Thin-Wall Injection Molding Process Requirements

Thin-wall injection molding is a critical technology driven by the trend toward lightweight and miniaturized products. It is generally defined by a wall thickness ≤ 1mm or a flow length-to-thickness ratio > 100:1. This process is widely used for electronic housings, automotive components, and medical devices. Compared to conventional molding, thin-wall molding presents unique challenges such as high flow resistance, rapid filling, short cooling times, and a high risk of warpage. Consequently, it demands precise coordination between mold design, material selection, equipment performance, and process parameters. This guide outlines the core requirements for successful thin-wall injection molding.

1. Mold Design Requirements

The mold is the foundation of thin-wall molding; its design directly determines fill quality and dimensional stability.

Gating & Runners: Use short, large-diameter runners to minimize resistance. Hot runner systems are preferred for temperature control and material efficiency. Gates should be large (e.g., fan gates) and located at the thickest section.

Cooling System: Uniform cooling is essential to prevent warping. Cooling channels must be densely packed (8-12mm spacing) and positioned close to the cavity (≤15mm). High-flow water (≥1.5m/s) ensures rapid heat extraction.

Venting: High-speed filling traps air, requiring deep vents (0.01-0.03mm) at the last points of fill to prevent burning.

Steel Selection: High cavity pressures demand hard, wear-resistant steels like H13 (HRC 48-52) or S136. A polished surface (Ra ≤ 0.2μm) reduces flow resistance.

2. Material Selection Requirements

Materials must possess high flowability, thermal stability, and low shrinkage.

High Flowability: Choose grades with high Melt Flow Rates (MFR). For example, ABS should have an MFR ≥ 15 g/10min.

Thermal Stability: Materials must withstand high shear and temperature without degradation.

Dimensional Stability: Fillers (glass/mineral) reduce shrinkage and increase rigidity. For instance, 30% glass-filled ABS reduces shrinkage from 0.5-0.8% to 0.2-0.4%.

3. Process Parameter Control

The core principle is "High Temperature, High Pressure, High Speed, Short Packing, Fast Cooling."

Temperature: Increase barrel temperature by 10-30℃ (e.g., ABS: 220-250℃) to lower viscosity. Mold temperature (40-60℃ for ABS) balances flow and cooling.

Pressure: Injection pressure doubles to 120-180MPa to overcome resistance. Use low packing pressure (30-50% of injection) for a short duration (2-5s) to avoid stress.

Speed: Utilize high injection speeds (500-1000 mm/s) to fill before freezing. Use a 3-stage profile: slow at the gate, fast in the cavity, and slow at the end.

Cooling: Shorten cycles to 5-15s, ensuring parts are rigid enough to eject without deformation.

4. Equipment Requirements

High-response, precision machines are mandatory.

Injection Unit: All-electric machines offer superior speed and accuracy. Use a screw with an L/D ratio ≥ 28:1.

Clamping Unit: High clamping force (based on projected area × cavity pressure × safety factor 1.2-1.5) prevents flashing under high pressure.

Auxiliaries: High-precision temperature controllers and efficient dehumidifying dryers are essential.

Conclusion

Thin-wall molding is a system engineering feat. Success relies on reducing flow resistance through mold optimization, ensuring material flowability, and precisely balancing filling and cooling parameters. By following these guidelines, manufacturers can achieve high efficiency and consistent quality in thin-wall production.