Introduction
PEEK (polyether ether ketone) is a high-performance plastic. It’s strong, resistant to heat, and holds up well under stress. That makes it a great choice for tough jobs—like medical, aerospace, or automotive parts.
But PEEK isn’t easy to mold. It needs special care, tools, and knowledge. If you don’t get everything just right, defects can show up. In this guide, you’ll learn the most common problems with PEEK molding and how to fix them.
High Melt Temperature and Flow Challenges
PEEK melts at very high temperatures—around 370 to 400°C. Most standard injection machines can’t handle that heat. You’ll need machines made to run at those levels, or the plastic may not melt evenly.
Also, melted PEEK is thick. That makes it hard to flow into every part of the mold. If your mold isn’t designed well, you might see:
- Voids (empty spaces inside the part)
- Weak spots (areas that break under pressure)
To avoid this, you need smooth flow paths and well-placed gates (the entry points where plastic flows into the mold).
Cooling and Crystallinity
After injection, the part needs to cool. If it cools unevenly, PEEK’s internal structure—called crystallinity—will also be uneven. That affects the part’s strength.
PEEK can shrink up to 2.5% as it cools. If your cooling system isn’t balanced, you’ll see:
- Warping (parts that bend or twist)
- Cracking or stress marks
A good mold has even cooling channels and keeps temperature under control during every cycle.
Surface Defects
PEEK can be sensitive to heat damage. If you don’t clean the barrel (the heated part of the machine) between runs, old material can break down and leave marks.
Common surface issues include:
- Burn marks
- Streaks or dark lines
You can avoid these by following strict purging routines. That means clearing out old plastic before you run PEEK. Using a screw (the rotating part that pushes plastic forward) made just for PEEK also helps.
Internal Stress and Post-Processing
If the plastic is injected too fast or cooled too quickly, stress builds up inside the part. That stress might not show right away, but over time it can lead to:
- Warping
- Cracking
- Weak points that fail early
To reduce internal stress, you can adjust:
- Melt temperature
- Injection speed
- Holding pressure
Another key step is annealing, a heat treatment that relieves stress and helps the part stay stable over time.
Key Tips for PEEK Injection Molding
Here are some proven strategies that work:
- Use machines designed for high temperatures
- Design molds with smooth flow paths and balanced cooling
- Always purge before running PEEK
- Use screws made for high-performance materials
- Monitor and adjust speed, pressure, and cooling
- Apply heat treatment (annealing) after molding
Conclusion
Working with PEEK takes skill. It’s not like molding other plastics. But with the right tools and methods, you can get strong, reliable parts every time.
Careful control of temperature, flow, cooling, and post-processing is what makes the difference.
