Copper electroforming problems

A. Hello Sebastian, you could be co-depositing some unwanted metallics in the bath. Your copper bath supplier should be able to do a full analysis on the bath that includes suspect metal concentrations. Iron is a big one to watch. You can also dummy plate the bath at low current densities. Watch the temperature during plating as well. As far as color change caused by different amperage, there must be a problem either with the solution, rectifier, or other parameters for the process.

A. Hi, D. Yes, as you suspect, the problem is not the limitations of the technology, but that you are doing something wrong :-)

The preservation of detail that you are looking for is not even a challenge for a properly operating process. Compact discs with their billions of precise dimples, and record stampers, wave guides, precision screening and a host of super critical items are made by processes similar to yours.

First, please talk to a plating chemical supplier and consider getting a proprietary copper plating bath. Their leveling/brightening agents are the result of decades of research and development. Follow their technical data sheet, and you'll quickly see dramatic improvement. Then control the temperature as recommended, and keep the amperage in a very low range. You may also want to get out to some local AESF meetings to discuss your situation and polish your skills still further.

Although you want to minimize the defects you speak of, they are on the outside of the electroform and it is the inside surface that is most important because it will be replicated. Good luck.

A. My company also does electroforming on wax shapes (for a totally different application) and it sounds like a bath control problem. Follow the previous advice and tank to a qualified vendor. We are using a product that was developed for rotogravure (printing) but we control to a lower hardness. It is a proprietary bath and I'm sure other vendors have good products too.

A. Hi, Mark.

Sorry that commercial products are expensive to buy and ship, but virtually every production plating shop finds that they really are worth it. Hopefully a reader can offer some ideas for specific generic formulas, but I don't have any. In fact, I think that you might benefit from considering a different proprietary salt rather than copper sulphate.

One point to remember is it takes time to make a quality electroform--a lot of time! While it may be possible to acid copper plate at 40-50 ASF, you'll probably need to electroform at a small fraction of that to avoid nodules. Best of luck.

A. One thing is very important. Are you using air for agitation of the solution? If not, this is very important for distribution of copper and leveling. Then, and this is for the last 41 years, is a product that I use: its called UBAC#1. I also have made electroformed copper guitar, one piece guitar. I can also duplicate any wooden instrument in copper, but that's a different story.

A. I have done an extensive amount of electroforming in my business. I have done everything from real flowers to baby shoes to wax models.

From some of your successful attempts, I assume that you are applying the conductive paint, silver nitrate, tin solution, etc., in a proper manner prior to plating. From my experience, you can look at the part after it had been in the tank for about a half an hour to get a very good indication whether your power (amps) is properly set. If the part is copper colored like a new penny, then your setting is perfect. Salmon-pink equals amps too low. Burnt brown or dark brown, amps too high. Try to calculate the area being electroformed as best you can. 10th of an amp per square inch … no less … no more. As for your rectifier, it may be on the blink.

Very exacting and informative, Henry. Thanks!

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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A. Hi Joseph, I can see that we have confused you a bit. Sorry, but please try to forget the idea of vinegar ⇦in bulk on eBay or Amazon [affil links] solution -- you might still be, by law, generating regulated hazardous waste anyway :-(

A realistic guideline about avoiding hazardous processes though would be to not consider using any cyanide-based solutions, any concentrated acid or alkali, any chromic acid, any cadmium, mercury or lead, or any fluoride compound no matter how dilute. copper sulphate based solutions can be used for electroforming, and copper sulphate is often used in high schools for similar experiments.

As for the desired concentration of copper, it's pretty much "the more the better". A simplified explanation is that the copper ions must migrate across the solution and through the boundary layer, and you do not want the cathode ever "starved for copper" because then the excess electrons will pull hydrogen ions out of solution instead, leaving behind OH ions to neutralize the acid you need and causing other problems. High circulation rates make for better filtration and better ion transport across the solution.

