Logo

Surface
Finishing

Select by material/environment/appearance to avoid over-specification that leads to cost increases

Part Finishing

Anodizing Type II/III
Electroless Nickel
Passivation
Powder Coating

Mold-surface Finishing

SPI/VDI Textures
EDM Texturing
Mirror Polishing
Chemical Etching
Surface Finishing Solutions
Ask for finishing recommendations
On this page:
Surface finishing and coating processes

Quick Answers

  • Corrosion resistance: Type III anodizing, electroless nickel, passivation
  • Wear resistance: Hard anodizing Type III, electroless nickel plating
  • Appearance enhancement: Type II anodizing, powder coating, polishing
  • Plastic textures: SPI polish, VDI/EDM texturing on injection molds
  • Matte finish: Sandblasting for metal, EDM texturing for plastic

Tips: Plastic surface textures are achieved through mold surface finishing, while metal treatments typically require post-processing.

Choose by Goal

Three-step selection process for optimal surface finishing

Define Your Goal

  • • Corrosion protection
  • • Wear resistance
  • • Appearance enhancement
  • • Surface texture
  • • Electrical properties

Select Material

  • • Aluminum alloys
  • • Steel (carbon/alloy)
  • • Stainless steel
  • • Plastic (via mold)
  • • Other metals

Consider Environment

  • • Indoor/outdoor use
  • • Salt spray exposure
  • • Temperature range
  • • Chemical contact
  • • Wear conditions

Quick Recommendations

Based on your selections, jump to the most suitable finishing options:

Type II Anodizing Type III Anodizing Electroless Nickel Powder Coating

Compatibility Matrix

Material and finishing process compatibility guide

Material Type II Anodizing Type III Anodizing Electroless Nickel Passivation Powder Coating Painting Sandblasting Polishing
Aluminum 6061/7075 ✅ ✅ ✅ ❌ ✅ ✅ ✅ ✅
Carbon Steel ❌ ❌ ✅ ❌ ✅ ✅ ✅ ✅
Stainless Steel 304/316 ❌ ❌ ✅ ✅ ✅ ✅ ✅ ✅
Brass/Copper ❌ ❌ ✅ ❌ ✅ ✅ ✅ ✅

Finish Library - Part Finishing

Complete guide to post-processing surface treatments

Type II Anodizing (Decorative)

Standard anodizing for appearance and basic protection

What it is

Electrochemical process creating a controlled oxide layer on aluminum for corrosion resistance and color options.

Best for

  • • Decorative applications
  • • Indoor use components
  • • Colored finishes
  • • Lightweight corrosion protection

Appearance

Clear, black, red, blue, gold colors available. Matte to semi-gloss finish depending on substrate.

Typical Thickness

0.0002" - 0.001" (5-25 μm) per MIL-A-8625

Dimensional Impact

Minimal - typically ±0.0005" on critical dimensions

Design Notes

  • • Specify masking for threads
  • • Avoid sharp edges (rounded preferred)
  • • Consider color matching requirements

Verification

Thickness measurement, color matching, salt spray testing

Best-fit processes: CNC machining, sheet metal fabrication

Type III Anodizing (Hard Coat)

Hard anodizing for maximum wear and corrosion resistance

What it is

Thick, dense oxide layer providing exceptional hardness and corrosion resistance through controlled electrolytic process.

Best for

  • • High-wear applications
  • • Outdoor/marine environments
  • • Sliding/bearing surfaces
  • • Aerospace components

Appearance

Typically dark gray to black. Limited color options. Matte finish.

Typical Thickness

0.001" - 0.004" (25-100 μm) per MIL-A-8625 Type III

Dimensional Impact

Significant - plan ±0.001-0.002" on critical dimensions

Design Notes

  • • Mask threads and critical fits
  • • Specify thickness requirements
  • • Consider post-machining if needed

Verification

Thickness measurement, hardness testing, wear resistance validation

Best-fit processes: CNC machining, sheet metal fabrication

Electroless Nickel (EN)

Chemical nickel plating for uniform coating and excellent properties

What it is

Autocatalytic chemical process depositing uniform nickel-phosphorus alloy coating without electrical current.

Best for

  • • Complex geometries
  • • Uniform thickness required
  • • Corrosion + wear resistance
  • • Steel and aluminum substrates

Appearance

Bright to semi-bright metallic finish. Can be polished to mirror-like appearance.

Typical Thickness

0.0002" - 0.002" (5-50 μm) per ASTM B733

Dimensional Impact

Predictable - typically ±0.0005" with proper planning

Design Notes

  • • Excellent for internal surfaces
  • • Specify phosphorus content (low/medium/high)
  • • Consider heat treatment for hardness

Verification

Thickness measurement, adhesion testing, corrosion resistance validation

Best-fit processes: CNC machining, metal stamping, sheet metal fabrication

Passivation

Chemical treatment to enhance stainless steel corrosion resistance

What it is

Chemical process removing free iron and enhancing the natural oxide layer on stainless steel surfaces.

