Molding pressure typically refers to a measurement of force within an injection molding machine. In injection molding, plastic resins are melted and pushed into a steel or aluminum mold, forming plastic parts. The amount of molding pressure should be enough to fill the mold completely, preventing what are known as short shots, or plastic parts that are not formed all the way. If this happens, the molding pressure should be increased. Once the mold is full, the pressure is reduced and stays level while the parts cool. Once the plastic cools, the mold is opened and the part is ejected from the injection machine.