Gas-assisted injection molding has the advantages of low injection pressure, small warpage of the product, good surface quality, and easy processing of products with large differences in wall thickness, and has developed rapidly in recent years. It has been used in developed countries for the production of plastic products for more than 20 years. Gas-assisted injection molding consists of plastic melt injection and gas injection (usually with nitrogen) injection molding. Compared with the traditional injection molding process, gas-assisted injection molding has more process parameters to be determined and controlled, and thus has special requirements for product design, mold design and molding process control.
The gas-assisted injection molding process first involves the injection of resin into the cavity, and then the high-pressure compressed nitrogen is introduced into the molten material, and the gas flows to the low-pressure and high-temperature regions of the product along the direction of the least resistance. As the gas moves through the article, it hollows out the thick wall section by replacing the molten material. These displaced materials fill the remainder of the article. When the filling process is completed, the holding pressure is continuously supplied by the gas to minimize the shrinkage or warpage of the shot.
Advantages of gas-assisted injection molding
Low injection pressure reduces residual stress, thereby minimizing warpage;
The low injection pressure reduces the clamping force requirement, and a small tonnage machine can be used;
Low residual stress also improves the dimensional tolerances and stability of the article;
Low injection pressure can reduce or eliminate the appearance of flashing of the product;
The thickness of the finished meat is hollow, thus reducing the plastic, up to 40%;
Compared with solid products, the molding cycle is shortened, less than half of the foam molding;
Gas-assisted injection molding offers significant advances in structural integrity and design freedom;
For some products with large differences in wall thickness, they can be formed at one time by gas-assisted technology;
The pressure in the cavity is reduced, the loss of the mold is reduced, and the working life is improved;
By reducing the injection point, the air passage can replace the hot runner system to reduce the cost of the mold;
The gas passage along the ribs and the protruding roots increases the stiffness, regardless of the sink marks;
Excellent surface finish, no need to worry about the swirling phenomenon caused by foam molding.
The use of gas-assisted injection molding technology allows designers to design products more complexly, while moldmakers can simplify mold construction. Increasing product functionality and reduced product components result in shorter production cycles without the need for assembly and post-finishing work. The production of molded CD trays and automotive electronic center press-fit laminates has shown that gas-assisted injection molding can be applied to the production of thin-walled articles. Advances in dimensional stability, reduction in residual stress of the product, and reduction in warpage are a major advantage of gas-assisted injection molding techniques. The application of gas-assisted injection molding technology will become more and more complex. Now, gas-assisted injection molding technology can be used to produce products with quality from 30g to 18kg.
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