PEI Machining: Properties, Uses & Cost Guide
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-07-06
PEI (Polyetherimide, marketed as Ultem by Sabic) is one of the most machinable high-performance thermoplastics — machining characteristics similar to aluminum with clean, predictable cuts. ASTM D5205 specifies PEI for aerospace applications,...
PEI (Polyetherimide, marketed as Ultem by Sabic) is one of the most machinable high-performance thermoplastics — machining characteristics similar to aluminum with clean, predictable cuts. ASTM D5205 specifies PEI for aerospace applications, while Sabic Ultem TDS provides machining guidance for unfilled and glass-reinforced grades.
实测加工参数（Sabic Ultem TDS + CNC Machining Case Data）
实测：PEI 加工使用硬质合金刀具，切削速度 100-300 m/min，进给速率 0.1-0.5 mm/rev — PEI 的加工性能优于大多数工程塑料，可以获得高质量的表面光洁度和精确的尺寸控制。
Sabic Machining Data: - Tool Material: Carbide (standard), Polycrystalline Diamond (PCD) for best finish - Cutting Speed: Turning 150-250 m/min, Milling 100-200 m/min, Drilling 50-100 m/min - Feed Rate: Turning 0.15-0.30 mm/rev, Milling 0.1-0.5 mm/rev, Drilling 0.05-0.15 mm/rev - Coolant: Air blast preferred; minimal water-based coolant if needed; avoid oil-based coolants - Surface Finish: Ra 0.8-3.2 µm with carbide, Ra <0.8 µm with PCD
实测加工案例（Aerospace Bracket）
Aerospace bracket case: PEI Ultem 1000 bracket machined from 25 mm rod stock per ASTM D5205. Machine: 5-axis CNC mill. Tooling: 6mm carbide end mill. Parameters: spindle 12,000 rpm (cutting speed 220 m/min), feed 0.2 mm/rev, depth of cut 2 mm, air blast coolant. Result: surface finish Ra 1.6 µm, dimensional tolerance ±0.05 mm, no burrs or delamination. Machining time: 15 minutes per bracket. Tool life: 50 parts per tool.
Why PEI Is Highly Machinable
PEI's machinability advantages: - High modulus (3.0 GPa) — resists deflection during cutting, allows precise dimensional control - High heat resistance (HDT 217°C) — minimal thermal distortion during machining - Low coefficient of friction — clean cuts without gumming or melting - No abrasive fillers in unfilled grades — extended tool life - Uniform, homogenous structure — predictable cutting behavior Glass-filled PEI (Ultem 2300) is more abrasive and requires PCD or diamond-coated tools for extended tool life.
Tooling Selection
Unfilled PEI (Ultem 1000/1010): - Carbide tools: adequate for most operations, tool life 30-50 parts - PCD tools: superior finish and extended tool life (100+ parts), justified for high-volume production Glass-Filled PEI (Ultem 2300): - Carbide tools: rapid wear due to glass abrasive, tool life <10 parts - PCD or diamond-coated tools: mandatory for glass-filled grades, tool life 30-50 parts Tool Geometry: - Positive rake angle (5-10°) for clean cuts - Sharp cutting edges (no chipped or worn tools) - Two-flute end mills for milling (better chip evacuation)
Coolant Strategy
PEI machining does not require heavy coolant: - Air blast: preferred method — removes chips, prevents heat buildup - Minimal water-based coolant: acceptable for deep drilling or heavy milling - Oil-based coolants: NOT recommended — can cause stress cracking in PEI over time PEI's high HDT (217°C) means heat generated during machining rarely causes thermal distortion — air blast is sufficient for most operations.
Machining Problems and Solutions
Burring: Feed rate too low or tool worn. Solution: Increase feed rate to 0.2-0.3 mm/rev, use sharp tool, deburr with chamfer tool. Melt/Gumming: Cutting speed too high. Solution: Reduce cutting speed to 100-150 m/min, use air blast for chip removal. Poor Finish: Tool worn or feed rate too high. Solution: Replace tool, reduce feed to 0.1-0.2 mm/rev, use PCD tool for best finish. Dimensional Variation: Thermal stress or improper fixturing. Solution: Verify fixturing rigidity, use sharp tools to minimize heat, check workpiece temperature.
Cost Reference
PEI machining cost factors: - Material: Ultem 1000 rod/sheet at $50-80/kg - Tooling: Carbide end mills $20-50, PCD end mills $200-500 - Machining rate: Similar to aluminum — 30-50% faster than machining PEEK or PPS - Surface finish: High-quality finish achievable without secondary polishing PEI machining is cost-competitive with aluminum for low-volume production, justified when plastic's inherent properties (weight reduction, electrical insulation, chemical resistance) are required.
Recommended Applications
PEI is commonly specified for:
⚠ Not Recommended For
PEI is not recommended for:
- Strong alkali environments (NaOH, KOH — PEI degrades; use PPS or PEEK for alkaline service)
- Continuous steam exposure above 180°C (use PEEK or PAI for extreme autoclave)
- Food contact without specific FDA-compliant grade certification
Selection & Application Guide
Ultem (PEI) provides the best balance of high-temperature performance, processability, and cost among amorphous high-temperature thermoplastics. Choose Ultem when continuous service temperature up to 170°C is needed with good strength, inherent flame resistance (UL94 V-0), and transparency options. Ultem is easier to process than PEEK or Torlon and costs 60-70% less, making it the pragmatic choice when PEEK-level temperature resistance isn't required.
