Meaning
Measurement of mass per unit volume within a mould throughout the solidification phase ensures the dimensional stability of a finished part. In precision moulding, cavity density tracking utilizes the relationship between pressure and temperature to monitor the state of the resin. This data provides a more accurate view of the part than simple pressure readings alone.
Variations in the cooling rate or the hold pressure directly influence the final density and the degree of shrinkage.
Shrinkage Monitoring
Monitoring the change in density allows for the prediction of the final size of the part before it even leaves the mould. When cavity density tracking identifies a drop in mass, it indicates that the packing phase was insufficient to fill the microscopic voids between polymer chains. This information helps in adjusting the hold time to meet tight tolerances.
Solidification Analysis
Analysis of the density curve shows the exact moment the polymer transitions from a compressible fluid to a rigid solid. Because the specific volume of the resin changes as it cools, cavity density tracking can pinpoint the gate freeze time with high precision. This mechanism is especially useful for semi crystalline materials where the formation of crystals causes a sharp increase in density.
Understanding this transition helps in optimizing the cycle time by ensuring that the part is only ejected when it has reached its target density.
Quality Validation
Validation of every shot against a master density curve reduces the risk of shipping parts with internal sink marks. Unlike surface inspections, this method looks at the bulk material properties.
