Hot-Formed, High-Strength, Integrated Automotive Parts: Numerical Analysis and Process Optimization

Hot-forming, as a typical representative forming technology of high-strength steel (HSS), is one of the most effective ways to manufacture structural components for achieving automotive lightweighting goal. In this paper, a newly-developed commercial microalloyed hot-formed steel is selected and its hot-forming is studied by experiments and simulations. The new steel has a wide undercooled austenite region, providing more suitable condition for the manufacturing of one-piece large-sized integrated parts. The high-temperature mechanical behaviors of the investigated steel show that the flow stress obviously decreases with the increase in deformation temperature, and it increases with the increasing strain rate. An integrated component assembly of the rear floor and longitudinal beam is selected as a typical one-piece integrated part when performing the hot-forming simulation to evaluate the formability. The influences of the key process parameters, namely forming velocity and frictional coefficient, on formability are further analyzed. Finally, the Latin Hypercube Sampling (LHS) method is used to generate the parameter combination and the Response Surface Method (RSM) is adopted in optimization. As a result, an optimal process parameter combination is obtained and its predicted result matches the simulated one very well, with a relative error of only 2.57%. The research results of this paper are favorable for understanding the mechanical behaviors of the hot-formed steel at elevated temperatures, improving the formability and providing a reference for the development of large-sized integrated hot-formed parts.