Machining thin wall soft aluminum

[TurboME]

I'm cutting contour profiles in a thin walled (.1") press formed soft aluminum shell, I think it's 6061-T0 or something close to that (I'm trying to verify now).

I'm using a .5" 2flt high helix HSS ball mill and am having chatter problems. I'm currently running at 16ipm (.001ipt) and 8,000 rpm (1000 sfm), .05 depth. I've cut the chatter down somewhat but it's still there and reducing the feed further doesn't seem to help much. The part already takes twice as long as I’d like so I need to avoid slowing it further.

I've tried a variety of feeds and speeds and depths and the above seems to be the best combination. Surface finish isn’t really an issue but I need the tool to last.

I have the part clamped in a vise using an aluminum insert inside the base of the part do it doesn't crush. I tried running a strap across the top as well but it didn't seem to help much.

Does anyone have any suggestions on how I further lessen the chatter and maybe run faster? Are there any special tools made for this type of job? TIA.

[Isoprenia]

Hi turbo, I ocassionally have to cut thin aluminum ( manually) I have found that the tools load up and cause various problems. I switched to roughing mills , that seem to make smaller chips and doesn't load up as much, also be sure to use some sort of lubrucant, A-9, cool tool etc doesn't take much to help a lot, if finish is too rough you can follow up with the high helix oe a standard end mill, the rougher should get your speed up though.

hope this helps or gives you an idea.
Isoprenia

[HuFlungDung]

Maybe you could try to damp the part by filling it with.....dare I say sand....or maybe some chips from the bandsaw? Pack it full and hold the stuff in with a cardboard. Perhaps use hot glue to glue the cardboard in just so you can turn it over safely without dumping the mess out on the table.

[Geof]

To take Hu's idea a bit further: It is possible to get low melting point alloys, one is called cerrobend, with a melting point around 65 degrees Celsius. You can fill hollow parts with these and after machining melt the alloy out in hot water. You can even retrieve the alloy that has gone into your chips by washing them with very hot water.

This is really only practical if you are dealing with something that has a high dollar value because these alloys are not cheap.

[One of Many]

A picture of the part would help. It sounds like a cover of some type rather than a tube. Not being able to see the whole setup, I think puts help at a disadvantage.

A couple possible solutions.

The ball end mill indicates a 3D contour ? Are you cutting through the wall at .05/pass or only .05 deep into the wall? What is your step over setting? Cutter length should be as short as possible too.

The high helix may be on the side of the endmill. If the nose has a high positive rake, it can bobble around in the material if the cutter is plowing out 180deg of material in the fresh path direction. Bound to set up a ringing in both the cutter and part as it cuts the path. A single flute nose may reduce this and still feed at .002/rev. At least take some of the rake out of it or try a different style cutter. I've used a cratex stick to dull up a cutter so it cancels out chatter, but still cuts very well. Just dragging it along the cutting edge a few times works.

You could coat the insert with Urethane rubber, butyl or other damping medium? Put some parting compound(wax, grease, cooking spray) on the part to get the part off the new plug and have a perfect mating surface without voids. Can this part be held down with vacuum?

Of course if you spend too much time try to resolve it completely, you will be done with the job and onto another day, another job.....

DC

[MarkT]

In lines with several of the other posts, I would recommend machining a mating "mold" of the inset. I would make it as precise as possible to provide the most rigidity and structural integrity. If clamping is still also an issue you could strategically drill holes in the mold, machine vacuum troughs and a pheriphery seal trough. Plumb lines to bottom of the mold and have vacuum "assist" in an effort to maximise holding.
Best of luck and email me at mark@cnccustomservices.com with follow up or post it here.

Mark T.