International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
A Review on Cooling System Design for Performance
Enhancement of Injection Molding Machine
Rupali P. Patil
M.E (Machine Design), SST’s College of Engg., Jalgaon
Navneet K. Patil
Asso. Professor, Department of Mechanical Engg.
SST’s College of Engg., Jalgaon
Jagruti R. Surange
Asst. Professor, Department of Mechanical Engg.
SST’s College of Engg., Jalgaon
ABSTRACT
Injection molding is one of the most flexible and
important operation for mass production of plastic
parts. In injection molding process, cooling system
design is very important as it largely affects the cycle
time. A good quality cooling system design can
reduce cycle time and attain dimensional stability of
the part. In order to reduce the cycle time, and
control the even distribution of temperature, it is
required to create conformal cooling channels,
which match to shape of cavity of the mold and core.
This paper presents a simulation study of various
I. INTRODUCTION:
Plastic injection molding process is the most
common process for economically mass producing of
various complex geometries and shapes plastic parts
[1]. In injection molding the molten plastic is
injected into the mold cavity and cooled
subsequently to form shape of the mold. Most
commonly used materials for injection molding
process are Thermosetting and Thermoplastic
Polymers. Injection molding machine consist of a
hopper through which granules of the plastic material
enter a screw-type plunger. The screw-type plunger
is operated by prime mover or any hydraulic system.
Heaters are provided on the exterior side of this
plunger which gradually heats the plastic granules as
it move forward through the screw. The molten
plastic is injected at the nozzle end through a small
opening in the mold cavity. The mold core clamps to
the cavity and mold area is formed where the filling
of molten plastic takes place. The mold is cooled by
water channels around the mold cavity. The three
main phases in injection molding are filling; cooling
and ejection. Out of these, cooling process takes
about 50-75% of cycle time. In conventional
ISSN: 2231-5381
types of cooling channels in an injection molded
plastic part and compares the results in terms of time
to ejection temperature, temperature profile,
contraction and part warpage to determining the
configuration which is more suitable to provide
uniform cooling with minimum cycle time. The
Autodesk Mold Flow Insight (AMI) simulation
software is used to study the results of the cooling
channels performance.
KEYWORDS: Injection Molding, conformal
cooling, mold flow, cycle time, simulation
Injection Molding process, straight holes are drilled
in the mold cavity through which water passes for
cooling the mold. A fine surface finish on the mold
can be obtained by using uniform cooling. This
increases the cycle time of product, which is
undesirable. On the other hand if cycle time of
product reduced, chances of getting improper surface
finish are higher. It is therefore important to obtain a
solution in which reducing cooling time also reduces
cycle time. It also shows that cycle time of product is
dependent on cooling of the mold. An efficient
cooling circuit design reduces the cooling time,
which in turn increases overall productivity. [10]
Moreover, uniform cooling improves part quality by
reducing residual stresses and maintaining
dimensional accuracy and stability (see Figure-2).
Some of the major problems facing injection molders
today are reduce cycle time, part warpage and
shrinkage alongside lowest costs. Nowadays it is
possible to design and simulate different cooling
configuration of the plastic part and investigate the
proper cooling system for the plastic part by using
computer simulation software AMI.
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Figure-1: Mold cooling accounts for more than two-thirds of the total cycle time [10]
Figure-2: Proper and efficient cooling improves part quality and productivity [10]
II. Components of Mold Cooling
System
A mold cooling system typically consists of the
following items:
Temperature controlling unit
Pump
Supply manifold
Hoses
Cooling channels in the mold
Collection manifold
The mold itself can be act as a heat exchanger, with
heat from the hot polymer melt taken away by the
circulating coolant.
III. Design of Part and Cooling Channels
In this study, a plastic part has been designed using
CATIA V5 as shown in figure 3. Part is of 2 mm in
thickness and 182 mm in height. The IGES (Initial
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Graphics Exchange Specification) CAD model of the
plastic part has been imported to AMI to analyze the
component.
