In the world of aerospace and high-tech manufacturing, precision is often measured in microns. However, a common pitfall in the design process is treating surface treatments as a purely cosmetic final step. At Euro Machining, we have seen how late-stage finish call-outs can trigger unexpected dimensional shifts, leading to costly rework or, worse, failed inspections. Understanding how finishes like anodizing and chem film interact with your part’s geometry is essential for maintaining tight tolerances and ensuring program success.
Understanding Dimensional Growth in Anodizing
Anodizing is a popular choice for aerospace components due to its superior corrosion resistance and surface hardness. However, unlike paint, which sits on top of a surface, anodizing is a conversion coating. This means it transforms the base aluminum into aluminum oxide. During this process, approximately 50% of the coating thickness penetrates the surface, while the other 50% builds outward.
For a standard Type II anodize, this might mean a growth of 0.0005” to 0.001” per surface. If your design features high-tolerance holes or interlocking assemblies, failing to account for this growth can result in parts that no longer fit. To avoid this, it is critical to specify whether dimensions apply “before” or “after” finish on your engineering drawings.
The Difference Between Anodize and Chem Film
While anodizing adds material, chemical conversion coatings (often called chem film or Alodine) behave differently. Chem film is primarily used for corrosion protection where electrical conductivity must be maintained. Because the layer is significantly thinner—often less than 0.00005”—the dimensional impact is negligible for most applications. In some instances, the pre-treatment cleaning and etching process can even lead to slight material removal.
Choosing between these finishes isn’t just about the environment the part will live in; it’s about the tolerance stack-up. If you are designing a part with +/- 0.0002” tolerances, even a “thin” anodize can push a part out of spec.
Integrating Surface Treatments into DFM Reviews
The most effective way to manage these variables is through early Design for Manufacturing (DFM) reviews. At Euro Machining, we work with engineers to bridge the gap between CAD models and finished products. By integrating finishing considerations into the initial machining plan, we can adjust our machining offsets to compensate for the expected growth or removal of material.
A proactive approach includes:
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CAD Accuracy: Ensuring that critical tolerances in the 3D model reflect the final, finished state.
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Clear Call-outs: Specifying plating thickness and whether tolerances apply to the raw machined part or the final treated component.
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Masking Strategies: Identifying areas—such as threaded holes or grounded surfaces—that must remain free of coating to maintain functionality.
Verification with Keyence and CMM Technology
In precision machining, hope is not a strategy. To ensure that surface treatments meet the required specifications without compromising tolerances, Euro Machining utilizes a rigorous pre- and post-finish validation process. We leverage state-of-the-art metrology equipment, including the Keyence IM-8000 and Mitutoyo CMM, to verify dimensions at every stage.
By measuring parts immediately after machining and again after they return from our certified finishing partners, we provide our clients with total transparency and confidence. This data-driven approach eliminates surprises at final inspection and keeps your aerospace programs on schedule.
Partner with Euro Machining for Your Next Build
Don’t let surface treatments compromise your project’s integrity. Whether you are working with aluminum, titanium, or stainless steel, our team provides the expertise needed to navigate complex material and finish requirements.
Ready to optimize your next project for precision? Contact Euro Machining today to request a DFM review or a quote for your high-tolerance machining needs.