PEEK glossary
56 terms that show up in a PEEK drawing, a quote or a certificate, each defined by what it changes for you rather than by what a textbook would say.
Material and behaviour
PEEK
Polyetheretherketone. A semi crystalline thermoplastic with a glass transition at 143 °C, a melting point of 343 °C and continuous service around 250 °C. It is specified when a part needs heat, load, chemical resistance and often electrical insulation at the same time.
PAEK family
The polyaryletherketone family that PEEK belongs to, alongside PEK and PEKK. Members differ mainly in melting point and price. If a supplier offers PEKK as a substitute, they are usually chasing a higher temperature, not a lower cost.
Semi crystalline
A polymer with ordered and disordered regions. This is why PEEK resists solvents well, why it keeps working above its glass transition, and why it moves after machining more than an amorphous plastic does.
Glass transition, Tg
The temperature where the polymer softens, 143 °C for PEEK. Below it the datasheet applies. Above it stiffness falls, expansion roughly triples and creep, not strength, sets the limit on a loaded part.
Melting point
343 °C for PEEK. It matters mostly as the ceiling that keeps an annealing soak safe, since stress relief happens around 200 °C.
Crystallinity
How much of the polymer is in ordered regions. Higher crystallinity means more strength and chemical resistance and slightly more shrinkage. Stock that was cooled quickly can keep changing crystallinity in hot service, which shows up as a part that drifts.
Annealing, stress relief
A controlled heat cycle above Tg that lets locked in stress relax, then a slow cool so no new stress is built in. On machined PEEK it belongs between roughing and finishing, so the movement it releases gets cut away.
Residual stress
Stress left in stock from the way it was cooled after extrusion or moulding. Machining removes material unevenly, the balance breaks and the part relaxes into a new shape over hours.
Coefficient of thermal expansion, CTE
How much a material grows per degree. Unfilled PEEK is about 47 µm/m·K below Tg against 12 for steel. This one number explains most fits that seize or fall loose when a machine warms up.
Creep
Slow permanent deformation under a constant load. It is the failure mode that catches metal designers out, because a plastic part can pass every strength calculation and still sag after a month at temperature.
Heat deflection temperature, HDT
The temperature at which a standard bar deflects under a set load, usually quoted at 1.8 MPa. Unfilled PEEK sits around 150 °C and filled grades above 300 °C, which is the clearest single argument for a filled grade on a hot loaded part.
Continuous service temperature
The temperature a material tolerates indefinitely without load. About 250 °C for PEEK. It is not the temperature at which the room temperature strength still applies, and quoting it as if it were is the most common mistake in plastics specification.
Hydrolysis resistance
Resistance to attack by hot water and steam. PEEK keeps its strength through hundreds of autoclave cycles where PEI and polysulfone lose theirs, which is why sterilisable instrument parts converge on it.
Environmental stress cracking
Cracking that appears only when a chemical and a stressed part meet. PEEK resists most solvents chemically, but a part carrying high residual or applied stress can still craze in some halogenated solvents.
Outgassing
Volatiles released by a material in vacuum or at temperature. It decides whether a plastic part is allowed inside semiconductor and vacuum equipment, and it is measured per grade and lot, not per polymer.
Static dissipative, ESD
Conductive enough to bleed off charge, not conductive enough to be a conductor. Carbon filled PEEK sits here, which is why wafer handling parts use it and why it cannot be used as an insulator.
Limiting oxygen index, LOI
The oxygen concentration needed to keep a material burning. PEEK sits around 35%, well above air, which is why it appears in rail, aerospace and enclosed equipment.
Radiolucent
Does not block X rays. PEEK is radiolucent, so an implant or a fixture made from it does not hide the anatomy or the feature being imaged, which metal would.
Grades and stock
Unfilled PEEK, virgin PEEK
PEEK with no reinforcement, natural beige or black. The toughest grade, the one that takes repeated steam, and the one that moves the most with temperature.
PEEK GF30
30% short glass fibre. Stiffer and far better against creep at temperature, still electrically insulating, abrasive to tooling and to any metal it slides against.
PEEK CF30
30% carbon fibre. The stiffest common grade, about half the expansion of unfilled, three to four times the thermal conductivity, and conductive enough to dissipate static.
Bearing grade PEEK
PEEK blended with carbon fibre, PTFE and graphite, typically around 10% each. Lowest friction and best dry wear in the family, and the weakest mechanically, so it is a surface material rather than a structural one.
PV limit
Pressure times velocity, the product that decides whether a dry running bearing survives. Ask the stock supplier for the PV chart at your temperature and duty cycle, because continuous rotation, oscillation and intermittent motion are three different loads.
Implant grade PEEK
Stock sold for long term body contact under a specification such as ASTM F2026, with lot traceability and documented biocompatibility testing. Mechanically it behaves like unfilled PEEK. What you pay for is the document chain.
Extruded stock
Rod, plate and tube pushed through a die and cooled. Cheaper and available in more sizes, and it carries more internal stress than compression moulded stock, which matters on thin or tightly toleranced parts.
Compression moulded stock
Stock pressed and sintered rather than extruded. Lower internal stress and the normal route to large plate and thick sections, at a higher price per kilo.
Near net blank
A blank moulded close to the finished shape so little material is cut away. It needs tooling, so it only pays above a few hundred pieces a year, and past that it changes the economics of an expensive material completely.
