Views: 0 Author: Site Editor Publish Time: 2025-07-18 Origin: Site
What they are: Surface dents caused by uneven cooling or insufficient material packing.
Common locations: Thick sections (ribs, bosses) or near gate areas.
Main causes:
Poor cooling design.
Low holding pressure or time.
Material shrinkage (e.g., unfilled PP shrinks more than ABS).
What it is: Thin excess plastic leaking from mold parting lines or gaps.
Common locations: Mold seams, ejector pins, or slider mechanisms.
Main causes:
Insufficient clamping force.
Worn-out mold surfaces.
Excessive injection pressure or melt temperature.
| Solution | How It Works | Example |
|---|---|---|
| Uniform wall thickness | Prevents uneven shrinkage (ribs ≤60% of main wall). | A 1.5mm main wall with 1mm ribs. |
| Improved cooling | Faster cooling in thick sections reduces sinks. | Copper inserts in core/cavity. |
| Gate optimization | Position gates near thick areas for better packing. | Side gates instead of pinpoint gates. |
Increase holding pressure & time: Compensates for shrinkage (e.g., 80% of injection pressure for 5 sec).
Moderate injection speed: Too fast causes jetting; too slow leads to premature freezing.
Raise mold temperature: Improves flow but balance with cycle time (e.g., 60–80°C for ABS).
Use low-shrinkage materials (e.g., glass-filled polymers).
Consider microcellular foaming for structural parts (reduces sinks but may affect surface finish).
| Action | Purpose |
|---|---|
| Polish parting lines | Ensures tight sealing (Ra ≤0.8μm). |
| Check clamping alignment | Prevents uneven force distribution. |
| Tighten sliders/inserts | Avoids gaps causing leakage. |
Increase clamping force: Must exceed injection pressure × projected area.
Lower melt temperature: Reduces material flowability (e.g., drop ABS from 240°C to 220°C).
Adjust cushion size: Prevents over-packing (3–5mm buffer recommended).
Add locking tapers (1–3°) to parting lines for better sealing.
Use harder steel (e.g., H13) for critical areas to resist wear.
Conflict: High holding pressure reduces sinks but risks flash.
Solution:
Multi-stage holding: High pressure (0.5 sec) + low pressure (3–5 sec).
Zone temperature control: Cool parting lines, heat thick sections.
Issue: Dents near mounting bosses.
Fix:
Redesigned ribs with gradual thickness transitions.
Increased holding pressure by 20%.
Issue: Flashing at mold seams.
Fix:
Restored parting line flatness via grinding.
Reduced melt temp by 15°C.
| Defect | Root Cause | Best Fixes |
|---|---|---|
| Sink Marks | Poor packing/cooling | Optimize wall thickness, boost holding pressure. |
| Flash | Mold wear/over-packing | Increase clamp force, lower melt temp. |
