Injection molding refers to a method of injecting a heated and melted material into a mold, and then cooling and solidifying to obtain a molded product.
Generally follow the following six sequences: mold clamping, injection, pressure holding, cooling, mold opening, and product removal.
- a. Air eye refers to the phenomenon that air is trapped in the cavity and the product produces bubbles.
- b. It is caused by the inability of gas to escape from the parting surface, ejector or exhaust hole when two melt forwards meet.
- c. The gas eye is usually located where the melt is finally filled.
- d. Lack of vents or undersized vents will cause air holes or other surface defects in the final filling area
- e. If the design of the product is uneven, it is also very easy to cause gas eye phenomenon.
Possible problems caused by gas eyes : The gas trapped in the cavity cannot be exhausted in time, which may cause surface blistering, air trapping inside the product, and injection dissatisfaction.
ways to improve:
|Structural design||1. Reduce thickness inconsistency and try to ensure uniform wall thickness|
|Mold design||1. Add an exhaust port in the final filling place 2.Redesign the gate and runner system 3. Make sure the exhaust port is large enough so that the gas has enough time and space to drain away|
|Process conditions||1. Reduce the last injection speed 2. Increase mold temperature 3. Optimize injection pressure and holding pressure|
Black spots / streaks are black spots or streaks on the surface of the part, or brown streaks.
Causes of black spots / streaks:
Material degradation: Plastic overheating will cause black spots or streaks. If the plastic stays in the closed barrel and the surface of the screw for too long, it will cause carbonization and degradation, which will cause black spots or streaks during the injection molding process.
Material pollution: The presence of dirty recycled materials, foreign materials, materials of other colors, or easily degradable low-molecular materials in plastic can cause the above phenomenon. Dust in the air also easily causes black spots on the surface of the workpiece.
Improvement method one:
|material||1. Use pollution-free raw materials 2. Place the material in a relatively closed storage bin 3. Increase the thermal stability of the material|
|Mold design||1.Clean the ejector pin and slider 2. Improve the exhaust system 3.Clean and polish any dead corners in the runner to ensure no accumulation 4. Clean the mold surface before injection|
Improvement method two:
|Injection molding machine||1. Choose the right tonnage for the injection molding machine 2. Check whether the inner surface of the barrel and the surface of the screw are scratched|
|Process conditions||1. Reduce the temperature of the barrel and nozzle 2. Clean all aspects of the injection molding process 3. Avoid the black spots / black lines from being recycled|
Brittleness of the part means that the part is easy to crack or break in some parts. Brittleness is mainly due to the breakdown of the macromolecules due to material degradation, which reduces the molecular weight of the macromolecules, thereby reducing the overall physical properties of the polymer.
Causes of crispness:
a. Dry conditions are not suitable
b. Injection temperature setting is incorrect
c. Improper gate and runner system settings
d. Improper screw design
e. The strength of the melting mark is not high
f. using too much recycled material
Improvement method one:
|material||1. Set appropriate drying conditions before injection: If the plastic is dried for several days or the drying temperature is too high, although it can remove substances such as volatiles, it will also easily cause material degradation, especially heat-sensitive plastics. 2. Reduce the use of recycled materials and increase the proportion of raw materials 3. Use high-strength plastic|
|Mold design||1. Reduce the temperature of the barrel and nozzle 2. Clean all aspects of the injection molding process 3. Avoid the black spots / black lines from being recycled|
Causes of flashing
1. Insufficient clamping force: If the clamping force is too small during the injection process, it is not enough to offset the injection pressure, and it is easy to produce flashing / burr on the parting surface.
2. Defects in the mold: If the mold is deformed, or there is a foreign object on the parting surface, or there is a defect in the mold design, it may cause flashing / burr phenomenon.
3. Unreasonable molding conditions: such as unreasonable technological conditions such as excessive melt temperature and excessive injection pressure may cause flash / burr phenomenon.
4. Improper design of the exhaust system: If the exhaust system is not set properly or the exhaust groove is too deep, it will cause flashing / burr phenomenon.
ways to improve:
|Mold design||1. Reasonably design the mold to ensure that the mold can be closed tightly without gaps. 2. Ensure that the mold can be fastened on the template to ensure that the mold is not damaged during molding 3. Check the size of the exhaust port 4. Clean the mold surface 5. Grinding makes the mold produce a loose clamping surface, so that the mold can be closed better under the clamping force.|
|Injection molding machine||1. Set an appropriate clamping force to ensure that the two mounting templates of the injection molding machine are parallel to each other 2. Increase the size of the injection molding machine. The flash may be due to the insufficient clamping force of the small injection molding machine.|
|Molding||1. Increase injection time and decrease injection speed 2. Reduce barrel temperature and nozzle temperature 3. Reduce injection pressure and holding pressure 4. Reduce the buffer length so that the melt does not overfill in the barrel|