Study of the Effect of an Improved Die Filling Shoe on Density Variations

摘要

Die filling is still today the operation that leads to most of the density variation in compact and in final components, thus leading to various problems including part distortion, uneven metallurgical and mechanical quality. The formation of air entrapment, an uneven vertical pressure over the die cavity, power fluidity, cavity width-to-depth ratio, and the stacking of powder in long parts during scraping are known to be major concerns that influence strongly the reproducibility and uniformity of compact density. In past research, several parameters have been studied on common die filling shoe. Some new designs have also been proposed. In this paper, we present a new design of die filling shoe incorporating the best solutions found so far for keeping powder fluidity, maintaining powder pressure over the cavity, allowing clean scraping while minimizing powder stacking, and at last providing lower density variation over the die cavity and from part to part over time. For testing, this shoe has been installed on a 6-axis instrumented compaction press to establish the effect of several parameters including the die filling strategy, the powder height in the shoe, the agitator speed, the part height and geometry and more. A specially made multi-cavity die is used along with stainless steel 409 powder. The new shoe has been tested over a longer period and compared with the performance of a classic shoe.