Research On The Compacting Process Of Block Vibration Forming Based On Distinct Element Method

Vibration is the main production mode used in this block forming progress.The research and design of block-making machine mainly has two kinds of methods. One is the design method and theory based on the continuum mechanics method, but it considers granular particles as a continuous whole, as a result it can not analyze the movement process of every particle and interactions between particles, so it can not solve problems existing during designing seed-metering device well. Another method is according to the experience and trial, whereas usually it is not only time-consuming but also strenuous without ideal results. A computer simulation of compacting process in vibration molding has been performed through distinct element method (DEM) for the first time.In seventies of the 20th century, Cundall et al. put forward the DEM primarily. The basic thought is to simplify granular colony as a set of particles with a certain kind of shape and mass, and endues the particle-particle and particle-boundary relationship with a certain kind of contact mechanics model and some parameters. The DEM is applied to research the contact effects, which influence the particle-particle and particle-boundary relationship, and the different physical and mechanical characteristics between particle and contacted boundary. The dynamic laxity method, the Newton's Second Law and time step iteration are introduced in DEM to calculate the movement and displacement of each particle, and thus it is especially compatible to resolve the nonlinear problem. Because of these virtues mentioned above, DEM has become a popular method on studying the kinetic problem of granular colony, and it is widely applied in the field of rock engineering and sands flowing; the transportation, mixing, classification of granular materials; the agglomeration and collision of granular materials; the interaction between granular materials and related mechanical parts; the equipment of chemical industry and mine engineering.The fundamental principle of DEM is introduced in this paper, and the calculation of normal or tangential contact force without adhesion between sphere particles is discussed. The reasonable parameters in DEM and its affection to calculation precision are discussed at the same time. For readers to understand the realization of DEM more clearly, the DEM program which will be adapted in the paper is introduced in detail in aspect of general structure, programming thinking, data restoring, iterated calculation, and the calculation of time step.The simulation of the vibrating process is done by the discrete element method analysis software- PFC2D. The change of porosity in the process of vibration of granule groups is studied and the change law is revealed. The effect of four aspects is also discussed, which are friction coefficient of granular, particle size, vibration frequency and amplitude. The porosity is positively related to friction coefficient of granular and negatively correlated to particle size. Quadric curve can be used to model the relationship between vibration amplitude and porosity. The fluctuation of change of porosity can be decreased by choosing higher vibration frequency. These research results possess a certain reference value to the design of vibration parameters and improve the quality of building block.