Recast Removal Alloy 42

All,

I am trying to find a source that would be comfortable remove the EDM recast layer on Alloy 42. My thought is that it will have to be a chemical etch because the EDM surface is a .016" wide slot. I was working with a company that specializes in doing this for titanium, and after a couple weeks of back and forth the vendor chickened out.

I am hoping to find someone in the midwest due to shipping times, but I am open to any options. Thoughts?

How thick is the part? How much material do you need removed (what's the final width of the slot)? What's the precision needed relative to the inside profile and outside envelope?

I've cut a fair amount of Invar and Kovar, it's not that bad. If the part is thin, and there's ~.002"/side to come off, I'd use a 1/64" three flute carbide endmill and slot cut on a CNC.

Thanks for the advice.

The part is .090" thick, and the estimated amount of material that needs to be removed is less than .0001" per side after EDM. We have an overall tolerance of ±.002" so that isn't a big deal.

The part is for one of the big aerospace guys. We ended up just milling the slots in complete to get the job done, and it worked out well, but there is some working coming down the line where the feature will be under .008" wide and I am not confident we would be able to mill that. So per the customer spec, I need to find a way to remove the recast layer, then sent out a test for destructive testing.

What EDM are you using?

We may be able to do it without recast.

Agiecut Evolution I believe is the machine that these would be run in.

mneuro said:

The part is .090" thick, and the estimated amount of material that needs to be removed is less than .0001" per side after EDM. We have an overall tolerance of ±.002" so that isn't a big deal.

The part is for one of the big aerospace guys. .

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Don't know which aerospace company you're referring to, but the 4 that I know of either:
A: Allows EDM process without recast removal
B: Allows EDM process with a minimum of .xxx of removal, where .xxx is in the 'hood of .004-.01 ( depending on big aerospace co's spec. )
C: Does not allow EDM process, where one is still allowed to use the EDM process, but a much larger amount (.05 - ish ) must be subsequently removed by mechanical means.

So, at the end of the day, to stay within specifications, lack of recast is not sufficient!
You must observe the appropriate spec and do as it says.

Again. I don't know what spec you must obey, but PW, Boeing, Hamilton ( now Collins ) and Lockheed "Specialty process" specs don't have a provision to take off only .0001.

Chemical etch BTW is also a specialty process, ( so is sandblasting )

The part is for space, so it is outside a lot of typical aerospace specs. The big concern is surface treatments and outgassing. An etch has been approved, as well as sandblasting as long as a cleaning spec is followed.

Good morning mneuro:
From what I have been exposed to in the medical device world, this is going to be a hard task to try to outsource, and the sticking point for any vendor is going to be the certification that they have actually successfully done what they believed they have done when they put it through their etch or whatever.
That's probably why your titanium guys backed off...there is no contract juicy enough for them to accept the risk of liability for a failure until everyone in the game has agreed on a protocol to distribute that risk.

From what little I have seen, these negotiations can be very long winded and consume a ton of resources for all the companies involved, so unless there are big bucks being tossed around, a prudent subcontractor will NO BID unless he has either experience with the exact same process or a contract that gives him wiggle room or he's so damn hungry he will take it on with eyes wide shut.

Is your project that kind of project?
If it is, there are probably only a very few subs who are even in the game, and your titanium guy probably knows who they are and could maybe be persuaded to spill the beans and get you contact information.

If not, you have four choices as I see it:
1) Develop the process in house...expensive distracting and risky.

2) Do as Milland suggests and find an alternative process that eliminates the need; accepting the development costs of that alternative process.
Maybe wire EDM combined with diamond honing could be made to work?

3) Petition the engineers who designed the part to re-design it so the slot(s) can be made another way, preferably as a two piece assembly, or a laminated stack that's been acid etched or milled from thin plates or whatever.

4) NO BID the job as your sub has done.

It's kind of self defeating for an ambitious company, eager for contracts to accept this reality, but sometimes other work is much easier to make a buck on...you have to make the choice (assuming it's even your decision to make).

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Thanks for all the advice. We specialize in doing what others can't or won't, so I will probably go with option 1 and see what I come up with.

The money wouldn't be lucrative for a subcontractor, but the total job is pretty good, so worth some R&D for sure.

mneuro said:

Thanks for all the advice. We specialize in doing what others can't or won't, so I will probably go with option 1 and see what I come up with.

The money wouldn't be lucrative for a subcontractor, but the total job is pretty good, so worth some R&D for sure.

