Dr David R Sigler
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The multi-ring domed (MRD) electrode weld face incorporates geometric features that include protruding circular rings. The rings of the electrode induce high levels of local strain on the outer surfaces of the aluminum to be welded, which breaks down the hard, insulating aluminum oxide layer inherent on all aluminum materials, enabling intimate contact between the electrode and aluminum metal. This reduces the contact resistance at the electrode/surface interface, leaving a higher faying interface resistance to initiate and develop a weld nugget under controlled conditions. The greatest benefit of this technology is the large resistance spot welding process window that it displays for welding of aluminum sheet, extrusion, casting, or combinations thereof, while also achieving high weld quality and eliminating surface expulsion. Furthermore, the technology is based on standard resistance spot welding equipment. The MRD electrode is created from standard electrodes for welding steel by tip dressing with a specially designed blade. A common weld gun can be used for welding either steel or aluminum, and lastly, a single MRD domed electrode can weld either steel or aluminum in the same cell, eliminating the need for material-dedicated equipment. © General Motors. Presented at: SME Annual Conference, June 2-4, 2013, Baltimore, MD.
By Philip D Rufe, CMfgE
By Ahmad K Elshennawy, Gamal S Weheba, PhD