Laser Cutting PEEK: CO2 Beams, Charred Edges, and Filler Effects

PEEK is cut on CO2 lasers at the 10.6 µm wavelength, not the fiber lasers (1064 nm) used for metals. The reason is absorption physics: polymers like PEEK strongly absorb the far-infrared CO2 wavelength, so the energy couples into the material and vaporizes it cleanly, while they poorly absorb or transmit the near-infrared fiber wavelength, which wouldn't cut effectively. This means you can't take PEEK to a fiber metal-cutting shop and expect results — you need a shop with CO2 laser capability set up for engineering plastics. It's a common source of confusion because the same word 'laser cutting' covers two entirely different machines for metals versus plastics. When sourcing PEEK laser work, specifically confirm CO2 capability and experience with high-performance polymers (not just acrylic and wood), because PEEK's high melting point and charring tendency demand proper parameters and fume handling that a basic CO2 hobby setup won't provide. The right shop will discuss edge quality, filler effects, and extraction up front.

Because CO2 laser cutting is a thermal process — it melts and vaporizes the polymer — so the cut edge inevitably experiences heat. PEEK has a high melting point for a plastic (around 343°C) and good thermal stability, which means it takes significant energy to cut, and the edge sees enough heat to discolor, and if pushed too hot or too slow, to char or leave a melted-and-resolidified layer. With well-tuned parameters on unfilled PEEK, the edge can be quite clean with only minor discoloration; poor parameters or excess thickness produce browning and char. The heat-affected zone also creates a small dimensional and taper effect that grows with thickness, which is why laser favors thin PEEK sheet. Whether the charred edge is a problem depends on the application: for gaskets, washers, and insulators it's often cosmetic and acceptable; for medical, semiconductor, sealing, or precision parts where the edge must be pristine and contamination-free, the char can be disqualifying, and machining is then the better process for a cool, clean edge.

Both filled grades cut less cleanly than unfilled (virgin) PEEK, which vaporizes uniformly as a homogeneous polymer. Glass-filled PEEK — commonly 30% glass fiber — is the problem case: the glass fibers don't vaporize the way the polymer matrix does, so they're left behind at the cut edge, producing a rough, fibrous, abrasive edge condition and degrading consistency. The thermal cut simply doesn't handle glass fiber well. Carbon-filled PEEK behaves differently again: carbon fiber and powder strongly absorb laser energy and conduct heat, altering the cut dynamics and often worsening the heat-affected zone, while the carbon fibers, like glass, don't cleanly vaporize. For both filled grades, when edge quality matters — structural parts, sealing surfaces, anything where a rough fibrous edge is unacceptable — machining (milling or routing) is usually the better process because it cuts the fibers mechanically without the thermal degradation. The rule: virgin PEEK is the best laser candidate, and the more filler content, the stronger the case for machining instead of laser cutting.

Choose machining over laser when edge quality, thickness, filler content, or precision rule out the thermal cut. Specifically: thick PEEK plate (beyond a few millimeters), where laser edge heating, taper, and char become pronounced; glass- or carbon-filled grades where the fibers leave a rough edge and a clean cut is needed; precision sealing surfaces and tight-tolerance features where laser's HAZ and taper can't hold the spec; and medical, semiconductor, or pharmaceutical parts where the edge must be pristine, contamination-free, and free of any heat-affected or charred layer. Machining (milling, turning, routing) gives a cool, clean, dimensionally precise edge with no char, at the cost of slower setup and tooling. Laser wins for thin virgin-PEEK flat parts — gaskets, washers, insulators, electrical components — in volume, where its tooling-free speed beats machining setup and a minor edge discoloration is acceptable. The decision is application-driven: if the edge is cosmetic and the part is thin virgin PEEK, laser; if the edge is functional, the grade is filled, or the part is thick, machine it.

Laser cutting favors thin PEEK sheet — practically up to a few millimeters (roughly 1-6 mm depending on laser power and acceptable edge quality), because the thermal cut's edge heating, char, and kerf taper grow with thickness. In that thin range, a well-tuned CO2 laser holds reasonable tolerances, on the order of ±0.1-0.2 mm, suitable for gaskets, insulating washers, shims, and electrical parts. As thickness increases, the edge taper and heat-affected zone widen the tolerance band and degrade edge quality, so thick PEEK is a machining job where milling can hold tighter tolerances with a clean edge. Filled grades also limit achievable quality, as glass and carbon fibers roughen the edge regardless of thickness. For precise features, sealing surfaces, or anything requiring better than about ±0.1 mm with a pristine edge, machining is the appropriate process. So treat laser as the fast option for thin, virgin, cosmetically-tolerant PEEK profiles, and machining as the route for thick, filled, or precision PEEK parts. Always specify your edge and tolerance requirements so the shop can advise on the right process.