The clamp force is the maximum force required to keep the mold closed during filling. This force can be calculated. Clamp force predictions for a part can then be compared with the clamp force limit of the injection molding machine to be used.
The calculated maximum clamp force is a function of injection pressure and the projected area of the part. The projected area is the area of the model that is projected onto the XY plane. For the clamp force calculations to be correct, the model must be positioned so that the clamp force is applied along the Z axis direction as shown in the following diagram. If your model is not oriented so that the clamp force is in the +Z direction, then you need to rotate your model so it is.
Clamp force is also calculated during the packing stage when the whole cavity might be pressurized to a higher value than it was during the filling stage.
Note: The clamp open direction of your mold must be known so the model can be oriented accordingly in the X, Y, and Z planes.