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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 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)
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Reduce
cooling times, thus reducing cycle time |
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Permits manufacture
of parts with large diameters |
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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.
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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.
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2.Injection of water with one or more Hydro
pumps
The injection of water takes place so rapidly in
such a way that,
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Water does
not evaporate and, |
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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.
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