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Machining Inconel 625 with ceramics and carbide

RKGCNC

Plastic
Joined
Aug 20, 2023
I have an upcoming job for some mill-turn parts from inconel 625. I ordered some ceramic turning inserts from kennametal. some CN and VN coated insets and some groover inserts. any info, rules of thumb, tips, feeds and speeds etc for machining with these inserts would be greatly appreciated. however the most troublesome features i will have to use carbide for.

One is a 3" deep bore at .297 dia. that requires an extremely smooth finish. probably in the neighborhood of a 2 or 4. i already ordered some special 2 point boring tools for the correct size from internal tool because i dont trust a reamer to deliver that kind of finish.

The other feature i am worried about, and the one that scrapped over half of the parts on the previous run is a tight tolerance face groove up against a shoulder for an o-ring. the ring isnt deep fortunately but its a .031 width and a diameter of about .375 so any face grooving inserts have to be tiny and flimsy due to the large relief needed for that diameter. the groovers typically only make one part then need to be replaced. im looking for something that will last longer. I dunno why but i got the idea to try milling the groove but im not super optimistic about that either. the tooling cost is not a huge issue, but extending the life of the tool for that groove will lead to less scrapped parts
 
requires an extremely smooth finish. probably in the neighborhood of a 2 or 4
It appears you are unsure of the finish requirement. Is it a 2, or 4, or something else?
Rough ream then finish ream may be able to do it depending on the actual requirement. May want to look at roller burnishing (Cogsdill has some good stuff).
 
Is this your first time running ceramic inserts? If so, bring an extra pair of pants the first day you run them.

Here's a couple tips: DON'T run coolant, inserts will explode. Ceramics work best by liquefying the material and wiping it off so the hotter (higher SFM) the better, chips should look like a molten waterfall. Cermaics take a lot of horsepower and rigidity. I hope you're trying this on a high end machine. The beauty of ceramics is that the edges might chip or breakdown quickly but it will keep working, let it run. Downside is its impossible to hold size or finish and all that heat will pretty much guarantee that whatever carbide insert that follows will be toast. But if you've got a lot of material to remove, its still way more efficient than carbide.
 
^^^yeah, ceramics need heat to work. I would also think about burnishing that hole, a 2/4 finish by boring seems optimistic.
 
Here's a couple tips: DON'T run coolant, inserts will explode.

Well ....

I'm about to find out how well these guys do, by week's end or early next week we're starting a job of 300+ pieces, bit north of #3000 worth of it.
 
Well ....

I'm about to find out how well these guys do, by week's end or early next week we're starting a job of 300+ pieces, bit north of #3000 worth of it.
Well NTX agrees with me when looking at what happened to competitor inserts with coolant.

Seems NTK developed a ceramic that can withstand the heat shock but at a cost, 180-250 smm is slow by ceramic standards. My experience is with whisker reinforced ceramics from 3 different major brands. I recall running those 300-550 smm.

This video is 10 years old but even then they were running over 300 smm.

 
Well NTX agrees with me when looking at what happened to competitor inserts with coolant.

Seems NTK developed a ceramic that can withstand the heat shock but at a cost, 180-250 smm is slow by ceramic standards. My experience is with whisker reinforced ceramics from 3 different major brands. I recall running those 300-550 smm.

I don't think a thermal shock is an issue as long as you either flood all the way or dry all the way.
About it being slow ... hell, when it comes to Inco or the like, I take a reliable cut and not having to stop mid way unexpectedly over any speedy method.
Also, this is on a 10" machine with part going from 4" to 1" dia. I don't have the RPM for the smaller features if the SFM requirement is too high.
 
took a while to everything dialed in, but its finally running good. wound up skipping the ceramic, the roughing is not taking a huge amount of time compared to other things. wound up using a sandvik carbide reamer with thru coolant for the bore. leaves a perfect finish if i run it slow. tool life is still an issue (the roughers only get 3-4 parts per edge) but it was always going to be.
 
Dealing with Inconel 625 can indeed be challenging. For the ceramic inserts, especially the ones from Kennametal, watch your speeds and feeds closely. They're great for roughing but can be a bit tricky. When it comes to the carbide for finer features, a smooth finish requires precise control of your machining parameters. Don't hesitate to experiment with different grades of carbide too, as Inconel can be quite demanding on tool life. Remember, with Inconel, sometimes slower and steadier wins the race in terms of tool longevity and surface finish.
 








 
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