PPAP Submission tolerances: what is realistic and what it costs
PPAP Submission is the production part approval process used in the automotive supply chain, at four levels of evidence. It is used for proving that a production process can make the part repeatedly, before series supply starts. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.
It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, oil and gas is used as the example: materials that work harden and still have to be certified.
What is realistic
The tolerance that can be held on PPAP Submission depends on the feature, the material and the batch size. A value held once on a first article is not the same as a value held across a thousand pieces.
| Aspect | Typical value |
|---|---|
| Process tolerance | as the drawing, with capability on critical characteristics |
| Measurement | a full dimensional report plus a capability study |
| Surface finish | as specified on the drawing |
| Batch effect | capability, not a single measurement |
| Documentation | IATF 16949 with a PPAP submission at the level stated by the customer |
| Cost effect | the documentation effort and the capability study |
What it costs to hold
Tolerance and cost are not proportional; they are closer to exponential once a process has to be controlled rather than simply performed. The documentation effort and the capability study, which is why the drawing should say which features carry the function and which do not.
How it is verified
A full dimensional report plus a capability study. Calibration dates and measurement uncertainty are recorded with the result, so a later order can be compared with the first instead of being measured from scratch.
Applications
PPAP Submission is used for proving that a production process can make the part repeatedly, before series supply starts, and in practice it appears most often in automotive series production, tier two supply, any customer working to IATF 16949, high volume repeat orders.
How it fits into a machining route
PPAP Submission applies to the whole drawing rather than to one operation. It sets how the part is measured as much as how it is made, which is why it belongs on the drawing from the first issue and not in a note added after a query.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: the documentation effort and the capability study. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.
Standards, documentation and what is issued
The documentation requirement is IATF 16949 with a PPAP submission at the level stated by the customer. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.
A full dimensional report plus a capability study is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.
Frequently asked questions
What tolerance should be specified for PPAP Submission?
as the drawing, with capability on critical characteristics is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
any is the usual choice, supplied against IATF 16949 with a PPAP submission at the level stated by the customer.
How is the result verified?
A full dimensional report plus a capability study, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
A control plan that describes a different process from the one that runs.
How long does it take and what does it cost?
A realistic cycle is a day of documentation for a level 3, and the cost driver is the documentation effort and the capability study.
Related capability
If you are specifying PPAP Submission on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.
Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.
Related entries
These entries sit next to PPAP Submission in the encyclopedia: EN 10204 Material Certificates, Geometric Dimensioning and Tolerancing, Lapping. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
