Process And Theory Of Vacuum Counter-pressure Casting Thin-wall Aluminum Alloy Castings Based On Intelligent Control

Near net shape,high accuracy,high performance,complicated and thin-wall nonferrous alloy castings is one of developing trend of foundry industry in the 21st century,and have important status and broad application prospect in basic industries such as aviation,airsPace,national defense,car and automobile industry fields. But existing processes have not satisfied producing demand of high-qulity,complicated and thin-wall nonferrous alloy castings completely. In the Paper,according to the characteristics of complicated and thin-wall aluminum alloy castings,a new counter-pressure casting process named vacuum counter-pressure casting was presented on the basis of suction casting,low-pressure casting and counter-pressure casting process,which adopted to low-pressure fill mould under the condition of vacuum and crystallize under high pressure. Meanwhile,its principle and theory were investigated,and its equipment based on intelligent control was developed,which solved middle or short run,high-qulity, complicated and thin-wall aluminum alloy castings forming accurately in national defense and civilian industries.First of all,vacuum counter-pressure casting process and principle were presented,and its technology principle adopted to low-pressure fill mould under the condition of vacuum and crystallize under high pressure. Meanwhile,its process wsa divided into five stages:vacuumizing,filling mould,rising pressure,keeping pressure and releasing pressure,additionally,filling mould and crystallization could carry on at different pressure. So it had predominant filling hydrodynamics and solidification mechanics condition,and it solved the problem of gas counter pressure and filling mould which existed in general counter-gravity casting complicated and thin-wall aluminum alloy castings. meanwhile,a set of VCPC-1 vacuum counter-pressure casting equipment was designed and developed by oneself,which had laid a good foundation for theory research and producing application of vacuum counter-pressure casting process.Intelligent control systems of vacuum counter-pressure casting were studied systemically. Through simulation analyses of vacuum counter-pressure casting digital PID control and fuzzy control algorithm based on MATLAB,its intelligent control systems were comfirmed to adopte fuzzy control algorithm. Meanwhile,visual interface of its intelligent control systems was developed by using Delphi language,which appeared in the form of window,and its functions was multiple,simple and practical,moreover , it had good persons-machine dialogue functions. Through serial communication technique,intelligent control systems of vacuum counter-pressure casting realized short range control of hypogynous machine and long-distance control of epigynous machine. Hypogynous machine adopted the single-chip computer to control,which was convenient to monitor the whole process course real-time at the scene. Additionally,epigynous machine adopted PC computer to control,which was used mainly to transmit,save and print data,and show and reproduce the whole process course,moreover,it could control on the range of 500m. Results indicated Intelligent control systems of vacuum counter-pressure casting developed were high efficient and reliable,and run well. Morover,they could meet process demand completely.Filling mould theory of vacuum counter-pressure casting process was studied systemically. Through a set of testing systems of intelligent electrode contacting method developed by oneself,filling mould flow morphology of vacuum counter-pressure casting aluminum alloy was tested under condition of different thick castings and filling velocity. Meanwhile,its filling regulation was investigated,and the concept of critical pressurizing velocity and filling velocity was presented. Additionally,obverse and inverse filling mould theory of vacuum counter-pressure casting process was established,and relation of flow morphology and castings quality was discussed,which had provided theoretical foundation for filling process of vacuum counter-pressure casting.Solidification feeding theory of vacuum counter-pressure casting process was studied systemically,and changing regulation of the density and microstructure of vacuum counter-pressure casting aluminum alloy sample under different crystallization and solidification pressure was investigated. Meanwhile,mathematical model of its solidification feeding course was established,and feeding velocity equation of X location between dendrite was obtained and shown below:It was pointed that feeding velocity equation of X location between dendrite depended on magnitude of keeping pressure Pk mainly,moreover,the higher keeping pressure Pk was,the quicker its feeding velocity was. On this basis,dendrite extrusion and infiltration feeding theory of vacuum counter-pressure casting process was presented,and extrusion and infiltration ability equation of molten metal was obtained and shown below:It was pointed that extrusion and infiltration effect depended on magnitude of keeping pressure Pk mainly too,moreover,the higher keeping pressure Pk was,the stronger its effect was,which could make molten metal Pass through narrow Passage between solidification dendrite to flow toward feeding area successfully. Therefore,it benefited from solidification feeding for interface between solid and liquid. Study of solidification feeding theory provided theoretical foundation for vacuum counter-pressure casting complicated,thin-wall and sound aluminum alloy castings.Finally , determinate principle of vacuum counter-pressure casting process Parameters such as vacuum degree,filling velocity,filling pressure difference,rising pressure velocity,crystallization pressure and keeping pressure time were established. Meanwhile,short run complicated and thin-wall shell and box body aluminum alloy military castings which the smallest wall was 0.8mm and the biggest weight was 20kg had been produced successfully,and VCPC-2 vacuum counter-pressure casting systems had been developed for aviation enterprise. Results indicated vacuum counter-pressure casting technology had possessed ability of producing near net shape,thin-wall and complicated castings under 1mm,and was suitable for many kinds of moulds such as investment casting,sand mould,permanent mould and gypsum mould,which had laid a good foundation for popularizing application of vacuum counter-pressure casting technology,and has broad application prospects.