Guide
What does a control plan example for a machined or die cast part look like?
A control plan is the supplier’s written summary of how each important product and process characteristic of a part is held in control during manufacturing: what is checked, at which operation, with which gauge, how many parts and how often, how the result is recorded, and what the operator does when a check fails. It is a short, operation-by-operation table, not an inspection report, and a good control plan example reads like a set of standing orders for the shop floor.
By Saola Manufacturing engineering team · Published · Updated
This guide is for supplier quality engineers who are about to ask a new machining or die casting supplier for a control plan, and for design engineers who have to judge the one that comes back. It walks through the columns, shows a filled-in set of rows for a cast and machined aluminum housing, and spends most of its time on the three columns where weak plans fall apart: which characteristics are listed, how often they are checked, and what the reaction plan actually says. The structure follows the AIAG Control Plan manual and the control plan requirement in IATF 16949; the frequencies in the example are illustrations of typical practice, not values taken from either document.
On this page
What does a control plan example for a machined part contain?
Every row ties one characteristic at one operation to a specification, a measurement method, a sample size and frequency, a control method and a reaction plan. The AIAG format adds identifying columns for the part, operation and equipment, and a column that flags special characteristics.
The layout most buyers recognize comes from the automotive quality manuals published by AIAG. The control plan used to live as a chapter of the AIAG Advanced Product Quality Planning manual; it now has its own AIAG Control Plan manual, which keeps the familiar column set and adds guidance on a safe-launch phase. Reading across a typical row:
- Part or process number and operation description. Matches the supplier’s process flow and routing, so every row can be found on the floor.
- Machine, device, jig or tool. The specific die, machine or fixture, because a characteristic that depends on fixture number two is a different risk from one that does not.
- Characteristic, split into product and process. A product characteristic is a feature of the part, such as a bore diameter. A process characteristic is a setting that drives it, such as die temperature, injection pressure or the tool-life count on a boring insert.
- Special characteristic class. The symbol your drawing uses for critical or significant features, copied across so nobody has to cross-reference.
- Specification and tolerance. Copied from the drawing revision named in the header, or from the process sheet for process characteristics.
- Evaluation and measurement technique. The actual gauge, not “measure.”
- Sample size and frequency. How many parts, at what trigger: first piece, per hour, per tool change, per lot, every part.
- Control method. How the result is held: a check sheet, a control chart, an error-proofing device, a first-and-last-piece record.
- Reaction plan. What happens to the process and to the suspect parts when a check fails.
The header matters as much as the rows. It should carry the part number and drawing revision, the phase (prototype, pre-launch, safe launch or production), the plan revision and date, and the key contacts. A plan with no drawing revision in the header cannot be audited, because nobody can tell which tolerances it was written against.
What does a filled-in control plan look like for a die cast and machined housing?
The rows below show a production-phase plan for an aluminum die-cast housing with a machined bearing bore, tapped holes and a pressure-tight wall. Notice that each row names a trigger and a containment action, and that process characteristics sit alongside product ones.
The part is hypothetical, and the specification values are chosen to be realistic for this kind of housing rather than copied from any real drawing. The bore tolerance shown is an ISO H7 fit on a 22 mm nominal size, which per ISO 286 gives a band of zero to plus 0.021 mm; the thread class is the common metric 6H. Frequencies and sample sizes are typical industry guidance for features of this kind; your own plan should derive them from the reasoning in the next sections.
| Op / characteristic | Specification | Method | Sample and frequency | Control method | Reaction plan |
|---|---|---|---|---|---|
| 10 Die cast: die temperature (process) | Per process sheet window | Machine thermocouple readout | Each shift start and after any die stop | Process log | Do not release shots until in window; scrap warm-up shots |
| 10 Die cast: cast height to datum A (product) | 23.90 to 24.10 mm | Height gauge on surface plate | 1 pc first shot, then every 2 h | Check sheet | Stop die; hold all parts since last good check; sort; repair die before restart |
| 20 CNC mill: bearing bore diameter (SC) | Ø22 H7 (22.000 to 22.021 mm) | Bore gauge set to master | 5 pcs per 50, plus first and last piece of each insert | X-bar and R chart | Out of limits: stop, quarantine back to last good subgroup, 100% check, offset or change insert, record |
| 20 CNC mill: boring insert life (process) | Change at counted tool-life limit | Machine counter | Every change | Tool-life log | Missed change: check all parts made past the limit |
| 20 CNC mill: bore position to A-B | Position Ø0.05 mm to A and B | Fixture gauge or coordinate measurement | 1 pc per shift and after any fixture change | Check sheet | Hold shift output; verify fixture locators; full check of held parts |
| 20 CNC mill: M6x1-6H tapped holes | GO enters full depth, NO GO per standard | Thread plug gauge | Every part | Gauge sign-off on traveler | Reject part; check tap; check parts since last tap change |
| 30 Wash: chips in cross holes | No loose chips or burrs | Visual with light and probe | Every part | Visual standard at bench | Rewash and recheck; review deburr step |
| 40 Leak test (SC) | Per drawing leak-rate limit | Pressure-decay tester | Every part, plus master leak at shift start | Tester with reject lock | Failed master: stop, recalibrate, retest all since last good master |
Three things make these rows useful rather than decorative. First, every frequency has a trigger tied to the way the feature can go wrong: cast features drift with die wear and temperature, so they get a time interval; machined bores drift with insert wear, so they get a count and a tool-change check; tapped holes fail suddenly when a tap breaks or wears, so they get every part. Second, each reaction plan names the suspect population, which is always “everything since the last good check.” Third, the process rows (die temperature, insert life) control the cause rather than waiting to catch the effect. The guide to leak testing cast aluminum housings covers how the leak-rate limit itself should be set, and go/no-go thread gauging covers the thread row.
