Fill and Pack Simulations

During the fill simulation, polymer material is injected into the mold cavity. The polymer is injected into the cavity at a prescribed rate, regardless of the required pressure.

The app calculates acceptable default values for all of the main parameters in a fill simulation, but you can customize any of them for your simulation.

• The fill rate profile defines the rate at which polymer material is injected and how this rate varies during the fill simulation. The default profile causes the cavity to fill at a constant rate over an automatically determined time.

  The default profile uses a constant rate such that the cavity fills in 1/10 of the automatic cooling time, $t_K$, as determined by the following equation:

  $$t_K\approx \frac{s^2}{{\pi }^2{a}_{\mathrm{eff}}}\ln \left(\frac{8}{{\pi }^2}\cdot \frac{{\theta }_M-{\theta }_W}{{\theta }_E-{\theta }_W}\right),$$
  where $s$ is the average thickness; ${\pi }^2{a}_{\mathrm{eff}}$ is the heat conductivity (expressed as density times specific heat); and ${\theta }_M$, ${\theta }_W$, and ${\theta }_E$ are the melt temperature, mold temperature, and ejection temperature, respectively.

• The filling time is computed automatically from the fill rate profile.
• The melt temperature is the temperature of the polymer entering the model at the injection locations.
• The mold temperature is the uniform temperature of the mold cavity walls.
• The ejection temperature is the temperature at which the part can be safely ejected from the mold.
• The default values for melt, mold, and ejection temperatures are derived from the values of the same name in the Characteristic Temperatures options in the material's simulation domain.
• The default maximum injection pressure is 100 MPa. This value represents the maximum pressure that the injection machine can produce. If the pressure required to produce the fill rate profile exceeds the maximum injection pressure, the fill rate is reduced automatically, and the resulting filling time increases.

During the first stage of the pack simulation, pressure is applied to the injection locations. In the second stage of the packing this pressure is removed and the polymer material cools further.

You can control the following aspects of the pack simulation:

• The pack switch point defines the percentage of filled cavity volume at which the packing simulation begins. To avoid abrupt pressure increases, it is common to begin packing just before the cavity becomes 100% full.
• The pack pressure profile defines the duration of the first stage of the packing simulation and how the pressure varies during this time.
• The holding time is the duration of the first stage of packing, where pressure is applied to the injection locations. It is computed automatically from the pack pressure profile.
• The pure cooling time is the duration of the second stage of the packing simulation, where pressure is removed and the material cools further.