PEEK (Polyether Ether Ketone) CNC Machining Material Manual
Last updated: May 23, 2026
PEEK (Polyether Ether Ketone) — CNC Machining Material Manual
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Rating legend — ★★★★★ best · ★☆☆☆☆ worst. For machinability/wear/heat resistance more stars = better; for cost, fewer stars = cheaper.
📋 Material Quick-Reference Card
┌──────────────────────────────────────────┐
│ Material Name: Polyether Ether Ketone │
│ (PEEK / high-performance thermoplastic) │
│ Category: Semi-crystalline high-temp │
│ engineering plastic │
│ Density: 1.30~1.32 g/cm³ (unfilled) │
│ Tensile Strength: 90~100 MPa │
│ Flexural Strength: 150~170 MPa │
│ Elastic Modulus: 3600~4000 MPa │
│ Melting Point: approx. 343 ℃ │
│ Machinability: ★★★☆☆~★★★★☆ │
│ Wear Resistance: ★★★★★ │
│ Chemical Resistance: ★★★★★ │
│ Cost: ★☆☆☆☆ (very expensive) │
│ Keywords: "aristocrat of plastics", │
│ high temperature, chemical- │
│ resistant, metal replacement │
└──────────────────────────────────────────┘
1. Material Overview
1.1 Introduction
PEEK (Polyether Ether Ketone) is a high-strength, high-temperature, chemically resistant semi-crystalline engineering plastic. It is often called the “aristocrat of plastics” because it combines heat resistance, mechanical strength, wear resistance, flame resistance, and chemical stability at a level far above most common machinable plastics.
- English Name: Polyether Ether Ketone / PEEK
- Common Nicknames: PEEK resin, high-temperature PEEK, metal-replacement plastic
- Famous Brand Names: Victrex, Ketron, TECAPEEK, SustaPEEK
1.2 Main Types ⭐ Important
| Type | Full Name | Characteristics |
|---|---|---|
| Unfilled PEEK | Natural / virgin PEEK | Best toughness and purity; good machinability; common for precision components |
| 30% Glass-Filled PEEK | PEEK-GF30 | Higher stiffness, lower thermal expansion, better dimensional stability; more abrasive to tools |
| 30% Carbon-Filled PEEK | PEEK-CF30 | Very high stiffness, wear resistance, and thermal conductivity; excellent for high-load parts; highly abrasive |
| Bearing Grade PEEK | PTFE / graphite / carbon filled | Lowest friction and best wear performance for bushings, bearings, seals, and sliding parts |
| Medical-Grade PEEK | Implantable / biocompatible PEEK | Biocompatible grades for implants, surgical instruments, and sterilizable medical components |
💡 Unfilled PEEK is preferred for general precision machining and medical purity. Glass-filled and carbon-filled PEEK are selected when stiffness, heat deflection, and dimensional stability are more important than tool life.
1.3 Raw Material Forms
Common forms for CNC machining:
- PEEK Rod (round bar): turned parts, bushings, seals, shafts
- PEEK Sheet/Plate: milled parts, insulators, fixtures, structural components
- Common colors: natural beige/tan, black; filled grades may be grey/black
2. Composition & Physical Properties
2.1 Material Composition
PEEK is a semi-crystalline aromatic polymer with repeating ether and ketone groups in the molecular backbone. This rigid molecular structure gives PEEK its exceptional heat resistance, chemical resistance, strength retention, hydrolysis resistance, and flame-retardant behavior.
