Guide for CNC Machining Aluminum Parts

Aluminum finds widespread application in everyday objects, because it is the most prevalent metallic element in the crust of the earth, It’s actually the most commonly utilized non-ferrous metal (i.e., one that doesn’t include iron). Aluminum can be found in commonplace items like cans and foil as well as highly specialized items like CNC machining aluminum parts of spaceship and submarine.

At Sungplastic, we delve into CNC machining services and custom aluminum parts manufacturing.

Properties of Commercial Aluminum

Aluminum stands out as the most widely used non-ferrous metal for numerous compelling reasons. Its exceptional ductility and malleability render it highly adaptable to a diverse range of applications. These properties allow aluminum to take the form of delicate aluminum foil or be drawn into sturdy rods and wires.

One of aluminum’s key advantages is its remarkable resistance to corrosion, thanks to a natural oxide layer that forms when it comes into contact with the atmosphere. Furthermore, this protective oxidation can be intentionally induced to enhance its resilience against environmental elements. While aluminum’s inherent protective layer outperforms carbon steel in terms of corrosion resistance, it falls slightly short when compared to the chromium-enriched stainless steel. Additionally, aluminum proves to be an excellent conductor of both heat and electricity, surpassing carbon and stainless steel in these aspects.

Aluminum offers the advantage of expedited and simplified machining in contrast to steel. Its outstanding strength-to-weight ratio positions it favorably for various applications requiring robust and durable materials. Additionally, CNC machining aluminum is renowned for its recyclability, with the potential to save up to 95% of energy when compared to the production of virgin aluminum.

Nonetheless, it’s important to acknowledge certain limitations associated with CNC machining aluminum, particularly when comparing it to steel. Aluminum lacks the hardness of steel, making it unsuitable for components subject to severe impacts or extreme load-bearing conditions. Furthermore, its significantly lower melting point (660°C compared to steel’s approximate 1400°C at the lower end) restricts its use in high-temperature applications. Its high coefficient of thermal expansion means that excessive heat during CNC machining aluminum can lead to deformation and challenges in maintaining precise tolerances. Lastly, aluminum can be costlier than steel due to its higher energy consumption during CNC machining aluminum production.

Aluminum Alloys Overview

When it comes to commercially available aluminum, which is commonly used in CNC machining projects, it is not in its pure form; rather, it incorporates small amounts of alloying elements. These alloying elements serve to enhance the strength and hardness of what would otherwise be a very soft metal. Typically, standard aluminum consists of 99 to 99.6% aluminum by weight, with additional elements such as silicon, manganese, magnesium, copper, and zinc constituting the remaining percentage.

The realm of aluminum alloys offers an array of possibilities, achieved by making slight adjustments to the proportions of alloying elements. However, certain compositions have proven more practical than others, and these common aluminum alloys are categorized based on their primary alloying element. Each series possesses distinct properties and characteristics. For example, the 3000, 4000, and 5000 series of aluminum alloys are not amenable to heat treatment and are instead subjected to cold working, also known as work hardening.

Key Aluminum Grades

1000 series:
The 1000 series of aluminum alloys contains the highest purity of aluminum, with at least 99% aluminum by weight. These alloys lack specific alloying elements and are nearly pure aluminum. For instance, aluminum 1199 consists of 99.99% aluminum by weight and is used in the production of foil. These grades are known for their softness but can be strengthened through work hardening, which enhances their resistance to deformation.

2000 series:
Copper serves as the primary alloying element in the 2000 series of aluminum alloys. These alloys can undergo precipitation hardening, which elevates their strength to a level approaching that of steel. Precipitation hardening involves heating the metal to a specific temperature, prompting the emergence of precipitates of other metals from the solid metal solution, contributing to increased yield strength. However, 2xxx aluminum grades exhibit reduced corrosion resistance due to the presence of copper. Aluminum 2024 also contains manganese and magnesium and finds application in aerospace components.

3000 Series:
Manganese is the predominant additional element in the 3000 series of aluminum alloys. These alloys can be work hardened as they cannot be heat-treated to achieve the required hardness levels. Aluminum 3004, which also contains magnesium, is the alloy used in aluminum beverage cans, along with its hardened variants.

4000 Series:
Silicon is the major alloying element in the 4000 series of aluminum alloys, and it lowers the melting point of aluminum 4xxx grades. For instance, aluminum 4043 is employed as filler rod material for welding 6000 series aluminum alloys, while aluminum 4047 is used in sheet and cladding applications in construction.

5000 series:
The 5000 series relies on magnesium as the principal alloying element, granting these grades excellent corrosion resistance. Consequently, they are often employed in marine applications and other settings subjected to extreme environmental conditions. Aluminum 5083 is a frequently used alloy in marine components.

6000 series:
The 6000 series combines magnesium and silicon, resulting in some of the most prevalent aluminum alloys. These alloys are generally easy to machine and can undergo precipitation hardening. Notably, 6061 is one of the most commonly encountered aluminum alloys, boasting high corrosion resistance and finding application in structural and aerospace uses.

7000 series:
Zinc, occasionally in combination with copper, chromium, and magnesium, forms the basis of the 7000 series of aluminum alloys. These alloys can achieve exceptional strength through precipitation hardening and are often preferred in aerospace applications due to their high tensile strength. A well-known grade within this series is 7075, which, while having lower corrosion resistance than some alloys, still offers superior resistance compared to 2000 series materials. It is widely used and particularly favored in aerospace applications.

