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Gas assisted molding, also known as structural web, is a process that adds pressurized inert gases to the plastic melt to aid and improve the flow and pack of the molded piece. It allows production of larger and stronger molded plastic parts with attractive surface cosmetics.

There are many benefits when using gas assisted molding. Miles Products made this short video to outline how the gas assisted molding process works and showcase

The benefits provided by gas assist.

The main benefit of gas assisted molding is the flexibility and opportunity it brings to the design of large and complex molded parts.

Design benefits include:

  • More latitude and options for introducing features such as ribs and bosses.
  • Taller ribs and bosses can be used in the design without sink on the opposing side.
  • Thinner walls can be produced for large structural components.
  • Improves the surface cosmetics of large molded parts by eliminating sink and swirls.
  • Smoother surfaces with consistent color and finish that rival high-pressure injection molding.
  • Hollow thicker sections can be molded which improves part strength.
  • Eliminates warp on larger flat molded surfaces.
  • Can eliminate finishing work such as coring out of thick sections.

Other production and cost benefits include:

  • Reduces cavity pressure needed during molding process.
  • Saves cost by allowing the use of a lower tonnage press.
  • Lower pressures allow for use of aluminum molds which saves on tooling costs.
  • Saves on tooling costs by eliminating undercuts.
  • Molded plastic parts can replace some parts that previously required metal.
  • Used along with multi-nozzle injection, gas assist helps produce larger sized parts or multiple parts simultaneously.
  • Produces larger stronger parts with lighter weights.

How gas assisted molding works.

Inlets and channels are incorporated into the part design and tool.

Specialized nozzles introduce pressurized gas into the molten plastic during the molding process.

This helps push the resin to the furthest extremes of the moldĀ and into difficult to reach sections of the part.

Example of a tractor fender part which was produced using gas assisted injection molding. Gas assist enables us to achieve an attractive exterior finish while using low-pressure molding. The location of the gas channels can be seen on the hidden back side of the part.

What is the process used for?

Many parts can benefit from gas assist. However, there are certain types of profiles, categories and part designs where the process is especially advantageous. These include:

  • Large Panels, Covers and Outer Casings
  • Parts requiring strong hollow sections such as handles
  • Complex Parts or when multiple parts are redesigned as a single piece
  • Large molded plastic parts that require good cosmetic surfaces

For more information on gas assisted injection molding and our structural foam molding capabilities please visit

Miles Products would be happy to discuss and advise on all your molded plastic part needs.

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Macay Hunter

Macay Hunter

An expert in plastics manufacturing, Macay works with engineers and supply chain managers during the planning, design and implementation stages of their molded plastic productions.