Introduction
PEEK (Polyether Ether Ketone) is a tough, heat-resistant plastic used in demanding fields like aerospace and medical.
But molding PEEK isn’t easy. It needs careful planning—especially in how the mold is designed.
If the mold design isn’t right, you can run into serious problems. Parts may stick, warp, or crack. The mold itself may even wear out too fast.
This guide breaks down what you need to focus on to design better molds for PEEK.
Why PEEK Needs Special Mold Design
PEEK melts at very high temperatures—between 370°C and 400°C. It also shrinks up to 2.5% as it cools.
That means the mold has to be able to handle heat, pressure, and shrinkage.
Gate and runner designs (the paths the melted plastic takes to fill the mold) must be adjusted to PEEK’s flow behavior. If not, the part might have weak spots or air pockets.
Draft Angles: Small Detail, Big Impact
A draft angle is a slight slope added to vertical surfaces of a molded part. It helps the part come out of the mold smoothly.
For PEEK, you should aim for 2–4 degrees of draft. That helps reduce friction during ejection. Less friction means less damage to the part and the mold.
Even a small draft angle—like 0.5°—is better than none.
Without enough draft:
- Parts can warp or crack during removal
- The mold surface can get scratched or worn
- The ejection system has to work harder, adding stress to both mold and machine
Shrinkage, Crystallinity, and Cooling
PEEK is semi-crystalline, meaning how it cools affects its strength and shape.
Uneven cooling causes uneven crystallinity. That can lead to weak areas or unwanted stress inside the part.
Good mold design manages this by:
- Placing gates in the right spot to control flow
- Keeping wall thickness even across the part
- Adding cooling channels to control how the part cools down
These steps help the part stay strong and stable after molding.
Handling Complex Part Designs
Some parts have features like deep holes, sharp corners, or textured surfaces. These details make it harder for the part to come out of the mold.
For these cases, you’ll need more draft angle—sometimes 5° or more.
For textured surfaces, add 1° for every 0.001 inch of texture depth. This keeps the texture from getting scraped off during ejection.
Also, make sure features like ribs or gussets (support structures) have draft. Any area that touches the mold surface needs it.
Why All of This Matters
Getting the draft angles right:
- Helps the part come out clean
- Reduces wear on the mold
- Protects surface finish
- Prevents stress that leads to cracks or warping
Summary Checklist
To mold PEEK parts the right way, your mold design should include:
- Gate and runner designs suited to high viscosity
- Proper draft angles (2–4° typical; more for textured areas)
- Uniform wall thickness to reduce stress
- Smart cooling channel layout
- Draft on all features, even ribs and textured surfaces
Conclusion
Molding PEEK the right way starts with the mold itself.
By designing for its high temperature, shrinkage, and flow needs—and paying close attention to draft angles—you avoid many of the common problems that lead to part failure.
This careful planning makes a big difference in getting strong, reliable parts that work in high-stress jobs.