8000 series:
The 8000 series serves as a catchall category for aluminum alloys that do not fit into the other defined series. These alloys may incorporate various additional elements, including iron and lithium. For instance, 8176 aluminum contains 0.6% iron and 0.1% silicon by weight and is utilized in the production of electrical wire.

Aluminum Conditioning, Treatments, and Surface Finishes

Heat treatment is a commonly employed process that alters the material properties of many metals, typically on a chemical level. Specifically, for aluminum, heat treatment is essential to enhance its hardness and strength. In its untreated state, aluminum is a soft metal, necessitating a conditioning process to make it suitable for various applications. The type of treatment applied to aluminum is denoted by a letter designation appended to the grade number.

Heat Treating

The 2xxx, 6xxx, and 7xxx series of aluminum alloys can all undergo heat treatment, leading to increased strength and hardness, rendering them suitable for specific applications. In contrast, the other alloys, such as the 3xxx, 4xxx, and 5xxx series, can only be strengthened through cold working. Different letter designations, known as temper designations, are used to indicate the applied treatments. These designations include:

“F” signifies that the material is as-fabricated, meaning it has not undergone any heat treatment.
“H” indicates that the material has experienced some form of work hardening, either in conjunction with heat treatment or independently. Numerical values following the “H” signify the type of heat treatment and the level of hardness achieved.
“O” denotes that the aluminum has been annealed, resulting in reduced strength and hardness. While this might seem counterintuitive, annealing produces a more machinable, potentially tougher, and more ductile material, which can be advantageous for specific manufacturing processes.
“T” indicates that the aluminum has undergone heat treatment, with the numerical value following the “T” providing details about the specific heat treatment process. For instance, Al 6061-T6 has been solution heat treated (held at 980 degrees F and then quenched in water for rapid cooling) and subsequently aged by maintaining it at a temperature ranging from 325 to 400 degrees F.

Surface Finishes

CNC machining aluminum can be subjected to various surface finishes, each offering cosmetic and/or protective attributes suitable for different applications.

• As-machined finish
  This finish involves no post-machining treatment. It is a quick and straightforward option but is often insufficient for cosmetic components. It is best suited for CNC machining aluminum prototype parts intended to assess functionality and fit.
• Smooth machining
  This finish is a step up from the as-machined finish. It entails more meticulous machining, including the use of sharp tools and finishing passes, resulting in a smoother surface finish. While it is a more precise method often used for CNC machining aluminum test parts, it may still leave machine marks and is not typically employed for final products.
• Bead blasting
  Bead blasting creates a matte finish by propelling tiny glass beads onto the CNC machining aluminum parts surface. It effectively removes most machining marks, providing a smooth yet slightly grainy appearance. This process is responsible for the iconic look and feel of certain popular laptops before anodizing.
• Anodizing
  Anodizing is a commonly used finish that involves the creation of a protective oxide layer on the CNC machining aluminum surface, akin to the natural oxidation process when aluminum is exposed to air. During artificial anodization, the aluminum component is suspended on a conductive rack and immersed in an electrolytic solution where a direct electric current is applied. The solution’s acidity dissolves the existing oxide layer, while the electric current releases oxygen at the surface, forming a new protective aluminum oxide layer.By carefully balancing the dissolution and buildup rates, the oxide layer develops with nanopores, allowing for extended coating growth beyond what naturally occurs. These nanopores are sometimes filled with corrosion inhibitors or colored dyes for cosmetic purposes and then sealed to create a protective coating.

Tips for CNC Machining Aluminum

CNC machining aluminum is a widely favored choice due to its exceptional machinability and impressive strength-to-weight ratio. Its machinability not only translates to quicker machining processes but also reduces labor and machine time costs. Additionally, it simplifies the task of achieving the precise tolerances often required for precision components.

However, it’s essential to be aware of certain considerations when CNC machining aluminum:

• Thermal Expansion Effects
  Aluminum’s relatively high coefficient of thermal expansion can impact tolerances, especially when working on CNC machining aluminum thin parts. To mitigate potential issues, it’s advisable to design toolpaths that avoid concentrating heat in one area for an extended period. This approach allows heat to dissipate, and you can fine-tune toolpaths within your CAM (Computer-Aided Manufacturing) software when generating the CNC machining aluminum program.
• Control Cutting Forces
  The softness of certain aluminum alloys can result in deformation during machining if excessive forces are applied. It’s crucial to adhere to recommended feeds and speeds specific to your aluminum grade to maintain the appropriate level of force during machining. As a rule of thumb, ensure that the CNC machining aluminum part’s thickness remains greater than 0.020 inches throughout to prevent deformation.
• Built-Up Edge Management
  Aluminum’s malleability can lead to the formation of a built-up edge on cutting tools. This accumulation obscures the sharp cutting surface, dulls the tool, and diminishes its effectiveness, resulting in an inferior surface finish on the workpiece. To address this issue, you can experiment with different cutting tool materials, such as carbide inserts instead of high-speed steel (HSS), and adjust the cutting speed. Furthermore, consider varying the amount and type of cutting fluid used to control built-up edge formation.

The use of CNC machining aluminum offers numerous advantages, and with the availability of various alloys and treatments, it proves ideal for a wide array of applications. We specialize in precision CNC machining aluminum alloys and are open to discussing your project requirements in detail. Feel free to reach out to us for further consultation!