Theory Research On Forming Characteristic Of High Strength Hot Rolled Sheet Metal

Automotive industry has developed very quickly in china these years, but it also caused a lot of environment problems. Consider of energy saving and air pollution reduction, as well as safety, high strength hot rolled sheet metals are widely used in structure parts in vehicles because of its low weight, high strength and low cost. However, high strength hot rolled sheet metals have some big defects, such as bad deformation performance and high spring back, so the traditional deformation evaluation system is not so suitable for them, but industry still use cold rolled sheet metals'deformation standards to guide high strength hot rolled metals'forming process, this will surely cause departures.This paper aims at determining a material mode that suits to high strength hot rolled sheet metals, hence, the results of FEA can direct the design of formability test tooling more reasonably. Furthermore, to get a complete forming performance value system for high strength hot rolled sheet metals.Firstly, three kinds of materials'deformation processes under uniaxial tensile, plane strain, equi-biaxial strain paths were compared respectively, so as to find a suitable constitutive equation and yield criterion for the following hot rolled materials, such as acid-washing steel QStE340TM, SAPH370, and galvanized steel ZStE260P. It's shown that Hollomon constitutive equation and Barlat (1989) yield criterion can reasonably predict strain paths of the materials mentioned above. Furthermore, the results under plane strain path best agrees with experimental data.Secondly, fracture criterion was studied in this paper. FLD (forming limit diagram) is the most common fracture criterion used in sheet metal forming simulation, its FLC (forming limit curve) is obtained by experiments, but it usually costs a lot to get FLC by experimental method. Here, FLC was forecasted with a few experiments by using a kind of minimum thickness criterion combines numerical simulation. Yield criteria Barlat 1989 was applied on forming limit simulation of three kinds of hot rolled sheet metals. Good agreement between predicted FLC and experimental FLC has been achieved by knowing the experimental data under plane strain. It means combining minimum thickness criterion with simulate data to derive FLC curve, only experiment data under plane strain path is needed, that will be a very efficient way to get FLC.Finally, FEA was used to analyze the drawing performance of those high strength hot rolled sheet metals. Limit drawing rate was forecasted and the sensitivity of cylinder drawing tooling was valued, besides, the main factors that affect lug height were also studied.