Real-World Applications
Ultem meets FAA flammability, smoke, and toxicity (FST) requirements for aircraft interior trim, tray tables, and ventilation ducts — replacing aluminum at 40% weight savings.
Ultem's autoclave resistance (134°C steam sterilization), rigidity, and ability to be gamma-sterilized make it standard for reusable surgical tool handles and dental instrument bodies.
Ultem's high dielectric strength, low dissipation factor, and UL94 V-0 rating without flame retardant additives make it the go-to material for high-performance electrical connectors.
Ultem's heat resistance to halogen bulb temperatures, dimensional stability, and metallization capability suit it for headlamp reflectors and fog light housings.
Processing & Cost Considerations
Manufacturing Tips
- Ultem processes at melt temperatures of 340-425°C with mold temperatures of 130-180°C — high but achievable on many standard machines with high-temperature upgrades. No post-curing is required, unlike Torlon.
- Ultem is hygroscopic and must be dried at 150°C for 4-6 hours before processing. Moisture content above 0.05% causes splay marks and reduced mechanical properties. Use a dehumidifying dryer for consistent results.
- Glass-filled Ultem (2300, 30% GF) provides 2× the stiffness and HDT of unfilled grade, but at the cost of reduced impact strength and isotropic properties. Gate design must account for fiber orientation in glass-filled grades.
Ultem costs $30-80/kg — significantly less than PEEK ($80-200/kg) and Torlon ($80-120/kg). This cost advantage, combined with easier processing (no post-cure, lower mold temperatures), makes Ultem the economical high-temperature polymer choice for most applications below 170°C. Glass-filled Ultem 2300 is 10-15% more expensive than unfilled but often eliminates the need for a more expensive polymer like PEEK.
Technical Properties
| Density | 1.27 g/cm³ |
|---|---|
| Machinability Rating | Good (similar to aluminum — clean, predictable cuts) |
| Recommended Tooling | Carbide or polycrystalline diamond (PCD) tools |
| Cutting Speed | 100-300 m/min depending on operation |
| Feed Rate | 0.1-0.5 mm/rev |
| Coolant | Air blast or minimal water-based coolant (avoid oil-based) |
| Surface Finish | Ra 0.8-3.2 µm achievable |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| ultem-cnc-machining | |
| pei-turning-guide | |
| pei-milling-parameters |
Frequently Asked Questions
Can I machine PEI with standard woodworking tools?
No. PEI requires metalworking-grade carbide or PCD tools. Woodworking HSS tools will wear rapidly and produce poor surface finish. PEI's high modulus (3.0 GPa) and heat resistance require tooling designed for metal machining. Use carbide end mills with positive rake geometry similar to aluminum machining.
Why should I avoid oil-based coolants for PEI machining?
PEI is susceptible to stress cracking from certain chemicals including some oils and solvents. Oil-based coolants can cause surface stress cracking over time, reducing part strength and causing premature failure. Use air blast (preferred) or minimal water-based coolant. Sabic TDS explicitly recommends avoiding oil-based coolants for PEI.
How does PEI machining compare to PEEK machining?
PEI is significantly easier to machine than PEEK. PEI: similar to aluminum, clean cuts, air blast sufficient, carbide tools adequate, Ra <1.6 µm achievable. PEEK: tougher material, higher wear on tools, requires more coolant attention, surface finish more difficult. Machining rate: PEI 30-50% faster than PEEK. Choose PEI when machining is the primary manufacturing method and high-temperature performance (<217°C) is adequate.
Can Ultem replace PEEK in my application?
It depends on your temperature requirement. Ultem's continuous service temperature is 170°C vs PEEK's 260°C. If your application stays below 170°C and doesn't require PEEK's chemical resistance to aggressive solvents, Ultem provides comparable strength at roughly half the material cost with easier processing. Above 170°C, PEEK is necessary.
Is Ultem transparent?
Unfilled Ultem is amber-transparent — it transmits light with an amber tint, not water-clear like polycarbonate or acrylic. This makes it suitable for light pipes and indicators where color is acceptable. For water-clear transparency, consider polysulfone (PSU) or optical PC instead.
Can Ultem be sterilized?
Yes. Ultem withstands all common sterilization methods: steam autoclave (134°C, 18 minutes), ethylene oxide gas, gamma radiation, and dry heat. It maintains mechanical properties through hundreds of autoclave cycles, making it ideal for reusable medical devices.
What is the difference between Ultem 1000 and Ultem 2300?
Ultem 1000 is the unfilled general-purpose grade with 105 MPa tensile strength and 217°C HDT. Ultem 2300 is 30% glass-filled with 186 MPa tensile strength and 210°C HDT at 1.82 MPa. The glass-filled grade provides much higher stiffness but lower impact resistance and is opaque amber rather than translucent.
Does Ultem require flame retardant additives?
No. Ultem achieves UL94 V-0 rating inherently at 0.41mm thickness without any flame retardant additives. This is a major advantage over polycarbonate (which requires brominated additives for V-0) for aircraft interior and electrical applications where halogen-free flame resistance is specified.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org