Resistance Spot Welding (RSW) Process Optimization for Uncoated 1.0 mm Boron to Uncoated 1.0 mm Boron for Automotive Applications

There has been a substantial increase in the use of advanced high strength steel in automotive structures in the last few years. The usage of these materials is projected to grow significantly in the next 5–10 years with the introduction of new safety and fuel economy regulations. Advanced High Strength Steels (AHSS) are gaining popularity due to their superior mechanical properties and weight advantages, as compared to mild steels. These new materials also pose significant manufacturing challenges, particularly for welding and stamping. Proper understanding of the weldability of these materials is critical for successful application on future vehicle programs. Due to the high strength nature of AHSS materials, higher weld forces and longer weld times are needed to weld AHSS materials. In this paper, weld lobe development for 1.0 mm uncoated boron to 1.0 mm uncoated boron 2T stack-up combination is discussed. Weld lobes were developed with Mid Frequency Direct Current (MFDC) equipment, ISO type B-16 tip, constant weld force of 3.43 kN (770 lbf), hold time of 5 cycles and the weld times were varied 10, 13 and 16 cycles. Based on the tensile, cross-tension and nugget data, there were no correlations were observed between tensile load and button size and also between cross-tension and button size. Microhardness data assessment found heat affected zone (HAZ) at the weld nugget area and similar HAZ was observed for all the welding cycles. The weld lobes, mechanical properties (tensile shear and cross-tension), cross-section examination, and microhardness of 1.0 mm boron to 1.0 mm boron 2T stack-up results are discussed.