Meaning
Optical measurement metrics quantify the fraction of incident light scattered by surface irregularities on moulded polymer optics or polished metal inserts. This total integrated scatter relates directly to the root-mean-square surface roughness of the measured part. In high-precision optical parts like lenses and light guides, high scatter reduces image contrast and transmission efficiency.
Moulders use this measurement to assess whether the surface finish of the tool has replicated successfully onto the plastic part, ensuring that quality standards are met without damaging the delicate components.
Surface Quality
High scatter values indicate either incomplete replication of the polished mould surface or the presence of surface defects like sink marks. Microscopic roughness from tool machining marks scatters light across a range of angles, degrading the optical performance of the part. This metric helps in determining the appropriate time to repolish or clean the injection mould.
Metrology Method
Instruments measure both the specularly reflected light and the diffuse scatter using an integrating sphere to collect the scattered photons. This method provides a rapid, non-contact evaluation of surface finish across a larger area than typical stylus measurements. It is particularly useful for delicate plastic surfaces that are easily scratched by physical probes.
Process Control
Variations in the scatter of the moulded parts often signal changes in injection speed or holding pressure. If the holding pressure is too low, the polymer fails to copy the highly polished surface finish of the insert.
