In-situ X-ray microtomography study of the movement of a granular material within a die

Abstract

AbstractOptimising the manufacture of powder-processed components requires an understanding of the 3-D movement and behaviour of granular materials during processing. X-ray microtomography has been employed to study the 3-D flow behaviour of a metallic powder in-situ within a die as a function of the displacement of a punch into the die. In particular, the powder transfer behaviour for various open and closed die/punch geometries has been compared, including situations where features exist within the die and on the punch, cases where the die is both open and closed at the top, and finally where the punch itself contains a groove in the centre providing a gap into which powder can flow. Digital image correlation (DIC) has enabled the determination of local vector displacements of powder around the features within the die cavity as a function of punch movement and powder constraint to reveal bulk granular movement and densification. Zones of relatively stagnant flow are observed above a fixed insert within the die cavity, at the opening of a gap within a punch, and as a result of a closed die configuration, the latter showing transitions between the stagnant zones and much more mobile regions and the resulting powder compaction/dilation. As well as providing a means of developing practical die fill and compaction strategies that homogenise densification and thus improve product quality, the technique can also provide unique 3-D flow trajectories for model development.