 The high @-@ pressure injection leads to a quick fill of the die , which is required so the entire cavity fills before any part of the casting solidifies . In this way , discontinuities are avoided , even if the shape requires difficult @-@ to @-@ fill thin sections . This creates the problem of air entrapment , because when the mold is filled quickly there is little time for the air to escape . This problem is minimized by including vents along the parting lines , however , even in a highly refined process there will still be some porosity in the center of the casting . 
