Lean Six Sigma Principles
Understanding RTY & The Hidden Factory
Key operational quality principles governing multi-stage process yield:
- The Illusion of Final Inspection: A high final-test pass rate (e.g. 98%) often masks the fact that 25% of products required multiple rework loops before passing.
- Multiplicative Compounding: Total yield decreases exponentially with the number of process steps: $RTY = prod Y_i$. Adding inspection or touch-up steps without fixing root causes reduces true throughput.
- The Hidden Factory Cost: Rework consumes skilled technician hours, slows production cycle times, creates buffer inventory WIP, and increases field warranty failure rates.
- Poisson Defect Modeling: In complex operations, Defects Per Unit ($DPU = -ln(Y)$) captures the true occurrence rate of multiple defects on single units.
Evaluate defect rates in the Six Sigma DPMO Lab.