Lot traceability
A chain of records tying the finished part back to the resin lot it was cut from. Required in medical and semiconductor work, impossible to reconstruct after the fact, and the reason to ask for it at RFQ time.
Regrind
Reprocessed polymer blended back into stock. Normal in some markets, unacceptable in medical and semiconductor work. If you need virgin resin only, write it on the drawing, because it is not the default everywhere.
In the shop
Roughing and finishing
Two passes with a purpose. Roughing takes the bulk out and releases stress, finishing cuts the final surface after the part has settled. On PEEK the gap between them is often an oven cycle.
Finishing stock, allowance
Material deliberately left on a feature so a later pass can bring it to size. Leaving 0.3 to 0.5 mm on toleranced features is what makes an annealing cycle useful instead of decorative.
Chip evacuation
Getting cut material out of the cut. In PEEK a chip that stays in a slot melts and welds to the wall, because the material cannot carry the heat away. It is the reason two flute cutters and air blast turn up on plastics jobs.
Rake angle
The angle that decides whether a tool slices or pushes. Plastics want a positive rake, typically 5 to 15 degrees, with a polished flute. A tool ground for steel rubs, and rubbing puts heat into a material that cannot lose it.
Surface finish, Ra
Average roughness in micrometres. Ra 0.8 µm comes off a normal finishing pass in PEEK and Ra 0.4 µm with a polished tool and light cuts. Filled grades show fibre ends, so a sealing face usually wants unfilled stock.
Peck drilling
Drilling in steps, retracting to clear chips. On PEEK it is not optional in deep holes: packed chips heat the wall and leave a bore that closes up after machining.
Soft jaws
Machinable jaws cut to match the part so clamping force spreads. Clamping pressure that leaves no mark on aluminium will deform a thin walled PEEK part enough to matter at ±0.05 mm.
Deburring
Removing the edge left by a cut. On PEEK it has to be done without smearing, and in medical or semiconductor work without steel tools, because metal traces in a plastic surface are a rejection.
Datum
The reference a drawing measures from. Pick one the shop can physically clamp and probe. A datum on a surface that gets machined away later is the most common drawing error we see on plastic parts.
General tolerance
The blanket tolerance applied to any dimension without its own. Setting it sensibly, around ±0.1 mm on PEEK, and only tightening the features that fit something, is the cheapest cost reduction available to a buyer.
Quality and documents
First article inspection, FAI
A full dimensional report on the first part from a new setup, before the batch runs. On PEEK it is worth asking for, because the first part also tells you whether the process holds size after the part has relaxed.
CMM
Coordinate measuring machine. For PEEK, ask what temperature the room was at and how long the part soaked before measurement. A 200 mm feature moves past ±0.05 mm with a 6 °C swing.
Certificate of conformance, CoC
The shop declaring the parts match the drawing and revision they were ordered against. Cheap to ask for, and the document that makes a later dispute about revision level short.
Material certificate
The stock maker document tying a batch of rod or plate to its test results. It comes from the material maker, is passed through by the shop, and cannot be produced after the parts are cut.
ISO 9001
A general quality management standard. It says a shop documents and controls its processes. It says nothing specific about plastics or about PEEK, so treat it as a floor rather than as evidence of niche capability.
ISO 13485
The quality system standard for medical devices. For a machine shop it means documented process control, traceability and change control. It is a real filter, and not something a general job shop happens to have.
ISO 10993
Biological evaluation of medical devices. Stock can be supplied with testing to parts of it. The testing belongs to the material and to the finished device, never to the machining, and no machine shop can grant it.
USP Class VI
A plastics classification from a set of biological reactivity tests. Commonly requested and commonly misread as an approval. It is a material classification, not a clearance for a device.
ASTM F2026
The specification for PEEK polymers used in surgical implant applications. It covers the material, with lot traceability and documented testing. It does not approve a finished device.
ISO 23936-1
How thermoplastics are assessed for oil and gas media. The reference to quote when a supplier claims a material is suitable downhole, because it asks for test data rather than a datasheet line.
Cleanroom packing
Cleaning and bagging done in a controlled environment, usually double bagged. It costs little and it is the step most often missing from a cheap quote for semiconductor or medical parts.
Buying and sourcing
RFQ
Request for quotation. For a PEEK part a useful one carries the grade, the service temperature, the features that actually need tolerance, the documents required and whether you supply the material.
DFM
Design for manufacturing. The feedback a shop gives before cutting: a radius here, a looser tolerance there, a different blank. On expensive material it is worth more than a discount.
MOQ
Minimum order quantity. On machined PEEK it is usually driven by setup cost rather than by a policy, which is why asking for a price at two quantities often costs nothing and reveals a lot.
Lead time
On PEEK it is two numbers, not one: stock availability and machine time. Common unfilled sizes ship in days, filled grades in large sections and tube can take weeks, so ask which one you are waiting for.
NDA
Non disclosure agreement. On this site, ticking the NDA box means only the anonymous preview is shared until a shop has signed with you, and your files stay with us until then.
Incoterms, EXW
The rules that say where the goods change hands and who pays for what after that. EXW means you collect from the shop and carry every cost and risk from the door onward, which is why an EXW price is not comparable to a delivered one.
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The numbers behind the terms
Property tables by grade, and two calculators that turn expansion and annealing into an answer.