Anodizing for Machined Aluminum Parts
Type II decorative and Type III hard coat anodizing per MIL-A-8625, clear or black, with masking, pre-coat sizing and post-coat CMM verification planned by KGL.
Anodizing at KGL
Anodizing converts the aluminum surface into a hard oxide layer, so the coating is part of the part, not a film that can peel. We run Type II decorative and Type III hard coat through an audited partner line, with the pre-anodize machining, masking callout and post-coat verification planned by KGL. Anodize practice per MIL-A-8625, with AMS 2471 covering Type II details and AMS 2468 hard coat details on drawings that call them out.
A real program pattern: one robotics customer ships joint housings, covers and brackets in 6061-T6 with black Type II anodize, threads masked, and a separate steel sub-family in the same shipment finished black. Batch color consistency is a named inspection item, not an afterthought.
Dimensional Change by Anodize Class
Values below come from our finishing standard, revision D, and are the numbers we pre-size to when a drawing carries anodize on tolerance-carrying features.
| Anodize class | Film thickness (μm) | Single-side dimensional change (μm) |
|---|---|---|
| Type II clear (undyed) | 9 to 14 | Profile and bores 2 to 4 |
| Type II colored (red, gold, yellow, blue) | 10 to 15 | Profile 3 to 6; bores below 2 mm 1 to 3, above 2 mm 3 to 6 |
| Type II black | 8 to 12 | Profile 3 to 5; bores below 2 mm 1 to 3, above 2 mm 3 to 5 |
| Type III hard coat, clear or black | 25 to 35 | Profile and bores 12 to 16 |
| Type III hard coat, heavy film | 40 to 50 | Profile and bores 20 to 25 |
| Type III hard coat, extra heavy film | 50 to 60 | Profile and bores 24 to 28 |
| Type III hard coat plus PTFE seal | 45 to 55 | Profile and bores 22 to 26 |
| Grit blasted plus clear anodize | 5 to 10 | Profile and bores 2 to 3; first article Faro-measured before batch |
| Chemical polish plus clear anodize | 5 to 10 | No machining allowance left |
When to Choose It
| Goal | Class | Typical thickness |
|---|---|---|
| Cosmetic color on housings and covers | Type II, clear or black | 8 to 15 μm coating |
| Wear and abrasion resistance | Type III hard coat | 25 to 50 μm coating |
| Dielectric and corrosion barrier | Type II or III per drawing | thickness per callout |
| Conductive grounding faces | Masked bare, or conversion coating instead | masking per drawing |
Specifications We Control
| Item | Specification |
|---|---|
| Standard | MIL-A-8625 Type II / Type III; AMS 2471; AMS 2468 |
| Coating thickness | Type II 8 to 15 μm, Type III 25 to 50 μm, measured per batch |
| Colors | Clear, black; Type III jet black per drawing |
| Masking | Threads, grounding faces and marked features plugged or taped |
| Dimensions | Specified dimensions apply after anodizing; CMM verified on critical features |
| Batch color | Same batch same color, agreed face map for cosmetic areas |
| Compliance | RoHS and REACH declarations available per shipment |
How We Run It and Check It
The sequence we control: machine with anodize growth in mind, deburr and clean, mask per drawing, anodize, then inspect. Coating thickness is spot checked per batch; dimension-critical features are re-verified on Hexagon or Zeiss CMMs after coating, because the coating is real height on the surface. Sealing quality and appearance are checked against the agreed face map before packing.
If a drawing marks anodize on a steel part, we flag it. On one shipment review the drawing called anodize on a C45 steel bracket, which cannot anodize; the fix was black oxide on the steel part and anodize stayed on the 6061-T6 family. Catching that at quote time is cheaper than catching it at goods-in.
Detail pages: anodizing standards (MIL-A-8625 Type II / Type III tables). Material side: aluminum CNC machining.
Cross entrances: by material | CNC machining | inspection and QC.
Frequently Asked Questions
Which alloys anodize to the most uniform color?
6061-T6 and 5052-H32 give the most even color. 7075 shows banding where copper-rich phases meet the surface, and 2024 is usually kept off cosmetic faces. On one humanoid robot joint program we ran 6061-T6 housings and covers in jet black Type II with batch-to-batch color held consistent.
Does anodizing change my dimensions?
Yes, it grows the surface, and the growth is predictable enough to plan for. In our finishing standard, clear Type II runs 9 to 14 micrometers of film and moves outer profiles and bores 2 to 4 micrometers per side; black Type II moves profiles 3 to 5 micrometers per side; Type III hard coat at 25 to 35 micrometers of film moves profile and bores 12 to 16 micrometers per side, and heavy-film hard coat moves them 20 to 28. Inside bores below 2 millimeters the change is smaller, 1 to 3 micrometers. We pre-size tolerance-critical features and verify them on the CMM after coating.
Can you mask threads and grounding faces?
Yes, masking per drawing is standard. Features marked on the drawing (for example with an asterisk convention) are plugged or taped so threads stay clean and conductive faces stay bare. Plug pull-through is checked before packing.
What colors can you hold?
Clear and black are the stock colors on Type II; Type III hard coat is normally left natural gray or dyed jet black. Custom dyes are possible but we agree a color sample and batch-consistency rule before production.
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