J. VANEK et al.: INJECTION MOLDING OF POLYCARBONATE THICK-WALLED PARTS USING A TOOL ...
299–305
INJECTION MOLDING OF POLYCARBONATE THICK-WALLED
PARTS USING A TOOL WITH VARIOUSLY DESIGNED GATE
INSERTS
UPORABA ORODJA Z RAZLI^NO OBLIKOVANIMI VLO@KI ZA
INJEKCIJSKO BRIZGANJE POLIKARBONATNIH
DEBELOSTENSKIH IZDELKOV
Jiri Vanek, Michal Stanek, Martin Ovsik
*
, Vlastimil Chalupa
Tomas Bata University in Zlin, Faculty of Technology, Zlin, Czech Republic
Prejem rokopisa – received: 2022-11-22; sprejem za objavo – accepted for publication: 2023-04-25
doi:10.17222/mit.2022.692
Injection molding is an advantageous technology for the mass production of plastic parts without the necessity for additional
procedures. The applicability of this method is still partially limited by the required properties of the manufactured parts. Espe-
cially in the field of optics, there is a need to produce thick-walled parts while maintaining their transparency. This paper reports
on how various shapes of gating systems affected the process parameters and cavity filling during the injection molding of
polycarbonate thick-walled specimens. These outcomes demonstrated that film gates and their alternatives are more suitable for
the standard injection molding of thick-walled optical products than the triple-edge gating systems. Favorable results were ob-
served particularly in the uniformity of cavity filling, size of shrinkage, and in the occurrence of defects such as voids or sink
marks.
Keywords: injection molding, cavity filling, thick-walled part, gating system
Postopek oblikovanja izdelkov z injekcijskim brizganjem je napredna tehnologija za masovno proizvodnjo plasti~nih izdelkov
kompliciranih oblik brez potrebe po nadaljnjih postopkih obdelave. Uporabnost tega postopka je {e vedno delno omejena z
zahtevanimi lastnostmi izdelkov, {e posebej na podro~ju optike, kjer je potrebno izdelovati debelostenske izdelke in pri tem
ohraniti njihovo prozornost. V ~lanku opisujejo, kako na razli~ne oblike sistemov zapiranja orodja vplivajo procesni parametri
in polnjenje votline orodja med injekcijskim brizganjem polikarbonatnih debelostenskih preizkusnih vzorcev. Rezultati
izvedenih preizkusov so pokazali, da so filmska vrata in njene alternative bolj primerne za standardno injekcijsko brizganje
debelostenskih opti~nih izdelkov kot pa trirobi sistemi zapiranja. Ugotovili so, da je pri{lo do bolj enovitega polnjenja votline
orodja z materialom in posledi~no se je pojavljalo manj napak na izdelkih, kot so na primer pore, luknjice, vdolbine, nalitja in
ostale povr{inske napake.
Klju~ne besede: injekcijsko brizganje, polnjenje votline orodja, debelostenski izdelki, sistem zapiranja orodja
1 INTRODUCTION
Injection molding is a method of processing plastics
that is still expanding. Currently, it is used for the manu-
facturing of most plastic products for a wide range of in-
dustries. Injection-molded parts are generally designed
as thin-walled shells, but with increasing demand, there
is a need in some areas to produce components with
greater thickness. For this purpose, the commonly known
injection-molding technology with foaming is often
used. Nevertheless, this process does not achieve the re-
quired transparency of optical parts as well as water- or
gas-assisted injection-molding technologies. Because
this area has been little studied so far, many unanswered
questions are arising in industrial practice towards the
fabrication of such parts. Therefore, the examination of
the cavity-filling process using differently shaped gates
presents essential knowledge leading to the production of
quality, thick-walled optical parts.
Several researchers have already studied possible so-
lutions for the injection molding of thick-walled compo-
nents. The options for producing thick lenses using the
method of sequentially injected layers were presented by
Maier.
1
Furthermore, an application of similar multilayer
injection-molding technology for optics was discussed
by Hopmann
2
and Nian.
3
A similar issue was further
studied by Liu.
4
Since these studies dealt with special in-
jection-molding methods, which may not be suitable for
more complex parts, their conclusions should not be uni-
versally applicable.
On the other hand, the numerical and experimental
single-component injection molding alternative of manu-
facturing thick products was examined by Han.
5
An anal-
ogous process focused on restraining voids generated in-
side a thick test sample was carried out by Motegi.
6
Within both of these studies, the injection-compression
molding method was applied to produce the samples.