Best for

  • • Stainless steel components
  • • Medical/food applications
  • • Post-machining treatment
  • • Corrosion prevention

Appearance

No visual change - maintains original stainless steel appearance and texture.

Typical Thickness

Molecular level - no measurable thickness added

Dimensional Impact

None - no dimensional change

Design Notes

  • • Required after machining/welding
  • • Specify citric acid method preferred
  • • Clean surfaces essential

Verification

Water break test, copper sulfate test, salt spray testing

Best-fit processes: CNC machining, sheet metal fabrication, metal stamping

Powder Coating

Electrostatic dry powder finish for durability and appearance

What it is

Electrostatically applied dry powder that's cured under heat to form a protective and decorative coating.

Best for

  • • Outdoor applications
  • • Architectural components
  • • Color and texture variety
  • • Environmental friendliness

Appearance

Wide range of colors, textures (smooth, textured, metallic), and gloss levels available.

Typical Thickness

0.002" - 0.008" (50-200 μm) depending on application

Dimensional Impact

Moderate - plan ±0.002-0.004" on critical dimensions

Design Notes

  • • Mask threads and critical fits
  • • Specify color and texture requirements
  • • Consider thermal expansion during curing

Verification

Thickness measurement, adhesion testing, color matching, impact resistance

Best-fit processes: Sheet metal fabrication, metal stamping, CNC machining

Painting

Liquid paint systems for decorative and protective finishes

What it is

Liquid coating systems including primers, base coats, and topcoats for protection and aesthetics.

Best for

  • • Smooth finish requirements
  • • Complex color matching
  • • Small batch applications
  • • Repair and touch-up capability

Appearance

Smooth, uniform finish with excellent color matching capabilities. Various gloss levels available.

Typical Thickness

0.001" - 0.005" (25-125 μm) including primer and topcoat

Dimensional Impact

Minimal to moderate - typically ±0.001-0.003"

Design Notes

  • • Specify paint system and color
  • • Consider substrate preparation
  • • Plan for masking requirements

Verification

Color matching, gloss measurement, adhesion testing, thickness verification

Best-fit processes: CNC machining, sheet metal fabrication, metal stamping

Sandblasting

Abrasive blasting for surface preparation and texture

What it is

Abrasive media propelled at high velocity to clean, texture, or prepare surfaces for subsequent treatments.

Best for

  • • Surface preparation
  • • Matte finish creation
  • • Paint/coating removal
  • • Stress relief (peening)

Appearance

Uniform matte finish with controlled surface roughness. Texture varies with media type and pressure.

Typical Thickness

Material removal: 0.0001" - 0.002" (2.5-50 μm)

Dimensional Impact

Slight material removal - plan +0.001" on critical dimensions

Design Notes

  • • Specify surface roughness requirements
  • • Mask critical dimensions and threads
  • • Consider media type (glass bead, aluminum oxide)

Verification

Surface roughness measurement, visual inspection, cleanliness verification

Best-fit processes: CNC machining, sheet metal fabrication, metal stamping

Polishing

Mechanical finishing for smooth, reflective surfaces

What it is

Progressive mechanical abrasion process using finer grits to achieve smooth, reflective surface finishes.

Best for

  • • Aesthetic applications
  • • Food/medical equipment
  • • Reflective surfaces
  • • Corrosion resistance enhancement

Appearance

Mirror-like to satin finish depending on final grit. Highly reflective with minimal surface defects.

Typical Thickness

Material removal: 0.0005" - 0.005" (12-125 μm)

Dimensional Impact

Material removal - plan +0.002-0.005" on polished surfaces

Design Notes

  • • Specify surface finish requirements (Ra)
  • • Consider accessibility for polishing
  • • Plan for increased lead time

Verification

Surface roughness measurement, visual inspection, reflectivity testing

Best-fit processes: CNC machining, sheet metal fabrication

Finish Library - Mold Surface Finishing

Texture and finish options for injection mold tooling

EDM Spark Texturing

Electrical discharge texturing for unique surface patterns

What it is

Controlled electrical discharge process creating consistent spark texture patterns on mold surfaces.

Appearance

Fine to coarse spark patterns creating matte to semi-gloss finishes with unique tactile properties.

