PEEK Injection Molding: The Complete High-Temperature Guide
Manufacturing Guide
PEEK Injection Molding: The Complete High-Temperature Guide
PEEK injection molding is the process that produces the strongest, hottest, most chemically resistant plastic parts that can still be injection molded into complex shapes. Polyetheretherketone (PEEK) survives continuous service at 260 °C, keeps its strength down to cryogenic temperatures, shrugs off strong acids and organic solvents, and wears better than most metals — which is why aerospace, medical implant, semiconductor, oil & gas, and food-processing engineers specify it where nothing cheaper survives.
The cost is real: PEEK resin is among the most expensive thermoplastics on the market, the process runs hotter than any standard molding shop can deliver, and the mold must be built and heated like a piece of high-temperature tooling. But when a part needs PEEK, there is usually no substitute — only alternatives with trade-offs. This guide covers the full engineering picture: peek injection molding process physics, parameters, mold design, tolerances, cost reality, applications, defect control, and when to step down to PPS, PEI, or PEKK instead.
Molditquick (东莞国宏精密) runs high-temperature molding alongside our standard 21 Sodick injection machines — the same tooling shop, wire EDM (9+4 machines), and 10,000 m² facility that builds production molds for automotive and medical programs under IATF 16949, ISO 13485, and ISO 9001.
Table of Contents
- What is PEEK injection molding?
- Why PEEK: material properties that justify the price
- PEEK vs PPS vs PEI vs PEKK: choosing the high-temperature plastic
- PEEK process parameters: melt, mold, and machine
- Drying PEEK before molding
- Mold design for PEEK: steel, temperature control, gating
- Glass-filled and carbon-filled PEEK compounds
- Tolerances and dimensional behavior
- Cost and lead time: what PEEK really costs
- Applications: aerospace, medical, semiconductor, industrial
- Metal replacement with injection molded PEEK
- Common PEEK defects and fixes
- DFM checklist for PEEK parts
- Quality and traceability for regulated programs
- Buying PEEK molding: what to ask a supplier
- FAQ
What is PEEK injection molding?
PEEK (polyetheretherketone, brand families such as Victrex PEEK, Solvay KetaSpire, Evonik Vestakeep) is a semi-crystalline high-performance thermoplastic. Injection molded PEEK — sometimes written “peek injection moulding” in European RFQs — is produced the same way as any injection-molded part, but at temperatures that disqualify most injection shops:
- Melt temperature: 340–400 °C — the barrel runs at 360–400 °C, hotter than any standard machine is specced for.
- Mold temperature: 150–200 °C — the tool must be actively heated and insulated; a “cold” 60 °C mold produces amorphous, weak, dimensionally unstable parts.
- High crystallinity is the goal. PEEK’s outstanding properties — heat resistance, chemical resistance, wear, fatigue — come from its crystalline structure, which only forms when the mold is hot enough and the cooling profile is controlled.
The process window is narrow. Too cold: amorphous parts that soften at 145 °C glass transition. Too hot, too long: degradation and charring. PEEK molding is genuinely different from molding ABS or even PC — it is closer to running a mini metal-casting operation than a standard plastic press.
Why PEEK: material properties that justify the price
| Property | Typical value | Why it matters |
|---|---|---|
| Continuous service temperature | 260 °C (short-term to 300 °C) | Operates where PA/PC/PPS fail (First Mold PEEK page) |
| Tensile strength | 90–100 MPa (unfilled) | Metal-class strength for a molded plastic |
| Flexural modulus | ~3.6–4 GPa (unfilled); up to 13+ GPa (CF-filled) | Stiff enough for structural brackets |
| Wear resistance | ~4× PTFE | Bearings and seals without lubrication (First Mold PEEK page) |
| Chemical resistance | Resists strong acids (except concentrated sulfuric), organics | Pump seals, chemical plant, downhole tools |
| Mold shrinkage | 0.1–0.5 % (unfilled ~1.1–1.4 % in-plane crystallinity effects; see section 8) | Small and controllable with process |
| Glass transition | ~143–145 °C | Below this, amorphous regions soften |
| Melting point | ~343 °C | Defines the entire process window |
| Flammability | UL94 V-0, halogen-free | Aviation and electronics compliance (First Mold PEEK page) |
| Density | 1.30–1.32 g/cm³ (unfilled); ~1.44 with 30 % GF | ~80 % lighter than steel — the metal-replacement argument |
Note on shrinkage: PEEK is semi-crystalline, so shrinkage depends strongly on crystallinity achieved in the mold. Published values cluster in the 0.1–0.5 % band for well-crystallized parts (First Mold PEEK page); mold temperature and cooling rate move the actual number, which is why mold design and process validation go together.
