Numerical Simulation And Process Optimization Of Low Pressure Die Casting Process Of Aluminum Alloy Automotive Cylinder Body

Casting is molding method of pouring molten liquid metal into the mold cavity for getting the necessary parts or ingot after solidification and cooling.When the liquid metal is poured into the mold cavity, temperature is passed to the cavity The process of castings formation in cavity is controlled by the heat and also transfer heat to the environment through mold . Changes of temperature are important external manifestation. The internal temperatures distribution of mold and casting change as time goes on. It is the different variation and distribution of temperature that lead to various changes of defect in the inside of the cast. If the process of transferring heat is controlled, that means the internal quality of casting is also controlled.At the same time ,it can accurately predict the distribution and change of temperature of casting during solidification.In a word,it can predict the internal defects in castings.However,this is a very difficult task,because the process of heat transfer conducts in three ways of radiation,heat conduction and convection from the way of heat transfer,and it is a Very complex process.Effective method of solving the above problem is exploit advanced mold filling and numerical simulation technology during the solidification.The casting simulation software PROCAST is used in this paper,and we simulate the filling and solidification process of Low-pressure casting aluminum alloy cylinder block .The whole process of cylinder filling and solidification are displayed by using the function of the computer visualization for optimizing the casting process ,eliminating the casting defects reducing costs and Improving the yield.The main results are as followed: 1.We study the ways of pre-treatment of the software ProCAST,solve the data transmission problems from geometric model of complex castings to finite element analysis model. Compared to other several pre-treatment methods,the results show,We can see it is an effective method to subdivide the model using Pro/ENGINEER to create the model and the Hypermesh to subdivide the plane which will finally ture into file format of OUT the MeshCAST can read and then the MeshCAST will subdivide the volume.2. We can forecast the defects of shrinkage by the temperature field, flow field and the rate of solid-state phase changes during the process of solidification,which we can get from the numerical simulation of the mold-filling and solidification process of the cylinder block of aluminium alloy.We can optimize the process depending on the result of the numerical simulation and the actual product.(1) Optimization of the gating systemConsidering the different effect that different gating systems have on the casting quality and the production efficiency by the numerical simulation of the mold-filling and solidification process,we will choose the best gating system.We will observe the following aspects:1) Time of the mold-filling and solidification process2) Whether the mold could be fully filled with the molten metal and obtaining products of clear shape and profile.3) The stability of the mold-filling process.4) Whether it could be easy for refilling.5) Tendency of the shrinkage and the shrinkage porosity.There will be defects of underfilling with two inside sprues to lead the molten metal into the mold.It spends so much time in the filling process causing rapid decrease of the molten metal's temperature with only two sprues that it can't make fine casting.We can obtain good castings with six or ten inside sprues,but it will make the size of the shrinkage smaller by contrast if we use ten sprues for the surface of the molten metal can rise more stably.It is logical that we choose ten inside sprues by integrative analysis.(2)Optimization of the pouring temperatureBy analysing the numerical simulation of the mold-filling and solidification process in different pouring temperature,we find the temperature of the surface of the molten metal is the key factor during the mold-filling process.The higher the pouring temperature,the higher the surface temperature and then the easier the filling process leading to more chance of oxidation.The refilling of the molten metal which mainly depends on the time the sprues seal up and the distribution of the temperature field of the thick part of the casting when the sprues solidify is the key factor during the solidification process.The higher the pouring temperature,the longer the solidification time and it will lower the production efficiency.Considering all the above,we will choose 725℃.(3) Optimization of the mold-filling pressurehe mold-filling pressure is an important parameter to obtain casting with clear shape and bright and clean surface.As for the chosen pressure, 0.1bar,it is too low to fully fill the mold.The lower the pressure,the more blurred the casting.The higher the pressure,the more chances gas hole appears.In the accepted range,we should choose the higher pressure to enhance the refilling ability and decrease or even eliminate the shrinkage and the shrinkage porosity.So,we choose higher pressure by contrast.0.15bar is better than 0.13bar by analysing the defects forecasting during the mold-filling and solidification process.(4)Chill appending and optimization of the sand cores in the crank shaftWhen the sizes of the sand cores in the crank shaft were increased, the solidification time of the runner increases, and the metal liquid can feeding more easily. Then, the area of the shrinkage porosity decreases. When the chills were used in certain positions, the solidification sequence of the casting can be controlled. Therefore, the area of the shrinkage porosity can also be decreased. These results indicate that changing the sand cores and appending the chills are reasonable.