Sorting Incoming Material
A manufacturer of cable reels had sporadic failures in high voltage proof tests. These assemblies are made using plastic brush post insulators obtained from an outside supplier. There was no reason to suspect one lot of material over another, but the re-work after failure was costly (~$10K annually).
The critical areas of the insulator components were visually examined by cutting several parts to reveal what happened during testing. The failures seemed to be characterized by a large cavitation blown through the thin wall in this region along the seam line.
Visual inspection was used to evaluate the condition at the seam of the injection molded plastic insulator by using a narrow diameter borescope equipped with a right angle mirror. This provided a clear view of the critical area. Suspect parts were then set aside for monitored assembly; a precursor to the blown out region, appearing as a small indent at the seam, was the target defect. In controlled experiments it was shown that this small flaw was indeed related to premature failure. Any parts having this feature could thus be screened out prior to assembly.