Numerical Simulation Study Of Mold Filling And Separation Behavior Based On CFD-DEM

Powder pressing process includes three processes of die filling,pressing and spraying.The flow behavior of powder in the three processes affects the final quality of products.The segregation behavior of powder often occurs in the process of die filling,which will lead to incorrect distribution of product components,thus changing the performance of the product.At present,the research on die filling mostly focuses on the production of tablets,while less attention is paid to high-density no-viscosity materials commonly used in the field of powder metallurgy,such as glass beads.Therefore,the segregation behavior of high-density no-viscosity particles during die filling was numerically simulated using a DEM method,and the influence mechanism of feeding speed,feeding shoe and die technological conditions and particle arrangement on the segregation behavior of the mixture was analyzed,so as to provide suggestions for improving the product quality,furthermore,the influence of air on the flow behavior when the mixture fills the die is considered in this paper.The numerical results show that increasing the speeding,reducing the inclination angle of the feeding shoe and using cylinder die instead of cuboid die can improve the uniform distribution of the mixture in the die,however,the action mechanisms of the three are different.Among them,increasing the feeding speed can reduce the sequence problem of filling the die with particles in the feeding shoe,while reducing the inclination angle of the wall surface of the feeding shoe can generate “funnel flow”,which is beneficial to inhibit the segregation behavior of the mixture.Using the layered filling method instead of industrial filling method has proved to be meaningless,but through the study of the initial distribution of particles,it is found that the initial position of particles has a profound influence on their segregation behavior,which indicates that we can improve the product quality by changing the initial position of product components.The effect of reducing the segregation index of the mixture by increasing the depth of the die is limited.Increasing a certain depth can improve the distribution uniformity of the mixture in the die,but it is meaningless to continue to increase.The presence of air plays an important role in the flow behavior when the mixture fills the die.The presence of air has an obvious blocking effect on the falling of particles.Different air escape modes have different effects on the flow behavior of the mixture.When the particles fall directly into the die,the air movement in the mold appears to escape upward as a whole,and the influence on the mass distribution of the particles in the die mainly appears in the Z direction.When particles have an initial velocity in the X direction,the movement of air in the die in the X direction cannot be ignored in the process of filling the die.Furthermore,the influence of the movement of air on the mass distribution of particles in the X direction in the die cannot be ignored.