Coupled Thermo-mechanical CAE Analysis On Hot Forming And The Optimization Of Mold Process

Hot forming is new stamping process, which is combined with the heat treatmentof cold stamping. Hot forming mold was heated by hot blank and cooled by cold water,simultaneously, withstands pressure from equipment, which leads to the complicatedrelationship between mold temperature and stress. It will cause performancedegradation and thermal fatigue on hot forming mold, if cooling performance is poor.Cooling performance was directly affected by process parameters in quenching stage,studying on the sensitivity analysis of mold cooling performance on the parameters ofquenching process, so as to provide the basis for optimizing the design parameters ofthe quenching process.For the complexity of relationship and variation between hot-forming moldtemperature and stress, the research is focused on thermal coupling analysis in hotforming by using ABAQUS software. Analysis showed: punch-matrix fillet firstcontacts sheet and sustains for a long time, temperature focus in mould fillet thatleads to thermal stress concentration. Mold temperature reaches a maximum at thebeginning of quenching, then the cooling rate of mold temperature decreases withquenching going. Mold thermal stress changes325Mpa within2.5s, which variesfrequently and changes too much that can easily cause mold thermal fatigue. Thecomparison of mold temperature and thermal stress shows that thermal stress iscaused by temperature difference and changes with temperature. After measurement,the ratio of mold stress, thermal stress and mechanical stress is11.25:10.31:1, whichshows that the proportion of thermal stress in mold stress is very large.To study the effect of process parameters on mold cooling performance, carry outnumerical simulation on the quenching stage of hot forming with the help ofMPCCI,ABAQUS and FLUENT, analysis the sensitivity of mold cooling performanceon quenching process parameters. The results show: Increasing holding pressurecauses retention time of high temperature rise in mold, but it can enhance cooling rateof the mold; Low-temperature, high-speed cooling water has little influence onmaximum temperature during quenching, but it is effective to reduce retention time ofhigh temperature in mold, improve cooling rate of the mold, cut down moldtemperature after quenching; Raising quenching time can reduce mold temperatureafter quenching, but the growth of mold cooling performance is slow down with time going on; Mold cooling performance is most sensitive to holding pressure, which caneffectively improve mold cooling performance, and reasonable to reduce coolingwater temperature, raise cooling water rate, extend quenching time are helpful toimprove mold cooling performance.