Ted Mooney, P.E. RET
- Pine Beach, NJ
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for Metal Finishing since 1989
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Separating copper and nickel for optics
Q. Hello,
To start off... I'm not a plating tech, I am a machinist, so I might not phrase everything correct. Here to learn!
Any thoughts as to why a copper substrate with features machined on top might be getting damaged during nickel plating? We use the copper as a mold core essentially and the nickel once separated becomes the cavity. Sometimes this works and sometimes the copper is ripped off with the nickel. the features are like tiny pyramids, very small, micromachined. Thank you so much, appreciative of any thoughts or ideas.
- Chicago
August 23, 2024
A. Hi Maggie,
In the plating industry we call what you are doing "electroforming". While it's actually the same process as electroplating, when you are using the plating as an independent object rather than as a coating on another object, that's what we usually call it.
Separating the electroform (the nickel) from the mandrel (the copper) requires that the shapes have a reasonable draft angle (which pyramids certainly do) and that the mandrel was properly 'passivated' before plating (prepared such that there will be only proper adhesion).
Too little adhesion is no good because the electroform can then partially separate during the plating, creating a mess of an electroform. But too much adhesion will cause the problem that you are seeing of inability to properly separate the electroform from the mandrel.
Historically, the most reliable passivating agent has been chromate. But environmental issues around hexavalent chrome, made famous by Erin Brockovich, has turned chromate into a red flag issue that many shops have been working to get away from. I have read that egg albumin has been successfully used as a passivating agent.
I should note though that patient and careful separation is required, not simply ripping one from the other, because there does need to be a good deal of adhesion or separation during plating will cause a ruined electroform. Sorry, but that's about all I can offer on the subject.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Hi Ted,
Thank you for your response. I do know that we use Dichromate. I believe it is brushed on. Sometimes I wonder if the brush actually takes some off of the very tips of the pyramids, where we see the damage. It's almost like they have been shorn off.
Machinist - Chicago
August 27, 2024
A. Hi again.
Again assuming that they are indeed pyramids with consequently good draft angles, I think you have a good understanding of the issue, although I would not be certain without further examination that your pretreatment steps (anything you might do after chromating and before nickel plating) are not the cause of the problem rather than inexact brushwork.
Similar processes and procedures have been used for mass production of vinyl records, CDs, video discs, and even DVDs, so I doubt that the problem is that your pyramids are too small.
You might try dipping the article into a vat of the chromate rather than brushing it on, and seeing if that helps or just makes it worse.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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