Gas Assisted Injection Molding (GAIM) is used when standard injection molding cannot effectively handle thick sections, sink marks, or part weight reduction.
By introducing pressurized gas into the mold, this process creates hollow channels inside the part, reducing material usage while maintaining structural strength and surface quality.
As a specialized process within injection molding, gas assist molding is widely used for structural and thick-walled plastic components where both performance and cost efficiency matter.
What is Gas-Assisted Injection Molding?
Gas Assisted Injection Molding (GAIM) is an advanced molding technique where pressurized gas (typically nitrogen) is injected into the molten plastic during the molding cycle.
Instead of fully filling the cavity with solid plastic, the gas pushes the melt outward, forming hollow sections inside the part. This helps:
- Reduce material consumption
- Eliminate sink marks in thick areas
- Improve dimensional stability
If you want to understand how this differs from the standard process, see our guide on the principles of injection molding process.
Gas Assisted vs Traditional Injection Molding
Gas assist is not just a variation—it changes how the part is formed. The process is used when the part structure becomes the limitation, not just material or tooling.
Standard injection molding creates a solid part that works well for most designs. However, in parts with thick sections, it often leads to sink marks, internal stress, and longer cooling times.
Gas assisted injection molding addresses this by injecting pressurized gas into the melt during filling. The gas pushes the material outward, forming a hollow core while keeping a solid outer surface. This helps reduce material usage and eliminates common defects in thick areas.
In practical use, the difference comes down to part design.
Standard injection molding is suitable for general parts with consistent wall thickness. Gas assist is used when the design includes thick ribs, structural sections, or when weight reduction and surface quality become critical.
When to Use Gas Assisted Injection Molding
Gas assist is suitable when standard injection molding starts to show limitations.
Use gas-assisted injection molding when:
- Parts have thick cross-sections prone to sink marks
- Weight reduction is required without sacrificing strength
- Components need high stiffness-to-weight ratio
- Surface quality is critical for visible parts
- Large parts require material cost optimization
For general part selection and process comparison, refer to our overview of injection molding types.
Types of Gas Assist Injection Molding Processes
There are two primary types of Gas Assist Injection Molding (GAIM) processes: Internal Gas Assist Injection Molding and External Gas Assist Injection Molding. Let’s explore each type in detail:
Internal Gas Assist Injection Molding
In Internal Gas Assist Injection Molding, the gas is injected directly into the molten plastic inside the mold cavity. The gas displaces the molten plastic, creating a hollow section within the part. The gas is injected through special gas pins or channels integrated into the mold design. These pins allow the gas to flow through the part and form the desired hollow geometry.
Internal gas-assist molding is suitable for parts with thick cross-sections or areas that are prone to sink marks. By introducing gas, the thick sections are hollowed out, reducing material usage and minimizing sink marks on the part’s surface.
In a word, Gas is injected directly into the molten plastic inside the cavity. It is the most common method and ideal for thick sections and structural parts.
External Gas Assist Injection Molding
In External Gas Assist Injection Molding, the gas is injected outside the mold cavity, between the mold surface and the solidified plastic part. The gas flows through specially designed gas channels on the external surface of the mold, displacing the molten plastic inside the mold cavity. This creates hollow sections within the part without affecting the part’s external appearance.
External gas-assist molding is often used for complex parts with intricate geometries or those requiring multiple hollow channels. It offers design flexibility and allows for the creation of parts with varied wall thicknesses and internal cavities.
In a word, Gas is applied between the mold surface and plastic. It is used for more complex geometries, but is less common in industrial applications.
Both types of gas-assist injection molding processes offer advantages in terms of material savings, reduced cycle times, improved part quality, and enhanced design possibilities. The choice between the two methods depends on the specific requirements of the part and the desired hollow geometries within the design.
Materials Used for Gas Assist Injection Molding
Compared to standard molding, material selection here focuses more on flow and pressure response, not just strength. Not all materials perform equally well in gas assist molding. The key requirement is stable flow behavior under high-speed injection and pressure.
Common materials include:
- PP (Polypropylene) – good flow and cost efficiency
- ABS – balanced strength and processability
- PC (Polycarbonate) – higher strength and dimensional stability
- PA (Nylon) – for structural applications
- PE (Polyethylene) – lightweight, with good strength and flexibility
- PS (Polystyrene) – good electrical insulating, and ease of processing
Applications of Gas-Assisted Injection Molded Parts
Unlike thin wall injection molding, which focuses on ultra-thin sections, gas assist is designed for thick and structural parts. Gas assist is best understood by looking at part structure, not just industries.
Typical applications include:
- Handles and grips (uniform surface, hollow core)
- Tubular or frame structures
- Large panels with thick ribs
- Automotive interior structural parts
- Furniture components requiring strength and weight reduction
Advantages of Gas Assist Injection Molding
Compared to standard molding, gas assist provides specific benefits:
- Eliminates sink marks in thick sections
- Reduces part weight (typically 20–40%)
- Improves stiffness-to-weight ratio
- Reduces material consumption
- Enhances surface quality
For general molding advantages and limitations, see injection molding advantages and disadvantages.
Disadvantages of Gas Assist Injection Molding
- Higher tooling complexity
- More demanding process control
- Additional equipment required
- Not suitable for thin-wall parts
Design Considerations for Gas Assist Injection Molding
Design plays a critical role in successful gas assist molding.
Key factors include:
- Gas channel design – determines hollow structure formation
- Gate location – must support controlled gas penetration
- Wall thickness – needs sufficient thickness to form hollow cores
- Flow balance – ensures uniform gas distribution
Conclusion
Gas assisted injection molding is not a replacement for standard injection molding—it is a solution for specific structural challenges. When used correctly, it helps reduce material cost, improve part performance, and eliminate defects that are difficult to control in conventional molding.
Zhongde, as a China custom manufacturer, is ready to cooperate with you and offer competitive molded products through our professional injection molding service.
