Projection welding of steel weld-nuts to advanced high strength steel (AHSS) in automotive applications allow for the reliable mounting of critical components with different thicknesses to the vehicle body. However, the galvanized coatings commonly used on AHSS result in electrode surface degradation during welding. In this study, the electrode degradation and its effect on the mechanical properties of welded steel nuts and AHSS sheets are investigated. Two common electrode materials – tungsten/copper and beryllium-free class III copper – both display the formation of an oxidized alloy surface layer and pitting as weld number increases. Unlike resistance spot welding, where electrodes grow in the contact area diameter as they degrade, projection welding electrodes do not experience this type of mechanical degradation. Instead, increased resistance at the electrode interface with increasing weld number results in higher temperatures at the weld interface and a larger fusion zone size, which is responsible for an observed 30% increase in weld strength over the span of 10,000 welds.
Evaluation of electrode degradation and projection weld strength in the joining of steel nuts to galvanized advanced high strength steel
Manuscript received April 3, 2019; final manuscript received June 27, 2019; published online xx xx, xxxx. Assoc. Editor: Wayne Cai.
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Enrique, P. D., Al Momani, H., DiGiovanni, C., Jiao, Z., Chan, K. R., and Zhou, Y. N. (July 17, 2019). "Evaluation of electrode degradation and projection weld strength in the joining of steel nuts to galvanized advanced high strength steel." ASME. J. Manuf. Sci. Eng. doi: https://doi.org/10.1115/1.4044253
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