Study On Vibration Filling Characteristics Of Powder Based On EDEM

Powder metallurgy products are widely used in aerospace,automobile industry,pharmaceutical industry,nuclear industry and other fields due to their advantages of strong shape adaptability,less machining volume,good quality and low cost.According to statistics,there are more than 1,000 kinds of PM materials used in the automotive industry alone.The types of parts made of powder metallurgy materials are even more innumerable,such as common synchronizer cone rings,timing gears,engine connecting rods,camshaft,etc.In the process of powder metallurgy production and processing,there are many processes that determine the final performance of the product,and the filling process is one of the most critical.The filling structure of the powder is not only very important for the selection of methods and parameters in the pressing and sintering process,but also affects the final performance of the fabricated zero device.During the filling process,the higher the packing density of the powder particles,the compacted green body will be uniformly shaped and formed with high density.The final structural members have excellent mechanical properties and service life.With the rapid development of global manufacturing,the requirements of high precision,uniform organization,full densification and complex shapes have become the development direction of powder metallurgy technology.Due to the complexity of particle shape,there are a lot of pores in the accumulated powder obtained in the traditional filling process,and the defects such as cracks often exist in the powder metallurgy products,which make the preparation of fully densified and high-performance powder metallurgy parts very difficult.Mixing and separation are the most common behavioral characteristics of particulate matter.Construction,pharmaceutical,agriculture and other industries often use methods such as vibration,stirring,and knocking to make the particle system mix evenly.To this end,this paper takes pure iron powder as the research object to study and analyze the filling process of powder particles under vibration environment,which provides a theoretical basis for improving the filling effect of powder.The main research contents and conclusions are as follows:(1)The discrete element theory is applied to the dynamic simulation of powder particles,and the motion characteristics of particles under vibration conditions are studied.The mathematical model of particle vibration filling is established.The results show that the soft sphere model of DEM is an important method to simulate the movement of a large number of particles under vibration conditions.The determination of the grid size and time step is very important for the accuracy of the research results.(2)The three-dimensional modeling software was used to establish the geometric model of the powder particles and the mold cavity respectively.The EDEM was used to simulate the filling process of the powder particles under vertical vibration.The position change diagram and pore size change diagram of powder particles in the cavity before and after vibration filling are obtained.Studies have shown that during the vibration enrichment process,mechanical vibration can change the position of each particle in the powder particle group,produce displacement,promote the relative position of the particles,and destroy the relatively stable arch structure formed in the powder system during the initial filling.The new arch structure was rebuilt,and the porosity of the powder was reduced.The apparent stacking height of the body decreased significantly,and the powder packing density was effectively improved after measurement.(3)The effects of physical parameters such as vibration characteristic parameters and recovery coefficients on the powder filling effect were studied,and the changes of the powder filling effect in the mold cavity before and after vibration were analyzed.The simulation results show that the packing density increases with the vibration time and tends to be stable;the vibration frequency and vibration amplitude will have a greater impact on the powder packing density.As the vibration frequency and vibration amplitude increase,the packing density first increase after decrease.When the vibration frequency is low or the amplitude is small,the packing density does not change much;when the amplitude is too large or the frequency is too high,the particles will "boiling" and the packing density will decrease.The coefficient of restitution affects the movement state of powder particles after collision and the filling effect of powder in the mold cavity.(4)In order to further explore the effect of mechanical vibration on the packing density of the powder,this paper optimizes the vibration characteristic parameters by using the orthogonal experiment method.The results show that:vibration frequency has the largest impact on packing density,followed by vibration amplitude,and vibration time has the smallest impact on packing density.Through the comprehensive analysis of range method and variance method,the optimal process conditions of the powder filling density in the cavity under the vibration condition are determined.(5)An experimental platform was set up to study the vibration filling process of powder.The influence of frequency and vibration duration on the filling effect of powder was analyzed.The reliability of DEM software in studying the vibration filling process of powder was verified by comparing with the simulation results.