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-----:Mandrel separation problems in Electroforming
Quickstart:
Electroforming is essentially the same process as electroplating. We call it electroforming if the plated layer becomes the actual object rather than being a coating on another object. Hollow gold teardrop earrings formed by plating onto wax teardrops are one example. The nickel stampers for vinyl records, which are created by plating onto a lacquer master and then separating the electroform from the master are another example.
Electroforms are generally much thicker than usual plated layers, which may dictate somewhat different chemistry or operating conditions. Nickel is the most often used metal for electroforms, but copper and gold are also common.
The mold or form which is plated upon to create the electroform is called the mandrel and it can be disposable -- made of wax which can be melted away, or aluminum which can be dissolved away -- or it can be a reusable/permanent mandrel of almost any material -- but in this case the electroform must be mechanically separable from the mandrel.
adv.
Alternate parting agents without dichromate
Q. I am currently researching alternatives to Dichromate passivation of copper and nickel mandrels for electroforming. I am seeking an effective method without the looming cost of expensive waste disposal. Is there a "safe" formulation for a passivating solution I can try? I plate in a nickel sulfamate bath at anywhere from 45-90 ASF.
Scott A Yox1996
Q. In our company we use electroforming for our cylinder production. In this process dichromate is used to build up a separation layer on the silver master for the following nickel plating process. Sometimes the silver surface becomes grey and the master is destroyed.
Can you give me a hint, to avoid this problem? Is it possible to use other chemicals than dichromate, because of the toxic problems of Cr(VI)?
Thanks,
Karl Poellmann- Weiden, Germany
A. Hi Scott, hi Karl. Egg albumin is probably not quite as good as dichromate, but may be good enough while eliminating the toxicity of hexavalent chromium. Good luck.
Ted Mooney, P.E.
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Mechanised method for stripping electroform from cathode
Q. Is there a mechanised method (i.e. not using a hammer) for stripping electroplated cobalt and copper from cathode plates without affecting the copper and cobalt. Since this matter is of great importance any information would be appreciated.
J.V.D.B.- Kitwe, Copperbelt, Zambia
2000
A. I'm not aware of a purpose-built mechanism, but in thread 424/45 Ed Perry explains his procedures including using compressed air, Geoff Smith describes using temperature change, and Trevor Crichton explains the need for and how to do proper polishing.
Note that in any case mandrels and electroforms must be properly designed, and you must passivate the mandrel with sodium dichromate, egg albumin, or another good parting agent for the particular metal.
Best of luck.
Ted Mooney, P.E.
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The fine line between too little adhesion and too much
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Electroforming in Restorative Dentistry (2000)
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Q. I am trying to plate Nickel onto copper to produce a mandrel for hot embossing. So I want to uniformly plate Ni that is easily lifted off.
I can plate nickel (sulfamate bath 55 °C) fine; my problem is I either get a non-uniform plate with poor adhesion, or a great plate with far too good adhesion to the substrate to lift off. Can anyone suggest a treatment for either the plating conditions, or the surface of the substrate that will allow me to plate well and easily remove the nickel.
Phillip McMahon- Melbourne, Australia
2002
A. Hi Phillip. What you probably need for your electroforming separation layer is a solution of about 10 percent sodium dichromate. You can adjust this concentration and the immersion time up or down, but you should be able to achieve uniform moderate to good adhesion. After good cleaning, immerse the part in the sodium dichromate and things should go a lot better. Good luck.
Ted Mooney, P.E.
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Problems removing tube shaped electroform from mandrel
Q. Hello,
I am a technician who is working on a project of nickel electroforming.
In practice I am starting from permanent mandrel, represented from a iron cylinder (features above) and I have to produce a tube from this, with a thickness of 120-150 µ and hardness about 400 HV, that will be entirely removed from the mandrel, without breakage.
The bath I'm using:
Ni sulphamate 680 cc/lt
Boric acid 23 grams/lt
Ni chloride 3 grams/lt
Antipit 2.6 cc / lt
I don't use other additives
15-20 A/dmq
50 °C
Cathode in rotation: 60 rpm
Nickel anodes in basket
Mandrel features:
diameter average : 200 mm
length (average) : 1300 mm.
The surface is coppered (150 mu)and chromed (7 mu) and appears very smooth (Ra =< 0, 30).
Mandrel preparation:
degreasing at room temperature
Passivation with a solution in water of potassium dichromate at 1,25%
Rinse.
The problem I meet is after the plating, It isn't possible to remove the sleeve from the mandrel.
This problem could be because I don't use additives? And if yes, what do You recommend?
Thanks for Your answer.
- MILAN, ITALY
March 18, 2009
A. I didn't get it clear if you are electroforming on the inside or the outside, but yes, stresses could tend to attach the electroform in either case. If stress is tensile an electroform deposited on the O.D. will tighten over the mandrel and make it difficult or impossible to extract without breakage (and vice versa). Do you use a tensiometer?
