Numerical simulation of the filling stage is a useful tool in mold design. In this report, filling time of the preform is demonstrated with the analytical approach. Darcy’s law and mass conservation equation are combined to construct the general equation. Numerical simulation of mold filling process is also performed for Isotropic cases. The simulation results are then compared to the analytical one. The comparison showed good agreement with the data for the square part. Three cases i.e. Edge, Central and peripheral flow were performed without taking shear into account as shown in figures below.
Analytical Approach
Impregnation is modeled as a Darcy’s flow. As a first approach, the focus is made on the flow front numerical modeling. The medium is assumed to be not deformable and of a constant permeability. The flow is considered as isothermal and resin viscosity is assumed to be constant, neglecting chemical reactions effects. The equations are derived for Edge, central and peripheral flow from Darcy’s law and filling time is calculated.
Numerical Simulation
The numerical method was validated by considering the case of an isotropic injection for un-sheared and shear media. In Edge injection, the resin enters from the left edge and flows through the preform till it reaches the other edge. whereas, in the peripheral flow, fluid is injected from all the edges. The resin enters from the center in center injection and flows through the preform describing circular patterns. Two vents located on the two different edges ensure the complete filling.
Filling patterns of un-sheared media for Edge injection (left), Center injection (middle) and peripheral injection (right)
Filling patterns of sheared media for Edge injection (left), Center injection (middle) and peripheral injection (right)
Filling time for different Case
There is marginal difference between the analytical and simulation results which conclude that Darcy's Law can provide a good approximation and it can only be used for the range of pressures. Shear plays an important role in the filling time. Presence of shear can affect the filling time by large value. As we can see there is large difference in filling time for sheared case compared to un-sheared case. In un- sheared preform, Fluid flows slower by 159 sec in Edge injection, 243 sec in Central injection and 32 sec in Peripheral injection.