Experimental Investigation of Springback Variation in Forming of High Strength Steels

The use of high strength steels (HSSs) in automotive body structures is a prominent method of reducing vehicle weight as an alternative to use of aluminum and magnesium alloys. However, parts made of HSSs demonstrate more springback than parts made of mild steels do. Moreover, variations in the incoming material, friction, and other process conditions cause variations in the springback characteristics, which prevent the practical applicability of the springback prediction and compensation techniques. Consequently, it leads to amplified variations and quality issues during assembly of the stamped components. The objective of this study is to investigate and gain an understanding of the variation of springback in the forming of HSSs. Two sets of experiments were conducted to analyze the influence of the material property (dual-phase steels from different suppliers), lubrication, and blank holder pressure on the springback variation. The experimental results showed that the variation in the incoming blank material is the most important factor. In summary, the thicker the blank is, the less the springback variation. On the other hand, blanks without a coating show less springback variation. The application of lubricant helps us to reduce springback variation, although it actually increases the springback itself. The more uniform the friction condition, the less the springback variation. The influence of blank holder pressure on the springback variation is not distinguishable from the system-level noise in our experiment.