Modelling Powder Compaction

Die compaction of powders is a process which involves filling a die with powder, compression of the powder using rigid punches to form a dense compact, and ejection from the die. The choice of powder composition and selection of process parameters determine the microstructure and final properties of the compacts. The practical issues in the powder-forming industries (powder metallurgy, ceramics, hard metals, pharmaceuticals, detergents, etc.) are related to mechanical strength, control of microstructure, avoidance of cracks and defects, content uniformity, etc. We review the modelling strategies used for powder compaction. The main focus is on the constitutive model development for finite element analysis. Knowledge of the following input factors is required: 1.constitutive equations which describe the deformation of a volume of powder under the loads applied during compaction 2.friction interaction between powder and tooling 3.geometry of die and punches 4.pressing schedule, e.g. sequence of punch motions 5.initial conditions that relate to the state of the powder in the die after die fill The constitutive model and friction relate to fundamental properties of the material and are reviewed in more detail. The methodologies used for model calibration are also described. The remaining factors (geometry, pressing schedule and initial conditions) are specific to particular problems. Their relative effect is discussed by presenting examples for a range of powder materials. We show how compact microstructure can be manipulated by changing the factors discussed above and illustrate the effect of microstructure on final properties. The model predictions are validated using experimental data. The use of numerical analysis in powder formulation design and optimisation of the process parameters is discussed.