Designing Restrained State Quality Fixtures for Flexible Plastic Assemblies
Restrained state fixtures simulate final assembly fasteners with calibrated clamps on datum targets to measure flexible plastic profiles accurately.
Tactile CMM Probing
Meaning
Physical coordinate data points obtained by touching a probe to the surface of a part as a contrast to its CAD model. Tactile CMM probing is the standard for high-precision verification of hole locations, boss heights, surface profiles and mating faces. The ruby tip of the probe triggers a signal the moment it touches the polymer, providing a data point with sub-micron accuracy.
This method is preferred over optical scanning for features that are hidden or inside deep cavities.
Surface Interaction
Deflection of the part under the probe force must be minimized to ensure accuracy. When performing tactile CMM probing on soft resins like thermoplastic elastomers, the contact force can temporarily deform the surface. High-quality machines use low-force sensors to avoid this error.
The choice of probe tip diameter also affects the result, as a smaller tip can drop into the texture of the plastic surface.
Programming Logic
Automated routines allow for the rapid inspection of complex geometries across multiple part lots. Tactile CMM probing follows a pre-defined path that hits every critical dimension in a repeatable sequence. This automation eliminates the variation that occurs when different operators use manual calipers or micrometers.
The resulting data can be used to track the wear of the injection mould over time.
Physical Contact
Physical contact takes more time than laser scanning.