anyone have experience cutting magnesium???

[superrat]

hello,

this is my first post on this site so i hope it's in the correct area...

i've got a possible project involving AZ31B magnesium which i understand to be a fairly common grade of magnesium. and from what i've read it is still flammable. does anyone have any experience with this material. i'll be cutting 1/4" plate (the end result being a bicycle sprocket). any info would be appreciated.

thanks --phil

[fireman_1977]

Have a Puple K Fire Extinguisher nearby. ABC extinguisher's will not put out this fire. If you pour water to it umm well Kaboom! We machined some of this a couple years ago at our shop and if I remember correctly we cut it at high rpm's, low feedrate, and dry. No coolant. I would confirm with someone else for speed and feed but I am positive about the fire risk. Purple K extinguisher's are not cheap either FYI.

[miljnor]

havn't done it in years and I don't know of any fire extinguisher that will put it out (and I've seen several firemen try to before), but maybe this purple k stuff is magic. But here is what I did:

have a container of sand on wheels nearby.

have thick gloves and welding shades handy

Get some tongs

make your fixturing in a vise or some other easily realesable fixturing (you will be under a little pressure! so K.I.S.S. is the way to go)

Now IF it lights up you can remove it and put it in the sand wheel it outside and let it burn baby!

on the machining side dont know the speeds and feeds but the machinist handbook was where i got that info. So its accurate.

fireman was right on NO WATER and machine it dry. water will attack the metal and so will most coolants.

Use a vacuum rig in some way to get the airborn chips (can you say mess?) these chips will float everywhere it makes a real mess.

Realisticaly you would have to be a true idiot to light this stuff up. its usually the chips that cause the problems or once you bury a cutter and don't stop it fast enough. If your experienced in dry cutting aluminum you should be ok. If you consistantly melt aluminum while machining it dry YOU should probably look for another metal to play with.

have fun.


Ps: I purposly lit this stuff up in a fake fixture for proof of concept (I don't recomend this to you ) I am used to lighting this stuff up though (Glamous ). So I know the sand thing is the way to go.

[miljnor]

by the way some city's have regulations about machining this stuff in their territory. So make the sand bucket deep and dont' do it at night! (its realy realy bright)

[lakeside]

Everytime I cut magnesium there will be one person (most likely wearing a tie) that will light the suff up "kids will be kids" try 1/2 spot drill 1500 rpm 2oo sfm 7.5 ipm .005 ipr

[txcowdog]

I've been working with mag for 27 years and only once got it to light up. Boy when it burns it REALLY burns. Amazing that a metal can catch fire. Problem with getting it to burn is you need very high temps and very fine particles. You could hold a match to the edge of your 1/4" plate all day and it would never catch fire but put a blowtorch on a pile of very fine chips and it would go up like fireworks. The only way to put it out is to smother it ie, keep all oxygen from the flames. I used a dry extingusher when I had the fire but looking back I think sand would have worked better but you would need at least 50 pounds because the fire, even a small one, is explosive in nature. Meaning anything you try to put on it to smother the flames will be blown off. That is why you would need a lot of sand to provide ample weight thereby preventint the flame from blowing the sand off the flame and increasing your chances of smothering the flame. I mill at 2000 rpm with a 4 flute 1/8" end mill and have no problems.

[Geof]

This is what you use for magnesium fires and powdered aluminum which can go up like magnesium in the right conditions.

"Class D Extinguishers:
Class D extinguishers contain a sodium chloride based dry chemical extinguishing agent. Heat from the fire coats the metal, excluding air and dissipating the heat from the burning metal, such as magnesium, sodium, potassium, sodium potassium alloys, uranium and powdered aluminum. They are specifically for use in areas where combustible metals are present." (From Associated Fire Protection)

Magnesium will even burn in 100% carbon dioxide gas; the the burning reaction uses the oxygen from the C02 and the residue that is left behind is pure carbon.

[WhiteTiger]

I may be thinking of some other material, but didnt they at one time machine mag under what amounted to a waterfall of oil? I have a hazy recall of such a pic in one of the old (20 some years back) machinist trade magazines, and I keep thinking the article was on production turning magnesium aircraft parts. Anyone know?


Tiger

[superrat]

thanks for the advice, the bucket-o-sand idea sounds great! i realize the possibility of fire is there but is it worth the risk? my little machine is only 6 months old and to be honest i'm a bit nervous about this project! i'll continue my research to try to calm my nerves.ha.
--phil

[miljnor]

i dont know the specifics but alot of coolant type oils on the market either stain or attack magnisium. and water definitly does. If your machining for an aircraft company, chances are they have a specification or two that tells you what not to use. And usually coolant/water is on the "list"

[shmoo]

Tooling for magnesium should have a negative rake angle and they should be run
at slighty higher speed and feed rates as for Aluminun, You can use the same type of
cutting fluids as that for Aluminum. There is A high potential for fire with magnesium
usually any dry type chemical fire extiguisher will work if the situation does arise.

[lakeside]

a slight neg. rake will give somewhat of a better finish if your turning as for the fire only the chips have a chance of fire if you put a match or very high heat source comon sence a simple pre-caution is all you need and maybe a bucket of sand (for the guy with the tie and the zippo lighter)