Machining PEEK

PEEK is a semi-crystalline high-temperature thermoplastic with a glass transition temperature of around 143 °C and a melting point near 343 °C. This is the key to almost all of its properties: the material stays dimensionally stable and mechanically loadable at temperatures at which most other plastics have long gone soft. The continuous service temperature is about 250 °C, briefly even higher – putting PEEK in a class with only a few other high-performance materials such as PPS, PEI or PAI.

PEEK machines well – turning, milling and drilling work about as well as with brass or aluminium. We use sharp, polished tools and dissipate heat in a targeted way, since the low thermal conductivity would otherwise cause stresses. For tight tolerances, annealing (stress relieving) of the stock before and between machining steps is recommended. This lets us reliably achieve tight tolerances down to ±0.02 mm – from single parts to series production.

PEEK pays off when several demanding requirements have to be met at the same time – for example:

• Continuous use at high temperatures (up to approx. 250 °C) where other plastics fail
• Contact with aggressive chemicals, hot water or steam
• Metal replacement for weight reduction at high strength (aerospace)
• Clean, low-abrasion applications (semiconductor, medical technology, sterilisability)
• Highly loaded sliding, bearing and sealing parts with long service life

PEEK is one of the most expensive engineering plastics – the raw material is roughly 30 to 100 times the price of POM or PA. As a rough guide, semi-finished PEEK natural (rod/plate) ranges from about 150–400 €/kg depending on dimension and quantity; carbon-/glass-fibre-reinforced and especially biocompatible/implant grades are significantly higher. The part price is mainly determined by grade, stock form and dimension, material utilisation (waste), machining effort and batch size. We are happy to quote binding prices on request based on your drawing.

Just as important are the limits – PEEK is not always the economically sensible solution:

• When a cheaper plastic is sufficient: at moderate temperatures and loads, POM, PA, PET or PVDF are often enough – PEEK would be unnecessarily expensive
• For purely cosmetic or lightly loaded parts without temperature/chemical requirements
• In contact with concentrated sulphuric acid and certain strongly oxidising media
• For permanent UV/outdoor weathering without protection – natural grade can yellow/embrittle; then use stabilised grades or other materials
• When the budget is tight and the high-performance properties are not actually needed

An honest assessment – and how the disadvantages can be mitigated in practice: Advantages:

Disadvantages:

Practical tip: the high cost can be put into perspective through material-saving programming, the right grade selection and making only the truly stressed parts from PEEK – for less critical parts we specifically recommend cheaper alternatives such as PVDF or PPS.

• Highest continuous service temperature (up to approx. 250 °C)
• Excellent chemical, hydrolysis and radiation resistance
• Very good wear, sliding and fatigue properties
• High strength/stiffness at low weight (metal replacement)
• Flame retardant (UL 94 V-0), sterilisable, biocompatible grades
• Very high material price
• High processing temperatures; annealing needed for tight tolerances
• Unstabilised tendency to UV yellowing outdoors
• Economically over-specified for simple applications