Thermo-mechanical Coupled Modeling Of Hot Stamping Process And Tool Fatigue Analysis

Nowadays,the hot stamping boron steel is more and more widely applied to the body structures because of its high specific strength,which satisfies the increasing demand for lightweight and crash performance.The hot stamping technology can avoid many problems such as cracking and springback which often occur in the formation of HSS or AHSS.However,the hot stamping technology also has its weaknesses.The productivity is in low efficiency and the life of hot stamping tool is short.As the forming and quenching tool for boron steel at elevated temperature,die and punch are the keys to solve the above problems.As a result,it's significant to study the hot stamping simulation method and analyze the tool fatigue failure,which will promote hot stamping in a wider application.In this paper,a thermo-mechanical sequential coupling simulation method is designed which is of high precision and efficiency,and a fatigue life prediction model is also built in n Code for the hot stamping tool.Then,the fatigue failure causes of hot stamping tool was analyzed.Several factors' influence on the tool fatigue life and blank quenching effect is also analyzed which include tool structure,tool material and hot stamping process.The main contents include:The tool material's properties are measured which include the thermos-physical properties,mechanical properties and fatigue properties at elevated temperature.They will provide accurate material parameters for the simulation model.An experiment platform is built to measure the heat contact transfer between the tool and the blank at elevated temperature.The thermo-mechanical coupled FEM and the iterative optimization were used to compute the heat contact conductance coefficient reversely,which will provide the accurate boundary condition for the thermo-mechanical coupled modeling.A simulation model with high precision and efficiency is established.The thermal field and mechanical field are decoupled and solved separately.The 3D rigid element is used to establish the hot stamping sequential cycle simulation model which will calculate the tool's thermal field.Then the node contact forces between blank and tool is computed through Dynaform model.The above results are treated as thermal and mechanical boundary conditions to build a thermo-mechanical coupled model which will compute the stress field of hot stamping tool.A new automatic loading method is designed which will load the node contact force on 3D mold grid in accordance with the node number.Finally,the fatigue failure of hot stamping tool is analyzed in n Code based on the results of thermo-mechanical model and the S-N fatigue curve.The thermal field,thermal stress field,mechanical stress field and thermomechanical coupled stress field of the hot stamping tool are studied in the whole process of hot stamping.And the fatigue failure causes of the tool is analyzed.In order to prolong the hot stamping tool's working life and reduce the holding time,the tool structure,tool material and tool hot stamping process are analyzed and optimized,which will cut the cost of hot stamped parts.