Introduction: When Standard Plastics Aren’t Enough

Hi, I’m Barry Zeng, a manufacturing engineer at Shanghai Yunyan Prototype & Mould Manufacture Factory. For most applications, ABS, nylon, or polycarbonate work fine. But when you need parts that withstand extreme heat, aggressive chemicals, or high mechanical stress — PEEK and PEI (Ultem) are the gold standards. These high‑performance polymers are used in aerospace, medical implants, oil & gas, and semiconductor equipment. In this guide, I’ll explain why PEEK and PEI dominate high‑performance applications, compare their properties, and provide practical guidance for CNC Machining Plastic Parts from these materials. You’ll learn about their heat resistance, chemical resistance, mechanical strength, and machinability. I’ll also share a case study where we replaced a metal bracket with a PEEK part, saving 70% weight and eliminating corrosion issues. Whether you’re designing for extreme environments or demanding applications, understanding PEEK and PEI will help you choose the right material for CNC Machining Plastic Parts.

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Chapter 1: What Makes PEEK and PEI “High‑Performance”?

PEEK (polyether ether ketone) and PEI (polyetherimide, branded as Ultem) belong to a class of polymers called “high‑performance thermoplastics.” They retain mechanical properties at temperatures where other plastics melt or soften. Key differentiators:

• Continuous use temperature: PEEK up to 250°C, PEI up to 170°C.
• Chemical resistance: Resists hydrocarbons, acids, bases, and solvents.
• Mechanical strength: Tensile strength 90–100 MPa (PEEK) and 50–60 MPa (PEI).
• Flame retardancy: UL94 V‑0 rating — self‑extinguishing.
• Low outgassing: Suitable for vacuum and aerospace applications.

For CNC Machining Plastic Parts in extreme environments, PEEK and PEI are often the only plastics that work.

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Chapter 2: PEEK – The Ultimate High‑Performance Polymer

PEEK is a semi‑crystalline thermoplastic with exceptional thermal and mechanical properties. Key characteristics:

• Tensile strength: 90–100 MPa (similar to aluminum).
• Elongation at break: 20–50% (tough, not brittle).
• Continuous use temperature: 250°C.
• Melting point: 343°C.
• Chemical resistance: Resists almost all organic solvents, acids, and bases.
• Wear resistance: Excellent — used for bearings, seals, and gears.
• Biocompatibility: ISO 10993 certified for medical implants.

PEEK is used in aerospace (brackets, fittings), medical (spinal cages, dental implants), oil & gas (seals, connectors), and semiconductor (wafer handling). For CNC Machining Plastic Parts, PEEK is challenging but rewarding.

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Chapter 3: PEI (Ultem) – The Flame‑Retardant Alternative

PEI (polyetherimide), sold as Ultem by SABIC, is an amorphous thermoplastic. Key characteristics:

• Tensile strength: 50–60 MPa.
• Elongation at break: 5–15% (less ductile than PEEK).
• Continuous use temperature: 170°C.
• Glass transition temperature: 217°C.
• Flame retardancy: UL94 V‑0, low smoke — ideal for aircraft interiors.
• Chemical resistance: Good — resists many acids, fuels, and solvents.

PEI is used in aircraft interiors (seat components, ducting), electrical connectors, and medical devices. It’s easier to machine than PEEK and less expensive (about 50–70% of PEEK cost). For many CNC Machining Plastic Parts requiring high heat resistance but not extreme strength, PEI is the better choice.

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Chapter 4: PEEK vs. PEI – Property Comparison

Property	PEEK (unfilled)	PEI (Ultem 1000)
Tensile strength (MPa)	90–100	50–60
Flexural modulus (GPa)	3.5–4.5	2.0–2.5
Elongation at break (%)	20–50	5–15
Continuous use temp (°C)	250	170
HDT at 1.82 MPa (°C)	150–160	150–160
Density (g/cm³)	1.32	1.27
Relative cost	High ($400–800/kg)	Medium ($200–400/kg)

Choose PEEK when you need maximum strength, temperature resistance, or wear resistance. Choose PEI when you need flame retardancy, good heat resistance, and lower cost.

