On the Effect of Particle Size Distribution in Cold Powder Compaction

Abstract

The effect of particle size distribution in powder compaction has been studied using the discrete element method. Both isostatic compaction and closed die compaction are studied together during the entire loading process. Particle rotation and frictional effects are accounted for in the analysis. The particles are, constitutively described by rigid plasticity, assumed to be spherical with the size of the radii that follows a truncated normal distribution. The results show that size distribution effects are small on global compaction properties like compaction pressure if the size distribution is small. Furthermore, the size distribution had no influence at all on the macroscopic behavior at unloading. To verify the model, comparisons were made on two different sets of experiment found in the literature where the particles were of varying sizes. Good agreement was found both on fundamental properties like the average number of contacts per particle and on more important properties from a practical point of view, like the compaction pressure

A numerical analysis of cold powder compaction based on micromechanical experiments

“…The simulations were done with 8000 particles of equal size knowing that the eect of particle size distribution is small [31]. Some simulations were performed with half and also doubled amount of particles with no visible dierence.…”

“…In this case, where single action uniaxial pressing is simulated, only the upper wall is moved. A more realistic way to simulate the lling process was tried in previous work, [31] but didn't notably change the macroscopic behavior more than at low relative densities, 30% -33%.…”

Discrete element simulation of powder compaction in cold uniaxial pressing with low pressure

“…A certain regularization would be necessary in the numerical algorithm in order to avoid non-unique force-displacement relationship during unloading. This is why Olsson and Larsson [20] combined the Storåkers model with the elastic unloading according to the Hertz model. This can be viewed upon as regularization of the Storåkers model.…”

“…This can be viewed upon as regularization of the Storåkers model. Our implementation follow the formulation presented [20]. The contact force during unloading is updated incrementally according to the following formula:…”

“…where β = 0.5−5 is suggested in [20], and the normal stiffness k p n is determined as the derivative of the expression (16)…”