Beyond viscosity curves: A critical rheological perspectives for converging material extrusion additive manufacturing and powder injection molding

Abstract

Rheological behaviour of highly filled polymer feedstocks critically governs their processability in material extrusion (MEX) additive manufacturing and powder injection molding (PIM). These converging technologies require robust flow control to achieve defect-free, dimensionally accurate parts. Despite extensive rheology-related literature, clear and transferable links between measured properties and process optimization remain scarce. This review summarizes rheological strategies for improving processing of highly filled compounds, with emphasis on maximum packing, wall slip, yield stress, powder-binder segregation and pressure-dependent flow. It also highlights conceptually inconsistent practices, including the widespread use of simple shear-thinning models for structurally complex feedstocks or activation energy evaluated at a constant shear rate. By focusing on a limited set of physically meaningful rheological parameters and their relation to typical processing failures, the review outlines a framework for material selection and formulation optimization in converging MEX and PIM technologies.