This procedure requires a specially designed injection
mold and places high demands on the injection-molding
Materiali in tehnologije / Materials and technology 57 (2023) 3, 299–305 299
UDK 678.027.74 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(3)299(2023)
*Corresponding author's e-mail:
ovsik@utb.cz (Martin Ovsik)

machine, which makes it not directly applicable to a con-
ventional injection-molding process.
Further research studying the production possibilities
of a thick-walled part using a standard injection-molding
technology was conducted by Gotlih.
7
The objective of
this work was to examine the influence of selected pro-
cess conditions on the resulting part quality. Parameters
such as deflection rate, volumetric shrinkage, and depth
of sink marks were determined as quality indicators.
Simulations of the injection-molding process for techni-
cal parts with large wall thickness with respect to process
parameters have been performed, evaluated and dis-
cussed in articles published by Fu
8
, Solanki
9
and
Dogossy.
10
The outputs of these studies could lead to the
improvement of some quality parameters of similarly de-
signed products, or to shortening the cycle time of their
production.
The study including an issue of designing a con-
formal cooling system of an injection mold for the opti-
cal part with a considerable wall thickness, was per-
formed by Hopmann.
11
This research was conducted to
reduce the deformations and internal stresses in the
molded part by controlling the temperature of the core
and the cavity mold inserts. The results can be applied
during the design of conformal cooling channels to pro-
duce thicker parts with fewer defects. An article covering
a similar topic of conformal cooling channels design was
published by Park.
12
and Torres-Alba.
13
In these studies,
conformal cooling channels were designed and simulated
to homogenize the temperature distribution of the
molded part during the injection-molding process. The
results of these works could provide basic general
knowledge about the complexity of conformal cooling
channels design, which may be applicable for the pro-
duction of thick-walled parts.
Another study carried out by Sykutera
14
aimed to de-
termine the effect of nitrogen pressure on the rheological
properties and structure of thick-walled parts produced
by microcellular injection-molding technology. Use of
this method affected the apparent viscosity value, which
led to the reduction of the pressure in the mold compared
to the standard technology. Subsequently, this could im-
prove the course of processes in the mold, thus increas-
ing the production efficiency.
The effect of process parameters and component
thickness on the shrinkage of an injection molded com-
ponent was analyzed using the appropriate tools by
Yang
15
and Studer
16
The results showed that increasing
melt temperature caused the effect of shrinkage to be
more significant. In addition, changing other process pa-
rameters, such as mold temperature, injection pressure,
holding time, and cooling time affected the shrinkage be-
havior to only a limited extent. This knowledge can con-
tribute to the efficient setting of process parameters
while manufacturing components with greater wall
thickness. Besides, according to the results presented by
Ch’ng,
17
Nasir
18
and Roslan,
19
the method of response
surface methodology could be beneficial while optimiz-
ing the settings of process conditions, therefore reducing
the deformation of injection-molded parts.
The approach of manufacturing plastic parts sup-
ported by simulation and subsequent experimental injec-
tion molding to reduce the time of development and the
production of large aspherical plastic lenses was per-
formed by Shieh.
20
The presented research consisted of
using a real amount of shrinkage after the initial injec-
tion molding of an aspherical plastic lens as a reference
for shaping a core insert. This approach can outline the
solution of shaping the cavity and core inserts to prevent
part deformations. Besides, the production of precise
plastic lenses concerning mold surface parameters, to-
gether with process conditions and their influence on op-
tical properties, was described by Lai,
21
Dick
22
and
Speck.
23
Injection compression molding with regards to pro-
cess conditions and their influence on the resulting qual-
ity of plastic lenses was studied by Young.
24
Further-
more, the studies where the standard injection molding
of relatively thick parts has been examined were realized
by Michaeli,
25
Höll,
26
Huang
27
and Chung.
28
However,
the conventional injection-molding method was dis-
cussed only marginally, contrary to the injection-com-
pression molding technique. These studies were focused
on the examination of the optical properties rather than
on the process itself.
Thus, this research deals with the conventional injec-
tion molding of thick-walled optical parts made of
polycarbonate (PC) using variously shaped gating sys-
tems. Acquired knowledge about the cavity-filling pro-
cess of such a component can significantly contribute to
the clarification of the questions arising from their manu-
facturing.
2 EXPERIMENTAL PART
The experiment was conducted to examine how vari-
ous shapes of gating systems affect the cavity filling dur-
ing the injection-molding process. Two variants of
thick-walled test specimens made of polycarbonate were
produced using a special injection mold with replaceable
gating inserts. This approach was preceded by the valida-
tion of the filling phase through the flow-analysis soft-
ware. As the uniform process parameters were defined, it
was possible to evaluate how different geometries of the
gating influences the individual aspects of cavity filling,
thus determining the overall quality of the specimens.
