Formability Enhancement Of High Strength Steel And Finite Element Analyses On Pvd Coated Die For Sheet Metal Forming

Abstract

High strength steels are most widely used in automobile industries due to their superior mechanical properties and light weight. However, the formability is poor compared to conventional steels due to high hardness and carbon equivalent. Several approaches are in use and in development to enhance the formability of high strength steel sheets, mainly by adjusting the process parameters and material properties. Process parameter, such as, contact with friction condition between the forming tools and the blank can be modified to enhance formability of high strength steel. Many grades of steels are used in automobile industries to introduce superior performance characteristics while retaining high strength-to-weight ratio. Strenx 700 CR EN10131 steel is one such steel widely used in automobile industries, which is extensively studied in this work. In this work, the forming die is coated with Titanium aluminium nitride (TiAlN) and the effect of TiAlN thin film coating on the formability of EN10 131 high strength steel is investigated. A small circular cup geometry was chosen for deep drawing experiments and Taguchi technique have been applied to design the experiments with different levels of the process parameters. The novelty of this study lies in the use of surface coating on the forming tool to modify the friction conditions that exist between high strength steel blank and the die. Tribological characterization was carried out on AISI D2 steel coated with TiN, AlCrN, TiAlN, DLC and WC-Co PVD coatings. TiAlN coating on the die has improved the formability of steel considered. The analysis of variance is carried out to study the influence of process parameters on the maximum punch force and their contribution was computed. Contact with friction condition plays a major role, in addition to the blank diameter, in improving the sheet metal formability. The quality of the deep drawn part, in terms of thickness distribution, is influenced by TiAlN newlinecoated die surface. The experimental results were compared with simulation