Exploration of die wall friction for powder compaction using a discrete finite element modelling technique

Abstract

The paper presents a micromechanical discrete-element modelling technique to investigate the friction mechanisms that are present between the powder and tool set surfaces in die compaction. The technique includes particle kinematics and deformations to be accounted for together and has allowed a theoretical exploration into particle sliding over smooth surfaces and locking into the asperities of rough surfaces. A two-dimensional model has been developed to represent a shear-plate technique that is used to measure friction in compacted powder systems and in this study assumes that the consequent cylindrical rods are of identical diameter.In the case of smooth surfaces and with no friction coefficient between the tool set surfaces and the powder, the particles simply slide over the surface and are not subjected to gross deformations. The mechanical resistance that may be expressed as a friction coefficient is small under these circumstances. When fine powders are used (fine in comparison with the roughness of the surface), the particles form a sticking layer and the consequent friction coefficient due to particle deformation is large due to the need to shear the powder mass. It is also noted that harder powder particles lead to a lower friction level. When mechanical friction is included between the powder and tool set surfaces, the combination is offset by the friction coefficient that is used between the powder and tool set surfaces. NomenclatureF contact force x displacement k stiffness t halo thickness (equation (1)) or time c damping v velocity

Changes in friction, surface roughness, and tensile strength upon compaction of Ficus deltoidea powder

“…The same observation was found in a previous study, which measured the wall friction and compaction characteristic of bentonite powder at compaction pressure of 70-665 kN 20 . Concerning the surface roughness, the increase in compaction pressure should make the tablet surface smoother and decrease the roughness of the tablet 21 . The arithmetic mean deviation (R a ) is usually used as quantitative parameter to measure the surface roughness.…”

Particulate Scale Multiparticle Finite Element Method Modeling on the 2D Compaction and Release of Copper Powder

“…In general, the MPFEM combines the characteristics of conventional FEM and DEM simulations and is capable of comprehensively simulating the compaction densification process of a powder, with large deformation at particulate scale, which cannot be achieved by FEM and DEM simulations. Hence, the MPFEM is widely used to investigate the influence of density distribution, particle size, and friction conditions on the forming process [29][30][31][32][33][34][35][36][37]. Furthermore, a series of studies has focused on the forming process of multicomponent particles and analyzed the influence of volume fraction of hard particles on the forming densification process [38][39][40].…”

An investigation into the kinetic (sliding) friction of some tablets and capsules

“…Powder friction measurements during punch-and-die compaction (conducted using instrumented tablet presses) have been widely reported Augsburger, 1985, 1988;Ernst et al, 1991;Guyoncourt et al, 2000Guyoncourt et al, , 2001Holzer and Sjogren, 1981a,b;Korachkin et al, 2008;Lewis and Train, 1965a,b;Strijbos, 1977), and the data generated used to identify potential issues during tablet manufacturing operations (e.g., premature tooling wear). Similar data have also been used as inputs for finite element computer simulations of tablet compaction (Cameron and Gethin, 2001;Cunningham et al, 2004;Sinka et al, 2003). On a much smaller scale, several reports have documented the measurement of kinetic friction between individual particles of pharmaceutical powders and solid surfaces (Bunker et al, 2006;Jones et al, 2004;Lee, 2007;Mullier et al, 1991).…”