What Is Gas-Assisted Injection Molding?
Introduction
Application of Gas-Assisted Injection Molding (GIM) Technology
Gas-assisted injection molding (referred to as GIM) has a history of many years as a very mature technology in the plastics processing industry. One of its most important application areas is the production of thick-walled parts, such as car handles and similar products. Plate-type parts or other locally thickened plastic parts are also important application areas.
Gas-assisted injection molding is a plastics forming technique that introduces high-pressure inert gas into the thick-walled section of the part to create a hollow core inside the molded part, driving the melt to complete the filling process and achieving uniform gas pressure holding, or utilizing the gas to directly achieve localized high-pressure holding and elimination of sink marks. Traditional injection molding processes cannot mold parts with both thick and thin walls together, and the parts have high residual stress, are prone to warpage and deformation, and have sink marks on the surface. GIM technology successfully produces parts with both thick and thin walls by hollowing out the interior of the thick section. Furthermore, the products have a good external surface, excellent quality, and low internal stress.
Resources Required for Gas-Assisted Injection Molding
① Injection molding machine;
② Gas source (Nitrogen generator);
③ Gas delivery pipelines;
④ Equipment for controlling the effective flow of nitrogen (Nitrogen control console);
⑤ Molds equipped with GIM settings (Gas-assisted molds).
Principles for Determining the Gas Inlet Method in Gas-Assisted Injection Molding
① The gas inlet methods for gas-assisted injection molding can be divided into nozzle-side gas injection and mold-side gas injection. Nozzle-side gas injection requires modification of the injection molding machine's nozzle to allow both melt and gas passage. Gas injection is performed by switching to the gas passage after melt injection is complete. Mold-side gas injection does not require modification of the injection molding machine's nozzle, but requires opening a gas passage in the mold and installing a special gas inlet component (gas pin) that works under gas pressure control to guide the gas into the mold cavity.
② The selection of the gas inlet method should be based on the specific condition of the part. With the nozzle-side gas injection method, the plastic and gas pass through the same runner, and the flow and filling direction are consistent, so the principle is almost the same as traditional injection molding. With the mold-side gas pin gas injection method, the gas flow direction may be opposite to the plastic flow direction. Nozzle-side gas injection is more suitable for front shells of TV sets, for example; mold-side gas pin gas injection is generally used for hot runner molds or parts requiring reinforcement or a remote gate location, such as molds for TV back shells and some long strip-shaped parts with larger movement lengths.
Advantages of Applying Gas-Assisted Injection Molding Technology
① Saves plastic raw materials, with savings up to 50%.
② Shortens the cycle time (CT).
③ Reduces the clamping force of the injection molding machine, up to 60%.
④ Increases the working life of the injection molding machine.
⑤ Reduces the pressure in the mold cavity, which reduces mold wear and increases the mold's working life.
⑥ For certain plastic products, mold materials can use softer metals.
⑦ Reduces the internal stress of the product.
⑧ Solves and eliminates surface sink mark problems on the product.
⑨ Simplifies the complicated design of the product.
⑩ Reduces the power consumption of the injection molding machine.
⑪ Reduces the investment cost in the injection molding machine and mold development.
⑫ Reduces production costs.