PEEK vs PPS vs PEI vs PEKK: choosing the high-temperature plastic
“Peek plastic molding” RFQs often arrive with the wrong material specified. The real choice is usually between four high-temperature polymers:
| Criterion | PEEK | PPS | PEI (Ultem) | PEKK |
|---|---|---|---|---|
| Continuous service | ~260 °C | ~200–220 °C | ~170–200 °C | ~250–260 °C |
| Tensile strength | 90–100 MPa | ~75–90 MPa (GF) | ~105 MPa | ~95–110 MPa |
| Toughness | Excellent | Brittle-ish | Excellent | Excellent |
| Chemical resistance | Outstanding | Very good (except chlorinated/oxidizing) | Good (sensitive to some solvents) | Outstanding |
| Wear resistance | Excellent | Good | Good | Excellent |
| Relative resin cost | Highest | Low-moderate | Moderate-high | High (similar to PEEK) |
| Ease of molding | Demanding (340–400 °C) | Moderate | Moderate (340–385 °C) | Similar to PEEK |
| Best use | Ultimate performance | Cost-sensitive hot/chemical parts | Transparent amber, flame-rated parts | PEEK-like with different processing |
When to step down from PEEK — the decision framework used by First Mold’s engineers and echoed across the industry: if the part operates below 150 °C and does not contact strong acids or alkalis, PEI cuts cost 30–40 % with stable long-term performance; a documented case switching an industrial gearbox to PEI cut costs 35 % while running five years in 120 °C lubricant (First Mold PEEK page). If the need is hot-and-cheap with good chemical resistance, PPS (often GF40) is the value pick. PEKK is the closest performance sibling when PEEK supply or processing is the constraint.
Rule of thumb from our DFM reviews: specify PEEK only where the requirement is ≥200 °C continuous service, aggressive chemistry, wear under load, or a combination — otherwise you are paying for capability the part never uses.
PEEK process parameters: melt, mold, and machine
Typical supplier-published processing windows (Victrex/Solvay/Evonik guidance), which we validate per grade at Molditquick:
| Parameter | Typical range | Notes |
|---|---|---|
| Barrel temperature | 360–400 °C (melt 340–400 °C) | Nozzle toward the top of the window for thin-wall parts |
| Mold temperature | 150–200 °C (unfilled 160–200 °C; CF/GF grades 170–200 °C) | Above 160 °C for full crystallinity |
| Drying | 150 °C for 3 h (some grades 120–150 °C) | Moisture < 0.02–0.05 %; prevents voids and splay |
| Injection pressure | 800–1,600 bar | High — melt is viscous |
| Hold pressure | High, 50–80 % of injection | Packs the semi-crystalline shrinkage |
| Injection speed | Medium | Too fast = shear degradation and burns |
| Screw speed | Low-moderate | PEEK degrades under high shear |
| Back pressure | 5–15 bar | Consistent melt density |
| Cycle time | 60–180 s typical | Hot mold + crystallinity = long cooling phase |
| Shrinkage | 0.1–0.5 % (process-dependent) | Mold temp and cooling rate shift the value |
Machine requirements that filter out most shops:
- High-temperature capable barrel — standard machines rated for 300 °C max cannot run PEEK safely.
- Heated, insulated mold — mold temperature controllers up to 200 °C plus insulation plates on both sides; heat loss to the platens is the classic reason parts come out amorphous.
- Corrosion-resistant barrel/screw — PEEK and its fillers are abrasive at 400 °C; hardened or bimetallic components are standard practice.
- Accurate melt-temperature control — the gap between 360 °C and 400 °C is 10 % of the absolute window; sloppy controllers either char the resin or fail to melt it.
