Need Help!- Has anyone cut 13-8 stainless

[crazymat14]

I have been trying to machine some parts out of 13-8 for a week and have seven part and $400 in broken carbide. Can anyone give me some advice?

[leftcoastlefty]

Machinability

This is a tough machining stainless steel. Although it can be machined in all conditions, best results can be obtained in condition H1150M. Compared to type 304 stainless, speeds should be roughly 25 % lower for optimum tool life and finish.

[cdlenterprises]

Drilling? Milling? Turning? 13-8 should cut similar to 304....

[little bubba]

13-8 sucks!!!!!!

It turns pretty easy, but milling out any quantity of material sucks, absolutely sucks. I'll take any inconel, titanium, unobtanium, over 13-8(did I mention I hate 13-8).

You really need to say what you are doing, milling/turning, tools, feeds/speeds/tools, to get a useful answer. "machining" doesn't cut it. I have no info to go on. I could spew off a couple of paragraphs on turning, a few more on hogging on a mill, a few more on pecking away and finishing with tiny endmills, but with the limited info of "machining" I'll just say toss it in the dumpster and use a different material.

If you have already lost $400 dollars in carbide(inserts? endmills?) you can at least waste 2 minutes to post something useful that we can use to help you.

[crazymat14]

I am milling an L shaped part with a closed angle. It is on a fourth axis and is being kellered with a .5" ball, 4 flute, tialncoated, .625loc, 3.5stick out for clearance and relieved behind the flute.
The rep for the cutter told us run it around 2700rpm and 30ipm that makes half a part if we are lucky. I can not give you all the details because it was our other programmers part and he has a hard time listening.

The problem only seems to be with the ball nose. As far as roughing and drilling go, we have made 32 parts on 2 roughers and the same drills.

[little bubba]

If you have the roughing down, you've licked 90% of the problems I've ever encountered.

You didn't say if you are running the finish ball wet or dry.

13-8 does not like dry very much, it is so damn gummy, even when heat treated well up into the 40s. The only true success I've had running dry is with a very small amount of radial engagement, about a 10% stepover, which you should have if you're just finishing.

If you are running wet, two things, first is the TiAlN coating, I've found on some long run jobs that uncoated will outlast TiAlN coated by about 30% when running wet. Maybe try uncoated, or a TiN coating. The other thing if running wet, your SFM is not unreasonable, but wet, you would be heat cycling the carbide causing premature failure, you would have to slow it down depending on where on the ball you are cutting.

Your chipload looks pretty good, should be enough to prevent buildup.

What kind of failure is the endmill experiencing, chipped edges? buildup? or just flat out wearing them out? That will tell you a lot.

[crazymat14]

They start to ball then shatter on the onsrud. But Data Flute chip the tip. They are running wet. Could the coolant mixture have an effect on them.

Thanks

[little bubba]

Originally Posted by cdlenterprises Drilling? Milling? Turning? 13-8 should cut similar to 304....

Should and does are two different words.

Crazymat, I don't know what "starts to ball means", but if you are chipping, then you are running too fast to run wet. If you could get the coolant exactly where it needs to be all the time everytime, then you could run it wet, but 99% of us don't have that capability.

Concentration of the coolant has little to do with it, what is happening is you are heat cycling the carbide. The faster you run the more heat you generate, carbide can take the heat, it can't take the hot in the cut, cooling on the way back around, heat cycling, 2700 times a minute. If you had high pressure thru coolant shooting right down the inside of the flutes, then you could run wet.

I would just turn the coolant off, its only a finish pass, if that doesn't work, I would ditch or change the coating and slow down to 180-200sfm and run wet.

[jimboh]

Originally Posted by leftcoastlefty Machinability This is a tough machining stainless steel. Although it can be machined in all conditions, best results can be obtained in condition H1150M. Compared to type 304 stainless, speeds should be roughly 25 % lower for optimum tool life and finish.

thanks for the speed reccomendation. i'm turning condition H950, on a c.n.c.
Lynx 200 lathe. Hanging out 16 inches from collet,NO STEADYREST, JUST A LIve CENTER! stepped out the roughing ops at G96 S250. but was very pleased that I
snuck up to 1500 rpms on the finish cut with no chatter, gonna try for 2000 rpms tomorrow.