One of the key steps in the injection molding process is the packing and holding phase, sometimes also referred to as the compensation phase. In this lesson the term packing phase will be used to describe the full process step. During the packing phase material is continuously “packed” into a cavity, thereby compensating for the shrinkage that occurs due to material cooling inside the mold. Processors can optimize a packing profile by understanding the material characteristics of the polymer to be molded. In this lesson we will focus on packing profiles of amorphous materials.
This lesson reviews the internal structure of amorphous materials, risks of over- or under-packing a part, pack pressure and how it relates to volumetric shrinkages, clamp tonnages, and cavity pressure, and how to optimize a packing pressure profile using an amorphous polymer.