Four Stages of the Injection Molding Manufacturing Process

Four Stages of the Injection Molding Manufacturing Process

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Nowadays, the trend of processing technology is developing with high and new technology. These technologies include micro injection molding, high-filling compound injection, water-assisted injection molding, mixing and using various special injection molding processes, foam injection molding, mold technology, simulation technology, etc.

The injection manufacturing process mainly includes four stages: filling, pressure maintaining, cooling, and demolding. These four stages directly determine the quality of the products. It is a complete continuous process.

  1.  Filling stage

The filling is the first step in the whole injection manufacturing process, from the beginning of injection molding when the mold is closed to about 95% of the mold cavity filling. Theoretically, the shorter the filling time is, the higher the molding efficiency is. But in practice, the molding time or injection speed is restricted by many conditions.

2. Pressure maintaining stage

The function of the packing stage is to apply pressure continuously, compact the melt and increase the density of the plastic to compensate for the shrinkage behavior of the plastic. In the packing process, the back pressure is high because the cavity has been filled with plastic. In packing compaction, the screw of the injection molding machine can only move forward slowly, and the plastic flow speed is also relatively slow. At this time, the flow is called packing flow.

3. Cooling stage

In the introduction of injection and mold, the design of the cooling system is very important. This is because only when the plastic products are cooled and solidified to a certain rigidity, can the plastic products avoid deformation due to external force after demoulding. Because the cooling time accounts for 70% – 80% of the whole injection molding manufacturing process, a well-designed cooling system can greatly shorten the molding time, improve the injection molding productivity and reduce the cost.

4. Demoulding stage

The injection molding manufacturing cycle consists of clamping time, filling time, holding time, cooling time, and demolding time. Cooling time accounts for the largest proportion, about 70% – 80%. Therefore, the cooling time will directly affect the plastic product molding cycle length and output size. In the demoulding stage, the temperature of plastic products should be cooled to lower than the thermal deformation temperature of plastic products, so as to prevent the relaxation of plastic products caused by residual stress, or warping and deformation caused by external demoulding force.


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