The test specimens were made of polycarbonate with
the trade name Makrolon LED 2245. This material is
widely used for the optics because of its versatility, ex-
cellent light transmittance, shape stability, and tempera-
ture resistance. In addition, another advantage of this
polymer is the light conductivity over a wide range of ra-
diation.
J. VANEK et al.: INJECTION MOLDING OF POLYCARBONATE THICK-WALLED PARTS USING A TOOL ...
300 Materiali in tehnologije / Materials and technology 57 (2023) 3, 299–305

The melt temperature was set to 325 °C during both
the simulations and the injection itself. Since the PC ab-
sorbs water, it was necessary to dry the raw material be-
fore processing for3hat120°C,which was done with a
Arburg Thermolift 100-2 dryer.
Within the experiment, a functional thick-walled op-
tical specimen was designed in two variants using the
same material. As can be seen in Figure 1, the difference
between variant A and variant B is the number of optical
ribs and the thickness of the mounting base, which was 3
mm for the first variant and 8 mm for the other. Since the
intended function of the sample is to distribute the light
beam consistently, there is an optical pattern on the un-
derside of the ribs. The largest dimensions of the sample
were (80 × 50 × 75) mm, whereas the maximum thick-
ness of the rib reached 10 mm.
All test specimens were prepared by injection-mold-
ing technology. As shown in Figure 2, a special injection
mold for testing differently shaped gates was used. Ac-
cordingly, the design of the mold allowed the simple at-
tachment of individual gating inserts. Moreover, to pre-
pare both specimen variants, the mold was provided with
replaceable cavity-defining parts. Other mold compo-
nents were standardized parts or conventionally designed
plates.
For the test sample in both variants, an injec-
tion-molding process was performed using three differ-
ent gating inserts to determine the most suitable filling
method. Figure 3 shows the visualization of individual
gating systems related to the injected part. In the first
case, a 1-mm-thick triple-edge gate was used. The sec-
ond variant was similar, but with the gate thickness in-
creased to 1.5 mm. Another option was the use of a
1-mm-thick film gate. The size and shape of the sprue
bushing was the same in all cases.
To determine the influence of different gating sys-
tems on the filling and packing phase, it was necessary to
prepare all the testing specimens under uniform process
conditions. Recommended values received from the ma-
terial sheet were considered as well as the parameters
suggested by the Moldflow software.
Table 1 shows that due to the thick-walled character
of the specimens, the conditions of the holding phase
were set manually. Because a thicker wall takes a longer
time to cool down, the holding time was set to 10 s. The
moment of switching from injection to the holding phase
was defined at a 99 %-filled cavity. The amount of hold-
ing pressure was determined as 80 % of the maximum
injection pressure. The values of these parameters were
derived from the results of a preliminary flow analysis.
Table 1: Selected process parameters
Fill time 4.7 s
Melt temperature 270 °C
Mold temperature 100 °C
Injection pressure 37–47 MPa
Holding pressure 80 % of max. injection pressure
Holding time 10 s
Switching point to holding at 99 %-filled cavity
The sample preparation itself was preceded by the
process validation through flow analysis, which was per-
formed by the Autodesk Moldflow Synergy 2016 soft-
ware. This enabled the simulation of filling, holding and
cooling phases of the process. Thus, it was possible to
detect and reduce the occurrence of defects and to iden-
tify those process parameters that could be optimized.
Moldflow includes an extensive database of polymeric
materials and injection molding machines, so the simula-
tion conditions were as close to reality as possible.
All test samples were produced using an electric in-
jection molding machine Allrounder 470 E 1000–290
Golden Electric with a maximum clamping force of
1000 kN.
J. VANEK et al.: INJECTION MOLDING OF POLYCARBONATE THICK-WALLED PARTS USING A TOOL ...
Materiali in tehnologije / Materials and technology 57 (2023) 3, 299–305 301
Figure 2: Testing injection mold (1 – gating insert, 2 – core insert, 3 –
cavity insert)
Figure 3: Different shapes of gating systems
Figure 1: Test specimens (1 – mounting base, 2 – optical rib, 3 – opti-
cal pattern)

3 RESULTS
All test samples were used to analyze how the indi-
vidual type of gating system affects the cavity-filling
process. In particular, it was essential to examine the in-
crease in the melt temperature due to high shear stress
that occurs when it flows through the gating system. This
phenomenon could cause overheating of the material and
its subsequent degradation. Additionally, the moment
when the gate solidifies was identified because only to
this point is the holding phase effective.
