Shreds in tool hole in aluminum PCB

Aluminum shreds were found inside the tooling hole after depaneling.

We ruled out contamination because the tooling holes were covered during depaneling. Out of three holes, only 2 holes with positioning columns inside have aluminum shreds residue.

The suspicion was the columns rubbing the insides of the holes when placing the panel, or the horizontal pressing & vibration during depaneling causing the inside of the tooling hole to leave shreds.

Anyone have suggestion how to counter this? We are now considering to polish the positioning columns but I'm not sure if it would be effective. Coating the inside of the tooling hole can be an idea but I'm not sure how plausible it is. Any advice is welcome.

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