Having difficulty machining Inconel

crossthread · Jul 10, 2020

I was given a pallet of heat treated 718 Inconel (about 1500 pounds). I have never machined this alloy before and I've just been playing around with some scraps. I have tried HSS, carbide and ceramic inserts and not having a lot of luck with the finish. I have tried various coolants, feeds and speeds and just don't seem to be able to have much luck with it. I don't have a hardness tester so I can't offer much there, but was told it was heat treated. Has anyone else used this material and if so could you offer any tips? Thanks very much.

TeachMePlease · Jul 10, 2020

"Having difficulty machining inconel"

In other news, water is wet!

Sorry, no real help from me, but others will be along shortly. All I know is you want a seriously low Surface Footage.... Like, tens, not hundreds.

It would probably get you better advice if you gave us a rough idea of the part shape/operations you need to perform.

crossthread · Jul 10, 2020

Thanks for the reply. I don't have to make anything out of this material yet. It was given to me and I am just playing with it at this point. I am turning a 1" piece of bar stock just to get a feel for how it machines so when I do need it, I will be more prepared.

Peter from Holland · Jul 10, 2020

Sell it and buy the material you need

Peter

Milland · Jul 10, 2020

Peter from Holland said:
Sell it and buy the material you need

Peter

Not a bad idea if you don't need that alloy itself - high nickel, can get some real money for it (but perhaps better to wait a bit).

If you want a good resource for 718 tips, check out the videos on this channel: YouTube David Wilks is a real treasure for information on trepanning, but also general turning tips on tougher materials. Worth the watch...

carlherrnstein · Jul 10, 2020

Inconel can be nasty. Tools must be sharp, well oiled, run stupid slow and replaced the instant they are dull.

plastikdreams · Jul 10, 2020

Inconel is between 1.00 and 2.75 here depending on grade and quality.

I'd keep a few pieces and cash in on the rest lol

DanASM · Jul 10, 2020

Titan Gilroy put some videos up of machining inconel with ceramic inserts. I saw like 2250 SFM and was shocked. I guess ceramic is inert and does not conduct heat. It gets the metal hot enough to soften it and as it becomes softer it cuts a chip.

This was milling not turning though. I saw some other videos of carbide being used and it runs very slow (10-15 SFM I believe) and the inserts dont last very long at all.

I do not know about finishing quality. not sure if the ceramic inserts are made for that or not.

If you have no need for it then just sell what you can and keep some pieces to play with.

dana gear · Jul 10, 2020

Milland said:
Not a bad idea if you don't need that alloy itself - high nickel, can get some real money for it (but perhaps better to wait a bit).

If you want a good resource for 718 tips, check out the videos on this channel: YouTube David Wilks is a real treasure for information on trepanning, but also general turning tips on tougher materials. Worth the watch...

Yup, if you don't have a job/project that flat out requires 718 Inconel, then I would do just what everyone else says to do and sell, It's bad enough to work with when you have too, let along for giggles and grins.

crossthread · Jul 11, 2020

Thanks everyone for the replies. I may very well be stepping on my pecker here. I am going to take the advice of you folks and dump it. I had no idea it was going to be this tough to machine and I really don't have a need for it or foresee one. Just thought I would chuck up a round and whack at for fun never having used it before. Kind of reminds me of the time I picked up a 5 gallon bucket of used exhaust valves thinking I would forge them into decorative rosettes for a barn door. Yeah right. You can get those things white hot and hit them with a hammer on the anvil and they just stare back at you.

Milland · Jul 11, 2020

If you have certs for the material, try offering it for sale first before looking at scrap. Here or on eBay, with certs you'll get more than scrap. Not sure how you'll do without them, but if you have a lot it may be worth getting your own lab cert - it should pay in higher sale price.

redlee · Jul 11, 2020

Milland said:
If you have certs for the material, try offering it for sale first before looking at scrap. Here or on eBay, with certs you'll get more than scrap. Not sure how you'll do without them, but if you have a lot it may be worth getting your own lab cert - it should pay in higher sale price.

Or send it back to hell where it belongs.

Milland · Jul 11, 2020

redlee said:
Or send it back to hell where it belongs.

If we ever get the aircraft industry running again, you'll be glad we have such a nasty, evil metal...

redlee · Jul 11, 2020

Milland said:
If we ever get the aircraft industry running again, you'll be glad we have such a nasty, evil metal...

And the Oil and Gas industry, I worked with Inconel for 30 years and don’t miss it.
I realize it loved by many industries but it’s nasty stuff to work with.
Oh you need 4 10-32 drilled and tapped how deep.

I always get a laugh when I see a thread titled I need help with 316.

number 2 · Jul 11, 2020

I haven’t turned 718 but I have turned 625 which is considerably kinder. As mentioned use a sharp tool, pick your speeds carefully, 718 will be pretty slow. Use a 45 degree tool, pre chamfer the start of the cut if you want, it does help. For drilling as soon as it dulls resharpen. If it work hardens it’s challenging to get through only to dull the drill again in the process. If you can’t get or use a 45 degree boring bar, I have used small milling cutters with a 45 angle with great success as boring tools. I think the grade of carbide is much tougher which helps also, but the tool angle is so important to successfull turning. Try both angles normal 90 ish and 45 or thereabouts the difference is incredible. Small changes in speed make a big difference to performance with upping the speed sometimes improving it. Happy learning. If your given 1500lbs of this stuff someone must really like you. It’s not cheap.

dana gear · Jul 11, 2020

Milland said:
If you have certs for the material, try offering it for sale first before looking at scrap. Here or on eBay, with certs you'll get more than scrap. Not sure how you'll do without them, but if you have a lot it may be worth getting your own lab cert - it should pay in higher sale price.

Even with the certs it would properly have to go as Inconel scrap, anyone needing 718 would most like have to be provided with mill certs directly traceable to the material and the mill that made it. I got a file cabinet full of old certs.

Bluechipx · Jul 12, 2020

When I worked at a turbine blade manufacturer (Inconel, cobalt and nickel based superalloys ) a machining vendor would be asked to quote machining a part. They would immediately ask the hardness and we would reply that isn't the problem and they would insist on a hardness number. We would tell them 36-38 rc and they would smile and say 'no problem'. We gave one of the vendors twenty parts to machine and later got a box back with nineteen untouched pieces, one messed up one and no explanation!
When I have a inconel type job (usually Haynes 230) I go to extremes on rigidity, on a lathe all non needed axis's are locked tight and over hang is absolute minimum. I had a lathe boring job once and mounted a boom stereo microscope on the tool post to swing over the insert at short intervals to check sharpness.

crossthread · Jul 13, 2020

Thanks Bluechipx. This stock did in fact come from a guy who retired from Intrarotor Inc. He said they made turbines. He had it in his barn and was tired of looking at it. I guess he didn't want to go to the trouble of selling it for scrap so he gave it to me as a favor for line boring and replacing the pins on his front end loader.

#40fan · Jul 13, 2020

I'd pay shipping on a short piece of ~1.5" round bar if you had it. I've never been privileged enough to even see the stuff, let alone try and turn it. I'm bored and locked down right now with nothing better to do.

Winterfalke · Jul 13, 2020

Lol I remember having multiple conversations about how it would be the perfect material to make gun barrels out of, but no one would ever attempt it because it's so nasty to work with. I want to say it EDMs pretty nicely, but that's only vague recollection.

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