ISO 25178 Areal Surface Texture Parameters for Optical Inspection
ISO 25178 defines 3D areal surface parameters like Sa and Sdr, replacing 2D profiles to qualify optical non-contact inspection on textured tool steel and mouldings.
VDI 3400 Finish
Meaning
Numeric scales created by the Verein Deutscher Ingenieure categorise the roughness of metal surfaces produced through spark erosion processes. A specified vdi 3400 finish allows moulders to request a specific texture intensity from thirty levels of increasing depth. This standard simplifies the communication between designers and tool shops by using a common set of physical plaques for comparison.
Erosion Scaling
Numbers range from zero to forty five to indicate how aggressive the electrical discharge machining was. Low vdi 3400 finish values produce a smooth, spark polished look while higher numbers result in deep, grippy textures. Most commercial polymer parts sit in the 18 to 30 range for interior trim.
Visual Consistency
Reference plates provide a physical touchstone for verifying that the machine is set correctly. Matching a vdi 3400 finish ensures that parts made in two different countries will look identical when assembled side by side. It removes the subjectivity of descriptions like medium rough.
Draft Angle
Higher finish numbers require steeper release angles to allow the part to eject safely. Choosing a vdi 3400 finish requires looking ahead to tool geometry constraints to avoid drag marks. Technicians use this data to plan the electrode wear paths.