gas-assist injection molding

Nitrogen is Cheaper Than PlasticGas assist improves cosmetics — and cuts costsDesign News Staff -- Design News, September 4, 2006
With resin costs running through the roof, it's a good time to take another look at gas-assist injection molding.
You remember gas assist. It's a process that uses an inert gas, particularly nitrogen to create one or more hollow channels within an injection-molded plastic part. At the end of the filling stage, nitrogen is injected into the still-liquid core of the molding. The gas follows the path of the least resistance and replaces plastic, usually in thick sections, with gas-filled channels. Gas pressure subsequently packs the plastic against the mold cavity surface. The gas is vented to atmosphere or recycled.
It's not brand new. But acceptance was weak because of concerns over patents, rights and royalty fees. Many of those original patents have expired, and there is less acrimony in the gas-assist field. There are still many opportunities to convert current aluminum and steel applications in automotive as well as other industrial applications to gas assist. Many designers have used gas assist to achieve an excellent surface finish on a cosmetic part. You can also create larger, more complex parts with fewer injection gates than is possible with conventional injection molding.
The three examples here are winners from the recent design competition held by the Alliance of Plastics Processors.