The finite element modeling of the resistance spot welding Process

The weld nugget in resistance spot welding of Type 347 stainless steel was found, using f inite element methods, to initiate in a ring shape at a distance from the electrode center. The ring-like weld nugget expands inward and outward during the welding cycles. The welding current, electrode pressure and hold time affected the thermomechanical interactions of the welding process and changed the f inal nugget geometry. Also, when spot welding workpieces of unequal thicknesses, it was found that the weld nugget formed mostly in the thicker workpiece than in the thinner workpiece, and when spot welding dissimilar materials, the weld nugget formed more in the workpiece of lower thermal conductivity or higher electrical resistivity.

Modeling of resistance spot weld nugget growth

Discontinuous contact of an anisotropic half-plane and a rigid base with disturbed surface

The contact resistance of several aluminum alloys with different surface conditions was measured as a function of the applied current and under different applied loads. The magnitude of the contact resistance varied over a wide range of values, depending upon load and surface condition. Usually the contact resistance decreased with an increase in load, but if a surface lubricant was present, an increase in resistance was observed. Extensive plastic deformation occurred under the loading conditions imposed by the electrode tips. A cup and cone profile was found at the contact region of the faying surface after unloading. Under slowly varying currents, ∼1 Ms, electrical breakdown effects were observed when the potential across the surfaces was ∼0.2 V. The nature of the change was ascribed to metallic conduction and local fusion rather than oxide film breakdown. Under rapidly varying currents, ∼10 7 A/s, typical of a spot welding operation, the contact resistance was found to decrease to ∼20 pΩ within the first quarter cycle of weld current, irrespective of the initial surface condition of the aluminum alloy. Continued weld current inputs caused a further decrease in the contact resistance to ∼10 pΩ. It is concluded that the results of contact resistance tests may be influenced by the test procedure if large currents are used that develop a significant potential difference, >0.2 V, across the interface.

A.O. Cakiroglu

Papers

Interface separation for an elastic layer loaded by a rigid stamp