Surface finishing is the final step in manufacturing — and often the difference between a part that looks "cheap" and one that commands a premium price. Whether you need corrosion protection, wear resistance, or a specific appearance, choosing the right finish is essential.
This guide covers all major finishing processes for metal and plastic parts, including process descriptions, material suitability, cost factors, and application guidance.
| Category | Processes | Primary purpose |
|---|---|---|
| Mechanical | Bead blasting, brushing, polishing, tumbling | Appearance, surface prep |
| Chemical | Passivation, chromate, black oxide, phosphating | Corrosion resistance |
| Electrochemical | Anodizing, electro-polishing, electroplating | Corrosion + appearance |
| Coating | Powder coating, wet painting, PVD, CVD | Appearance + durability |
| Thermal | Hot-dip galvanizing, thermal spray, nitriding | Corrosion + wear |
Fine glass beads or aluminum oxide particles are propelled at the part surface to create a uniform matte finish.
| Parameter | Value |
|---|---|
| Surface finish (Ra) | 0.5-2.0 µm |
| Substrate removal | None (cleaning only) |
| Suitable for | Metals, plastics, glass |
| Typical cost | $0.50-3.00 per part (small) |
Best for: Removing tool marks, uniform cosmetic appearance, surface prep for coating
An abrasive belt or wheel creates a directional grain pattern on the surface.
Best for: Decorative panels, architectural metal, kitchen equipment, appliances
Parts are placed in a vibrating bowl or barrel with abrasive media and compound. Removes sharp edges, burrs, and improves surface finish.
| Abrasive media | Material | Best for | Result |
|---|---|---|---|
| Ceramic triangles | Hard metals | Deburring, edge rounding | Fast stock removal |
| Plastic cones | Soft metals, plastics | Smoothing, polishing | Gentle finish |
| Steel balls | All metals | Burnishing (bright finish) | Mirror-like surface |
| Corn cob / walnut shell | Soft, delicate parts | Drying, fine polishing | Non-abrasive |
Best for: Batch deburring, edge breaking, reducing surface roughness
An acid bath removes free iron from the surface of stainless steel, forming a thin, transparent chromium oxide layer that naturally resists corrosion.
| Standard | Typical use |
|---|---|
| ASTM A967 | General corrosion resistance |
| ASTM A380 | Cleaning and passivation |
Best for: Medical devices, food processing, marine, pharmaceutical equipment
A chemical conversion coating that produces a black finish (Fe3O4) on steel surfaces.
| Type | Process temp | Corrosion resistance | Cost |
|---|---|---|---|
| Hot black oxide | 135-145°C | Moderate (needs oil/sealer) | Low |
| Cold black oxide | Room temp | Poor (needs sealer) | Very low |
Best for: Tooling, fasteners, automotive under-hood, optical parts (reduces glare)
A chromate coating on aluminum that provides corrosion resistance and electrical conductivity. Required for aerospace.
| Type | Color | Corrosion resistance | Electrical conductivity |
|---|---|---|---|
| Class 1A | Clear/golden | Excellent | Yes |
| Class 3 | Yellow/gold | Good | Yes |
Best for: Aerospace parts, electronics enclosures, structural aluminum
An electrochemical process that converts the aluminum surface into a hard, porous aluminum oxide layer. The pores can be sealed (natural finish) or dyed (colored).
| Type | Thickness | Hardness | Color options | Typical use |
|---|---|---|---|---|
| Type II (Decorative) | 5-15 µm | Moderate | Clear, black, many colors | Consumer products, electronics |
| Type III (Hard coat) | 25-100 µm | Very hard (60-70 HRC) | Dark gray only | Aerospace, military, wear parts |
| Sulfuric acid anodize | 15-25 µm | Good | All colors | General purpose |
Sealing options: - Hot water seal: Most corrosion resistant, no color change - Nickel acetate seal: Standard, some color change - Cold seal: Lower cost, slight haze
Best for: Aluminum parts needing wear resistance, corrosion protection, or colored appearance
Using electric current to deposit a thin metal layer onto a part.
