How to specify PEEK on a drawing

PEEK is a high performance thermoplastic that holds its properties at temperature and resists chemicals. It is used for parts that have to work where a metal corrodes or where weight and insulation matter. 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, automotive is used as the example: a fixed takt, because a late delivery stops the line.

What belongs on the drawing

A clear drawing for PEEK states the function, the tolerance and the verification, and leaves the route open where the function allows it.

• The feature and its tolerance: ±0.05 mm, because of thermal expansion, applied to the features that locate the part.
• The material and its condition: PEEK, with the certificate requirement.
• The surface finish: Ra 0.8 µm achievable with sharp tools, called out only where it does something.
• The verification: material certificate with the batch, and the standard the report is written to.

Mistakes that cost money

• Machining it with a steel cutting geometry, which melts rather than cuts, which makes the part more expensive without making it better.
• Measuring it straight off the machine, before it has cooled, which makes the part more expensive without making it better.

A workable note

Where a general note is used, say so once in the title block and keep the feature level call outs for the dimensions that matter. Tolerance to the thermal expansion, not to steel practice

Applications

PEEK is used for parts that have to work where a metal corrodes or where weight and insulation matter, and in practice it appears most often in semiconductor handling, medical devices, pump wear parts, insulators.

How it fits into a machining route

The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: material cost is high per kilogram. 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 material certificate with the batch. 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.

Dimensional inspection at 20 °C after stabilising 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 PEEK?

±0.05 mm, because of thermal expansion is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.

Which material is usually used?

PEEK is the usual choice, supplied against material certificate with the batch.

How is the result verified?

Dimensional inspection at 20 °C after stabilising, with the results recorded so a repeat order can be compared with the first.

What is the most common mistake?

Measuring it straight off the machine, before it has cooled.

How long does it take and what does it cost?

A realistic cycle is fast cutting, but with care on heat build up, and the cost driver is material cost is high per kilogram.

Related capability

If you are specifying PEEK 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 PEEK in the encyclopedia: 316L Stainless Steel, 304 Stainless Steel, Splined Shafts. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.