Gas-assisted injection molding

The gas-assisted injection molding system directly injects inert gas (usually nitrogen) into the melt plastic in the mold cavity through the sectional pressure control system, which makes the plastic part expand and cause hollowness, but still keeps the shape of the product surface.

Gas-assisted injection molding can be regarded as a variant of hollow blow molding. The process of gas-assisted injection molding is to inject an accurately measured plastic melt which accounts for a certain proportion of the mold cavity.

This process is called “short-shot-injection molding”, and then directly inject a certain volume and pressure of high-pressure nitrogen into the molten plastic, and the gas diffuses along the direction of minimum resistance surrounded by the plastic melt.

Because the plastic temperature near the mold wall is low and viscosity is high, while the plastic melt in the center of the thicker part is of high temperature and of low viscosity, the gas can easily penetrate the plastic melt in the center, developing an air passage in the thick part of the part.

The molten plastic  is pushed to the end of the mold by gas pressure until it fills the mold cavity full.

In the cooling stage, the gas is compressed to maintain pressure and compensate the plastic melt shrinkage.

After the product is cooled and solidified, the gas is discharged, and then the mold is opened and plastic part is ejected.

There are two kinds of gas-assisted injection molding:


It is a method of injecting gas directly into the mold cavity to make the finished plastic product hollow.

There is no need to adopt a movable valve, and the air-assisted air nozzle is installed in the mold through simple mold processing.

On the same mold, there can be one or more places for injecting gas, which depends on the needs of the product, and it is required to make the product have good effect and provide  flexibility in product design.


A special closed air injection nozzle can be installed on the injection molding machine.

Gas-assisted injection molding pros:

Free design

Plastic parts with complex comprehensive functions can be assembled into a single assembly.

Thick-walled and thin-walled parts can be combined on the same part.

The hollow “ribs” can improve its strength.

Improve the quality of parts

As the stress is reduced, the distortion and deformation are reduced.

Eliminate shrinkage marks

As the number of gates is reduced, the welding lines are correspondingly reduced.

Reduce the production cost

As the wall thickness is reduced, the total weight of finished parts is reduced.

Because the wall is hollowed, the cooling time and cycle time are shortened.

Because of the reduction of clamping force and injection molding pressure, the energy consumption  is reduced.

Because of the integration of different parts, the assembly cost is reduced.


Reduce investment cost

Because the injection pressure is low, the clamping pressure of injection molding machine can be reduced, and injection molding machines with smaller tonnage can be used.

Because the injection pressure is low, the manufacturing cost of the mold is reduced.

Because the injection pressure is low, the loss of the mold is reduced, thus reducing the maintenance cost.


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