A Comprehensive Guide to CNC Machining Magnesium Alloys
Magnesium is a lightweight metal that is highly machinable and can be CNC machined to create parts with high strength and excellent corrosion resistance. However, magnesium can easily catch fire or explode if proper precautions are not taken, making it difficult to machine. This presents a hazard to CNC machinists: machining magnesium creates chips and dust that are extremely flammable. Without proper care and preparation, CNC machining magnesium can present a serious safety risk. This article explores best practices for safely machining magnesium and other flammable metals. Proper chip removal, precautions, and other tips for reducing the risk of fires in a machine shop are discussed.
1.Why machine magnesium?
If magnesium is dangerous, then why machine it? It’s a fair question, but as long as safety guidelines are followed, magnesium can be an excellent material choice for CNC machining. Magnesium is the lightest structural metal and also provides an excellent surface finish after machining. This is due in part to magnesium’s excellent machinability. Magnesium requires much lower cutting forces than aluminum, which has many benefits for machinists:
- It can be machined quickly
- Chip breaks cleanly and consistently
- Less power required
- Cutting tool wear is reduced, resulting in longer life
2.Why is magnesium dangerous?
While magnesium workpieces are difficult to ignite, the material becomes extremely flammable when reduced to powder or shavings. This means that shavings from machining magnesium alloys can be a fire safety hazard. The risk to machine shops is heightened by the fact that magnesium fires are difficult to extinguish. Combustion will continue in nitrogen, carbon dioxide, and water. (This is why magnesium powder has been used in some explosive devices.)
3.Get the Right Fire Extinguisher
Fires caused by ignited magnesium shavings cannot be put out with water—water only makes the situation worse—so it’s critical that machine shops be prepared to put out fires in the worst-case scenario. Fire extinguishers are an essential part of any machine shop, and there are several types of extinguishers for different situations. In the event of a magnesium fire, you’ll want to use a Class D extinguisher designed specifically for metal fires. Class D extinguishers typically contain agents such as sodium chloride or copper powder.
Additionally, a bucket of sand can be used to put out metal fires. Generally, sand can be used to control small fires, while a fire extinguisher should be used when the flames are larger and the entire fire cannot be put out with sand. The bucket of sand should be placed close to the machine that processes magnesium, but the fire extinguisher should be placed a little further away. Otherwise, the fire extinguisher may be lost in a fire.
4.How to process magnesium safely?
Although it sounds scary, CNC machining magnesium is completely safe if the right precautions are taken.
① Avoid narrow clearance angles
Although magnesium can be machined quickly without affecting part quality, it is best to avoid using small clearance angles because contact between the tool and the workpiece increases friction and cutting temperatures.
② Maintain proper tool condition
Sharp cutting tools can reduce the risk of fire when machining magnesium. Blunt tools rub and create friction, which creates sparks and builds up heat where sensitive magnesium chips are produced. Needless to say, sharp tools also produce better parts. Most machinists use carbide cutting tools with large clearance angles to machine magnesium.
③Avoid using water-based coolants
While coolants can reduce processing temperatures, water-based coolants actually increase the risk of magnesium fires because it produces hydrogen. Avoid using coolants altogether, or use light mineral oil instead of standard coolants. Compressed air or argon can also be used to reduce temperatures without exacerbating potential fire risks.
④Make discontinuous chips
When CNC machining magnesium, it is better to make well-interrupted discontinuous chips rather than ribbon chips that are more likely to ignite.
⑤Use only explosion-proof chip vacuum cleaners
If a vacuum suction system is used to remove chips, the system should be as fireproof as other processing equipment.
5.Storage of magnesium alloy parts and chips
Finished magnesium parts are unlikely to catch fire, but chips need to be handled with care. Even after processing is completed, magnesium remains hazardous. If possible, chips should always be kept dry and stored in closed boxes, such as steel drums, separate from chips of other materials. Storage containers should be kept away from flammable materials. If the chips are wet, they should be stored in a remote location, such as an outdoor storage shed. Magnesium chips can be recycled in many countries. While finished magnesium parts do not need to be stored in a remote location, they should be kept dry to prevent irritation.
6.Other Flammable Metals
Magnesium is not the only metal that can pose a fire hazard during CNC machining. Other flammable substances include titanium, which is widely used in machining, as well as sodium and lithium. Titanium should be handled with the same care as magnesium. Only sand and a Type D fire extinguisher should be used to extinguish titanium fires, and similar measures should be taken to avoid debris accumulation.
7.Machining Magnesium Alloys with Xavier
Xavier is an experienced CNC machining service and custom parts provider that can fabricate parts from magnesium, titanium, and many other metals. Request a quote for your next project.