As for what you might be missing that "jumps out at me", it's that real plating processes are not home-brew affairs :-(
You don't mix them from basic chemicals; you buy a proprietary plating/electroforming solution from suppliers who have figured out, from years of research, exactly what they need to contain besides the bulk ingredients like copper sulphate. The thing is, it's drop dead easy to move metal from the anode to the cathode, but getting that material to actually constitute a useful robust deposit is difficult. One other thing that jumps out is that you might find it productive of your time to look for the "Metal Finishing Guidebook", the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] , or another plating textbook; books are invariably arranged in a structured tutorial fashion where learning is straightforward; smatterings of info from different sites offers no organizational structure, so progress can be tedious, and always involves ten steps forward / nine steps back because you're guaranteed to partially misunderstand things when the information doesn't come to you in proper sequence and context :-)
Best of luck!

A. Hi Ornella. I don't necessarily see environmental harm from either of these processes. The potential environmental harm comes from misuse or mishandling of the process solutions, not from the electroformed object. But silver plating may only be practical from cyanide based solutions and they are quite dangerous to use, and only for the experienced, not for beginners. Copper should be fine, and if you need a contrasting color, maybe think of nickel rather than silver?

A. Acid copper electroforming is a comparatively harmless solution if compared with cyanide-based. As Silver electroforming solution you can use ferrocyanide bath (1% of cyanide toxicity and it works), phosphate bath (according to one ex-USSR handbook), or thiosulphate bath (according to one expired US patent) or you can buy proprietary bath. Hope it helps and good luck!

A. Ted is right. All plating solutions are harmless to the environment until they are wrongly used and processed and let loose into the environment. However, if you want to take account of the carbon footprint of the solutions, then you need to do a complete life cycle analysis and I am not sure this has been done in the chemical industry. Electroforming is a precise and delicate science that has taken many years to perfect. It is not possible to formulate a new electrolyte that is green (although nickel solutions are all green!) as the requirements are for specific deposit properties. The best electroforming solution for nickel is nickel sulphamate and for silver it is silver cyanide. The trick to making these environmentally green is to keep them away from the environment and have sufficient environmental protection that they cannot get in contact with the environment.

A. In electroforming the basic principles involve the selection and special treatment of the mother surface to permit separation and a proper chemistry and plating parameters to produce very thick coatings without cracks, distortion or premature separation. From this very brief idea you can follow that you need a pattern with exactly the negative surface of the electrode (positive to the EDM mold surface). The rest is a matter of either years of personal research and involvement or the hiring of a professional in the field. One organization that could help you is The Nickel Development Institute.

A. I think you should get a copy of the book Properties of Electrodeposited Metals and Alloys [affil link to Amazon or on AbeBooks affil links] , by W. Safranek. It's full of references to the properties of electroplated or electroformed copper (and other metals too) using different electrolytes and conditions. Also, mechanical work hardens copper (all kinds) and makes it more resistant.

A. Also get ASTM B832, 'Standard Guide for Electroforming with Nickel and Copper',
and a freebie, 'INCO NICKEL ELECTROFORMING PROCESSES AND APPLICATIONS' at www.inco.com/customercentre/nickelplating/science/pdf/EcopyElectroformingGuide.pdf

The above items together are basically an update of the Electroforming chapter in Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] , 4th Edn., although omit iron electroforming.

The Electroforming chapter in The Canning Handbook [on eBay, Amazon, AbeBooks affil links], pages 573-590 (23rd Edn.), gives more information on plating Ni-Co alloys.

The Electroforming chapter in ASM Handbook, Vol. 5 Surface Engineering, is short but gives more iron plating solutions and mentions periodic current reversal for producing fine-grained copper of excellent mechanical properties in greater thicknesses.

One probably can locate additional information by searching on the authors and titles of papers presented at the 1996 AESF & NiDI Electroforming Course & Symposium, www.finishing.com/library/conferences/eform96.html

However, I have some doubt that an electroformed copper pressure vessel is permissible under the ASME Boiler and Pressure Vessel Code. Staying below 10 inches diameter will avoid the regulations.

