The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Ideal type of mandrel to be used for photo-electroforming

Q. Hi. I'm a process engineer in an electroforming company here in the Philippines. We're using photo-electroforming and we're using a copper clad mandrel. We are using the nickel sulfamate bath and we usually have problems in removing the electroform from the mandrels. any suggestion on what kind of mandrel to be used? or are there any additives that can help remove the electroform easily?

Marylou P. Bacordio
process engineer - Cebu City, Philippines
2007

---

Q. We are manufacturer of Nickel screen by way of electroforming process.we are using stainless steel 316 grade mandrel. we usually problem is after removing of nickel screen from mandrel, nickel screen working face finish is white ( dull) and non working face is good. Finished products slot is uniform, Good ductility, Thickness is ok. I am not happy with finish. please any suggestion.

A .A.SHUKLA [returning]
- Nagpur, India
2007

---

Q. We are giving you our present electroforming details

We use etched permanent mandrel & used epoxy resin araldite GY 250 AND HARDENER 2969. Our electroforming bath Nickel Contains 55, Nickel Chloride 11.66, Boric acid 30.73, density 21 to 22, Operating Solution temperature 55 to 60, Mandrel Size 3.5 feet x 4 feet, Applied Current 450 amp(32 AMP PER sQ FEET) We use Inco s Nickel Round.
I want mirror or Decorative finish on working Face.

A .A.SHUKLA [returning]
- Nagpur, India
2007

A. Something confuses me. You say you use etched permanent mandrel. What exactly does this mean? Etching leaves a rough (grained) pattern. I am sure you know that if you want to get mirror electroforms, the mandrel must also be mirror polished. The main advantage of electroforming is that it replicates the mandrel finish to the sub-micron scale. Please explain further.

Guillermo Marrufo
Monterrey, NL, Mexico

---

A. My guess is you are using nickel sulphamate. Two things come to mind. Firstly, there is no brightener in your bath, so you will not get a bright nickel deposit. My favourite is sodium saccharin, because although it is not a truly recognised brightener, it is a good hardener and doesn't usually induce much tensile stress if used properly. However, it does produce a bright deposit. Alternatively, ask your supply house for a brightener. The chemistry of them is quite complex and you may need to add stress relievers to alleviate any induced stress. Secondly, the use of epoxy is presumably as a mask - sometimes epoxy can leach out into the plating bath and cause havoc - it all depends on how the mandrel has been pretreated and if the pretreatment has started to attack the resin. Trevor Crichton R&D practical scientist Chesham, Bucks, UK A. An etched permanent mandrel is a stainless steel plate, in which notches are etched, which are filled with an insulator. This mandrel is ground after filling, so you get a flat surface with conductive and non conductive areas. The electroforming will only grow on the conductive areas. You will have (of course) two different surface, the quality of the surface which is on the mandrel is only influenced by mandrel preparation, the better you grind the mandrel, the better your surface will be. The second surface is influenced by the mandrel and by the electroforming. If you use an electrolyte which contains no additives, you always will get a dull surface here. I don't know which side you refer to as the "working side", if it is the mandrel side, grind it better or even polish it, if it is the electroforming side, use a different nickel bath. Marcus Hahn - Lucerne, Switzerland