Comparative Rheology Techniques for Assessment of MIM Titanium Metal Powder Feedstocks

Abstract

In this work standard industrial processing equipment, the torque mixer and twin screw extruder, are used to measure the melt flow of several titanium metal powder feedstocks. The study was to determine whether test data from specialised rheology equipment might be reproduced with standard processing equipment used by the MIM industry.Considering the wide range of flow defects possible with MIM there is a valid assumption that flow behaviour measurement will be better represented by a number of processes, especially those most representative of the injection moulding process.In this study process data was collected and analysed based on mixing torque, screw work, specific mechanical energy and viscosity. Viscosity was further calculated relative to (L/D) ratio and strain rates during extrusion. Subsequently the data was compared with viscosity values from a capillary rheometer both without, and with, account for end effects and slip.The results showed that all the techniques provide similar ranking for the feedstocks with regard to melt flow during processing. The results also showed an inversion of the ranking where the shear rate increased from (1000 to 5000) s-1 as a result of shear sensitivity. The agreement of results from the different techniques clearly show that conventional processing equipment may provide valid feedstock assessment. The results if not definitive will provide good comparative measure where upper and lower bounds can be determined.