Simulation of micro powder injection moulding
Complex materials which are strongly deformed remain a computation challenge. Smoothed particle hydrodynamics (SPH) is adapted to the requirements of the micro powder injection moulding of ceramics and metals.
Yield stress effect
Feedstocks for micro powder injection moulding posses a significant yield stress. Therefore, a yield-stress material was modelled by means of the viscosity regularisation technique, i.e., the approximation of the yielded and unyielded domains of the material by two different viscosities. Incorporated into the particle based SPH-formalism, the model successfully reproduces an experimental observation of splitting in a channel with cylindrical obstacle as shown in figures 1 and 2.
Simulation of segregation
Shear induced powder migration was incorporated by means of Phillips’ diffusive flux model . This model was discretised by formulating an SPH-equation of motion for the occupied volume of the solids fraction with exact conservation properties. The simulations correctly predict powder migration to regions with the lowest shear rates. For injection moulding into complex geometries such as in figure 3 the simulations help to predict an accumulation of the solids fraction at convex corners (pointing outside of the cavity) and a depletion at concave corners (pointing inside the cavity) as shown in figure 4. In Figure 5 the migration to reqions with low shear rates is clearly visible in the narrow channels at the top and at the bottom.
 R. J. Phillips, R. C. Armstrong, R. A. Brown, A. L. Graham, J. R. Abbott, A constitutive equation for concentrated suspensions that accounts for shear-induced particle migration. Phys. Fluids A, 4(1):30–40, 1992.
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