Study On Process Of Low Pressure Filling-reverse Pressure Solidification Of Shaped Tube Simulated Parts

In this paper,ZL205A alloy was used as the research material to cast large thin-walled complex special-shaped cylinder with reverse synchronous pressure after low-pressure mold filling.The feeding law of casting solidification process was analyzed,the distribution characteristics of temperature field and stress field of complex special-shaped cylinder were studied,and the influence of reverse pressure on the shrinkage cavity and porosity of the casting was studied,the casting process parameters were optimized,and the defects of shrinkage cavity and porosity of the casting were improved.The law of solidification and feeding of reverse pressure casting ZL205A alloy was studied by capillary model,and the feeding speed model was established.In this model,the solidification pressure P was the main factor.When the solidification pressure P increased,the feeding speed and feeding capacity increased significantly.On the basis of the feeding velocity model,the relationship between pressure and critical solid rate is established by combining darcy's law,fluid mechanics theory and dendrite breakage theory.Within a certain range,the critical solid rate increases with the increase of pressure,which greatly improves the feeding capacity of liquid metal,and the shrinkage porosity and porosity gradually decrease.However,beyond the appropriate range,the increase of pressure has no significant impact on the critical solid rate,and has little impact on casting feeding.Based on Darcy's law of interdendrite flow and continuity equation,the formula of pore volume during casting solidification and shrinkage is obtained.The greater the reverse pressure,the greater the resistance to gas formation,the less likely to produce shrinkage.The filling and solidification process of a large thin-walled complex special-shaped cylinder was simulated.The temperature at the junction between the gate and the casting was the highest,followed by the position of the internal rib plate,and the corresponding area between the two slit sprue had the lowest temperature.The shrinkage cavity and porosity defects of the casting were mainly concentrated in these areas.The feeding behavior in different directions is analyzed,and it is found that the temperature gradient in the middle and upper part is smaller than that in the bottom part,and there will be certain blocking of feeding channel.Reverse pressure mainly affects the volume fraction of shrinkage cavity and porosity of casting.The location of shrinkage cavity and porosity of the casting shows consistency and symmetry,and the distribution is symmetrical acm~3ording to the structure of the casting.With the increase of pressure,shrinkage cavity and porosity gradually decrease,and the improvement effect on the middle and upper part is more obvious than that on the bottom.When the filling speed gradually increases,the filling time decreases,the solidification fraction in the filling stage gradually decreases,and the solidification time gradually increases.However,the impact on the casting will become greater with the increase of the actual liquid flow velocity of the casting,and the shrinkage porosity and porosity of the casting presents a trend of first decreasing and then increasing.When casting temperature gradually increases,the solidification sequence of alloy liquid does not change significantly,mold filling capacity improves,and the phenomenon of solidification while filling is reduced.Shrinkage porosity and porosity of casting become more concentrated from small dispersion,showing a trend of decreasing first and then increasing.Through simulation calculation and analysis,the optimal process parameters are obtained as follows:casting temperature of 725?,mold filling speed of 500mm/s,and reverse pressure of 30kPa.