Process Adaptation for Glass Fiber Reinforced Plastic Injection Molding
Glass fiber reinforced plastics (GFRP) have high strength, high rigidity and good dimensional stability, and are widely used in electronics, automotive and machinery industries. However, the addition of glass fiber reduces melt fluidity, increases shear sensitivity and accelerates equipment wear, so targeted process optimization is required to avoid defects such as glass fiber exposure and product warping.
Raw Material Preparation and Equipment Adaptation
Raw Material Drying
Most glass fiber reinforced materials are based on hygroscopic substrates such as PA, PBT and PET. Moisture in raw materials will cause bubbles, silver streaks and fiber detachment, so full drying is required before production:
PA-based GFRP (PA6+GF, PA66+GF): Dry at 100–120℃ for 4–6 hours, moisture content ≤0.05%.
PBT/PET-based GFRP: Dry at 130–150℃ for 3–4 hours, moisture content ≤0.05%.
PP+GF (non-hygroscopic): Dry at 80–100℃ for 2–3 hours if stored in a humid environment.
Equipment Requirements
The addition of glass fiber will wear the screw, barrel and other components, so special equipment is required:
Screw: Glass fiber-specific screw with length-diameter ratio of 20–25:1 and compression ratio of 2.5–3.0, screw tip and check ring made of wear-resistant alloy.
Barrel and Nozzle: Inner wall treated with wear-resistant coating, self-locking nozzle to prevent melt drooling, appropriate nozzle aperture to reduce flow resistance.
Mold: Cavity and runner made of wear-resistant steels such as H13 and S136, surface polished to reduce friction.
Precise Temperature Parameter Control
Barrel Temperature
Set 10–30℃ higher than non-reinforced materials to improve fluidity, but avoid excessive temperature to prevent material degradation:
PA6+GF: 240–270℃; PA66+GF: 270–300℃; PP+GF: 200–230℃; PBT+GF: 240–260℃.
Nozzle Temperature
5–10℃ lower than the front section of the barrel, preventing melt drooling and glass fiber degradation, adjusted according to the substrate type (PA+GF: 250–260℃; PP+GF: 210–220℃).
Mold Temperature
Appropriately increase to improve fluidity and reduce defects: PA+GF 60–100℃, PBT+GF 80–120℃, PP+GF 40–60℃; thick-walled products can appropriately increase mold temperature.
Optimization of Injection and Holding Pressure Processes
Injection Speed
Adopt segmented control (medium-low→high→medium-low):
Initial stage: Medium-low speed to avoid glass fiber splashing and shear damage.
Middle stage: High speed to quickly fill the cavity and ensure uniform fiber dispersion.
Final stage: Medium-low speed to avoid overfilling and internal stress.
Overall speed is 10–20% lower than non-reinforced materials.
Injection Pressure
10–30% higher than non-reinforced materials to ensure full filling: PA+GF 80–120MPa, PP+GF 60–90MPa, PBT+GF 90–130MPa, adjusted according to product structure.
Holding Pressure and Time
Holding pressure is 60–80% of injection pressure, holding time extended by 10–30% according to wall thickness, preventing product shrinkage and warping.
Adjustment of Screw Speed and Back Pressure
Screw Speed: 50–150rpm, not too high to avoid glass fiber breakage; high glass fiber content materials (＞30%) control at 50–100rpm.
Back Pressure: 5–15MPa, appropriately increasing to ensure uniform fiber dispersion and remove gas; PA/PBT-based GFRP 8–15MPa, PP+GF 5–10MPa, avoiding excessive back pressure to prevent melt overheating.
Control of Cooling and Demolding Processes
Cooling Time: 20–50% longer than non-reinforced materials, 10–40 seconds according to wall thickness; uniform cooling channels, cooling water temperature 20–30℃, cooling inserts added for thick-walled parts.
Demolding: Draft angle increased to 1.5°–3° (3°–5° for deep-cavity products); uniform ejection mechanism, air-assisted ejection for deep-cavity products; cavity polished to Ra≤0.8μm to facilitate demolding.
