Surface Finishing

Understanding finishing process types:

Mechanical Finishing:

Grinding:
- Precision surface finish
- Dimensional accuracy
- Many abrasive types
- Centerless, surface, cylindrical

Polishing:
- Improved appearance
- Smoother surface
- Progressive abrasives
- Mirror finish possible

Buffing:
- Final luster
- Soft abrasive compounds
- Appearance focus
- After polishing typically

Deburring:
- Remove machining burrs
- Manual or automated
- Various methods
- Safety and function

Blasting:
- Abrasive cleaning
- Profile creation for coating
- Various media
- Grit, shot, glass bead

Mass Finishing:

Vibratory:
- Tub or bowl vibration
- Parts and media together
- Deburring, surface improvement
- High volume

Tumbling:
- Rotating barrel
- Parts and media
- Lower cost
- Longer cycle

Centrifugal:
- High energy
- Fast processing
- Smaller parts
- Premium finish

Chemical/Electrochemical:

Electropolishing:
- Reverse of plating
- Removes surface layer
- Smooth, bright finish
- Stainless steel common

Chemical Polishing:
- Acid-based
- No electricity
- Brightening
- Specific alloys

Passivation:
- Oxide layer enhancement
- Stainless steel
- Nitric or citric acid
- Corrosion resistance

Etching:
- Controlled material removal
- Pattern creation
- Pre-treatment
- Decorative/functional

Adding material to surfaces:

Electroplating:

Process:
- Electrolytic deposition
- Metal ions to cathode (part)
- Thickness controllable
- Various metals available

Common Types:
- Zinc: corrosion protection
- Nickel: corrosion, appearance
- Chrome: wear, appearance
- Copper: undercoat, conductivity
- Gold: electronics, corrosion
- Silver: conductivity

Considerations:
- Rack vs. barrel plating
- Thickness specification
- Hydrogen embrittlement (steel)
- Environmental regulations

Electroless Plating:

Process:
- Chemical reduction (no electricity)
- Uniform thickness (even recesses)
- Catalytic
- Limited thickness

Types:
- Electroless nickel (most common)
- Electroless copper
- Various compositions

Advantages:
- Uniform coverage
- Complex geometries
- Hardness (Ni-P)
- Lubricity (with PTFE)

Conversion Coatings:

Anodizing (Aluminum):
- Oxide layer growth
- Type II: decorative, corrosion
- Type III (hard coat): wear, thickness
- Color options (dye)

Phosphating:
- Iron or zinc phosphate
- Paint preparation
- Corrosion protection (oil)
- Steel and iron

Chromate Conversion:
- Legacy process (hexavalent restricted)
- Trivalent alternatives
- Aluminum and zinc
- Corrosion, paint adhesion

Organic Coatings:

Liquid Paint:
- Spray, dip, brush
- Wide color range
- Multiple coat systems
- Curing variations

Powder Coating:
- Electrostatically applied
- Oven cured
- Durable finish
- Environmental advantages

E-Coat:
- Electrodeposition
- Uniform coverage
- Primer application
- Automotive common

Specifying and verifying finishes:

Surface Roughness:

Parameters:
- Ra (average roughness)
- Rz (ten-point height)
- Rmax (maximum height)
- Various others

Measurement:
- Profilometer
- Stylus or optical
- Portable or bench
- Proper technique

Specification:
- Drawing callout
- Industry standards
- Application requirements
- Tolerance on values

Typical Ra Values:
- As-machined: 63-250 microinch
- Ground: 8-32 microinch
- Polished: 4-16 microinch
- Mirror: <2 microinch

Coating Specifications:

Thickness:
- Specification requirement
- Measurement method
- Location requirements
- Tolerance

Adhesion:
- Cross-hatch test
- Bend test
- Pull-off test
- Pass/fail criteria

Hardness (Plating):
- Microhardness testing
- Vickers or Knoop
- Per specification
- Affects wear performance

Appearance:
- Visual standards
- Color measurement
- Gloss measurement
- Defect criteria

Industry Standards:

Plating:
- ASTM B633 (zinc)
- ASTM B456 (nickel-chrome)
- ASTM B177 (chrome)
- AMS specifications

Coating:
- ASTM D standards (paint)
- MIL specifications
- Industry standards

Surface Finish:
- ASME Y14.36 (symbols)
- ISO 4287/4288
- Industry-specific

Quality Control:

Process Control:
- Bath chemistry
- Temperature
- Current density
- Time

Inspection:
- Visual per sample
- Thickness testing
- Adhesion testing
- Functional testing

Documentation:
- Lot traceability
- Test reports
- Certifications
- Process records

Surface finishing careers:

Technical Roles:

Plating/Finishing Technician:
Process operation:
- Equipment operation
- Quality checks
- Maintenance
- $40,000-$60,000

Finishing Engineer:
Process development:
- Process optimization
- Problem solving
- Specification development
- $65,000-$95,000

Quality Inspector:
Verification focus:
- Testing and inspection
- Documentation
- Nonconformance
- $45,000-$70,000

Process Engineer:
Manufacturing focus:
- Process selection
- Supplier management
- Cost optimization
- $65,000-$95,000

Work Environments:

Captive Operations:
- In-house finishing
- Product-specific
- Integrated manufacturing
- Control over process

Job Shop/Contract:
- Outside finishing service
- Wide variety
- Customer-focused
- Flexibility

Specification:
- Design engineering role
- Finish selection
- Supplier coordination
- Problem solving

Skills Development:

Technical:
- Process understanding
- Testing methods
- Specification interpretation
- Problem solving

Practical:
- Hands-on operation
- Quality verification
- Troubleshooting
- Equipment maintenance

Training:
- On-the-job primary
- NASF (finishing society)
- Equipment manufacturer
- College courses

Industries:
- Automotive
- Aerospace
- Electronics
- Medical
- Consumer products
- Industrial equipment

Surface finishing expertise supports product quality and performance.