Tips on cutting magnesium

[JeffreySgroi]

Does anybody have any tips on cutting magnesium? Bits? speed? Feed? I need to make a .094" (3/32) wide groove x .094" deep.

Thanks!

[billp]

Jeffrey,
Are we speaking about the same metal that some of us use to start camp fires, etc.? If so I am not too sure it's a very good idea to have a spinning carbide bit anywhere NEAR thin slivers of the stuff as it tends to produce an incredibly hot flame that is very difficult to extinguish ! If you were to generate small chips/dust, and then have any of that matter hit your carbide bit at 12,000 rpm I'd think that you are creating the perfect environment for a dust collector fire that will be hot enough to burn the dust collector...
Here's what Wikipedia says about the stuff;
Magnesium is a highly flammable (http://en.wikipedia.org/wiki/Flammability) metal, but while it is easy to ignite when powdered or shaved into thin strips, it is difficult to ignite in mass or bulk. Once ignited, it is difficult to extinguish, being able to burn in nitrogen (http://en.wikipedia.org/wiki/Nitrogen) (forming magnesium nitride (http://en.wikipedia.org/wiki/Magnesium_nitride)), carbon dioxide (http://en.wikipedia.org/wiki/Carbon_dioxide) (forming magnesium oxide (http://en.wikipedia.org/wiki/Oxide) and carbon (http://en.wikipedia.org/wiki/Carbon)) and water (forming magnesium oxide and hydrogen). This property was used in incendiary weapons used in the firebombing (http://en.wikipedia.org/wiki/Firebombing) of cities in World War II (http://en.wikipedia.org/wiki/World_War_II), the only practical civil defense (http://en.wikipedia.org/wiki/Civil_defense) being to smother a burning flare under dry sand to exclude the atmosphere. On burning in air, magnesium produces a brilliant white light. Thus magnesium powder (flash powder (http://en.wikipedia.org/wiki/Flash_powder)) was used as a source of illumination in the early days of photography (http://en.wikipedia.org/wiki/Photography). Later, magnesium ribbon was used in electrically ignited flash bulbs. Magnesium powder is used in the manufacture of fireworks (http://en.wikipedia.org/wiki/Fireworks) and marine flares (http://en.wikipedia.org/wiki/Flare_%28pyrotechnic%29) where a brilliant white light is required. Flame temperatures of magnesium and magnesium alloys can reach 3,100 °C (3,370 K; 5,610 °F) [7] (http://en.wikipedia.org/wiki/Magnesium#cite_note-Dreizin.2C_Edward_L..3B_Berman.2C_Charles_H._and_V icenzi.2C_Edward_P._2000_30-6), although flame height above the burning metal is usually less than 300 mm (12 in).[8] (http://en.wikipedia.org/wiki/Magnesium#cite_note-DOE-7) Magnesium may be used as an ignition source for thermite (http://en.wikipedia.org/wiki/Thermite), an otherwise difficult to ignite mixture of aluminium and iron oxide powder.
If it's a different magnesium, OR if you have factored all of the above into your project, then maybe I'm the one who is off base here. Please give some more details...

[carve_1]

I boared some of that at Black and Decker many years ago,,,, it had to be awash in coolant. Bill is right,,, once it ignites, you will be hard pressed to put it out.

[myxpykalix]

In experiments with a flint and a drill, It probably would look like this the minute the bit hit it. BTW thats me in the middle setting the front lawn on fire...oops!!



(if you think thats funny you should see the video!)

[dlcw]

The only way to extinguish burning magnesium is to use a PKP or purple K agent. Magnesium, along with other metals like aluminum, burn EXTREMELY hot. As the Hazmat coordinator in charge of hazmat response for the county I live in, burning metals are WAY up there on the "OH ****" scale.

If you were to ignite the stuff while cutting it, you would be VERY hard pressed to put the fire out and you'd probably loose your CNC, dust collector and possibly your shop unless the fire department arrives VERY fast with the correct extinguishing agent on the truck. In our fire department we carry a medium sized fire PKP extinguisher on our truck.

My advise, as a trained Fire Fighter and State Certified Hazmat Technician, is don't even consider playing with it unless you have all the proper extinguishing agents in large quantity and are trained in how to use it. Also, don't tell your insurance company that you are even considering it as they will probably drop you like a hot potato.

[JeffreySgroi]

Those are the answers I feared. I figured it was a bad idea. Thank you all for confirming!!!

Jeff

[stump]

As the Maintenance Manager at a magnesium die casting facility I can tell you that magnesium chips are the danger. I can hold a torch to a casting and it either won't start or will quickly burn out if it does ignite. Chips on the other hand can be lit with a spark - the camp fire starters referred to earlier. Your potential fire is generally limited to the number of chips you are making, (fuel) so limiting the amount of chips is the key to safety.

Yes, burning magnesium reacts to water like gasoline. It's kinda fun. We do a mag burn for all employees every year and we will ignite some chips, turnings, flash, and trimmings from the die castings, then add water. We will also burn chips drenched in coolant. They burn hot and fast, usually reduced to ash in seconds. Yes, we also do the boring things, like putting the fire out with Class D extinguishers or graphite chips...

So, is this a one off thing or a production run? Are you going to be making a lot of chips or just a few that can be blown away with an air hose? How long is the slot you are making? Is it worth the risk?

[quietpainter]

Do they make extra long bits so that one could put the Mg under water? (I really don't know if that would work either but Mg is a ubiquitous material in the real world is it not?) -h

[dlcw]

Magnesium will continue to burn in when submerged in water. That's why we we have to use the special extinguishing agents in the fire department.

[ssflyer]

Here's an interesting tidbit I found:
"Magnesium exhibits excellent machinability. Machining magnesium is normally limited by the speed and power of the machine rather than the tool. Machining magnesium can usually be performed up to ten times faster than steel and twice as fast as aluminum. "

A pdf datasheet on machining magnesium can be found here. (http://www.magnesium-elektron.com/data/downloads/Machining%20-%20Web%20Brochure.pdf)

There are many coolant fluids for machining magnesium, but mineral oil apparently works fine. It can be machined dry, as long as you go fast, with a one or two flute bit, to get large shavings.

Of course, there is always the risk of ignition, even with coolant, so if you decide to try it, take all precautions.

Ron

[JeffreySgroi]

I looked over the data sheer (thanks Ron) and I am going to attempt to cut the groove, hopefully by the end of this week. I am waiting for my customer to bring in the sample rod. I will post my results and hopefully I won't have to post pictures of a burned down shop....

Jeff