PEEK Sheet Fabrication: A Plastic in a Metal Process, and How It Actually Works

No, PEEK is not a metal; it is a high-performance thermoplastic (polyether ether ketone), so the press-brake bending that defines sheet metal fabrication does not apply to it. What it shares with sheet metal is that it is sold as flat sheet stock and fabricated into flat parts by cutting and machining, which is why it appears alongside metals in a fabrication context. PEEK sheet parts are made by cutting the stock to a blank and then CNC routing, milling, drilling, and turning the features, producing plates, spacers, insulators, seals, and machined components. It machines well and holds tight tolerances. Where a genuinely bent or three-dimensional shape is needed, PEEK can be thermoformed by heating the sheet above its glass transition (around 143 C) and shaping it over a mold, but that is specialized and far less common than machining the geometry from thicker stock. So expect a PEEK sheet part to be a precision-machined flat or near-flat component, not a folded one, and design sharp bends out in favor of machined geometry unless thermoforming is specifically intended.

The filler tunes both performance and machining. Unfilled PEEK is the base grade, tough and ductile, with the best impact resistance and the choice where biocompatibility matters (implants, surgical tools) and for general high-temperature, chemical-resistant parts. Glass-filled PEEK, usually 30 percent glass fiber, roughly doubles stiffness and improves dimensional stability and creep resistance while cutting thermal expansion, making it good for structural parts and bearings, but it sacrifices some toughness and is abrasive, so it wears cutting tools faster and favors carbide tooling. Carbon-filled PEEK (carbon fiber reinforced) goes further still on stiffness and strength, adds thermal and electrical conductivity (useful where static dissipation or heat transfer matters), and offers the best wear resistance and lowest thermal expansion, ideal for high-load structural and bearing applications, though it is the most expensive and most abrasive to machine. Choose unfilled for toughness and biocompatibility, glass-filled for general stiffness and stability, and carbon-filled for maximum stiffness, wear resistance, and conductivity. The fill also affects machining cost, since filled grades wear tooling and slow the process.

Because PEEK carries internal stress and crystallinity that can move the part after machining if not relieved. Stock PEEK sheet retains residual stresses from how it was manufactured, and aggressive machining adds more localized stress, so a part cut to tight tolerance can warp, bow, or drift dimensionally as those stresses relax over hours, days, or with temperature exposure, especially in thin, asymmetric, or heavily machined geometries. Annealing is a controlled heat-treat cycle, typically a slow ramp to around 200 C or higher, a hold, and a slow controlled cool, performed before final machining, after rough machining, or both, that relieves the stress and stabilizes the crystalline structure so the finished part holds its dimensions in service. For tight-tolerance semiconductor and medical PEEK parts, annealing is effectively mandatory; skipping it yields parts that pass inspection at the shop but then drift out of tolerance later. It adds lead time because the cycles are slow and ovens batch parts, and it is a genuine cost driver. A good plastics fabricator will build the annealing strategy into the quote for any precision PEEK component.

Choose PEEK only when the environment combines demands that cheaper plastics cannot meet together, because PEEK stock costs many times the price of common engineering plastics. Its justified niche is the overlap of high temperature (continuous service to around 250 C), broad chemical and solvent resistance, good wear resistance, inherent flame retardance with low smoke, and biocompatibility. That is why it dominates semiconductor wafer-handling parts in hot aggressive chemistry, downhole oil and gas seals at high temperature and pressure, aircraft interior and structural components needing flame and smoke ratings, and steam-sterilizable medical implants and instruments. If your part runs at moderate temperature with ordinary chemical exposure, acetal (Delrin), nylon, or PEI (Ultem) will perform at a fraction of the cost; for room-temperature low-stress parts, even cheaper plastics suffice. Specifying PEEK by reflex for anything demanding-sounding wastes significant money. The disciplined approach is to define the actual maximum temperature, chemicals, load, and biocompatibility requirement and step up to PEEK only when a cheaper engineering plastic genuinely fails one of them; when those demands truly stack, PEEK is often the only material that meets them all.