| Thin-walled shell products are widely used in high-horsepower engines in various fields,where includes weapons,ships,and others.However,the casting process stability is poor and the rate of finished castings is low,So,it is difficult to meet the production needs of thin-walled shell castings.In order to improve this problem,this paper takes the investment casting process of 1Cr20Ni14Si2 complex thin-walled shell casting as the research object,uses theoretical calculation and numerical simulation method to predict the shrinkage and hot crack defects in the casting process,which is helpful to optimize the casting process and reduce the production cost.It has certain academic significance and application value.Firstly,on the basis of establishing 1Cr20Ni14Si2 material database by using casting simulation software Pro CAST2018,the gating system of connecting shell casting is designed and optimized by cup capacity supplement method.Taking the Temperature Field,Solid Phase Ratio,Shrinkage Cavity and Cracking Defects during mold filling and solidification as the evaluation criteria,the effect of additional subsidy in gating system on casting quality is explored.Secondly,the effects of casting process parameters,including casting temperature,casting speed,shell preheating temperature,on the shrinkage volume,distribution and hot cracking behavior of castings were studied,and the casting process parameters suitable for connecting shell castings were optimized according to the results.Finally,the casting of the connecting shell is trial-produced to verify the simulation results.The results are as follows:(1)the addition of subsidy at the gravity gating system with cross gate and double inner gate improves the smoothness of liquid metal filling,prolongs the solidification time of the casting,enhances the feeding capacity of the gating system,and reduces the internal shrinkage volume of the casting by 47%.The hot tearing indicator of the hot crack sensitive part of the casting is reduced,the HTI value is 0.0122,and the final effective stress is 255 MPa.(2)Increasing the casting temperature increases the fluidity of the alloy liquid,improves the feeding ability of the alloy,and reduces the shrinkage defects in the castings.When the temperature reaches 1650 ?,the internal shrinkage volume of the castings decreases by 96.5%.The shrinkage defects in the inclined groove of the casting gradually disappear;the effective stress value of the paste zone in the hot crack sensitive area of the casting gradually decreases,and the final effective stress value gradually increases.If the casting speed is too low or high,it will increase the shrinkage defects in the casting,and there is only the critical value of the optimal casting speed.When the preheating temperature of the mold shell is increased,the cooling rate of the casting is reduced,the feeding time is prolonged,and the shrinkage defect inside the casting is reduced.When the temperature reaches 1050 ?,the internal shrinkage volume of the casting is reduced by 98%.The effective stress value of the paste zone in the hot crack sensitive area of the casting gradually decreases,and the final effective stress value is stable at 268 MPa.(3)The optimized casting process parameters of connecting shell casting are as follows:casting temperature is 1650 ?,casting speed is 3 kg/s,and preheating temperature of mold shell is 1050 ?.The total volume of shrinkage defects in castings is 0 cc,and the final effective stress at the hot crack sensitivity is 259 MPa,which is less than 1Cr20Ni14Si2 yield strength 295 MPa.So,it is predicted that shrinkage porosity and hot crack defects will occur in castings.(4)Through the trial production of actual products and industrial CT testing,the accuracy of the simulation results is verified.It is concluded that after optimizing the pouring process parameters,the surface and internal defects of the connecting shell castings basically disappear,and the castings meet the qualified standard. |
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