Polypropylene has been assigned as a material for
plastic part. Melt temperature and mold surface
temperature have been maintained at 225°C and
38°C respectively. The best gate location analysis
has been done and it is found to be located in the
middle of the base of the plastic part. Water was
selected as the coolant liquid for all analysis because
it has high cooling property, economically viable and
also environmentally friendly. Figure 4 shows four
types of cooling channels considered in this analysis.
All cooling channels had the same diameter of 10
mm. The depth of the cooling channels from cavity
surface and distance between cooling channels
centers were 25 mm and 40 mm respectively. The
coolant Reynolds number was calculated to be 9750
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and temperature at coolant inlet was 20°C, which
indicates that flow of water was fully turbulent.
Figure 3: CAD Model of the plastic part
(a)
(b)
(c)
(d)
Figure 4:Cooling channel types: (a) Normal, (b) conformal combination with baffle, (c) conventional
combination with conformal and (d) conformal
IV. Plastic Simulation Study:
Autodesk Mold flow Insight has been used to design
the cooling channels and perform Cool, Flow, Pack
and Warp analysis. Dual Domain Meshing (Fusion
mesh) was used with number of elements being
30770. The quality of the mesh can be improved with
manual meshing techniques. The maximum aspect
ratio was improved significantly from 20 to 10.
Similarly match percentage has improved from
81.4% to 91.6% as well as reciprocal percentage has
improved from
7.2% to 88.3%. Molding Windows is quick analysis
to evaluate the best material conditions that are
needed to produce part. Molding Windows is used to
determine the best processing conditions and
ISSN: 2231-5381
evaluate the sensitivity of the part to the molding
process. It also evaluates gate locations and gains a
measure of part design quality to improve
manufacturability. It also helps to determine
variation in mold temperature, melt temperature and
injection to produce high quality of the part. Figure
5shows the zone plot for Polypropylene material
Purell HP570R. The X-axis is melt temperature and
injection time. The Y-axis mold temperature. The
zone plot has three areas, which are green, yellow
and red. It is clear from the fig.5 that the zone plot
selected is within green area (Preferred). This means
we are able to mold the part and the quality will be
high and hence the part will be acceptable by
customers after producing.
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Figure 5: Molding Windows
V. Results and Discussion
The simulation results in terms of time to reach part
ejection temperature (time to freeze) indicates that
normal cooling channels took around 75 seconds to
reach ejection temperature for most of the plastic
parts as shown by blue colors in figure 6 (a). It
shows that this cooling channel is the slowest
cooling system as it requires more time than other
systems. This is because of its structure that
consists of straight drilled holes in the mold. These
holes have limitations in terms of geometric
complexity, non uniform cooling between the
surfaces of the part and cooling fluid mobility
within the injection mold [1]. However, time to
reach part ejection temperature decreased to around
44 seconds with the use of conformal cooling
channel combination with baffle showing
significant improvement as can be seen in blue
shades in Figure 6 (b) and faster by nearly 43% in
comparison with that of normal straight channels
for same pitch distance and the same channel
diameter. With the use of conventional cooling in
combination with conformal cooling channel in the
core, the value of time to reach part ejection
temperature reduces to around 43 seconds as can be
seen in blue in figure7 (a). The cooling time then
reduced to around 37 seconds for the fully
conformal cooling system as can be seen in blue
figure7 (b) thus cooling the product the fastest, by
49.6% faster than normal cooling channel, and up
to 12% faster than conformal cooling channel in
combination with baffle, that is the lowest value
when compared to the rest of the cooling channel
used in the analysis.
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(a)
(b)
Figure 6: Time to reach part ejection
temperature (Time to freeze part) with (a)
normal, (b) conformal combination with baffle,
cooling channels [1]
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International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
(a)
(a)
(b)
Figure 7: Time to reach part ejection
temperature with (a) conventional combination
with conformal, (b) conformal, cooling channel
[1]
This is due to conformal cooling lines follow the
part geometry in the mold and because of optimum
placement resulting in uniform mold temperatures.
