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Magnesium is one of the lightest structural metals, weighing 33% less than aluminum. Though abundant in the Earth’s crust, it’s not as widely used in industry as other metals. Why is that? Is it due to magnesium’s reactive nature or some challenges of machining it?
This article explores the complexities of CNC machining magnesium, covering its processes, challenges, safety precautions, and applications.
Magnesium: Key Properties
Magnesium is a silvery-white, structurally light metal with a density of about 1.73 g/cm³. Its hexagonally packed crystalline structure offers good strength, but this configuration also makes magnesium less ductile compared to other metals.
Why CNC machining of magnesium?
Magnesium is not found naturally in its pure form but is extracted from minerals such as dolomite and magnesite. It has several key characteristics that make it a strong candidate for modern machining applications:
- High Strength-to-Weight Ratio: Magnesium has a strength-to-weight ratio of 130 kN/kg, making it a highly efficient material for weight-sensitive applications. This is significantly higher than steel (38 kN/kg) and close to aluminum (158 kN/kg).
- Easy Machinability: Magnesium’s softness and low cutting forces make it easy to machine at high cutting speeds. This machinability is one of its primary advantages over harder metals.
- Electromagnetic Interference (EMI) Shielding: Magnesium alloys provide effective shielding against electromagnetic interference, protecting sensitive electronic components from external signals. That’s why it’s common in electronic casings, like that of cameras and phones.
- Recyclability: Magnesium is the 8th most abundant element in the Earth’s crust and can be recycled with relative ease. This makes it an environmentally friendly choice for industries focused on sustainability.
Magnesium CNC Machining Processes
Based on the type of structure and shape you need to achieve, magnesium commonly undergoes these machining techniques:
Laser Cutting
Laser cutting uses high-powered lasers to precisely cut magnesium sheets. This method is effective when creating thin and intricate parts.
CNC Drilling
CNC drilling is used to create precise holes in magnesium workpieces. This process involves rotating drill bits that penetrate the material to achieve consistent hole dimensions.
CNC Turning
CNC turning is a machining process where a rotating magnesium workpiece is cut using a stationary cutting tool. This method is well-suited for creating cylindrical and symmetrical shapes like shafts, pins, and threaded parts
CNC Milling
CNC milling uses rotatory cutting tools to shape magnesium workpieces into desired geometries. In this case, the workpiece remains stationary, while the cutting tool moves along multiple axes to remove material. Milling is popular for producing detailed parts, such as housings, brackets, and intricate components.
Common Magnesium Alloys for CNC Machining
Magnesium alloys are classified into two main categories: wrought and cast. Wrought magnesium alloys are processed through methods like rolling, extruding, or forging, while cast magnesium alloys are created by melting and pouring into molds.
Some popular magnesium alloys in the machining industry are illustrated in the table:
| Magnesium Alloy | Tensile Strength (MPa) | Hardness (Brinell) | Elongation (%) | Density (g/cm³) | Features |
| AZ31B | 290 | 73 | 15% | 1.77 g/cm³ | High machinability, lightweight, commonly anodized for corrosion resistance, often used as an alternative to aluminum. |
| AZ91D | 230 | 63 | 3-7% | 1.81 g/cm³ | Excellent corrosion resistance, widely used in die casting. |
| AZ61B | 310 | 68(Brinell) | 15% | 1.80 g/cm³ | Good strength, lightweight, suitable for applications balanced strength, and ductility. |
Challenges in CNC Machining of Magnesium
Magnesium offers some great machining characteristics, yet its chemical nature poses of a lot safety risks:
Reactive Nature
Magnesium belongs to the class of Alkali earth metals, which is known for its high reactivity. They have two valence shell electrons and they are always ready to give that up to stabilize. That’s why it’s flammable and reacts readily, in presence of water-based cutting fluids.
Flammable
Magnesium is highly flammable, especially in fine chip or dust form, as a flying spark can ignite it and put it on fire.
Low Melting Point
Magnesium has a low melting point, 650℃, compared to other metals. This poses a challenge when machining at higher speeds, as excessive heat generation can lead to chip welding and smearing on the cutting tool, resulting in poor surface finish.
Tool Wear
Magnesium is slightly abrasive, and its machining can lead to gradual tool wear over time, particularly if the cutting tools are not appropriately coated or selected.
