Visualization of Powder Behavior for Filling

Dimensional tolerance of P/M parts is improved by uniformly filling powders in a die cavity. This study is aimed at clarifying the powder behavior in filling the die cavity. A visual apparatus was developed for observing the powder behavior, Using this apparatus, the powder behavior in filling die cavity and during movement of feed-shoe were investigated for gravity filling of atomized iron powders (including Fe-Zn, Fe-Cu-Zn and STARMIX). It is clarified that the particle size segregation in filling occurs independently on the shoe speed and die cavity shape. Coarse particles segregate in the place where the powder falls along the angle of repose, while fine particles segregate in the thin-walled part and the position where the empty space finally disappears. It is also clarified that the behavior of filled powders during the feed-shoe movement after filling is divided into three regions; where the powders move as rolling, where the powders slide, and where the powders do not slide with the movement of the feed-shoe. Moreover, as the width of the cavity becomes thinner, the powders are more difficult to move; therefore, the none-sliding region increases. When shaking of the feed-shoe is repeated, the moving distance of powders in a vertical direction becomes larger, and the filling density increases, However, the increasing moving distance of powders is greatly affected by the width of the die cavity.