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Gas Assisted Injection Molding

Gas-assisted injection molding (GAIM) is a type of injection molding that uses inert gas to create hollow part walls. This leads to lightweight parts that use less material than conventional injection molding, but that maintain their strength and have a better surface finish. GAIM is used in a wide variety of industries to create lightweight and strong parts while saving on material.

This article will discuss the gas-assisted injection molding process, how it works, materials, application, advantages, and disadvantages.

What Is Gas-Assisted Injection Molding?

Gas-assisted injection molding (GAIM) is a manufacturing process in which molten plastic and inert gases are injected into a mold to create 3D parts with channels in the part walls. The process is similar to conventional thermoplastic injection molding but additionally injects inert gas into the mold to create hollows or channels in the walls of the plastic part.

Gas-assisted injection molding produces lightweight parts that retain most of their strength. Parts are generally cheaper than those made with injection molding due to using less material per part. However, gas-assisted injection molding is not suitable for transparent materials, requires more complex molds, as well as high initial costs due to the specialized equipment required.

What Is Gas-Assisted Injection Molding For?

Gas-assisted injection molding is a manufacturing process used for creating 3D plastic parts with hollow walls. These parts are lightweight with high strength, excellent surface finish, and dimensional accuracy.

When To Use Gas-Assist Injection Molding?
Gas-assisted injection molding is used when lightweight 3D plastic parts with high strength, excellent accuracy, and surface finish are required. It is also used for parts that contain hollow sections, or when material needs to be saved.

How Is Gas-Assisted Injection Molding Used in Manufacturing?

Gas-assisted injection molding is a manufacturing process that uses inert gas as part of the injection molding process to create 3D plastic parts with hollow walls or channels. It is used to create strong, but more lightweight parts than those produced by conventional injection molding. Additionally, GAIM produces parts with exceptional surface quality and high dimensional accuracy, all while using less material than conventional injection molding.

What Is the Gas-Assisted Injection Molding Process?

The gas-assisted injection molding process consists of the following steps:

Clamp the mold together, ready to receive the molten plastic.
Feed the plastic pellets into the hopper, and heat until melted.
Inject the molten plastic into the mold. In GAIM, only around 70–80% of the mold gets filled with the molten plastic.
Inject the inert gas into the mold, which forms a bubble in the molten plastic, pressing it evenly against the sides of the mold.
As the plastic starts to cool, it contracts, reducing pressure in the mold, and potentially resulting in deformation and inaccuracies. In this stage, more gas is injected to maintain even pressure across the part.
Once the part has cooled and hardened, it gets ejected from the mold to make space for the next part.
How Long Does the Gas-Assisted Injection Molding Process Take?
The gas-assisted injection molding process can take anywhere from a few seconds to several minutes, depending on the material type, part geometry, and wall thickness. Compared to conventional injection molding, gas-assisted injection molding has an extra step in which gas is injected into the part wall and pressure is maintained until the part has sufficiently cooled. However, even with this additional step, gas-assisted injection molding is generally quicker than conventional molding, as the hollow walls need less time to cool and harden.

How Does Gas-Assisted Injection Molding Differ From Other Molding Process Types?
Gas-assisted injection molding is similar to conventional injection molding in that molten thermoplastics are injected into a mold to create a 3D plastic part. Where gas-assisted injection molding differs from conventional injection molding, is that inert gas is also injected into the mold with the molten plastic, resulting in channels or hollow walls.

Gas-assisted injection molding uses less pressure than conventional injection molding, as there is less material to fit into all the details of the mold. The low-viscosity gas requires less pressure than the material it replaces. Gas-assisted injection molding also spreads the pressure within the mold more uniformly, resulting in better accuracy, a smoother surface finish, and fewer internal stresses in the final product.

To learn more, see our full guide on Other Molding Process Types.

Is Gas-Assisted Injection Molding Better Than Injection Molding?

Gas-assisted injection molding uses inert gas within the injection molding process to create hollows or channels within part walls. When compared to conventional injection molding, this results in parts that have better dimensional accuracy, better surface finish, and that are cheaper and lighter in weight.

This comes at the cost of being a more complex process, requiring skilled machine operators and higher initial equipment and tooling costs.

To learn more, see our full guide on Injection Molding Processes.

What Molds Are Used for Gas-Assisted Injection Molding?

Molds for gas-assisted injection molding are typically made from aluminum, hardened steel, or beryllium-copper alloy. Steel molds are the most durable, but also the most expensive. Aluminum is an economical option but doesn’t have the durability of steel. Beryllium-copper alloy is used for fast heat transfer, which reduces cycle time and improves the part’s surface finish.

These molds are custom-designed and manufactured. They come in two or more sections to allow for ejecting the part after it has been produced, and they also have inlet and outlet holes for gas to pass into the mold.

What Are the Materials Used for Gas-Assisted Injection Molding?

