[Mysta2]

I've been experimenting with dry machining some of our aluminum parts and have had a fair amount of success with half inch cutters, but have not been able to achieve a decent finish with anything smaller.

This is what a profile cut looks like with a 1/4" .030r carbide two flute.



The cutter was out of the holder about 3/4 of an inch and that wall that I was cutting is about half an inch tall. 7500rpm 50ipm I had already roughed it with a 1/2" .090r and left .020 to be cut which I did in Zsteps of .025 with two XY finish passes.

This is the whole setup:



The clamp is just holding a stop block.

I'd appreciate any advice you might have on how to improve my finishes. As I've said we do run coolant on our machines also. But it's water based (Tri-Cool) and wreaks havoc on the whole machine. We decided on the Tri-Cool because we also cut a lot of foam and plastic which would become unpaintable if it gets impregnated with anything oilbased.

I appreciate any and all input.

thanks

Kit Headley
Modelmaker

[dertsap]

high helix would improve the finish , try end mills with ZrN coating if your going to run dry , its not a replacement for coolant but it should reduce the risk of the aluminum sticking to the cutter


.

[dblox]

I dry machine a fair amount of aluminium but I always use a strong jet of compressed air aimed at the cutter. I've been experimenting with misting raw ethanol too with good results. No fires yet!
Obviously, use uncoated cutters, and if the cutter has milled anything except aluminium or plastic it's not going to work.
I'd always been told to use two flute cutters too, but after breaking a fair number of them I've switched to three flute with no problem at all.

[dertsap]

[QUOTE=dblox;1129815
Obviously, use uncoated cutters.[/QUOTE]

Why is that ?
ZrN coating is used on aluminum cutters and is superior to uncoated when cutting aluminum


.

[dblox]

I've never had a problem using uncoated carbide while cutting dry, using an air blast.
I know there are several coatings designed specifically for aluminium, perhaps if evacuating the chip doesn't work you could give those coated cutters a try.

[harryn]

I know some guys at SP3 that to a lot of diamond coated tooling for Al work. Perhaps they can give you some ideas.

There is a fair amount of cutting done for semiconductor equpment using either dry or 2-propanol / water 50/50 mix to avoid part contamination. They actually use DI water and semi grade alcohol to keep things clean enough.

The advantage of 50/50 mix is that it is a lot less flamable than 90% alcohol blends.

[Mysta2]

We do a lot of "lights out" machining, so misting alcohol scares the hell out of me, I wouldn't sleep well at night. I'll look into ZrN coatings. Sorry I left out that I also use compressed air on all our cutting when not using liquid coolant.

This is the cutter in question:

Would you not consider that a high helix?

So I'm getting the impression that this surface finish is in fact much worse than most can achieve with a dry cut, and I should be able therefore to improve on it.

This is all with a HAAS VF3 by the way.

[dblox]

That is a very shallow helix for aluminium. The greater the angle the better the finish is the rule of thumb. Also that is a long overhang how that I can see it. Try using a three flute cutter (more core strength).
Also I'm a metric guy so maybe I've done the conversion wrong but you are taking 0.08mm per flute with a 0.5mm stepover? That's keen. With that overhang I'd be taking a finish cut of 0.03mm per flute at 0.1mm radial max.
But I'm probably being too conservative.

[uli12us]

You are right, thats a bit heavy feed for this small endmill. I think with 30IPM/750mm/min it will be much better. I would decrease the finishamount to 0.01". although you rough your part dry, its much better, you finish your part wet. If you use a brush to bring a small amount of Spiritus, kerosene, or other liquid to the area, that is enough. You can use a small garden spraygun as well. You should use clockingmill (i hope thats the right word thats the only one I found in the online dictionary, it means, that the tool rotation and the feed direction are in the same direction. If you machine an outside contour, the feed runs clockwise.)

[Ben S]

If he's doing lights out machining I don't think he wants to have to brush something on.

[Mysta2]

Man I feel stupid. I had the definition of "high helix" completely backwards in my head. Looking at an actual high helix I thought chips would get jammed up in the tighter spiral.

The cutter is out much farther in the pic than it was for that cut (that's the setup for the following side)

Yes in a lot of cases I can not stand by to brush something on, but at the moment I'm just trying to learn how to increase my finish quality. Once I learn some better techniques I can decide how best to implement them for our various situations.

Thanks again all

Please keep the suggestions coming.

