In injection molding, design of glue injection system directly determines product quality and production efficiency. A small mistake in design of glue inlet may lead to fatal defects such as product shrinkage, weld marks, and pores. Today, we deeply analyze industry-recognized "13 Glue Injection Rules" to help you control process from source and avoid ten years of detours!

 

Glue injection system is channel for molten plastic to enter mold cavity from injection molding machine nozzle, including main channels, branch channels, gates and other structures (diagrams can be inserted here). Its core task is to allow plastic to fill mold evenly, quickly and completely, while avoiding energy loss and material waste.

Rule 1: Balanced flow principle
Principle: Ensure that flow path of molten material is balanced when it enters cavity from different gates.
Function: Avoid warping and internal stress concentration caused by uneven filling.
Case: In multi-cavity molds, a symmetrical runner design is used (figure compares effects of unbalanced and balanced runners).
Rule 2: Shortest path principle
Principle: The shorter melt flow path, the smaller energy loss.
Function: Reduce pressure loss, improve filling efficiency, and reduce risk of material shortage.
Rule 3: Gate size adapts to material characteristics
Principle: High-viscosity materials (such as PC) require larger gate sizes, and low-viscosity materials (such as PP) can be appropriately reduced.
Formula reference: Gate thickness ≈ 0.5~0.8 times product wall thickness.
Rule 4: Avoid injection phenomenon
Principle: High-speed melt directly injected into cavity will form serpentine patterns.
Solution: Use fan-shaped gates or lap gates to reduce flow rate (with injection defects and improvement comparison diagrams).
Rule 5: Gate location optimization
Principle: Gate location should avoid being in product stress concentration area or appearance surface.
Function: Reduce product appearance defects and structural weaknesses.
Case: Gate position of electronic product shell is selected on non-appearance surface or edge.
Rule 6: Rationalization of number of gates
Principle: Too many gates will lead to more weld marks, and too few gates may lead to insufficient filling.
Function: Balance filling efficiency and product quality.
Formula reference: Number of gates ≈ product area/effective area of a single gate.
Rule 7: Smooth transition between main channel and branch channel
Principle: Reduce resistance of molten material in main channel and branch channel.
Function: Improve flow efficiency and reduce material degradation.
Solution: Use rounded corner design and reasonable flow channel cross-sectional area.
Rule 8: Avoid shear overheating at gate
Principle: Excessive shear rate will lead to local overheating and material degradation.
Solution: Optimize gate shape and injection speed to reduce shear stress.
Rule 9: Symmetrical design of gate
Principle: Symmetrical gate design helps to fill evenly.
Function: Reduce warping and dimensional deviation.
Case: Application of symmetrical design in large automotive parts.
Rule 10: Avoid cavitation near gate
Principle: Pressure changes near gate may cause cavitation.
Solution: Optimize gate position and exhaust system design.
Rule 11: Cooling design of gate
Principle: A reasonable cooling system helps control temperature near gate.
Effect: Reduce thermal expansion and contraction.
Case: Apply cooling water channel design in high-precision molds.
Rule 12: Material adaptability of gate
Principle: Different materials have different sensitivities to gate shape and size.
Solution: Adjust gate design according to material properties, such as transparent materials need to avoid gate marks.
Rule 13: Maintainability design
Principle: Gate should be easy to trim or automatically separate.
Application: Successful cases of latent gate design in automotive parts.
III. Cost of violating rule: Analysis of common defects
Shrinkage: Gate solidifies too early and cannot compensate for shrinkage → Check gate size and holding time.
Welding marks: improper intersection angle of multiple streams → optimize gate position or increase venting.
Flow marks: too large temperature difference near gate → adjust mold temperature or gate shape.
IV. Practical skills: 3-step quick self-check injection design
Simulation analysis: use software such as Moldflow to predict filling effect.
Trial mold observation: focus on the first batch of samples in gate area.
Parameter fine-tuning: compensate for design deficiencies by adjusting injection speed and pressure.
Conclusion: Injection system is "Ren and Du Meridians" of injection molding process. Mastering these 13 rules is equivalent to getting pass code for high-quality products. If you are still worried about product defects, you might as well start with injection design and re-examine it!