Electro-polishing stainless steel 1

[antknee]

Hi,

I need to know how much material is removed from stainless steel with electro-polishing. I have some laser drilled holes that are 10 microns (10 millionths of a metre) in diameter and i want to know how much the diameter will increase if they are electro-polished? And how much rounder will the holes get?

Regards,

Antknee.

 

[berkshire]

This is a bit like asking " how long is a piece of string." Immersion times for electro polishing can vary from a few minutes to several hours.
Here is a link to somebody with a bit more job knowlege.
B.E.

http://www.neelectropolishing.com/passivation.php

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[antknee]

Surely there is a limit to how big the laser drilled holes will become in anything like a practical time? And if for example the holes started out as squares would they ever end up round in a practical amount of time? I realise the question is a bit length of stringish

 

[TVP]

A typical process time is 5 to 15 minutes. You can expect material removal of ~ 5 micrometers from the surface.

 

[antknee]

That is interesting and more removal than i'd thought likely. It appears I could increase the diameter of these holes by 10 microns to 20 microns.

Does anyone know of a company that can electro-polish specialist parts for research and development? I've attached the job I need doing, it's very specialist.

Regards,

Antknee.

 

[EdStainless]

So you need to EP one face of a disc?

You must make electrical contact with the part. For this one you might need a contact spring on the back and then seal the edges with wax.
There will also be a working electrode. It will be similar shape to your part.
I don't know of any way to control the EP of half of the edge.
How has the part been prepared? this is the other half of the question on what surface finish do you need?
Contrary to popular perception EP only improves the micro surface finish, not the macro.
The mechanical polish prior to EP is critical to getting a consistent finish.
When we EP we aim to remove about 0.0005" of metal.

Is your hole through the disc? If so and you EP from one side the hole will become tapered.
In order to keep the hole straight and uniform you would need to have an electrode strung through it.
At this size I don't see that happening.

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Plymouth Tube

 

[antknee]

So you need to EP one face of a disc?

You must make electrical contact with the part. For this one you might need a contact spring on the back and then seal the edges with wax.
There will also be a working electrode. It will be similar shape to your part.
I don't know of any way to control the EP of half of the edge.
How has the part been prepared? this is the other half of the question on what surface finish do you need?
Contrary to popular perception EP only improves the micro surface finish, not the macro.
The mechanical polish prior to EP is critical to getting a consistent finish.
When we EP we aim to remove about 0.0005" of metal.

Is your hole through the disc? If so and you EP from one side the hole will become tapered.
In order to keep the hole straight and uniform you would need to have an electrode strung through it.
At this size I don't see that happening.

Hi Ed, yes I need to EP one face of the disc. The drilled holes are completly through the part, all 0.2mm, and the intention of the procedure is to shape the hole, giving the top half a bigger diameter. The surface finish isn't a consideration.

There is a way of doing this, but I'm not sure which companies could do it, or the exact mechanics. It is for R&D so I need just a couple of small parts at a time, and not rack upon rack. Does anyone who can do this spring to mind?

Removing 0.0005" (12 microns) will be too much so I presume I'd just get these EP for a short time?

Thanks,

Antknee.

 

[EdStainless]

Yes, shorter time, and/or colder or at lower current densities.
You could try this on the bench top.
A glass battery box, some Cu plate and leads, a DC power supply, and EP solution (sulfuric/phosphoric with some additives).
It will take you longer to mount each part then EP it. This is a few minutes each is all.


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Plymouth Tube

 

[antknee]

I could try this, I'd have some health and safety concerns though... how concentrated would the acid need to be? And what sort of current? It doesn't look too difficult in theory, I can even remember doing some electroplating at school many years ago!

Regards,

Antknee.

 

[EdStainless]

You do it in a fume hood, there will be a little acid vapor and some Hydrogen.
Buy the EP solution premixed from a supplier.

Info is out there on current density and such.
I won't try to remember, and risk telling you wrong.

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Plymouth Tube

 

[antknee]

The best mixes appear to be 45% sulphuric and 55% phosphoric acid. I couldn't get permission to use that because spillages would result in hospitalisation. I could use some diluted sulphuric, the type that would be used in a school lab etc. I'm guessing that would work? but take longer, probably hours. Thanks, Ant.

 

[berkshire]

Antknee,
I have had good results electropolishing stainless steel with just Dilute Phosphoric acid.
Since you are in the UK. I do not know what health and safety would have to say about that.
Are you still working in a test lab situation, or do you have your product into a manufacturing stage yet?
Berkshire.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[EdStainless]

The ratio is about 45sulfuric/55phosphoric, but the solution is more dilute, there is a lot of water in it.
There are standard commercial sources for it pre-mixed, with additives in it.
You don't want to just use straight acid.

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Plymouth Tube

 

[antknee]

I'm working in a test lab, so I will be seeing what works and what doesn't myself. I've spent an hour googling for dilute electropolishing solution suppliers but drawn a blank. Can anyone give me a heads up where to look? (Preferably in the U.K.) I wont be able to use a test hood, probably, but the rest of the kit I either have or can source easily. Thanks Ant.

 

[EdStainless]

Looks like a few prospects

https://www.google.com/

stainless+electropolishing+solution+UK

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Plymouth Tube

 

[antknee]

I guess I was looking for a retail type shop to sell me 1 Litre or so. I'll have to try industrial companies. Regards, Ant.

 

[MiketheEngineer]

This may be a dumb answer and not what you want - but how about polishing before drilling the holes??

 

[HDS]

It sounds like you are not really electropolishing for polishing. You want to electrochemical machining or forming. There are probably better ways to make your small tapped hole in the precision you are after.

 

[antknee]

I'm not going to be able to get any EP solution that is safe or in smallish quantities. I think I'll get some sulphuric that is 1-5% concentrated, so safe and experiment with that. For Mike and HDS, you've skipped to the end of the conversation while missing my third post which gives more info. Regards, Ant.

 

[MiketheEngineer]

Go figure - I don't listen to my wife either.

You can buy sulfuric acid at Lowe's - here in the states. - a big box hardware store. Used to clean driveways, etc...