Simulation Study On Thermal Cycle,Stress And Fatigue Of Aluminum Alloy Die-Casting Dies

Thermal fatigue cracking is one of the main failure form of die-casting dies,which is due to the thermal stress induced by the heating and cooling cycles in die-casting.Therefore,in order to predict the fatigue life and failure position of actual aluminum alloy die-casting die,the temperature,stress and strain changes during die-casting cycle were solved,and the life was calculated based on the reported fatigue life model.The research is helpful to simulate the temperature change of die-casting cycle more accurately,so as to optimize the process and die structure,improving the quality of casting and prolonging the life of die.Firstly,an experimental device for spray cooling of H13 steel was designed to simulate the actual spray process of die casting molds,thourgh spray experiments at different spray pressures and heights,temperature changes of H13 steel plate were measured.Based on Beck's inverse method,the change of interfacial heat transfer coefficient(IHTC)of the molds during the spray process was solved.The influence of different spray pressures and heights on change of the wet region and the IHTC were analyzed and discussed.A circulating temperature field calculation program was designed on a finite-difference method-based(FDM)casting simulation software ICAST(development version),according to the die-casting process.In the program,the IHTC during spray process was imported as the boundary conditions of the temperature field simulation in mold-opening stage.The actual diecasting experience of ADC12 aluminum alloy regulating wheel was carried out,in which temperature changes of fixed and movable die during the cycle were measured.The cycle temperature field was calculated by the program,which was compared with the measured result,it came out that the two were in good agreement during the die-casting cycle.Taken the mold temperature field during the die-casting cycle as the load,the thermalmechanical coupling numerical simulation of the die-casting die was carried out based on the finite-element-method-based(FEM)software ANSYS Mechanical,in which the stress-strain relationship of H13 steel under different temperatures was considered.The stress and strain of the actual aluminum alloy regulating wheel die-casting die were simulated,and the local fatigue life of the die was predicted based on the strain-based and temperature-based fatigue models of H13 steel reported in literatures.Sampling and analysis were made from the fixed die core of the actual die,in which crack widths were measured by scanning electron microscopy(SEM)and the 3D surface morphology of the die core was observed by using a 3D optical contour scanner.The relationship between the simulated results and the crack characteristics as well as surface morphology was analyzed,it showed that simulated stress and strain level had an important effect on the surface morphology of the die.Through the comparison between the die life simulation prediction and the actual use of the regulating wheel die casting,it was found that the fatigue model of H13 steel based on temperature agreed with the actual die casting situation.