Common Defects in Plastic Thread Injection Molding
Plastic thread injection molding is widely used in electronics, automotive, and household appliances. However, various defects frequently arise during production.
1. Thread Deformation
Causes:
Unreasonable mold design: Inappropriate thread angle, depth, or clearance design can lead to deformation.
Uneven cooling: Poorly designed mold cooling systems result in uneven shrinkage across the thread, causing deformation.
High material shrinkage rate: Materials with high and uneven shrinkage rates can cause thread deformation.
Improper injection process parameters: Inappropriate settings for injection pressure, temperature, or holding time can induce internal stress and deformation.
Solutions:
Optimize mold design by adjusting thread angle, depth, and clearance.
Improve the mold cooling system to ensure uniform cooling.
Select materials with a lower shrinkage rate or modify materials to reduce shrinkage.
Adjust injection process parameters to minimize internal stress.
2. Insufficient Thread Filling
Causes:
Poor gate position: A gate positioned too far from the thread results in poor flow and insufficient material filling.
Low injection pressure: Inadequate pressure prevents molten plastic from filling the thread cavity.
Excessive thread depth: Deep threads make it difficult for molten plastic to reach the bottom.
Solutions:
Adjust the gate position to bring it closer to the thread.
Increase injection pressure to ensure sufficient material filling in the thread cavity.
Reduce thread depth or use a multi-gate system.
3. Thread Flash
Causes:
Mismatch at the mold parting line: Gaps at the mold parting line allow molten plastic to leak and form a flash.
Excessive injection pressure: High pressure causes molten plastic to overflow, leading to flash.
Rough mold cavity surface: A rough surface increases the adhesion of molten plastic, causing flash.
Solutions:
Precisely adjust the mold parting line to ensure a tight fit.
Reduce injection pressure to prevent material overflow.
Improve the mold cavity surface finish.
4. Thread Sticking to the Mold
Causes:
Poor mold surface treatment: Inadequate surface treatment causes molten plastic to stick to the mold.
Improper use of release agents: Incorrect or excessive use of release agents leads to sticking.
Insufficient cooling: Inadequate cooling causes the part to bond with the mold.
Solutions:
Polish the mold surface to improve its finish.
Choose an appropriate release agent and use it in the recommended amount.
Enhance the mold cooling system to ensure adequate cooling.
5. Insufficient Thread Strength
Causes:
Inappropriate material selection: Materials with inadequate strength fail to meet thread strength requirements.
Unreasonable thread design: Poor thread profile design results in insufficient strength.
Improper injection process parameters: Incorrect parameters cause internal defects like voids or shrinkage, reducing thread strength.
Solutions:
Select higher-strength materials.
Optimize thread design by increasing thread depth or modifying the profile.
Adjust injection process parameters to avoid voids or shrinkage.
