PEEK (Polyether Ether Ketone) is a high-performance engineering plastic that is often used as a substitute for metals in CNC machining. The strength of PEEK is comparable to aluminum alloys and some stainless steels, and its weight is half that of aluminum, which has important value in lightweight design. PEEK can maintain stable performance at temperatures up to 250 °C and is resistant to fuels, lubricants, and acidic or alkaline environments. Medical-grade PEEK can be machined into implants for direct use. With these characteristics, PEEK is widely used in aerospace, automotive, medical, and electronic fields, and has also become one of the most important high-performance plastics in CNC machining.
What is PEEK
The chemical name of PEEK is Polyether Ether Ketone, and it belongs to the PAEK family. PEEK is a semi-crystalline thermoplastic with high strength, high toughness, and heat resistance. The density is about 1.30 g/cm³, which is much lighter than metals and is an ideal choice for lightweight applications. Tests show that the tensile strength can reach 90–100 MPa, and the flexural modulus is about 4 GPa. The glass transition temperature is 143 °C, and the melting point is close to 343 °C, so it can still remain stable in high-temperature environments. CNC machining can achieve a tolerance of ±0.02 mm, which is suitable for components with strict dimensional requirements.
Typical Properties of PEEK
| Property | Value | Relevance |
|---|---|---|
| Density | ~1.30 g/cm³ | Lightweight, suitable for aerospace and medical |
| Tensile Strength | 90–100 MPa | Comparable to aluminum alloys |
| Flexural Modulus | ~4 GPa | Provides rigidity and stability |
| Glass Transition Temperature | 143 °C | Determines processing temperature range |
| Melting Point | ~343 °C | High thermal stability |
| Hardness | Rockwell R126 | Causes faster tool wear |
| CNC Tolerance | ±0.02 mm | Achievable for precision parts |
Advantages of PEEK in CNC Machining
PEEK combines the light weight of plastics with the strength of metals, making it an excellent choice for CNC machining. The rigidity and strength are close to aluminum alloys, but the weight is significantly reduced. PEEK can still maintain mechanical stability at 250 °C, while most engineering plastics cannot work properly at this temperature. Its resistance to fuel, lubricants, and chemicals makes it widely used in aerospace, automotive, and oil and gas industries. Medical-grade PEEK has passed ISO 10993 and USP Class VI certification, and it can ensure safe use for implants even after CNC machining. For engineers, PEEK realizes a balance between metallic performance and plastic machinability in environments where strength, heat resistance, and chemical resistance are required.
Limitations of PEEK
Although PEEK has excellent performance, the raw material is expensive, and waste during production will significantly increase costs. The hardness is also higher than most plastics, and tool wear is also higher; in batch production, standard carbide tools are inefficient. Coated tools or diamond tools are usually required to extend tool life. PEEK is sensitive to heat; poor chip removal or insufficient cooling will cause warping or micro-cracks. Aerospace- and medical-grade materials also often have long delivery times, which may delay projects.
Applications of PEEK
Aerospace
Often used to manufacture structural brackets, clamps, and under-hood components, meeting AMS and ASTM standards.
Medical
Many times used to manufacture spinal cages, dental implants, and surgical instruments, and biocompatibility is maintained after machining.
Automotive
Includes bearing retainers, seals, and engine compartment parts, which must be resistant to heat and lubricants.
Electronics
Manufacturers use PEEK to make insulators and high-temperature connectors. Some oil and gas components must also meet API standards.
Case Example: JeekRapid produced a batch of aerospace PEEK brackets. Compared with the original metal design, the weight was reduced by 40% while maintaining ±0.02 mm tolerance. These parts successfully passed performance verification tests.
Tooling, Cutting Speed, Cooling, and Surface Finish
When machining PEEK by CNC, tool selection is very important. Standard carbide tools can be used, but wear quickly during continuous machining. Coated carbide tools or diamond tools have longer service life. Cutting speeds are usually set between 150 and 200 m/min; for a 6 mm carbide end mill, exceeding this range usually causes tool failure within two hours. The feed per tooth should be moderate to ensure smooth chip removal and avoid excessive heat buildup. Compressed air cooling is recommended to control temperature and remove chips, while flood coolant may cause stress cracking. The typical milled surface roughness is Ra 1.6–3.2 µm, and post-polishing can reduce it to below Ra 0.8 µm for medical or optical parts.
Machining Guidelines for PEEK
| Factor | Recommendation | Notes |
|---|---|---|
| Tooling | Coated carbide or diamond | Standard carbide wears in 1–2 hours |
| Cutting Speed | 150–200 m/min (6 mm end mill) | Above 200 → tool fails in <2 hours |
| Feed Rate | 0.05–0.08 mm/tooth | Too low → poor chip removal; too high → overheating |
| Cooling | Compressed air or mist | Flood coolant may cause cracking |
| Surface Finish | Ra 1.6–3.2 µm; polished <0.8 µm | Required for medical and optical parts |
PEEK is one of the most important high-performance plastics in CNC machining, combining high strength, low weight, thermal stability, and chemical resistance. It is applied in aerospace, medical, automotive, and electronics. Although challenges such as high cost, tool wear, and heat management exist, they can be addressed by using proper tools, machining parameters, and cooling strategies. JeekRapid has successfully machined PEEK components in multiple projects, always maintaining ±0.02 mm tolerance and reliable surface quality. Engineers can upload CAD files directly to the JeekRapid platform to quickly obtain feasibility analysis and quotations for PEEK machining.
FAQ
Can PEEK replace metal parts?
Yes. Its strength is close to aluminum, while its weight is reduced by about 40%, so it is often used in aerospace and medical parts.
What tolerances can be achieved with PEEK?
±0.02 mm can be achieved under stable CNC setups.
Does PEEK require special cooling?
Yes. Compressed air or light mist cooling is recommended; too much coolant may cause cracking.
Can medical-grade PEEK be machined?
Yes. It maintains biocompatibility after machining and meets ISO 10993 and USP Class VI standards.
What is the tool life when machining PEEK?
Carbide tools may fail after 1–2 hours of continuous use. Diamond-coated tools can last 3–5 times longer.
What finishing processes are suitable for PEEK?
Common processes include polishing, bead blasting, and plasma cleaning. Medical and optical components usually need polishing to Ra <0.8 µm.
Is PEEK suitable for mass production?
Because of high raw material cost and tool wear, PEEK is more suitable for small-batch, high-value part production.