Considerations When CNC Machining Magnesium
Every metal, including magnesium, has a unique set of physical and chemical properties that require customized machining approaches. When machining magnesium parts, the following key factors should be considered:
Design Considerations
Magnesium is brittle compared to many other metals, so you need to maintain an appropriate wall thickness that prevents cracking or deformation during machining. A minimum wall thickness of 0.03 inches (0.8 mm) can be achieved in most cases.
The tolerance range of machining varies between 0.01 to 0.005 inches. Moreover, factor in magnesium’s low melting point and high thermal expansion rate when designing.
Cutting Tools
Magnesium’s low melting point and slightly abrasive nature require sharp, durable tools that resist these challenges. Some popular choices are:
- High-Speed Steel (HSS) Tools: They are affordable tough, handle interrupted cuts well, and can be easily re-sharpened.
- Carbide Tipped Tools: Best known for their superior wear resistance. Carbide tools maintain sharpness longer and allow for higher machining speeds.
- Coated Carbide Tools: Tools with coatings like Titanium Nitride enhance surface hardness, heat resistance, and longevity.
- Polycrystalline Diamond (PCD) Tools: PCD tools provide exceptional wear resistance and enable high-speed machining, which makes them ideal for high-volume production.
Cutting Speeds, Feed Rate, and Clearance Angles
For machining magnesium, use high cutting speeds ranging from 500 to 1800 m/min for turning and boring, with feed rates above 0.25 mm/rev. Face milling can reach speeds up to 3000 m/min.
Avoid tight clearance angles to prevent discontinuous magnesium chips and heat buildup, which can increase the risk of fire.
Cutting Fluids
Water-based coolants are not recommended for magnesium machining as they can react with magnesium, to produce flammable hydrogen gas. Instead, use mineral-based coolants, and never use water to quench a magnesium fire.
Safety Tips for Machining Magnesium
Magnesium is soft and easier to machine than other metals. Yet, it’s highly reactive and flammable, so safety precautions must be taken. Follow these tips to ensure safety during the machining process.
Declare the Machining Area as No-Smoking Zone
Magnesium’s flammability makes it essential to eliminate any sources of ignition. Smoking or open flames in the area can trigger a fire, so it should be avoided in all cases.
Use Proper Safety Gear
Wear safety glasses, gloves, and fire-resistant clothing when machining magnesium. This gear protects against burns and eye injuries in the event of sparks or ignition.
Keep Magnesium Parts in Dry and Closed Containers
After machining, store magnesium parts in dry, closed containers to prevent reactions with moisture or other materials in the vicinity.
Use Class D Fire Extinguishers
Class D fire extinguishers are designed for metal fires. They contain dry powder agents that smother the flames without reacting with the burning metal. An alternate option is sand, as it effectively isolates the fire from oxygen
Discontinuous Chips
Set up the CNC machine to produce discontinuous (broken) chips, which dissipate heat more efficiently than continuous chips. You can achieve this by setting a low rake angle, high cutting speed, and a low feed rate.
CNC Machined Magnesium Applications
Magnesium’s lightweight and high strength-to-weight ratio make it valuable in several industries including automotive, medical, aerospace, and electronics.
| Industry | Specific Applications | Characteristics Achieved |
| Automotive | Steering wheels, seat frames, transmission cases | Weight reduction, improved fuel efficiency |
| Aerospace | Fuselage frames, helicopter gearboxes | Weight reduction |
| Electronics | Laptop & camera casings, mobile phone bodies | Lightweight, excellent electromagnetic shielding |
| Sporting Goods | Tennis rackets, golf club heads | Lightness, high strength |
| Medical Devices | Biodegradable screws, plates | Biocompatibility, degradability within the body |
FAQs
Is magnesium hard to machine?
No, it’s relatively easier to machine magnesium due to its soft nature and low cutting forces. However, you need coated carbide cutting tools and high speed to achieve that.
What is the ideal cutting speed for magnesium?
It depends on the CNC machining operation. However, usually, a high cutting speed is recommended. For turning, it needs to be between 500 to 1800 m/min.
Is magnesium as strong as steel?
In terms of strength-to-weight ratio, we can say that. Steel’s ratio is 38 kN/kg while that of magnesium if 130 kN/kg.
Choose Richconn for Magnesium Machining Services
Designing a product or prototype involving magnesium? Or in need of specialized magnesium machining? Choose Rich Conn’s CNC machining services. Our state-of-the-art CNC mills and turning centers, combined with our experienced engineering team, ensure that you get the expert support you need.
Looking for high-quality, precise parts that meet industry standards? Contact us today for a free quote and let us bring your designs to life.
