PEEK Injection Molding: What You Need to Know

Introduction

If you’re struggling to mold complex, high-performance parts that can withstand extreme heat, chemicals, or stress, PEEK might be the answer—but only if you know how to work with it.

PEEK (Polyether ether ketone) is one of the toughest thermoplastics available, but it’s also one of the hardest to mold. That’s why many engineers and manufacturers face defects, high scrap rates, or inconsistent quality when using it.

This guide walks you through what PEEK is, why it’s different, how to mold it properly, common issues to avoid, and where it’s used. If you’re thinking about using PEEK, this is what you need to know to get it right.

I. Understanding PEEK Material

A. What Is PEEK?

PEEK stands for Polyether Ether Ketone. It’s a type of plastic.

But it’s not your average plastic. PEEK belongs to a group called PAEK (Polyaryletherketone), known for being high-performance and semi-crystalline. That means it has an ordered structure that gives it special strength and heat resistance.

PEEK was first made in 1977. It became available for industrial use in 1981.

Compared to regular plastics, PEEK is at the top of the pyramid. It can cost up to 20 times more than standard engineering plastics. But many industries still use it because it performs better under tough conditions.

B. Key Properties of PEEK

Here’s what makes PEEK special:

• Withstands High Heat
  It holds up in high temperatures.
  • Softens at 143°C (Tg)
  • Melts at 343°C (Tm)
  • Can handle 250°C for long periods
  • Can briefly take up to 300°C
• Chemical Resistance
  PEEK stands strong against most chemicals—acids, alkalis, and solvents.
  But it does not do well with strong acids like sulfuric acid or halogens like chlorine and fluorine.
• Strong and Tough
  PEEK is stiff but flexible. It handles stress over time without cracking.
  It also resists wear, holds its shape, and doesn’t shrink much.
• Self-Lubricating
  It slides well, especially when filled with extra materials like PTFE (a slippery additive).
• Safe for the Body
  Medical-grade PEEK can be used inside the body. It’s safe, clean, and can be sterilized over 3,000 times.
• Good for Electronics
  It insulates electricity well, even in heat and at high frequencies.
• Water and Steam Resistance
  PEEK doesn’t break down in hot water or steam.
• Radiation Tolerance
  It can take a lot of gamma radiation—more than polystyrene can.
• Low Flammability and Smoke
  PEEK doesn’t catch fire easily and produces very little smoke or toxic gas.
• Stays Dry
  It absorbs very little water, even in wet, hot environments.
• Strong in Coatings
  PEEK resists peeling, so it’s great for coated wires.
• Viscosity and Shrinkage
  It’s thick when melted, which makes it harder to fill complex mold shapes.
  But it shrinks less than other plastics (0.9%–1.8%).
• Low Thermal Expansion
  It doesn’t expand much with heat, so it holds tight dimensions.

C. Types and Grades of PEEK

PEEK comes in different forms depending on how it’s used:

• Basic Types:
  • Unfilled (pure PEEK)
  • Glass fiber-reinforced (adds stiffness)
  • Carbon fiber-reinforced (adds strength and conductivity)
• Special Types:
  • Anti-static
  • Conductive
  • Wear-resistant
  • High-strength
• Fillers Used:
  • Glass fiber
  • Carbon fiber
  • PTFE
• Colored Grades:
  Black PEEK is common but can weaken mechanical properties.
• Modifications:
  PEEK can be blended or chemically changed to improve performance.

II. PEEK Injection Molding Process

PEEK injection molding isn’t like molding ordinary plastics. It needs special care, the right machines, and strict temperature control. Why? Because PEEK melts at very high temperatures and solidifies quickly.

A. Key Equipment Requirements

You need the right tools for the job. Here’s what matters:

• Injection Machine
  Use a machine that can handle up to 450°C barrel temperatures and high injection pressures. PEEK is thick when melted and needs extra force to fill molds.
• All-Metal Parts
  Everything that touches PEEK must be metal. No rubber seals or plastic parts—they’ll melt or degrade.
• Material Drying
  PEEK must be dry before molding. Moisture causes bubbles, burns, and weak parts.
  • Dry at 150°C for 3–5 hours in a vacuum or dry-air oven
  • Keep moisture below 0.02%
• Hot Runner Molds (optional)
  If using a hot runner system, it needs to handle temperatures up to 400°C. Many hot runners can’t take this, so cold runners are more common.