If a prospective molder says “we can try it on our standard machine,” they cannot actually produce injection molded PEEK to spec — high-temperature tooling is a fixed cost of entry.
Drying PEEK before molding
PEEK absorbs moisture at a low but meaningful rate, and at 380–400 °C any moisture becomes steam — producing voids, splay, and surface defects in parts that cost more per gram than silver. The published rule: dry at 150 °C for 3 hours (120–150 °C per grade) to a residual moisture below 0.02 % (some datasheets allow 0.05 %).
Shop rules at Molditquick:
- Dehumidifying dryer with dew-point verification — never a hot-air oven.
- Drying time from full-load temperature, not switch-on.
- Dried PEEK molded within minutes; the hopper is purged with nitrogen or run sealed where the grade and machine allow.
- In-process moisture spot-checks on critical aerospace and medical programs.
Mold design for PEEK: steel, temperature control, gating
Steel and construction
PEEK molding is a thermal and abrasive challenge for tooling:
- Prototype tools: H13 or P20 can run Class 105–104 volumes for validation (RJC Mold).
- Production tools: H13, S136/420 stainless, or D2-class steels, hardened; hot-work grades survive the 150–200 °C mold and abrasive CF/GF compounds.
- Cavity inserts for high-wear zones get nitriding or PVD coating.
- Mold-class expectations follow the industry ladder — Class 105 prototype (<500 shots, 10–18 day lead) up to Class 102 (<1M shots) and Class 101 for ultra-high volume (RJC Mold, Xometry).
Temperature control — the make-or-break system
- Mold temperature 150–200 °C, held uniformly with oil or high-temperature water heaters.
- Insulation plates between mold and platens; heat leaks turn the cavity cold and the part amorphous.
- Cooling channels still matter: the mold must arrive at 180 °C and then hold 180 °C through the cycle — a paradox that requires sized heaters and balanced channels, not just “hot oil.”
Gating and venting
- Large gates (edge, fan, or full-round) — PEEK’s viscosity demands unrestricted fill; pinpoint gates shear the melt and cause gate blush and degradation.
- Cold slug wells on every drop.
- Hot runners are used for high-volume PEEK tools but must be high-temperature-rated with minimal dead zones — stagnant PEEK chars in a hot runner quickly.
- Venting — PEEK outgasses as it fills; vents at 0.02–0.05 mm on the parting line prevent burns.
- Ejection — hot, strong parts need large ejector areas and slow ejection; thin-walled PEEK parts are stiff and brittle-ish on ejection if under-packed.
Glass-filled and carbon-filled PEEK compounds
A large share of “peek plastic injection molding” work uses filled compounds, because unfilled PEEK’s strength is good but its stiffness and wear are what filled grades dramatically improve:
| Compound | Typical properties gained | Typical uses |
|---|---|---|
| PEEK GF30 (30 % glass) | Stiffness ~2× unfilled, lower CTE, lower cost per unit stiffness | Pump housings, structural brackets, compressor parts |
| PEEK CF30 (30 % carbon fiber) | Highest stiffness and strength, excellent wear, dissipates static, lower coefficient of friction | Aerospace brackets, semiconductor wafer-handling parts, gears, bushings |
| PEEK + PTFE + CF/graphite (bearing grades) | Lowest friction and wear | Unlubricated bearings, seals, thrust washers |
| PEEK ESd (static-dissipative) | Surface resistivity ~10⁶–10⁹ Ω/sq | Semiconductor and electronics handling |
Processing notes: filled compounds flow worse and abrade the barrel more; mold temperature must stay at the top of the window to crystallize the matrix; shrinkage of filled grades sits at the low end of the 0.1–0.5 % band and becomes more anisotropic (direction of fill matters in tolerance analysis).
Tolerances and dimensional behavior
PEEK can hold real precision — that is one reason semiconductor and medical engineers choose it — but the rules differ from amorphous plastics:
- Shrinkage is process-coupled. Mold temperature, cooling rate, and wall thickness move the actual shrinkage between ~0.1 % and ~0.5 %. A supplier that quotes “0.3 % flat” without process validation is guessing.
