The exhaust system of injection molds is critical for smooth melt filling and defect elimination, directly impacting product quality and production efficiency. Poor design causes bubbles, charring, short shots, and weld marks, and may even raise injection pressure and extend production cycles, increasing manufacturing costs. This article outlines optimization strategies from design principles, structural optimization, process adaptation, and technological upgrading, based on practical production needs.
Exhaust channels must rapidly discharge gas, with cross-sectional areas ≥0.5 mm² (small cavities) and ≥1.5 mm² (medium cavities). Linear designs avoid bends; gas flow resistance stays below industry critical values (generally ≤0.02 MPa·s/cm³), ensuring discharge speed matches melt advancement to prevent gas entrapment.
Exhaust structures target melt’s last-fill zones (cavity ends, weld line intersections, deep cavity dead corners) identified via flow analysis, prioritizing machinable areas (parting surfaces, insert fits) to reduce mold modification difficulty.
Groove depth: 0.01–0.03 mm, width: 3–5 mm (≤0.02 mm for high-flow plastics like PE/PP with melt flow rate ≥10 g/10min; ≤0.03 mm for low-flow plastics like PC/PMMA with melt flow rate ≤5 g/10min). Effective exhaust length ≥10 mm, with bell-mouth ends to prevent air backflow and ensure stable gas discharge.
Reserve 0.01–0.03 mm gaps at last-fill positions, extending outside the mold. Large parts use segmented grooves (20–30 mm/segment, 5 mm spacing) to maintain mold strength. Complex cavities combine with insert fit gaps for auxiliary exhaust, especially for deep or irregularly shaped cavity sections.
Control fit clearances (0.01–0.02 mm) for inserts/ejector pins. Deep cavities use ejector pin arrays; inserts add 0.02 mm-deep, 2 mm-wide shallow grooves along gas flow. These designs leverage existing mold components to avoid additional machining while enhancing exhaust efficiency.
Gradient channels (0.02–0.1 mm depth) connect to waste slots for large trapped air areas. Precision parts add adsorption devices at slot ends to accelerate gas extraction, which is particularly effective for high-gloss or surface-sensitive plastic products.
Embed porous plugs (30%–40% porosity, 0.05–0.1 mm pores) in blind holes/deep cavities; clean regularly to prevent clogging by plastic debris, making them ideal for mass production molds with long-term operation requirements.
Heat-sensitive plastics (PVC/POM) need 5–8 mm-wide grooves to avoid thermal decomposition; glass fiber-reinforced plastics use enhanced structures/plugs to prevent fiber blockage; crystalline plastics (PA/PP) require more slots to balance cavity pressure during shrinkage.
High-speed injection needs larger slot cross-sections/more exhaust points to handle rapid gas compression; high-pressure injection ensures unobstructed channels to avoid scorching; thin-walled parts reduce speed to extend exhaust time, matching the optimized exhaust structure for better quality.
Moldflow/Simcenter simulates filling to locate trapped gas, optimizing exhaust slot design pre-mold trial and quantifying efficiency, which can reduce mold modification times by 30%–50% in practical applications.
3D printing creates conformal grooves (0.1–0.2 mm diameter) for complex cavities, integrating micro-channels in inserts for high-precision molds. This technology enables exhaust designs that are impossible with traditional machining, improving exhaust uniformity for irregular parts.
Exhaust system optimization integrates structural design, process adaptation, and technology. Guided by "precise, efficient, production-adaptive" goals, it combines simulation and new manufacturing, with dynamic adjustments based on part structure, materials, and processes. This not only improves product qualification rates but also shortens production cycles, ultimately enhancing overall manufacturing efficiency and competitiveness.
