Technologic Characteristics Of Aluminium Alloy With Vacuum Low Pressure-Expendable Pattern Shell Casting Process

The forming technique and methods for complicated thin-walled parts is always oneof the goals of foundrymen. In order to solve it, a vacuum and low pressure cast withprocess of expendable pattern shell was put forward.In this new process, the complex shellwas prepared according to the foam pattern,then the liquid metal was poured into theempty shell using vaccum low pressure casting machine use vaccum low pressure castingmachine,with the purpose of getting complicated thin-walled castings of high precisionand high quality.This paper focuses on the study of the process of vacuum and lowpressure cast with expendable pattern shell. Also, the structure and property of castings,the forming process of typical complicated thin-walled parts were studied, which providesa basis for its mature application in industry.In this paper, the effect of process parameters (pouring temperature, gas flux,vacuum, charge pressure) on filling ability and the inner quality of casting wassystematically investigated.The results show that the filling ability is respectivelyimproving as the increasing of pouring temperature, gas flux, vacuum, charge pressure, inwhich gas flux has more obvious influence. As the increase of pouring temperature,theporosity of casting increases first,then decrease.As the increase of the other processparameters,the porosity of casting decrease as well as the density of casing increase, andthe inner quality of casting is improved too.The optimum process parameters of aluminumalloy casting in vacuum and low pressure with expendable pattern shell are: pouringtemperature720℃～750℃,gas flux12m3/h～19m3/h,vacuum-0.03MPa～-0.04MPa,charge pressure0.03MPa～0.04MPa.The microstructure and property of A356aluminum alloy by vacuum and lowpressure with expendable pattern shell are studied, meanwhile compared with other threedifferent casting processes (expendable pattern casting, lost foam casting, the casting viavacuum and low pressure with expendable pattern shell).The results show that the as-castmicrostructures of A356aluminum alloy by vacuum and low pressure with expendablepattern shell casting consists of α-Al,Si and Mg2Si. And of the eutecticum and Si particles distribute unevenly in the grain. This alloy has excellent mechanical properties with theultimate tensile strength, elongation and hardness being278.27MPa,8.1%and93.1HBSrespectively. Compared with expendable pattern casting with vacuum and low pressure,expendable pattern casting,lost foam casting,the casting via vacuum and low pressure withexpendable pattern shell has the smallest grains,highest density and lowest porosity,and itstensile strength, elongation and hardness are much better than those of the other threeprocesses,implying a best comprehensive mechanical properties.The forming of tow typical complicated thin-walled parts (thin-walled cylinder,intake manifold) with vacuum and low pressure using-expendable pattern shell wasproceeded for practice, and the typical defects were analyzed and some relevantprevention measures were given. The tow parts are suceessfully obtained by the newprocess,which reflects the advantage of the new process on the forming of complicatedthin-walled parts.To prevent the common defects,such as hole, misrun, sand inclusion andghost, which exist in the casting by vacuum and low pressure with expendable patternshell,optimizing pouring system,improving quality of the shell,setting process parametersreasonably,preheating the shell and casting apparatus,standarding operation etc. can betaken.