Scope of this guide
This senior guide covers the hard cases: combined variables, boundary conditions and the judgement calls that separate consistent lines from lucky ones.
Process: Quality & Testing. Figures in this guide are industry-standard starting ranges; confirm against your supplier TDS before locking settings.
Working ranges and control points
The table below is the daily reference for a QC lab. Set by the card, verify by the control point column.
| Test | Standard basis | Sample rate | Watch out |
|---|---|---|---|
| Salt spray (NSS) | ISO 9227 style hours by spec | Per lot, 3 parts | Bad edge prep lies low |
| Thickness (XRF) | Per spec layer stack | 3 points × 5 parts | Curved faces need stand-off |
| Adhesion | Bend or grid per spec | 2 parts per lot | Test after 24 h, not fresh |
| Colour | Standard card, D65 | Every batch | Viewer variation — one trained judge |
| Function (slider pull) | Per customer spec | AQL sample | Test rig wear drifts |
Push The Boundary: the senior view
Beyond the basic card, this is the layer that matters at your level:
| Hard case | Why it is hard | Method | Data to keep |
|---|---|---|---|
| Mixed-alloy loads | Different windows collide | Split by family or map positions | Per-family thickness trend |
| Seasonal humidity swings | Flash and dry times move | Season-set viscosities | Monthly setting log |
| Recesses at spec limit | Throwing power ceiling | Auxiliary anode trials | Before/after thickness maps |
| Repeat claim from one customer | Use conditions differ | Reproduce their test | Claim-vs-lab correlation |
Standard routine
- Prepare salt-spray edges exactly per spec
- Log chamber position for every sample
- Read thickness with calibrated foil check first
- Photograph every failure before handling
- Write claims with data: lot, hours, points, photos
Engineer notes
- Salt spray compares lots, not absolute field life
- Adhesion tested fresh reads better than 24-hour truth
- XRF needs geometry: flat, clean, right distance
- One colour judge or recorded light box — both is better
- Claim responses with photos settle faster than arguments
Safety: Salt spray chambers run hot, corrosive mist. Open with the exhaust on; wash skin after handling samples.
FAQ
How many parts per salt spray run?
Three parts per lot minimum, edges prepared exactly per the customer spec.
Why does adhesion fail in test but parts look fine?
Fresh-out-of-line plating reads better; test after 24 hours per spec.
What belongs in a customer claim pack?
Lot id, test hours, thickness points, photos of each failure mode.
How do I train juniors on this judgement?
Have them log the variable they changed and the measured result; review the log weekly against line outcomes.