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Anodizing for CNC Machined Parts

What is Anodizing for CNC Machined Parts?

Anodizing is a specialist surface finishing option for CNC machined parts.

It is an electrochemical process that creates a thin, protective oxide layer on the surface of a metal part, typically aluminium or its alloys. This oxide layer provides improved corrosion resistance, hardness, and wear resistance to the part. In addition, anodizing can also enhance the aesthetic appearance of the part by allowing for various colour options.

The anodizing process involves immersing the part in an electrolyte bath and applying a direct current, which causes the formation of an oxide layer on the surface.

Let’s look at this process in more detail….

Anodized Metallic Components

What is the Process for Anodizing a CNC Machined Part?

The anodizing process involves several steps:

  1. Preparing the part: The first step is to thoroughly clean the part to remove any dirt, grease, or other contaminants from its surface. This is usually done using a solvent or detergent and water. This step ensures proper adhesion of the anodized coating.
  1. Surface treatment: After cleaning, the part may undergo a surface treatment process called etching or desmutting. This step involves the use of a chemical solution to remove any remaining oxides, scale, or residual metals that could interfere with the anodizing process.
  1. Anodizing bath: The part is then immersed in an anodizing bath, which consists of an electrolyte solution, typically sulfuric acid. The part serves as the anode, while a cathode is also present in the bath. When an electric current is passed through the bath, an oxide layer forms on the surface of the part due to the electrochemical reaction.
  1. Anodizing process: The voltage and current applied during the anodizing process are carefully controlled to achieve the desired thickness and quality of the anodized layer. The type of alloy used in the part, desired colour or finish, and other factors determine the parameters of the anodizing process.
  1. Colouring (optional): If a specific colour is required, the anodized part may be immersed in a dye bath. This allows the pores in the anodized layer to absorb the dye, resulting in a coloured finish.
  1. Sealing: After anodizing and dyeing (if applicable), the part is often sealed to improve corrosion resistance and durability. Sealing involves immersing the part in a hot water bath or applying a sealant to close the pores of the anodized layer.
  1. Quality inspection: The anodized part undergoes quality inspection to ensure that the desired specifications, such as thickness, colour, and surface finish, have been achieved. This inspection may include visual examination, measurement, and various testing methods.

What are the Different Types of Anodizing Processes?

There are various types of anodizing processes that can be used for CNC machined parts. Some of the more common types include:

Type I Anodizing: Also known as regular or decorative anodizing, this is the most typically used anodizing process. It creates a uniform oxide layer on the surface of the part and provides corrosion resistance and improved aesthetics.

Type II Anodizing: This type of anodizing is typically used for parts which do not require high wear resistance. The process involves placing the aluminium in a sulphuric bath instead of using chromic acid. Type II anodized parts can easily absorb dyes, paints, and adhesives.

Type III Anodizing: Also known as hardcoat anodizing or sulfuric anodizing, this process produces a thicker and harder oxide layer compared to Type II anodizing. It offers enhanced wear and corrosion resistance, making it suitable for parts exposed to harsh environments or for those which require increased durability.

Chromic Acid Anodizing: This type of anodizing, also referred to as Type I anodizing, uses chromic acid as the electrolyte. It forms a thin, dense, and corrosion-resistant oxide layer on the part’s surface. Chromic acid anodizing is often used for parts that require high-temperature resistance or electrical conductivity.

Titanium Anodizing: This specialised anodizing process is specifically used for titanium CNC machined parts. It forms a thin oxide layer on the surface, providing improved corrosion resistance, wear resistance, and colour options.

Anodized Yoyo with Colour Splash

Hard Anodizing: Hard anodizing is a form of the Type III anodizing process that creates an even thicker and harder oxide layer. This process is commonly used for parts which require extreme wear resistance, such as pistons, gears, and bearings.

Coloured Anodizing: Anodizing can also be combined with colouring techniques to provide various colours on the surface of CNC machined parts. This is achieved by dyeing the porous oxide layer formed during anodizing or by using proprietary colouring processes.

The appropriate type of anodizing for a CNC machined part will depend on the desired properties, functionality, and aesthetic requirements of the part.

The Benefits of Anodizing a CNC Machined Part

There are several benefits of anodizing a CNC machined part, including:

Enhanced corrosion resistance: Anodizing creates a protective layer on the surface of the part, making it more resistant to corrosion caused by moisture, chemicals, and other environmental factors.

Improved durability: The anodized coating makes the part more wear and scratch-resistant, increasing its lifespan and reducing the need for maintenance or replacement.

Aesthetic appeal: Anodizing allows for a wide range of colour options, providing an attractive and decorative finish to the part. This is crucial for products which need to be visually appealing.

Improved hardness: Anodizing can significantly increase the surface hardness of the part, making it more resistant to scratches and dents.

Better adhesion: Anodizing provides a textured surface with excellent adhesion properties, making it easier to apply paints, adhesives, or other coatings.

Electrical insulation: Anodized coatings have electrical insulating properties, making them useful in applications where electrical conductivity needs to be minimised.

Eco-friendly option: Anodizing is a relatively environmentally friendly process compared to other coating methods. It doesn’t involve the use of heavy metals, or the types of volatile organic compounds (VOCs) often found in other surface treatments.

Overall, anodizing a CNC machined part can improve its performance, aesthetics, and durability, making it a popular choice for a wide range of industries and applications.

Telescope with Anodized Finish
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