In conformal cooling, results show the predicted
temperature difference across the part thickness is
drastically reduced and becomes more uniform
than other cooling channels. In addition, in a
conformal cooling channel, the mold surface
temperature is fairly uniform around the part.
Figure8 (a) shows temperature profile for normal
cooling channel, to demonstrate the temperature
distribution. Since mold surface temperature is
38°C in all types of cooling channels, as a result,
the normal cooling channel has non-uniformity of
temperature distribution within the range from
42.46°C to 131.2°C as shown in figure8 (a), which
means that lowest value (42.46°C) is more than
mold surface temperature which is 38°C. In
contrast, small temperature variation from 27.09°C74.39°C is with the use of conformal cooling
combination with baffle as can be seen in figure8
(b).
(b)
Figure 8: Temperature profile of part with (a)
normal, (b) conformal combination with baffle,
cooling channels [1]
In conventional cooling in combination with
conformal, temperature distribution lies within the
range from 26.61°C to 74.53°C as shown in figure
9 (a). These cooling channels cannot provide the
uniformity for all portions of part. On other hand,
the temperature is uniformity distributed for all
portions of part 21.79 °C with the use of conformal
cooling channel as described in figure 9(b). Also
the highest temperature in the whole analysis is
reduced by more than 36%.
Figure 9: Temperature profile of part with (a)
conventional combination with conformal, (b)
fully conformal cooling channels
Therefore, it can be concluded that this result gives
clear evidence that conformal cooling channel
provides better temperature consistency and
uniformity than other cooling channels even in
complex part. Figure 10 summarize the results
obtained from Autodesk Mold flow Insight
analysis. Figure 10 shows the comparison for time
to freeze and maximum temperature profile.
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Figure 10: Comparison of time to reach ejection temperature and maximum temperature [1]
Volumetric shrinkage is inherent in the injection
molding process, where the molded plastic part
shrinks with cooling and solidifying of material.
Shrinkage can sometime be to the extent of 20
percent by volume. Figure 11(a) shows that in
normal cooling channel, volumetric shrinkage is
17.01%, which is highest among all types of
channels. This rapid increase of volumetric
shrinkage and its spread around the part center is
due to premature pressure removal [1]. This high
value of shrinkage can be reduced by changing the
sharp corners to radius and improve some part
features. On the other hand, the value of shrinkage
has been decreased to 16.72% with the use of a
conformal cooling combination with baffle as
shown in figure 11 (b). It shows that by adding
baffles to the conformal cooling channel,
volumetric shrinkage can be reduced and made
more uniform. In case of conventional cooling
combination with conformal in figure 12 (a), the
result shows that volumetric shrinkage has been
reduced slightly to 16.70 %. In the conformal
cooling channel, the value of volumetric shrinkage
has been decreased to 15.72% that is the lowest
percentage among all cooling channels as shown in
figure 12 (b). It points out that volumetric
shrinkages are distributed more consistently and
show more uniformity in conformal cooling
channels [1].
(a)
(b)
Figure 11: Volumetric shrinkage of part with (a)
normal, (b) conformal combination with baffle,
cooling channels
(a)
(b)
Figure 12: Volumetric shrinkage of part with (a)
conventional combination with conformal, (b)
conformal, cooling channels
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The results of warpage analysis and sink analysis
of different cooling channel design are shown in
the following chart.
Figure 13: Comparison of volumetric shrinkage, sink mark and warpage
VII. CONCLUSION:
[5]
It is observed from the above study that conformal
cooling channel is the most suitable cooling system
for the plastic part as compared to other cooling
channels. It gives better cooling properties due to
lower volumetric shrinkage and the lower sink
mark percentage. It also shows the lowest time to
reach the ejection temperature, which leads to
lower cooling time and reduced overall cycle time.
The conformal cooling channel shows more
uniform cooling which makes it most favorable
cooling system. The conformal cooling channels
are mostly preferred because the cooling lines are
located to follow the part geometry in the mold.
The injection molding analysis software provides
helpful information regarding cycle time, shrinkage
and warpage for plastic product and design of mold
to reduce time and cost of production especially for
complex parts.
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