Water assisted injection moulding

Water Assisted Injection Molding (WAIM) is a new development in the field of Injection Moulding and said to be an alternative to Gas Assisted Injection Moulding (GAIM). Using this process, Tubular hollow parts and Rod shaped products can be manufactured cost effectively.

This idea of Injection of Fluids (Water or Oil) was proposed in 70’S but at that time, the use of water did not succeed satisfactorily, due to difficulty in achieving high flow rates and pressure.

Recently, IKV (Institution for Kunststoffverarbeitung), Germany in association with finders Anglagentechnik has developed a Proto type production line (Demonstration Plant ) and carried out water injection successfully.

 Benefits of WAIM (in comparison with GAIM)

	Reduce cooling times, thus reducing cycle time
	Permits manufacture of parts with large diameters
	Wall thickness of the parts can be minimized.

During demonstration of the WAIM process, for a test part of 10 mm diameter the cycle time was found to be reduced from 60 to 10 sces and wall thickness was reduced from 1.5 to 1 mm in comparison to the corresponding GAIM.

A PP based Charge air-pipe section with 60mm diameter and 400mm long was produced with a cycle time of 50 seconds.

Process Principle The Principle of WAIM is similar to sandwich injection molding. The process can be easily understood from the figure and the steps involved are as below: 1.Injection of melt The Quantity of melt injected should be less than the total volume of cavity.

 2.Injection of water with one or more Hydro pumps

The injection of water takes place so rapidly in such a way that,

	Water does not evaporate and,
	There is no hydraulic degradation.

The injected water in the melt forms a cavity by the same principle as GAIM i.e. it forms a hollow cave by displacing the molten melt in to spaces of the mold that have not yet been filled.

At the transition, between waterfront and melt, a thin plastic membrane is solidified, and acts like a displacing piston on the molten core, pushing the polymer melt further. Thus hollow body is formed.

Compared to gas used in GAIM, water provides better cooling effect and thus leads to shorter cooling and cycle time. 

3.Water is forced out of the part by compressed air.

The water can be recirculated via a storage tank.

 Conclusions

WAIM can be used for production of certain parts (eg. Ducts) that are not feasible with GAIM. Thus some limitations of GAIM process creates opportunities for WAIM, as this process offers cost reductions.

But the most important task is performance requirements in balancing and process sequences in the process of water injection. Further investigations and research works are going on at IKV to improve the process.