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CNC Machining for Aerospace

The extremely high level of precision needed within the aerospace industry makes CNC machining a suitable manufacturing process for the sector.

 

This article provides you with a complete guide to aerospace machining and its importance.

 

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CNC Machining eBook

If you want to produce high-quality machined parts with a sleek appearance, it’s essential to consider some critical factors related to CNC machining. 

 

Here, we’ve gathered some basic information and important considerations to help you achieve the desired results.

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RapidDirect Alodine Finish Services

Create a protective film of alodine coating using our alodine finish services. Our alodine finish has a thickness of 0.00001 to 0.00004 inches, leaving a clear finish without affecting the material's base color.
alodine finish services
what is alodine finish

What's Alodine?

Alodine conversion coating is a surface finish process primarily for aluminum and its alloys, increasing their corrosion resistance, paint adhesion, and electrical conductivity. 

 

The coating process involves a chemical reaction of a chromate solution and the part surface forming a protective layer of chromium compounds. There are two common types of alodine coating: MIL-DTL-5541 Type 1 and Type 2.

 

MIL-DTL-5541 Type 1 uses hexavalent chromium; hence, the name “hex chrome” forming a gold or brown film. However, it is unsafe due to the hexavalent chromium and requires stringent adherence to legal processing and regulations.

 

MIL-DTL-5541 Standard Type II uses trivalent chromium compounds, hence the name “hex-free chrome,” forming a clear coating. Due to its safety, Type I alodine coating took over from Type 2 alodine coating and is the standard in our alodine finish services. 

 

The alodine process is essential in aerospace, automotive, and electronics industries that use aluminum and its alloys, where parts require corrosion resistance and improved performance with minimum dimensional change. 

Alodine Specifications

Applicable MaterialsColor OptionsVisual AppearanceIndustrial ApplicationsThickness
AluminumClear, YellowIt creates a thin protective film on the metal, leaving a clear finish without affecting the material's base color.Aerospace, automotive, and electronic industries that require corrosion resistance and paint adhesion.0.25-1.0 µm 0.00001-0.00004 inches
Advantages
  1. It forms a strong chemical film aluminum part with high corrosion resistance
  2. Improves the adherence of paints and primers
  3. The coating maintains the aluminum part’s electrical conductivity
  4. Thin coating ensures an insignificant dimensional change
  5. The hex-free chromate process is safer
  6. It does not alter the part’s mechanical properties
  7. It is a cost-effective coating process.
Notes
  • Type 1 alodine conversion coating produces transparent parts or slightly bluish transparent colors, which are difficult to identify with the naked eye.
  • Type 2 alodine conversion coating produces a yellowish or iridescent appearance.

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FAQs

Anodizing differs from alodining based on how it works and the final part’s properties and applications.

Anodizing is an electrolytic process that involves immersing a metal electrode attached to the anode and another metal into the cathode. Passing electrical current through the circuit causes the cathode to attract positive ions from the anode, while the anode attracts O2 ions from the solution to form a passive oxide layer. In contrast, alodine aluminum treatment is a chemical conversion process.

Anodized parts offer a stronger corrosion resistance and a thick oxide layer. Alodination, conversely, produces parts with thinner coatings, offering lower protection. Anodized surfaces can be dyed in various colors, while alodined part surfaces usually have a yellow or clear chromate finish.

Alodination is important when CNC machined parts require better corrosion resistance, paint adhesion, and electrolytic conductivity with stringent dimensional tolerance requirements. Part assemblies rely on surface finishing to prevent scratches and minor damage during handling, transportation, and assembly.
Lastly, they are an important surface finish for industries that want to adhere to regulatory standards, such as aerospace, automotive, and defense.

The application process for alodine aluminum treatment involves the following:
1. Clean the part to remove contaminants such as rust and scale
2. Etch the parts that you don’t want to be coated by the alodine finish
3. Deoxide the part to removes oxides, oxygen, and related compounds
4. Immerse or spray the coating with the alodine file (the alodine finish depends on whether it is type 1 or 2) on the part. You can also apply the alodine conversion coating on the part with a brush
5. Rinse the part with deionized water and dry for a specific time

According to the USA MIL-Spec, the maximum temperature tolerance for alodine coating is 140°F. Exposure to higher temperatures can degrade the coating’s protective properties, leading to loss of corrosion resistance and hardness and reduced electrical conductivity.

Alodine coatings usually air dry quickly, often within 30 minutes at room temperature. The curing time, however, depends on factors such as workpiece size, complexity, and the alodination process.

No, the alodine finish is incompatible with stainless steel as the chromate conversion process is primarily for aluminum and its alloys. A better option is to use other methods, such as passivation or black oxide coating for stainless steel parts. The alodine finish service is the best surface finish option for stainless steel

Yes, the alodine chromate conversion Type 2 process is safe due to the use of trivalent chromium. On the other hand, Type 1 alodine aluminum treatment uses hexavalent chromium, which is unsafe and requires proper safety protocols, including personal protective equipment (PPE) and adequate ventilation.

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