Built-up edge

[gerry maddenParticipant @gerrymadden53711]

I have started machining the face of a large bar end of aluminium 150mm max diameter at about 1000 RPM. All went well for about 20 mins then suddenly the cut goes to the dogs.I take the tip off and see this….

It won't pick off with a finger nail and knowing how fragile the tips are I don't want to force it. I've not had this issue with any previous aluminium cutting with these inserts.

Any suggestions on (a) how to remove it safely and (b) how should I change my conditions to help avoid it again ?

For now I've put the tip in an ultrasonic cleaner but not hopeful this will do much really. I suppose I could heat the tip to the melting point of aluminium and let it drip off

Gerry

[gerry maddenParticipant @gerrymadden53711]

[Brian WoodParticipant @brianwood45127]

Gerry,

It should push off with a screwdriver blade. Refit it to the holder to secure it and then push from under from the bunched up material shown in your second picture to shove it off into fresh air.

Trying cutting aluminium with some paraffin lubrication in future, that should prevent another such accumulation.

Regards

Brian

[Brian GParticipant @briang]

Aluminium left in extrusion dies is removed with hot caustic soda, IIRC a 25% solution, but I have no idea what that does to carbide. You could perhaps use an oven cleaner that carries a warning not to use on aluminium

We used a light mist of neatcut oil to prevent aluminium build-up on tooling, and I have heard that WD40 can be used for the same purpose (and it comes in a handy spray can).

Brian G

[old martParticipant @oldmart]

I use AC90, but WD40 and paraffin are effective in stopping the build up. Little and often is the best way.

[Howard LewisParticipant @howardlewis46836]

Paraffin, (kerosene ) is the standard lubricant for Aluminium (alloys). AC90 and WD40, containing a high percentage of paraffin serve the same purpose.

Howard

[not done it yetParticipant @notdoneityet]

A hot solution of 25% caustic soda is not a nice combination and ppe should be selected appropriately.

The cause is that the aluminium has reached a sufficiently high temperature at the shear point and actually melted the metal. Sharp cutters and, as above coolant/lubricant will mostly avoid the problem, as will machining more slowly (the combination of speed, depth and feed) if cutting dry.

Remember Aluminium melts at only 660 Celsius (think here that heavy machining of steel can produce red hot chips), so momentarily melting the surface at the shear point of the Aluminium, while not the whole chip (heat will be conducted through the material very quickly, so no radiant light output like steel).

[Gary WoodingParticipant @garywooding25363]

I sometimes get the same problem even when using WD40. The weldup is sometimes quite difficult to remove even with a screwdriver bit, but it eventually does come off with no detriment to the cutting tip.

[Clive HartlandParticipant @clivehartland94829]

You have not said what type of Alu you have. I would expect HE15 or HE30 to machine quite well at the speed you quote.

Having one time ordered Alu as HE30 I got some Alu which turned like chewing gum, changed my supplier PDQ.

[VicParticipant @vic]

Yes I’ve had alloy like that as well. It was just too gummy to mill so I binned it. I have been given some offcuts that were supplied specifically for CNC machines, no idea of grade but it machines really nicely.

[HopperParticipant @hopper]

Posted by gerry madden on 13/10/2019 13:33:59:

… I have started machining the face of a large bar end of aluminium 150mm max diameter at about 1000 RPM. All went well for about 20 mins then suddenly the cut goes to the dogs…

1000 RPM is pretty high for 150mm diameter (even with carbide tooling and ally material) and will generate the kind of heat that is welding material to the cutting edge. Try slowing the rpm down. Maybe try 500 and see how it goes.

And 20 minutes is a long time to face a piece of bar. It may be that too slow a feed rate is letting the tool rub on the job and generate heat without cutting, resulting in the fine ally particles building up in a welded mass on the edge.

And +1 on use a bit of WD40 when machining ally. Seems to reduce the stickiness and is not as stinky as kerosene (parafin)

 

Edited By Hopper on 13/10/2019 23:09:15

[mechman48Participant @mechman48]

Posted by Hopper on 13/10/2019 23:01:02:

Posted by gerry madden on 13/10/2019 13:33:59:

… I have started machining the face of a large bar end of aluminium 150mm max diameter at about 1000 RPM. All went well for about 20 mins then suddenly the cut goes to the dogs…

1000 RPM is pretty high for 150mm diameter (even with carbide tooling and ally material) and will generate the kind of heat that is welding material to the cutting edge. Try slowing the rpm down. Maybe try 500 and see how it goes.

