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Abstract
In order to expand the application of high strength steel sheets to automotive bodies, stabilizing nugget diameter of resistance spot welds is required in the presence of several industrial disturbances. This study aims to ensure the nugget diameter of high strength steel sheets regardless weld spacing by utilizing adaptive control technology based on real-time feedback of heat quantity. Short weld spacing leads to expulsion from the sheet surface applying conventional adaptive control welding for mild steel sheets, whereas decrease in nugget diameter due to reduction of effective welding current for high strength steel sheets. On the other hand, two-stage adaptive control method enables to ensure nugget diameter regardless of steel strength even with 10 mm weld spacing, in which heat quantity was controlled independently in each stage of welding. The mechanism of these phenomena was revealed by verifying the influence of physical properties of steel and welding current pattern on the shunting phenomena using numerical simulation.