| With the rapid development of China's auto industry,the car's lightweight and safety performance has received increasing attention.Since the ultra-high-strength steel sheet after hot stamping has the advantages of light weight and high strength,in order to meet the needs of the industry,the application of ultra-high-strength steel sheets on automobile bodies is increasingly widespread.Compared with ordinary cold stamping,the mold used in hot stamping technology not only bears a large pressure to maintain during the forming process,but also needs to withstand large fluctuations in temperature,so the hot stamping die is easy to fail and has a low service life.The design of the cooling system of the thermoforming mold not only affects the structural strength of the mold,but also has a great influence on the temperature change of the mold.Therefore,this paper takes the automobile B-pillar mold with low fatigue life designed by a company as the test object,and studies the influence of the cooling system of the thermoforming mold on the fatigue life of the mold.The main tasks are:Firstly,according to the B-column mold structure parameters,the simplified U-shaped mold model is established by UG modeling software.Then the FLUENT software is used to calculate the heat transfer coefficient of the simplified mold cooling system,and then the heat transfer coefficient is imported into LS-DYNA to simulate Thermal fluid-solid coupling calculates the mold stress results.Analyze the variation characteristics of stress under the combined action of temperature and pressure during hot stamping.Secondly,the orthogonal test design of the U-shaped mold cooling system is carried out.The three factors affecting the temperature and stress distribution and the numerical value of the pipeline design: the pipe diameter,the two pipe spacing and the distance from the upper profile are orthogonally designed.Nine groups of models were established,and the test results were analyzed.The effects of various factors on mold stress and fatigue life were obtained.The fatigue life of the optimized U-shaped mold model is improved.Finally,a set of B-column mold model is geometrically processed to extract the cooling system inside the mold.The convective heat transfer coefficient of the cooling system is calculated by FLUENT software,and the heat transfer coefficient is imported into LS-DYNA and set according to the process parameters provided by theenterprise.The parameter conditions were calculated to simulate the mold temperature and stress results by simulating heat flow-solid coupling.By comparing the simulated sheet temperature results with the thermal image of the sheet in the actual production,the simulation method and the actual situation are verified.After that,the LS-DYNA analysis results were imported into nCode software,and the load spectrum and the material S-N curve were set.The fatigue life of the mold was calculated,and the fatigue life and the damage-prone parts of the mold were predicted.Research shows that optimizing the cooling system of hot stamping die can effectively improve the service life of the die;the maximum stress on the die may appear in the cooling waterway,causing cracking of the die;the temperature on the die is not uniform,and the cooling effect is poor.The fatigue life is also short.The simulation method used in this paper can calculate and analyze the large model like the B-pillar mold in practice,which provides a new idea for the simulation analysis of the hot stamping forming process. |
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