Turning 4140 heat treated to R60

[chrisryn]

I am currently trying to machine some bearing races that have been case hardened to R60 .06 deep. I haven't found anything tooling wise that will machine the part after heat treat that will last longer than one part. I machine the part .02 over size with extra material on the back to help keep warp down. I then turn the .02 off to final size ( to remove warp). Then part off the final race. My inserts are usually shot after one part. I have used several different grades of inserts and even tried a pcd insert. I know that grinding is the best way to do this but the shapes of the race prevent this. Any suggestions?

[PinMan]

In my experience, CBN inserts work best for anything 60Rc+.
Here is a good article on Sandvik's new insert.

[HuFlungDung]

You don't mention how big the part is, or insert grades that you have tried.
Kennametal K090 ceramics (with T-hone) will machine that easily and they will stand up for quite a while under smooth, uninterrupted cut conditions. Much less pricey than CBN, and you can get far more cutting tips for the dollars you spend. I've never been comfortable with running $200 inserts unless the job really requires something special

You might opt for a semi and a final finish tool. This will make the finish tool last longer.

[chrisryn]

The OD is 6.745 the ID is 6.045 and it is .352 thick. It has a 46.55 degree angle on the surface were the rollers will sit. I have tried a Sandvik PCD insert ( I can't give more info because the rep brought 2 in for demo and when they broke he took them with him.) We currently are trying a Sandvik 3115. These .125 parting inserts. We haven't tried anything other than a standard insert on the turning. My boss wanted to find a grade that will part it off then use that grade for turning. I have suggested ceramics but at this point we haven't tried them.

[DareBee]

Turning is the easy part.
I wouldn't attempt the parting, but it likely can be done.

You could also rig up a toolpost grinder and part off with that.

[chrisryn]

Do they make tool post grinders for cnc? I have used them on a manual but haven't ever seen it on cnc.

[HuFlungDung]

Yes, I missed the part about the parting-off That is a tall order.

Parting off the piece might also cause some warpage due to stress relief. Is it not possible to hold these on a magnetic chuck for boring, or perhaps, in full pie jaws?

[chrisryn]

Originally Posted by HuFlungDung Yes, I missed the part about the parting-off That is a tall order. Parting off the piece might also cause some warpage due to stress relief. Is it not possible to hold these on a magnetic chuck for boring, or perhaps, in full pie jaws?

The problem with that is that the part is so thin that the case hardening creates to much warp on the part.

[mactec54]

Hi chrisryn

Iscar is the only one for parting of your part any of there grades will do it for turning go with the ceramics or titanium

[DareBee]

Originally Posted by chrisryn Do they make tool post grinders for cnc? I have used them on a manual but haven't ever seen it on cnc.

You obviously work in a machine shop.

You make it work.

Part of my job entails thinking outside the box and to design or think up ways to do anything that is asked of us, so maybe I am envisioning this as being a lot easier than other people would.
(Interesting to see half a milling machine clamped to a hoe to slot a new piece that we welded on for repair or to see some of the wild 1-off satellite components going out the door.)

Anyway, I forget that you are only case hardened.
For parting you could, turn a start notch on the OD, bore a start notch on the ID and then you will only have to part through the core of the material.

[chrisryn]

The process you described is exactly how we are doing it. I am not sure how the heat treat company is doing the case hardining but my experince tells me its heat treated all the way through. Thats were are problems are I think.


I like to think outside the box also. It doesn't allways go my way though.

[DareBee]

4140s maximum hardness without case hardening is 50Rc.
That would be the extent of the hardness that you are dealing with.

As I said earlier - I would not consider trying to part that material, although my experience in hard machining is limited compared to others here.