Machining Aluminum question

I'm getting tiny amounts of swarf that are 'kinda welded on the cut

Climb cut the last couple thou, it'll knock the hairs off and leave a nice finish. Don't spare the RPMs.

I can tell you are "conventional milling" it, where the side of the cutter is moving against the movement of the work. This causes the cutter tooth to approach the just-cut surface and skate along it until the pressure develops to the point that it penetrates the surface and starts to cut. This sliding at the beginning is indeed welding the chips back onto the just-cut surface, and is called "chip rewelding" and a number of other bad words.

The opposite direction is called "climb milling", where the cutter tooth moves in the same direction as the work feed, and so it first hits the uncut surface and immediately plunges in and starts cutting. If a chip is still attached to the cutting edge, the abrupt impact with the workpiece just knocks it off.

The downside to climb milling is it can pull the work and table into the cutter by the amount of backlash in the machine. If you have a lot of backlash (0.010" is enough to make real problems) you can only climb mill on light cuts, or you have to apply a lot of drag with the axis clamps. If you always make a light finish cut (like .005") in the climb-mill direction, you will get rid of the rough surface.

If your machine is tight, then you can climb-mill all the time, and extend your tool life. That skating at the beginning wears out cutting tools very early.

Jon

What Ned said, and don't be afraid to moisten the cut with some kerosene. What's happening is you're getting a slight amount of chip welding to the cutter, which then streaks off on the part. A tiny amount of lubrication will prevent that from happening, and improve the surface finish in ways you won't believe. Something as simple as dragging a moistened acid brush on the cutter will make a huge difference. You need not flood the material, and if you have an aversion to kerosene, use some paint thinner. If you choose paint thinner, it will even evaporate cleanly, so it's not very messy. Don't machine aluminum dry if you want good performance. Use an air hose for cleanup. Those of us that work(ed) in the industry do-----and none of us are dead up to this point. Air hoses are an important part of a shop. . Just don't blow chips towards the ways.

The nice material you spoke of is likely 7075------if not, it's likely 2024. Both of them machine much nicer than 6061, which tends to be a little soft by comparison, assuming they are artificially aged (T condition from T351 upwards). 7075 is high in zinc, and cuts very clean, with a shiny surface.

Did you use the same end mill for machining steel previously? That's a mistake. End mills that are ground for steel have less clearance, and lose the keen edge, desirable for aluminum, fairly quickly---------resulting in a poor finish when used on aluminum.

There are special grinds available expressly for aluminum----might be worth the investment. They're marked aluminum on the shank.

Harold

By the way, less smelly kerosene is being sold for decorative lamps.

I use mineral spirits for cutting, and especially tapping, the gummy aluminums. It evaporates off the parts fairly quickly. Yes, it is somewhat flammable, I apply with an acid brush sparingly. Get the 'odorless' variety, while not totally odorless it's not too bad. I've also applied it out of something like an Elmer's Glue bottle, just letting it drip from the spout, not squirting it. If you have work lights close at hand keep it out of them just to be safe.

Regards Paul

Disclaimer: I am a total greenhorn at milling, so take what I say with a grain of salt, as they say. Also, I have a small horizontal mill, if that makes a difference.

When I climb mill I take small cuts (.005 or less) AND I use hand pressure on the table to take out the backlash. I.e., I push on the table in the direction of travel. Works for me.

Bob

"Ultra-Pure Lamp and Candle Oil" ??? I use it for valve oil on my trumpet. I haven't tried it for cutting fluid (I wonder why not). I got onto an argument with a guy on a trumpet forum as to whether it is kerosene or not. He said yes, I said no. Apparently it is a highly refined kerosene (shrug). Randy

========== Two items:

(1) In addition to the alloy specification there is a heat treat condition designated by T as 6061-T6. This is a hardened condition and machines much nicer. More than likely this was your aircraft alloy.