| Type | Molecular / Filler Structure |
|---|---|
| Unfilled PEEK | Pure semi-crystalline PEEK resin; balanced strength, toughness, and machinability |
| Glass-filled PEEK | PEEK resin reinforced with approx. 30% glass fiber for stiffness and heat deflection |
| Carbon-filled PEEK | PEEK resin reinforced with approx. 30% carbon fiber for stiffness, wear, and thermal conductivity |
| Bearing grade PEEK | PEEK blended with PTFE, graphite, and/or carbon for low friction and long wear life |
2.2 Physical Properties
| Property | Value |
|---|---|
| Density | 1.30~1.32 g/cm³ (unfilled; filled grades higher) |
| Melting Point | approx. 343 ℃ |
| Glass Transition Temp. | approx. 143 ℃ |
| Heat Deflection Temp. | approx. 150 ℃ unfilled; up to 300+ ℃ filled |
| Long-term Service Temp. | approx. 250~260 ℃ |
| Thermal Conductivity | approx. 0.25 W/(m·K), higher for carbon-filled grades |
| Water Absorption | approx. 0.1~0.5% (low) |
| Coefficient of Thermal Expansion | approx. 45~55×10⁻⁶ /℃ unfilled; much lower for filled grades |
💡 PEEK has the highest continuous service temperature among common machinable thermoplastics. Filled grades further improve heat deflection and dimensional stability, but they also increase tool wear.
3. Mechanical & Chemical Properties
3.1 Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | 90~100 MPa unfilled; higher for filled grades |
| Flexural Strength | 150~170 MPa unfilled; higher for filled grades |
| Elastic Modulus | 3600~4000 MPa unfilled; much higher for glass/carbon-filled grades |
| Elongation | 20~50% unfilled; lower for filled grades |
| Hardness | approx. 85~95 (Rockwell M) |
| Impact Strength | Good; unfilled grades are tougher than filled grades |
| Coefficient of Friction | approx. 0.30~0.40 unfilled; lower for bearing grades |
⚠️ PEEK is strong and tough, but filled grades are more brittle and abrasive. For thin walls, sharp internal corners, or impact-loaded parts, choose the grade carefully and avoid unnecessary stress concentration.
3.2 Chemical Resistance
| Medium | Resistance |
|---|---|
| Fuels, oils, alcohols, hydrocarbons | ✅ Excellent |
| Weak acids, weak bases | ✅ Excellent |
| Most organic solvents | ✅ Excellent |
| Steam / hot water / hydrolysis | ✅ Excellent |
| Radiation exposure | ✅ Excellent |
| Concentrated sulfuric acid | ❌ Poor |
| Strong oxidizers / extreme chemical attack | ⚠️ Evaluate by grade and temperature |
3.3 Notable Characteristics
- Top-tier heat resistance: continuous service around 250~260 ℃, far above POM, nylon, PC, and PTFE in structural load-bearing use
- High strength at high temperature: retains stiffness and mechanical strength where many plastics soften
- Outstanding chemical resistance: resists almost everything except concentrated sulfuric acid and extreme oxidizing conditions
- Excellent wear and fatigue resistance: suitable for bearings, bushings, seals, and sliding parts
- Low outgassing: widely used in semiconductor, vacuum, aerospace, and analytical equipment
- Inherently flame-retardant: commonly UL94 V-0, with low smoke and low toxicity
- Biocompatible grades available: medical and implantable PEEK grades are used for surgical and orthopedic applications
4. CNC Machining Process ⭐⭐ Core
4.1 Machinability Rating
★★★☆☆~★★★★☆ Good but demanding machinability — PEEK can be machined to tight tolerances, but it is not as forgiving as POM:
- Cuts cleanly with sharp tools and stable clamping
- Tight tolerances are achievable when stock is properly stress-relieved
- Filled grades are hard and abrasive, causing fast tool wear
- Heat buildup can soften the surface or release internal stress
- Raw material is very expensive, so scrap prevention is a major machining priority
4.2 Recommended Tooling
| Item | Recommendation |
|---|---|
| Tool Material | Carbide for general PEEK; PCD/diamond tooling for glass-filled or carbon-filled grades |
| Cutting Edge | Very sharp, polished edge; replace tools early to avoid heat and burrs |
| Rake Angle | Positive rake angle (10°~20°) to reduce cutting force and heat |
| Helix Angle | Medium to high helix angle for smooth chip evacuation |
| Flutes | 2 flutes for roughing and chip clearance; 3~4 flutes for stable finishing where heat is controlled |
4.3 Recommended Cutting Parameters
| Operation | Spindle Speed (RPM) | Feed Rate (mm/min) | Depth of Cut (mm) |
|---|---|---|---|
| Rough Milling | 3000~8000 | 500~2000 | 0.5~3 |
| Finish Milling | 6000~12000 | 300~1200 | 0.1~0.5 |
| Turning | 800~2500 | 0.05~0.25/rev | 0.3~2 |
| Drilling | 800~2500 | 30~150 | — |
📌 Parameters are for reference only; adjust based on machine rigidity, tool diameter, grade, filler content, coolant method, and part geometry.
