Guide complet de finition de surface pour pièces CNC (2026)
Guide d'ingénieur pour choisir la finition de surface adaptée : anodisation, galvanoplastie, polissage, PVD, sablage et plus — apparence, protection, coût, compatibilité.
Choisir la mauvaise finition de surface peut ruiner une pièce par ailleurs parfaite. Ce guide passe en revue chaque finition courante appliquée par JLYPT — ce qu'elle fait, ce qu'elle coûte, avec quels matériaux, et quand la spécifier.
Why surface finishing matters
A bare CNC-machined surface is rarely the final state of a part. The chosen finish affects three things at once:
- Appearance. Colour, gloss, texture — for consumer products this is often the dominant requirement.
- Protection. Corrosion, wear, UV, chemicals — extends part life, sometimes by 10× or more.
- Function. Electrical conductivity, thermal emissivity, biocompatibility, hardness, friction.
Anodising (aluminium parts)
Anodising electrochemically grows an aluminium-oxide layer into the part surface. It’s harder, more corrosion-resistant, takes dye well, and is integral to the part — it cannot peel like paint.
Type II (decorative)
- Layer thickness 5–25 µm.
- Excellent for colour: clear, black, blue, red, gold, etc.
- Mild abrasion resistance, good corrosion protection.
- Cosmetic standard for consumer electronics, drone frames.
Type III (hard anodising)
- Layer thickness 25–75 µm; hardness ~60 HRC.
- Very high wear and corrosion resistance.
- Limited colours (usually grey-black or natural).
- Used for hydraulic cylinders, military, industrial machinery.
See our aluminium anodising services for capacity, colours and lead times.
Electroplating and electroless plating
Plating deposits a thin metallic layer on the part — typically nickel, chrome, zinc, gold or silver. Used when you need a property the base metal lacks (corrosion, conductivity, lubricity, wear).
| Plating type | Thickness | Best for | Notes |
|---|---|---|---|
| Zinc | 5–25 µm | Cheap corrosion protection on steel | Yellow / blue / black chromate options. Outdoor: 8 µm minimum. |
| Electroless nickel (EN) | 10–50 µm | Uniform corrosion + wear coating | Conformal — ideal for complex geometry, threaded parts. |
| Hard chrome | 25–250 µm | Wear surfaces, hydraulic rods | Hexavalent variant being phased out in EU/US. |
| Decorative chrome | 0.25 µm | Cosmetic shine on plumbing/automotive | Always over a copper + nickel base. |
| Gold | 0.05–5 µm | Electrical contacts, RF connectors | Very expensive; spec only on contact area. |
| Silver | 5–25 µm | Bus bars, high-conductivity contacts | Tarnishes; needs sealing for outdoor use. |
| Tin | 5–15 µm | Solderable surfaces, food-contact (FDA) | Avoid pure-tin in cold environments (whiskers). |
PVD (Physical Vapor Deposition) coatings
PVD evaporates a metal target in a vacuum chamber and deposits a thin (1–5 µm) ceramic-like layer on the part. The result is extremely hard, low-friction and chemically inert.
| Coating | Colour | Hardness (HV) | Best for |
|---|---|---|---|
| TiN (Titanium Nitride) | Gold | 2300 | Cutting tools, dies, decorative gold finish |
| TiCN (Titanium Carbonitride) | Bronze | 3000 | Tougher tools, dies handling abrasive materials |
| TiAlN (Titanium Aluminium Nitride) | Violet/black | 3300 | High-temp cutting (e.g., milling steel dry) |
| CrN (Chromium Nitride) | Silver | 1750 | Plastic injection moulds, food-contact |
| DLC (Diamond-Like Carbon) | Black | 3000 | Wear-resistant + ultra-low friction |
| ZrN (Zirconium Nitride) | Light gold | 2800 | Watches, decorative high-end consumer |
See our PVD coating services for available colours, substrates and lead times.
Mechanical finishes
These don’t add a layer — they alter the existing surface mechanically. They’re cheap, fast and often used as a prep step before anodising or plating.
Bead blasting
Glass beads or aluminium oxide propelled at high pressure, creating a uniform matte texture. Hides minor tool marks. Common pre-treatment for anodising.
Brushing / graining
Linear scratches with a fine wire wheel, producing the “brushed steel” look common on appliances. Directional grain hides scratches.
Polishing
Multi-stage abrasive process down to 1 µm grit, producing a mirror finish. Required before chrome plating; ~Ra 0.05 µm achievable.
Tumbling / vibratory
Parts in a bin of ceramic media. Removes burrs, eases edges, leaves a soft uniform satin. Excellent for small batches and irregular geometry.
Electropolishing
Electrochemical removal of microscopic peaks, leaving a bright corrosion-resistant surface. Standard for medical-grade stainless.
