Heat Treated Inconel machining

metalmadness · Apr 20, 2021

Ohhhh boy I need to machine a fun part. It is a rocket fuel injector for a liquid fuel rocket. The initial part was made additively using Inconel 718, and naturally it was sintered in the oven, and then stress relieved during heat treating. So this shit is hard and tough.

Rockwell 40-45.

All that really needs to be done is post process, which consists of face milling and then cutting grooves. Facing is fine, ill survive.

I want a tool that can handle the groove milling operation...I have looked at Harvey tools for their keyseat mills but I honestly don't know if those will be able to handle this. The geometry of this part clearly makes turning impossible, otherwise I would just use a ceramic insert groove tool.

Any other vendors you can think of that will give a superalloy keyseat/groove mill tool that can stand up to this heat??? Grooves are 0.1 inch tall and 0.05 deep.

Milland · Apr 20, 2021

metalmadness said:
Ohhhh boy I need to machine a fun part. It is a rocket fuel injector for a liquid fuel rocket. The initial part was made additively using Inconel 718, and naturally it was sintered in the oven, and then stress relieved during heat treating. So this shit is hard and tough.

Rockwell 40-45.

All that really needs to be done is post process, which consists of face milling and then cutting grooves. Facing is fine, ill survive.

I want a tool that can handle the groove milling operation...I have looked at Harvey tools for their keyseat mills but I honestly don't know if those will be able to handle this. The geometry of this part clearly makes turning impossible, otherwise I would just use a ceramic insert groove tool.

Any other vendors you can think of that will give a superalloy keyseat/groove mill tool that can stand up to this heat??? Grooves are 0.1 inch tall and 0.05 deep.View attachment 319432

You should be able to cut those with a good coated carbide T-slot cutter. If worst comes to worst, at that hardness a CBN grinding disk shaped tool at high speeds/low feeds will do it, just flush like crazy with coolant.

plastikdreams · Apr 20, 2021

I'd get some custom made slot mills made from solid carbide. We cut "similar" material all the time with good ol carbide. Doesn't last too long but it works. For instance we rework castings in the tool room, it entails drilling a .020 hole in a superalloy casting about .500 deep. We get about 3 or 4 castings per endmill.

cunaf85 · Apr 20, 2021

Fullerton? makes a slitting saw I've used to keyway Inconel. Sandvik makes some super expensive multi insert keyway cutters that work good. Horn makes a keyway cutter that works good and is probably the best solution because you can hold it in an ER collet.

metalmadness · Apr 20, 2021

cunaf85 said:
Fullerton? makes a slitting saw I've used to keyway Inconel. Sandvik makes some super expensive multi insert keyway cutters that work good. Horn makes a keyway cutter that works good and is probably the best solution because you can hold it in an ER collet.

Yea I have looked at Sandvik in the past and I wish i took the plunge then because now i need it. Also $$$... Always better to have the tools you may not need right away than to not have the tools you DO need right this second.

Ill look into the PH Horn option as well, but I may stick with the Harvey option as it is affordable and will get here quick. It is a very small batch so tool life is important but not critical. My worry with the Harvey is that the relief doesn't look aggressive enough so I wonder if that will cause issues.

metalmadness · Apr 20, 2021

plastikdreams said:
I'd get some custom made slot mills made from solid carbide. We cut "similar" material all the time with good ol carbide. Doesn't last too long but it works. For instance we rework castings in the tool room, it entails drilling a .020 hole in a superalloy casting about .500 deep. We get about 3 or 4 castings per endmill.

Harvey sells a 3/8 6 or 7 flute keyway cutter that is the exact thickness of our slot. More custom than that?

SeymourDumore · Apr 20, 2021

Looks like you need external grooving, so a carbide slitting saw would work like a champ.
Boatload of teeth and you can get them as small as a 3/4OD x 3/8 ID so it'll be rigid.
I use Fullertons on Inco625 and it has a reasonable tool life, though I know 718 in hardened form will suck a bit more.
Quite a bit more.

I hate Sandvik!

metalmadness · Apr 20, 2021

SeymourDumore said:
Looks like you need external grooving, so a carbide slitting saw would work like a champ.
Boatload of teeth and you can get them as small as a 3/4OD x 3/8 ID so it'll be rigid.
I use Fullertons on Inco625 and it has a reasonable tool life, though I know 718 in hardened form will suck a bit more.
Quite a bit more.

I hate Sandvik!

Slitting saw could work! Pricey blades maybe.