Which characteristics belong on the control plan, and which do not?
List the characteristics that are marked special on the drawing, the ones the process FMEA ranks high, and the process settings that drive them. Do not copy every dimension from the drawing; the first article report already covers those once.
The most common weak control plan is a ballooned drawing turned sideways: forty rows, every one checked “1 pc per lot” with a caliper. It looks thorough and controls nothing, because it treats a chamfer and a sealing bore the same way. A control plan is a risk document. It gets its row list from three places.
- The drawing’s special characteristics. If your drawing marks critical or significant features, each one must appear, with its symbol. If your drawing marks nothing, that is the first thing to fix, because the supplier has no basis for treating any feature as more important than another.
- The process FMEA. Failure modes with high severity or poor detection should show up as rows, and where the FMEA names a cause, the matching process characteristic should be on the plan too. Clause 8.5.1.1 of the IATF 16949 automotive standard requires control plans to draw on the process FMEA and the process flow for this reason.
- Features that the process makes in one stroke. On a die casting, many dimensions are fixed by the tool. Once a first article proves them, they only move as the die wears, so one row for “tool-formed dimensions, layout check per die maintenance cycle” can replace a dozen individual rows.
Everything else is still required to meet the drawing; it is simply verified at first article, by periodic layout inspection, and by your incoming inspection, rather than given its own standing check. The ballooned drawing guide covers the full-dimension report, and first article inspection with an overseas supplier covers how that one-time check is run.
How should sample size and frequency be set for each line?
Set the frequency from how fast the characteristic can drift and how many parts you are willing to sort if a check fails. The interval between checks is the size of your suspect lot.
Engineers often pick frequencies by habit, then discover the cost when a check fails and the whole shift has to be sorted. Work it the other way around. Decide how many parts you can afford to quarantine and re-inspect, and make the check interval no longer than that. Then match the trigger to the failure mechanism:
- Setup-driven features (anything a wrong offset or wrong fixture would ruin) need a first-piece check after every setup, program change or fixture change, and a last-piece check before the setup is broken down so the run can be released.
- Wear-driven features (bores, turned diameters, cast features near a wearing die surface) need a count- or time-based interval, plus a check at every tool change.
- Sudden-failure features (tapped holes, drilled holes that can be skipped, a missing operation) need every-part checking, ideally by a device rather than a person: a thread gauge, a probe, a presence sensor or a tester that locks out rejects.
Where a characteristic is charted, the subgroup size and frequency have to suit the chart. Take each subgroup from consecutive parts, so the variation inside it is short-term and the chart shows drift between subgroups. The NIST/SEMATECH e-Handbook page on X-bar and R charts gives four or five parts as a typical subgroup size, which is why five consecutive parts is a common choice on machined diameters. Capability numbers from that data are covered in the guide to Cpk vs Ppk; lot acceptance sampling, which is a receiving decision and not a process control, is covered in AQL sampling for machined parts. A control plan that lists “AQL” as the control method for a special characteristic is a warning sign: sampling a finished lot does not control the process that made it.
Finally, check that the gauge can see the tolerance. A bore with a tight band checked with a handheld caliper is not controlled. The AIAG Measurement Systems Analysis manual sets out gauge R&R studies for exactly this question, and the plan should name a gauge that would pass one.
What makes a good reaction plan?
A good reaction plan tells the operator to stop, contain the suspect parts back to the last good check, correct the cause, verify the correction and record what happened. “Adjust machine” or “notify supervisor” on its own is not a reaction plan.
Read the reaction column first when a control plan comes in, because it shows whether the supplier has thought about failure or only about measurement. Each entry should answer five questions without the operator having to ask anyone:
- Stop. Does the machine or die stop, or does it keep running while someone decides?
- Contain. Which parts are suspect? The answer should be “all parts since the last good check,” with a physical hold: tagged, segregated, out of the flow.
