Effects of lubricant on green strength, compressibility and ejection of parts in die compaction process

Abstract

Abstract Lubricants improve the flow of metal powders, reduce friction and extend tool life during the die compaction process. Fe-2%Cu-0.5%C powders mixed with various amounts (0–0.8 wt.%) of ethylene-bis-stearamide (EBS) were used to determine the effects of lubricant amount on several green properties of the die-compacted parts in the present study. The green density and green strength for the powder mixed with various amounts of EBS increased with increase in compaction pressure. The effect of lubricant on the green density was found to be marginal at high compaction pressures. The green strength however decreased with the addition of EBS. Regression analysis was carried out to evaluate the applicability of existing models to predict the green strength as well as the compression behavior of the powder mixtures. The green strength models developed by Kawakita, Halldin et al., and German showed reasonable applicability for predicting the strength of compacted powders with varying amounts of EBS. The compression models developed by Kawakita, Heckel and Panelli–Ambrosio Filho were suitable for correlating the variation of compressibility of the powders with increasing amounts of EBS. The compressibility of the powders increased with an increase in the amount of EBS. In situ compression curves were experimentally obtained to determine the compressibility of powders as a function of increasing compaction pressure. The compressibility curves for powder with varying amounts of EBS were fitted to a power law equation. The ejection forces were found to be sensitive to the dimensions of the part as well as the amount of EBS. A new model was developed to estimate the ejection force based on the part dimensions and amount of EBS. The models showed a reasonable agreement with the experimental data. It is anticipated that the models evaluated in the present study will be useful in identifying appropriate amounts of lubricants required to optimize various green properties in die compaction components.