Does anodizing affect part dimensions in precision CNC components?

Understanding the Anodizing Process

Anodizing is a controlled electrochemical process that enhances the corrosion resistance, surface hardness, and appearance of aluminum and other non-ferrous CNC components. It is often applied after CNC machining, CNC milling, or CNC turning operations to protect the substrate. During anodizing, a thin oxide layer—typically ranging from 5 to 50 microns—is formed on the surface. Part of this layer penetrates into the base metal, while the rest builds outward, slightly increasing overall dimensions.

Dimensional Change Considerations

The dimensional change caused by CNC aluminum anodizing service depends on the thickness of the oxide layer. Roughly one-third of the anodized layer grows inward, and two-thirds outward. For example, a 25 µm Type II coating typically increases the dimension by about 12–15 µm per surface. Engineers often compensate for this growth by undersizing precision features during machining. For critical tolerance zones, our team utilizes precision machining services and in-process metrology to ensure the final dimensions are maintained after surface finishing.

Material-Specific Behavior

Anodizing primarily applies to Aluminum 6061, Aluminum 7075, and Aluminum 5052, all of which respond differently depending on alloy composition. While titanium alloys like Ti-6Al-4V can also undergo anodizing for color coding or oxide thickening, the dimensional impact is negligible compared to aluminum. For hybrid assemblies involving stainless steel 304 or copper C110, the process must be isolated, as these materials do not anodize effectively.

Surface Quality and Tolerance Control

To maintain tight tolerances, engineers often integrate CNC grinding or CNC boring after the removal allowances for anodizing are defined in the machining model. Surface preparation before anodizing—like as-machined finish or CNC part tumbling and deburring—affects the uniformity of oxide buildup and coating thickness control.

Industry Applications

In aerospace and aviation, anodized aluminum parts provide excellent corrosion resistance and weight savings. For medical device applications, anodizing ensures biocompatibility and easy sterilization. Within automotive manufacturing, anodized surfaces enhance wear resistance for engine and chassis components that are exposed to harsh conditions.

Conclusion

Anodizing does affect part dimensions, but with accurate process control, pre-machining allowance, and post-treatment inspection, dimensional integrity remains within specification. Partnering with an experienced CNC shop ensures that both visual and dimensional requirements are achieved consistently across production batches.