Areal Surface Texture Filtering Selection in High-Precision Micro Injection Moulding
Selecting areal surface texture filter cutoffs under ISO 25178 matches transmission bandwidth to moulding replication limits, preventing false tooling rejects.
Primary Surface
Meaning
Total measured surface profiles that remain after the removal of nominal shape and tilt represent the starting point for polymer surface evaluation. This raw data set, termed the primary surface, is obtained by scanning the moulded plastic part with a stylus or optical metrologist. It contains both the high-frequency roughness and the long-wave deviations caused by the moulding process.
Analyzing this unfiltered data allows moulders to assess the absolute surface condition before digital filtering separates specific features.
Filter Application
Applying a digital filter removes unwanted spatial frequencies from the raw measurement. When the primary surface is filtered, it is separated into a roughness profile and a waviness profile. This step is necessary to isolate localized texture issues from macro-scale tooling defects.
Measurement Integrity
Instrument noise and scanning vibrations can introduce errors into the collected height data. High-resolution optical scanners must be isolated from environmental vibrations to avoid adding false roughness to the primary surface. Stylus force must also be controlled when measuring soft polymer surfaces.
A heavy stylus can scratch the plastic, creating artificial grooves that distort the subsequent calculations.
Industrial Specification
Component drawings use standardized surface texture parameters to define the quality of high-precision moulded parts. The primary surface is the source for parameters like root-mean-square height and maximum profile peak height. These metrics must be kept within specified limits to ensure proper part function in optical lenses and sealing surfaces.