Best for

  • • Automotive interior trim
  • • Consumer electronics housings
  • • Appliance components
  • • Hiding weld lines and flow marks

When to avoid

  • • Optical clarity required
  • • Deep draw applications
  • • Food contact surfaces

Design notes

  • • Minimum 1° draft angle required
  • • Consider texture direction for ejection
  • • Specify texture intensity level

Verification

Sample parts, texture intensity measurement, draft angle verification

SPI Polish Grades

Society of Plastics Industry standard polish levels

What it is

Standardized polishing grades (A1-D3) defining surface finish quality from mirror polish to stone finish.

Appearance

A1 (Grade #1): Mirror finish, diamond polished

A2 (Grade #2): High gloss, 600 grit diamond

B1 (Grade #3): Semi-gloss, 400 grit paper

C1 (Grade #6): Matte, 320 grit stone

Best for

  • • Optical components (A1-A2)
  • • Cosmetic housings (B1-B2)
  • • Functional parts (C1-D3)

When to avoid

  • • High polish on textured parts
  • • Deep ribs or complex geometry
  • • Cost-sensitive applications

Design notes

  • • Specify SPI grade clearly
  • • Higher grades increase cost significantly
  • • Consider parting line visibility

Verification

SPI standard comparison, gloss measurement, sample part approval

VDI/Chemical Etching

VDI standard chemical etching for controlled textures

What it is

Chemical etching process following VDI 3400 standard creating controlled surface roughness levels.

Appearance

VDI 12-18: Fine texture, leather-like

VDI 21-27: Medium texture, pebble grain

VDI 30-39: Coarse texture, heavy grain

VDI 42-45: Very coarse, deep texture

Best for

  • • Automotive interior panels
  • • Appliance housings
  • • Grip surfaces
  • • Hiding surface defects

When to avoid

  • • Tight tolerance requirements
  • • Food contact applications
  • • Optical clarity needed

Design notes

  • • Minimum 1.5° draft for VDI 30+
  • • Specify VDI number clearly
  • • Consider cleaning requirements

Verification

VDI standard comparison plates, surface roughness measurement, sample approval

Laser Texturing (Optional)

Advanced laser surface texturing for custom patterns

What it is

Precision laser ablation creating custom patterns, textures, or functional surfaces on mold steel.

Appearance

Highly controlled custom patterns including wood grain, fabric textures, geometric patterns, or functional micro-structures.

Best for

  • • Custom decorative patterns
  • • Functional textures (grip, anti-slip)
  • • Brand-specific requirements
  • • High-precision applications

When to avoid

  • • Cost-sensitive projects
  • • Standard texture adequate
  • • Very large surface areas

Design notes

  • • Requires detailed pattern specification
  • • Consider draft angle requirements
  • • Plan for extended lead times

Verification

Digital pattern verification, sample parts, dimensional accuracy check

Selection Guide

When to choose mold texturing vs. post-processing

Mold Texturing vs. Post-Processing

Criteria Mold Texture Post-Process
Material Plastics only All metals
Volume High volume (1000+) Any volume
Setup cost High (mold modification) Low to moderate
Unit cost Low (no additional process) Additional cost per part
Consistency Excellent Good to excellent
Functionality Appearance only Function + appearance

Quick Selection by Goal

Performance Requirements

Corrosion resistance: Post-process
Wear resistance: Post-process
Electrical properties: Post-process
Chemical resistance: Post-process

Appearance Goals

Plastic texture/grip: Mold texture
Metal color/finish: Post-process
Hide plastic defects: Mold texture
Mirror finish: Both options

Quality & Verification

Standards and testing methods for surface finish validation

Acceptance Criteria Checklist

Coating Thickness

Measured per specification (±10% typical tolerance)

Color Matching

ΔE ≤ 2.0 for critical color matches

Adhesion Testing

Cross-hatch test per ASTM D3359 (4B minimum)

Surface Roughness

Ra measurement per specification

Masking Quality

Clean edges, no coating on masked areas

Visual Appearance

No visible defects, uniform coverage

Testing Standards

Anodizing

  • • MIL-A-8625 (thickness, quality)
  • • ASTM B137 (salt spray testing)
  • • ASTM B680 (seal quality)

Plating

  • • ASTM B733 (electroless nickel)
  • • ASTM B117 (salt spray corrosion)
  • • ASTM B571 (adhesion testing)

Coating

  • • ASTM D523 (gloss measurement)
  • • ASTM D3359 (adhesion)
  • • ASTM D2794 (impact resistance)

Texture

  • • VDI 3400 (surface comparison)
  • • SPI standards (mold finish)
  • • ISO 4287 (surface roughness)

Need Quality Assurance Support?

