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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