PEEK Injection Moulding: Properties, Grades & Design Guide
PEEK (polyether ether ketone) is the benchmark high-performance engineering thermoplastic for applications where stiffness, continuous high-temperature service above 200°C, and chemical resistance must coexist. Parts injection-moulded from unfilled PEEK carry tensile strengths of around 100 MPa — comparable to some aluminium alloys — at a fraction of the weight. Nordmould supplies PEEK-moulded components for aerospace, medical, and semiconductor customers where no lower-cost polymer qualifies.
What are the mechanical and thermal properties of PEEK?
PEEK is a semi-crystalline aromatic polymer. Its semi-crystalline structure delivers low and predictable creep, strong chemical resistance, and excellent fatigue resistance. Processing above the mould temperature threshold of 160°C allows the polymer to crystallise correctly; below that, parts form an amorphous, brittle structure and must be rejected.
| Property | Unfilled PEEK | 30% GF PEEK | 30% CF PEEK | Test Standard |
|---|---|---|---|---|
| Tensile Strength | 100 MPa | 170–180 MPa | 200 MPa | ISO 527 |
| Flexural Modulus | 3,600 MPa | 10,000–11,000 MPa | 14,000 MPa | ISO 178 |
| Izod Impact (notched) | 55 J/m | 70 J/m | 55 J/m | ISO 180 |
| Heat Deflection Temp (1.82 MPa) | 160°C | 315–328°C | 315°C | ISO 75 |
| Continuous Use Temp | 240–260°C | 240°C | 240°C | — |
| Density | 1.30 g/cm³ | 1.49 g/cm³ | 1.40 g/cm³ | ISO 1183 |
| Mould Shrinkage | 1.0–1.4% | 0.2–0.8% | 0.1–0.5% | ISO 294-4 |
| Water Absorption (24 h) | 0.06% | 0.06% | 0.04% | ISO 62 |
The very low water absorption is one of PEEK's key practical advantages in precision components. Dimensional change due to moisture is negligible, which matters in high-precision bushings, bearing cages, and medical instrument bodies. Note that the dramatic jump in HDT for filled grades (unfilled: 160°C; GF30/CF30: 315°C+) reflects the reinforcement suppressing the glass transition rather than any change in the polymer chemistry.
Where is PEEK injection moulding used?
PEEK's combination of thermal stability, chemical resistance, radiation resistance, and biocompatibility makes it the first choice when other engineering polymers reach their limits.
Aerospace: Structural brackets, cable glands, fluid-system seals, bushings, and bearing cages in nacelles and engine compartments. PEEK's strength-to-weight ratio and service temperature exceeding 200°C qualify it for proximity-to-engine parts that would soften other polymers.
Medical and dental: Spinal interbody fusion cages, orthopaedic fixation systems, dental abutments, and reusable surgical instrument handles. Implant-grade PEEK has over two decades of clinical data. Autoclave sterilisability (134°C, many hundreds of cycles without measurable property loss) makes PEEK preferred for reusable surgical tools.
Semiconductor and electronics: Wafer carriers, chemical-resistant fixtures for wet benches, test sockets, and high-temperature connectors. PEEK's dimensional stability under thermal cycling is critical in semiconductor process equipment.
Oil and gas: Seal housings, valve seats, and downhole instrumentation components. PEEK withstands sour gas (H₂S), steam, and hydraulic fluids at elevated pressures.
High-performance automotive: Transmission bushings, engine management sensors, fuel system fittings, and turbocharger-adjacent components.
What are the moulding characteristics of PEEK?
PEEK is one of the most demanding injection-moulding materials. It requires dedicated, well-maintained equipment and strict process control. Processing in machines contaminated with lower-temperature polymers risks degradation and cross-contamination of the next run.
Melt temperature: 360–400°C. Consistent barrel temperature is essential; hot spots above 420°C cause thermal degradation — darkening, viscosity reduction, off-gassing. A dedicated PEEK barrel or thorough purge sequence is required when switching from other materials.
Mould temperature: 160–200°C. This is non-negotiable for achieving the semi-crystalline morphology that gives PEEK its mechanical properties. Standard water-cooled mould temperature controllers are insufficient; oil-heated or electric mould heating systems are required. Tooling must tolerate repeated thermal cycling at these temperatures.
Injection pressure: 140–200 MPa. PEEK's high melt viscosity demands high injection pressure and robust screw/barrel design. Machines used for PEEK must be rated for these pressures with wear-resistant screws and check rings.
Drying: 150–160°C for 3–4 hours to below 0.02% moisture. Dehumidifying dryer mandatory; standard hot-air ovens are insufficient for consistent results.
Tooling: Hardened tool steel (P20, H13, or equivalent) throughout. Aluminium tooling is inappropriate for PEEK processing temperatures and pressures. Cooling channels should be designed for oil flow if mould temperatures above 180°C are required.
Shrinkage: 1.0–1.4% for unfilled grades, highly sensitive to mould temperature and cooling rate. Glass and carbon-filled grades exhibit much lower and more anisotropic shrinkage; gate positioning is critical for dimensional control.
Draft angles: Minimum 1° on walls. PEEK's rigidity aids ejection but high adhesion to polished steel at 180°C+ mould temperatures requires adequate draft.
Which PEEK grades and variants are available?
| Grade | Key Feature | Primary Application |
|---|---|---|
| Unfilled PEEK | Balanced properties, FDA/USP compliant | Medical instruments, fluid handling |
| 30% Glass-filled PEEK | ~3× stiffness increase, HDT 315°C+ | Structural brackets, pump components |
| 30% Carbon-filled PEEK | Maximum stiffness and fatigue resistance | Aerospace, high-load bearings |
| Bearing-grade PEEK | PTFE + CF + graphite blend | Bushings, wear pads, sliding parts |
| Implant-grade PEEK | ISO 10993 / USP Class VI validated | Spinal cages, orthopaedic implants |
| ESD PEEK | Carbon-black or CNT-loaded, static-dissipative | Semiconductor fixtures, IC trays |
Bearing-grade PEEK achieves a dry coefficient of friction of 0.1–0.2, eliminating the need for external lubrication in applications such as bushing rings that would be impractical to service.