Gas-assisted injection molding can use a range of thermoplastics, including:

Polybutylene Terephthalate (PBT): Food-safe, with excellent heat and UV resistance, and is used in medical and food processing applications.
Polypropylene (PP): Has good strength, good chemical and heat resistance, and low electrical conductivity, but is susceptible to UV degradation.
Polycarbonate (PC): Has excellent impact, wear, abrasion, and thermal resistance, but can be expensive.
High-impact Polystyrene (HIPS): Has high impact resistance and dimensional stability, as well as being cost-effective and fairly easy to process, however, it does not have good chemical resistance.
Polyphenylene Ether (PPE): Has a good strength-to-weight ratio, and good temperature and chemical resistance.
Polyethylene (PE): Has good chemical resistance and a good strength-to-weight ratio. PE comes in different varieties in terms of strength and stiffness, with high-density polyethylene (HDPE) being a popular variety for GAIM.
Polyamide (Nylon): Has good tensile strength and chemical, abrasion, thermal, and fatigue resistance.
Acrylonitrile Butadiene Styrene (ABS): Has good durability, strength, and impact resistance, but can be difficult to process.
Polyphthalamide (PPA, Zytel®): Has high strength and stiffness, good fatigue, thermal, and chemical resistance, and good dimensional stability.
What Are the Applications of Gas-Assisted Injection Molding?
Gas-assisted injection molding is used in a range of applications that require lightweight, strong components with hollow walls, such as:

Automotive parts, including: spoilers, bumpers, and door handles.
Industrial components, including: pipes, containers, and valves.
Medical devices, including inhalers and syringes.
Consumer goods, including toys and sporting goods.

What Is the Quality of GAIM Products?

Gas-assisted injection molding products are high-quality and lightweight with high strength. They also tend to have better surface finish and fewer defects than conventional injection molding. Lastly, by injecting gas into the mold, pressure is distributed uniformly throughout the part, resulting in lower internal stresses.

How Long Do GAIM Products Last?
Gas-assisted injection molding products have similar life spans and life span factors to conventional injection molding products. These plastic products last in the order of years, but this life span depends on the material type, environmental conditions in which the product is used, and the product design.

What Are the Advantages of Gas-Assisted Injection Molding?

Gas-assisted injection molding has the following advantages over conventional injection molding:

Hollow and Lightweight Parts: The main purpose of gas-assisted injection molding is to create parts with hollow walls. This reduces the weight of the final part while maintaining strength.
Reduced Sink Marks: The injected gas maintains pressure consistently on all points in the mold, helping to reduce sink marks.
Complex Geometries: Gas-assisted injection molding can create ribbing and other support features without sink marks or other defects.
Improved Aesthetics: The uniform pressure due to the gas ensures that a smooth finish is achieved throughout the part.
Minimized Warping: By having hollow walls, there is less shrinkage and warping.
Material Savings: Gas-assisted injection molding uses 20–30% less material than conventional injection molding.
Shorter Cycle Times: Hollow walls mean that there is less material, which leads to quicker cooling and cycle times.
What Are the Disadvantages of Gas-Assisted Injection Molding?
Gas-assisted injection molding has the following disadvantages over conventional injection molding:

Complex Process: Using gas-assisted injection molding is a complex process, requiring skilled and trained operators.
Initial Investment: The use of gas requires specialized equipment, making the initial investment higher than for conventional injection molding.
Mold Design Complexity: The design complexity of molds is increased due to having to channel the gas correctly.
Gas Flow Control: The part requires multiple inlet and outlet holes for gas to flow, which may not be desirable from an aesthetic point of view.
Limited Material Compatibility: Plastics that have high flow rates are not suitable for gas-assisted injection molding. Transparent plastics are also unsuitable, due to how the process affects the cosmetics of the part.
Production Rate: The extra step of injecting gas lowers the production rate slightly.

Is Gas-Assisted Injection Molding Cheap?

Yes. Gas-assisted injection molding is relatively inexpensive per part for large production runs. Similar to conventional injection molding, gas-assisted injection molding has high initial costs due to specialized equipment needs, as well as high tooling costs due to complex molds that need to be manufactured per product type produced. Both of these costs are more expensive for gas-assisted injection molding, as the equipment and molds need to support the use of gas within the manufacturing process.

Running costs for gas-assisted injection molding are cheaper than for conventional injection molding, due to the process using less material per part. For large production runs, gas-assisted injection molding will end up being cheaper per part than conventional injection molding, once the higher initial costs have been recouped.

Is Gas-Assisted Injection Molding Cheaper Than Thermoplastic Injection Molding?
No. Gas-assisted injection molding has higher initial costs and higher tooling costs than thermoplastic injection molding. However, the running costs per part for gas-assisted injection molding are cheaper than for thermoplastic injection molding because it uses less material for the hollow walls it produces.

In terms of total costs, thermoplastic injection molding starts cheaper than gas-assisted injection molding. Once the initial and tooling costs are recouped for larger amounts of parts, gas-assisted injection molding becomes cheaper than thermoplastic injection molding.


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