- Correct. What is the usual fix: offset, insert change, die repair, fixture locator check?
- Verify. What check restarts the process? Normally a fresh first-piece check, not just the next scheduled sample.
- Record and escalate. Where is it written down, and when does the customer hear about it? If suspect parts may already have shipped, your purchase order should require notification, and a repeat should trigger a formal corrective action.
The containment step is where most plans are thin. “Segregate nonconforming parts” only deals with the part that failed the check. The parts made between the last good check and the failed one are the real exposure, and a plan that does not name them will ship some of them.
What should the drawing, purchase order and RFQ say about the control plan?
Mark the special characteristics on the drawing, name the control plan format and approval point on the RFQ and purchase order, and say what happens when the plan changes. Without those three, the supplier will send a generic plan after the order is placed.
Example drawing note:
CHARACTERISTICS MARKED ◆ ARE SPECIAL CHARACTERISTICS. EACH SHALL APPEAR ON THE SUPPLIER CONTROL PLAN WITH ITS MEASUREMENT METHOD, FREQUENCY AND REACTION PLAN.
Example RFQ and purchase order text:
Supplier shall provide a pre-launch and a production control plan for P/N 4410-220 Rev C in AIAG Control Plan format, covering all ◆ characteristics, the process characteristics that control them, and a reaction plan for every row. The control plan is part of the first article submission and requires buyer approval before production release. Changes to methods, frequencies or reaction plans require written notice before implementation.
On the RFQ, also ask the supplier to name the gauge for each special characteristic and to say whether any of them will be checked by a device rather than by hand. The answers affect price, and you want them in the quote, not discovered after tooling. If you also want a full approval package, the guide to PPAP for non-automotive parts explains where the control plan sits among the other records and how to scale the package down. You can send all of this with the drawing through the quote form.
How does Saola work to a customer’s control plan?
If you send the control dimensions marked on your drawing and any cosmetic standard you use, we build our inspection around them rather than asking you to adopt ours. A dimension you mark as a process-capability control point is checked through the run, more often than the rest of the print, not only at first article.
What we can send today is listed on the quality page: first-article inspection on every new part, a dimensional inspection record with every lot, and process routing sheets on request per part number. If a first-article measurement is out of tolerance, we stop and tell you before a sample ships, with the measured value, the proposed fix and a revised date. The factory page shows an inspection plan written before the first shot for a die-cast base: machined holes checked on every part with go/no-go pin gauges, and cast features checked at a fixed time interval because they only move as the tool wears, which is the same logic as the example above. Machining of castings runs on our CNC milling line, and turned parts on CNC turning.
Said plainly: ISO 9001 certification is in progress and not yet held, no third-party quality audit has been performed, and we have not compiled a published PPM record. If your approved-vendor process needs any of those before it will review a control plan, tell us at the RFQ stage.
Frequently asked
Is a control plan the same as an inspection plan?
No. An inspection plan usually lists what is measured at a given stage, often every dimension at first article or at final inspection. A control plan covers the whole process flow, includes process settings as well as part features, and adds the reaction plan. Many suppliers keep both; the control plan is the one that governs ongoing production.
Who writes the control plan, the buyer or the supplier?
The supplier writes it, because it describes their operations, machines and gauges. The buyer supplies the inputs: the drawing with special characteristics marked, any required format, and the approval step. The buyer reviews it and can reject rows that are too weak, but should not dictate machine settings it does not own.
What are the prototype, pre-launch, safe-launch and production phases?
They are versions of the same plan for different stages. The prototype plan covers checks during prototype builds, the pre-launch plan covers trial and pilot runs before full production, and the production plan is the steady-state document. The 2024 AIAG Control Plan manual adds a safe-launch phase: extra, temporary checks and containment carried into the start of production until agreed exit criteria are met. That is where heavier sampling belongs, not in the steady-state plan.
How often should a control plan be revised?
Whenever the process, drawing, gauge or a reaction plan changes, and whenever a defect escapes to the customer. An escape means a row was missing, a frequency was too long or a gauge could not see the problem, and the plan should change along with the corrective action. A plan whose revision date never moves is usually not being used.
Does a non-automotive part need a control plan at all?
It is not mandatory outside sectors that require it, but it is the cheapest way to make a new supplier write down how they will keep a sealing bore or a safety thread in tolerance after first article. Ask for it on parts with marked special characteristics and skip it on simple brackets.
Sources
- Control Plan, 1st edition (CP-1), AIAG, 2024
- Advanced Product Quality Planning, 3rd edition (APQP-3), AIAG, 2024
- Measurement Systems Analysis, 4th edition (MSA-4), AIAG, 2010
- IATF 16949:2016, about the standard, International Automotive Task Force, 2016
- NIST/SEMATECH e-Handbook of Statistical Methods, Shewhart X-bar and R and S Control Charts, NIST, accessed October 2026