Gas-assisted injection molding

Gas-assisted injection molding to provide an internal hollow shape (Green and blue colors indicate inert gas and polymer melt respectively)

The basic concept of the gas-assisted molding process is quite similar to regular injection moulding process. In this gas-assisted molding, the plastic material is melted with the help of extruder barrel and injected into the mold cavities like the regular injection moulding process but only up to 70%~80% of the mold voulme. Plastic melts in contact with the mold walls begins to solidify and nitrogen gas is injected into the mold through strategically designed and placed gas channels, providing pressure that pushes the plastic material into the mold extremities and finally the molded part is ejected like the regular injection molding process.[1]

This process forms a hollow, plastic injection molded part and parts are lighter, greener and cheaper than traditionally injection molded equivalents. Moulded parts also cool faster in this process because of constant pressurization by the gas. There is also usually less shrinkage as the thicker wall sections are hollowed out by the pressurised gas resulting no sink mark problems.[2]

Some of the benefits of this process are:[3]

• Thicker parts can be moulded
• No sink marks
• Minimal residual stresses
• Reduced part deformation (warpage)
• Low clamp force
• Lightweight products

This molding technique is very difficult to apply for multi-cavity mold, especially if the cavity sizes are dissimilar. Clear or transparent plastic materials are an inappropriate option for this technique as cosmetic-appearance can deteriorate.[4]

• Molding (process)
• Direct injection expanded foam molding
• Fusible core injection molding
• Metal injection molding
• Multi-material injection molding
• Reaction injection molding