Questions about Ceramic Inserts...

[Crashmaster]

The shop I work for has asked me to look into getting ceramic inserts for some of the jobs we are running on our old Wasino lathe. I know nothing about ceramic inserts other than coolant is not needed. I am under the impression that the lathe will be needing to spin damn fast to generate the kind of heat a ceramic insert needs to cut. My lathe can only go up to 3500 rpm, is this fast enough? Oh yeah, we will be dealing with mostly 12L14 steel. Also, I could use some tips on running with a ceramic insert. THANKS!

[HuFlungDung]

On large diameters, its not too difficult to get the sfm required, but on small soft stuff, you are correct, you need a lot of rpm to get the tool up in the 1600sfm range.

I've not ever tried soft turning with ceramics, I do not know if it will work, or whether you will get rapid cratering of the insert from built up edge, and a poor surface finish, or rapid insert wear if the work wants to eat the particular grade of ceramic that you are using. You have to be quite fussy about which ceramic you use with which material.

The chip flow from ceramics is also less than desirable, as it is difficult to get chip break in ductile materials. In finish cuts on hardened materials, this may not be such a big issue, at least one can deal with it.

Perhaps cermet might be better in your application. Unfortunately, due to some unimpressive experiences with my initial applications of cermets, I've never gotten back into using them, therefore, I am pretty ignorant of their application.

Surely, a carbide salesman (like Kennametal's tech support) would help you figure out exactly what will suit your application.

[Geof]

.....Oh yeah, we will be dealing with mostly 12L14 steel. Also, I could use some tips on running with a ceramic insert. THANKS!

What diameter are you turning? You may not be able to go fast enough to get any benefit using ceramics.

It seems a bit of overkill using ceramics for leaded steel; I always thought their real application was turning hard steel that would lose strength at the heat ceramics are capable of cutting at.

[Delw]

use cermet inserts you will get perfect finish's on 12l14 even at the slower RPMS.

we cut 12l14 for shafting on size's below 1/2" dia. I used my omniturn and ran 2000 rpms rgh it out then run a .020 finish pass with a cermet, we ran coolant and oil. we did have a max .008 fillet rad call out in the corner, so a sharp insert was a must.
one thing make sure your tool is just below center on this material otherwise you will get a few parts that have a non mirror finish part way down the cut, we center drilled the ends so we left it just below center about .002-.005
we ran 5000 parts a week for 2 years on one job.

Geof
you should try ceramics on leaded steels and alum you would be really suprised at what you can do with them, and teh finish is like a mirror they will cut metal off faster and heavier than any carbide out there. we always used the 1/2 round inserts when we could as the squares and the cnmg styles didnt hold up that well.

when using ceramics is that don't run a dry pass(or setting up a machine) at size due to the pressure, cause you will undercut your part by alot.

coolant is a touchy, if you cant flood it, it will reduce the insert life

[Crashmaster]

I would be turning down 1" dia to about .625" We are actually looking for that mirror finish but were actually hoping by using ceramics we could avoid using coolant.

[Mazaholic]

You will have better luck with cermets,you can use them with or without coolant.
With 12L14 i'm not sure it's neccessary,it's hard to get too much sfpm with any insert.
You could also try a burnishing wheel,they work great in a CNC.The finish will look as good as grinding.

[Delw]

just looked at the old old program( I save everything) one machine ran with out coolant one ran with. we used a .015 rad. to rough 2 pass's from .500 down to .280 then one finish pass(different tool) face chamfer od at .24975 generated a .005 rad in corner then shoulder face and chamfer to.500 ( bar stock size).
cermet inserts

[Crashmaster]

Assuming I am using a cermet insert on 12L14 steel, what would you guys recommend for DOC and SFM?

[Mazaholic]

Finish DOC about .02 per side.
12L14 i would think you could attain 800 SFPM or higher.

[Geof]

Finish DOC about .02 per side.
12L14 i would think you could attain 800 SFPM or higher.

Not possible with .625" dia and maximum speed of 3500 rpm.

Possible with the starting size of 1" dia., but it is on the finishing cut you need the very high sfm to get the nice finish possible with ceramics.

[Mazaholic]

Yeah i missed the 3500 max rpm part.
For roughing i'd say 650 SFPM atleast.
We only used cermets for stainless and had very good results with tool life and finish.
Personaly i wouldn't use them on free machining steel,i don't think there will be much improvement over a good tin coated carbide.
We could turn 12L14 at 650-700 SFPM with tin coated inserts,and get a very good finish.

[Zumba]

12L14 is more forgiving as far as surface finish goes than other steels, especially 1018.

Max out your RPM, .020-.025 DOC (radius), .002-.0025" IPR feed. 3500RPM should be more than adequate.

You may want to try some other metals in the future. I get ground-like finishes on 4140 prehard using cermet inserts at 1000+ SFM. Pretty much eliminates any reason to use leaded steel the first place.

Not to mention 12L14 will rust if you look at it too long.