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Rise of RGIM
In conventional GAIM process,
Formation of hesitation marks areneeded to be removed.
The material for injection moulding areto be greatly reduced (removal ofoverflow pad).
The gas in the hollow shape acting ashot core needed to be removed forfaster cooling of moulding.
For satisfying these requirements, a
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Reverse Gas InjectionMoulding(RGIM)
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Steps in RGIM
The first step is filling. A meltinjected from a hot runner fills themould cavity about 98100% such
as full shot method. The second step is hollowing out
the melt after a constant delay
time. A pressured gas is injectedinto the mould cavity to make ahollow shape. Simultaneously, the
pushed melt that is still in a molten
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Difference between GAIM &RGIM
In addition to a normal GAIM system,there are some special units includednamely
the overflow buffer that is used toreduce a material.
an air unit that is used to vent and
remove the hot nitrogen gas in hollowshape.
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Comparison of GAIM &RGIM
Experiments were conducted toverify the cooling efficiency of theRGIM and compared with
conventional GAIM.
Materials considered,
General purpose polystyrene (GPPS, LGChemical 25SPI)
Polypropylene (PP, LG Chemical M580)
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Experimentation &Analysis of GPPS Taguchi method is followed to find
the parameter affecting coolingefficiency.
Three injection variables that willaffect the mould quality are selected.
Melt temperature (C)
Delay time for air blowing (sec)
Duration time for air blowing (sec)
3 levels of DOE & L9 orthogonal array
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Observations
Moulding was donewithout air-cooling
at melttemperature of
220C.
Moulding was donewith air cooling
Observations: After cooling for 30
sec, the injectedmoulding temperatureis 175C.
Observations: The moulding
temperaturemeasured in the 7thprocess condition(94C) shows an
increase of approx
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The S/N ratio was calculated basedon the measured moulding
temperature.
Duration of air blowin was the
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p mum resu scalculated by ANOVA
from MinitabTM software Optimum process variables are, Melt temperature = 220C
Delay time for air injection = 21 s Duration of air blowing= 70 s
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umer ca ca cu a on ocooling time for the
RGIM The efficiency of air blowing wascalculated with a numerical coolingequation.
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Numerical solutions
Without air-cooling With air-cooling
The cooling time without
air blowing was 733 s ascalculated with the Fouriercooling equation.
The cooling time of
moulding was calculated126 s. This cooling time byair blowing was faster 5.5times than the case 1
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empera ure s r u onsimulation by MARC
software Without air-cooling,
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empera ure s r u onsimulation by MARC
software With air-cooling,
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Conclusion
The reverse gas injection mouldingwas devised to solve the problems ofslow cooling time and to improve
surface quality on a mouldingproduced in the conventional GAIM.
It was found that the efficiency of the
RGIM process was approximately50% better than the conventionalGAIM process. Also, this experimental
result was confirmed in the
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