Understanding PEEK Injection Molding

When you’re working with tough jobs that need strong, reliable plastic, PEEK might be what you’re looking for.

PEEK stands for Polyether Ether Ketone. It’s part of a group called engineering thermoplastics. These are plastics that can take high heat, handle strong chemicals, and keep their shape under pressure. PEEK is one of the top materials in this group. It’s often used in aerospace, automotive, medical, and electronics industries.

Injection molding is the process of melting plastic, then forcing it into a mold to form a part. When done right, it’s fast and efficient. But with PEEK, it’s a bit more complex. Because PEEK is so strong and heat-resistant, it needs special equipment and precise control to mold correctly. Still, the benefits make it worth the extra effort.

Let’s start with the basics.

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What is PEEK Plastic?

PEEK is short for Polyether Ether Ketone. It’s a semi-crystalline plastic. That means part of its structure is ordered like a crystal, which gives it extra strength and heat resistance.

The name comes from its molecular structure. It has ether (–O–) and ketone (–C=O) bonds. These bonds make it both flexible and tough.

PEEK was first made in 1977. By 1981, it was being produced for use in industries. It’s part of a family of plastics called PAEK (Polyaryletherketone). PEEK is the most used and best known in that group.

What makes PEEK special is where it stands among other plastics. Think of it like this: if plastics were a ladder, PEEK would be near the top. It performs better than most plastics in harsh conditions.

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Key Material Properties of PEEK

PEEK’s value comes from its properties. Here’s what it can do:

• Handles high temperatures:
  • Glass transition temp (Tg): ~143°C
  • Melting temp (Tm): ~343°C
  • Can work non-stop at 250°C
  • With 30% glass fiber, heat deflection temp can reach 316°C
  • Works in steam and high-pressure water up to 300°C
• Chemical resistance:
  • Resists most chemicals
  • Not affected by oils, greases, fuels, or solvents
  • Avoid concentrated sulfuric acid
• Strong and tough:
  • High strength and stiffness
  • Impact-resistant
  • Good fatigue resistance (holds up under repeated stress)
• Wear-resistant and self-lubricating:
  • Great for parts that slide or rotate
  • Even better with added fillers
• Safe for the body and tools:
  • Biocompatible (safe for contact with human tissue)
  • Can be sterilized many ways: autoclave (up to 134°C), gamma rays, dry heat, ethylene oxide
• Electrical insulation:
  • Works well across a range of temps and frequencies
• Low flammability:
  • UL 94V-0 rated — self-extinguishing without added flame retardants
• Resists water damage:
  • Very low water absorption
  • Keeps shape in steam and moisture
• Holds its shape:
  • Low shrinkage
  • Resists changes from heat or moisture
• Creep resistance:
  • Keeps performance under long-term load
• Radiation resistance:
  • Handles gamma radiation up to 1100 Mrad (much higher than many plastics)
• Low smoke and gas release:
  • Meets BSS 7239 standards for low toxicity

Sources: Victrex, Solvay, Plastics Technology

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Common PEEK Grades and Variations

PEEK doesn’t come in just one type. There are different grades for different jobs:

• Unfilled (“G”)
  • Pure PEEK
  • Good flexibility and toughness
• Glass fiber filled (“GL”)
  • Stronger and stiffer
  • Less flexible
  • Higher heat resistance
• Carbon fiber filled (“CA”)
  • Even higher stiffness
  • Lower weight
  • Good thermal and electrical properties
• Pigmented grades
  • Add color
  • May reduce some strength or flexibility

Each type has trade-offs. You choose based on what your part needs to do.

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Want help deciding which PEEK grade works for your part?

The PEEK Injection Molding Process

PEEK (Polyether Ether Ketone) is not like most plastics. It’s strong, stable, and performs well in extreme conditions. But molding it isn’t easy. To get good results, you need the right setup and tight control over the process.

Why PEEK Injection Molding is Challenging

You can use standard injection molding machines for PEEK, but only if they’re set up correctly.

PEEK melts at very high temperatures and is thick (high viscosity) when molten. This makes it hard to fill fine details or thin parts.

To get the best from PEEK, it must form crystals in the right way. That needs exact control of the mold temperature.

If the temperature is too high or the plastic stays in the machine too long, PEEK can degrade or even cross-link (a chemical reaction that ruins flow).

PEEK is expensive. So mistakes cost more. Even one bad part can mean real losses.

What Makes PEEK So Expensive?