4.4 Machining Challenges & Solutions
| Challenge | Cause | Solution |
|---|---|---|
| Tool wear | Glass-filled and carbon-filled PEEK are abrasive | Use carbide minimum; use PCD/diamond tooling for long runs; monitor edge wear closely |
| Thermal deformation / surface smearing | Poor thermal conductivity and excessive cutting heat | Use sharp tools, air blast or coolant, moderate spindle speed, and good chip evacuation |
| Internal stress release distortion | High-performance stock can contain residual stress, especially thick plate/rod | Anneal/stress-relieve before machining; use rough machining → annealing → finish machining |
| Warping or cracking after machining | Asymmetric material removal, sharp corners, insufficient stress relief | Remove material symmetrically, use generous radii, slow controlled annealing, avoid aggressive clamping |
| High scrap cost | PEEK stock is among the most expensive machinable plastics | Confirm toolpaths, use test cuts, leave finishing allowance, protect stock from handling damage |
| Burrs / fiber breakout | Dull tools or reinforced fibers at edges | Use sharp carbide/PCD tools, climb milling, proper support, and controlled deburring |
4.5 Annealing Recommendation ⭐
To reduce machining distortion and cracking, annealing is strongly recommended before machining precision PEEK parts and between roughing/finishing, especially for thick, asymmetric, glass-filled, or carbon-filled components:
Reference Annealing Process:
• Temperature: slow controlled heating per supplier schedule, often multi-step around 150 ℃ → 200 ℃
• Time: based on wall thickness; hold long enough for the core to equalize
• Cooling: very slow furnace cooling to room temperature (avoid rapid cooling)
💡 For high-precision PEEK parts, the rough machining → stress relief annealing → finish machining workflow is often the difference between a stable part and an expensive rejected part.
4.6 Cooling Methods
- Air cooling: common for general machining; keeps chips moving and avoids coolant residue
- Water-soluble coolant: useful for drilling, deep pockets, tight tolerance work, and heat control
- Mist coolant / minimum lubrication: effective when heat must be controlled without flooding the part
- ❌ Avoid overheating or burning the material; do not let chips melt or smoke in the cut
5. Surface Treatment
PEEK has high chemical resistance and relatively low surface energy, so surface finishing is mainly mechanical. It can be machined to a high-quality functional finish, but painting and bonding require pretreatment.
| Process | Feasibility | Notes |
|---|---|---|
| Polishing | ✅ Good | Achievable on unfilled grades; filled grades are harder to polish uniformly |
| Mechanical texturing / sandblasting | ✅ Feasible | Useful for matte appearance, grip, or controlled surface roughness |
| Laser marking | ✅ Excellent | Common for medical, aerospace, semiconductor, and traceability marking |
| Screen printing | ⚠️ Requires pretreatment | Adhesion depends on surface activation and ink system |
| Painting / coating | ⚠️ Difficult | Chemically resistant surface; plasma/flame/chemical pretreatment may be required |
| Dyeing | ❌ Limited | Usually supplied in natural or black; color is normally selected at stock stage |
💡 PEEK parts are usually specified by machined surface finish + laser marking, not decorative coating. If appearance-driven painting or plating is required, choose another plastic or redesign the finish requirement.
