The general topic here is injection molding machine capacities and the specific capacity considered is clamping force. Clamping force is needed to hold the mold closed during melt injection and part solidification. The clamping force needed is due to the melt pressure acting in the sprue, runners and mold cavities. To explain the general concept of how required clamping force depends on part and runner shapes and mold pressure a single mold cavity will be considered. The extension to including runners and multiple mold cavities is straightforward, once the general concept is clear.
Another important injection molding machine capacity is the amount of melt material available for injection into the mold. This amount of material depends not only on the volumetric capacity of the machine. The ability of the machine to raise a given amount of material to the desired injection temperature in a specified length of time is also an important molding machine capacity.
In the exercise a formula for calculating the clamping force required to hold a mold closed against mold cavity pressure will be deduced.