Unraveling the Mystery of Cracks in Plastic Injection Molding
2024/9/30 195

Cracks, narrow fissures appearing on injection-molded parts, can stem from issues with the injection molding machine, mold, molding process, and raw materials.

1. Injection Molding Machine: The Test of Plasticizing Capacity

Insufficient plasticizing capacity, resulting in incomplete melting, is a primary cause of cracks. Upgrading to a machine with greater plasticizing capacity is crucial.

2. Mold: Where Details Make or Break

  • Poor ventilation leads to flow marks, weakening part strength.

  • Oversized gates cause overpressure in molded parts.

  • Leaks in cavities or cores; check for micro-cracks.

  • Excessively thin part design requires reinforcing ribs.

  • Ensure mold cavities and cores have adequate draft angles.

  • Mold maintenance is needed to prevent ejector pin oil from contaminating surfaces.

  • Increase ejector pin diameter and reduce ejection speed.

Medical Injection Molding

3. Injection Molding Process: The Art of Precise Control

  • Adjust barrel temperature to avoid material decomposition at high temps or insufficient welding strength at low temps.

  • Manage injection pressure; elevate temperature for smooth mold filling and reduced viscosity; reduce pressure to avoid internal stress-induced cracks.

  • Decrease preform back pressure and screw speed to prevent material degradation.

  • Appropriately increase injection speed.

  • Extend cooling time to ensure proper solidification, preventing jetting cracks or marks.

4. Raw Materials: Ensuring Purity and Dryness

  • Completely dry raw materials to prevent moisture-related cracks.

  • Identify and control impurities in raw materials.

  • Determine the appropriate proportion of recycled material through testing to avoid excessive addition.