Aluminum is a non-ferrous metal commonly used in various industries for different purposes. From aircraft parts to intricate consumer electronics, aluminum’s versatility is unmatched. Its unique properties and adaptability have made it a top choice in CNC machining to produce lightweight, durable, and precision-engineered components.
But what makes it so ideal for CNC machining? To answer this, let’s begin with aluminum’s origin, and the role of its alloys.
Introduction to Aluminum and Its Alloys
Aluminum is the most abundant metal element in the Earth’s crust. According to the International Aluminum Institute, the global annual production of primary aluminum reached approximately 67 million tons in 2023. Like most other metals, aluminum exists in the Earth’s crust as an ore, primarily in the form of bauxite. To extract aluminum for industrial use, a two-step process is employed. First, the Bayer process is used to refine bauxite into alumina (aluminum oxide). Then, alumina undergoes electrolysis to produce pure aluminum.
Pure aluminum (99% or higher) is lightweight, malleable, resistant to most forms of corrosion, non-magnetic and an excellent conductor of heat and electricity. However, it is too weak for most commercial applications.
To overcome this limitation, aluminum is combined with elements such as magnesium, silicon, zinc, and copper to form alloys. These alloys also further enhance aluminum’s natural properties. Additionally, by adjusting the composition of alloying elements, the properties of aluminum alloys can be tailored to meet the specific requirements of different applications.
Benefits of Using Aluminum for CNC Machining
Next, let’s take an in-depth look at the key advantages of using aluminum for CNC machining.
Machinability
Aluminum is one of the easiest metals to machine due to its soft and ductile nature. Manufacturers can machine it three or even four times faster than other common machining materials such as steel and titanium. This means less labor and time are required, resulting in lower production costs.
Moreover, aluminum’s smooth cutting action produces clean chips and minimizes interference during the cutting process. This facilitates the precise production of intricate geometries and tight tolerances. Its low risk of deformation during processing ensures high accuracy, which is particularly valuable for precision applications in industries such as aerospace and medical devices.
Strength-to-Weight Ratio
Aluminum is about one-third the density of steel but offers excellent strength. This high strength-to-weight ratio has led to its widespread use in transportation industries, including automobiles, trains, aircraft, and boats. As fuel efficiency becomes a greater priority, aluminum has increasingly replaced heavier metals in the construction of exterior panels and internal structures, helping reduce weight without sacrificing durability or strength.
Corrosion Resistance
Aluminum naturally forms a protective oxide layer when exposed to air, helping to prevent further corrosion. This inherent property avoids the need for heavy and expensive anti-corrosion coatings that are often required by other materials in many applications.
It is important to note that the corrosion resistance of aluminum varies significantly across different grades, which depends on their ability to withstand oxidation and chemical damage. We will discuss this topic in more detail later.
Electrical and Thermal Conductivity
Aluminum is a highly conductive material, both electrically and thermally. Electrically, its conductivity is second only to copper. This is why aluminum is so popular in applications like cables, power transmission, and electronic devices, especially when lightweight materials are required.
Thermally, aluminum also performs well, with about 60% of the thermal conductivity of copper. This helps prevent excessive heat buildup during CNC machining and is also valuable in applications such as electronic heat sinks, automotive engine components, and air conditioning systems.
Performance at Low Temperatures
Unlike some materials that become brittle and lose strength at low temperatures, aluminum maintains its mechanical properties well in subzero conditions. This property is essential in the space industry and liquefied gas storage for applications such as cryogenic tanks and systems.
Anodizing Potential
Machined aluminum parts are particularly popular in consumer electronics, such as smartphones, laptops, tablets, and flat-screen TVs. This is not only because of their strength and lightweight nature, but also due to their aesthetic appeal. Aluminum naturally has a sleek, silver surface that is highly receptive to paints and tints. More importantly, aluminum is ideal for anodizing, a process that thickens the protective oxide layer on the part.
Anodizing also makes it easier to color machined aluminum. The anodized layer is highly porous, allowing dyes to penetrate and bond with the metal. As the color is embedded in the tough oxide layer, it is less prone to chipping or flaking, ensuring a long-lasting finish.
