Gas assist injection molding is another specialized molding technique in the plastic injection molding family. Similar to structural foam molding, it creates a part that is lighter and cheaper than traditional injection molding. Given its versatility and cost savings, gas assist molding has become a huge player in medical device manufacturing. Whether your project is a consumer product or a medical device, here are some things you should know about gas assist injection molding.
What is gas assist injection molding?
Gas assist injection molding is a type of plastic injection molding utilizing physical inert gas to fully pack out a part. The gas is introduced into the mold after the resin has been injected, resulting in a hollow part that is light and inexpensive to make. Due to its availability and cost, nitrogen is the preferred gas of choice. Gas assist molding is especially useful in applications where the components have thick geometry and complex designs. There are two types of gas assist injection molding: internal gas assist and external gas assist.
Internal gas assist
In internal gas assist, the gas is introduced into the middle of the part geometry, forcing the molten resin to balloon outward packing the mold. The middle of the part is left with a hollow channel where the gas was introduced. In certain cases, the gas is introduced while the cavity is only partially filled with resin with the aim of assisting the remaining resin in filling the part before it is packed out. This type of gas assist molding is specifically used for parts with thick sections and for producing lighter, hollow parts.
External gas assist
External gas assist occurs when gas is introduced to the non-aesthetic exterior side of a part. The high-pressure gas pushes the uncured resin away, packing it into the opposite side of the tool. Since the gas is responsible for packing the resin into the tool, lower injection pressures are required. Even distribution of the gas prevents warping and internal stress of the part, improving quality. External gas assist can easily pack out thick geometries that would otherwise have sink marks or warping from traditional molding.
Benefits of gas assist injection molding
Gas assist injection molding offers several advantages over traditional plastic injection molding. It increases the aesthetics of molded parts due to the gas pressure pushing the plastic resin evenly throughout the mold cavities. It also helps fulfill the holding phase of the mold process faster, reducing cycle time. Additionally, the gas reduces required press tonnage to fill out the part. Both shorter cycle times and smaller press tonnage decrease tooling and manufacturing costs. From a product design perspective gas assist allows engineers to create larger, thicker, and more complex moldable parts that would not be possible using traditional methods. Some commonly made gas assist parts are handles due to their thick cylindrical shapes while others include doors, cabinets, and coverings.
Design considerations for gas assist inject molding
A few design considerations need to be taken for gas assist molded parts when designing for manufacturing. The part design must be adapted to include features that control where, when, and how gas is introduced on the plastic surfaces. There needs to be gas zones and modified thicknesses in areas where the gas is applied to the part. Internal gas assist requires design modifications that add overspill pins and gas pins. Overspill pins help to remove any extra resin and gas pins are where the gas is inserted. Specialized gas control equipment must be programmed to insert the gas at the correct timing and pressure during the molding process. A common issue with external gas assist is that the process of the gas pushing against the plastic leaves a wavy unaesthetic marking on one side. In these cases, external gas assist should only be used on parts where the nonaesthetic side is hidden in the final assembly.
About Synectic Product Development: Synectic Product Development is an ISO 13485 compliant, full-scale product development company. Vertically integrated within the Mack Group, our capabilities allow us to take your design from concept all the way to full scale production. With over 40 years of experience in design, development, and manufacturing, we strive for ingenuity, cost-effectiveness, and aesthetics in our designs. Learn more about our contract manufacturing services and see how we can help your next project.