Optical Profilometry Metrology Protocols for Indirect Tool Cavity Topography Verification
Calibrated silicone replicas combined with optical profilometry yield sub-micron tool cavity topography metrics without destructive sectioning.
Stylus Profilometry
Meaning
A contact measurement technique determines surface roughness and topography by moving a physical probe across a material. In quality control, stylus profilometry provides highly accurate vertical displacement data by tracking a diamond-tipped stylus as it traverses the moulded part surface. This method is the standard for verifying that part finishes comply with specified design tolerances.
Measurement Mechanism
The instrument works by maintaining a constant force between the stylus and the surface as the sample translates beneath it. Vertical movement of the stylus is converted into an electrical signal, generating a two-dimensional profile of the surface. This raw data is then processed to calculate surface roughness parameters like Ra and Rz. Because the stylus physically touches the sample, it is highly sensitive to minute surface variations.
Moulding Assessment
Moulders use this technique to monitor tool wear and replication quality over the course of a production run. By comparing the surface profile of the moulded part with that of the tool cavity, engineers can assess replication fidelity. A decrease in peak heights on the part suggests that the polymer is not fully filling the tool textures.
This data helps moulders adjust process variables like melt temperature or pack pressure to restore surface quality.
Instrument Limitation
Despite its high accuracy, the physical nature of the technique introduces certain constraints. The stylus can scratch soft polymer surfaces, and extremely narrow trenches may be too small for the tip to penetrate. For these delicate or complex surfaces, non-contact optical methods are preferred.