Best Coatings for Cutting Aluminum Dry

[BrandanS]

Hey again fellow SB'ers,

I am looking for some advice from those who cut aluminum regularly (or even those who have good experience). I plan on cutting some pockets into aluminum, but already know that thermal dissipation will be an issue.

I have a cold air system which will assist in keeping the cutter clear and cool, but was wondering if anyone has run into a particular coating which can help keep chips away from the cutter.

I know that I will want to use a tighter helix with lessor flutes (2-3) and currently have hold of cutters with TiN and cobalt coating (I have yet to play with them yet). Has anyone cut with TiAIN or another cool coating?

I don't plan on using any misting or coolant. With a regular carbide cutter, I am already very close to keeping the aluminum from welding.

Thanks,

Brandan

[feinddj]

I use an air cooler with a single flute O bit. I don't use a coating or any coolant.

low rpms, higher feed speeds. Don't take too much of a bite on any given pass.

And MOST importantly: check your alloy. some alloys will not machine well at all. They will weld to the bit almost instantly no matter what you do. If this happens change the material.

David

[Brady Watson]

Has anyone cut with TiAIN or another cool coating?


TiALN = Titanium Aluminium Nitride ~ If you want AL welded to your bit, this is the one you want. Otherwise...David is on the right track.

Since you are routing & not milling, you would do best with an uncoated single flute spiral-O (solid carbide). No coolant is needed up to about 1/2" deep. Keep those step down/ pass depths @ .02-.04" max per pass. Go as fast as it will let you...which should be in the 1.5-1.7 IPS range depending on your machine and tool diameter.

You want to avoid high helix end mills since they have a tendency to walk out of the collet.

HSS can be good in AL for a few reasons. It is actually sharper than carbide & resists snapping since it is not crystalline like carbide. It tends to absorb vibration as well. It just isn't as hard, and in turn, doesn't last as long...but is cheaper per piece.

If you are set on using a coating, ZrN is the one you'll want to experiment with...I always route dry with a single flute spiral-O or 2FL HSS. You might want to check out OSG Blizzard or SGS Ski Carb end mills if you find the SFSO isn't producing desired results.

Remember...you have a light weight router...not a milling machine, so certain provisions need to be made for that.

-B

[BrandanS]

Hmm not really the answers I was expecting... I cut only aluminum with my SB and before now has only had to do slight machining. My latest job will have some pocketing, and from what I've heard TiAlN is one of the best coatings. It surprises me you guys are recommending is opposite. Have you run with TiN or TiAlN coated cutters?

Please Reference :

http://www.cnccookbook.com/CCDryMachining.html

[Brady Watson]

What model ShopBot & spindle are you running?

Have you attempted any cutting with a single flute spiral-O ?

What tools have you tried & what numbers are you running? (diameter, tool material, # of flutes, pass depth, max depth of pocket, XY,Z speeds, RPM) ???

What alloy number is the AL that you are cutting?

Where are you running into problems?

-B

[BrandanS]

Hey Brady,

I am running a PRSalpha with an HSD spindle.

I have used anything from from 1/2" to 3/16" dia. (2-3 flutes; I've never run with a single flute). Mass depth, feeds etc, vary based on IPT of tooling. I can run anything from 10 to 40 IPM. Clearance and pocket depth vary based on operation. All run with carbide or carbide cemented cutters.

I am typically (95% of the time) 6063 Al alloy but sometimes 6061.

I haven't run into any problems as of yet, I am curious to see what coatings, if any, that people have used used. I plan on cutting some trials with Co., TiN and TiAlN. TiAlN, is rated and recommended for cutting aluminum dry, in fact they are intended to run warm. Which should be an advantage for us. Higher temp = Higher RPM = Higher Feedrate.

I've now read two schools of thought, one which supports TiAlN from the link above, but discussions from Cnczone.com support Brady's choice in Coating (ZrN), and also recommend TiB

http://www.cnczone.com/forums/general-metalwork-discussion/24122-tialn-coated-vs-uncoated.html

I'll see if my supplier can grab some ZrN for me.

[Brady Watson]

I can only tell you what has worked for me. I have never taken advice about cutting from anyone (aside from my suppliers) or any site on the web. Everything I advise is from first hand experience. Not long ago, only a handful of us were cutting non-ferrous metals on their CNC router...there wasn't anybody to ask or poll. If you wanted to eat, you had to just figure it out on your own. I am sure you will find a number of suggestions on how to cut it - but nothing trumps first hand experience. So don't rob yourself of that. The machine will tell you what to do if you just observe & listen.

If I were hired by a shop to come in to train them or set them up on a job cutting AL, I would spec out Onsrud or Belin single flute spiral-O tooling. I would begin by cutting at 13,000 RPM at 1.2,0.7 IPS, .02-.04" per pass to begin & make adjustments along the way to optimize for production. You start with a baseline & feather in more feed or lower RPM until quality suffers. Then adjust VR settings to minimize shock loads and fine tune the machine to the shapes you are cutting.

If you use the search function, you'll see that there are a ton of posts regarding proper routing of AL. It seems every week or two someone gets on and asks about cutting AL (http://www.talkshopbot.com/forum/search.php?searchid=1483724). Check it out.

-B

[BrandanS]

Ok Brady thanks a ton! I am about to start the trials, I'll post my results.

[pkirby]

While were on the subject.... Brady, about how long will your 1/4" Onsrud Single O bit last when cutting aluminum? I'm sure it depends on a variety of conditions, but is it more like a couple good hours of cutting or 10+ hours of cutting? Thanks.

[Brady Watson]

Paul,
A 1/4" should last more than 10hrs of cutting depending on alloy and shape of the parts. If you have a lot of start/stops or conditions that heat the bit (like slow corners) life will be reduced. Firm hold down makes a difference too since vibration or material movement can kill cutters. Smaller diameter cutters don't last as long - E.G. - I only get a few hours out of a 1/16" tool compared to a 3/16 or 1/4" tool.

-B

[BrandanS]

So quick update,

I've found that the TiAlN runs the best of all the coatings I have tried. It tool is a 3/16" 2 flute standard with TiAlN coating. Feeds and Speeds: 25IPM @ 14000RPM machining in .08" passes. The TiN and cobalt coating didn't do much is terms of heat dissipation.

I am now trying to get a hold of a ZrN and think that a modified tool geometry may help with chip clearance. I am hoping that so long as I can cut and get rid of the chips immediately, some of the heat will go with them. This project would be MUCH easier if I had access to coolant, but it's also been a learning experience.

Brandan

[Brady Watson]

You owe it to yourself to at least try a single flute spiral O tool just for comparison...it is specifically designed for routing non-ferrous metals. Regardless of what works for this job, it is good to have at least one in your toolbox for future jobs. Onsrud makes a nice 3/16" dia with 1/4" shank. I'm not sure why you are resistant to trying what was recommended, but glad you are having success.

-B