Process Design And Optimization On Thin-walled Aluminum Alloy Casting With Typical Structure

Complicated and thin-wall aluminum alloy castings show broad prospect of application and high practical value in many basic industries such as space, aeronautics, automobile,machinery manufacturing, shipping and national defense. However, current casting process can not meet the demand of high-quality, small, complicated and thin-wall aluminum alloy castings, especially the shell castings with more than 70% of thin-walled area, complicated internal cavity and oil circuit inside, less than 2mm minimum wall thickness and change in wall thickness, whose precise foundry process is still far from perfection.In this paper, after the calculation and design for the vacuum differential pressure casting process, the parameters are set as follow: OKPa for vacuum degree, 0.1 MPa for filling pressure, 2.3 m/s for filling velocity, 0.15 MPa for dwell pressure, 1×104 Pa/s for rising pressure velocity and 7min for keeping pressure time.The bottom rain type gating system with bottom feed head was selected and the micro riser at the top of casting was replaced by densener. Meanwhile, the densener set in hot spots is retained while its thickness is increased. The high stability of metal liquid filling process,the improvement of quality in hot spots and thick area of castings and the better feeding ability after solidification can be obtained in this gating system. The reasonable design and coordinated application of gating system, feeding system and densener guarantee the smooth filling and progressive solidification.The processes of filling and solidification are simulated by the method of numerical simulation. The simulation results show that, at the pouring temperature of 720℃, partial turbulent flow phenomenon occurs in the process of filling, the distribution of temperature is very unhomogeneous in the cavity, the solidification is unordered and high residual stress exists at the connection of the cavity and the bottom riser. Shrinkage porosity prediction results showed that a lot of defects distributing broadly in the casting are detected, which leads to bad quality of casting. Combining analysis and optimization for the pouring temperature, an important influence factor on the quality of filling and solidification, and the simulation of computer, the status of flow field, temperature field and stress field are better in process of filling and solidification and the amount and size of shrinkage porosity are smaller and the quality of casting is higher when the pouring temperature is 740℃. The best pouring temperature is 740℃ in the thin-wall aluminum alloy shell casting after optimized analysis.The experimental samples obtained according to the optimized casting process card show holonomic shaping and good quality of surface. The fluorescence detection, X ray detection, mechanical performance testing and metallographic observation results show that the casting with good microstructures and mechanical properties can meet the aviation standards and the demand of resistance of high temperature, high pressure and acid corrosion for aircraft engine.The optimizations of casting process parameters under computer numerical simulation effectively shorten the development cycle, improve the rate of finished products, save the cost of development and guarantee high quality of casting. This method will be a development direction of the small complex thin-walled aluminum alloy casting in vacuum differential pressure casting in future and plays a significant role in the development of casting technology.