The packing phase begins after the cavity was filled. This involves further application of pressure to the material in an attempt to pack more material into the cavity, in order to produce uniform shrinkage at reduced levels and consequently, reduce component warpage. Once the material has filled the mold cavity, and the packing phase has begun, material flow is driven by the variation of density across the part. If one region of a part is less densely packed than an adjacent region, then polymer will flow into the less dense region until equilibrium is reached.
This flow will be affected by the compressibility and thermal expansion of the melt in a similar way to which the flow is affected by these factors in the filling phase.
The material‘s PVT characteristics provide the necessary information so that when combined with the material viscosity data, accurate simulation of the material flow during the packing phase is possible. Packing Analysis is to analyze the packing/holding process in the injection molding. During the packing process, the relation between pressure and time is illustrated as below.