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Chapter 5: Machining PEEK – Tips for Success

CNC Machining Plastic Parts from PEEK requires careful attention. Here’s what works:

• Tools: Sharp carbide end mills (2 or 3 flutes). Uncoated is fine, but AlTiN coating reduces heat.
• Speeds: 100–300 m/min (lower for larger tools, higher for small tools).
• Feeds: 0.05–0.15 mm/tooth. Maintain chip thickness to avoid rubbing.
• Coolant: Flood coolant or air blast. PEEK is heat‑sensitive — avoid overheating.
• Annealing: Anneal PEEK after machining (200°C for 2–4 hours) to relieve internal stress and prevent cracking.
• Workholding: Use soft jaws or vacuum chucks. PEEK is slippery — don’t rely on clamping alone.

Common mistake: Using dull tools. Dull tools cause heat buildup, melting the surface and creating a “fuzzy” finish.

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Chapter 6: Machining PEI (Ultem) – Tips for Success

PEI is easier to machine than PEEK. For CNC Machining Plastic Parts from PEI:

• Tools: Sharp carbide. Uncoated is fine.
• Speeds: 150–400 m/min (higher than PEEK).
• Feeds: 0.05–0.20 mm/tooth.
• Coolant: Air blast or mist. PEI is less heat‑sensitive than PEEK.
• Annealing: Anneal at 150°C for 2–4 hours to relieve stress, especially for thin parts.

PEI machines cleanly with good surface finish. It’s less prone to melting than PEEK.

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Chapter 7: Applications – Where PEEK and PEI Excel

• Aerospace: Brackets, fasteners, ducting, interior panels (PEI for flammability, PEEK for high temp).
• Medical: Spinal cages, dental implants, surgical instruments (PEEK for biocompatibility).
• Semiconductor: Wafer handling components, chamber liners (PEEK for purity, chemical resistance).
• Oil & gas: Seals, backup rings, connectors (PEEK for high pressure, temperature).
• Electrical: Connectors, insulators (PEI for dielectric strength).

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Chapter 8: Case Study – Metal Replacement with PEEK

A semiconductor equipment manufacturer needed a bracket that could withstand 200°C and aggressive plasma cleaning. The original was 6061 aluminum, but aluminum corroded in the plasma environment. We proposed PEEK. The CNC Machining Plastic Parts from PEEK weighed 70% less than aluminum, resisted corrosion, and withstood 250°C. The bracket cost 3× more than aluminum, but eliminated replacement every 6 months. Over 2 years, PEEK saved $50,000 in downtime and replacement parts.

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Chapter 9: Cost Considerations – Is Premium Worth It?

PEEK and PEI are expensive. PEEK raw material: $400–800/kg. PEI: $200–400/kg. Compare to ABS ($5/kg) or aluminum ($5/kg). But the total cost of ownership often favors high‑performance plastics when:

• Metal parts corrode or fail prematurely.
• Temperature exceeds 120°C (where most plastics soften).
• Weight reduction is critical (aerospace, drones).
• Chemical resistance is required.

For CNC Machining Plastic Parts in demanding environments, the premium is justified.

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Chapter 10: Summary – PEEK vs. PEI Decision Matrix

• ☐ Need continuous use >170°C? → PEEK.
• ☐ Need maximum strength (90–100 MPa)? → PEEK.
• ☐ Need wear resistance (bearings, seals)? → PEEK.
• ☐ Need UL94 V‑0 flame retardancy? → PEI (or PEEK also V‑0).
• ☐ Budget is limited? → PEI.
• ☐ Need easier machining? → PEI.

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Conclusion: Choose PEEK or PEI for Extreme Performance

PEEK and PEI are the gold standards for high‑performance plastic parts. PEEK offers superior strength, temperature resistance, and wear properties. PEI offers excellent flame retardancy at a lower cost. We specialize in CNC Machining Plastic Parts from both materials. Send me your CAD file and application requirements. I’ll recommend PEEK or PEI, provide a free DFM report, and quote your project — within 24 hours. Let’s machine the parts that other shops can’t.

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👇 Need High‑Performance Plastic Parts – PEEK or PEI?

Send me your CAD file and application temperature/strength needs. I’ll recommend PEEK or PEI — and provide a free DFM report and quote within 24 hours.

Not sure whether to use PEEK or PEI? Just say: “Barry, here’s my part and operating temperature — which polymer?” I’ll guide you.

🔧 CNC Machining Plastic Parts — PEEK & PEI Excellence 🔧

P.S. Mention “PEEK guide” when you email, and I’ll send you a machining parameters chart and a material selection flowchart.

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Barry Zeng
Senior Manufacturing Engineer, Shanghai Yunyan Prototype & Mould Manufacture Factory
(10+ years machining PEEK and PEI for aerospace, medical, and semiconductor. Let me help you choose the right high‑performance plastic.)