Optical Coherence Measurement Fundamentals for Deep Tooling Cavities
Optical coherence measurement uses broad-bandwidth infrared interference to capture deep cavity topographies without mechanical probe contact or lens clipping.
Sinker EDM Texture
Meaning
The micro-structured surface finish produced on a tool steel cavity through the controlled erosive action of electrical sparks between a shaped electrode and the workpiece represents the main alternative to chemical etching for texturing injection moulds. This sinker EDM texture is transferred directly onto the surface of the polymer during the injection cycle. Molders use this method to achieve a uniform matte finish that hides sink marks and scratches on the finished part.
When the texture is applied correctly, it improves the tactile and visual quality of the product.
Surface Replication
Molten polymer replicates the microscopic peaks and valleys of the steel surface as it is packed into the mold cavity under high pressure. The replication of sinker EDM texture depends on the melt temperature and injection velocity, as low temperatures prevent the plastic from fully filling the fine details of the metal texture. This incomplete replication leads to uneven surface gloss.
Draft Requirement
Demolding forces increase significantly when the mold surface has a rough profile. To prevent scuffing and ejector pin push-through, a sinker EDM texture requires a larger draft angle than a polished finish. This angle must be increased as the texture depth increases to allow the part to release without friction.
Tooling Wear
Electrode wear during the machining process alters the resulting surface roughness over time. This degradation of sinker EDM texture requires regular electrode maintenance or replacement to ensure that different mold cavities produce identical part finishes. Maintaining consistent cavity texturing is essential for multi-cavity production runs.