Views: 0 Author: Site Editor Publish Time: 2026-06-03 Origin: Site
Introduction
PEEK (Polyether Ether Ketone) is a high-performance thermoplastic known for its exceptional mechanical strength, chemical resistance, and thermal stability. However, injection molding PEEK is far more challenging than molding common plastics like ABS or PP. Due to its high melting point (~343°C), high crystallinity, and sensitivity to cooling rates, deformation (warpage or shrinkage) is a common headache.
If you're struggling with warped PEEK parts, don't worry — you're not alone. The good news is that deformation can be minimized or even eliminated with the right approach. Here’s a systematic guide to achieving dimensionally stable PEEK injection molded parts.
The root cause of most deformations lies in the mold itself.
Gate location & type: Place the gate at the thickest section of the part. Use multiple gates or fan gates to ensure uniform flow front advancement. Avoid single-point gating on one side — that creates internal stress and warpage.
Cooling system design: PEEK crystallizes evenly only when the mold temperature is uniform. Design cooling channels to keep temperature variation across the cavity within ±5°C. Uneven cooling = uneven crystallinity = deformation.
Ejection system: PEEK has high shrinkage and strong mold grip. Use larger ejector pins or, better yet, a stripper plate to push the part out evenly. Uneven ejection force will bend the part immediately.
Wall thickness: Avoid abrupt thickness changes. Keep walls as uniform as possible. For ribs, their thickness should be 50–60% of the main wall thickness.
PEEK has a narrow processing window. Precision control is non‑negotiable.
Mold temperature — the #1 factor:
This is where most people go wrong.
Low mold temperature (<160°C) → incomplete, uneven crystallization → severe warpage and post‑mold shrinkage.
Recommended range: 160°C – 200°C (typically 175–190°C).
Use an oil temperature controller or cartridge heaters to achieve these high mold temperatures.
Melt temperature: 360°C – 400°C depending on grade. Too low → poor melting; too high → gas degradation.
Injection speed: Medium to high — fill the cavity quickly before the melt cools prematurely.
Packing pressure & time: High packing pressure (80–120 MPa) and long packing time — until the gate freezes. This compensates for crystallization shrinkage.
Cooling time: Long enough to bring the core temperature down below the mold temperature. Premature mold opening causes hot deformation.
PEEK absorbs moisture. Wet resin = hydrolyzed parts, bubbles, brittleness, and deformation.
Dry at 150°C – 160°C for 3–4 hours.
Moisture content must be below 0.02%.
Use a hopper dryer if possible.
Even with perfect molding, complex or thick PEEK parts benefit greatly from annealing — a controlled heat treatment that removes internal stresses and stabilizes crystallinity.
Typical annealing procedure:
Place parts in an air‑circulating oven.
Heat slowly (2–3°C/min) to 200°C – 230°C (below the heat deflection temperature, but above the glass transition temperature of 143°C).
Hold for 2–4 hours.
Cool very slowly to room temperature (furnace cooling).
After annealing, the part will be dimensionally stable — no “post‑mold warpage” days or weeks later.
Problem | Likely Cause | Immediate Fix |
|---|---|---|
Overall bow / twist | Uneven mold temperature | Check cooling lines; raise mold temp to 180±5°C |
Sink mark near gate | Excess packing | Reduce packing pressure, use multi‑stage packing |
Thin section warp | Low mold temp, short fill | Increase mold temp & injection speed |
Ejection‑related bend | Uneven ejection | Add more pins or switch to stripper plate |
Delayed deformation (days after) | Post‑mold crystallization | Mandatory annealing |
PEEK injection molding is demanding, but deformation is not inevitable. The winning formula is:
Uniform high mold temperature (≥170°C) + adequate packing + uniform cooling + proper ejection + mandatory annealing
If you currently have a PEEK part that warps, start by measuring the actual mold surface temperature. Most shops mistakenly run molds at 80–120°C — that’s fine for ABS, but disastrous for PEEK.
Get the mold hot, pack it well, and anneal afterward. Your PEEK parts will come out straight, stable, and ready for demanding applications.
