Can PEEK be machined?
Yes, with care. Use sharp carbide, control heat and anneal stock and roughed parts. Glass- and carbon-filled grades need diamond-coated or PCD tools.
PEEK is a semi-crystalline, high-temperature thermoplastic: glass transition at 143 °C (289 °F), melting at about 343 °C (649 °F) and continuous service up to about 250 °C (480 °F). It is machined for medical devices, semiconductor wafer handling, aerospace clips and brackets, and oil and gas seals and valve seats. It cuts cleanly with sharp carbide and holds size well once it is stable. The care comes from three things: internal stress, heat and cost. PEEK stock often costs more than ten times acetal by weight, so scrap and rework are expensive and a first article is worth proving before a full run.
Extruded PEEK rod and plate carry residual stress from cooling. Buy annealed stock, and for thin walls, long slender parts or tolerances under about ±0.05 mm, rough the part, anneal it and then finish it. Stock makers publish the cycle; it is typically a slow ramp to around 200 °C (390 °F), a hold that scales with wall thickness and a slow cool through the 143 °C glass transition. PEEK conducts heat poorly, so dull tools, dry deep pockets or aggressive drilling concentrate heat at the cut and push the surface toward its glass transition, where it moves. Use sharp, polished tools with positive rake, flood coolant or air, and peck drill deep holes. Unfilled PEEK expands about 50 µm/m·°C below Tg, and the rate more than doubles above it.
Filled grades machine differently. 30% glass-filled and 30% carbon-fiber-filled PEEK are three to six times stiffer than unfilled and more stable, but the fibers are abrasive: uncoated carbide wears out within a handful of parts. Use diamond-coated carbide or PCD tools. Bearing grades with carbon fiber, graphite and PTFE behave like carbon-filled. Drilling large holes in thick filled stock is where cracking usually starts, so step drill and keep tools sharp. Medical and semiconductor parts add process limits: implant-grade PEEK (ASTM F2026) and ultra-clean parts may restrict coolants and require validated cleaning, so agree coolant and cleaning before quoting.
CNC Machining for PEEK parts: where to send them
What to specify
- Grade: unfilled, 30% glass-filled, 30% carbon-filled or bearing grade, with the resin maker and grade where qualified (for example Victrex 450G or an equivalent)
- Annealed stock, plus a post-roughing anneal for thin walls and tolerances under ±0.05 mm
- Tolerances: ±0.05 mm (0.002") on small features, ±0.1 mm (0.004") general, measured at 20-23 °C
- Coolant and cleaning restrictions for medical, implant (ASTM F2026) or semiconductor parts
- Material certification traceable to the stock and resin lot
- Surface finish on sealing and bearing faces, and whether visible tool marks are acceptable
Pitfalls
- Skipping the anneal and having parts move days after inspection
- Heat from dull tools or dry deep pockets distorting the surface near the 143 °C glass transition
- Uncoated carbide on glass- or carbon-filled PEEK wearing out within a few parts
- Cracking when drilling large holes in thick filled stock; step drill with sharp tools
- Scrapping expensive stock on first articles; prove the program on cheaper plastic and quote near-net blanks
- Standard shop coolant on implant or ultra-clean parts without an agreed cleaning process
Frequently asked questions
- Does PEEK need to be annealed before machining?
- Buy stock that the supplier has already annealed. For close tolerances or thin walls, also anneal after roughing and before the finish cut, so stress released by machining does not move the finished part.
- What tools cut carbon-filled PEEK?
- Diamond-coated carbide or PCD. Carbon and glass fibers wear uncoated carbide quickly, and a worn edge adds heat and fuzz. Unfilled PEEK cuts well with sharp, polished uncoated carbide.
- Why are machined PEEK parts expensive?
- Mostly the stock, which costs many times more than acetal or nylon, plus annealing cycles, diamond tooling on filled grades and the cost of any scrap. Cycle times are similar to other engineering plastics.
