Cold Compaction of Copper Powders Under Mechanical Vibration and Uniaxial Compression
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COLD compaction of metal powders is one of the most important steps in powder metallurgy (PM) production, since high performance compacts with high packing density q (also called volume fraction F, is dimensionless and defined by q = Vp/V, where Vp is the volume occupied by particles and V is the volume of the container), uniform density distribution, and stress distribution are the precondition for high quality PM products and can simplify subsequent processes such as sintering and post treatment. Compared with other powder compaction processes, the uniaxial closed die compaction has been applied to produce the majority of PM components in industry for many decades due to its easy operation and low cost. Therefore, it is now still frequently in use for mass production of large and geometrically complicated PM components. Physically, much work carried out in the past was mainly focusing on the compaction theory and behaviors of various powders in closed die.[1–7] These physical experiments largely emphasized on the powder compaction stage, other stage such as initial packing in die filling, which can create key effects on compact density and property, was not considered or being ignored. Actually, an XIZHONG AN, Professor, is with the School of Materials and Metallurgy, Northeastern University, Shenyang 110004, P.R. China. Contact e-mail: [email protected] ZHITAO XING, formerly Master Student with the School of Materials and Metallurgy, Northeastern University, is now Engineer with the Rizhao Steel Company, Rizhao 276800, Shandong, P.R. China. CHENGCHANG JIA, Professor, is with the Institute of Powder Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. Manuscript submitted September 15, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
important characteristic of the powders is the packing structure they achieve as they fill the die. It has been identified that the packing density can be affected by the geometrical properties (size distribution, shape, specific surface) and mechanical properties (hardness, plasticity, etc.) of the powders.[8] When these properties are fixed, a reproducible and sufficiently high packing density is essential for avoiding defects during the subsequent compaction step.[9,10] In this regards, some effort was paid on the initial packing in the die,[11–16] however, most of them were related to gravity/drop filling with loose initial packing density. Fewer studies were conducted systematically on how to improve initial packing property to realize high performance compacts. In real process, tapping or vibration is an effective way to obtain higher initial packing density of powders, but its role in the packing densification and especially its influence on the compact property and microstructure still needs further study. Our previous numerical and physical studies on the packing of macro spheres (particle diameter d ‡ 1 mm) have demonstrated that the transition of initial packing from random loose to random dense can be reproduced under one-dimensional (1D) mec
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