Problem- Gummy 6061 Aluminum Rod - Heat Treatment Options?

[cjjonesarmory]

I gave it a fair shake trying to look this up on my own, but no luck. I even tried some quick heat treatment following no particular directions to see what would happen.

I'm cutting off a huge number of 1.75" long parts from 6ft rods of 3/8" dia 6061 (temper unknown) using a carbide cutoff tool on my lathe. Not only does the cutoff tool cut (this metal) poorly (it's a good bit), but pretty much any other lathe tool I use to machine (facing, turning, etc) this cr@p leaves a horrible finish and poor quality parts. It's essentially too gummy and squishes instead of cuts. All I really need to go is get a clean cut off, and a decent looking face (after facing operation). Right now it just scrubs and squishes and looks terrible.

I already bought a large quantity of the 3/8" dia rods for using in manufacture of parts, so just "trying another source" won't work. I have to use what I have and I have to find the best way to cut it. The process for making these parts is pretty much set in stone so I don't have much option. It has to be done on the CNC lathe. Previous batches of the same rod from the same company did not have this issue so I imagine it's either a problem with the temper of the aluminum, or it is a "bad batch" of metal.

I do not know what the temper is (T6, O, T651, etc), just that it's 6061 aluminum. I've heard of other's doing some heat treatment to improve it's machinability but can not find any more info.

On my own, just to try it, I attempted to heat up a section of rod with a handheld torch for several minutes, then plunged it into a troph of water to quench. Seemed to make a slight improvement in machinability, so I'm assuming that attempting to harden the material is the correct course of action rather than trying to further anneal it.

I did find instructions that said to heat to 900 degrees F for two hours then quench in water. Not sure I can stand there with a torch for 2 hours :-), so just wondering if anyone else has an experience with "real world" heat treatment as a fix for gummy aluminum. Tips, tricks, something easier than standing there for 2 hours with a torch, all help appreciated! Especially feedback on positive or negative experiences with heat treating in similar circumstances.

[mactec54]

cjjonesarmory

By heating it up like that you will just soften it even more, it would not be pracitical to try to heat treat 3/8 dia rod, you would really need to have it done at the fractory were it came from normal 6061 is T6

So for machining it what tooling are you using, post some photos of your set up, it may be your tool that is not right for the job

[neilw20]

What coolant - well really as lubricant?

You can use carbide, but they must be special have high top rake.
Talk to the tooling suppliers.

[RomanLini]

Try HSS tools instead of carbide. And sharpen the HSS tool quite pointy with lots of rake. I 'm not a machinist as such but I do cut a lot of soft materials including low melt point materials.

[djr76]

For facing/profiling I use a Kennametal WNGP432K KC5410 insert for aluminum. As for the cutoff, cut off .01-.02 longer and face with aforementioned insert. It has a high top rake angle like neilw20 suggested to use and the coating is made for non ferrous. Lubrication is key to cutting aluminum since it easily welds to the tooling.

[cjjonesarmory]

I HAVE been using carbide lathe tools to cut the aluminum. I assumed that my tooling was fine, I never had a problem cutting aluminum before with the same tooling, however, based on the advice here I will certainly try the ideas regarding using HSS tool bits and look into high rake tool bits.

For coolant, I usually use one of the following, not necessarily on the aluminum, it's just what I have in stock: Rustlick WS5050, WS11, or a mist coolant (Kool-Mist 77 I think, I haven't bought it in a while and don't remember). I've tried all three as well as using no coolant and also just using plain old air through the mist nozzle. I normally use just an air blast for most operations. The air blast worked just fine for previous batches of the aluminum. I suppose that since the rod was only 3/8" diameter that the air provided enough cooling and the tool bit didn't have time to heat up and fuse. I don't think that is the problem here. There is no aluminum adhereing to the cutoff bit, it just kind of pushes out of the way instead of cutting.

I am being conservative on the rpms since the 6 foot rod tends to whip a bit. I have been cutting at only 300 RPM with a conservative feed. I'll have to check the settings for the exact feed rate.... don't remember. I just set up the machine according to my notes and let er rip.

I guess the thing that confuses me is what is wrong with this batch of aluminum that makes it so gummy. This is the first batch that has really given me problems.

