DMAIC|5 min read
Building a Control Plan that survives the audit
The Control phase of DMAIC is where gains die. A control plan is the sustainment architecture that prevents that. One row per Critical-to-Quality (CTQ) characteristic. One reaction plan per row. Signed and trained.
The 7 columns
| Column | Example |
|---|---|
| Process step | Capping — torque application |
| CTQ (what we monitor) | Torque value |
| Specification | 10.5 ± 0.3 Nm |
| Measurement method | Calibrated digital torque driver, auto-log to MES |
| Sample size + frequency | n=1 per vial, continuous via driver; n=5 audit per shift |
| Responsible role | Line 2 Capping Operator (in-line); Shift Lead (audit) |
| Reaction plan | If out-of-spec: stop line, verify driver calibration, escalate to Eng within 15 min |
What separates good from bad
- Reaction plan is specific and timed — not 'investigate and fix'
- Responsible role is named — not 'team' or 'operator'
- Sample size + frequency is rational — tied to risk, not convenience
- Spec is numeric — not 'acceptable'
- Every CTQ is in the plan — no gaps
Link to Standard Work
The control plan drives the Standard Work. Every CTQ and reaction should show up as a step or a note in the SOP the operator follows. A control plan that lives in a binder while operators follow a different SOP is theater.
The handover
A signed control plan without a named owner is a paper exercise. Handover requires: (1) a named process owner, (2) their commitment in writing, (3) the 30/60/90 day sustainment check dates on the calendar, (4) the finance verification of benefit. Miss any of those and the gain evaporates.