Clamping force refers to the force applied to a mold by the clamping unit of an injection molding machine. In order to keep the mold closed, this force must oppose the separating force, caused by the injection of molten plastic into the mold. The required clamping force can be calculated from the cavity pressure inside the mold and the shot projected area, on which this pressure is acting. The calculated tonnage can be used to select a capable machine that will prevent part defects, such as excessive flash.