Water-assisted injection

The water-assisted injection (WAI) process is paradoxically older than gas-assisted injection (GAI). . Indeed, the first patent describing water-assisted injection dates back to 1938 (figure 1 ).

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The process is exactly the same as for gas-assisted injection molding. Although there are significant differences, the final objective remains the same: to produce hollow bodies.

For the time being, water-assisted injection molding applications are more limited, with the sole aim of reducing cycle times.

Unlike nitrogen, water is inexpensive and readily available.

Of course, all the advantages of gas-assisted injection are there:

• increased rigidity by creating a tube effect, up to 80 mm in diameter;

• reduction in part mass ;

• reduced closing force in case of partial filling ;

• reduced shrinkage ;

• increase in stiffness at equivalent quadratic moment.

Today, water-assisted injection makes up for some of the shortcomings of gas-assisted injection, particularly in the field of heat exchange.

Even more than gas-assisted injection molding, water-assisted injection molding is a process in which every stage must be optimized, from part design to choice of material, and from tooling selection to injection press selection. It only takes one neglected parameter to risk random production, or even poor quality. Material suppliers have formulated specific resins to delay crystallization phenomena.

The process is becoming increasingly popular, with applications in fields as varied as...