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.
VDI 34 Finish
Meaning
The spark erosion scale established by the Association of German Engineers to standardize the surface texture of electrical discharge machined tools defines the roughness levels for textured polymer surfaces. A VDI 34 Finish corresponds to a very rough, heavily textured surface with an average roughness of approximately five micrometres. Molders select this specific texture to hide sink marks, weld lines, and other cosmetic flaws on the molded part.
It is commonly used for heavy duty industrial housings or textured handles.
Surface Specification
Machining a mold cavity to this standard involves using high energy electrical discharge pulses that erode the steel to create deep pits. The VDI 34 Finish requires precise control over the pulse duration and current to maintain a uniform texture across the entire tool surface. Consistent texturing is crucial to ensure that the molded parts have an even, non-reflective appearance.
Draft Requirement
Deep surface textures generate high friction forces when the plastic component is ejected from the tool. A VDI 34 Finish demands a minimum draft angle of six or seven degrees to prevent scuff marks and part deformation during demolding. This design constraint must be incorporated into the part geometry during the early stages of development.
Part Quality
Part aesthetics can be compromised if the texturing is uneven or if the mold accumulates residue. This VDI 34 Finish helps to disguise superficial molding flaws, but it also increases the risk of polymer trapping if the draft is insufficient. Regular tool maintenance is needed to prevent this issue.