What are PEEK's advantages and limitations?
Advantages:
- Highest continuous use temperature among standard injection-moulding thermoplastics (240–260°C unfilled)
- Tensile strength approaching aluminium alloys; excellent specific strength
- Outstanding chemical resistance including steam, acids, bases, and most organic solvents
- Negligible moisture absorption — dimensions unaffected by humidity
- Biocompatible and sterilisable grades for demanding medical applications
- Excellent fatigue and creep resistance under sustained load
- Radiation resistance (useful in nuclear and medical imaging environments)
Limitations:
- Highest material cost among standard engineering thermoplastics — justified only when no alternative qualifies
- Requires specialised high-temperature moulding equipment; not processable on general-purpose machines
- Hardened steel tooling mandatory — significant tooling investment
- Mould temperature control at 160–200°C demands oil-heating or electric systems
- Shrinkage and warp sensitivity in semi-crystalline grades requires experienced gate and cooling design
- Limited recycling infrastructure; regrind can be reused but contamination risks are high
When should you choose PEEK over alternative materials?
PEEK vs PPS: PPS serves many of PEEK's applications up to 200°C continuous at materially lower cost. Choose PEEK when the application exceeds 200°C, requires implant-grade biocompatibility, or demands higher impact resistance. PPS is the rational choice when the thermal requirement stays under 200–220°C.
PEEK vs PEI (Ultem): PEI is cheaper and amorphous (no crystallisation control issues) with good thermal and electrical properties to 170°C. Choose PEEK when continuous temperature exceeds 200°C or the part must resist a broad chemical spectrum including ketones and halogenated solvents. PEI is the preferred choice for lower-cost high-temperature structural components where chemical exposure is limited.
PEEK vs metal: PEEK replaces aluminium and titanium where weight reduction, corrosion immunity, or electrical insulation in load-bearing roles is required. Metal milling remains competitive for very low quantities or geometries that injection moulding cannot achieve.
Is PEEK recyclable?
PEEK is not collected in consumer or standard industrial recycling streams. Regrind from clean, single-grade PEEK production scrap is commercially reused for non-critical engineering parts, typically blended at up to 20–30% with virgin material without significant property loss. Implant-grade and ESD-grade regrind must be tested before re-use or discarded. PEEK's long service life and extreme durability offset its end-of-life limitations for most lifecycle analyses. Nordmould can advise on regrind inclusion policies for specific applications.
Frequently asked questions
What temperature can PEEK injection-moulded parts withstand?
Unfilled PEEK has a continuous use temperature of 240–260°C and a heat deflection temperature of approximately 160°C (at 1.82 MPa) for standard grades, rising to over 300°C for 30% glass or carbon-filled variants. PEEK retains significant strength well above 200°C — no common engineering thermoplastic matches it at continuous elevated temperature.
Does PEEK need to be dried before injection moulding?
Yes. PEEK absorbs moisture slowly but even low levels cause voids, splay, and reduced mechanical properties. Drying at 150–160°C for 3–4 hours in a dehumidifying dryer to below 0.02% moisture is standard before processing. Pre-dried material should be held in sealed containers until press-side.
How much does PEEK injection moulding cost compared to standard materials?
PEEK raw material typically costs 50–100× more per kilogram than commodity ABS or PP. Tooling also requires hardened steel and oil or electric mould heating systems. Nordmould positions PEEK for applications where no lower-cost polymer meets the performance requirements — confirming that at the DFM stage.
What are the melt and mould temperatures for PEEK injection moulding?
PEEK melt temperature is 360–400°C. Mould temperature must be held at 160–200°C to achieve the semi-crystalline microstructure that delivers PEEK's characteristic mechanical and thermal properties. Below 150°C mould temperature, parts are amorphous, brittle, and dimensionally unstable.
What industries use PEEK injection-moulded parts?
PEEK is used in aerospace (structural brackets, seals, bushings), medical (implant-grade devices, surgical instruments, sterilisable housings), semiconductor equipment (wafer-handling, chemical-resistant fixtures), and high-performance automotive (transmission components, engine bay parts).
Can PEEK be injection moulded for medical implants?
Implant-grade PEEK (PEEK-OPTIMA and equivalents) carries ISO 10993 and USP Class VI compliance and is established in spinal cages, orthopaedic fixtures, and dental components. These grades require validated, contamination-free processing. Nordmould can source implant-grade material and apply appropriate process controls — confirm requirements at the DFM review stage.
What are the main grades of PEEK for injection moulding?
Key grades are: unfilled PEEK (balanced properties, FDA-compliant), 30% glass-filled PEEK (higher stiffness, lower creep), 30% carbon-filled PEEK (maximum stiffness and fatigue resistance), bearing-grade PEEK (PTFE + CF + graphite, very low friction), and implant-grade PEEK (biocompatibility-validated, limited to medical OEMs).
Is PEEK chemical-resistant enough for fluid-handling components?
PEEK resists concentrated acids, bases, hydrocarbons, ketones, and steam at elevated temperatures. It is attacked by concentrated sulphuric acid and some halogenated solvents. For aggressive fluid-handling, PEEK routinely outperforms nylon, acetal, and even many metals.
Send your STEP file to Nordmould for a free DFM review — we will confirm whether PEEK is the right material choice and identify any tooling, gate, or thermal control considerations specific to your design.