PEEK is costly because of how it’s made and processed. Here’s why:

• Needs pure raw materials and strict chemical processes.
• Polymerization (the process of making the plastic) happens in oxygen-free, high-heat environments.
• Processing demands special tools, such as temperature-resistant screws and molds.
• Developing new PEEK types takes a lot of research and testing.
• It’s usually made in small batches and in many special versions.
• There are few suppliers, so prices stay high.
• Parts often need tight tolerances and extra steps after molding.

Essential Processing Considerations and Parameters

Equipment and Tooling

You’ll need a high-heat injection molding machine. It should control temperature accurately and apply enough force to close the mold tight.

The screw inside the machine must resist heat over 350°C. Avoid copper parts—they react with PEEK.

All equipment must be clean. PEEK is sensitive to contamination. Use high-temp purge compounds like Asaclean before switching materials.

Molds must be steel that holds up to heat, like H13 or S136. Use oil heaters or electric plates to keep the mold hot. Insulation around the mold helps hold temperature steady.

Drying the Material

PEEK absorbs moisture from the air, which can cause problems like streaks or bubbles.

Before molding, dry it at 150°C–160°C for 2–4 hours (or longer if needed). Use a dryer that keeps air dry (dew point below -40°C).

Store the material in airtight containers to keep it dry.

Mold Design Tips

Design the mold to avoid common problems like warping or cracking.

• Runner system: Keep runners short and wide to fill the part easily.
• Gates: Use large gates. Tab, side, or fan gates are good. Avoid small or long narrow gates.
• Draft angles: Use at least 0.5°–2° to help with part removal.
• Cold slug wells: These trap solidified material before it reaches the part.
• Wall thickness: Stick to 1–3 mm. Thinner is okay if the part is strong enough.
• Corners: Avoid sharp ones. Use radii at least 25% of wall thickness.
• Tolerances: You can get tight fits (like ±0.05%), but mold design and heat control matter.
• Shrinkage: Plan for it. Unfilled PEEK shrinks 1–1.8%, while filled types shrink less.

Key Processing Parameters

• Barrel Temperature: Keep it between 360°C–400°C. Too hot (>410°C) and it might degrade.
• Mold Temperature: Must stay hot (170°C–200°C) to build strong crystals. This is key to PEEK’s strength.
• Injection Pressure: Use 800–1500 bar (8–15 MPa). Adjust speed and temperature to reduce pressure if needed.
• Holding Pressure: Prevents voids and sink marks.
• Back Pressure: Removes air and keeps the melt consistent.
• Injection Speed: Fast enough to fill, slow enough to avoid defects. High screw speeds may cause streaks.
• Cooling: Needs to be controlled. Fast cooling can cause stress. Too slow, and crystals can grow too large.

Timing Details

• Dwell time in barrel: Don’t leave PEEK hot for over 15 minutes.
• Drying time: Typically 2–8 hours, depending on material state.
• Injection and hold times: Around 6–8 seconds per part, but varies.
• Cooling time: Controlled cooling (often ~35 seconds) helps avoid warping.

Common Problems and How to Solve Them

Cold Material (Cold Slugs)

Cause: Melt solidifies too early due to cold spots or contact with air.
Fix: Use cold slug wells. Set up proper suck-back timing. Keep nozzle/mold hot enough.

Silver Streaks

Cause: Moisture or gas in the melt.
Fix: Dry thoroughly to <0.02% moisture. Keep drying temp at 150°C+. Vent mold properly.

Gas Voids (Porosity)

Cause: Poor mold design, trapped air, or low pressure.
Fix: Add vents. Adjust mold to avoid dead zones. Raise injection pressure if needed.

Warping

Cause: Uneven cooling, poor part design, or too much filler.
Fix: Use uniform wall thickness. Avoid sharp bends. Balance temperature and pressure.

Other Issues

• Weld lines: Where flows meet, can weaken the part.
• Short shots: Part isn’t fully filled. Often a venting or flow issue.
• Sink marks: Low holding pressure or thick spots.
• Cracking: Stress from poor cooling or design flaws.
• Contamination: Dirty equipment or regrind can cause black spots.
• Surface abrasion: Often from too high injection pressure.
• Bubbles: Too much pressure can trap gas.

Cooling and Post-processing

Cooling Process

Use slow and even cooling. Keep the mold temperature steady to help PEEK form crystals. This step is key for strong parts.

Post-processing

Some PEEK parts need extra work like cutting, grinding, or polishing.

Large gates may leave marks that need to be cleaned up. PEEK can be machined and polished easily without harming the material.

