Need Advice for Turning Hardened Interrupted cut (60HRC)

thanh tam · Dec 16, 2019

Hi everyone, i need some advice from u guys about the Hardened interrupted cut.
We have a problem when we turning and facing the product which has 8 holes on the face, the hardness is about 60HRC. We are using the ceramic insert with data cutting: Vc= 80-120, ap= 0.25 for facing and turning, fr=0.08.
Because of the small tolerance (5-10 mirco) we use coolant when turning (which is not good for hardness turning).

The inserts do ok when they do the continuous cutting, but break when they meet the holes (1-2 passes break)
Do you have any idea about that?
BTW does the data cutting is ok?
Sorry for my bad English...
Thank guys!

Bobw · Dec 16, 2019

Ceramics are almost the polar opposite of carbide.

When you have an issue, do the opposite thing you would do with
carbide.

You need more surface speed through the interruption.

chip_maker · Dec 16, 2019

CBN is your friend!

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Mike1974 · Dec 16, 2019

My limited experience with ceramic inserts is no coolant and no interrupted cuts, which you are doing both... Have you tried "roughing" and finishing with carbide inserts with a 'good' coating, something designed for hard turning? Couldn't tell by pic, but also maybe you could grind the face with the holes, then just turn the OD? That would save alot of problems and frustration IMO, if you can do it that way...

Matt_Maguire · Dec 16, 2019

Surface speed is way too low! As mentioned above ceramic recipes go the opposite direction from HSS and carbide. I’ll get to the interrupted cut later → First, how it works;

Pure ceramic needs enough heat in front of the shear point to make the material plastic (wisker ceramics = “ceramic + solid carbides mixed” works much the same it’s just tougher). The chip will be a very bright red to orange ribbon when it’s running right. If you see sparks behind & underneath the chip that’s the wear land slowly eroding (still leaving a good edge) & it will run a very long time before failure.

Your Vc (speed) looks like my data from Metcut in 1966… Ceramics for machining were just getting started. By the 1970’s we had whisker ceramics that were doing well with 60Rc steels running in the 200M/m range, DRY. That put on quite a show...

With interrupted cuts some estimated the percentage of the void & increased the speed recipe by that percentage amount (easy for the machinist). Industrial engineers writing part routing, ops & programs would actually calculate the voids, reduce the circumference by that amount and set speed for that (reduced) diameter. They both end up close.

Good luck,
Matt

twjames79 · Dec 23, 2019

Use a low content solid CBN. The only company that offered the low content in solid used to be Ceramtec out of Germany. Not sure if anyone else had done the same. It is specifically designed for interrupted cuts.

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EmGo · Dec 23, 2019

This is why they make grinders ....

Mtndew · Dec 23, 2019

EmanuelGoldstein said:
This is why they make grinders ....

In a perfect world yes, but in the real world sometimes you have to finish a part on the lathe. :rolleyes5:

Larry Dickman · Dec 23, 2019

EmanuelGoldstein said:
This is why they make grinders ....

grinding of heat treated steel is forbidden in the aerospace world.

I second the CBN.

Delw · Dec 23, 2019

Mike1974 said:
My limited experience with ceramic inserts is no coolant and no interrupted cuts, which you are doing both... Have you tried "roughing" and finishing with carbide inserts with a 'good' coating, something designed for hard turning? Couldn't tell by pic, but also maybe you could grind the face with the holes, then just turn the OD? That would save alot of problems and frustration IMO, if you can do it that way...

Mike
interrupted cuts work just fine with ceramics, but you have to go fast SFM. basically your faking the insert to think its a solid cut.
with ceramics you can achieve enough rpms to fake it out. with carbide you cant as it will burn up the tool.

HuFlungDung · Dec 23, 2019

CBN might be the answer, although I am not convinced that an interrupted cut will still not damage it.

My money is on silicon carbide whisker reinforced ceramics like Greenleaf's WG300 (or maybe they have a better thing by now). You can get a lot more corners for $200 bucks than a single CBN will give you. Don't expect them to last very long. I don't really believe hyperspeed is necessary on fully hardened steels, either, just so long as you are getting a red hot chip, that's fast enough. Going too fast in very hard steel will still degrade the edge prematurely, IMO. Going ultra fast over an interruption just equals more shock. The hot zone of the cut is interrupted and there is no way around that when the insert crashes into the hole on the other side, it's got to get that hot zone going again.

