Study On Various Pressure Grade Filling Of Aluminum Alloy During Vacuum Counter-pressure Casting

Vacuum counter-pressure casting (VCPC) is an advanced precision formingmethod of the anti-gravity, its filling and solidification processes were completed atdifferent pressures. It has excellent filling and solidification mechanical condition andone of the most practical process for fulfill technical request of high-quality, large andcomplicated thin-wall castings. This technique has broad application prospects in theaerospace, defense, automotive and other fields.At present, the filling stage of vacuum counter-pressure casting are adoptconstant pressure difference. It’s not conducive to smooth filling of liquid metal andgases emitted in time. Especially, lead to turbulence and splashing phenomena easilydue to mutations of filling section for production of large and complicated thin-wallcastings, so that make succession and smoothness of casting filling process werespoiled. Based on the above issues, study on vacuum counter-pressure grading processof large and complicated thin-wall casting in the project. Meanwhile, grading offilling speed be achieved on the basis of filling completion.In this paper, grade filling process of VCPC has been studied by adopt a methodthat combine simulation with experiment. The filling process of complicatedthin-wall castings under the condition of VCPC was simulated by ProCAST software,the simulation process is in the different filling pressure and rising pressure velocity.The simulation results show that, change metal liquid filling pressure timelyaccording to structural characteristics of castings, which is able to carry on sectionalprecision control in the filling process, and suggests that grade filling behavior ismuch better than the single-stage filling. For location of cross-section mutate ofcastings, we can change the flow pattern of liquid metal and achieve smoothtransition of filling process by change filling pressure, rising pressure velocity andkeeping pressure time and so on.In test, the electrode contacting method was applied to study filling behavior ofthree-dimensional castings under the optimal grade filling simulation processes, andconduct theoretical analysis for grade filling flow pattern of vacuum counter-pressurecasting. At the same time, the relevant mathematical models decribing the relationship between rising pressure velocity, filling speed and filling section have been built. Theresults of the simulation and the test datas were achieved by electrode contactingmethod is basically the same. Through repeatedly correct, the optimum technologicalparameters for grade filling process of VCPC were obtained. As a comparison, thesingle-stage flow pattern of metal liquid under35KPa have also been tested, theresults show that liquid metal filling flow pattern more smoothly and orderly underthe grade filling process.To obtain high-quality and complicated thin-wall castings, one of the keytechnology is control the filling process. The grade filling new process of VCPC hasgreatly improved the filling flow pattern and contribute to get high-quality thin-wallcastings, and achievable fragment precision control at filling process according tostructural characteristics of castings change filling pressure timely, and it has broadapplication prospects.