Experimental Study On Cold Compaction Of Copper Powders Under Mechanical Vibration And Uniaxial Compression

In this thesis, systematic physical experiments were carried out on the compaction of two different sized fine copper powders (We name1#copper powder with the size of about300μm and2#copper powder with the size of about200μm) under uniaxial compression with/without external mechanical vibrations. The influence of one-dimensional (1D) vibration parameters such as vibration time t, vibration frequency co, amplitude A, and vibration intensity T on the packing density of the two powders was studied, and the compaction process and the microstructure of the compacts obtained with (we use the densest packing structure obtained by vibration) and without vibration were characterized and analyzed to study the effects of the applied mechanical vibration on the structure and property of compact in powder metallurgy. The results indicate that:1. Physical experiments on the packing of copper powders under1D vibration(?) The packing density p of the two copper powders increases rapidly with the vibration time t to a high value, and then keeps constant with the further increase of t.(?) The influences of vibration amplitude A and frequency co on the packing density p of the two copper powders indicate that p increases with the increase of A or ω to a maximum value and then decreases with the further increase of A or ω, i.e. there exists an optimal A or co to realize the densest packing structure.(?) The influence of vibration intensity Γ on packing density p also takes on similar trend as that of A or ω, which, to some extent, reflects the combined effects of A and co. However, we cannot simply use Γ to characterize the packing densification of the two copper powders, the effects of A and co should be considered independently.(?) The optimal vibrations obtained from the experiments are:1#copper powder, A=0.35mm, ω=140Rad/s,Γ=0.7, the corresponding maximum packing density ρmax=0.6640;2#copper powder,A=0.50mm,ω=130Rad/s, Γ=0.8622, here ρmax=0.6566.(?) The size of copper powders can influence the packing density, with each packing condition, finer powder is not helpful for the packing densification.2. Experiments of powder compaction under compression(?) The packing density of copper powders increases rapidly with the compaction process and then tends to be constant. Under same conditions, the larger the compression pressure P, the higher the packing density of the powder compact. With each P, the packing density of copper powder subjected to mechanical vibration is higher than that without vibration.(?) The p-P curves have been plotted and fitted with equation, which reflects the relationship between compression pressure and packing density.(?) During compaction, the plastic deformation of the copper powder increases with the pressure P, and the shape of the copper particles changing from spheres to polyhedron (polygon at the surface). The contact between particles changes gradually from point contact to face contact.(?) With the vibration, the deformation of copper particles become regular, most of them are regular polyhedrons. And the pore distribution between particles is uniform, which indicates that the periodical vibration before compaction can produce high performance compacts and the effectiveness of vibration in the powder metallurgy production.