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Machining aluminum & magnesium castings and filtration

Q. As a high volume manufacturer of both magnesium and aluminum machined castings for the power tool industry we have always meticulously segregated aluminum parts, chips and coolant from magnesium. Both types of castings are processed in the same department on the manufacturing floor with separate, custom built CNC, auto load/unload machining centers. It was recently proposed to reduce set up time, that the same CNC machines be used for both magnesium and aluminum castings. By running weekly batches of aluminum parts, then carefully cleaning chips out of the equipment and changing the coolant before running magnesium it would be a more cost effective operation. Is it a common practice in the high volume aluminum and magnesium machining industry to use the same CNC equipment for both materials on a daily basis? Is it safe? What problems might we encounter? What advice can you give me?

James Bolhuis
- Heber Springs, Arkansas, USA

A. Machining magnesium also requires a LARGE special fire extinguisher as regular ones have negligible effect as the Mg fire can make its own O2 from water. I believe that it requires Purple K ^ Class D extinguisher. Machine Mg on both, you now need another extinguisher (giant economy size). Overall, with the controls that you mentioned, my guess is that it would be ok. Aluminum dust and Mg dust are an explosive mixture, but I do not know the % mix or any special conditions.

James Watts
- Navarre, Florida

A. We use the same machine for both aluminum and magnesium. The important thing in our humble opinion might be obvious, never use cutting tools on magnesium that have been used on aluminum. Strict segregation of cutters is a great idea. I can not say I know all the reasons but I trust those who have come before us (Busk, Emley) who advised against it.

Josh Deetz
Berlin, Easter Cape, South Africa

"Filtration system for CNC work on magnesium"

Q. I am looking for a filtration system for CNC machine (magnesium metal working), company with reference for using this system with magnesium chips.

Tomer Eliyahu
Engineer - Azor, Israel
October 25, 2010

A. Hi, Tomer. Readers are very welcome of offer technical tips about how to do this, and we encourage discussion of the issues involved in good filtration of magnesium CNC chips. But sorry, we can't suggest manufacturers or sources ( huh? why?).


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
October 26, 2010

A. I would guess that a series of sieves preceding a filter would be appropriate. Then it gets into how fine a filter do you need. My thought is that a fine screen would be preferable to a "filter" from a safety standpoint. Really fine Mg with cutting fluid is fuel for an uncontrollable fire/explosion. It would need to be emptied once a shift, so ease of operation would really help to see that it was done and done correctly. Avoid anything that is even remotely acidic or an oxidizer. Purple K ^ Class D is the only extinguisher that will work.

James Watts
- Navarre, Florida
October 28, 2010

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