Plastic injection molding

The principle of plastic injection molding (plastic molding process)


plastic injection molding



Plastic is everywhere in our daily life. In our daily life, more than 60% of daily necessities are plastic products, and the most common

production method of plastic products is "plastic injection molding".



What is plastic injection?


To put it simply, plastic injection molding consists of three elements, namely: "plastic material", "plastic mold" and "plastic injection

machine", and these three elements will be subdivided into many different parts due to different manufacturing requirements.



"Three Elements of Injection Molding"

►Plastic raw materials
     Crystalline material: PP, PE, PA...
     Amorphous materials: PS, ABS, PC...
►Plastic mold
     Two-plate mold, three-plate mold, hot runner
►Plastic injection machine
     Hydraulic crankshaft type, two-plate direct pressure type, all-electric type


Before understanding the process of injection molding, let's briefly understand the structure of the injection machine:

Injection machine structure

• Drum : The location where the raw material is stored

• Feed tube : the passage of raw material to the mold

• Screw : The material tube is covered with a "screw". The function of the screw is to melt and knead the plastic, and inject a

                   certain amount of plastic into the mold.

• Mould : It is like a model for making chocolate, into which raw materials are injected to form a product of a specific shape.

• Ejector : "Ejector" is a part of the mold, and its main function is to push the molded product out of the mold, that is, to separate

                      the product from the mold.


5 steps of injection molding

The process of plastic injection molding can be simplified into a "5-stage, continuous cycle" process, which are:
Plasticizing  ⇒  Filling  ⇒  Packing  ⇒  Cooling  ⇒  Ejecting

Plastic injection manufacturing process

1. Plasticization
     The raw material is melted in the material tube (the screw is actuated to make the raw material knead evenly)

2. Filling
     The material is "filled" into the mold through the screw

3. Pressure retention
     After the raw material is filled into the mold, in order to avoid the backflow of the raw material, the space in the mold is

        continuously pressurized to ensure the compactness of the raw material filling.

4. Cooling
     The product is rapidly cooled and shaped in the mold.

5. Ejection
     The cooled product is pushed out of the mold through the ejector pin on the mold.

The principle of plastic injection molding is like making chocolate. The raw materials are poured out of the machine, heated and

melted, and then injected into the model. After the product has cooled, it is demolded and the finished product is completed.

Plastic injection molding is an easy and rapid prototyping method, but because plastic itself has the characteristics of "cooling shrinkage",

it requires the technology and experience of product designers and processing manufacturers to be able to adjust the size and size

of the product. The appearance is well controlled to create a good plastic product!



Further understanding for Plastic injection molding

This is just a partial overview of plastic injection molding. Are they the right knowldge for you? Not sure how to apply them to your

next project? Just contact our technical experts and we can offer helpful advice about how to get the best results from its processes. 

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