| In recent years,due to the need for energy saving,environmental protection and safety,the lightweight of automobiles has become the main development direction of the automobile industry.High-strength steel sheets for automobiles,especially advanced high strength steel sheets,have excellent properties such as high-strength,appropriate ductility,good formability,and very effective fracture toughness.They are appropriate for the manufacture of various body parts and have been widely used in the automotive industry.However,the high strength steel plate has poor plastic forming ability at room temperature,and the parts made by the cold stamping process are prone to springback and other problems,so that the parts cannot meet the requirements of product assembly.Therefore,how to reduce springback behavior in the stamping forming process has become an urgent problem to be solved in the field of automobile manufacturing.This paper takes DP980 high strength steel sheet as the research object,and uses ABAQUS finite element simulation to analyze its sheet springback under different temperature conditions with U-bending experiments as an example,and discusses the results of the influence of different groove structures and process hole orientations of the sheet on springback.The main research work and conclusions are as follows:(1)Based on the warm uniaxial tensile test of DP980 high strength steel,the rheological behavior of DP980 high strength steel at different forming temperatures and rolling directions was explored.The flow stress of DP980 high-strength steel sheet was less sensitive to temperature,and the flow stress decreased significantly when the temperature exceeded 300℃.With the increase of forming temperature,the elastic modulus and yield strength of DP980 high strength steel material decreased significantly,and under the same temperature conditions,the yield strength was the largest in the 90° direction and the smallest in the 45° direction.(2)Through finite element software,numerical simulation of U-bending hot stamping was established,and springback behavior of DP980 high-strength sheet under warm and hot stamping conditions was analyzed.It was found that the temperature can effectively reduce the springback.The springback of the sheet took into account the initial temperature,and decreased with the increase of the temperature.When the temperature reached 400°C,the bending springback angle reached the minimum.(3)The finite element numerical simulation of the bending process of the discontinuous structure sheet at room temperature is carried out,and the influence of the thickness,width,position and process hole direction of the groove on the bending springback is analyzed and discussed,and the U-shaped bending experiment is verified.The research results showed that the discontinuous grooved sheet can reduce the springback of the bending part,and the U-shaped bending springback gradually increased with the increase of the groove thickness,and gradually declined with the increase of the groove width.Under the same groove thickness and width,when the groove position was at the rate of the rounded corner of the punch,the springback angle was larger than that when the groove position was set at the rounded corner of the female die.When the direction of the process hole was different,the springback result of the sheet material was also unlike.When the process hole direction was 45°,the springback angle was the smallest,and when the direction of the process hole was 0°,the springback angle was the largest.In addition,compared with ordinary sheet at room temperature,the sheet with grooves and process holes has a smaller springback,indicating that the plate with discontinuous structure can effectively control the springback of high strength steel sheet. |
PDF Full Text Request