Study On The Mathematical Models And Temperature Measurement Tests Of Die-casting Die

Die service life is an important part of the cost of die casting.Thermal fatigue failure is the main factor that affects the life of die casting die.During die casting process,the thermal loads of the cavity surface are the results of the heat conduction of castings and the cooling effect of die releasing agent.The surface temperature exhibits regular changes with the die casting cycle,which can lead to the generation of periodic thermal stress.When the thermal stress is bigger than the yield strength of the material,the plastic deformation occurs.After enough cycles,many cracks form and lead to fatigue failure ultimately.It is important to find out the failure mechanism of the die casting dies by studying the temperature field,the thermal stress field,the thermal fatigue life and the depth of thermal fatigue zone on surface layer.Firstly,this article outlined the characteristics of die casting and the selection of process parameters,and then introduced the study status of failure mechanism of the die casting dies.It was found that the temperature gradient was a key factor that led to thermal fatigue.Based on the unsteady heat transfer theory,the heat transfer model of the contact surface for the 1-D semi-finite object was established,and then the temperature field model of the cavity surface of the die casting was constructed during the multiple continuous casting process.Eventually,the die temperature-time curves of zinc alloy,aluminum alloy and copper alloy die casting were drawn.According to the thermal elastic-plastic theory,the thermal stress field model of die cavity surface was constructed based on the temperature field model and the thin plate model that was in accord with the change rule of the thermal stress in die-casting die.The thermal stress-time curves of different kinds of alloy die casting were drawn.Through the research on thermal fatigue mechanism.The computational formula of the thermal fatigue life and the calculation method of the depth of thermal fatigue zone were given.The result shows that the depth of thermal fatigue zone of copper alloy die casting is 3mm.Through the pouring experiments of zinc alloy,aluminum alloy and cooper alloy.the temperature profiles at different depths(0.2,1.5,3.0 and 5.0 mm)from the die surface were measured,respectively.The correctness of the temperature field model was verified by comparing with the measured temperature.