Removing Aluminium From a Cutter

Last week I was cutting a 6mm deep slot in Aluminium to make a window for an optical sensor.

Not really having the time, I rushed the job, ignored the mill's complaints, and ended up with aluminium stuck firmly in the cutter and blocking the flutes. (Not convinced it has a practical application, but I learned it's possible to soften Aluminium sufficient to make a horrible slot with only the frictional heat generated by a blocked cutter!)

Some of the aluminium unpeeled when attacked with a pick, but most was stuck solid.

I tried removing it chemically.

Aluminium resists acids, but reacts with alkalis. An hours immersion in a hot concentrated solution of Washing Soda (Sodium Carbonate) made very little impression. I switched to Caustic Soda (Sodium Hydroxide), which is much more aggressive. Roughly half the Aluminium dissolved over 90 minutes and most of the remainder was loosened enough to come off manually.

Success except the reaction also seems to have attacked the gold Titanium Nitride film used to improve the underlying High Speed Steel.

Does anyone have any comments on the method; is the TiN compromised or just stained?

Mostly though, does anyone know of a better way to remove aluminium stuck to a cutter? (Yes I know I the best way to avoid the problem is to let the cutter do the work and lubricate, but I guess a fair number of us get caught occasionally. Some Ali alloys are more likely to do this than others.)

Dave

Also don't use coated cutters on aluminium.

I wonder if freezing would have loosened it? I doubt many have access to liquid nitrogen (I don't any more) but the liquid phase of a CO2 cylinder might be sourceable from a dud extinguisher or friendly publican?

pgk

Hydrochloric (Muriatic) Acid has been used for many years to remove Galled Aluminium deposits from Small engine Crank Journals, usually as a result of a seized engine. Plenty of demos on WWW.

You needed a stronger pick and a birminham screwdriver, I reckon.​

Punch, or pick, and a hammer works fine.

Andrew

"No apparent reaction occurs between either TiN or ZrN and aqueous NaOH" according to **LINK**

My guess is that the TiN was removed by rubbing with hot aluminium during the original cutting process. I think it is significant that the affected section starts where the clearance grinding on the OD of the tool stops - and the object of a clearance angle is to reduce rubbing.

Perhaps if the cutting had been restricted to the section with clearance the problem would not have happened, or been so bad.

Cheers, Tim

Sodium Hydroxide solution (Caustic soda) is the best to get rid of Al deposits. Does not react with TiN, if in Doubt place undamaged TiN coated item in it.

I am using caustic soda for standard treatment of Al clogged files. They need fast rinse with water, then isopropanol and then very slight oiling with WD40 afterwards to prevent rusting.

Martin

Just get under it with a knife, chisel or screwdriver and knock it off.

Got that way because the job got hot. Aluminiums and titaniums heat come up quick and retain it for longer hence why coolants used. Not only do the cutters last longer you get a better job.

Worst thing you can do is oil a file.
Prevention of clogging just watch what happens with the stroke, alter it job done 90% of the time.

Thanks guys, that all makes good sense, especially:

• Use a bigger hammer and pick!
• Caustic soda is OK on TiN
• Damage caused by rubbing, not chemical action
• Don't use coated cutters

It hadn't occurred to me that the coating might cause trouble. Jason is absolutely right to highlight it: following his clue I soon found this advice on the web . It includes: 'The Physical Vapor Deposition (PVD) coating application process on TiN, TiCN, TiAIN, and AlTiN tools makes them unsuitable for an aluminum application. The PVD coating process creates two modes for aluminum to bond to the tool—the surface roughness and the chemical reactivity between the aluminum and the tool coating. '

I already keep separate sets of files, drills and carbide inserts for brass, aluminium &/or steel etc. Time to buy some milling cutters specifically for aluminium methinks - I often work with it.

Many thanks,

Dave

Edited By SillyOldDuffer on 30/04/2018 11:59:01

It usually picks off easily enough with a scriber, it won't be a solid chunk, but compacted swarf.

+1 for uncoated cutters, whether HSS or carbide.

You will also find that the cutters specifically for aluminium have a different geometry with higher helix angle and usually just two flutes all of which help to get rid of the large volumes of swarf. The HSS and carbide ones from ARC have been working well for me over the last couple of years and not too costly.

If I had a situation like that I'd probably use a ball burr to break up and winkle out the aluminium from the flutes. Since ball burrs come as small as 0.3mm in diameter, they take even very small gaps in their stride.

Dave,

While it won't restore the TiN, stick the cutter back in the mill and take some (similar) cuts off a piece of mild steel.

Add a drop or two of turpentine (or similar) at the same time.

Good luck,

Sam

Edited By Sam Stones on 30/04/2018 20:16:54

Top tip unless the flutes are totally clogged an easy way of clearing up to half full flutes is spin in reverse with coolant and just literally take a slight cut. Works 90% of the time.

Because the heat comes through quick it can catch the hardened out running dry often with no warning or sound difference.

Is it possible that the TiN was removed where you cut through the oxide layer that had formed on the surface of the aluminium? I mean, that has got to hurt.

I use Pound shop oven cleaner to remove ally, usually an overnight soak shifts it.

HE30 (6082-T6) has a far less tendency to clog cutters than HE9 and using WD40 as a lubricant when cutting helps.

Regards Ian.

Edited By Circlip on 04/05/2018 08:52:37

The new Al specific milling cutters have an amazing mirror polish. This very fine surface finish helps to stop the Al building up and binding to the cutter, or cold welding to the cutter. Almost any oil mist will help prevent the buildup on the cutter. In my air mister I use a little of rice bran oil pointing at the cutter to blow away the chips, and a vacuum cleaner to draw away stuff as well. I found that if you just see the oil on the paper after like nearly 1/2 a minute, that is still enough to make it effective. I can't make it use less than that. The harder AL Alloys are definitely easier to cut and get a nicer finish on, over the softer alloys.

The best way to remove Al deposited on a cutter is to soak it in Caustic soda solution. Do this out side so you don't get hit by the fumes. Just the ready diluted drain cleaner will work fine. I don't recommend any of the mechanical means like knocking it out etc.

Neil

Edited By Neil Lickfold on 04/05/2018 09:29:36