Measurement methods for the determination of powder properties for compaction modelling

• Main Author: Korachkin, Dzmitry
• Published: Swansea University 2006
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.751982

In this thesis an experimental investigation into the measurement methods for determination of model parameters for the compaction, unloading and ejection stages and a numerical investigation on the effects of fill density distribution are presented. The numerical investigation explored the effect of fill density distribution on green density in powder compacts and on tool forces. This was achieved by comparing the results of simulations with uniform and non-uniform fill density distributions. The investigation considered three different powder types (ferrous, hard metal and ceramic), a selection of different geometries and a selection of fill density distributions based on the review of die filling research. Non-uniform fill density was found to result in higher density variation and in increased tool forces. A novel floating die modification to the shear plate friction measurement apparatus has been proposed. The equipment was used to measure the friction coefficient for a wide range of loading conditions, where the compaction and normal load have been explored independently. For ferrous powders friction was found to reduce with the compaction load and for lower compaction pressures also with normal load. Admixed and die wall lubricant performance was also assessed, with even small quantities providing significant reduction in friction. The compact surface was examined in a bid to explore the friction mechanisms with regards to lubrication. A review of different experimental techniques for measurement of parameters for the unloading and ejection stages is presented. The instrumented die, the unconstrained compression, the three point bending and the Brazilian disc tests have been explored for a selection of powders. A correction function has been proposed to enable the measurement of radial pressure in the instrumented die during ejection. A novel split die modification to the instrumented die test has been introduced and used to explore the axial recovery during ejection.