What is injection molding?

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What is injection molding?


The method of manufacturing plastic materials using plastic injection molding machines and molds into plastic products is called injection molding.




The plastic raw material is dried and fed into the barrel, and is heated to be molten. Under the push of the screw or the piston, the nozzle and the feeding system are injected into the closed cavity, and after cooling, the hardening is set. The tool used in the molding process is called Injection mold.





The injection mold consists of seven systems: the guiding system, the supporting system, the forming part system, the pouring system, the cooling system, the ejection system, and the exhaust system.


The mold consisting of the above systems, the plastic through the pouring system, through the gate into the cavity, after the filling pressure is cooled by the cooling system, the product is condensed and solidified, and then ejected through the ejection system to complete a molding cycle.

Gating system: The passage through which the plastic melt flows out of the nozzle of the injection machine before reaching the cavity.

The molded part system is mainly designed to allow the finished product to be smoothly shot and molded to obtain an ideal product.

The mold cooling system includes: a cooling water channel, a mold temperature controller, and a heating assembly.


(1) The role of setting the cooling waterway

1. Control the mold temperature to improve the quality of the plastic parts. Mainly manifested in: the effect on surface finish, residual stress, crystallinity, thermal bending.

2. Shorten the molding cycle. 80% of the molding cycle is used for cooling, and a well-designed cooling system is necessary to increase productivity.

3. Cool large sliding parts to avoid jamming.


(2) Cooling method:

1) Water cooling

2) Oil cooling

3) Air cooling

4) chilled water cooling


Ejection system
The ejector of the product is the last step in the  injection molding process. When the product is cured in the mold, an effective way is needed to eject it from the mold. The quality of the topping will ultimately determine the quality of the product. Therefore, the ejection of the product cannot be ignored. Moreover, in the ejection, the product cannot be deformed, whitened, broken or the like to damage the product. This device is the ejection system. The ejector system has the following categories:

 1. Dome needle 2. Flat thimble 3. Sleeve 4. Ejection block 5. Stripping plate 6. Oblique pin 7. Gas cap.



Exhaust system:

Exhaust purpose: to reduce the wind, scorch and other defects caused by the presence of gas in the mold.


Gas source:

a. The air present in the feed system and cavity

b. Evaporation of water in plastics

c. Plastic decomposition produces gas

d. Decomposition or chemical reaction of certain additives in plastics


Guidance system:

In the mold, the guiding mechanism is mainly used to ensure the exact matching between the male mold and the female mold or other parts in the mold to ensure the shape and dimensional accuracy of the plastic products, and to avoid various parts in the mold. Collision and interference occur.


Support system:

Function: The injection molding machine has a large injection pressure. When the span between the two mold feet is large and the strength of the male template is not enough, the male template will produce twist deformation. The use of the support column (SP) is formed at the bottom of the male template. The fulcrum minimizes the deformation of the male formwork. 




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