B. Temperature Control

Temperature is the most critical part of molding PEEK.

Here’s what to control:

• Barrel Temperature
  Set between 370–420°C. Too low? It won’t flow. Too high? It’ll degrade.
• Mold Temperature
  Should be 160–200°C, depending on the part.
  This helps create crystalline structure and better mechanical properties.
• Nozzle Temperature
  Keep it close to the barrel temp: around 400°C.
• Uniform Heating
  Hot spots or cold zones will ruin the part or cause warping.

C. Mold Design Considerations

Designing the mold right makes or breaks your success.

Here’s what to watch for:

• Material
  Use hardened tool steel or stainless steel. PEEK is abrasive—it wears out soft molds fast.
• Ventilation
  Gas must escape fast. Add deep and wide vents (around 0.02 mm). Trapped gas = burns and voids.
• Gate Design
  • Use large gates like fan gates or edge gates.
  • PEEK doesn’t flow easily, so bigger gates help it fill better.
• Ejector System
  Parts shrink tightly on the core. Add strong ejector pins and draft angles of at least 1°–2°.
• Flow Channels
  Keep runners short and thick. Use cold runners unless you have a special hot runner made for PEEK.

II. PEEK Injection Molding Process

PEEK injection molding isn’t like molding ordinary plastics. It needs special care, the right machines, and strict temperature control. Why? Because PEEK melts at very high temperatures and solidifies quickly.

A. Key Equipment Requirements

You need the right tools for the job. Here’s what matters:

• Injection Machine
  Use a machine that can handle up to 450°C barrel temperatures and high injection pressures. PEEK is thick when melted and needs extra force to fill molds.
• All-Metal Parts
  Everything that touches PEEK must be metal. No rubber seals or plastic parts—they’ll melt or degrade.
• Material Drying
  PEEK must be dry before molding. Moisture causes bubbles, burns, and weak parts.
  • Dry at 150°C for 3–5 hours in a vacuum or dry-air oven
  • Keep moisture below 0.02%
• Hot Runner Molds (optional)
  If using a hot runner system, it needs to handle temperatures up to 400°C. Many hot runners can’t take this, so cold runners are more common.

B. Temperature Control

Temperature is the most critical part of molding PEEK.

Here’s what to control:

• Barrel Temperature
  Set between 370–420°C. Too low? It won’t flow. Too high? It’ll degrade.
• Mold Temperature
  Should be 160–200°C, depending on the part.
  This helps create crystalline structure and better mechanical properties.
• Nozzle Temperature
  Keep it close to the barrel temp: around 400°C.
• Uniform Heating
  Hot spots or cold zones will ruin the part or cause warping.

C. Mold Design Considerations

Designing the mold right makes or breaks your success.

Here’s what to watch for:

• Material
  Use hardened tool steel or stainless steel. PEEK is abrasive—it wears out soft molds fast.
• Ventilation
  Gas must escape fast. Add deep and wide vents (around 0.02 mm). Trapped gas = burns and voids.
• Gate Design
  • Use large gates like fan gates or edge gates.
  • PEEK doesn’t flow easily, so bigger gates help it fill better.
• Ejector System
  Parts shrink tightly on the core. Add strong ejector pins and draft angles of at least 1°–2°.
• Flow Channels
  Keep runners short and thick. Use cold runners unless you have a special hot runner made for PEEK.

III. Troubleshooting Common Defects

Even with the right setup, PEEK injection molding can run into problems. Knowing what to look for—and how to fix it—helps you reduce waste and improve quality.

A. Cold Material Marks

What it looks like:
Small, rough, dull spots on the surface.

