PL · engineering plastic
Polyetheretherketone PEEK (unfilled and 30% GF)
Machines cleanly for a plastic but it holds heat at the cut and the swarf will not break. Unfilled PEEK is the easier of the two; the glass-filled grade is abrasive and eats tooling.
Quoting this material
- Typical lead time
- 10–18 working days
- Condition
- Extruded or compression-moulded stock; annealed before machining where dimensional stability matters
- Achievable finish
- Ra 1.6 µm typical · Ra 0.4 µm best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
Machines cleanly for a plastic but it holds heat at the cut and the swarf will not break. Unfilled PEEK is the easier of the two; the glass-filled grade is abrasive and eats tooling.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength | 100 | MPa |
| Modulus of elasticity | 3.6 | GPa |
| Hardness | 85–95 | Shore D |
| Continuous service temperature | 250 | °C |
| Thermal conductivity | 0.25 | W/m·K |
| Density | 1.30 | g/cm³ |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Extruded or compression-moulded stock; annealed before machining where dimensional stability matters
Heat treatment
Not a metal-style heat treatment, but it must be annealed: PEEK stock carries moulded-in stress, and a machined part released from stressed stock will move. Annealing at 200 °C before machining is standard practice on a toleranced part.
Achievable surface finish
Ra 1.6 µm
Ra 0.4 µm
Takes a fine finish with sharp tooling. Machining marks are difficult to remove afterwards - polishing PEEK generates heat and smears the surface.
Tooling and cutting parameters
Cutting speed
- 150–400 m/min (uncoated carbide, sharp)
Feed
- 0.10–0.30 mm/rev turning · 0.10–0.30 mm/tooth milling; climb milling preferred
Tooling
- Uncoated polished carbide with high rake and generous clearance; no coatings
Coolant
- Compressed air or mist - flood coolant is unnecessary and the stock absorbs moisture
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Medical instrument components
- Semiconductor wafer handling parts
- Aerospace bushings and seals
- Chemical pump and valve parts
- Electrical insulators in hot service
DFM notes for this grade
- Anneal the stock before machining: a PEEK part machined from stressed extrusion bows by several hundredths of a millimetre after it is released
- Glass and carbon-filled grades are abrasive - they cut the tool life by a factor of several and need diamond-coated cutters on a production run
- Thermal expansion is around 5× steel: a tolerance has to state the temperature, and a part that fits at 20 °C may not fit at 60 °C
Questions buyers ask
- Why does a PEEK part move after machining?
- Because the stock has residual stress from extrusion or moulding, and removing material releases it. The fix is to anneal the stock before the final machining, which relaxes the stress, and then take light finishing passes so the new surface is not stressed either.
- Is glass-filled PEEK worth the extra cost?
- When the part needs stiffness and wear resistance at temperature, yes. It costs more, it is far harder on tooling and it is more abrasive to the mating surface - so it is a functional choice, not a general upgrade. On a bearing surface, unfilled PEEK is often the better wear pair.
Grades we would quote instead
PEI (Ultem)
5/10A hard, stiff, amber-coloured plastic that machines like a tough wood: clean chips, crisp edges and good dimensional stability.
PPS
5/10Hard, brittle and dimensionally stable.
POM-C (Acetal Copolymer)
8/10The best-machining plastic in this catalogue: it produces clean chips, holds a tolerance without drama and takes a fine finish.