Also, pure copper isn't very strong and suffers from creep when moderately heated, so normally isn't used for pressure vessels. The wrought Cu alloys typically used are alloyed with Ni, Sn, Al, Fe, Zn, Mn, etc.^* and have annealed strengths 1.5 to 4 times that of pure Cu. For higher strengths, Cu can be clad onto steel.^** The NASA rocket application requires extremely high thermal conductivity rather than high strength -- an oxygen-hydrogen combustion chamber is cooled by liquid hydrogen -- so the only alternatives to copper are silver & gold.

* ASTM B171/B171M, 'Standard Specification for Copper-Alloy Plate and Sheet for Pressure Vessels, Condensers, and Heat Exchangers,' and ASTM B96/96M, 'Standard Specification for Copper-Silicon Alloy Plate, Sheet, Strip, and Rolled Bar for General Purposes and Pressure Vessels.'

** ASTM B432, 'Standard Specification for Copper and Copper Alloy Clad Steel Plate.' "The material is generally intended for pressure vessel use but may be used in other structural applications where corrosion resistance or conductivity of the alloy is of prime importance."

A. Hi Robert,
If this was high current density burning you would think you would be getting it at the top or at the point of rack/wire to part or outer edges. Because I don't know of your exact bath make-up, I can only suggest fixturing a copper thieving strip an inch or so below the part. If you can't incorporate the thief strip on the rack or wire you can hang the strip from the cathode bar with two pieces of copper wire for placement. This will help, and most likely eliminate burning. Good Luck!

A. Either the bottom of your anodes hangs well below the part, or you are getting stray current through something metallic which is below the part. Piping, heater, etc.

A. I think that Mark is on the right track. Current will bounce off the floor of the tank and increase plate on the bottom. I also wonder if you have enough agitation in the tank.

A. The most common copper electroforming electrolyte is an acid based one, using 200-250 g/l copper sulphate ⇦this on eBay or Amazon [affil links] with 50-75 g/l sulfuric acid; temperature about 25-30 °C and current density 2-10 A/dm2. Anodes are phosphorus deoxygenated and agitation is air or mechanical

A. Hi Eric. I'm only half understanding your clever use of copper scrub pads, which is something I've never heard of. But I think I can guess what is wrong with your graphite-only or copper paint-only approach to large objects, and that is that the metallization can only carry a very low current without burning. When you are plating a small object the thinness and limited conductance of the graphite/paint isn't a severe limitation, but on larger objects it is. I think you need to find a way, whether it is with copper scrub pads or some other way, to bring electrical contact to many points so you don't have more current flowing through the metallization layer than it can sustain. Alternately, it may be possible to electroplate at a very low current density for a little while until you have a good conductive "shell" that can carry many times more current than the graphite "shell" … then you can up the current density to your usual values.

Regards,

A. Good, usable and download free book on that subject is Die Galvanoplastik by russian german Moritz Herman von Jacobi (inventor of electroforming). Hope it helps and good luck!

A. Hi Sylvia. Electroplating/electroforming isn't necessarily easy. For some of the regular readers and visitors to this forum, electroplating has been their career for 50 years, yet they are still learning. So patience is a requirement.

Semantics: the difference in "electroplating" vs. "electroforming" is pretty simple: if you have an object and you put a thin coating of a metal on it (like the chrome plating on a truck bumper or the rhodium plating on a white gold ring), we call that 'electroplating'. But if the plating actually becomes the object, not just a coating on it (for example, hollow gold earrings which are made by plating gold onto wax which is later melted away), then we call it electroforming … simply because we've 'formed' an object.

When we electroplate onto a leaf or a flower, most people will call it 'electroforming', but it's a bit ambiguous -- is it a flower that has been plated, or was the flower just a form and the metal is the object of interest?

Yes, in general you can use electroplating solutions to do electroforming. But in every endeavor, tweaks are possible, and customizing to a given purpose can improve performance. A plating solution optimized for plating bright nickel will probably not be great for electroforming heavy layers because the metal will be very highly stressed. So those who say you should use 'electroforming' solutions are not exactly wrong either :-)

I don't know what kind of metallizing paint you used and what kind of plating solution you are using, and we have no other data, so it's hard to say why the plating isn't sticking to the paint. There could be a lot of reasons. But I'd suggest you practice plating on metal and become reasonably competent at it before you introduce plating onto conductive paint as yet another variable to tame. Best of luck.