Why it happens:

• No cold slug well in the mold
• Material touches cooler mold steel or air
• Long contact time at the nozzle
• Big temperature difference in thick areas

How to fix it:

• Add a cold slug well at the end of the runner
• Reduce contact time between gate and nozzle
• Adjust barrel removal timing
• Set up rubber extraction if needed

B. Silver Streaks

What it looks like:
Silver lines or marks, often near the gate.

Why it happens:

• Moisture in the raw material
• High screw speed traps air
• Gases released during plasticizing

How to fix it:

• Dry PEEK to below 0.02% moisture
• Lower screw speed
• Set back pressure to push out trapped gases

C. Warpage or Distortion

What it looks like:
Twisted or bent parts.

Why it happens:

• Uneven cooling
• Different wall thicknesses
• Sharp corners or bends
• Stress inside the part

How to fix it:

• Use uniform wall thickness
• Avoid sharp angles
• Control mold and cooling temperature
• Adjust injection and holding pressure

D. Gas Voids or Porosity

What it looks like:
Bubbles or holes inside the part.

Why it happens:

• Trapped air in flow dead zones
• Not enough venting

How to fix it:

• Add proper venting channels
• Use ultrasonic testing to find hidden voids

E. Fusion Marks

What it looks like:
Visible lines where two melt flows meet.

Why it happens:

• Low melt temperature
• Poor mold temperature control
• Weak venting or slow fill

How to fix it:

• Increase melt and mold temperature
• Boost injection speed
• Improve venting design

F. Nozzle Freezing

What it looks like:
Material blocks the nozzle; nothing flows.

Why it happens:

• Nozzle gets too cold
• Long idle time during production

How to fix it:

• Use beryllium copper tips to keep heat in
• Maintain consistent cycle times

IV. Cost Considerations

PEEK is not a cheap plastic. It costs a lot more than common engineering plastics, but there are reasons for that.

A. PEEK Is Expensive

PEEK can cost up to 20 times more than materials like ABS or nylon. It’s at the top of the polymer “performance pyramid.”

B. Why It Costs So Much

Here are the main reasons:

• Complex production
  PEEK is made under high heat (310–340°C) and oxygen-free conditions. This requires strict controls and equipment.
• Raw materials are costly
  The building blocks are high-purity and hard to make.
• Special processing
  PEEK needs high-temperature barrels, screws, molds, and close temperature control.
• Skilled operators
  Molding PEEK requires experience and tight process control.
• Small batch sizes
  There are many grades and custom requirements. That means fewer economies of scale.
• Tough specs
  Many parts have tight tolerances or complex shapes. That leads to more machining and more labor.
• High R&D cost
  New grades, designs, and mold trials all take time and money.
• Trial phase for customers
  Many users are still testing PEEK, which slows down full-scale production.

C. Comparing with Other Materials

While PEEK seems pricey, it can replace machined titanium or aluminum in small parts. This saves weight and often cuts total cost—especially when parts are made in higher volumes or need fewer finishing steps.

D. Saving Material and Costs

You can lower costs with experience:

• Design parts close to final shape (near-net shape)
• Reuse clean sprues and runners
• Optimize drying and molding to avoid waste
• Machine only where needed

V. Applications of PEEK Injection Molding

PEEK is used when strength, heat resistance, and reliability are critical. It’s often chosen to replace metals or ceramics, especially in tough environments.

A. General Use Cases

You’ll find PEEK in parts that need:

• High strength
• Heat and chemical resistance
• Low wear over time
• Lightweight structure

It’s one of the most popular high-performance plastics in specialized fields.

B. Key Industries and Specific Parts

Here’s how different industries use PEEK:

• Aerospace
  Aircraft engine parts, brackets, clips, interior panels, and even components in rockets.
• Automotive
  Used in engines and transmissions—seals, bearings, clutch rings, gaskets, and brake parts.
• Medical
  Surgical tools, implants, and devices. PEEK is one of the few plastics strong and safe enough to go inside the human body. It also handles sterilization well.
• Electronics / Semiconductors
  PEEK provides electrical insulation. It’s used in circuit boards, wire coatings, connectors, and switch components.
• Industrial
  Found in pumps, seals, gears, and valves. It resists wear and keeps shape under stress.
• Oil & Gas
  Used in downhole tools, seals, and parts exposed to high pressure and chemicals.
• Office Equipment
  Bearings, chains, gears, and separation claws in printers or copiers.
• Wire Insulation
  Covers wires that face heat and chemicals.

