Finite Element Modeling on the Compaction of Copper Powder Under Different Conditions
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RODUCTION
IN the past decades, powder metallurgy (PM) has attracted more and more people’s eyes due to its increasingly application in industry. In PM production, powder cold compaction in the die is one of the most important steps because a high performance compact with high relative density, uniform density and stress distributions can not only simplify the subsequent processes such as sintering and finishing but also produce the part with superior quality and property and low cost.[1–3] Therefore, numerous studies either physically or numerically were carried out in this regard for powder cold die compaction,[3–13] whereas most of which were focusing on the forming of powders with relatively low initial packing density. Actually, die filling in the PM production is also a critical step; researchers have realized that high relative density and homogeneity in initial powder packing formed during die filling are of key importance for subsequent procedures.[14–20] While compared with mostly studied compaction and sintering processes, this step is less concerned. Based on previous studies on the packing of coarse particles or fine powders, An et al. have identified that by using external energy generated by mechanical vibration or compression, the transition from the so called random loose packing (RLP) to random close packing (RCP) can be reproduced numerically and physically,[21–26] where the obtained RCP structure with densest random packing
density, small pore size, and uniform pore size distribution can provide the researchers with effective starting point, useful ideas, and references for high-quality PM production. However, to date, corresponding studies which considering the effects of initial packing structures on the packing densification during powder die compaction is limited. Much less work was conducted on the systematic analysis of powder compaction with different initial packing densities and under different forming conditions; especially their role on the structure and properties of compacts still needs to be further studied. In this paper, we use finite element method (FEM) to systematically study (1) the single-action die compaction of copper powders with loose and dense initial packing structures, and (2) cyclic die compaction on initially dense packing of copper powders. In simulation, the loose and dense initial packings are constructed through mesh generation with the packing density of about 0.56 and 0.61, respectively, which is the same as those from our physical experiments on the packing of copper powders under one-dimensional (1D) mechanical vibrations.[24] Besides identifying the relationship between relative packing density and pressure, we also analyzed and compared the density distribution and stress distribution inside the compacts and studied the powder behavior during forming. Relative physical experiments were conducted to validate our numerical results.
II. XIZHONG AN, Professor, YUXI ZHANG, Master Student, and SHUO YANG, Master, are with the School of Materials and Metallurgy, Northeastern
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