A comprehensive guide to surface finishes for CNC machined and sheet metal parts: corrosion resistance, aesthetics, and thickness callouts.
Surface finishing transforms as-machined or fabricated metal parts into functional, durable, and aesthetically pristine products. Selecting between sulfuric anodizing, electroplating, electroless nickel, and powder coating requires balancing dimensional tolerance allowances, environmental exposure, hardness, and electrical conductivity.
- Always account for coating build-up on precision bearing bores and fine threads.
- Mask critical tolerance surfaces and grounding points before anodizing or powder coating.
- Passivate stainless steels to ASTM A967 standards to prevent galvanic corrosion.
1. Anodizing (Type II vs. Type III Hardcoat)
Anodizing converts aluminum surfaces into durable aluminum oxide:
- Type II (Sulfuric): 8-25 µm layer thickness. Offers wide color dyeing (black, clear, blue, red) and corrosion protection.
- Type III (Hardcoat): 25-50 µm layer thickness. High Rockwell hardness (60-70 HRC equivalent) for extreme wear and dielectric resistance.
2. Chemical Conversion (Chromate / Alodine)
MIL-DTL-5541 chemical conversion preserves electrical conductivity while providing corrosion protection and primer adhesion for painting.
3. Powder Coating & Electroless Nickel Plating
Powder coating provides heavy impact resistance for industrial sheet metal enclosures (60-120 µm thickness), while electroless nickel plating deposits uniform thickness inside threaded blind holes and intricate internal channels.
Actionable Manufacturing Recommendations
Indicate all critical masking areas on your 2D engineering drawings. Sango CNC provides in-house plating, anodizing, and powder coating with CMM dimensional verification.
Need a competitive manufacturing quote?
Upload your 3D CAD files for instant pricing, engineering review, and automated DFM feedback.