Research On Springback Prediction And Control For Hot Stamping Of Tailored Strength Parts

With large number of high-strength steel applying in automotive, hot stamping technology has been improved gradually. But in the past hot stamping can get a part that only has one expected performance. However, more special requirements have been put forward with the development of intelligence and individualization in machinery industry. Based on the request of B-pillar, which should be designed to have high strength to resist deformation at the top and low intensity to absorb energy at the bottom, this article simplifying it to a T-piece, this article studies the springback prediction and how to reduce it by achieving tailored strength stamping process.The springback mechanism is analyzed based on high-strength steel hot stamping, especially the stress change, which is the basic reason causing springback. The specific reasons are introduced in detail, including the springback caused by unloading of external force, unbalanced hot stress and structural stress.The finite element model is established with DYNAFORM. The software is modified to obtain different temperature in heating, transiting and cooling zone, perfecting the function of the thermal coupling analysis. In order to study the influence rule of friction coefficient, sheet thickness, holding time, pressure, and heating temperature, numerical simulations have been done to predict springback, which can get the change of stress and temperature field.Establishing the platform of high-strength steel hot stamping to make experiments about friction, pressure, holding time and heating temperature. To control the heating temperature automatically a program is wrote with PLC. Trends and patterns of springback in numerical simulation prediction is verified, determining the reasonable parameters, namely pressure is 30 MPa, holding time is 10 s, the heating zone temperature is 450℃, friction condition is in a natural state.The controlling measures are taken based on the size and place of springback produced in simulation, mainly through compensation and adjustment of parameter. Taking into account every error after compensation, reasonable compensation factor calculation is put forward. Finally, a final qualified mold surface can make the springback angle within 0.5°and the displacement less than 5mm after adjustment of parameters, twice compensation for the overall and local mold.