Try it while you read
Open the free Control Plan tool and click Load sample: it reproduces the case study below.
Theory: the operating manual of quality
The control plan describes how every important characteristic is controlled in production: what is checked, with which gauge, how often, how it is recorded and what happens when it is out of tolerance. In IATF 16949 it is mandatory (clause 8.5.1.1) and it is one of the core PPAP documents.
It is the logical consequence of the process FMEA: every current control listed in the FMEA must appear in the control plan, and every high risk in the FMEA should be covered by a control.
Special characteristics
CC (critical) characteristics affect safety or legal compliance; SC (significant) characteristics affect fit, function or a following process. They usually require capability proof and tighter control. Customer-specific symbols vary; the tool uses CC, SC and HI.
Key point
Step by step with the tool
- Draft from the FMEA: in the FMEA tool click “Create control plan draft”; process steps, characteristics and controls are copied.
- Complete each card: operation number, machine, characteristic, special characteristic class, specification.
- Control: measurement technique, sample size, frequency and control method.
- Reaction plan for every line.
- Check the table view for completeness and download PDF or CSV.
Example: control plan for a shaft
The Load sample control plan has four lines:
| Op. | Characteristic | Class | Check | Reaction |
|---|---|---|---|---|
| 10 Turning | Bearing seat Ø25 h7 | SC | Air gauge, 5 parts every 20, X-bar/R chart | Stop, adjust offset, check last 20 parts |
| 10 Turning | Tool offset after insert change | Probe cycle each change, machine interlock | Machine stops, call setter | |
| 20 Heat treatment | Hardness 58–62 HRC / furnace 850 ± 10 °C | CC | 3 parts per load, continuous temperature log | Quarantine load, notify quality |
| 30 Final inspection | Circlip present | CC | Vision system, 100 % | Reject to red bin, daily check with master |
Every line traces back to an FMEA failure mode: the probing and SPC chart come from “diameter oversize”, the temperature log from “hardness below spec”, the vision system from “circlip missing”. Each control is also a candidate item for layered process audits.
Common mistakes
- Control plan and FMEA that do not match.
- Gauges in the plan without an MSA study.
- Frequencies that are never followed on the shop floor.
- Not updating the plan after complaints or process changes.
Frequently asked questions
What is the difference between prototype, pre-launch and production control plans?
They are the same format at different APQP phases. The pre-launch plan usually has more and tighter checks; the production plan is the long-term version after the process has proven stable and capable.
How do I choose the sample size and frequency?
From the risk (severity, special characteristic), the capability (a process with Cpk 2 needs fewer checks than one with Cpk 1.33) and the time to react: check often enough that you can contain all parts since the last good check.