Runner Design Standards for LCP Thin-Wall Molds

LCP (Liquid Crystal Polymer) features ultra-low viscosity, fast solidification and strong shear sensitivity, widely used for 0.1–0.5 mm ultra-thin precision electronic parts. Unreasonable runner design easily causes short shots, weld lines, warpage and carbonization defects. Standardized runner systems are essential to stabilize thin-wall filling and molding quality.

I. Cold Runner Design Specifications

Cold runners apply to small-batch production. Circular cross-section is preferred for minimum pressure loss, while trapezoidal runners must retain R≥0.8 mm rounded corners to avoid dead-corner material retention. Semicircular narrow runners are forbidden. Standard runner diameter ranges 2–4 mm, and ultra-thin parts under 0.2 mm wall thickness adopt 1.5 mm minimum diameter to reduce heat loss. Main runner taper is 0.5°–1° with mirror polished inner walls to prevent fiber accumulation. Multi-cavity molds use equal-length balanced runners with length error within 0.5 mm and total runner length controlled under 50 mm. Each sub-runner is equipped with sufficient cold material wells to trap low-temperature melt and avoid silver streaks and incomplete filling.

II. Hot Runner Structural Standards

Mass production ultra-thin LCP molds adopt valve-gate hot runners to eliminate stringing, drooling and material waste. Open hot nozzles are only allowed for non-cosmetic parts with strictly controlled ±2°C temperature accuracy. Hot runner manifolds use full arc transition without steps or dead zones to prevent long-term retention and carbonization. Nozzle aperture matches thin-wall thickness, ensuring zero-gap sealing with cavities. Multi-nozzle molds use sequential gating to balance filling speed, reduce molecular orientation and minimize warpage. Smooth anti-stick coating inside runners reduces fiber adhesion and residue accumulation during repeated production and material changes.

III. Gate Layout and Dimension Standards

Pin-point gates are the first choice for LCP thin-wall products to reduce shear heat. Ultra-thin parts use 0.3–0.5 mm gate diameter with short step length below 0.8 mm to avoid material degradation. Side gate depth is 70% of product wall thickness with minimum 0.2 mm to prevent filling difficulty. Gates are placed at the thickest material area to ensure smooth filling and avoid remote weld convergence. Transition fillets eliminate sharp shear points, and terminal overflow grooves relieve welding stress. Shear rate is strictly controlled within a safe range to prevent overheating and material decomposition. Multi-gate layout is avoided to reduce weld lines.

IV. Runner Balance, Exhaust and Temperature Control

Moldflow simulation verifies cavity balance with filling pressure difference controlled below 5 MPa. Exhaust grooves are evenly opened along runners and melt terminals to rapidly exhaust air and prevent burning and bubbles. Cold runner cooling circuits are reasonably arranged to avoid premature melt solidification. Hot runner manifolds adopt segmented temperature control, keeping manifold temperature slightly lower than nozzle temperature to prevent thermal decomposition. Smooth arc runner transitions reduce flow velocity fluctuation and shear stress, ensuring stable and uniform filling for ultra-thin cavities.

V. Anti-Carbonization Processing and Acceptance

LCP material is prone to carbonization when retained. Runner cavities adopt S136H high-polish stainless steel with high corrosion resistance and smooth finish. All splicing surfaces are precisely sealed within minimal clearance to prevent hidden residual melt. Finished runners are inspected for dimension uniformity, surface smoothness and fillet integrity. Continuous trial production verifies zero black spots and zero residual defects. Regular hot runner disassembly and cleaning eliminate carbon deposits, and all runner edges are rounded to avoid scratch adhesion and material stagnation during long-term production.

Conclusion

LCP thin-wall runner design focuses on low shear, balanced filling and anti-retention. Standard cold runners suit small-batch production, while valve hot runners optimize mass production stability. Scientific gate layout reduces weld lines and deformation. Matched exhaust, cooling and temperature control ensure complete filling. Strict processing and maintenance standards eliminate carbonization and residual defects. This standardized system effectively solves common thin-wall molding problems and improves yield and stability of precision LCP molds.