Polyetheretherketone (PEEK) injection molding needs barrel temperatures of 350–400°C, mold surface temperatures of 160–200°C, and pre-dry moisture content below 0.02% to keep the polymer in its semi-crystalline state with tensile strength up to 100 MPa [S2].
Standard presses rated to 300°C barrel temperature cannot run PEEK without thermal instability, screw corrosion, and shot-to-shot drift, which is why molders such as ZetarMold dedicate specific machines in a 47-press fleet exclusively to PAEK-family resins and run a material-qualification shot before any production tool is released [S2].
PEEK's processing window versus standard engineering thermoplastics
PEEK is a semi-crystalline polyaryletherketone (PAEK) with a melting point of approximately 343°C and a glass transition temperature (Tg) of 143°C [S1][S2]. At mold temperatures below Tg, the part freezes in an amorphous state, with lower chemical resistance, lower stiffness, and significantly higher brittleness than the semi-crystalline form, which is why a mold surface held at 160–200°C is the single most important process variable for the part, not the steel underneath it [S2].
The cost gap is also a process-design driver: PEEK raw resin is roughly 50–100x the price of ABS, so defect prevention is a financial requirement, not a quality preference [S2]. The practical consequence is that any candidate press for a PEEK tool must hold all barrel zones inside a tight 350–400°C band without overshoot, and the mold must deliver ±3°C uniformity across the cavity, or differential shrinkage will produce warpage on precision parts [S2].
Selecting the injection press: barrel, screw, and mold-temperature unit
Three hardware items are non-negotiable for a PEEK-capable cell. First, barrel heater bands rated to at least 430°C, because the process sits 50–100°C above the ceiling of a standard 300°C machine [S2]. Second, a corrosion-resistant bimetallic or nickel-alloy screw, because PEEK melt at 380–400°C chemically attacks standard screws within a few hundred shots and changes part quality before it changes melt flow [S2]. Third, an oil-circuit or high-pressure water mold-temperature controller sized to hold 160–200°C continuously; electric cartridge heaters alone cannot maintain the required surface uniformity on a production cycle [S2].
Capacity matching matters as much as the heater rating. A 300°C-rated press pushed to 390°C drifts in plasticizing and produces unmelted particles, surface roughness, and unstable shot weight, which are the same defects attributed in PEEK extrusion to low barrel or die temperature and uneven residence time [S1][S2]. Engineers reviewing a candidate press should ask for a temperature-stability log over a full cycle, not a nameplate maximum, before committing a PEEK tool.
Mold steel, surface treatment, and tooling stack-up
Mold steel selection for PEEK follows the same logic as for any high-temperature thermoplastic: a pre-hardened P20 or H13 tool works for short runs, but glass- or carbon-filled grades accelerate cavity wear, and amorphous grades (formed when the mold runs cold) put less thermal load on the steel than semi-crystalline grades, so steel choice should follow the grade, not the polymer family [S1][S3]. Filled grades containing carbon fibre, graphite, or PTFE improve stiffness and wear but also change shrinkage, flow, surface finish, and mold wear, which means the steel hardness and the surface treatment must be re-validated for each filler system [S3].
Conformal cooling channels are the second decision that drives steel layout. Uniform mold temperature within ±3°C is required to prevent differential shrinkage and warpage on precision parts, and that uniformity is only achievable with conformal cooling routed near the cavity surface, not with straight drilled channels [S2]. For tight-tolerance work, post-mold annealing at 140–200°C for 1–4 hours relieves internal stress and stabilises crystallinity, but annealing is a process step, not a substitute for proper mold-temperature control during the shot [S2].
Drying, material handling, and the reject economics
Material drying is mandatory, not optional: 3–4 hours at 150–160°C, targeting moisture below 0.02% [S2]. Moisture above that threshold hydrolyses PEEK chains during the melt and produces splay, voids, and brittle parts that look like a steel or press problem but are actually a handling problem. For context, the same moisture mechanism drives bubbles, voids, rough surface, and unstable flow in PEEK extrusion, where the symptoms are blamed on the die when the dryer is the real source [S1].
The reject economics justify a dedicated dry-air hopper, a verified dew point, and a logged residence-time limit on the machine throat. A single wet lot can scrap an entire shift's worth of parts, and at 50–100x the cost of ABS, the dryer's operating cost is rounding error against the material at risk [S2]. For a related read on selecting high-performance thermoplastics for structural parts, the PEEK selection for aerospace: grade, reinforcement, and process route in 2026 article covers filler strategy and certification in more depth.
When PEEK is the wrong choice: selection criteria and alternatives
PEEK is the right material when the part must hold shape at continuous service temperature of 260°C, resist a broad chemical envelope, and survive long-term load or wear, which is why it shows up in seals, bushings, pump parts, medical components, semiconductor fixtures, and aerospace brackets [S1][S2][S3]. It is the wrong material when a standard engineering plastic (PPS, PPA, PA66, or PPA-based compounds) can meet the temperature and chemical envelope, because the 50–100x resin premium cannot be recovered on a non-demanding duty cycle [S2][S3].
Carbon-filled PEEK grades may also be partially conductive, so specifying PEEK for electrical insulation without checking the filler system is a common spec error, particularly when the project inherits a "PEEK = insulator" assumption from unfilled-grade datasheets [S3]. For a complementary view on selecting a different engineering plastic for non-PEEK duty cycles, the Polycarbonate selection for general fabrication: a spec-first buying guide article walks through the lower-temperature alternative path.
Process-control checklist before committing a PEEK tool to a mold
Before cutting steel for a PEEK tool, the engineering team should verify five things in writing: a press log showing 350–400°C barrel stability over a full cycle, a screw material certificate (bimetallic or nickel alloy), a mold-temperature controller sized for 160–200°C with ±3°C cavity uniformity, a drying station with a dew-point meter and 0.02% moisture verification, and a documented annealing cycle of 140–200°C for 1–4 hours if the part is tight-tolerance [S2]. Missing any one of these converts a PEEK tool into a scrap generator on the first production day [S1][S2].
Track the following two signals over the next two quarters: (1) whether mold-temperature controller suppliers are quoting more 200°C-class oil units to mid-volume molders, which would indicate PEEK is moving down-market from aerospace-only into industrial and medical volume, and (2) whether nickel-alloy screw retrofits are being offered as standard on late-model 400°C presses, which would signal that press OEMs are accepting PEEK as a baseline material rather than a specialty resin.
The underlying component specifications are covered under lighting equipment and electric lamps, casting mold, and mold base.