And 20 minutes is a long time to face a piece of bar. It may be that too slow a feed rate is letting the tool rub on the job and generate heat without cutting, resulting in the fine ally particles building up in a welded mass on the edge.

And +1 on use a bit of WD40 when machining ally. Seems to reduce the stickiness and is not as stinky as kerosene (parafin)

Edited By Hopper on 13/10/2019 23:09:15

Same opinion from me; I always use WD40 when machining aluminium, usually run at between 600-800 rpm with a fast feed on & using carbide inserts. Facing off a 150mm for 20 min is far too long.

George.

[Anonymous]

Never had a problem with BUE when turning aluminium alloy with aluminium specific inserts. Birdsnesting of the swarf yes, but not BUE. Two things are odd about the pictures. One, the insert doesn't look quite as polished as I'd expect for a CCGT insert. Two, the built up edge seems to run down the side of the insert, not just on the top where you'd expect it to be.

So, as per previous posts, summat isn't right. Cutting speed is correct according to Machinery's Handbook. But we need more details on the material, source of the insert, depth of cut and most importantly, feedrate.

Andrew

[Dave HalfordParticipant @davehalford22513]

Posted by Gary Wooding on 13/10/2019 22:04:51:

I sometimes get the same problem even when using WD40. The weldup is sometimes quite difficult to remove even with a screwdriver bit, but it eventually does come off with no detriment to the cutting tip.

And sometimes the tip does flake anyway depending on carbide quality.

[SillyOldDufferModerator @sillyoldduffer]

As answered by others. Scrapes off when sufficient force is applied. Paraffin / WD40 / correct metal removal rate etc reduce the chance of welding. Some Aluminium alloys are more prone to weld than others.

I've used Caustic Soda (Sodium Hydroxide) to remove Aluminium without damaging the carbide. The milder Washing Soda (Sodium Carbonate) also dissolves Aluminium but takes much longer, at least overnight. The reaction is speeded up by heat but don't add Caustic Soda to hot water!!!

Not much benefit in using an Ultrasonic Cleaner because the Aluminium is dissolved, not cleaned. Does help to disperse the bubbles of Hydrogen that slow down the reaction by keeping the solution away from the metal. I prefer to sleep on the job rather than speed things up by stirring.

Dave

[mark costello 1Participant @markcostello1]

Cutting a piece of steel will take it off also.

[gerry maddenParticipant @gerrymadden53711]

Hi all and thanks again for your comments. I should say that I'm privileged (?!) to have my workshop in the house (and in a carpeted room whats more) so I cant really use cutting fluids. Occasionally I dab on a bit of white spirit but that soon turns to smoke and generates lots of complaints. HOWEVER, my problem of BUE has been solved.

I discovered that the cause is (as Andrew mentioned) the re-digestion of swarf into the cutting zone. By stopping the process and clearing the build-up, or changing the speed allowing the spirals to shoot off in a harmless direction the BUI simply never happens. And even if it does happen, I also discovered that just ignoring it and pushing on will often cause the BUE to break off and get everything back on track.

The only harm the BUE seemed to do was make a noise and mess up the surface finish. A light finishing cut takes care of that.

By the way, the U/sonic cleaner did help but for all the wrong reasons. A quick 5 minutes had no effect at all. But as an experiment I left the tip in the tank and by next morning the aluminium had corroded. The U/S had no difficulty removing this so I just repeated this giving it 5 mins per day and a week later there was no sign of the aluminium and the carbide itself was as good as new !

[Nigel Graham 2Participant @nigelgraham2]

A point regarding paraffin (neat or in WD-40) is that it is best brushed on to keep the quantity and spread down. These materials will wash the oil out of bearing surfaces like the slides.

WD-40 will lubricate, but only briefly and rather poorly though good for cutting aluminium. Its real purpose is as its name says, "Water Dispersant".

Also, if you use a lathe like mine (Myford ML7), you don't really want the poor motor right by the chuck, swallowing the over-spray. A simple shield will protect it from the worst of that, and of course from flying swarf.

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