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Increasingly stringent requirements for auto safety, fuel consumption and environmental friendliness require lightweight and efficient vehicle designs. Advanced High Strength Steel (AHSS) tubes, including hydroformed tubular parts, are one of the key enablers used today. However, conventional tube joint designs, in general, are difficult to utilize with spot welding processes, a preferred and commonly used assembly process in North America's automotive industry. This is particularly true for light gauge tubes. In this paper, a new tube joint design is proposed and this new proposed joint is applicable for spot welding, adhesive bonding, and other joining methods. From a performance perspective, this joint design utilizes the advantages of the box joint, which distribute load more uniformly through the whole joint structure, and thus it provides better stiffness and stability to the vehicle structure.

Static and dynamic strength tests were performed on spot welded specimens made of dual-phase (DP) 780 and mild steels (DQSK). Lap-shear (LS) and cross-tension (CT) as well as a new mixed mode specimen were studied using MTS hydraulic universal testing machine for static tests and drop weight tower for dynamic tests. Three weld nugget sizes were made for each steel and CT and LS. DP780 with one weld size was also tested in mixed mode. Load and displacement as functions of time and fracture mode of the spot welds were recorded. Representative data are reported in this paper.

The risk of skid lines for Class A panels has to be assessed before releasing the die development for hard tooling. Criteria are needed to predict skid lines in the formability evaluation stage to avoid expensive changes to tooling and process for resolving skid line issue in production. In this study, criteria using three different measured parameters were developed and validated. A draw-stretch-draw (DSD) test procedure was developed to generate skid lines on lab samples for the physical evaluation. This was done using tooling with various die entry radii and different draw beads. The skid line severity of lab samples was rated by specialists in the inspection of automotive outer panel surface quality. The skid line rating was correlated with geometric measurements of the lab samples after the DSD test. The sensitivity of the appearance of skid lines to tooling and process parameter variations was identified.