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I have sent you a PM with my email, give me an email if you would like to discuss some options to do this part.

We produce several parts that are 3 inches tall with .0095 slots top to bottom, our finishing department uses 15 micron lapping film to remove recast from inside the slots.

We manufacture several products for semiconductor field this are very sensitive to impurities. For these jobs we use Moly wire. No recast
We use lime away to remove brass recast.

CPM2014 said:

We manufacture several products for semiconductor field this are very sensitive to impurities. For these jobs we use Moly wire. No recast
We use lime away to remove brass recast.

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What machine brand do you have?

I am not sure what Moly wire and no recast has to do with one'nutter.

Ditto for Limeaway and brass deposit removal.

Electronics, nuclear and some other field work means no copper deposits, ergo Moly wire.
At the same time, while moly wire will leave no brass deposits, it will still leave a recast layer.


Now, regarding recast layer ....
15-20 years ago, perhaps there was a reason to guard against it.
Nowadays though, I would be very very curious to see a study on how much negative impact does the recast + HAZ have.
And I don't mean some metallurgist take an analysis using a Megatron Supercollider Hydrovibrator Uberscope.
Rather, a down-and-dirty destructive test on identical components machined using mechanical removal vs EDM removal.

Excellent point Seymour:
Probably THE definitive, most quoted study was done by Makino maybe 15 years ago.
It found that with a modern generator, the recast layer for wire EDM was measured in microns and fractions of microns.

That was then...I have no doubt machines are available that are even better now and I'll betcha, if you tossed enough money their way, any one of the big players would set up a custom machine for you optimized for negligible recast and probably even certify it for you.

Of course, pissy bureaucrats being who and what they are; they just might still refuse to accept it...after all common sense is not a positive trait in anyone who is in that sort of career.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

I don't know if it would be acceptable or not, but Muriatic (hydrochloric) acid works to remove recast. When sandblasting parts is to difficult, i use little rinse bottle to sprits on the wire cut area to dissolve the recast, it ends up looking as clean as if it were sandblasted. You have to neutralize the parts immediately after or the parts will rust. If you try it do it in a well vented area or underneath a fume hood.

Again, I have to stress that I do not no if it causes any degradation to the base material.

Hi TheBigLebowski:
Sadly the problem is not to find a process that works, it is to be able to certify it worked on 100% of the parts you intend to deliver.
That's always the rub on aerospace and medical and other high tech parts.

Just the convoluted hoop jumping that needs to occur to certify is sometimes massive, and of course, as soon as they make the specification, you KNOW they care and will be totally unforgiving if you didn't do what you promised to do; regardless if the part actually failed or not.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

implmex said:

Hi TheBigLebowski:
Sadly the problem is not to find a process that works, it is to be able to certify it worked on 100% of the parts you intend to deliver.
That's always the rub on aerospace and medical and other high tech parts.

Just the convoluted hoop jumping that needs to occur to certify is sometimes massive, and of course, as soon as they make the specification, you KNOW they care and will be totally unforgiving if you didn't do what you promised to do; regardless if the part actually failed or not.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

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Exactly why I hate aerospace work. I've shared the +/-.005 out 1 and 2 tenths so I won't re-hash it here again. I was given a print one time (mind you we had a UMC750 and ST20) with a piece of plastic, not sure exactly what it was, but they wanted to know if I could cut blanks about 1/4" long with a 45deg bevel on one end, then polish the ends so it would pass light thru. I was like... ummm, no?

I guess the original vendor quadrupled the previous price so they wanted to do it in-house.

edit: the plastic parts were somewhere around 1/8" diameter

implmex said:

Of course, pissy bureaucrats being who and what they are; they just might still refuse to accept it...after all common sense is not a positive trait in anyone who is in that sort of career.

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This is the big problem. To the best that I can figure, the minuscule recast layer will have no effect in this application, but they want what they want.

TheBigLebowski said:

I don't know if it would be acceptable or not, but Muriatic (hydrochloric) acid works to remove recast. When sandblasting parts is to difficult, i use little rinse bottle to sprits on the wire cut area to dissolve the recast, it ends up looking as clean as if it were sandblasted. You have to neutralize the parts immediately after or the parts will rust. If you try it do it in a well vented area or underneath a fume hood.

Again, I have to stress that I do not no if it causes any degradation to the base material.

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This is an acceptable option. I was actually just reading about it today. As long as I can send test samples out for destructive testing, I can get our in house process approved. I am hoping to give this a try next week some time, if my schedule permits.