Study on laser spot pattern design for joining ultra high strength steel

This study aims to find the effect of spot welding pattern prior to designing a laser spot welding device for joining ultrahigh strength steel; spot welding is a favorable method for those metals. Since the joining strength is influenced by nugget formation in welding, numerical investigation was performed with respect to single lap joints having three spot welding patterns, 'C', 'O', and 'S' type patterns. In FE constructions, welded material and base metal were individually modeled to have their own mechanical response. To characterize the parent material, tensile tests and notch strength tests were carried out. On the other hand, to extract the mechanical response of the welded material, flat specimens with heat affected zones were tested using Digital Image Correlation measurement. As a result, single lap joints with shapes of 'C' and 'S' showed 5% greater joining strength than that of the 'O' type pattern joints.