Kit

[uli12us]

The problem with Ally is, if you use a soft alloy, you have problems to get a smooth surface, because the cut only works good, if your tool is razorsharp. If you have a thin liquid film on your surface, than the chips don't adhere together and with your tool.
If you can't stand near the machine to give sometimes a bit oil on it, you can use a small airbrush to spray a thin film to the tool.

[TechGuy5002]

Question: What is the issue using flood coolant? I saw some mention "contamination", but can someone fill me?

Thanks.

[Mysta2]

Contamination of parts was a concern with oil based coolant. Corrosion of the machine itself and bacteria is a concern with waterbased. Dry is just cleaner, faster, cheaper and easier (faster and cheaper are debatable).

[Bob La Londe]

Very little high grade oil is actually needed. Soemthing like Tap Magic is pretty amazing. A few drops on a 3D pocket that takes an hour to cut or more can achieve dramatic results. Pair that with a simple compressed air blast to keep chips clear and you may be amazewd at how good of a finish you can get. Even just air is usually dramatically better than nothing.

[SORCHEROR]

first of all,uncoated carbide is best with aluminum with or with out coolant,aluminum will slowly build up on coated cutters,without coolant it will stick to any endmill when it heats up,the best thing would be to get a spray mister less coolant,less mess,buy a good synthetic mister soluble oil

[leix_99]

I recently put agein in service the flood system on a 96 VF0-E... Best thing i've ever done.
It's kind of a mess if you work with dusty materials like wood or foams but milling aluminium with coolant is just... a lovely experience.

After this, i've used a homemade misting system, plugging a tube next to the air line and some alcohol, althrough it worked, i got low air alarm a couple of times, the air regulator is old and does crazy things.

As said before, i'd go for a "mist" solution using alcohol, less mess, better tool life, no chips welding to the tool and better finishing.

Cheers

[RalphWilson]

We sometimes forget why we use coolant in the first place and when we find a job we have to do without it , we are stumped.
Today I drilled eight .265 holes in each of 12 AL boxes, and no coolant no air , just drilled them.

Ok I just took out the M8 and cut my speed by 65% and pecked "G73" them in at .015 a peck. I know your milling, So so the same, slow it down to a non AL melting speed and take a little heaver cut.
try around 500 to 600 SFM


the lack of friction by going with a old fashionable HHS cutter and a high helix side.

[dertsap]

Man I feel stupid. I had the definition of "high helix" completely backwards in my head. Looking at an actual high helix I thought chips would get jammed up in the tighter spiral.
Kit

the hi helix will have a much better chip evacuation and it will handle the depth better , a decent hi helix is designed for full slot cutting at 1 x dia or more , where a standard end mill is typically 1/2 x dia . Chances are that the biggest problem is chatter which is being caused by too much depth of cut for that small of a diameter tool . It may help if you try to profile in two depth passes , also conventional milling helps these issues quite often , but without the use of coolant then the finish will probably come out poor with conventional . Personally I'm not keen on using standard end mills on aluminum , they work but high helix blow them away , the chip evacuation is better , they'll perform at much greater speeds and feeds , and the shearing action due to the angle produces a much better finish (to name a few advantages) , there is a difference in price , but they are cheaper in the big scheme of things if parts are being machined faster and better

first of all,uncoated carbide is best with aluminum with or with out coolant,aluminum will slowly build up on coated cutters

that may have been the case a number of years ago , coatings for aluminum cutters shouldn't get confused with coatings for meant steel . the coatings on the aluminum cutters are without a doubt a much better choice than using uncoated cutters .
I run a lot of aluminum in a day and while my toolpaths are what I'd consider passive aggressive , I do like to push the tools to the max when I can . I've had numerous occasions when I've optimized jobs using the coated end mills and they've run great for a number of runs . I've had occasions when the coated end mills weren't available or on hand , and I've swapped out for identical uncoated end mills and ended up with less than desirable results on the same jobs (melt down ) . Generally I find the performance difference to be 10 - 25 % . this has happened on numerous occasions with identical tools , the only difference was either being coated or not . I'm not sure whether that difference in performance is substantially important to anyone , but it is in the shop that I work in

[TechGuy5002]

What about using cold air blaster that uses shop air to drop the air temperature for machining:

ChillyBits(tm), Air Colder Than 32 F - Milling and Drilling Accessories - Machine Tool Accessories - 1MEB7 : Grainger Industrial Supply