C. Why PEEK Works in These Areas

PEEK is often chosen for:

• Light weight
• Long life under stress
• Performance in heat, chemicals, or water
• Reducing part count or replacing metal

VI. Sustainability and Environmental Considerations

PEEK is not just strong and heat-resistant. It can also support sustainability when used the right way.

A. How PEEK Contributes to Sustainability

Because PEEK parts last a long time, you don’t need to replace them often. This reduces waste and lowers the need to make new parts from scratch.

In industries like aerospace and automotive, using lighter parts (like PEEK) can also help lower fuel use. That means less energy consumption and fewer emissions over time.

B. Recyclability

PEEK can be recycled, but it must be done carefully. You can’t mix it with other plastics, and it needs to be kept clean.

Two ways it’s reused:

• Internal recycling (closed loop): Regrind leftover sprues or scrap in the factory.
• External recycling: Use high-quality, unmixed recycled PEEK from outside sources.

C. Resource Efficiency

Using PEEK helps reduce the need for:

• Replacement parts
• Extra processing steps
• Virgin (new) raw materials

That means fewer resources are used over the product’s lifetime.

D. Supports ESG Goals

ESG stands for Environmental, Social, and Governance. Many companies now focus on these goals. Using durable, efficient materials like PEEK helps meet environmental and performance targets.

E. Lightweighting

PEEK helps companies reduce the weight of their parts. This is especially useful in:

• Automotive: Lighter cars use less fuel
• Aerospace: Lower weight helps improve fuel efficiency and payload

Less weight means better efficiency—and a smaller environmental footprint.

VII. Partnering with Manufacturers

Working with PEEK is not easy. It takes the right tools, experience, and deep technical knowledge. That’s why choosing the right injection molding partner matters.

A. Why Skilled Injection Molders Matter

PEEK is tricky to mold. It needs:

• High temperatures
• Careful moisture control
• Precise equipment
• Clean, contamination-free environments

Not all molders are ready for that. You need experts who know how to handle it without wasting material or making bad parts.

B. Design for Manufacturability (DFM)

DFM means designing parts that are easier—and cheaper—to make. Skilled molders can work with your design team to:

• Improve moldability
• Reduce warpage and defects
• Optimize gate locations and part geometry
• Balance quality and cost

Early feedback can save you time and reduce expensive mistakes during production.

C. What a Good Molder Offers

Experienced molders offer more than just the injection process. Look for partners who can provide:

• DFM feedback
• Help with material selection or custom formulations
• CNC machining and secondary operations (like trimming or drilling)
• Cleanroom molding or medical-grade production
• Assembly and testing services
• A network of trusted suppliers and engineers

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Final Thoughts

PEEK injection molding is complex—but the results are worth it. When done right, it creates parts that are strong, light, and built to last. If you’re exploring this material, work with people who truly understand it from start to finish.

conclusion

PEEK (polyether ether ketone) is a high-performance plastic known for its strength, heat resistance, and chemical durability. It belongs to the PAEK family and is used in demanding industries like aerospace, medical, and automotive.

The injection molding process for PEEK requires:

• Careful material drying
• High temperatures (up to 400°C)
• Specialized equipment and mold design
• Tight control of pressure, speed, and cooling
• Clean handling to avoid defects

Although PEEK is expensive, it replaces metals in many cases and reduces weight without sacrificing performance. Choosing the right molder with PEEK experience ensures part quality, efficiency, and lower long-term costs.

If you’re considering PEEK for your next project, start by connecting with a molder who knows the material inside out. The right partner will help you design smarter, manufacture better, and get the most from this powerful polymer.