Water Assist Injection Moulding

Water Assist Injection Moulding:

Water Assisted Injection Moulding (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 Kunststoff verar) Germany in association with finders Anglagentechnik has developed a Proto type production line (Demonstration Plant) and carried out water injection successfully. 

WAIM PROCESS PRINCIPLE:

The Principle of WAIM is similar to sandwich injection moulding. 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 mould 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. 

Water is forced out of the part by compressed air. The water can be recirculated via a storage tank.

WAIM PROCESS:

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. 

Why water works:

The chief difference between water and gas is that gas is compressible, while water is incompressible.

When injected into the melt, the leading edge of the water forms a solid boundary or highly viscous membrane. The membrane forces molten material forward, instead of the polymer forcing the water to the side

The primary reason for this action is the higher viscosity and incompressibility of water compared with gas 

APPLICATION OF WAIM:

Tubular parts, automotive fuel lines and other fluid systems, handles, roof racks, fascias, bumpers, door handles, clutches, and steering-column supports.

Other products being considered include baby strollers, handles for kitchen items, office furniture, shovels, brackets, and general fittings.