The results of how each type of the gate affected spe-
cific values of the actual injection-molding conditions
are shown in the following tables. These are accompa-
nied by figures displaying the result of a simulation per-
formed by the Moldflow software. Its output is a graphi-
cal evaluation of the time required to fill the mold cavity,
with the blue areas being filled first and the red ones last.
It is assumed that the uniformity of filling illustrated by
the analysis corresponds sufficiently to the injection
molding.
As can be seen in Table 2, an uneven filling of the
mold cavity occurs since the center rib is filled first,
while the side ribs are almost unfilled. Due to the mini-
mum flow rate of the melt through the side gates, they
are already frozen in the cycle time of 3 s. This caused
the holding phase to be effectively performed for only 5
s. Besides, due to the high flow rate of the polymer melt
through the central gate, enormous shear stress occurred,
resulting in excessive heating of the melt.
According to Table 3, it is apparent that the filling of
the cavity by the film gate is more uniform than the pre-
vious gate type. However, the melt has reached the rest
of the cavity only after the center was filled, similar to
the previous case. At the cycle time of 9.9 s, the gate was
already completely solidified, thus the holding phase
lasted only for 4.5 s.
Table 4 shows that using a 1.5-mm-thick side gate
led to a significantly lower melt temperature, mainly due
to the enlarged size of the gate. Nonetheless, it exceeded
the absolute maximum recommended by the Moldflow
database.
As presented in Table 5, due to the lack of one opti-
cal rib and the greater thickness of the mounting base,
the mold cavity is filled nearly evenly, although still
mostly through the central gate. For this reason, the side
gates were almost solidified during filling at a time of
5.4 s. In addition, the polymer melt was shear stressed,
J. VANEK et al.: INJECTION MOLDING OF POLYCARBONATE THICK-WALLED PARTS USING A TOOL ...
302 Materiali in tehnologije / Materials and technology 57 (2023) 3, 299–305
Table 2: Results for sample A with a 1-mm tripple-edge gate
PARAMETER VALUE UNIT FILL TIME (s) (MOLDFLOW)
Fill time 6.9 s
Max. injection pressure 47 MPa
Max. melt temperature 430 °C
Side-gate solidification time 3 s
Central-gate solidification time 11.7 s
Defined/Effective holding time 10/5 s
Cooling time 48.7 s
Total cycle time 65.6 s
Table 3: Results for sample A with a 1.5-mm triple-edge gate
PARAMETER VALUE UNIT FILL TIME (s) (MOLDFLOW)
Fill time 6.7 s
Max. injection pressure 37.7 MPa
Max. melt temperature 341.5 °C
Time of gate solidification 4 s
Defined/Effective holding time 10/5.5 s
Cooling time 166 s
Total cycle time 182.7
s
Table 4: Results for sample A with a 1-mm film gate
PARAMETER VALUE UNIT FILL TIME (s) (MOLDFLOW)
Fill time 5.4 s
Max. injection pressure 37.2 MPa
Max. melt temperature 325.9 °C
Time of gate solidification 9.9 s
Defined/Effective holding time 10/4.5 s
Cooling time 182.3 s
Total cycle time 197.7 s

thus reached high temperatures causing the degradation
of the material.
Table 6 shows that considering the design of the part,
the central optical rib is filled first, followed by the fill-
ing of the mounting base, resulting in a more intensive
melt flow into the right optical rib. Since the gate solidi-
fies already in 10.3 s, the effective time of the holding
phase is only 5.6 s. Despite that, this gating system is the
only one that meets the absolute maximum melt temper-
ature for the defined process conditions.
As shown in Table 7, compared to the alternative
with a 1-mm triple side gate, the filling time decreased
from 6.7 to 5.1 s, moreover, the melt temperature
dropped significantly. Due to both the increased gate size
and the reduced filling time, the melt was notably less
shear stressed.
It is generally known that the melt passing through
the gate is heated by shear stress. When using a triple
side gate, the cavity filling took a relatively long time,
thus the melt was considerably shear stressed, which re-
sulted in its degradation. An increase of the gate size to
above 1.5 mm would reduce the shear stress, therefore,
the melt may not overheat. Further, the more prolonged
holding phase would be achieved. As shown in Figure 4,
an improvement of the cavity- filling uniformity could be
achieved by increasing the cross-sectional dimension of
the side distribution channels. However, this modified
version of the gating insert was not tested in this study.
4 DISCUSSION
In our research, more satisfactory results in both sam-
ple variants were obtained when using a film gate. Since
its cross-section is larger than was in the previous case,
the melt was not heated so intensively, which allowed the
production of functional samples shown in Figure 5.
