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Parting solution for Nickel electroforming of Brass

Q. Respected Sir,

I have been working on Nickel electroforming on Cu/Brass workpieces for a while now. My end product is to produce 3-D micro-structures by electroforming on a brass/Cu workpiece, which is produced by a non-conventional machining process (e.g., EDM). I have been using Nickel Sulfamate as an electrolyte, and Nickel pellets as Anode, while cathode being a Cu/Brass workpiece. I used Sodium Sulfide as a parting solution (concentration of 8 g/L) on a Brass workpiece, by immersing the Brass workpiece into the solution for 60 secs. Unfortunately, deposition did not happen as expected, let alone parting. Could you please suggest the parting film/solution that is to be used for my requirement, along with concentration and application time?

Awaiting your response.

Thanking you,

Sincerely,
Anand Pratik
Student - Mumbai, Maharashtra, India
September 25, 2010

A. Firstly, you need to make sure you have a draw angle on your electroform; that is, the electroform is tapered, so it can be pulled off your mandrel. Next you need to make sure the mandrel is highly polished and there are no surface features that can cause the electroform to become physically attached to it. Finally, you need to make sure you have a good release layer. I would recommend sodium metabisulphite at about 200g/l and leave the mandrel in it for about 10-15 minutes. This will make the brass go blackish. Rinse the mandrel, but do NOT put it into any acid, as this will dissolve the layer.
You can also use potassium permanganate ⇦ on eBay or Amazon [affil link] solution if you are unhappy with metabisulphite.
You may find it better to use stainless steel mandrels as they can be polished better

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

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