- Post-mold dimensional drift occurs as crystallinity equilibrates; parts are often post-crystallized (annealed) for critical dimensions — and the mold is designed with the annealed value in mind.
- Low moisture absorption (~0.1–0.5 % equilibrium) means dimensions stay stable in humid environments — a decisive advantage over PA66 for precision parts.
| Feature | Realistic tolerance | Reference |
|---|---|---|
| General linear dimensions | ±0.1 mm | Industry standard (ISO 2768-m / DIN 7168-m) |
| Precision features | ±0.05 mm | (First Mold) |
| Critical dimensions (validated) | ±0.02–0.05 mm | Process validation + CMM |
| Mold cavity machining | ±0.02 mm; cores ±0.005 mm | (First Mold, RapidDirect) |
Published platform references for comparison: Protolabs machining tolerance ±0.003 in (0.08 mm) plus resin ±0.002 in/in (Protolabs); Zetar ±0.1–0.2 mm general / ±0.05 mm critical (Zetar); tolerance tables per DIN 16901 / ISO 20457 (Boyan).
At Molditquick we treat PEEK tolerances as a process development item: mold design review, first articles on CMM, and a capability check on the critical dimensions before production release — standard practice on IATF 16949 and ISO 13485 programs.
Cost and lead time: what PEEK really costs
Cost structure of injection molded PEEK:
- Resin — PEEK costs roughly 10–30× ABS by weight (grade and volume dependent). This is the dominant line item.
- Scrap discipline — runners and gates are regrindable in limited ratios for some grades, but aerospace/medical often forbid regrind; yield management is a real cost lever.
- Machine and tooling overhead — high-temperature machines, heated molds, hardened tooling, and slower cycles all raise the hourly rate.
- Process development — first articles and validation runs cost more than for standard plastics.
Lead-time reference bands: rapid prototype tooling 7–12 days, production tooling 25–30 days (automotive class to 45 days) (First Mold); prototype tools 10–18 days, production tools 4–6 weeks standard (RJC Mold, Zetar); platform no-MOQ production about 7 days after tool validation (Protolabs).
Volume planning: PEEK parts are typically low-volume (hundreds to tens of thousands per year) — aerospace and medical rarely need millions. That fits Molditquick’s model: in-house tooling, 21 Sodick presses, and low-volume-to-production runs in one facility, with global shipping. Budget the resin cost early — it dominates the piece price and can shock first-time buyers who priced the part in aluminum.
Applications: aerospace, medical, semiconductor, industrial
Aerospace & aviation — wire-harness connectors, cable clamps, actuator bushings, fuel-system components, seat mechanisms, drone motor brackets. PEEK replaces aluminum with ~30 % weight saving (equivalent to ~5 % fuel-efficiency improvement in aircraft applications) and holds strength down to −60 °C cryogenic service (First Mold PEEK page). UL94 V-0 plus low smoke/toxicity satisfy cabin flammability requirements.
Medical & implants — spinal fusion cages, endoscope sealing heads, pacemaker housings, surgical instrument handles, dental components. PEEK is biocompatible (ISO 10993 / FDA long-term implant history), radiolucent (X-ray transparent — postoperative imaging is unobstructed), and steam/E-beam sterilizable (First Mold PEEK page). Surgical instruments mold with walls under 0.1 mm in some designs — PEEK is one of the few plastics that survives being that thin.
Semiconductor & electronics — wafer-handling rings, chucks, insulators, socket bodies, cleanroom fixtures. Static-dissipative PEEK grades protect ESD-sensitive devices; chemical resistance survives the aggressive etch and clean chemistries.
Oil & gas / industrial — downhole sealing elements rated to 150 MPa pressure, chemical pump seals, compressor valve plates, food-processing bearings, valve cores for coffee machines, foldable-phone hinges rated past 100,000 open/close cycles, deep-sea drone housings (First Mold PEEK page).
Metal replacement with injection molded PEEK
The engineering case that justifies PEEK’s price in most programs:
- Weight: ~80 % lighter than steel, ~65 % lighter than titanium — decisive for aircraft, drones, and robotics.
- Corrosion: replaces stainless where chlorides and acids attack metal — pump parts, marine, chemical.
