5.5 Cosmetic Inspection Standards (Visual Quality)

Cosmetic inspection is the most dangerous phase of manufacturing because it is subjective. Without quantifiable physics, the production line devolves into an art critique session, driving up scrap costs without adding value. This chapter converts "it looks bad" into binary pass/fail logic. We inspect to protect the Brand and ensure consistency, not to hunt for microscopic anomalies that the user will never see.

Surface Zoning Logic

Do not inspect the entire unit with the same severity. Apply criteria based on the surface's function and visibility.

Zoning Decision Matrix:

• If surface is constantly viewed by the user (Screen, Top Bezel, Primary Buttons) → Define as Zone A.
  • Action: Target Zero Defects. Any visible imperfection at arm's length is a Reject.
• If surface is visible only during setup, handling, or cleaning (Back Panel, Side Vents) → Define as Zone B.
  • Action: Allow minor imperfections (e.g., single scratch < 5 mm) if they do not penetrate the coating.
• If surface is internal, bottom-facing, or service-only → Define as Zone C.
  • Action: Ignore cosmetic flaws. Reject only for structural issues (corrosion, stripped threads, burrs).

The Physics of Inspection

Standardize the environment. If the lighting changes, the acceptance rate changes.

Viewing Conditions:

1. Illuminance: Maintain 800 – 1000 Lux (Cool White).
   • Why: < 800 Lux hides defects; > 1200 Lux causes glare and false failures on textured plastic.
2. Distance: Inspect from 600 mm (Arm's length).
3. Time: Scan for 5 – 10 seconds per unit.
4. Angle: View at 45˚ – 90˚ relative to the light source.

The "Scan" Rule:

• If the defect is not visible within 5 seconds of scanning → Then it is not a defect.
• If you must tilt the unit at a specific angle to "catch the light" to see the scratch → Then it is Acceptable.

Pro-Tip: Never use magnification for cosmetic inspection. Microscopes are for Root Cause Analysis (RCA), not for sorting. If a defect requires 10x magnification to be seen, it does not exist to the customer.

Defect Quantization

Replace adjectives with dimensions. A "big scratch" is an opinion; a "5 mm scratch" is data.

Scratch & Dent Logic:

• Zone A:
  • If Scratch Length > 0 mm (Visible) → Fail.
  • If Dot/Inclusion > 0.3 mm diameter → Fail.
• Zone B:
  • If Scratch Length ≤ 5 mm AND Separation > 50 mm → Pass.
  • If Dent Depth ≤ 0.1 mm → Pass.
• Texture/Molding Issues:
  • If "Knit Lines" (weld lines) are visible in Zone A → Fail (Process parameter issue).
  • If "Gate Vestige" is flush with surface (Zone B/C) → Pass.

Final Checklist