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AssigneePaul Opprecht
InventorWerner Urech
Estimating the term…
Spot- and projection-welding of aluminum sheets has always been connected with difficulties mainly because of the surface layers of aluminum oxide, and even by pickling, these difficulties could be only partly eliminated. The main difficulties have always been insufficient electrode life times, the unsatisfactory quality of the weld and especially the unsolved problem of achieving good quality welding and long electrode-life when using un-pretreated aluminum sheets. The problem has been solved in principle by using electrodes having profiled contact-surfaces, by means of which the layer of oxide is broken during pre-pressing and a direct contact between the electrode and unoxidized material of the workpiece is provided, the contact-resistance of which is lower than the portion of the overall resistance of the point of weld formed by the metal of the aluminum sheets to be welded together. In an appropriate welding machine, the means for switching-on the welding current are controlled in such a manner that the welding current is switched on only after a sufficiently large contact area and therewith a sufficiently low contact-resistance of this contact has been reached.
In an electrical resistance-pressure-welding process for welding together parts of aluminum metal and/or its alloys carrying a surface layer of aluminum oxide, by a welding current supplied through opposed electrodes, each provided with a resilient electrode follow-up, in which the parts to be welded together are first pre-pressed together by means of said resilient follow-up before the welding current is switched on and such pressure is continuously maintained during the flow of welding current, the improvement wherein at least one of the surfaces of such parts facing the electrodes is superficially deformed plastically during said pre-pressing without penetrating the part thickness to thereby disrupt the surface-layer of aluminum oxide at the locations of deformation and bring substantially unoxidized metal of said part thus exposed into direct pressure contact with the adjacent electrode, the extent of the resultant direct contact between the electrode and the substantially unoxidized metal being sufficiently large that contact-resistance across the interface between each such electrode and the corresponding part is significantly lower than the resistance at the point of weld between the parts, and the duration of welding and welding current are controlled in relation to each other so that the temperature of such electrode at said interface is below the alloying-on temperature of the metal in contact therewith.
In an electrical resistance-pressure-welding apparatus for welding together parts made of aluminum metal and/or alloys thereof and having surface layers of aluminum oxide, comprising electrodes for supplying welding current to the parts, means for switching on the welding current and means including a resilient electrode follow-up for at least one electrode for pre-pressing the workpiece-parts to be welded together, before the welding current is switched on, and for maintaining a continual pressure upon the parts to be welded together during the flow of the welding current, the improvement wherein at least one of the electrodes is provided with means for causing superficial plastic deformation of the adjacent part surface during the pre-pressing to thereby disrupt said oxide surface-layer and bring substantially unoxidized metal into direct contact with the electrode, and including means for controlling said switching-on the welding current in response to the achievement of sufficient plastic deformation of said surface that the contact resistance across the interface between each such electrode and the corresponding part is significantly lower than the resistance at the point of weld between said parts, and means for regulating the duration of welding current flow and the magnitude of the welding current in relation to each other so that the temperature of the electrode at said interfaces can be maintained below the alloying-on temperature of the metal in contact therewith.
Dependencies are inferred from the claim text.