- Wear without lubrication: replaces bronze/PTFE-lined bushings with self-lubricating PEEK bearing grades.
- Integration: injection molding produces the bearing, seal groove, snap features, and mounting holes in one shot — eliminating machining, fasteners, and assembly (see CNC vs injection molding for the crossover math).
- Radiolucency: replaces titanium in implants where imaging access matters.
The honest caveat: PEEK does not beat metal on stiffness per dollar in high-volume structural parts — it wins on system cost (weight + integration + corrosion + wear) in demanding applications. Run the total-cost comparison, not the price-per-kilo comparison.
Common PEEK defects and fixes
| Defect | Appearance | Root cause | Fix |
|---|---|---|---|
| Low crystallinity / weak parts | Part softens below 260 °C, low stiffness | Mold too cold (<150 °C) | Heat mold 150–200 °C, insulate platens |
| Voids / bubbles | Internal cavities | Moisture, insufficient packing | Dry 150 °C/3 h, raise hold pressure |
| Splay / silver streaks | White lines near gate | Moisture, degradation | Dry, lower melt temp, purge |
| Burns / charring | Black streaks, acrid odor | Melt over-temperature, long residence, dead zones | Reduce barrel temp, purge, clean hot runner |
| Gate blush / haze | Frosted ring at gate | Pinpoint gate shear, cold gate area | Larger gate, hotter mold, slower fill |
| Short shot | Incomplete thin-wall fill | Viscosity, cold mold, weak machine pressure | Raise melt/mold temp, enlarge gate, high-flow grade |
| Warpage | Twist out of plane | Asymmetric cooling/crystallinity | Balance mold temperature, uniform wall, anneal |
| Sink marks | Depressions at thick sections | Semi-crystalline packing shortfall | Higher hold pressure/time, thin sections |
| Flash | Fins at parting line | Melt pressure vs clamp | Raise clamp, clean parting, check mold steel wear |
| Ejector damage | White stress marks, cracks at pins | Hot, strong part, small pins | Larger ejectors, slower ejection, hotter mold |
| Brittle parts | Cracking under load | Insufficient crystallinity, degradation | Verify mold temp and melt history, dry properly |
| Dimensional drift | Parts change size after molding | Crystallinity equilibration | Post-crystallize/anneal, design mold to annealed value |
DFM checklist for PEEK parts
- Wall 1–3 mm typical; thin walls (<0.5 mm) only with high-flow grades and validated process.
- Uniform wall — PEEK’s semi-crystalline shrinkage punishes transitions.
- Radii ≥0.5× wall; avoid sharp notches (PEEK is tough but notch-sensitive under load cycling).
- Draft 0.5–1° minimum; more for textured surfaces.
- Large, unrestricted gates; no pinpoint gates into critical zones.
- Ribs 0.5–0.6× wall; bosses cored and gusseted.
- Tolerance callouts with an explicit note on annealed vs as-molded dimensions.
- Grade + compound specified (GF30/CF30/bearing/ESd/medical), not just “PEEK.”
- Environmental spec: continuous temperature, chemicals, sterilization method, radiation.
- Regrind policy stated (virgin-only for aerospace/medical?).
- Surface finish and appearance class — PEEK parts are often functional, not cosmetic; say so on the drawing.
Full checklist: DFM checklist guide.
Quality and traceability for regulated programs
High-performance PEEK parts usually land in regulated industries, so the quality system is part of the product:
- Aerospace — full material traceability (resin lot to part lot), certificate of conformance, dimensional reports, AS9100-style documentation where required; Molditquick’s IATF 16949 infrastructure delivers the PPAP/FAI discipline these programs expect.
- Medical — ISO 13485 quality system, biocompatibility documentation (ISO 10993), validated process parameters, lot traceability, and UDI-friendly labeling for implant-adjacent components.
- Semiconductor — cleanliness, static-dissipative verification, and particle-conscious handling.
CMM first-article inspection, in-process QC (IPQC), and end-of-line AQL sampling are standard on every Molditquick program regardless of industry.
Buying PEEK molding: what to ask a supplier
- “What barrel temperature rating are your machines?” — anything below 400 °C capability is a no.
