ABS is a widely used engineering plastic with good mechanical strength, impact resistance and processing performance. However, during the injection molding process, various defects may occur in ABS products due to factors such as material properties, process parameters or mold design. This article will analyze the common defects in ABS injection molding and provide corresponding solutions to help optimize production quality.
Common defects and causes of ABS injection molding
1. Shrinkage (sink marks)
Phenomenon: Depressions appear on the surface of the product, usually in the thick wall area or the position of the reinforcing ribs.
Cause:
Insufficient holding pressure or too short holding time, resulting in insufficient shrinkage after the material cools and shrinks.
The melt temperature is too high, and the shrinkage rate increases during cooling.
The mold temperature is uneven and the local cooling is too fast.
2. Flash (burrs)
Phenomenon: Excess plastic overflows at the edge or parting surface of the product.
Cause:
Insufficient clamping force and unable to resist injection pressure.
The mold is worn or the mold is not tightly closed, resulting in excessive gaps.
The injection pressure or speed is too high, and the melt breaks through the mold gap.
3. Silver streaks (gas streaks)
Phenomenon: Silver streaks appear on the surface of the product, usually distributed along the direction of melt flow.
Cause:
The material is not fully dried, and the residual moisture vaporizes at high temperature.
The melt temperature is too high, causing some materials to decompose.
The screw speed is too fast, and shear heat causes local degradation of the material.
4. Welding mark (mold line)
Phenomenon: Visible fusion lines appear on the surface of the product, affecting the appearance and strength.
Cause:
The temperature of the melt is too low when it converges in the mold, and it cannot be fully fused.
The gate design is unreasonable, resulting in a long melt flow path.
The injection speed is too slow, and the melt front cools too quickly.
5. Black spots or impurities
Phenomenon: Black spots or foreign matter appear on the surface or inside of the product.
Cause:
Material contamination (such as mixing with other plastics or dust).
Degraded materials remain in the barrel or screw.
The mold cavity is not cleaned.
6. Warping
Phenomenon: The product bends or twists after cooling.
Cause:
Uneven cooling leads to uneven internal stress distribution.
Wall thickness difference is too large and shrinkage rate is inconsistent.
Ejection is unbalanced and the product is unevenly stressed.
Solutions to ABS injection molding defects
1. Improvement measures for shrinkage
✅ Adjust holding parameters: Increase holding pressure (usually 50%~80% of injection pressure) and holding time to ensure sufficient shrinkage compensation.
✅ Optimize cooling system: Ensure uniform mold temperature and strengthen cooling in thick wall areas.
✅ Reduce melt temperature: Avoid excessively high material temperature (ABS usually recommends 200~240℃).
2. Solutions to flash
✅ Increase clamping force: Check whether the equipment clamping force is sufficient (usually ≥ injection pressure × projected area).
✅ Repair mold: Check whether the parting surface is worn, and polish or replace it if necessary.
✅ Reduce injection pressure/speed: Adjust parameters appropriately to prevent the melt from breaking through the mold.
3. Methods to eliminate silver streaks
✅ Fully dry the material: ABS needs to be dried at 80~90℃ for 2~4 hours (humidity ≤0.1%).
✅ Control the melt temperature: Avoid exceeding 240℃ to prevent material decomposition.
✅ Reduce screw speed: Reduce shear heat and avoid local overheating.
4. Optimization plan for weld marks
✅ Increase melt temperature: Ensure that the melt remains sufficiently fluid when it converges.
✅ Speed up injection speed: Shorten melt flow time and reduce cooling effects.
✅ Optimize gate design: Use multi-point injection or adjust gate position to improve fusion effect.
5. Prevention of black spots/impurities
✅ Clean the barrel and screw: Clean regularly to avoid degradation of residual old materials.
✅ Use filter: Install filter at the nozzle (usually 80~120 mesh).
✅ Standardize material storage: Avoid moisture or contamination of ABS.
6. Control of warping deformation
✅ Balanced cooling: Adjust the cooling water path of the mold to ensure uniform heat dissipation.
✅ Optimize product design: Avoid sudden changes in wall thickness and increase reinforcement to balance shrinkage.
✅ Adjust the ejection system: Use multi-point ejection to avoid local stress concentration.
General suggestions for preventing ABS injection molding defects
Material management: Strictly control the ABS drying process to avoid excessive moisture content.
Process optimization: Find the best injection parameter combination through DOE (experimental design).
Mold maintenance: Regularly check mold wear, venting grooves and cooling systems.
Equipment maintenance: Ensure that the screw and barrel of the injection molding machine are clean to avoid accumulation of degraded materials.
Conclusion
Defects in ABS injection molding are often caused by multiple factors such as materials, processes, molds or equipment. By systematically analyzing the root causes of the problem and adjusting parameters or optimizing the design, the product yield can be significantly improved. It is recommended that manufacturers combine the mold trial report and process window analysis to establish a stable production standard.
