Three‐dimensional free surface flow simulation of segregating dense suspensions

Abstract

SUMMARYThis paper presents a 3D numerical solution algorithm for the simulation of free surface flows of dense suspensions including particle migration phenomena. Segregation of the solid phase in processes such as powder injection molding and molding of semi-solid materials affects the rheology of the mixture and therefore the filling pattern. Segregation affects also the final properties and characteristics of such molded parts as a non-uniform particles distribution leads to non-uniform shrinkage, warpage and non-uniform mechanical properties. In this paper, particle migration is modeled using the diffusion flux model of Phillips et al. (Phys. Fluids A 1992; 4:30-40) and is extended to address 3D mold filling problems. The solution algorithm is validated against flow problems for which experimental and numerical data are available: circular Couette flow, piston-driven flow and sudden contraction-expansion flow. The particle migration model is then used to simulate mold filling problems in which the piston movement in the sleeve is known to induce particle migration before the material enters the cavity. An arbitrary Lagrangian-Eulerian (ALE) formulation is developed and combined to a level-set front capturing method to simulate the piston movement and the evolution of the free surface in molding simulations. The ALE formulation is first compared with an Eulerian solution for the case of the piston-driven flow problem. The approach is then applied to injection molding problems to study the evolution of particle distributions during molding and in the final molded parts.

A review of micro-powder injection moulding as a microfabrication technique

“…With regard to simulation of feedstock segregation, there is a general agreement that for conventional PIM, simulation tools should be based on multiphase flow models in order to take care of the heterogeneous behaviour of the feedstock and, hence, predict segregation [129,130,[137][138][139]. This is likely to be required for developing simulation packages for μPIM, and this is why recent simulation attempts for μPIM relied on multiphase flow [68].…”

“…A major challenge for commercial simulation packages is the ability to predict powder-binder segregation [128]. Segregation usually happens during the mould-filling stage, and its effect is amplified during the debinding and sintering stages causing a number of quality issues in the final component, such as visible defects, porosity, non-uniform mechanical properties, warpage and cracks [128][129][130][131]. Since segregation is usually attributed to high shear rate gradient during injection moulding [49,128,130], this problem is likely to be more dominant during micromoulding due to high-shear rates associated with flow in micro-scale cavities [132].…”

3D Numerical Modelling of Mould Filling of a Coat Hanger Distributer and Rectangular Cavity

“…For injection moulding of polymers, time-and temperature-dependent effects are seen in conjunction with non-Newtonian rheology [Ilinca & Hetu, 2001;Kumar & Ghoshdastidar, 2002]. In powder injection moulding for ceramic and metal forming, a suspension of particles is injected into a mould to create a green part, which later sees further processing steps to produce the final part [Hwang & Kwon, 2002;Ilinca & Hetu, 2008]. Numerical methods for these problems range from finite difference, to finite volume, and finite element.…”