6. Applications & Material Selection
6.1 Typical Application Industries
| Industry | Application Parts |
|---|---|
| Aerospace | Lightweight brackets, structural components, clamps, high-temperature insulators |
| Medical | Implantable components, surgical instruments, sterilizable device parts |
| Semiconductor | Wafer handling parts, test sockets, vacuum components, seals, precision fixtures |
| Oil & gas | Downhole components, high-temperature seals, valve seats, insulation parts |
| Mechanical transmission | Bearings, bushings, wear rings, gears, sliding blocks |
| Electrical / electronics | High-temperature insulators, connectors, coil supports, ESD-safe filled parts |
| Pump & valve equipment | Valve seats, seals, backup rings, impellers, wear components |
| Metal replacement | Lightweight structural parts replacing aluminum, stainless steel, or titanium in demanding environments |
6.2 Pros & Cons Summary
| ✅ Advantages | ❌ Disadvantages |
|---|---|
| Excellent high-temperature resistance, continuous use around 250~260 ℃ | Very expensive; among the highest-cost machinable plastics |
| High strength, stiffness, and creep resistance | Filled grades rapidly wear cutting tools |
| Outstanding chemical resistance and hydrolysis/steam resistance | Requires careful annealing and stress control for precision machining |
| Excellent wear, fatigue, and dimensional stability | Not ideal for low-cost or non-critical parts |
| Inherently flame-retardant, low smoke/toxicity, low outgassing | Surface treatment, painting, and bonding can be difficult |
| Medical-grade and implantable grades available | Concentrated sulfuric acid resistance is poor |
6.3 Material Selection Guide
✔ Recommended for PEEK:
- High-temperature parts requiring continuous service above 150 ℃ and up to approx. 250~260 ℃
- Metal-replacement structural parts needing high strength, low weight, and corrosion resistance
- Components exposed to aggressive chemicals, steam, fuels, oils, or sterilization cycles
- Semiconductor, aerospace, medical, and oil & gas parts where performance justifies high material cost
- Bearings, bushings, seals, and sliding parts requiring excellent wear and fatigue resistance
✘ Not recommended for:
- Cost-sensitive general mechanical parts → choose POM, nylon, or PC
- Simple low-temperature wear parts where POM or nylon is sufficient
- Parts needing rich decorative painting, plating, or dyeing → choose ABS or PC
- Direct exposure to concentrated sulfuric acid → choose PTFE or verify a specialty material
- Designs with large asymmetric material removal and no allowance for annealing/stress relief
⚠️ Safety & Handling Notes
| Hazard | Detail | Precaution |
|---|---|---|
| Thermal decomposition | PEEK has a high decomposition temperature, but burning or severe overheating can produce irritating fumes | Avoid burning, smoking chips, or dull-tool overheating; ensure ventilation/extraction |
| Dust inhalation | Fine machining dust may irritate the respiratory tract | Use dust extraction; wear a mask or respirator for prolonged dry machining |
| Glass/carbon-filled dust | Reinforced PEEK dust is more abrasive and may irritate skin, eyes, and lungs | Wear safety glasses, gloves as needed, and suitable respiratory protection |
| Low toxicity | PEEK is generally low-toxicity and many grades are biocompatible | Use certified medical grades only for implantable or regulated medical applications |
| Material cost / scrap risk | PEEK stock is very expensive; mistakes are costly | Verify setup, toolpath, stock orientation, and workholding before cutting |
⚠️ Do not treat PEEK like a cheap plastic. The main practical risks are heat buildup, abrasive filled grades, residual stress, and expensive scrap. Sharp tools + controlled heat + proper annealing = stable, high-value PEEK parts.
🔗 Related Pages
- Plastic Materials Handbook (overview)
- PTFE — superior chemical inertness and low friction
- PEI — high-temperature amorphous alternative with better dimensional predictability
- PI — ultra-high-temperature upgrade for extreme service conditions