Correct coating?

[Jhawk117]

I am milling a case hardened (52-56 Hrc)investment cast steel part that is giving me a headache. The part has a slot down the middle that needs .004' removed from the inside of one side of the slot. I have torn up two USA made 4mm end mills (TiN) in thirty parts. Any suggestions on a better coating choice for something this hard and such a small end mill. The size of the slot necessitates the small end mill. Would a AlTiN work better?

 

[Tom Griffin]

JHawk,

If it's that hard you won't be cutting it with a high speed steel end mill. Carbide will be your only option, hopefully the slot is not too deep. Check McMaster Carr as a source. I would suggest a four flute as big as you can fit in the slot.

Tom

 

[Jhawk117]

Thanks Tom

I forgot to mention the end mills are Ultra tool micro-grain carbide from McMaster. The slot is 40 mm long and 4.25mm wide and the rpm is 1000. Maybe too fast or too slow?

 

[Tom Griffin]

It looks like you are at the upper limit of hard metal machining. It looks like you'll need one of the six flute carbide end mills for mold steels (McMaster Carr 8942A52). It's supposed to be good to Rc 62(it ought to be for $96!). Are you using a CNC or manual mill? The key to making end mills survive on hardened steel is to keep the chip load high so they carry the heat away from the tool, and that may be difficult on a manual machine. The RPM may also be an issue. It looks like you'll need, believe it or not, at least 20,000 RPM for a 1/8" end mill.

Here is an article on hard metal machining that may help:

Hard Metal Machining

And here's a little video showing how it's done:

[video=youtube;MGhRNcC41Zs]http://www.youtube.com/watch?v=MGhRNcC41Zs[/video]


Any chance of grinding it instead? It would be easy work for someone with a jig grinder.

Tom

 

[Jhawk117]

I am using a manual machine.... with such a shallow cut and slow feed I might be fighting a losing one here. I am going to try an AlTiN coated 4 flute at 3000RPM and a fast hand to see what I can do. Then if not off to find a jig grinder locally.

Thanks for the article too, good read.

 

[brucer]

I would use a good quality carbide endmill such as garr or osg and use air only to cool and get chips out of the way..
garr has some endmills designed specifically for cutting tool steels above 45rc, they call their coating "Xceed" and they are nice endmills.. osg's coated endmills are also very good..


You'll be running your spindle wide open..

 

[Jhawk117]

Ok so here is the results. Using a accupro 4 flute AlTiN carbide 4mm dia. Spinning 3000RPM (all she is got) I was able to rework 50 parts per endmill with a very nice finish using just air to clear chips. Thanks for all the advise Tom & brucer.

 

[Tom Griffin]

Outstanding! I'm glad it worked out for you.

Tom

 

[brucer]

good deal.

 

[brucer]

Ok so here is the results. Using a accupro 4 flute AlTiN carbide 4mm dia. Spinning 3000RPM (all she is got) I was able to rework 50 parts per endmill with a very nice finish using just air to clear chips. Thanks for all the advise Tom & brucer.

also, How did you like the accupro endmill? I've seen them in msc i believe, but have never used one.