Recyclability
Aluminum is one of the most recyclable materials on earth, with a recycling rate exceeding 75% globally. This high recyclability means that used aluminum components can be melted down and reused without significant loss of quality, reducing waste and conserving natural resources. In CNC machining, where large amounts of chips and waste materials are generated due to the subtractive nature of the process, aluminum’s recyclability is especially advantageous.
What Grades of Aluminum Are Used in CNC Machining?
As mentioned earlier, aluminum comes in many different alloy types. Aluminum alloys are generally categorized into varied grades (series) based on the primary alloying elements they contain, such as copper, magnesium, silicon, or zinc. This section discusses the common aluminum alloys based on the primary alloying element.
Softness vs. Strength: Softer alloys (1000, 3000, 4000 series) are easier to machine but require careful chip management. Harder alloys (2000, 7000 series) demand slower speeds, rigid setups, and advanced tooling.
Corrosion Resistance: The 5000 series alloys have excellent corrosion resistance, widely used in marine environments. The 7000 series and 2000 series alloys are more susceptible to corrosion and typically require additional protective coatings when exposed to harsh environments.
Specialized Applications: The 4000 series is often used in niche applications that require a precise surface finish or specific properties for welding, cladding, or construction. The 8000 series is more commonly associated with packaging (like aluminum foil and coils) and electrical applications.
Versatility: The 6000 series alloys are among the most versatile and widely used aluminum alloys due to their balance of strength, corrosion resistance, and machinability. These alloys are ideal for a wide variety of applications, from structural components to consumer goods.
Popular Aluminum Alloys Used in CNC Machining
Aluminum 6061: It’s one of the most popular aluminum alloys due to its excellent balance of strength, machinability, and corrosion resistance. As a heat-treatable alloy, 6061 can be significantly strengthened through heat treatment, with the T6 temper being the most common for structural applications. It also has good workability and can be welded using most common methods such as TIG and MIG welding. While not as corrosion-resistant as 5000 series, 6061 still offers good to excellent corrosion resistance in many environments. Additionally, it takes anodizing very well, which can enhances both its corrosion resistance and aesthetic finish.
Aluminum 6063: Unlike 6061, which is commonly used in structural applications like aerospace components, frames, and high-load-bearing parts, the strength of 6063 is lower. However, it still offers sufficient strength for applications such as window frames, doors, and furniture. It can be easily formed into complex shapes, such as profiles, tubes, and bars. Often referred to as "extrusion aluminum", which helps lower production costs and makes it more suitable for mass production. Additionally, 6063 is preferred over 6061 for anodizing.
Aluminum 7075: 7075 is often considered one of the strongest aluminum alloys, with a tensile strength comparable to that of some steels. This strength can be further enhanced (approximately 83,000 psi) when heat-treated to the T6 condition. As a result, 7075 is commonly used in parts that require maximum strength while remaining lightweight, such as in aerospace, military vehicles, and weaponry. However, it has lower corrosion resistance compared to other alloys, and it is difficult to machine and poorly weldable.
Aluminum 2024: Like 7075, 2024 is one of the highest-strength aluminum alloys available, but it generally performs better than 7075 in long-term fatigue testing. However, in high-stress applications where ultimate strength is more important than fatigue resistance, 7075 is often preferred due to its superior strength.
Aluminum 5052: It's one of the most corrosion-resistant alloys in the aluminum family, even in extreme conditions like saltwater and chemical exposure. 5052 offers a good balance of strength and formability, with excellent weldability. It's a go-to alloy for applications that require deep drawing or bending.
Choosing the Right Grade
The choice of aluminum grade depends on the specific requirements of the application:
For general-purpose applications, 6061 is often the preferred choice due to its balanced properties.
For high-strength needs, 7075 or 2024 is better suited.
For corrosion-resistant environments, 5052 or 6063 is ideal.
Common Aluminum CNC Machining Processes
In this section, we will introduce the most common machining methods for aluminum alloys.
