Meaning
Geometric transfer accuracy measures the degree to which an injection moulded polymer part reproduces the microstructured or nanostructured details of the mould insert. This metric, known as replication fidelity, is calculated by comparing the height and width of the replicated plastic feature to those of the nickel master. High fidelity is required in optical and diagnostic components where small dimensional errors can ruin performance.
It is affected by the resin viscosity and the mould temperature. When these variables drift, the moulded microfeatures may exhibit rounded crests or reduced height.
Process Control
Achieving high replication fidelity requires the polymer melt to remain fluid until the mould cavity is filled. Processors use high mould temperatures to delay skin freezing. This allows the melt to penetrate the microstructures.
Dynamic mould heating helps achieve this without increasing the cycle time.
Material Impact
Polymer molecular weight and chain structure determine how easily the melt flows into micro-scale patterns. Low molecular weight resins exhibit lower viscosity, which yields superior replication fidelity compared to high viscosity resins under identical moulding conditions. The addition of glass fibres or fillers can hinder this flow, reducing replication quality at the feature edges.
Quality Control
Metrology instruments like atomic force microscopes and confocal microscopes assess the replication quality. If the replication fidelity drops below ninety percent, the resulting parts may be rejected for optical scattering or poor micro-fluidic flow. This monitoring allows the processor to adjust the pack pressure before the run drifts out of tolerance.
