| The hot stamping forming process of ultra-high strength steel is becoming hotresearch to meet the need of car lightweight to ultra-high strength steel. Temperaturestatus in every time of sheet steel is the key factor to impact the hot stampingformability when forming. Thus, this dissertation presents a research on ultra-highstrength steel(UHSS) BR1500HS, by establishing hot-force coupling finite elementmodel of left anterior column, optimized the pressing way and parameters of performingprocess, solved the forming defects, such as cracking, wrinkling, fold material and so on,which caused by unreasonable design of pressing surface, inappropriate choice of hotstamping technology and unscientific choice of forming technology parameters.The main works of this dissertation are as follows.①Rresearch on the formability of ultra-high strength steel(UHSS) BR1500HS. Gleeble1500thermal simulator was used to do high-temperature thermal-simulation tensile teston BR1500HS. Meanwhile, take control of the real tress-strain curve of the material atdifferent temperature and different strain-rates. The effects of temperature andstrain-rates on high temperature rheological behavior of sheet metal are summarized.Through analyzing the experimental results in SPSS, the effect of temperature turns outto be most significant. It is analyzed and showed that the BR1500HS forming has goodthermoplasticity when the temperature is between900-950℃.②The influence of pressing way on hot stamping formability of ultra-high strengthsteel(UHSS) BR1500HS. By analyzing the influences of A and B the two pressingways on temperature field, equivalent strain and wall thickness of sheet metal when hotstamping forming. Type B pressing way was adopted, because dropping speed of sheetmetal temperature is more slowly, material flowing is better distributed when using typeB, so formability of hot stamping is better. This pressing way reduced sheet steeldefects caused by the unreasonable choose of pressing way and the rapid decline oftemperature of sheet steel when forming, efficiently. It provides important reference forchoosing the pressing way of hot stamping process when research the hot stampingforming process.③The influence of different hot stamping forming process on hot formability ofultra-high strength steel(UHSS) BR1500HS. For the cracking defects of left anteriorcolumn appeared in hot stamping direct process, it was forced on to control the temperature of sheet steel when forming, put forward the indirect forming technology toreduce forming defects of sheet metal, analyzed the causes why the indirect process canimprove the formability of material. And it’s the first time to discuss the influences ofblank-holder force and deep drawing trip on hot stamping formability when usingindirect process for cold preform in this paper.④Resolved the key problems of mould design in hot stamping forming, such asthe choose of locating equipment of sheet steel, the design way of mould cooling waterchannel, the material of mould and so on. and completed the manufacture of hotstamping for the left anterior column. After doing the test for the accuracy of specimensand the analysis for slice metallographic of specimens, obtained the parts which meetprocess requirements.Compared the test results with the simulation results of finite element analysis, theanalysis shows that the theory and practical results have a good match, this verified thereliability of finite element simulation analysis theory for hot stamping forming,provides effective reference for hot stamping forming technology of high strength steelplate in real application. |
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