EmGo · Dec 23, 2019

Larry Dickman said:
grinding of heat treated steel is forbidden in the aerospace world.

Excuse me ... have you ever looked inside a Pratt & Whitney radial ? Or watched the ballscrews extend the flaps ? There's a ton of grinding on heat treated steel in the aerospace world. That's why there are aerospace procedures for nital etch.

CarbideBob · Dec 23, 2019

Get the edge prep right. That means playing with t-land angle and size.
You are into ceramics, cbn, or very special carbide grades.
If edge done right even brittle cermets can play in this field also due to their high hot hardness.
The trick here is at the point of interruption does the tool tip first take the hammer hit or is the hit up on the t-land and into the body of the insert.

Insane people will try to 3-D model this all out and come up with custom things to try. So much time and energy,
Sane people will ask their tooling rep for some free samples of edge types available and toss them in the machine.
And if that's not good ask another vendor for some more free test stuff.

Often interrupted cuts like bigger lands, higher angles on those lands and almost always negative geometries.
Bob

pat pounden · Dec 23, 2019

EmanuelGoldstein said:
Excuse me ... have you ever looked inside a Pratt & Whitney radial ? Or watched the ballscrews extend the flaps ? There's a ton of grinding on heat treated steel in the aerospace world. That's why there are aerospace procedures for nital etch.

guys like you ,who know TOO much...are a pleasure to read!i learn more stuff just browsing here than anywhere....

twjames79 · Dec 23, 2019

CarbideBob said:
Get the edge prep right. That means playing with t-land angle and size.
You are into ceramics, cbn, or very special carbide grades.
If edge done right even brittle cermets can play in this field also due to their high hot hardness.
The trick here is at the point of interruption does the tool tip first take the hammer hit or is the hit up on the t-land and into the body of the insert.

Insane people will try to 3-D model this all out and come up with custom things to try. So much time and energy,
Sane people will ask their tooling rep for some free samples of edge types available and toss them in the machine.
And if that's not good ask another vendor for some more free test stuff.

Often interrupted cuts like bigger lands, higher angles on those lands and almost always negative geometries.
Bob

Use a low content solid CBN. Hone the edge on a T style. Don’t push the nose forward, use a tool and start on the backside and pull the insert towards you. You can take a deeper depth of cut and you will have 6 edges to use. I can get exact feed/speed in a bit, but you will run it faster than standard turning.

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twjames79 · Dec 23, 2019

twjames79 said:
Use a low content solid CBN. Hone the edge on a T style. Don’t push the nose forward, use a tool and start on the backside and pull the insert towards you. You can take a deeper depth of cut and you will have 6 edges to use. I can get exact feed/speed in a bit, but you will run it faster than standard turning.

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The low content in the CBN makes it less susceptible to breaking. The binder being cobalt will not be as hard, but it is tougher and less brittle.

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CarbideBob · Dec 23, 2019

twjames79 said:
The low content in the CBN makes it less susceptible to breaking. The binder being cobalt will not be as hard, but it is tougher and less brittle.

I just want to say Welcome aboard TW,,,,, Or is it James...
We can always use tool guys.

Matt_Maguire · Dec 23, 2019

It would be interesting to get some input from the ceramic tool maker. In the Binns video linked in another thread the (on edge) ceramic tool recipe was described, feedrate, speed, tool approach angle, rake and T-land size with it’s angle rotation to rake face… For a 200hp cut!

As for grinding being a no-no for aerospace (and a ton of low temp applications). It has its problems, as does any machining if done poorly. Residual stress possibilities and hydrogen embrittlement probability are the biggies.

Good luck,
Matt

twjames79 · Dec 23, 2019

CarbideBob said:
I just want to say Welcome aboard TW,,,,, Or is it James...
We can always use tool guys.

Thanks for the warm welcome. Actual name is Tony Wayne James.... but that’s just too long of an ID to have. Haha

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Mtndew · Dec 23, 2019

Larry Dickman said:
grinding of heat treated steel is forbidden in the aerospace world.

I'm curious why that is (I don't do aerospace).

Need Advice for Turning Hardened Interrupted cut (60HRC)

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