Introduction
In injection molding, the structural design of the part directly determines the distribution and intensity of local shrinkage. Uneven wall thickness, dense ribs, and sharp corners often cause inconsistent cooling rates across different regions, resulting in uneven shrinkage or warpage. A balanced structure layout is key to controlling local shrinkage.
On the other hand, the alignment between mold design and material characteristics is equally important. Each polymer has a unique shrinkage rate, flow property, and cooling behavior, making early thermal-flow analysis essential. Integrating structure and mold optimization greatly improves dimensional stability and surface uniformity.
How Does Wall Thickness Variation Cause Local Shrinkage?
When an injection part has significant wall thickness variation, the cooling rate differs locally. Thick areas cool slowly and tend to form sink marks or stress concentration, while thin walls solidify faster, increasing internal stress imbalance. Wall thickness inconsistency is one of the main causes of local shrinkage.
- Optimize Wall Thickness Design: Maintaining uniform wall thickness reduces cooling time differences.
- Improve Gate Positioning: Proper gate layout balances flow speed and packing pressure.
- Localized Cooling Optimization: Add cooling channels near thick sections to balance temperature gradients.
- Material Drying Control: Prevent voids or irregular cooling that lead to localized shrinkage.
If thickness variation is not optimized, it becomes the root cause of local shrinkage.
How Do Ribs and Reinforcing Features Affect Shrinkage?
While ribs and bosses enhance structural strength, they often introduce localized shrinkage or sink marks. If the rib base exceeds 60% of the wall thickness, it may cause surface depressions and stress accumulation. Proper rib thickness ratios and balanced placement can significantly reduce shrinkage risk.
- Control Rib Thickness: Keep rib thickness at 50–60% of wall thickness.
- Uniform Rib Distribution: Avoid multiple rib intersections that trap heat.
- Mold Venting Optimization: Remove trapped gas to prevent voids.
- Simulation Validation: Identify high-risk zones early and adjust structures accordingly.
Ribs enhance rigidity, but poor design can turn them into shrinkage traps.
How Does Cooling System Layout Adjust Local Shrinkage?
The cooling system layout directly influences polymer solidification speed and temperature balance. If cooling channels are too far from thick regions, heat buildup can cause excessive shrinkage; overcooling may lead to warpage. An efficient cooling layout significantly reduces local shrinkage differences.
- Optimize Cooling Circuits: Improve heat transfer and temperature uniformity.
- Control Coolant Flow Rate: Maintain consistent cooling and stable mold temperature.
- Use High-Conductivity Inserts: Enhance thermal exchange and improve part stability.
- Dynamic Temperature Control: Precisely adjust temperature in critical zones.
Balanced cooling is the invisible key to preventing localized shrinkage.
Comparison of Structural Features Influencing Local Shrinkage
|
Structure Type |
Shrinkage Risk Level |
Cooling Rate Difference |
Stress Concentration |
Recommended Improvement |
| Uneven Wall Thickness | High | Large | High | Optimize wall design |
| Dense Rib Network | Medium-High | Medium | High | Reduce rib intersections |
| Unbalanced Flow Channel | Medium | Medium | Medium | Improve gate balance |
| Uneven Cooling Layout | High | Large | Medium-High | Redesign cooling system |
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How Can Simulation and Process Integration Optimize Structures?
In modern injection design, structural simulation (Moldflow) and process integration are key tools for reducing local shrinkage. By predicting flow, temperature, and stress distribution during the design stage, engineers can fine-tune ribs, wall thickness, and cooling layout. Digital verification ensures every mold launch is more accurate and efficient.
1.Virtual Molding Validation: Avoid repeated mold rework.
2.Iterative Structural Optimization: Adjust wall thickness, ribs, and corner radii.
3.Process Parameter Integration: Coordinate injection speed and holding pressure.
4.Real-Time Production Monitoring: Track thermal balance using sensor feedback.
Conclusion
Even small structural variations in an injection part can trigger significant differences in local shrinkage. By optimizing wall thickness, rib design, and cooling layout, manufacturers can achieve consistent dimensions and improved surface quality. Introducing structural simulation and thermal balance analysis early in the design phase is the foundation for stable mass production.
For expert assistance in implementing structural optimization for your production needs, visit our resource center or contact us. Let’s help you scale up your manufacturing with precision and efficiency!
Post time: Oct-22-2025