Surface Treatment and Finishing
Eight finishing routes controlled under the same quality system as our machining: choose the treatment by the problem it solves, and we plan pre-coat sizes, masking and verification into the route.
Pick by the Problem You Need Solved
| Goal on the drawing | First choice | Alternatives | Typical parts |
|---|---|---|---|
| Corrosion resistance on aluminum plus color | Anodizing Type II | Conversion coating, powder coating | Housings, brackets, enclosures |
| Wear surface on aluminum | Anodizing Type III hard coat | Nickel plating | Slides, pistons, tooling plates |
| Corrosion resistance on stainless after machining | Passivation | Electropolishing | Fluid parts, medical components |
| Corrosion barrier on carbon or alloy steel | Black oxide with oil seal | Zinc plating | Rotors, shafts, brackets |
| Wear and dimensional build on steel | Hard chrome | Nickel plating | Wear pads, gauge surfaces |
| Change hardness or release stress | Heat treatment | Cryogenic or vibration aging | Tooling, structural parts |
| Low Ra on sealing or optical-adjacent faces | Polishing | Surface grinding | Seals, lenses mounts, spools |
| Outdoor weather and color on covers | Powder coating | Anodizing, wet paint | Enclosures, panels, frames |
| Permanent traceability marks | Laser engraving | Dot peen, silk screen | All part families |
Film Thickness and Single-Side Dimensional Change
Coating thickness is not an afterthought, it is a dimension. Our finishing standard, revision D, qualifies every process by its film-thickness window and the resulting single-side dimensional change, with tighter rules inside small bores and holes. We pre-size or mask the features that carry tolerances so the finished part still measures to the drawing.
Anodizing and Conversion Coatings on Aluminum
| Process | Film thickness (μm) | Single-side dimensional change (μm) |
|---|---|---|
| Chromate conversion (gold), chemical conversion film | 1 to 2 | Outer profile 0 to 2; hole diameters unchanged |
| Clear sulfuric anodize (Type II) | 9 to 14 | Profile and bores 2 to 4 |
| Colored anodize (red, gold, yellow, blue) | 10 to 15 | Profile 3 to 6; bores below 2 mm 1 to 3, above 2 mm 3 to 6 |
| Black anodize (Type II) | 8 to 12 | Profile 3 to 5; bores below 2 mm 1 to 3, above 2 mm 3 to 5 |
| Hard anodize clear or black (Type III) | 25 to 35 | Profile and bores 12 to 16 |
| Hard anodize, heavy film | 40 to 50 | Profile and bores 20 to 25 |
| Hard anodize, extra heavy film | 50 to 60 | Profile and bores 24 to 28 |
| Special hard anodize | 50 to 60 | Profile and bores 20 to 24 |
| Hard anodize plus PTFE seal, clear or black | 45 to 55 | Profile and bores 22 to 26 |
| Type III hard coat plus PTFE seal | 25 to 35 | Profile and bores 12 to 16 |
| Hard anodize, green | 25 to 35 | Profile and bores 12 to 16 |
| Grit blasted (60# or 180#) 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 |
| Chrome-free passivation on aluminum | 1 to 2 | Profile and bores 0 to 2 |
Electroless and Electrolytic Nickel Plating
| Process | Film thickness (μm) | Single-side dimensional change (μm) |
|---|---|---|
| Electroless nickel on aluminum | 3 to 5 | Profile 3 to 5, bores 2 to 4 |
| Electroless nickel on steel | 3 to 5 | Profile and bores 3 to 5 |
| Electroless nickel on copper | 3 to 5 | Profile and bores 3 to 5 |
| High-phosphorus electroless nickel (9 to 12% P), steel | 10 to 12 | Profile and bores 10 to 12 |
| Black electroless nickel, aluminum | 3 to 5 | Profile 3 to 5, bores 2 to 4 |
| Electrolytic nickel on steel | 12 to 15 | Profile 12 to 15; bores below 3 mm unplated, above 3 mm 8 to 12 |
| Heavy electrolytic nickel on steel | 13 to 25 | Profile 13 to 25; bore allowance set per drawing |
| Nickel under silver on aluminum (Ni 2 to 3, Ag 4 to 7) | 6 to 10 total | Profile and bores 6 to 8 |
Chrome, Silver and Gold Plating on Steel
| Process | Film thickness (μm) | Single-side dimensional change (μm) |
|---|---|---|
| Hard chrome, standard | 3 to 6 | Profile 3 to 6; bores and slots unplated |
| Hard chrome, heavy | 5 to 8 | Profile 5 to 8; bores and slots unplated |
| Industrial thick chrome | per drawing | Dimension change equals film thickness; bores and slots unplated |
| Decorative or matte chrome | 3 to 6 | Profile 3 to 6; bores and slots unplated |
| Electroless nickel plus black chrome | 18 to 24 total | Nickel layer 15 to 18, black chrome 3 to 6 |
| Silver plate | 3 to 5 | Profile and bores 3 to 5 |
| Gold plate | 0.3 to 0.5 | Profile and bores 0.3 to 0.5 |
| Heavy gold plate | 3 to 4 | Profile and bores 3 to 4 |
| Titanium nitride coating | 0.5 to 2 | Profile and bores 0.5 to 2 |
| Nickel-fluorocarbon (Poly-OND) | 12.5 to 18 | Profile 12.5 to 18; bore allowance per drawing |
