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Abstract

A process and apparatus for projection welding of overlapping nonferrous sheets, particularly thin aluminum sheets. One of the sheets is provided with a projection therein, and the sheets are positioned so that the tip of the projection contacts a surface of the other sheet. The sheets are not subjected to surface pretreatment to remove the surface oxides therefrom. A projection welding head assembly is positioned with the electrode thereof engaged with one of the sheets, and the other sheet is positioned against a stationary backup or electrode. The electrode of the welding head imposes, in rapid time succession, a series of welding pulses to the overlapping contacting sheets. The series of welding pulses includes two and preferably three pulses which progressively step up in amperage to provide for precise control of the heating of the projection and the associated contact area on the other sheet to cause heating to the plastic state, and then forging (i.e. collapsing) of the projection with subsequent and progressive creation of the desired weld nugget. The series of weld pulses also preferably includes, at the end of the series, one or two pulses which progressively step down in current magnitude to permit greater control over the plasticity of the projection and the forging together of the overlapping sheets to create the desired weld bead.

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First Claim