Black oxide and passivation
Black oxide (carbon & tool steels)
- Chemical conversion — does not add measurable thickness.
- Mild corrosion resistance; needs oil seal.
- Cosmetic black on tools, screws, gun parts.
- Cheaper than blueing, faster than painting.
Passivation (stainless steels)
- Removes free iron from machined surfaces.
- Restores the natural chromium-oxide passive layer.
- No visible change but dramatically improves corrosion resistance.
- Required for medical and food-contact stainless parts.
Powder coating and wet painting
Both put a polymer layer on the part, but they differ in process and durability:
| Feature | Powder coating | Wet painting |
|---|---|---|
| Application | Electrostatic powder + bake at 180–200 °C | Spray gun, multiple coats, air-dry or bake |
| Thickness | 60–125 µm | 20–80 µm |
| Durability | Higher — chip and UV resistant | Moderate |
| Surface preparation | Critical (sandblast or phosphate) | Critical (degrease + primer) |
| Substrate | Heat-tolerant materials only | Most materials including plastics |
| Colour matching | Limited to powder library | Unlimited (custom mix) |
| Cost (high volume) | Lower | Higher |
Powder coating wins for industrial enclosures, outdoor furniture and automotive parts. Wet painting wins for low-volume custom colours, plastic parts, and complex multi-tone finishes.
Finish-at-a-glance comparison
| Finish | Hardness | Corrosion | Cost (relative) | Lead time |
|---|---|---|---|---|
| As-machined + deburr | Substrate | Substrate | 1× | 0 days extra |
| Bead blast | Substrate | Substrate | 1.2× | 1 day |
| Anodise Type II | High | Excellent | 1.5× | 3–5 days |
| Anodise Type III hard | Very high | Excellent | 2.5× | 5–7 days |
| Zinc plate | Soft | Good | 1.3× | 3 days |
| Electroless nickel | Hard | Excellent | 2× | 5 days |
| Hard chrome | Very hard | Good | 3× | 7 days |
| PVD (TiN/TiCN/DLC) | Extremely hard | Excellent | 4–6× | 7–14 days |
| Powder coat | Soft | Good | 1.5× | 3 days |
| Black oxide + oil | Substrate | Mild | 1.2× | 2 days |
| Passivation (stainless) | Substrate | Restored | 1.3× | 2 days |
| Electropolish | Substrate | Excellent | 1.8× | 3 days |
How to choose: a practical decision tree
Is the part aluminium and visible?
Yes → Type II anodise (decorative) or Type III (industrial). Done.
Is the part stainless and food/medical?
Passivate at minimum. Add electropolish for surgical/implant parts.
Is the part carbon steel and indoor only?
Black oxide + oil for cosmetic; zinc plate for mild outdoor exposure.
Is the part carbon steel and outdoor / aggressive?
Electroless nickel for general; powder coat for colour; hard chrome for wear.
Does the part need extreme wear or low friction?
PVD coating — TiN for tools, DLC for low-friction sliding surfaces.
Is appearance the only requirement?
Bead blast, brush or polish based on the desired look. Cheapest route.
Foire aux questions
- Les revêtements PVD prennent généralement 7–14 jours car les pièces doivent être envoyées à un spécialiste avec chambre à vide. L'anodisation dure et le nickelage chimique suivent à 5–7 jours.
- Oui, plusieurs manières : anodisation Type II (alu), Type III naturel, oxyde noir (acier), poudrage noir, PVD DLC (noir profond, prix premium).
- Galvanoplastie et poudrage ajoutent une épaisseur mesurable (5–125 µm). L'anodisation pénètre ~50 % et sort ~50 %. Le PVD ajoute 1–5 µm — généralement négligeable.
- Même lot = excellente correspondance. Lots différents = petite variation. Pour les travaux à couleur critique, spécifier "lot unique".
- Oui. Empilements courants : sablage → anodisation, nickel → chrome, passivation → électropolissage (inox médical). Chaque couche ajoute coût et délai.
- Oui. Le chrome hexavalent est interdit dans de nombreuses régions pour les nouvelles pièces auto et électroniques (RoHS, REACH). Le cadmiage est similairement restreint. Nous utilisons par défaut des alternatives conformes.
Quelle finition a le délai le plus long ?
Puis-je obtenir des pièces en noir pur ?
Comment la finition affecte-t-elle la tolérance ?
La couleur d'anodisation correspond-elle entre lots ?
Puis-je combiner plusieurs finitions ?
Certaines finitions sont-elles restreintes par la réglementation ?
À propos de l'auteur
JLYPT Engineering Team
Senior CNC Application Engineers
Our application engineering team brings 15+ years of combined experience producing precision components for aerospace, medical, robotics and industrial automation customers.
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