| Plating type | Substrate | Thickness | Properties | Typical use |
|---|---|---|---|---|
| Zinc plating | Steel | 5-15 µm | Corrosion protection (sacrificial) | Fasteners, brackets |
| Nickel plating | Steel, brass, zinc | 10-50 µm | Decorative, wear resistant | Automotive trim, hardware |
| Chrome plating | Nickel-plated parts | 0.5-2 µm (decorative) up to 500 µm (hard) | Decorative or hard wearing | Automotive, tools, cylinders |
| Tin plating | Copper, steel | 3-10 µm | Solderable, food safe | Electronics, food equipment |
| Silver plating | Copper, brass | 5-20 µm | Electrical conductivity | Connectors, switch contacts |
| Gold plating | Nickel undercoat | 0.5-5 µm | Corrosion + conductivity | Electronics, connectors |
The reverse of electroplating — the part is made anodic, removing surface material to create a smooth, bright, passivated surface. Primarily for stainless steel.
Electrostatically charged dry powder is sprayed onto the part, then cured in an oven. More durable, thicker, and more uniform than wet paint.
| Parameter | Value |
|---|---|
| Thickness | 50-150 µm |
| Hardness | Excellent (3H-6H pencil) |
| UV resistance | Good to very good (formulation dependent) |
| Chemical resistance | Good to excellent |
| Colors | Any RAL color + custom + textures |
Cure temperature: 180-200°C for 10-20 minutes
Best for: Outdoor equipment, heavy machinery, automotive, consumer products
Traditional spray painting using liquid paint. Lower film build, smoother appearance.
Best for: Large parts, low-volume custom colors, high-gloss automotive finishes
A thin film coating applied in a vacuum chamber. Used for both decorative and functional applications.
| PVD coating | Color | Hardness | Wear resistance |
|---|---|---|---|
| Titanium Nitride (TiN) | Gold | 2,300 HV | Excellent |
| Chrome Nitride (CrN) | Silver-gray | 2,000 HV | Excellent |
| Titanium Aluminum Nitride (TiAlN) | Violet-gray | 3,200 HV | Very high temp resistance |
| Diamond-like Carbon (DLC) | Black | 2,000-5,000 HV | Exceptional (low friction) |
Best for: Cutting tools, molds, dies, decorative hardware, watch cases
Parts are dipped in molten zinc (450°C). Creates a thick, durable zinc-iron alloy coating.
| Parameter | Value |
|---|---|
| Coating thickness | 50-150 µm |
| Corrosion life | 20-50+ years (varies by environment) |
| Suitable for | Steel, iron |
Best for: Structural steel, outdoor enclosures, utility poles, fencing
Nitrogen diffuses into the steel surface at 500-550°C, creating a hard, wear-resistant surface without quenching.
Best for: Gears, shafts, injection mold cores, extrusion screws
| Requirement | Recommended finish | Alternative |
|---|---|---|
| Corrosion protection (indoor) | Black oxide + oil | Zinc plating |
| Corrosion protection (outdoor) | Hot-dip galvanizing | Powder coating |
| Wear resistance | Hard anodize (Al) or electroless nickel | Nitriding or DLC |
| Decorative appearance | Powder coating or anodizing | Plating or PVD |
| Food contact | Passivation (SS) or electroless nickel | Tin plating |
| Electrical conductivity | Chromate (Al) or gold plating (precision) | Silver plate |
| Anti-galling (screw threads) | Phosphate coating | Nitriding |
| Low friction / wear | DLC coating | PTFE (Teflon) coating |
| High temperature (250°C+) | PVD (TiAlN) or nitriding | Hard chrome |
| Finish | Relative cost (per part) | Setup cost | Best volume |
|---|---|---|---|
| Vibratory tumbling | Very low | None | 100+ |
| Bead blast | Low | Low | 50+ |
| Passivation | Low | Very low | 1+ |
| Black oxide | Low | Low | 100+ |
| Zinc plating | Low | Low | 500+ |
| Powder coating | Low-Medium | Low | 50+ |
| Anodizing (Type II) | Medium | Medium | 50+ |
| Hard anodize (Type III) | High | Medium | 50+ |
| Electroless nickel | Medium-high | Medium | 100+ |
| Electro-polishing | Medium | Low | 1+ |
| PVD coating | High | Very high | 500+ |
| Hot-dip galvanizing | Medium | High (by weight) | 100+ |
| Hard chrome plating | High | Medium | 50+ |
Add finishing to your next part order — upload your files for a quote including all surface treatments.
→ Back to: Capabilities Overview → Related: CNC Surface Finish Guide → Related: Sheet Metal Fabrication Guide