Constitutive data and friction measurements of powders using instrumented die

An instrumented die has been developed to measure friction and constitutive data on powders during compaction. Such data is useful for quality assurance and as input data for computer models of die compaction. The measurement system consists of a die with radial stress sensors, punch force measurement, and a displacement transducer to measure punch displacement. The outputs of these sensors enable simultaneous measurement of density, die wall friction coefficient, and the triaxial stresses acting on the powder during the course of compaction. The die system has been tested at three industrial sites on automated and manual presses measuring ferrous, ceramic, and tungsten carbide powders at applied stresses of up to 650 MPa and speeds of up to 26 mm s -1 . Sensor outputs were sufficiently noise free to permit the recording of useful data down to stresses less than 1 MPa. Typically the run to run reproducibility of friction coefficients was better than ± 0·005, depending on the type of powder and the applied stress. Variations in constitutive data were usually better than ± 4%, again depending on material and the stress. Die wall friction coefficients are found generally to decrease with increasing density and stress. It has been possible to discriminate between different grades and batches of the same material using the frictional and constitutive data. Constitutive data for all types of powder can be accurately represented by an analytical relationship involving four adjustable parameters. This parametric form of data is suitable as input to finite element mathematical models.