Regards,

A. Hi again. Glad to hear of your improving success.

I tried to answer your question about electroplating vs. electroforming, but I'll try again:
Electroplating is usually (although not always) very thin. Gold or rhodium plating, for example, is usually well under a micron thick (40 millionths of an inch). But an electroform, since it is an actual usable object, is thousands of times thicker. The problems that may arise at this thickness include too much internal stress in the plating, which will causes the electroformed object to curl up. This is especially a problem in nickel electroforming, for which much different solutions are used than in bright nickel electroplating. But copper is a soft and low stress metal, and some copper plating solutions seem to be fine for both applications.

Luck & Regards,

A. Hi again. A given copper sulphate bath can be used for both copper plating and electroforming, so those who say one bath is all you need are right not wrong. But absolutely anything can be optimized.

Canned coffee sellers offer this grind for Mr. Coffee machines, another for electric percolators, another for expresso, yet another for old fashioned percolators -- is it actually important to pick the perfect grind? Are we to believe that copper plating solution is the one thing that absolutely cannot be optimized for plating vs. electroforming? Certainly it is possible to put a brightener into a copper plating bath that is designed to make the plating hard and bright, but which will not be ideal in an electroforming bath.

It's just life that some will point out a distinction and call it important and others will call it a distinction without a difference :-)

Regards,

A. Hi. Copper concentration tends to grow in acid copper plating, especially if you are plating at low current density, which is usually the case when electroforming. Are your anodes phosphorized copper? If not, that should help. Please see letter 848 for a good discussion of copper anodes. For now, you may have to dilute the solution to get the copper concentration down.

Regards,

A. Hi Nola. This is not generally considered harmful. Large plating shops almost always leave the anodes in their tanks all the time.

Regards,

A. Hi Rachel. The rectifiers you mention have far, far more voltage than you need. You'll almost surely never use even 6 Volts. And 5 Amps should be more than enough for any ring-sized object; Henry suggests 1/10 Amp per square inch of surface area and I'm confident that he's right and you should not exceed this.

I think you'll be able to plate onto brass substrates with reasonable adhesion from copper sulphate.

Regards,

A. Hello Caitlin, there are a few causes for rough plating. Brighteners are a grain refiner for your deposit. After plating so many pieces it should be added by a certain amount of ampere hours. Your tech data sheet for the solution will give you that info. I find that a Cu sulphate bath plates/electro-forms best at 70-75 °F. If the temp rises, a small chiller or an easy method of cooling (your discretion). Another cause is organic contamination. I don't know the volume of your solution so maybe a small filter with a carbon pack for 2 hours maximum. The other common cause is particulate matter in the Cu solution. Filtering through a 5-10 micron filter will solve that. Depending on your anode setup if using small Cu anodes they should be bagged with polypro or Dynel bags. Do not use any bags with a cotton content. You have some measures available to you to keep the solution longer. Good Luck!

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A. Hello Ian. There are wetting agents made for air agitated plating baths to prevent this foaming; the supplier of your copper plating bath should know about them. Electroplating baths are "equilibrium processes" which are designed to -- if all goes well -- run forever; in industrial applications, copper plating baths are filtered, and various purification steps are taken as needed, and the plating bath is almost never dumped and re-made.

If your library has a copy of The Canning Handbook.
it has a good chapter on copper plating, and another good one on electroforming.

Regards,

A. Hi Julie. I suspect that nobody except the particular vendor who is offering that solution can tell you what it means. Both solutions are probably "acid copper sulphate" based.

Regards,

A. Alexandra: It sounds like you are getting little if any current flow. Check that all electrical connections are clean and tight. It would be best if you had an ampere meter, but even a simple DC volt meter will help. You can pick one up at a big-box hardware store that will read low voltages. Depending on your setup, you'll probably need 2 or 3 volts. Or if you can measure amps, maybe 4-8 amps per square foot of surface being plated.

Are you certain you don't have the connections reversed?

(+) to the anode (-) to the part.