PEEK Precision Injection Molding and Mold Design Points

PEEK (Polyetheretherketone) is a high-performance special engineering plastic, widely used in medical, aerospace, automotive, and semiconductor fields for its high temperature resistance, strength, corrosion resistance, and biocompatibility. However, its high melting point, poor fluidity, and anisotropic shrinkage make precision molding challenging. To mass-produce PEEK products with ±0.02mm tolerance, a systematic approach covering materials, equipment, mold design, and process control is required. This article details the core points for on-site guidance.

Core Molding Characteristics of PEEK Materials

PEEK’s molding difficulties stem from its properties: melting point ≈343°C, requiring 360-400°C molding temperature; high melt viscosity and poor fluidity, sensitive to shear (high speed causes degradation); 1.2%-2.5% shrinkage, highly dependent on cooling rate (affecting crystallinity and dimensional stability); high moisture sensitivity (hydrolysis at high temperatures reduces strength and causes surface defects); and easy internal stress concentration (leading to cracking if unrelieved). Balancing crystallinity, fluidity, and stress is key to successful molding.

Requirements for Special PEEK Injection Equipment

Ordinary injection machines are unsuitable; special high-temperature equipment is required:

Barrel, screw, and nozzle: Made of Hastelloy (high-temperature/corrosion-resistant), with smooth inner walls and no dead corners to avoid material retention.

Temperature control: ±1°C precision, multi-stage independent control for barrel sections (feeding, compression, homogenization) to prevent local overheating.

Screw: L/D ratio 20:1-24:1, compression ratio 2.5:1-3:1, pointed head design to avoid material degradation.

Clamping force: Matches product projected area to prevent template deformation and flash.

Oil temperature machine: 160-220°C stable output, ±2°C precision, ensuring uniform mold temperature for consistent crystallization.

Key Points of PEEK Precision Mold Design

Mold design directly determines yield and stability:

Steel and Rigidity: Cavities/cores use S136/STAVAX (HRC 52-56) for wear resistance; reinforced mold base with support pillars to avoid high-pressure deformation; parting gap ≤0.02mm.

Gating System: Hot runners are preferred to reduce pressure loss and degradation. Runners are short, thick, and polished (Ra ≤0.4μm); gates are 30%-50% larger than ordinary molds, placed at thick-walled areas. Multi-cavity molds require balanced runners for synchronous filling.

Temperature Control: Conformal cooling/heating waterways (15-20mm spacing) with independent circuits for cavity/core, ensuring ±2°C surface temperature difference to control crystallinity.

Venting: 0.015-0.02mm deep grooves at filling ends, weld lines, and dead corners to avoid air trapping and burn marks.

Ejection: Balanced multi-ejector design (≥3mm diameter); draft angles ≥0.5° (precision parts) or ≥1.5° (ordinary parts); air ejection for deep-cavity parts to prevent deformation.

Precision Process Control

Raw Material Drying: 150°C for 4-6 hours, dew point ≤-40°C, using dehumidifying dryers to avoid hydrolysis; heat-preserving hoppers prevent secondary moisture absorption.

Temperature Control: Barrel gradient (360-400°C from rear to front); nozzle 385-395°C (5-10°C lower than front section) to prevent drooling.

Injection/Packing: 80-120MPa injection pressure, multi-stage medium speed to avoid shear degradation; 50%-70% packing pressure (matched to wall thickness) to prevent sink marks.

Post-Treatment: 200°C annealing for 2-4 hours (slow cooling) to eliminate internal stress and stabilize dimensions.

Mass Production Stability Control

CAE simulation predicts shrinkage/warpage for mold compensation. SPC controls key dimensions (CPK ≥1.33). Regular parameter checks and mold maintenance ensure long-term stability. Common defects: silver streaks (re-dry raw materials), warpage (optimize cooling), yellowing (lower temperature/clean barrel).

PEEK precision injection integrates materials, equipment, mold, and process. Strict control of high-temperature molding, uniform temperature, and balanced ejection ensures high-quality mass production.