Research On Hot Forming Limit Numerical Simulation Of High Strength Steel B1500HS And Its Application

Hot stamping process is an important approach to improve the car collision safety performance and through the parts’ thickness and parts’ numbers reduction to achieve lightweight automobile body. It has aroused automobile industry’ and researcher institutions’ wide attention. In the hot stamping process,a high strength blank is heated up austenitizing temperature and after complete austenitization, quickly transferred to the press and subsequently stamped and quenched in the hot stamping die. The hot stamping process can effectively solve some forming defects like difficult forming and large amount of springback etc. And the hot stamping parts have much higher strength and hardness than cold stamping parts, which strength can reach more than 1000 MPa.The forming limit curves is the most intuitive and effective judgments of sheet metal forming. Due to many factors like temperature, strain rate, microstructure, the friction at high temperature, strain measurement etc, make the research of hot forming limit curves is very little. In the industry, it remain as a key thickness reduction as failure criterion of hot stamping parts. In the this paper, the hot forming limit curves’ finite element prediction models of high strength steel sheet B1500 HS based on Dynaform is set up to build isothermal forming limit curves at 700~900℃, and which is verified by isothermal Swift deep drawing tests. Finally the box hot stamping finite element simulation model is developed with hot forming limit curves depended on temperature(T-FLC) to research formability of high strength steel sheet. The main research content of this article is as follows:(1) The isothermal uniaxial tensile tests with different temperature and different strain rates were conducted to study the influence of temperature and strain rate on the stress and strain values. And a viscoelastic rheological model was developed based on Inouse Katsuro rheological model and a softening coefficient Z to describing the rheological properties of the high strength steel sheet at high temperature.(2) Combined with a small amount of hot forming limit tests, the isothermal and non-isothermal hot forming limit prediction model is developed, and the effects of tool’s temperature on forming limit curves was studied. And the isothermal Swift deep drawing tests were carried out to verified the reliability of isothermal forming limit curves.(3) A 2D hot stamping finite element simulation model of tools which is designed by our research group to make sure the best parameters like cooling water velocity,quenching time and stamping speed of hot stamping process. And on this basis, a 3D box hot stamping finite element simulation model is developed with hot forming limit curves depended on temperature(T-FLC) as the failure criterion to study the influences of initial stamping temperature of high strength steel, holder force and friction coefficient on formability.