Fill analysis calculates the maximum clamp force required to keep the mold closed during filling.
Clamp force calculation
The calculation for clamp force uses two values:
- Area
- The area of the model projected onto the XY plane.
- Pressure
- The injection pressure distribution.
The maximum force required to hold the mold closed is calculated by finding the integral pressure over the projected area of the cavity. That is, the area is divided into small segments, and the pressure is calculated for each of the small segments. The total clamp force is the sum of the products of each of these Pressure and Area components:
Clamp force = 
where:
-
= the number of segments into which the total area is divided -
= the area of each segment -
= the average pressure at each segment
For the clamp force calculation to be correct, the model positioning must be such that the clamp force is applied along the Z axis direction.
You can prepare your model at any convenient rotation, and when finished, correctly position it with the model manipulation tools.
Clamp force during filling and packing
Typically, both the pressure and the clamp force increase progressively during filling. Once into the packing phase, the cavity pressure becomes more uniform and, if the filling pressure is maintained, the clamp force will increase significantly. Under normal molding conditions, the packing pressure is lower than the filling pressure and so the clamp force required during packing may be higher than or lower than the clamp force required during filling.
Over-predicting clamp force
The projected area of the cavity is the sum of the area of all of the surfaces projected perpendicularly onto the parting plane. In some cases, some of these projected surfaces may overlap (see image below). The second and all subsequent overlapping surfaces do not contribute to the actual clamp force required in real life, but they are taken into account by the analysis during the clamp force calculation. As a result, the predicted clamp force can be greater than the amount actually required to keep the mold closed.
This is a very common problem when dealing with such undercut geometries normally requiring slide core molds to mold them, as well as with stack or multi-plate molds. It is difficult for the program to distinguish these special cases, so you may need to manually exclude undercuts from the clamp force calculation.