Common defects and causes of ABS injection molding
1. Shrinkage (sink marks)
Phenomenon: Depressions appear on the surface of the product, usually in the thick wall area or the position of the reinforcing ribs.
Cause:
Insufficient holding pressure or too short holding time, resulting in insufficient shrinkage after the material cools and shrinks.
The melt temperature is too high, and the shrinkage rate increases during cooling.
The mold temperature is uneven and the local cooling is too fast.
2. Flash (burrs)
Phenomenon: Excess plastic overflows at the edge or parting surface of the product.
Cause:
Insufficient clamping force and unable to resist injection pressure.
The mold is worn or the mold is not tightly closed, resulting in excessive gaps.
The injection pressure or speed is too high, and the melt breaks through the mold gap.
3. Silver streaks (gas streaks)
Phenomenon: Silver streaks appear on the surface of the product, usually distributed along the direction of melt flow.
Cause:
The material is not fully dried, and the residual moisture vaporizes at high temperature.
The melt temperature is too high, causing some materials to decompose.
The screw speed is too fast, and shear heat causes local degradation of the material.
4. Welding mark (mold line)
Phenomenon: Visible fusion lines appear on the surface of the product, affecting the appearance and strength.
Cause:
The temperature of the melt is too low when it converges in the mold, and it cannot be fully fused.
The gate design is unreasonable, resulting in a long melt flow path.
The injection speed is too slow, and the melt front cools too quickly.
5. Black spots or impurities
Phenomenon: Black spots or foreign matter appear on the surface or inside of the product.
Cause:
Material contamination (such as mixing with other plastics or dust).
Degraded materials remain in the barrel or screw.
The mold cavity is not cleaned.
6. Warping
Phenomenon: The product bends or twists after cooling.
Cause:
Uneven cooling leads to uneven internal stress distribution.
Wall thickness difference is too large and shrinkage rate is inconsistent.
Ejection is unbalanced and the product is unevenly stressed.
Solutions to ABS injection molding defects
1. Improvement measures for shrinkage
✅ Adjust holding parameters: Increase holding pressure (usually 50%~80% of injection pressure) and holding time to ensure sufficient shrinkage compensation.
✅ Optimize cooling system: Ensure uniform mold temperature and strengthen cooling in thick wall areas.
✅ Reduce melt temperature: Avoid excessively high material temperature (ABS usually recommends 200~240℃).
2. Solutions to flash
✅ Increase clamping force: Check whether the equipment clamping force is sufficient (usually ≥ injection pressure × projected area).
✅ Repair mold: Check whether the parting surface is worn, and polish or replace it if necessary.
✅ Reduce injection pressure/speed: Adjust parameters appropriately to prevent the melt from breaking through the mold.
3. Methods to eliminate silver streaks
✅ Fully dry the material: ABS needs to be dried at 80~90℃ for 2~4 hours (humidity ≤0.1%).
✅ Control the melt temperature: Avoid exceeding 240℃ to prevent material decomposition.
✅ Reduce screw speed: Reduce shear heat and avoid local overheating.
4. Optimization plan for weld marks
✅ Increase melt temperature: Ensure that the melt remains sufficiently fluid when it converges.
✅ Speed up injection speed: Shorten melt flow time and reduce cooling effects.
✅ Optimize gate design: Use multi-point injection or adjust gate position to improve fusion effect.
5. Prevention of black spots/impurities
✅ Clean the barrel and screw: Clean regularly to avoid degradation of residual old materials.
✅ Use filter: Install filter at the nozzle (usually 80~120 mesh).
✅ Standardize material storage: Avoid moisture or contamination of ABS.
6. Control of warping deformation
✅ Balanced cooling: Adjust the cooling water path of the mold to ensure uniform heat dissipation.
✅ Optimize product design: Avoid sudden changes in wall thickness and increase reinforcement to balance shrinkage.
✅ Adjust the ejection system: Use multi-point ejection to avoid local stress concentration.
General suggestions for preventing ABS injection molding defects
Material management: Strictly control the ABS drying process to avoid excessive moisture content.
Process optimization: Find the best injection parameter combination through DOE (experimental design).
Mold maintenance: Regularly check mold wear, venting grooves and cooling systems.
Equipment maintenance: Ensure that the screw and barrel of the injection molding machine are clean to avoid accumulation of degraded materials.
Conclusion
Defects in ABS injection molding are often caused by multiple factors such as materials, processes, molds or equipment. By systematically analyzing the root causes of the problem and adjusting parameters or optimizing the design, the product yield can be significantly improved. It is recommended that manufacturers combine the mold trial report and process window analysis to establish a stable production standard.