A Guide to PEI (Polyetherimide) CNC Machining
Last updated : 2026/7/13
Key Takeaways
PEI is a high-performance thermoplastic with continuous heat resistance up to 170°C, strong chemical durability, and stable electrical insulation.
It is frequently used in medical, aerospace, automotive, and semiconductor applications.
Highly machinable but notch-sensitive, PEI supports injection molding, extrusion, and precision machining
PEI Overview
PEI (Polyetherimide) is a high-performance engineering plastic known for exceptional heat resistance, mechanical strength, and chemical durability. As a member of the super-engineering thermoplastics family, it is widely used in precision machining and industrial applications.
Originally developed by General Electric in 2000, PEI is available today under trusted brands such as JURATRON® (Mitsubishi Chemical Advanced Materials) and ULTEM™ (SABIC).
The name PEI reflects its chemical structure: “ether” bonds enhance processability, while “imide” bonds improve heat resistance and durability. Standard PEI is amber and transparent, while grades filled with glass, PTFE, or carbon fiber are opaque and typically appear in colors such as light brown, black, or gray.
Key Properties
Feature | Description |
|---|---|
Electrical Insulation | Provides stable performance across wide temperature and frequency ranges. |
High Heat Resistance | Continuous service temperature up to 170 °C, glass transition point 216 °C. |
Weather and Radiation Stability | Resists UV exposure and repeated sterilization through radiation. |
Chemical Resistance | Strong resistance to acids and alkalis; some organic solvents may still degrade material. |
Excellent Formability | Compatible with injection molding, extrusion, thermoforming, and machining. |
Low Smoke and Non-Toxic Combustion | Burns with minimal smoke and toxic gases. |
Dimensional Stability | Maintains shape and size under temperature and humidity changes. |
Wear Resistance | Provides solid wear resistance; non-crystalline structure may limit heavy wear applications. |
Applications
PEI’s exceptional combination of heat resistance, flame retardancy, chemical stability, and mechanical strength makes it suitable for multiple industries:
Medical: Precision components that require repeated sterilization.
Food-Contact Components: Oil-resistant and easy-to-clean surfaces.
Automotive: Engine components and carburetor parts.
Electronics & Semiconductors: Connectors, housings, and electrical components.
Aerospace: High-strength and flame-resistant components.
Machining Considerations
When machining PEI, careful attention is required due to its hardness and notch sensitivity:
Internal Corners: Avoid sharp corners to prevent chipping, cracking, or fractures; use rounded corners.
Burr Formation: Optimize tool selection and feed rates to minimize finishing work.
Fine Features: Small holes or narrow grooves should be machined at slower speeds and lower feed rates.
Bonding: Solvent bonding is not suitable; mechanical fastening or adhesives must be used instead.
Nominal Dimension Tolerances (mm)
PEI tolerances vary by grade and part size:
Nominal Dimension Range (mm) | Grade 1 (mm) | Grade 2 (mm) |
|---|---|---|
1–16 | ±0.1 | ±0.3 |
16–40 | ±0.2 | ±0.6 |
40–63 | ±0.3 | ±0.8 |
63–100 | ±0.4 | ±1.0 |
100–160 | ±0.5 | ±1.2 |
160–250 | ±0.6 | ±1.4 |
250–400 | ±0.7 | ±1.7 |
400–630 | ±1.0 | ±2.0 |
630–1000 | ±1.5 | ±2.5 |
Stock Availability
PEI is readily available in standard sheets and rods, with options for special grades:
Sheets: 6–50 mm thick, 300–1200 mm long.
Rods: 6–152 mm diameter, 300–1200 mm long.
Special Grades: Glass-fiber reinforced and conductive PEI are available upon request.
Standard stock allows for quick delivery, though lead times may be required for certain grades. Slight color changes over time do not affect performance.
PEI CNC Machining at Yumoto Electric
Yumoto Electric delivers high-quality components fast, worldwide. We provide precision machining for a wide range of engineering plastics, including PEEK, PPS, MC Nylon, and POM.
If you’re unsure about material selection or machining methods, we offer complimentary consultations to help optimize your design and production. For any questions, please feel free to contact us.
We support R&D teams