Seems like everyone either loves Sandvik or hates them deeply

SeymourDumore · Apr 20, 2021

Actually they are not that bad, in fact far less than a T-slot cutter would be.
The only issue is the arbor!
They are a bit pricey, and more often than not they get trashed when the saw breaks.
The saws have no key, so when they break, they trash the locating surface.
BUT!!!
I make my own arbors out of 1/2" C'less ground 4140 and make them double sided.

Delw · Apr 20, 2021

metalmadness said:
Slitting saw could work! Pricey blades maybe.

Seems like everyone either loves Sandvik or hates them deeply

there not pricey at all if you can get the size you need from maritool. The work extreamly well and last a long time.
Tool Holders, Collets and Machine Accessories Solid Carbide - MariTool

plastikdreams · Apr 21, 2021

metalmadness said:
Harvey sells a 3/8 6 or 7 flute keyway cutter that is the exact thickness of our slot. More custom than that?

Hmm, I was thinking 7.5 or 8.375 flute

fmari --MariTool- · Apr 21, 2021

Solid carbide slitting saw in a nice short holder like this would work great.

CAT40-SSA1.0-2.5 Slitting Saw Arbor Holder - Made in USA MariTool

We can quote a 1-3/4 diameter saw so it will be nice and stout. We can add corner radius and staggered tooth with Tialn coating.

TeachMePlease · Apr 21, 2021

If I wanted a high performance keyseat cutter, I'd be calling GWS or MAFord, personally. Internal tool makes a nice keyseat cutter for standard machining, but I'm not sure they'd hold up in your application.

Kingbob · Apr 21, 2021

I mill a fair amount of inconel and for this I would recommend going with a largeish slitting saw. Reason: No matter what you use it will breakdown fairly quickly. In my experience it's best to spread that wear across as many teeth as possible, I don't know the rigidity of your set up but I would go with something in the 2 to 3 inch range with a lower than average tooth count to keep the cutting forces down. That being said a regular product of ours is splined hasteloy shafts and I run those with off the shelf 3/4" coated harvey tools.

metalmadness · Apr 21, 2021

Well I ended up going with Harvey to start, there are only 3 of these parts so we shall see. If that doesn't work then a slitting saw will be my next choice..

I also make my own slitting saw arbors out of 4140 or 304, they work great, but I don't grind them cuz I don't do grinding. Might have a gander at Maritool's offering.

metalmadness · Apr 21, 2021

On another note, I have conflicting opinions of speeds and feeds.

Kennametal for example suggests 200-300 SFM and 0.003fpt for their 1/2" Harvi I TE end mill...my speed and feed software, both of them suggest more like 85sfm with 0.001fpt. Soooo yea. Either kennametal is crazy or my speed and feed softwares are wrong. Gwizard and HSM Advisor both spit out very similar numbers.

Kingbob · Apr 21, 2021

I'd go with the lower number, that kennametal number is designed to get you to buy more inserts after you burn up the ones you got lol.

CORONA VIRUS · Apr 21, 2021

Inconel really isn't that hard to machine. I do not know why it gets such a bad rap. There are many much worse materials. Try stelite. That always makes an interesting day.

fmari --MariTool- · Apr 21, 2021

Had a customer going thru ball endmills like crazy in 316 stainless. He, Re-did the program and rotated the part so he can slit it with a full radius slitter. We made him a custom 2" x .156 thick full radius with staggered tooth profile and Tialn coating for @ $110.00 each. Used one saw for the whole job, he purchased 8. Cycle time was reduced, job was more reliable, and slot looked 10x nicer.

SeymourDumore · Apr 21, 2021

fmari --MariTool- said:
slit it with a full radius slitter. We made him a custom 2" x .156 thick full radius with staggered tooth profile and Tialn coating for @ $110.00 each. Used one saw for the whole job, he purchased 8. Cycle time was reduced, job was more reliable, and slot looked 10x nicer.

Wait Frank!
Did you make a T-slot cutter or a full rad slitting saw?
If the saw, then how thin can you go with full rad?
Reason I ask is that I have a family of parts that I use a slitting saw to rough and a full rad T-slot to finish the slots.
Annually perhaps a thousand or so pieces, but the finished widths range from .035 through .130.
These are in 347 Stainless. Tool life is not bad, but the primary mode of failure is the full rad cutter is dulling at the tip as it sees more material from the flat tip saw.
The saws I buy are in batches of 10, the cutters in lots of 6 as that's where the price break is.

Heat Treated Inconel machining

Hot Rolled

Diamond

Diamond

Plastic

Hot Rolled

Hot Rolled

Diamond

Hot Rolled

Diamond

Stainless

Diamond

Titanium

Diamond

Stainless

Hot Rolled

Hot Rolled

Stainless

Banned

Titanium

Diamond

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