What’s gas assisted injection molding?
Gas-assisted injection molding (GAM or GAIM) refers to injecting inert high-pressure nitrogen when the plastic material is filled into the mold cavity (filling like 75% ~ 99.9%), and the gas pushes the molten plastic to continue filling the mold cavity and do the pressure holding instead of plastic, which is a new injection molding technology.
Gas-assisted injection can be realized by adding an air supply device to the existing injection molding machine. The air supply device is composed of an air pump, a high-pressure gas generating device, a gas control device, and a gas nozzle.
The gas control device continuously supplies air with a special compressor, and is controlled by an electric control valve to keep the pressure constant. There are usually three levels of pressure. One set gas control device can be equipped with multiple sets of injection molding machines.
Advantages of gas assisted injection molding
- Save raw material up to 30%
- Eliminated shrink marks, improve surface quantiy of product
- Reduce the production cycle time up to 30%
- Reduce deformation, improve product strength
- Simplify the mold, reduce the mold cost
- Prolong lifetime of the mold, reduce energy consumption
Technical characteristics of gas-assisted injection molding molds:
- The design of the mold cavity should try to ensure the flow balance to reduce the uneven penetration of the gas, and to ensure the flow balance is also a design principle of ordinary injection molding molds, but this is more important for gas-assisted injection molding products.
- The mold design should consider the impact on process parameters, because gas-assisted injection molding is much more sensitive to process parameters than ordinary molding. In injection molding, slight differences in wall temperature or injection volume of mold can cause asymmetry of gas penetration in symmetrical parts.
Gas-assisted injection molding equipment:
- injection molding machine (it its better if the machine has better metering accuracy).
- Nitrogen control system, including self-enclosed gas-assisted nozzle.
- High pressure nitrogen generator.
- Industrial nitrogen tank and air compressors that provide boosting power.
- plastic mould designed and manufactured for gas-assisted injection.
- gas-assisted injection gas-assisted nozzle
if Nozzle intake method, it is using a dedicated self-enclosed gas-assisted nozzle. After the injection of plastic, high-pressure gas is relied on the nozzle to directly enter the interior of the plastic. Cooling, before the mold is opened, the nozzle is forcibly separated from the product material channel by backward moving of the injection unit, so that the gas is discharged from the product.
- gas needle
If the gas needle air inlet method , it is to install an exhaust device—gas needle—in a specific position of the mold. After the plastic is injected into the cavity, the gas needle is wrapped inside the plastic; at this time, the high-pressure gas is discharged, and the gas needle forms an extended closed space in the plastic according to the air channel—the air cavity, and maintains a certain pressure until it cools, and the mold opens Previously, the gas in the air cavity was ejected from the inside of the plastic by the control device by means of a gas needle.
The gas-assisted injection molding process can be divided into four stages:
- The first stage of gas-assisted injection: plastic injection. The melt plastic enters the cavity and encounters the lower temperature mold wall, forming a thinner solidified layer.
- The second stage of gas-assisted injection: gas incident. The inert gas enters the molten plastic, pushing the unsolidified plastic in the center into the cavity that has not yet been filled.
- The third stage of gas-assisted injection: the end of the gas incident. The gas continues to push the plastic melt until the melt fills the entire cavity.
- The fourth stage of gas-assisted injection: gas do holding pressure. In the pressure-holding state, the gas in the air channel compresses the melt and is fed to ensure the appearance of the product.
Generally, what kind of product can use the gas-assisted injection molding technology?
please see below picture.