Surface Roughness Ra

Texture Definition

Gloss levels are influenced by the cavity finish. A low surface roughness ra results in a high gloss finish, while a higher value creates a matte appearance.

Release Interaction

Friction during the ejection phase is often easier to manage with a specific range of roughness. If the surface roughness ra is too low, a vacuum can form between the part and the tool, making removal difficult. Conversely, if it is too high, the plastic may lock into the undercuts of the texture, increasing the risk of scuffing.

Measurement Accuracy

Profilometers use a diamond stylus or a laser to scan the surface and calculate the average height. In production, surface roughness ra must be checked regularly to identify wear on the tool or the build up of additives. Maintaining a consistent Ra value ensures that parts from different batches or different cavities look identical.