What Are the Steps in Plastic Injection Molding?

Plastic injection molding is a continuous process, and each stage directly affects the quality of the final product. Controlling the accuracy of these stages is essential for producing high-quality plastic products. The process steps involved mainly include the following stages:

1. Preparation before molding

In order to make plastic injection molding proceed smoothly and ensure the quality of the product, a series of preparations need to be carried out before production, including raw material pretreatment, cleaning the barrel, preheating the inserts and selecting release agents.

2. Injection process

Feeding: Plastic injection molding is an intermittent process, which requires quantitative (constant volume) feeding to ensure stable operation, uniform plasticization of plastics, and finally obtain high-quality plastic parts.

Plasticization: The molding material (plastic) is heated, compacted and mixed in the barrel of the injection machine, and is transformed from a loose powder or granular solid into a continuous homogenized melt.

Injection: The plunger or screw starts from the metering position in the barrel, applies high pressure through the injection cylinder and piston, and quickly delivers the plasticized plastic melt into the closed mold cavity. Injection can be further divided into the following stages:

Flow filling: The melt enters the mold cavity and fills the mold.

Pressure maintenance and shrinkage compensation: Continue to apply pressure to ensure that there are no air bubbles inside the mold and the plastic is fully filled. This stage helps to improve the density and mechanical strength of the plastic part.

Backflow: The melt cools and solidifies in the mold, and part of the melt will flow back due to shrinkage.

Cooling: When the plastic in the pouring system has frozen, the plunger or screw can be withdrawn and the pressure of the plastic melt can be relieved. At the same time, a cooling medium (such as water, oil or air) is introduced into the mold to further cool the mold. The cooling process starts from the injection of the plastic melt into the cavity and continues until the plastic part cools to a certain temperature and can be demolded.

Demolding: The plastic part is pushed out of the mold under the action of the ejection mechanism. Careful operation is required at this stage to avoid damage to the product.

3. Post-processing of the product

After the product is demolded, it may also need to be humidified to stabilize the color, performance and size of the plastic part to complete the complete plastic injection molding process.