- “What mold temperature can your tooling and controller deliver?” — 150–200 °C sustained, with insulation, is the answer you need.
- “Show me your PEEK process validation data” — crystallinity check, shrinkage measurement, first-article reports from a real program.
- “What compounds have you molded?” — GF30/CF30/bearing-grade experience matters; a virgin-PEEK-only shop will struggle with compounds.
- “What is your regrind and yield policy?”
- “Which certifications do you hold?” — IATF 16949 / ISO 13485 / ISO 9001 for regulated programs.
- Get a DFM review before tooling — gate placement, wall balance, and tolerance realism on PEEK are worth a second opinion (free at Molditquick).
FAQ
1. What is PEEK injection molding? Molding polyetheretherketone at melt temperatures of 340–400 °C into heated molds (150–200 °C) to produce high-temperature, high-strength parts. Also written “peek injection moulding” or “peek plastic molding.”
2. What temperature is PEEK injection molding? Barrel/melt 340–400 °C (typically run 360–400 °C), mold 150–200 °C, drying 150 °C for ~3 hours. Only high-temperature-capable machines can run it.
3. Is PEEK easy to injection mold? No — it needs specialized machines, heated and insulated molds, and tight melt-temperature control. That is why most standard injection shops decline it.
4. What is the shrinkage rate of PEEK in injection molding? 0.1–0.5 % for well-crystallized parts (First Mold PEEK page); the exact value depends on mold temperature, cooling rate, and fill level, so it is validated per program rather than assumed.
5. What is PEEK used for in injection molding? Aerospace (connectors, brackets, fuel components), medical (implants, surgical instruments), semiconductor (wafer handling), oil & gas (seals to 150 MPa), and industrial wear parts (bearings, valves, pump seals).
6. PEEK vs PPS — which should I use? PPS for cost-sensitive hot/chemical parts up to ~200–220 °C; PEEK when you need 260 °C service, toughness, or wear performance PPS cannot deliver.
7. PEEK vs PEI (Ultem) — which is better? PEEK wins on temperature (260 °C vs ~170–200 °C), chemical resistance, and wear; PEI is transparent amber, cheaper, and cuts cost 30–40 % where <150 °C service suffices (First Mold PEEK page).
8. Can PEEK be injection molded with thin walls? Yes — surgical instruments and seals mold below 0.1 mm wall in some designs, with high-flow grades, hot molds, and high injection pressure.
9. Why is PEEK injection molding so expensive? Resin cost (10–30× ABS by weight), high-temperature machine requirements, heated hardened tooling, slower cycles, and regulated-industry documentation all contribute.
10. What tolerances can PEEK injection molding hold? General ±0.1 mm, precision ±0.05 mm, validated critical dimensions ±0.02–0.05 mm — with mold cores machined to ±0.005 mm and CMM verification.
11. Does PEEK need a heated mold? Yes — mold temperature of 150–200 °C is required for crystallization; a cold mold yields weak amorphous parts that fail at ~145 °C.
12. Can PEEK parts be sterilized? Yes — steam autoclave, E-beam, and gamma sterilization are common; PEEK’s chemical and radiation resistance make it a medical-device workhorse.
13. Is PEEK biocompatible? PEEK has a long implant history with ISO 10993 biocompatibility documentation; medical programs at Molditquick run under ISO 13485 with full lot traceability.
14. What is the difference between PEEK and PEKK injection molding? Both are high-temperature (ketone-family) polymers with similar performance; PEKK is often chosen when PEEK supply or specific processing characteristics matter — the closest drop-in sibling.
15. Where can I get PEEK injection molding done? From high-temperature-capable molders with heated-tooling experience. Molditquick runs PEEK programs on dedicated high-temp machines with in-house tooling — send your model to our injection molding service for a DFM review and quotation.
16. Does PEEK injection molding require MOQ? PEEK programs are usually low-volume; platform and low-volume molders run from hundreds of parts (Protolabs). See our low-volume injection molding service.
Planning a high-temperature part? Send your model and service spec to our injection molding service for a free DFM review, grade recommendation, and costed quotation. Compare materials in the plastic material selection guide and injection molding material comparison, and explore the materials library.