In this program, the capabilities of medium-frequency direct current (MFDC) electric servo resistance welding guns for the welding of complex stack-ups were investigated. Capabilities of interest from these guns include the ability to apply forge forces and currents, as well as the ability to sequence the current and forging profiles. The complex stack-up under study included a 1-mm outside sheet attached to two 2-mm sheets. Work was done using design of experiment (DOE) techniques. The experiment included a range of processing variations deliverable from the MFDC servo-gun, as well as two electrode variations (materials and sizes). Heat balance during resistance welding of this stack-up was found to be dominated by the electrode variations. As electrode variations are not considered a solution for automotive complex stack-up applications, a best practice was defined from the DOE that included similar-sized class 2 electrodes. This best practice included short overall weld times, a moderate forge force, a significant (40 %) increase in current during forging, and a weld time relative to the forging portion of the weld schedule. This yielded nugget penetrations of roughly 50 % into the thin attached sheet. It was noted that, at these penetrations, indentations on both sides of the joint reached 0.45 mm and that process variations could be used to trade off penetrations with overall indentations.
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The EWI acknowledges the contribution of the State of Ohio, Department of Development and Thomas Edison Program, which provided funding in support of Edison Technology and Industry Center Services.
Doc. IIW-2275, recommended for publication by Commission III "Resistance Welding, Solid State Welding and Allied Joining Processes"
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Gould, J., Peterson, W. & Cruz, J. An examination of electric servo-guns for the resistance spot welding of complex stack-ups. Weld World 57, 243–256 (2013). https://doi.org/10.1007/s40194-012-0019-x
Keywords (IIW Thesaurus)
- Resistance spot welding
- Heat balance
- Electric servo-gun
- Design of experiments