Zinc Plating and Black Oxide on Steel and Cast Iron
| Process | Film thickness (μm) | Single-side dimensional change (μm) |
|---|---|---|
| Zinc plating, clear or blue | 5 to 8 | Profile 5 to 8; bores below 15 mm 3 to 5 |
| Thick-film blue zinc | 12 to 18 | Profile 12 to 18; bores below 15 mm 3 to 5 |
| Zinc plating, yellow, iridescent or black | 5 to 10 | Profile 5 to 10; bores below 15 mm 2 to 4 |
| Black oxide on carbon and tool steel | 0.5 to 1 | Profile and bores 0.5 to 1 |
| Black oxide on copper or cast iron | 0.5 to 1 | Profile and bores 0.5 to 1 |
| Black oxide on austenitic stainless | 0.5 to 1 | Profile and bores 0.5 to 1 |
Passivation, Polishing and Advanced Coatings
| Process | Film thickness (μm) | Single-side dimensional change (μm) |
|---|---|---|
| 300-series stainless passivation | 0.05 to 0.1 | Profile and bores 0.05 to 0.1 |
| 440C stainless passivation | 0 to 0.2 | Profile and bores 0 to 0.2 |
| Electropolish, austenitic stainless | 0 to 0.5 removed | Profile minus 3 to 5; bores below 20 mm minus 1 to 2 |
| Electropolish, titanium | 0 to 0.5 removed | Profile minus 2 to 4; bores below 20 mm minus 1 to 2 |
| PTFE spray (Xylan family) | 5 to 10 | Profile 5 to 10; bore allowance per drawing |
| Heavy PTFE spray | 12.7 to 25.4 | Profile and bores 12.7 to 25.4 |
| DLC coating on stainless | 2 to 3 | Profile 1 to 2; bores unchanged |
| ADLC coating on steel | 1 to 2 | Profile and bores 1 to 2 |
| Thermal diffusion chromium coating | 2 to 4 | Profile 2 to 4; hole diameters unchanged |
| Powder spray coating | 50 to 70 | Profile 50 to 70; bore allowance per drawing |
Internal process codes (C035, C079, C056, C108, C119, ATS and similar) map to vendor work instructions in our purchasing system. If your drawing calls one of them, name the code in the RFQ and the same qualified window applies. Where a bore or slot must stay dimensionally untouched, we state it on the traveler and the plater masks it.
Find Your Route Faster
Anodizing
Type II decorative and Type III hard coat for aluminum, clear, black or colored, masking per drawing.
Passivation
Nitric or citric passivation for stainless and titanium, removes free iron after machining.
Heat Treatment
Stress relief, solution, aging, hardening and annealing, sequenced into the machining route.
Electroplating
Zinc, nickel and hard chrome plating for corrosion and wear, thickness verified after plating.
Polishing
Mechanical and electrolytic polishing, Ra ladder down to 0.2 micrometers on sealing faces.
Powder Coating
RAL color powder coat for enclosures and covers, edge coverage and weather resistance.
Black Oxide
Alkaline black oxide with oil seal for carbon and alloy steel, near-zero dimension change.
Laser Engraving
Permanent logos, serial numbers and data matrix marks for traceability per drawing callout.
How finishing fits the machining route: roughing, then stress relief where stock removal is heavy, finish machining with coating allowance left on coated faces, deburring, coating, then final inspection on the CMMs. Coating thickness is measured and reported; dimensions that carry tolerances are verified after coating.
Surface Treatment FAQ
Do you finish parts you did not machine?
Yes, if the parts are within our inspection scope. We measure incoming dimensions, note any risk the coating could push a feature out of tolerance, and quote the finish as a standalone service.
Who performs the treatment?
Anodizing, plating, powder coating, black oxide and heat treatment run through our qualified partner network under KGL purchase control; laser marking, polishing, grinding and passivation-ready cleaning run in house. Incoming and final inspection happens at KGL either way, and one certificate package leaves with the shipment.
Can you hold dimensions after coating?
We plan for it. Every coating in our finishing standard carries a film-thickness window and a known single-side dimensional change, from about 0.05 micrometers on stainless passivation to 12 to 16 micrometers per face on hard anodize. The table on this page lists the values we design to; tell us the coating with the drawing and we pre-size, mask or post-finish the features that carry tolerances.
Where do the film thickness and dimension change values come from?
From our internal finishing standard, revision D, which governs every outsourced coating job: each process has a qualified film-thickness range and a measured single-side dimensional change, including separate rules for bores and holes below a critical diameter. First articles for blasting plus anodize are measured on the Faro arm and approved before the batch runs.
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