Study On Investment Casting Of TiB₂/Al Impeller And The Numerical Simulation

The advantage of particle reinforced aluminum matrix composites including high specific strength and modulus, corrosion and high temperature resistance,excellent stability of dimensional, low thermal expansion coefficient,etc has been made a hot research spot in recent years. Especially, the demand of this material is increasing in the field of the aerospace,auto,electronic etc.The technique of impeller castings of Ti B2/Al composites was selected as the research object in this paper. In view of hot crack in the actual production, casting process was simulated by using the commercial casting simulation software ProCAST, which including thermal stress field,flow field and temperature field etc.The position and reason of hot crack which may occur was predicted and analyzed by observing the metal casting process,and to improve the original casting process.The optimum technological scheme used for sample production needs by the repeated simulation experiment,the purpose is to eliminate this kind of material impeller cracking defects.It is difficult for this kind of material performance parameters in the solid-liquid two phase measurement,in view of the lack of thermal-physical parameters and mechanical performance parameters of TiB2/Al composites in the material database of ProCAST.The materials database of 10% volume proportion of reinforcing particle of TiB2/Al composites was found by using the formula of particle reinforced aluminum matrix composites and the relationship between thermal physical parameters,mechanical properties and temperature of TiB2 and A356,numerical simulation of metal casting for this kind of materials research.In order to verify the reliability of the performance parameters of TiB2/Al composites,the casting parameters which factory provided including pouring temperature 730℃, shell preheat temperature 350℃, casting speed 0.06m/s was selected as the initial process parameter to simulate and analyze the casting process.The simulation results show that the blades of impeller castings has the uneven thickness, which leads to the casting stress,as well as mechanical hindered because of the shell accumulated the casting stress, it can lead to the formation of hot crack when the stress value was beyond the limit stress of bombproof material. The simulation results agreed well with the actual results, which verifies the certain reference values of the material properties of TiB2/Al and the reliability of numerical simulation in the investment casting process of the impeller castings.In order to eliminate hot crack of the impeller, theoretical guidance of optimum process solutions was provided by comparison and analysis of simulation results under different parameters,in which casting pouring temperature, shell preheat temperature and casting speed was set up three variable parameters of multiple sets of orthogonal simulation test.The final optimum process parameters including pouring temperature 750℃,shell preheat temperature 350℃, casting speed 0.08m/ s.Compared with the simulated results of the initial solution analysis:the high shell preheat and casting pouring temperature can reduce the gate edge bottom of the heat loss,to ensure the gate edge bottom blade parts of the solidification sequence and avoid the blade casting hot phenomenon stress concentration and accumulation effectively.Finally,The actual casting trials was carried out based on the final optimum process parameters, including the design and preparation of pressure-type and wax film, the selection and preparation of shell material, dewaxing, roasting, the preparation of composite material and casting processes.The free of defects impeller castings was obtained successfully in the actual casting trial, the observation shows that in reaction method to generate rules of TiB2 particle shape,uniform distribution,assumes the prismatic or granular and combine closely,no obvious reaction between particles and matrix.It verifies the reliability of numerical simulation in the investment casting process of the impeller castings again, provides scientific guidance and theoretical basis for scale production of this material casting.