Study On Deformation Heat Of High Strength Steel DP780 During Warm Forming

In recent years,the development of automobile industry is changing with each passing day.In automobile production,more and more attention is paid to energy conservation and environmental protection,and the concept of automobile lightweight is becoming more and more important.From the perspective of automobile production and manufacturing,in order to realize the lightweight of the whole vehicle body and ensure the good crash safety performance of the vehicle,the use of high-strength steel plate in the whole vehicle manufacturing has become one of the main methods.Due to the high strength of high-strength steel plate,there are many problems in the cold forming process,such as large stamping pressure,easy fracture or excessive deformation of the workpiece,etc.;while in the hot forming process,for the surface of a workpiece,it is easy to be oxidized,poor surface quality,large energy consumption and other shortcomings.Warm forming technology is a new technology developed in recent years.This technology can make up for some shortcomings in the cold and hot forming of high-strength steel plate,and can also inherit their advantages.In this paper,the warm formability of DP780 high-strength steel plate is studied by the method of experiment and numerical simulation.Through the research of this paper,we can get a more in-depth and detailed understanding of the relevant properties of DP780high-strength steel plate and the relevant process of warm forming of this steel plate.Using MT5105 microcomputer controlled electronic universal testing machine of Jiangsu University,the hot tensile test of DP780 high strength steel plate was carried out in the range of 20 ? ?500 ?.By changing the temperature and strain rate,the relationship curve between the steel plate and the above two variables,i.e.true stress-strain curve,was obtained.The results show that the flow stress of DP780 decreases with the increase of temperature.However,when the temperature reaches300 ?,the flow stress will appear abnormal state,and it is also found that the flow stress increases with the increase of strain rate.Further study and analysis of theinfluence of the experimental temperature on the elongation,modulus of elasticity and Poisson's ratio of the material.The results show that when the temperature increases gradually,the modulus of elasticity of the steel plate decreases gradually,while the elongation and Poisson's ratio increase gradually,indicating that higher temperature and lower strain rate are conducive to the plastic deformation of the high-strength steel plate.In this paper,the cupping test of DP780 sheet metal is established,and the FLD of DP780 in the range of 20??500? is obtained.It is found that the forming temperature has a great influence on the FLD of DP780 high strength steel.In general,when the temperature rises,the FLD curve will also move up.However,when the temperature reaches 300?,the high-strength steel plate will appear "blue brittleness",FLC appears abnormal,indicating that the plastic deformation ability is lower than room temperature.The cup value IE is greatly affected by the forming temperature and punch speed.IE increases with the increase of temperature and decreases with the increase of punch speed.At the same time,increasing the width of the sample can reduce the forming force of the material.The results show that deformation at warm state is beneficial to improve the plasticity of high strength steel plate.In the ABAQUS / CAE simulation software,the simulation model of oil tank temperature stamping is established to study the influence of blank holder force,initial temperature of die and initial forming temperature of sheet metal on the stamping results of high strength steel DP780.It is found that 150 kn is the most suitable blank holder force for the stamping of oil tank by taking the final temperature and thickness distribution of sheet metal as the measurement standard and considering the quality of forming parts.If the initial temperature of the die is properly increased before stamping,the temperature distribution of the forming part will be more uniform,which is beneficial to the improvement of the structure and properties of the forming part.The smaller the minimum thickness of the shape.With the increase of the initial temperature of sheet metal,the temperature difference of sheet metal will gradually increase after the final forming,and the minimum thickness will be smaller.