Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Voids are internal air pockets or gaps that form in molded plastic parts, often due to trapped air, insufficient material fill, or shrinkage during cooling. They weaken the part's structural integrity and appearance, so preventing them is crucial for quality production.

Key Prevention Methods

1.Optimize Material Dosage and Cushion

Ensure the injection molding machine delivers enough material to fully fill the mold without bottoming out the screw. Maintain a consistent cushion (e.g., 5-10% of shot size) to compensate for shrinkage. This prevents under-packing, a primary cause of voids.

2.Adjust Injection Pressure and Hold Time

Increase injection pressure to push material into all areas, and extend hold time and pressure to allow full packing before cooling begins. This helps displace trapped air and reduces shrinkage voids.

3.Control Temperatures

Lower the melt temperature slightly to promote even flow and reduce gas entrapment, while cooling the mold more effectively (e.g., via better coolant flow) to prevent premature solidification in thick sections. Avoid overheating, which can introduce moisture or gases.

4.Improve Gate and Runner Design

Position gates near the thickest sections of the part to ensure even filling and minimize cooling differentials that lead to voids. Use larger gates or runners to reduce flow resistance, and avoid direct gating into large open spaces to prevent jetting (high-speed material streams that trap air).

5.Enhance Venting

Add or enlarge vents in the mold at the end-of-fill areas to allow trapped air to escape. Proper venting (typically 0.001-0.003 inches deep) is essential for air evacuation without flash.

6.Select Appropriate Material and Viscosity

Choose lower-viscosity resins that flow better and allow air to escape more easily. Dry hygroscopic materials thoroughly to eliminate moisture-induced voids.

7.Slow Down Injection Speed if Needed

Reduce injection speed to allow gradual filling and better air release, especially for complex geometries. Combine with slower screw forward time for controlled packing.

8.Redesign the Mold or Part if Persistent

For chronic issues, modify thick sections to thinner, uniform walls, or incorporate ribs/supports to equalize cooling. Simulate filling with software to identify problem areas before production.

Implementing these steps systematically can significantly reduce void defects, improving yield and part quality.