Gummy aluminium

[Janger]

Hi
I’m making these parts still for somebody. They are aluminium led lights. You can see in the photo I’m having a hard time with the swarf sticking to the part. It’s cutting and then sticking to the cutter and then getting deposited again to the part. It leaves a bad surface finish. Details 1” dcmt cutter with two dcmt inserts. Steel type not aluminium cutting type. It’s what I have. Tried rpm of 3000,2000,1600. Feed is 3” per min but 6” does the same thing. The part gets hot very quickly. I switched to new inserts same problem. Depth of cut about 0.05”. It’s worse with deeper cuts.
Thoughts?

Coolant via spray bottle?

 

[Janger]

And how do I clean this up? Another pass at a slightly larger (0.004”) diameter helps only a little as you can see.

Edit: sand paper helped a lot ...

 

[Dabbler]

R U using enough lube, and what composition is it if you do?

 

[Janger]

Dry. No coolant.

 

[PeterT]

I use the same style of insert on aluminum but they are un-coated & very sharp nose radius, 1/64" or whatever the metric value is. I use either Alumtap or WD-40 as cutting lubricant (just spritzed I don't have mister or flood). Both seem the same to prevent stick but WD can vaporize and make you see unicorns after a while. What I have not done is pocket milling like that using insert tool, only facing on the bottom edge or (occassionally) off the end of bar stock with side edge but in both cases where chips are free to fall off.

What I think might do a better job is a high helix uncoated endmill specifically for aluminum. I've done pocketing with those & they cut on the sides very nicely & make better chips. (Carbide aiexpress special). You might also have to blast chips out of there if its not leaving the pocket & re-munching them along the side wall. Also what alloy? Some aluminum is just plain gummy crap but most of the aircraft stuff isn't too bad like 6061, 2024 in lower cost regime.

 

[PeterT]

Not quite your scale but give you an idea. The pocket is maybe 0.4" wide x maybe 0.6" deep so quite a bit of EM side milling. The connecting rod end is maybe 0.4" depth. Actually these may have been regular carbide end mills, I didn't have the high helix aluminum ones when pics were taken, but I recall they cut quite nice.

 

[Janger]

It’s 6061 but not sure what grade. Metal supermarket sourced. I’ll try wd40 and some AL-9 and see. I did square pockets on the other size with a 3/8” regular end mill and it did work much better Peter.

 

[Dabbler]

For Aluminum I mix WD40, 4 parts, to 1 part sulfated oil for my best results. You are running higher RPM than I do, so your results might vary.

6061 is not usually 'gummy' - sounds like 2420 or one of the other softer alloys. Sometimes MSM sells stuff with the wrong designation (sometimes even marked differently) I don't trust their 7075 any more, as we tested a few coupons and found them to not be high tensile. My hope is that it was an isolated incident.

 

[DPittman]

I've had pretty good luck with WD-40 but it can be messy at the high speed you turn aluminum at. I've also haven't experienced the unicorns yet but may be I need to try something different! LOL
Don

 

[Bofobo]

Cutting fluid is a must with aluminum, the 3 flute endmils work great but a 2 can do just as well where a 4 flute will tend to get gummy quick if you dont use enough cutting fluid. You Could use compressed air to cool the part/tool and expel the chips. (in deep cuts i advise this with cutting fluid also)

 

[Janger]

Ok so for a 1” diameter tool what rpm might you guys suggest? Interesting how the suggested figures 4 x cutting speed / diameter , 4*250/1=1000 Rpm for HSS maybe too high?

 

[DPittman]

I really doubt that would be too high, but I've got a lot to learn myself and just basing that opinion on my own experience

 

[PeterT]

Some light reading
https://materialsdata.nist.gov/bitstream/handle/11115/200/Machining of Al.pdf?sequence=3

 

[Janger]

Hey that’s a good article thanks Peter. Based on that information I am going to slow to 500 rpm and use a spray bottle of coolant. I'll try A9 and Dabblers 4:1 WD40 with oil. I'll report back.

 

[Janger]

Slowed to 490rpm and just brushed on Relton A9 aluminum cutting fluid into the part and on the inserts and cut 0.04” depth. Much better! Wow!

Thanks everyone.

 

[PeterT]

That looks better.
I just have to ask - what application are those LED light fixtures with external cooling fins? LOL

 

[Janger]

Terrarium lights!

 

[Janger]

Another member also told me to switch to a high helix end mill. I found a two flute in the drawer and this works better. I can increase the feed and depth of cut so it's progressing much faster. I'm still using some A9 fluid but only on the last cut.