Guillermo MarrufoMonterrey, NL, Mexico
A. I will assume that you do not have wrap-around (edges of sleeve), because that will be too simple. I am involved with electroforming printing plates, and do not use additions. Any undercut to the engraving will cause the plate to grab those undercuts. I do not know if your mandrel has been machined, or how you achieved the surface smoothness. But any low and/or high spot can lock it on. I would first put a dial indicator on the surface.
David Williams- Ft. Worth, Texas
Q. Sorry I thought was clear: the electroforming is for outside and I do not use a tensiometer.
In any cases, my electroformed is 170 HV and those of the European competitors is 450 HV.
The cylinder have on both corners, an aluminium tape around the circumference just to define the extremes of the plate or more specifically, the pipe that will form.
The cylinder surface of copper and chrome-plated is already finished with grinding and further smoothed with extremely fine abrasive wheels. It has no holes or undercuts, is perfectly smooth.
Thanks
ERMANNO GIORGIO [returning]- ITALY
March 25, 2009
A. Ermanno
You have chosen a very difficult shape. It is relatively easy to break the bond between the electroform and the mandrel. Heat it to about 100 °C and drop it into cold water. However, you then have to remove the extremely tight fitting formed tube and it is much too thin to grip.
PMMA = PolyMethyl MethAcrylate
Suggestions:
1. If it is possible to have a slight taper on the mandrel it will be easier
2. PMMA makes a good mandrel. Good surface finish and easy to silver for conductivity
3. After plating - Low melting alloy (recyclable) or wax and conductive paint
4. Plate a thicker ring (flange) of Ni at one end and use it to hold the electroform while you push out the mandrel
5. Drill a hole through the mandrel, stop it off with wax and paint with a conductive paint. Plate the mandrel and also this end to form a closed tube. Use hydraulic pressure to blow the form off. Do not use air as the possibility of a burst tube is high and use a shield in case it does. If the air does not burst the tube it will fly for many meters, be a considerable hazard (and destroy your perfect tube!)
Geoff Smith
Hampshire, England
|
Q. First of all, I want to thank all those who with their suggestions have worked to solve my problem. - ITALY A. Electroforming with a cylindrical mandrel should not be a problem, as long as some basic rules are followed. Firstly, your deposit needs to have either neutral or slightly tensile stress -preferably very slightly tensile. I notice you do not have any additives, so I would recommend about 0.5 g/l sodium saccharin - this will not only give you a bright deposit, but it will also make it harder and make the deposit less compressive. Secondly your mandrel needs to have a slight taper to one end of it, so you can pull your electroform off the narrower end. Thirdly, the mandrel needs to be very well polished and putting down a passive film will be useful; this can be done by giving the mandrel a dip in either sodium dichromate solution (ca 2%) for about 2 minutes, or using a sodium metabisulfite dip (200 g/l) for about 10-15 minutes; alternatively use an electrolytic dichromate dip for about 30 seconds. Fourthly, mask off the ends of your cylinder so that no metal is deposited around the ends; if it does get deposited, it will stop the electroform form coming off the mandrel. Finally, electroform your cylinder in the vertical plane and have it rotating at about 60 rpm; make sure you have sulfur depolarized nickel anodes equally spaced around the sides of your tank.  Trevor Crichton R&D practical scientist Chesham, Bucks, UK |
Hi Trevor,
Thanks for your support.
Now I'm using the sulphamate bath (680 cc/lt. 9,5 gr/lt Nickel chloride. 23 gr/lt boric acid. 2,6 cc/lt antipit) with 2 gr/lt of saccharine.
The pH is a little too high (4,8)
DDC: 12-20 A/dmq
The hardness is around 380 HV and the deposit is very brittle.
I have modified the temperature at 40-43 °C to avoid some detachment during the electroforming from the mandrel in some areas. This effect is similar to bubbles and appears with very smooth surfaces and when the temperatures begin to be at 50-53 °C.
The use for printing process doesn't allow even a slight taper.
The mandrel surface is very well polished.
I have treated the chrome surface with a solution at 2,0 gr/lt of potassium dichromate for 3 minutes at room temperature according to your suggestion.
The ends are masked and protected with aluminium tape to avoid nickel deposition and to define the width of the sleeve.
The cylinder is rotating at 60-80 rpm in horizontal plane, and the basket with nickel anodes (not S) are equally spaced.
In these conditions, the parting from mandrel is often difficult and impossible to use in production; need a nickel plating less attached to the base or to break (or increase?) the stress.
- ITALY
A. This sounds exactly like what we do. The easiest way is to coat your smooth mandrel with PMMA by immersion and then slowly pulling it out. This makes it even smoother than before and puts down a layer about 5 microns thick. Then, you evaporate a thin layer of gold about 300nm thick, this is your conductive surface. Next you electroform at nearly zero stress. You have to mask the ends so it does not overlap the ends.
