What is Gas Assisted Injection Molding

Principle: Gas-assisted injection molding is a system in which an inert gas (usually nitrogen) is injected directly into the plasticized plastic in the mold cavity through a segmented pressure control system, causing the internal expansion of the plastic part to cause hollowing, but still keeping the surface of the product intact.

Gas-assisted injection molding can be considered a variation of hollow blow molding, which involves injecting a precisely measured percentage of molten plastic into the mold cavity, a process known as "under-injection", and then injecting a certain volume and pressure of high-pressure nitrogen gas directly into the molten plastic. The gas is surrounded by the plastic melt and diffused in the direction of least resistance.


Due to the mold wall part of the plastic temperature is low, the surface viscosity is high, while the production of thicker parts of the center of the plastic melt temperature is high, viscosity is low, so the gas is easy to the center of the plastic melt penetration and evacuation, in the thick part of the product to form the air channel, and the gas evacuation of the molten plastic and gas pressure to the end of the mold until filled with mold cavity, in the cooling phase of the compressed gas on the plastic melt to keep pressure to fill the shrinkage. After the product is cooled and solidified, the gas is removed and then the mold is opened and ejected.

There are two main methods of gas-assisted injection molding as follows.

(1) Closed gas injection (SEALED INJECTION GAS) method.

It is a method of injecting gas directly into the mold cavity to make the finished plastic hollow. There is no need to use a live valve, just a simple mold processing, the gas auxiliary gas nozzle installed in the mold.

In the same mold, there can be a single or multiple places to inject gas, depending on the needs of the same product, which requires good results and provides greater flexibility in product design.

2) Injectable gas from the injection molding machine (IN-GAS NOZZLE) Method.

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

The application of gas-assisted injection molding technology has the following advantages.

Freedom of design

    Complex plastic parts can be assembled into a single component.

    The possibility to combine thick and thin walled parts on the same part.

    The use of hollow "reinforcement" parts increases their strength.

Improved part quality

    Less distortion and deformation due to reduced micro-shrinkage.

Elimination of shrinkage marks.

    Reduction in the number of injection points and therefore in the number of ripples and fusion lines.

Reduction of production costs

    Reduction of the total weight of the finished part due to the reduction of the wall thickness.

    Reduced cooling time and cycle time due to smaller wall thickness.

    Lower energy consumption costs due to lower clamping force and holding pressure.

    Reduced assembly costs due to the integration of parts.

Reduced investment costs

    Due to lower injection pressure, the clamping pressure of the injection molding machine can be reduced and a smaller tonnage of injection molding machine can be used.

    Due to the lower injection pressure, the mold manufacturing cost is reduced.

    The lower injection pressure reduces the wear and tear of the mold, thus reducing the maintenance cost.