基于分数步长法的压铸充型过程数值模拟

Numerical simulation of die-casting mold filling process based on fractional step method

为了模拟型腔内流体的流动形态并预测气孔缺陷,应用充型过程数值模拟方法,采用分数步长法来求解非稳态的Navier-Stokes方程,可以在每个时间步长内仅求解一次动量和压力方程.动量方程求解中采用Adams-Bashforth方法处理对流项,采用Crank-Nicolson方法处理扩散项.搭建了压铸过程水模拟系统,设计了型腔尺寸沿充填方向逐渐递减的有机玻璃模具.通过彩色高速摄像机以500帧/秒的速度记录充填形貌.将数值模拟结果和水模拟结果相比较,两者吻合较好.同时采用SOLA-VOF法模拟了同一充型过程,结果表明,分数步长法和VOF法相结合要比SOLA-VOF法更能准确地预测压铸过程中的卷气现象.

To simulate the flow patterns of molten metal in the die cavity and predict the gas porosity defect in die-castings, a fractional step method was applied in numerical solution of unsteady Navier-Stokes equations, which can be implemented with a single solution to the momentum/pressure equations in each time step. A hybrid explicit/implicit scheme was used to solve the momentum equations in which advection terms were treated by Adams-Bashforth method and diffusion terms were treated by Adams-Mouhon method. A water analog sys- tem was developed to simulate the die casting process. An acrylic glass die with size gradually reduced along the direction of mold filling process was designed. Data of fluid flow patterns were recorded by a high-speed camera with capturing rate of 500 frames per second. Simulation results agreed well with experimental results. The same mold filling process was simulated by the SOLA-VOF method. Results show that the combination of fractional step method and VOF method is more accurate for air entrapment prediction during die Casting process compared with SOLA-VOF method.