Meaning
Volume reduction during phase change measures the density increase from liquid melt to solid state. Most plastics exhibit volumetric contraction as the randomly arranged chains move into closer quarters as heat energy leaves the system. This reduction requires extra material to be pushed into the mold to prevent hollow spots from forming inside the part.
Density Logic
Management is performed by a holding pressure phase that continues until the gate freezes shut. Because volumetric contraction happens differently across varying wall thicknesses, thick sections might pull inward and create unsightly sink marks. Calculating this change in advance informs the size of the mold cavity to hit the right final size.
Shrinkage Calculation
Accuracy depends on knowing the exact thermal behavior of the chosen resin under production pressures. Volumetric contraction is usually specified as a percentage of the overall mold dimensions. If the calculation is early or wrong, expensive steel adjustments are needed to make the part fit within the blueprint limits.
Yield Impact
Result is seen in the physical fit between moving part assemblies. High levels of volumetric contraction force shops to slow down their cycles to manage the cooling. Success involves making a part that hits its design goal once it reaches room temperature.