The Machinery's Handbook details some ways of heat treating aluminum, not too sure what all of it means, but I want to keep trying that route. My first attempts at increasing machinability by heating and quenching the aluminum rod DID seem to make a difference, but common sense says it would probably be better for me to purchase some different tooling as suggested in this thread.

Thanks for the replies.

[djr76]

300 rpm? for 3/8 diameter, you need to be running much faster. With the poor finish, it sounding now that you are get chips interfering with your cut. Try 3000 rpm, with lots of coolant.

[universalfab]

What are you doing leaving 6 feet of 3/8" hang out of your hole through spindle? Thats no good buddy, you need to hack that down into 3 pieces and raise your spindle speeds.

[Delw]

your problem is using 300 rpms and NO support on the back end, this is causing the part you are cutting not to run true. the "whip" will actually transfer to the front that you are cutting.


First thing you need to do is support the back end. on alum rod that small anything will work even a coworkers hands if you have a roll around tool box just open a drawer and let the bar run on it, then crank your rpm up to 1200

even cutting a V in a 4x4" block of wood and sitting it on a 55 gal drum filled with coolant will do the trick.
we used to do hundreds of 2" dia brass stainless alum and steel rods like this all the time. an old guy showed me this scared teh crap out of me for 2-3 months but if I wanted stock for the cnc machine I had to do my own and that was the only set up he had.
I use my manual lathe to cut 12 foot rods of alum everyday from 1/4" dia to 3/4" dia. I chamfer them and cut them in half for my cnc, ive used the same micro 100 cut off tool for over 4 years and still get a nice finish. my coolant of choice is what ever is laying close to the machine with in hands reach. usually a can of wd 40 every 10 or so bars if that.

That all being said I know perfectly well a 12 foot pcs of 3/8 or 1/2" alum will NOT whip in a 16x40 hand lathe running at 880- 1200 rpm, due to the flex and its own weight of the rod. I also only use the Job button and not the spindle on handle. 58s is a different story as it will whip. 3/8"-1/2" dia you can go down to about 6foot in length before it whips.




Ive been on lathes for the last 28 years so I know my limitations, I dont reccomend this to guys who dont have lathe experiance

I do it all the time when I am working late.
BTW you can still get a good finish on alum on a hand lathe at 300 rpms using a cut off tool, I wouldnt do it as its too slow and takes too much time. what ever RPM you use you MUST be on center other wise your pushing material.

if you still feel uncomfortable doing this grab a piece of 1/2" or 3/4" conduit and c clamp it to your roll around tool box. as long as the conduit is close to being inline it works great, you and acutually run the conduit at a angle and it will still be fine do to the material haveing flexability.

you just need to control the whip and keep it from getting out of control. works for bars 3/4" or smaller.

Delw

[cjjonesarmory]

Thanks for all the replies. Just wanted to mention a couple of things so I don't seem like a total machinist-moron :-p

I'm poking some fun at myself here, and "tone of voice" is hard to determine in written posts, so just know it's all good natured: Yeah I know leaving 6 feet feet hanging out is a problem, but it was easier to automate with the long rod and previous batches of this aluminum worked fine like this. But I am not so hard headed not to realize I was being a bit naive about this. We all do things in attempts to improve production that go against better judgement. Sometimes it's a good thing and it works out great, other times you blow it!

I suppose I'll have to adjust my settings and try some different cutting methods. Thanks again for the advice!

[djr76]

Originally Posted by cjjonesarmory Thanks for all the replies. Just wanted to mention a couple of things so I don't seem like a total machinist-moron :-p I'm poking some fun at myself here, and "tone of voice" is hard to determine in written posts, so just know it's all good natured: Yeah I know leaving 6 feet feet hanging out is a problem, but it was easier to automate with the long rod and previous batches of this aluminum worked fine like this. But I am not so hard headed not to realize I was being a bit naive about this. We all do things in attempts to improve production that go against better judgement. Sometimes it's a good thing and it works out great, other times you blow it! I suppose I'll have to adjust my settings and try some different cutting methods. Thanks again for the advice!

Bar liners for different size bars go a long way. Make a universal one, a magazine type that you can cap at one end, then make 3-4 inch long bored out inserts of different sizes for your different bar size diameters.

[Shane123]

if you must use long bars, you can also use pvc pipe c-clamped on a fixed object to stop tail whip.