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Applications and Benefits of PEEK Injection Molding

PEEK stands for polyether ether ketone. It’s a type of plastic known for being very strong, heat-resistant, and safe for the body. Even though it’s harder to mold than regular plastics, it’s worth it when you need something that can handle tough jobs.

Core Advantages of PEEK Injection Molding

Using injection molding to shape PEEK has many benefits. Injection molding is when melted plastic is pushed into a mold to create a part. With PEEK, this process can make parts that are strong, clean, and last a long time.

Here’s why PEEK is so useful:

• Handles high heat (up to 250°C or more)
• Strong and stiff (good mechanical properties)
• Safe for medical use (biocompatible)
• Doesn’t react with most chemicals (chemical resistance)
• Lighter than metal but still very tough
• Keeps its shape well (dimensional stability)
• Doesn’t wear out quickly (wear resistance)
• Releases very little gas, even in space (low offgassing)
• Easier than other methods for making complex shapes

Source: Victrex, a major PEEK supplier (victrex.com).

Key Application Areas

Because of these benefits, PEEK is used in many industries. It often replaces metal or ceramic parts where strength and temperature resistance are needed.

Aerospace

• Used in aircraft interiors, engine parts, and brackets
• Replaces metal to reduce weight
• Handles heat and pressure well

Medical

• Used for spinal cages, surgical tools, and dental parts
• Safe inside the human body
• Can be cleaned using high heat (sterilized)

Automotive

• Found in engine parts, seals, and sensors
• Stands up to friction and heat
• Helps make cars lighter and more fuel-efficient

Oil & Gas

• Used in tools, pumps, and valve parts
• Can take on high pressure, heat, and chemicals
• Lasts longer in tough environments

Electronics and Semiconductor

• Found in circuit boards, switches, and connectors
• Excellent at insulating and staying stable over time
• Used where clean materials are needed (like chip-making)

Industrial Machines

• Used in gears, seals, and pistons
• Doesn’t wear out fast
• Handles high loads and tough jobs

Office Equipment

• Found in copiers, gears, and bearings
• Lightweight and doesn’t need oil to run smoothly

PEEK is also used in many other special areas where metal or ceramic used to be the only choice. It keeps working even in harsh, high-temperature, or chemically aggressive conditions.

Sustainability and Partnering in PEEK Injection Molding

When you’re working with PEEK (short for polyether ether ketone), it’s important to think about both the environment and who you team up with. This high-performance plastic has some real benefits—not just in how strong it is, but in how it supports cleaner, more efficient manufacturing. It also needs the right kind of handling. Let’s break that down.

Sustainability Considerations

PEEK helps support sustainability in a few clear ways:

• It’s strong and lasts a long time. This means fewer broken parts and fewer replacements over time.
• Because it doesn’t wear out easily, it helps save raw materials and energy over the product’s life.
• PEEK creates less waste. Some companies even collect and reuse scrap pieces and leftover material (called sprues) through internal recycling systems.
• It’s recyclable, especially when sorted and processed in a controlled setting.
• Using PEEK in place of metal can lower the weight of parts. This saves fuel in things like cars or airplanes, cutting down on carbon emissions.
• PEEK fits well with eco-friendly goals, like using fewer resources and creating less pollution during production.

By choosing PEEK, you’re picking a material that supports long-term environmental goals and helps reduce your impact.

The Value of Experienced Partners

PEEK is not a beginner-level plastic. It needs special tools, machines, and know-how. That’s why it’s smart to work with people who’ve done this before.

Experienced partners can:

• Give advice early in the process (DFM, or design for manufacturability, means helping you make your design easier to mold and cheaper to produce).
• Help improve the mold design and make sure the finished part is accurate and clean.
• Use special tools and machines that are built to handle PEEK’s high temperature and pressure needs.
• Offer custom blends or grades of PEEK that are best suited for your use.

Here are a few trusted names in the field:

• Victrex – Makes high-quality PEEK resin and supports sustainable applications.
• Ensinger – Over 30 years of PEEK molding, with global locations and over 50 million parts made each year.
• Protolabs – Offers fast, digital manufacturing and connects you to a network of trusted molders.
• Fictiv – Another digital partner with expert DFM support and vetted suppliers.
• FOW Mould – A full-service shop with more than 40 years of experience in tooling and injection molding.

Working with the right team means fewer problems and better results. They can guide you through the process, from design to finished part.

Would you like help choosing a partner for your project?