Also, the influence of the holding phase was more appar-
J. VANEK et al.: INJECTION MOLDING OF POLYCARBONATE THICK-WALLED PARTS USING A TOOL ...
Materiali in tehnologije / Materials and technology 57 (2023) 3, 299–305 303
Table 5: Results for sample B with a 1-mm triple-edge gate
PARAMETER VALUE UNIT FILL TIME (s) (MOLDFLOW)
Fill time 6.7 s
Max. injection pressure 37.4 MPa
Max. melt temperature 343 °C
Side-gate solidification 5.4 s
Central-gate solidification 11.4 s
Defined/Effective holding time 10/5.3 s
Cooling time 44.8 s
Total cycle time 61.5 s
Table 6: Results for sample B with a 1-mm film gate
PARAMETER VALUE UNIT FILL TIME (s) (MOLDFLOW)
Fill time 4.7 s
Max. injection pressure 37.3 MPa
Max. melt temperature 323 °C
Time of gate solidification 10.3 s
Defined/Effective holding time 10/5.6 s
Cooling time 206.7 s
Total cycle time 221.4
s
Table 7: Results for sample B with a 1.5-mm triple-edge gate
PARAMETER VALUE UNIT FILL TIME (s) (MOLDFLOW)
Fill time 5.1 s
Max. injection pressure 38.2 MPa
Max. melt temperature 336 °C
Side-gate solidification 4.2 s
Central-gate solidification 9.5 s
Defined/Effective holding time 10/4.8 s
Cooling time 206.2 s
Total cycle time 221.3 s
Figure 4: Possible modification of the gating insert

ent, as it lasted longer. This improvement reduced the
shrinkage and occurrence of defects such as voids or sink
marks. Additionally, the use of a film gate appears to be
efficient due to a more uniform cavity filling. Based on
this knowledge and the results in Tables 3 and 6,i ti s
possible to assume that contrary to the edge gating sys-
tems, film gates and their alternatives are more suitable
for the injection molding of thick-walled optical prod-
ucts.
One of the possible procedures for the specific evalu-
ation of deformations and defects is scanning the surface
of the manufactured sample with a 3D scanner and sub-
sequent comparison of the obtained data with the geome-
try of the reference model. In this way, dimensional and
shape deviations can be graphically displayed, their ex-
tent evaluated, and determined whether the obtained val-
ues lie within the tolerance range. Based on the results
obtained, the influence of the individual process parame-
ters on the occurrence and size of deformations can be
investigated, or the design of the mold can be adjusted
and thus come as close as possible to all the defined re-
quirements.
Figure 5 compares the scanned areas of the injected
sample with the reference model. The surface of the in-
jected sample was scanned with a 3D scanner to obtain a
cloud of points, which was then converted to a mesh.
The surfaces generated in this way were interlaced with
the surface of the reference model, and then the individ-
ual geometries were compared and the degree of defor-
mation was evaluated. In this case, however, these are
only indicative results used to verify the applicability of
the chosen method. The quality of the results is closely
related to the accuracy of the scanning and the subse-
quent processing of the obtained data, so to receive rele-
vant results, it is necessary to pay more attention to this
issue.
5 CONCLUSIONS
The study examined the influence of various shapes
of gating systems on cavity filling during the injection
molding of PC thick-walled specimens in two variants.
The results provide information about specific values of
process parameters affected by differently shaped edge
and film gating systems. Accordingly, the application of
the film gate seems more appropriate than the triple-edge
gate since the cavity filling is more uniform, and the oc-
currence of defects is noticeably lower.
In conclusion, the overall quality of standard injec-
tion-molded PC thick-walled specimens is more favor-
able when using the film gate. The main reason is the
lower shear stress of the polymer melt, which minimizes
its overheating. Furthermore, the duration of the holding
phase is more effective since the film gate solidifies later
than with the triple-edge gate. These findings may be
valuable for the design of the optical parts themselves
and the injection molds for their production. The knowl-
edge about the cavity filling through differently shaped
gating systems could save time and resources during the
development of injection molds for producing transpar-
ent thick-walled parts. Nevertheless, the influence of the
other applicable gating systems on the cavity-filling pro-
cess of such parts has not been considered in this study
and requires additional examination.
Acknowledgment
This work was supported by the Internal Grant
Agency of TBU in Zlin: no. IGA/FT/2023/005 and pro-
ject "Plastics, metals and technology (PLAKOTECH)",
CZ.01.1.02/0.0/0.0/15_007/0003397..
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304 Materiali in tehnologije / Materials and technology 57 (2023) 3, 299–305
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J. VANEK et al.: INJECTION MOLDING OF POLYCARBONATE THICK-WALLED PARTS USING A TOOL ...
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