Pressing defect

[Andyber]

Hello everybody,

firstly, thank you for the acceptance to your community. I work as a technologist of electroforming in czech company and we have an issue during the pressing.

Here is the summary about the issue:
- both stampers and record are damaged (one stamper is damaged more than the other one) immediately after the first pressing cycle
- it´s not getting worse with more pressing cycles
- Cu plates/mothers are OK, so it´s not a problem with separation
- the issue appears always only on first track (approximately 2 cm from the edge)
- the issue doesn´t appear on every stamper or every pressing machine, it´s "coincidence"

Please, does anybody have an idea what´s wrong?

Thank you very much
Andrea

Some photos attached

[Aussie0zborn]

Are your stampers "kissing" by any chance? Kissing stampers would usually damage more than just one groove but that's what this damage looks like. Is the OD of your stamper formed properly to fit snugly onto the mould? Which presses are you using?

[Andyber]

It depends, sometime it´s only one groove, sometimes the first track is damaged all around perimeter. Because we have two "types" of forming machines (old one and new one), we made some test to see, how the stampers fit onto the mould. Our first idea was same as yours, we thought that stampers with large pringle shape (from the new machine) cause this issue, but during this test, we found out, that stampers with flat shape (from the old machine) fit onto the mould less properly than with the pringle shape. Just for sure, we stopped using the new forming machine, but this issue is still there.
For pressing we are using automatic presses Alpha Toolex.

Thank you

[andybee]

looks like the stamper is too thin, so it cracks at the bottom of the groove? if there are very deep grooves,
this can be a problem. have you measured the thickness of stamper? should have arround 0.25mm