Debugging Skills for Water-Assisted Injection Molding Process

Water-assisted injection molding (WAIM) is a specialized injection molding technology widely used for producing hollow, thick-walled plastic products. The key to stable molding lies in precise control over melt injection, water injection timing, water pressure, pressure holding, cooling, and water drainage. Proper debugging can effectively prevent defects such as piercing, uneven wall thickness, shrinkage, and flow marks.

Preliminary Preparation and Process Mode Selection

Before official debugging, check the stability of the water system, including pressure, flow rate, and temperature, and ensure no bubbles in the water circuit. Choose the appropriate process mode based on product structure. The under-filled method is suitable for simple tubular products, while the overflow method is ideal for complex hollow parts requiring high uniformity. Set reasonable material temperature, mold temperature, and basic injection parameters to ensure stable melt flow.

Debugging of the Melt Injection Stage

Control the melt injection volume properly. For the under-filled method, the injection rate is generally 60%–80%, leaving sufficient space for water penetration. Adopt multi-stage injection speed: low speed at the initial stage to avoid jetting, medium speed for stable filling, and low speed before water injection to form a stable surface layer. Maintain melt temperature within the recommended range to ensure sufficient fluidity without thermal degradation.

Debugging of Water Injection Parameters

Water injection delay time is critical. Too short a delay causes piercing, while too long leads to insufficient hollowing. The typical range is 0.5–5 seconds. Water pressure should be higher than the melt pressure inside the cavity, usually 6–15 MPa, and can be adjusted gradually from low to high. Use multi-stage water flow control: low speed at startup to prevent turbulence, medium-high speed for stable penetration, and low pressure for steady holding.

Pressure Holding, Cooling and Drainage

After water penetration, maintain proper water pressure holding to compensate for shrinkage and improve dimensional stability. Cooling time can be shorter than conventional injection molding, but ensure the product is fully solidified before ejection. Release pressure slowly before drainage to avoid springback, shrinkage, or internal vacuum defects.

Common Defects and Solutions

Piercing: extend delay time, reduce water pressure, lower melt temperature.

Insufficient hollowing: increase water pressure, shorten delay time, optimize water needle position.

Flow marks and poor surface quality: improve venting, reduce initial water injection speed, stabilize pressure.

Uneven wall thickness: adjust water needle position, balance melt flow, ensure uniform mold temperature.