3. The injection molding experiments in the RGIM
process
The experimental equipments consisted of a mold
that included the function of the RGIM process, a gas
pressure-generating unit and an air unit. The mold has
one cavity and was used to make an electric microwave’s
handle. The mold temperature was 50 ◦C. The gas
pressure-generating unit was made by GAIN Technologies
[8]. The air unit is for cooling a molding (Fig. 3). The air
temperature was 15 ◦C. We used the LG injection molding
machine (LGH 140N) (Fig. 4).
3.1. DOE for the RGIM process
The experiments were conducted to verify the main cool-
ing efficiency of the RGIM with two kinds of polymers
that are general purpose polystyrene (GPPS, LG Chemi-
cal 25SPI) and polypropylene (PP, LG Chemical M580). To
increase efficiency and confidence of the experiment, we
planned the experiments with the Taguchi method [9]. The
ANOVA in statistical software MINITABTM was used for
the analysis of the experimental results [10]. Three injec-
tion variables that would have most effective on the molding
quality were selected. These were also used as variables in
the design of experiment (DOE). Table 1 shows the variables
and levels for the experiment.
Table 2 shows the DOE schedules for this experiment.
The experimental samples were molded five times at each
process condition. After dismissing the first and last samples,
the averaged value of the other three samples was taken as
input data.3.2. Experiment and analysis for GPPS
The GPPS polymer was used first in the experiment. We
measured the temperature, length (Fig. 5) and weight of the
ejected moldings. Table 3 shows the measured values.
Table 1
Experimental variables and levels
Melt temperature
(
◦C)
Delay time for
air blowing (s)
Duration time for
air blowing (s)
Level 1 210 21 50
Level 2 220 31 60
Level 3 230 41 7
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