Gas Assisted Injection Molding

As plastics are synthesized from petroleum and injected at high temperature and pressure, the gas used is mainly nitrogen, with a residual oxygen content of less than 1.5%.

The first applications of IAG gas-assisted injection had just one aim: to save materials. Very quickly, the applications of gas-assisted injection multiplied, and today gas-assisted injection can be used for :

• improve or even replace the pressure-holding phase and reduce shrinkage;

• reduce cycle times by ensuring better polymer-tool contact;

• increase rigidity by creating a tube effect;

• reduce production costs by reducing closing force

This transformation technique can be implemented using a number of different processes, each with its own advantages and disadvantages. In order to facilitate understanding of the phenomena involved, we will focus on the partial filling process, as it combines all the advantages of gas-assisted injection molding:

• reduced part weight ;

• shorter cycle times because less material is injected;

• reduced closing force for the same reason;

• reduced shrinkage, as the gas can be guided into critical areas;

• increase in stiffness at equivalent quadratic moment ;

• improved appearance.

Gas-assisted injection molding is a process in which every step must be optimized, from part design to choice of material and tooling optimization, right through to the choice of injection molding machine. It only takes one neglected parameter to risk random production, or even poor quality. The choice of material is crucial, especially for crystalline and filled polymers. The vast majority of resin suppliers have developed specific grades for polyamides, polypropylenes and other polybutylene terephthalates, adapted to gas-assisted injection molding. Choosing an unsuitable grade for an optimized technical part often leads to a dead end, with appearance defects having such an influence that the entire project may be called into question. This process is now finding a new lease of life, after a rapid start-up followed by a long period of disillusionment.

The process is becoming increasingly popular, with applications in fields as varied as toys, household appliances, medical devices, DIY and furniture. Just 15 years ago, the process was considered "reserved" for the automotive industry and television facades. This recent evolution is due to the creativity shown by designers...