In injection molding, during filling and packing phase the two mold halves are hold closed with the clamping force against the pressure of the melt. If the driving force of the cavity pressure is higher than the clamping force, the mold is pushed open by a few thousandths to hundreds of millimeters. This is known as the so-called mold breathing. Too large mold breathing can lead to flash formation, while too low mold breathing results to air compression with burn marks.
In order to optimize the required clamping force, dial gauges can be attached to the mold to determine the mold breathing. Permissible respiration depends on the quality requirements of the injection molded part, the material and the size of the machine.