ships, railway cars, bridges, oil platforms and so on extruded aluminium or aluminium alloy profile sections are of interest as building components in view of their corrosion resistance, light weight, etcetera. Because the dimensions of the profile sections produced today by the extruding technique are comparatively small and because the welding methods used at present for joining together aluminium profile sections fail to provide a wholly satisfactory result with respect to strength, finish, and deformation, aluminium has not gained but restricted use, despite the above-mentioned advantages that this material possesses.
By instead using the friction stir welding technique a joint is produced the bottom face of which has a fine and smooth finish, with resulting few points of load concentration. In addition, the strength of the joint produced by this joining method is almost equal to that of the basic material. One problem encountered when using the welding technique according to the above patent publications to join together aluminium profile sections is that this welding technique can only be used to join together workpieces separated by a very narrow air gap. Should the air gap exceed this critical value, which among other things depends on the thickness of the sheet metal from which the profile sections are made, a joint is produced having internal cavities and impaired strength. In consequence thereof, extruded aluminium profile sections that cannot be produced to exactly precise dimensions by existing manufacturing methods, require some pre-treatment to avoid too large gaps between the profile sections. This is particularly important in the case of the welding together of elongate profile sections, in which even small deformations may give rise to unacceptable deviations. To produce aluminium plating for hulls, aluminium profile sections having for example a width of 300 mm and a length of 12 m are used.
Another problem encountered in friction stir welding is that deformations of the profile sections may occur also during the welding operation proper, as the sections are exposed to the effects of heat. However, this deformation is of lesser magnitude than in the case of MIG and TIG welding, since the temperature never reaches the melting point. However, the result may be that the dimensions of the end product fail to be within the acceptable tolerance range, despite the pre-treatment of the profile section. This problem is encountered also in applications wherein the tolerance range of the end product is narrower than that of the participating workpieces.
SUMMARY OF THE INVENTION
One object of the present invention thus is to provide a plant for friction stir welding, enabling two workpieces to be welded together in such a manner that the resulting end product is imparted high strength and falls within a specified tolerance range without the profile sections having to be subjected to a pre-treatment in a particular unit prior to their being presented to the plant or in between the discrete welding operations. In this manner, production time as well as production costs are reduced.
Another object of the present invention is to provide a plant for friction stir welding, wherein it is possible to produce an end product having a narrower tolerance range than the participating components.
These objects are obtained in accordance with the present invention by means of a plant for friction stir welding of the kind defined in the introduction, which plant is characterised in that it also comprises a milling tool.
Because of the incorporation in the plant of a milling tool it becomes possible to effect a milling operation before and/or after each separate welding operation, which ensures acceptable tolerance ranges in the discrete aluminium profile sections as well as the formed aluminium panels without the sections or panels having to be passed through an external pre- or post-treatment unit. An additional advantage is that the aluminium profile sections will be given such a degree of straightness in the milling operation that the inter-workpiece air gaps do not exceed the value at which a faulty joint is produced.
The welding probe may be exchangeable for the above-mentioned milling tool and preferably the latter tool is driven by the drive unit serving the welding probe. Alternatively, the welding probe and the milling tool are driven by separate drive units. In the latter case, the milling tool may be positioned adjacent the welding probe or be positioned remote therefrom.
The plant could also be formed with a recess in the work table in front of the milling tool in order to enable milling operations to be performed throughout the thickness of the workpiece. In this case, the operative position of the milling tool must be separate from the operative position of the welding probe, since during welding direct backing of the joint from the working table is essential in order to achieve a smooth bottom face of the joint. The clamping means could be placed in the same or in different positions during welding and milling whereas the workpiece must assume different positions laterally during the welding and the milling operations. As a result, deactivation and activation, respectively, of the clamping means is effected to release and re-clamp the workpiece.
The plant could likewise comprise a spacer member which is placed intermediate the workpiece and the working table when the milling tool is in its active position. owing to this arrangement, the clamping means and the workpiece may assume the same position laterally during welding and milling, obviating the need for making the clamping means laterally displaceable. From a machine-constructional point of view this is a considerable advantage.
REFERENCES:
patent: 4043497 (1977-08-01), Jones
patent: 5794835 (1998-08-01), Colligan et al.
Burns Doane Swecker & Mathis L.L.P.
Elve M. Alexandra
Esab AB
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