Abstract
Experiments and finite element analysis were performed to investigate the compaction densification mechanism of Ag57.6-Cu22.4-Sn10-In10 mixed metal powder. Firstly, the friction coefficient for lubricated and unlubricated die between the powder and die wall were determined experimentally. It is observed that the friction coefficient varies with the top punch pressure, and μ increases with the top punch pressure at low pressure regime (≤100MPa), while maintain constants at high pressure regime (>100MPa). The difference between the friction coefficients of lubricated/unlubricated die indicates that the lubrication (zinc stearate alcohol solution) could reduce the die wall friction greatly. Furthermore, the relative density distribution in the compacts for lubricated and unlubricated die compaction were characterized and mapped experimentally using the Vickers hardness method. Globally, the agreement between simulation calculation and experimental measurement of relative density distribution is reasonably good, indicating that the model parameters give an adequate description of the compaction behavior for the mixed metal powder. Moreover, a nonlinear compaction equation containing the die wall friction effect was proposed and established as: ln1−D1−D0=kP1−k1μ+b1−k2μP, k1 and k2 are correction coefficients related to the powder property. It is shown that the established nonlinear compaction equation could represent the relative density-compaction pressure relationship for the mixed metal powder under different die wall friction. At last, the influence mechanisms of die wall friction on the compaction behavior of mixed metal powder were detailedly analyzed in simulations using the modified Drucker-Prager Cap model. The results show that the friction induced inhomogeneous stress distribution and powder flows in compact during compaction, which caused density gradient and the occurrence of cracks and capping during ejection.
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