Learn more about our comprehensive quality control and inspection processes

View Quality & Inspection Details

Design Tips

Best practices for surface finishing success

Design Do's

  • Add generous fillets and rounds (R0.010" minimum) to improve coating coverage
  • Specify masking requirements clearly on drawings for threads and critical dimensions
  • Design functional surfaces separate from cosmetic surfaces when possible
  • Provide adequate draft angles (1.5° minimum) for textured mold surfaces
  • Consider texture direction for part ejection and cleaning requirements
  • Specify color standards (Pantone, RAL) and acceptable tolerance ranges

Design Don'ts

  • Don't specify "black anodizing" without material - stainless steel cannot be anodized
  • Avoid sharp edges and corners that cause coating buildup and appearance issues
  • Don't ignore dimensional changes from coating thickness on tight tolerance features
  • Avoid deep pockets or blind holes that trap processing chemicals
  • Don't mix different metal types in the same coating batch without consultation
  • Avoid specifying texture on parting lines where consistency cannot be guaranteed

Need DFM Guidance?

Get expert design for manufacturing advice for your surface finishing requirements

View DFM Guidelines

Injection Molding Textures

Learn more about mold design and texturing options for plastic components

Injection Molding Guide

Frequently Asked Questions

Common questions about surface finishing processes

What's the difference between Type II and Type III anodizing?

Type II is decorative anodizing (0.0002"-0.001" thick) primarily for appearance and basic protection. Type III is hard coat anodizing (0.001"-0.004" thick) for maximum wear resistance and corrosion protection. Type III is darker, harder, and more expensive but provides superior performance.

Does electroless nickel plating affect part dimensions significantly?

EN plating typically adds 0.0002"-0.002" per surface. The coating is uniform, so plan for ±0.0005" change on critical dimensions. Unlike anodizing which grows into and out of the surface, EN builds up uniformly on all surfaces including internal features.

Can stainless steel be anodized?

No, anodizing only works on aluminum and some other non-ferrous metals. For stainless steel, use passivation for corrosion resistance, electroless nickel for wear resistance, or powder coating/painting for color and protection.

Why does "black anodizing" color vary between parts?

Black anodizing color depends on alloy composition, surface preparation, and process parameters. Different aluminum alloys (6061 vs 7075) produce different black tones. For consistent color matching across mixed alloys, consider powder coating or painting instead.

What surface treatments work best in salt spray environments?

Type III hard anodizing provides excellent salt spray resistance for aluminum. Electroless nickel with proper thickness (0.001"+) works well for steel. Marine-grade powder coatings are also effective. Avoid Type II anodizing in severe marine environments.

How should I specify masking on my drawings?

Clearly mark areas to be masked with "MASK" callouts and dimension the masked areas. Specify thread callouts like "MASK THREADS M6x1.0" and critical fit dimensions. Include a general note about masking requirements and acceptable coating buildup on edges.

What is EDM spark texturing and when should I use it?

EDM texturing uses electrical discharge to create consistent spark patterns on mold surfaces. It's ideal for hiding weld lines and flow marks on plastic parts, creating uniform matte finishes, and reducing glare. Best for high-volume plastic parts where texture consistency is critical.

What's the difference between SPI and VDI texture standards?

SPI (A1-D3) defines polish levels from mirror to stone finish using progressive abrasives. VDI (12-45) specifies chemical etching depths for controlled surface roughness. SPI is for smooth to semi-textured finishes, VDI is for distinct textured patterns. Both use physical reference standards for comparison.

How much draft angle do textured mold surfaces need?

Minimum 1° for light textures (SPI B1, VDI 12-18), 1.5° for medium textures (VDI 21-30), and 2-3° for heavy textures (VDI 33+). EDM spark textures typically need 1-1.5°. Insufficient draft causes sticking, drag marks, and part damage during ejection.

Can mold textures be consistent across different cavity areas?

Yes, with proper planning. Chemical etching (VDI) and EDM texturing provide excellent consistency across large areas. Avoid texture transitions at parting lines where perfect matching is difficult. Laser texturing offers the highest precision but at increased cost for large areas.

Get Your Surface Finishing Recommendation

Submit your requirements and receive expert finishing recommendations with detailed specifications

Click to upload CAD files, drawings, or drag and drop

Include masking requirements and critical dimensions

Related Resources

Explore our comprehensive manufacturing and quality guides

DFM Guidelines

Design for manufacturing best practices for all processes

Quality & Inspection

Comprehensive quality control and testing procedures

Injection Molding

Mold design, texturing, and plastic part production

CNC Machining

Precision machining capabilities and surface finish options

Sheet Metal Fabrication

Laser cutting, bending, and finishing for metal parts

Metal Stamping

High-volume precision stamping and finishing options

Cross-Reference Note: All manufacturing process pages link back to this Surface Finishing guide, particularly to the Selection Guide section for integrated finishing recommendations.