Meaning
Optical density variation within a given linear distance characterizes the rate of feature transition across an image surface. Spatial frequency describes the density of edges and patterns in a visual field or a polymer surface relief. High values indicate tight, rapid successions of light and dark, while low values represent broad, flat, or gradual gradients.
This metric defines the limit of resolution in imaging systems and the fidelity of surface detail in moulded parts.
Tooling Precision
Mould cavity texture governs the reproduction of microscopic patterns on polymer surfaces. Finished parts often require specific surface finishes to mask flow marks or to create functional grip patterns. High frequency features demand superior tool steel grain refinement to ensure that molten resin captures the intended geometry before cooling initiates.
Poor cavity polish forces the resin to bridge gaps rather than conform, leading to ghosting or loss of surface detail.
Moulding Control
Process variables like injection speed and melt temperature dictate how accurately the polymer replicates the mould surface. Faster injection rates improve the filling of intricate details during the short window of high pressure. Residual stress profiles change when the resin cools against high frequency tool textures, altering the final part stiffness and impact resistance.
Improper temperature gradients cause uneven shrinkage, which distorts the fine surface features and increases the rate of visual rejects at inspection.
Resin Suitability
Polymer grade selection influences the success of reproducing high detail, as melt flow index determines how effectively a material fills microscopic voids. Amorphous resins perform better than semi-crystalline materials because their lack of crystal structure allows for better flow into tiny surface features. Virgin material maintains consistent rheology, whereas regrind introduces impurities that disrupt the flow front and blur the resolution of fine textures.
Uniformity in the bulk material properties prevents variations in how the plastic interacts with the mould at the microscale.
