What Is Back Pressure in Injection Molding?
Injection molding is one of the most widely used manufacturing processes for producing plastic parts — from everyday consumer goods to high-precision automotive and medical components. While many factors influence the quality of an injection-molded part — such as temperature, injection speed, and cooling time — one often overlooked but critical parameter is back pressure. In this article, we’ll break down what back pressure is, why it matters, how it affects product quality, and how to optimize it for consistent molding results. What Is Back Pressure in Injection Molding? In simple terms, back pressure is the resistance applied by the hydraulic system to the screw as it rotates and moves backward during the plasticizing (or recovery) phase of the injection molding cycle. When the screw rotates, it melts the plastic pellets and conveys the molten material toward the front of the barrel. As the molten plastic accumulates in front of the screw, the screw gradually moves b...