(2) Try using WD-40 spray for the lube, if this is actually a lube problem. If you need a larger coolant flow to mechanically remove the chips because they are getting re-cut and welded to the part a "mist lubricator" works wells [if you have compressed air] but is messy. The air flow blows the chips out of the cut zone in addition to the cool lubricant. Indeed you may try just an air blast first. see

Unka' George [George McDuffee] ============ Merchants have no country. The mere spot they stand on does not constitute so strong an attachment as that from which they draw their gains.

Thomas Jefferson (1743-1826), U.S. president. Letter, 17 March 1814.

There's a freecutting aluminum: 2011T3. Not really common, but I used a lot of it years ago to make intricate fittings for air brake valves. It cuts really nicely, with the short chips familiar to some in the leaded steels like 12L14. And it has the same cold-shortness as the freecutting steels. Cracks easily when bent. And corrodes quickly, too, due to the copper content. Can't have everything.

Dan

As much maligned as water soluble lube is (AKA toilet water) it works well for this. Even a little brushed on will help stop chip weld to the cutter.

It washes off with hot water! :-)

When I have to clean up ends like that, I do it in two passes. Conventional to remove the bulk, and climb back.(or was it the other way round?) Power feed is pretty much a requirement, to make it work without being work, though. I suppose lever feed on a small mill would do the same. The first crossing of the cutter has a bit of spring to it, allowing for there to be a bit of material removed on the second pass.

Puts the vise back at the same start point, too.

Whatever you do, try to keep the stock from heating up. Hot aluminum becomes soft aluminum. Sorta like machining warm chewing gum. Ewww! 6061 round is usually -T6 IIRC. Should machine OK, but not as well as

Cheers Trevor Jones

How hot is too hot? Not looking for a specific temperature here, but general guidelines -- obviously a dull red glow would fit in the "too hot" category, but where does "too hot" begin on a scale like warm to the touch, uncomfortably warm, painfully hot to the touch, sizzles when water dripped on it, etc?

Chips go dead soft, part builds up heat. Uncomfortable warm. That kind of range.

You know you are too hot when the chips start to bung up the flutes, eh! Watching the behavior of the material while it is being cut is a pretty good indicator. If it starts to smear, it's definately too hot, the tool is too dull, or both.

For the most part, too hot to touch the part, right after a cut, is way too hot, IMO. It's a good place to start, for me, anyways.

I think you would have a puddle, if you got a dull red.:-)

I like coolant, if I can use it. The mess is often worth it, for the easier machining, and finish.

For annealing aluminum, I have used a sharpie marker, and heated until the line dissapeared. That leaves the area dead soft. It will naturally age harden to about a -T3 temper in a few weeks. In a general sense, anyway.

The specific heat treat schedules for specific alloys have to be followed if you want exact type results.

Cheers Trevor Jones

Thanks!

As anyone who's welded aluminum knows, it doesn't glow, it just gets liquid. You aren't going to get smoking blue chips flying like you do with steel to clue you in as to the temp of the AL you're milling. Uncomfortably warm is nothing on a metallurgical level. If it's hot enough to sizzle water it may still not be truly too hot metallurgically, but it could also be. I'd say painfully hot to touch is when you should look for coolant options.

"Tom Gardner" wrote in news:gOMzi.47592$ snipped-for-privacy@newssvr12.news.prodigy.net:

Heh..I'll spare you the description on how to _really_ machine aluminum, but for your application and situation, I would suggest some 3-36 and climb milling, at least on the last cut. An air nozzle aimed at the cut can help too. Don't spare the feed or rpm either.

While it's not comfortable to hold, such a part will not have its hardness effected. The soak temperature for artificial aging is much higher.

Only if it is taken to a full solution anneal first. That requires a temperature of about 950 degrees F for a period of time. Once a piece has been heated to the point of losing its T condition, it will not return without the solution anneal, even by furnace.

Precisely!!

Harold