## Common Defects in Injection Molding and Prevention Strategies Injection molding is the primary manufacturing method for plastic products, yet various quality defects frequently occur during production. Below is an analysis of common defects along with preventive measures. ### 1. Sink Marks **Symptom:** Localized depressions appear on the surface of the part, typically occurring at areas with thick walls or reinforcement ribs. **Cause:** Insufficient material packing during plastic cooling and shrinkage. **Preventive Measures:** - Optimize holding pressure and holding time - Minimize wall thickness variations to avoid significant differences - Increase mold temperature to improve material compensation - Select engineering plastics with lower shrinkage rates ### 2. Flash (Burr) **Symptom:** Excess thin layers of plastic overflow from the parting line or around inserts. **Cause:** Insufficient clamping force or wear on the mold mating surfaces. **Preventive Measures:** - Increase clamping force or reduce injection pressure - Inspect and repair mold parting lines to ensure a tight seal - Control melt temperature to prevent excessive fluidity - Regularly check mold guide components for wear ### 3. Bubbles and Silver Streaks **Symptom:** Bubbles or silver-colored streaks appear inside or on the surface of the part. **Cause:** High moisture content in raw materials or excessive volatiles. **Preventive Measures:** - Dry raw materials thoroughly to meet specified moisture levels - Reduce screw speed to minimize shear heating - Increase back pressure to enhance plasticization density - Optimize gate size and location ### 4. Warpage **Symptom:** Parts bend or twist after ejection from the mold. **Cause:** Uneven cooling or release of internal stresses. **Preventive Measures:** - Optimize cooling channel layout to ensure uniform cooling - Adjust the holding pressure curve to reduce residual stress - Extend cooling time to allow proper setting - Perform annealing if necessary to relieve internal stresses Systematically analyzing defect causes and implementing targeted measures are key to improving injection molding yield rates.