Analysis Of Densification Process And Influencing Factors Of Compacts In High Speed Compaction Of Metal Powders

Compared with the traditional powder compaction,the HVC technology is advantageous to significantly increase the density and uniformity of the green compact,which has attracted wide attention from the academic and industrial circles.Different from the traditional quasi-static loading method,HVC belongs to the transient compaction process,and the powders change drastically in an extremely short process.Therefore,it is urgent to analyze the densification process and its influencing factors.In this paper,the HVC with hammer type is used to start the compaction experiment under different loading quality and compact height.It is found that the average density of the compact increases with the increase of the energy per unit mass.At the same time,the relationship between the density and the peak pressure of the shock is still in good agreement with the classical equations of Kawagami and Huang Peiyun.When analyzing the force characteristics of the powders,it is found that the lateral pressure coefficient and the force-transfer ratio showed a first-order decrease,middle-stationary,and finally-rising change rule during the compaction,and the friction coefficient between the powder and the sidewall shows first rise,middle Smooth,and final decline.In addition,the compact velocity has a great influence on the force transmission ratio and the friction coefficient.On the other hand,Drucker-Prager Cap powder model and explicit dynamic finite element method are used to simulate the HVC process.The variations of density with time and space are obtained.Combined with orthogonal test and analysis of variance,the variation of powder density with process parameters is first studied.It is found that the trend of average density with energy per unit mass is in good agreement with the experimental trend,but not with sidewall lubrication conditions,ratio of height to diameter and the initial loosening density.When we further study the change of density uniformity,we find that the coefficient of sidewall friction,ratio of height to diameter,and energy per unit mass have a great influence on the uniformity of density.In summary,the study of the characteristics of the force characteristics and friction coefficient,the density of green compacts and the uniformity of compaction during HVC are helpful to explain the mechanism of powder compaction at high speed and provides guidance for improving the quality of products.