Next, once it is electroformed, Immerse it in liquid nitrogen for maybe 10 minutes. The mandrel will contract more than the tube allowing it to easily release.
Next, you use a cyanide gold stripper to remove the gold leaving a tube with very smooth interior surface. Rinse in
acetone
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to remove any PMMA before stripping the gold. The mandrel should be washed in acetone to remove PMMA and then re-used.
We can make very small tubes this way.
- Tallahassee, Florida
A. Ermanno,
I think you need to use a stress reliever. Ask your chemical supply house for a recommendation. One of the nice things about sulphamate nickel is that it does not need chloride, which can induce stress, but if you use a chloride free bath, you MUST use S nickel as the anode, otherwise you will have issues with anode dissolution.
David has also given you some pretty neat ideas too, so they may be worth a try. You can also consider using either aluminium as a mandrel and treat them as either permanent or disposable -- you can dissolve aluminium in sodium hydroxide. Have you considered using wax?
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
A. This is a late reply. However, if the goal is to make a smooth straight tube, using a precision smooth roll and not to pick up any printing impressions from it (which would themselves be undercuts and not permissible) then there are several options to apply thin and dissolvable coatings. One coating as suggested earlier is to PMMA via a dilute solution, but surface tension and non-uniform evaporation could induce slight non-uniformities. The dichromate coating is uniform if the cylinder is rotated and anodes disposed all around it as suggested earlier. Egg albumin as a stearic coating is also suggested. I am wondering why can't soft pure graphite by rubbed as a conductive lubricant and parting film ? ⇦ Answer?
Yannoush Greek- Athens, Greece
March 23, 2011
Precision electroforming with limited resources
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Q. How can I proceed for precision electroforming? What are the best methods to make mandrels with limited available resources?
Vaibhav Mishra- India
October 22, 2017
A. Hi Vaibhav. People have spent their whole careers in precision electroforming, decades of study & experience, so it's hard to answer "how do I do it?" in a forum answer.
Please tell us about your electroplating experience, what resources you have have available (where in India are you?), plus what you want to build of what metal (hollow gold earrings, nickel bellows, copper wave guides), then people can probably suggest the next step to start making progress. Good luck!
Regards,
Ted Mooney, P.E. RET
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Q. Sir I am doing my project at undergraduate level. I tried electroforming on PCB substrate and used potassium dichromate for parting purpose whereas the solution didn't work out properly and discontinuous electroforms were obtained. I am using Watts Bath for electroforming.
Can you suggest me the solution for passivation to be used?
- Ahmedabad, Gujarat, India
November 15, 2017
A. Hi cousin Vaibhav. The toxicity of dichromate might be a reason to try to use something else, but dichromate is the simplest, most widely used, most effective, and most reliable parting agent. Don't blame it for your first attempt at electroforming not being fully successful.
"Didn't work properly" and "discontinuous electroforms" are helpful, thank you ... but maybe not enough. Please <send pics for posting>, or describe more exactly what didn't work, and what you mean by 'discontinuous'. I assume that PCB means printed circuit board, but I think we need more info than that about the substrate and exactly what you are trying to do. Thanks again and good luck!
Regards,
Ted Mooney, P.E. RET
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Separating electroformed nickel object from copper base
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". It's actually the same process as electroplating, but we call it electroforming when you use the plated layer as an independent object rather than as a coating on another object.
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 be properly polished and 'passivated' before plating (prepared such that there will be 'proper' adhesion).
on AmazonToo little adhesion is no good because the electroform can then partially separate during the plating process, resulting in plating on the underside of the electroform and ruining it. Too much adhesion will cause the problem that you are seeing of the inability to properly separate the electroform from the mandrel.
Historically, and for many situations the most reliable passivating agent has been sodium 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. Egg albumin has been successfully used as a passivating agent.
I should note that patient and careful separation is required, not simply ripping one from the other
Luck & Regards,
Ted Mooney, P.E. RET
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Q. 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
A. Hi again.
Again if I am understanding that they are 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 with the chromate.
But be assured that similar processes and procedures have been used for mass production of vinyl records, CDs, video discs, and even DVDs with millions of tiny holes, so I'm sure that the problem is not 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.
As previously noted you need sufficient adhesion that the electroform doesn't separate from the mandrel ... but that doesn't demand strong adhesion right at the tips, so if just the tips are the problem, you could try a layer of egg albumin on top of the chromate, applied with a roller or similar method so only the tips of the pyramids receive it.
Luck & Regards,
Ted Mooney, P.E. RET
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Although we try hard to filter this forum by topic, public discussions still always wander a bit. Readers may also be interested in these related and somewhat duplicative threads:
• Topic #401/25 "Electroforms only partially stick to smooth mandrels"
• Topic #425/47 "Parting/passivation Agents to Keep Electroforms from Sticking to Cathode/mandrels"
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