CNC Milling
CNC milling is one of the most common and versatile methods for machining aluminum parts. It uses rotating cutting tools to shape material from the aluminum workpiece. With the introduction of computer numerical control (CNC) systems, automatic tool changers, and tool carousels, these machines can create complex geometries, holes, and surface contours with greater precision and efficiency. CNC milling machines are available in configurations ranging from 2 to 12 axes, with 3 to 5 axes being the most commonly used.
CNC Turning
CNC turning is primarily used for manufacturing aluminum cylindrical or conical parts, such as shafts, bushings, and threads. During this process, the aluminum workpiece is rotated, while a stationary cutting tool removes material to achieve the desired shape. This method allows for high precision and excellent surface finish in a relatively short time, making it especially suitable for high-volume production. Typical operations performed on a CNC lathe include turning-related tasks such as cylindrical turning, tapering, facing, and threading. Modern CNC lathes can also perform secondary operations like drilling, slotting, and tapping, enabling greater versatility.
CNC Laser Cutting
By using a focused laser beam, CNC laser machines burn or vaporize aluminum to create clean, burr-free edges with high precision. It is suitable for producing intricate designs, sharp corners, and tight tolerances, particularly in applications like aerospace, electronics, and decorative panels. CNC laser cutting offers superior precision and edge quality. But it is less effective for cutting thicker aluminum sheets due to heat distortion and slower cutting speeds. Despite this limitation, laser cutting remains a popular choice for projects involving thin to medium-thickness aluminum components.
CNC Plasma Cutting
CNC plasma cutting uses a high-velocity plasma arc, generated by heating compressed air to extremely high temperatures, to melt aluminum up to six inches thick. A computer-controlled torch head follows a precise cutting path, while the compressed air blows away the molten material for a clean cut. This method is fast, cost-effective, and relatively easy to operate. Although it is less precise than laser cutting and may require additional finishing to smooth rough edges, CNC plasma cutting remains a popular choice in industries such as construction, shipbuilding, and heavy manufacturing.
CNC Waterjet Cutting
Unlike laser and plasma cutting, waterjet cutting does not generate heat. It’s a cold-cutting process using a high-pressure stream of water mixed with abrasive material to cut aluminum. This method preserves aluminum’s properties by avoiding burning, warping, or altering its structure. Waterjet cutting can handle aluminum of any thickness with exceptional precision and smooth edges. While it is slower than plasma cutting, it is ideal for intricate designs and is commonly used in aerospace, automotive, and custom fabrication, requiring minimal post-processing.
Key Challenges in Aluminum CNC Machining
Although aluminum is highly regarded for its machinability and versatility, certain challenges can arise during CNC machining. Below are some of the most common challenges encountered:
Chip Control
Aluminum tends to produce long, continuous chips during machining, especially with softer grades like the 1000 and 3000 series. These long chips can become tangled, potentially clogging the cutting tool and disrupting the machining process, leading to inefficiencies or defects. To manage this, cooling fluids, air blowers, or chip management systems should be adopted.
Built-Up Edge (BUE)
Aluminum’s malleability and softness can cause material to adhere to the cutting tool edges—a phenomenon known as built-up edge (BUE). This build-up reduces tool life, affects surface finish, and leads to dimensional inaccuracies. Using sharp tools with appropriate coatings, such as titanium nitride (TiN), and applying proper lubrication can minimize this problem.
Heat Generation and Dissipation
Although aluminum alloys have high thermal conductivity and dissipate heat efficiently, high cutting speeds and heavy cutting loads can prevent the heat from dispersing quickly through the material. In these cases, using coolant and optimizing cutting speeds and feed rates can help mitigate the negative effects of thermal expansion.
Workholding Challenges
During machining, aluminum’s lightweight nature can sometimes lead to instability in positioning, particularly with thin-walled or longer parts that are prone to deformation. Therefore, in CNC machining, proper fixture design and stable workholding methods are crucial to ensuring precision and preventing part distortion.
Conclusion
Looking for custom CNC aluminum parts? With its lightweight, strength, reliability, and cost-effectiveness, aluminum has become one of the most versatile materials for manufacturing. At Chiggo, we have over a decade of experience in processing aluminum, making up about 70% of the materials we work with. Reach out today to get started!
