Introduction
Making strong, reliable parts from PEEK (Polyether Ether Ketone) takes more than just the right material.
You also need a smart mold design, careful process control, and the right post-processing steps.
If any of these areas are weak, you can end up with warped, cracked, or misshaped parts. This article explains how all three areas must work together to get the best results.
Mold Design: The Foundation
PEEK is tricky to mold. It flows thick (high viscosity) and shrinks more than other plastics—up to 2.5%.
To avoid problems, you need a mold designed for PEEK’s unique behavior.
That means:
- Using gates (entry points for melted plastic) and runners (flow paths) that match PEEK’s flow rate
- Keeping walls the same thickness to help with even cooling
- Adding draft angles (small slopes on vertical walls) so parts come out cleanly
- Including strong cooling systems to prevent uneven shrinkage
Most PEEK parts need draft angles between 2° and 4° to reduce ejection force and avoid damage. If the angles are too small, the part can stick and deform during removal.
Real-Time Process Control
Even with a great mold, PEEK won’t mold well if the process is off.
You need to watch and control the injection process in real time. This includes:
- Keeping melt temperature between 370°C and 400°C
- Holding barrel temperatures steady at around 380–400°C
- Using injection pressures between 800 and 1400 bar to fill the mold properly
- Monitoring cycle times, mold temperature, and cooling rate
Too much heat can break down the material. Too little pressure can leave voids or incomplete parts.
Using sensors to monitor temperature and pressure helps you catch issues before they become defects.
Controlling Cooling for Crystallinity
PEEK is semi-crystalline, which means how fast it cools affects its strength and shape.
To control this, use water-temperature control units or mold temperature controllers. These tools help manage how quickly the part cools down and sets.
Fast or uneven cooling leads to stress inside the part, causing warping or cracking later.
Post-Processing: Heat Treatment and Machining
Even with a perfect mold and tight process control, internal stress can still build up in PEEK parts.
To fix this, use annealing—a type of heat treatment that slowly heats and cools the part.
Annealing usually happens at 180–220°C, between PEEK’s glass transition point and melting point. This process lets the molecules settle into place, reducing stress and improving shape stability.
Once annealing is done, you can safely machine the part to tighter tolerances. At this stage, the part won’t deform as easily during cutting.
Quality Control
Every step needs to be double-checked. After molding, parts should go through:
- First-article inspections (a detailed check of the first piece)
- CMM (coordinate measuring machine) checks for accurate dimensions
- Visual inspections, sometimes under magnification, to spot small surface flaws
- Biocompatibility testing if the part is used in medical devices
For sensitive applications, it’s also important to keep full traceability of materials and process settings.
Summary Checklist
Here’s how you can reduce common PEEK molding problems:
- Design molds with correct gate placement, wall thickness, cooling, and 2–4° draft angles
- Maintain melt temps of 370–400°C and monitor pressure, time, and cooling rates
- Use mold temperature controllers to manage crystallinity
- Anneal parts at 180–220°C before machining
- Inspect each part using CMM and visual tools, with traceability and documentation
Conclusion
Making high-quality PEEK parts takes careful planning from start to finish.
When mold design, molding process, and post-processing all work together, you get stronger, more reliable parts that hold up in tough applications.
