C.-C. KUO, C.-M. HUANG: A HIGH-EFFICIENCY AUTOMATIC DE-BUBBLING SYSTEM FOR LIQUID SILICONE RUBBER
995–1000
A HIGH-EFFICIENCY AUTOMATIC DE-BUBBLING SYSTEM FOR
LIQUID SILICONE RUBBER
VISOKOZMOGLJIV SISTEM ZA ODPRAVLJANJE MEHUR^KOV V
TEKO^I SILIKONSKI GUMI
Chil-Chyuan Kuo, Chuan-Ming Huang
Ming Chi University of Technology, Department of Mechanical Engineering, No. 84, Gungjuan Road, Taishan Dist. New,
Taipei City 24301, Taiwan
jacksonk@mail.mcut.edu.tw
Prejem rokopisa – received: 2014-06-13; sprejem za objavo – accepted for publication: 2016-10-27
doi:10.17222/mit.2014.089
The silicone-rubber mold is regarded as an important method for reducing the cost and time to market a new product by
shortening the development phase. A commercial, automatic, vacuum machine is widely used to degas in the manufacturing of a
silicone-rubber mold, but the hardware is costly. A low-cost, high-efficiency degassing system was designed and implemented
from a regular vacuum machine. The control style was based on a human-machine interface. It was found that the whole
degassing-process sequences consist of the explosive phase, the balanced phase and the convergence phase. The time saving in
the degassing process can be at least 42 %. Six predicted equations for both the balanced phase and the convergence phase are
investigated and the maximum relative error of these equations can be controlled to within 6.34 %. The advantages of the
developed de-bubbling system include saving labor, reducing the human error of the operator and a higher degassing efficiency.
Keywords: air bubbles, de-bubbling, silicone rubber mold, rapid tooling
Forma iz silikonske gume je pomembna pri zmanj{evanju stro{kov in skraj{anju ~asa razvojne faze pri uvajanja novega izdelka
na trg. Pri izdelavi forme iz silikonske gume se za razplinjevanje uporabljajo drage komercialne vakuumske avtomatske naprave.
Iz obi~ajne vakuumske naprave je bil izdelan poceni in u~inkovit razplinjevalni sistem. Kontrola stroja temelji na povezavi
~lovek-naprava. Ugotovljeno je, da razplinjevanje sestoji iz eksplozivne faze, faze uravnote`enja in iz faze konvergence,
Postopek razplinjevanja omogo~a 42 % prihranek ~asa. Preiskanih je bilo {est predvidenih ena~b pri obeh uravnote`enih fazah
in pri konvergen~ni fazi in maksimalna napaka zna{a 6,34 %. Prednosti razvitega sistema razplinjevanja so: prihranek dela,
zmanj{anje ~love{kih napak operaterja in ve~ja u~inkovitost razplinjevanja.
Klju~ne besede: zra~ni mehur~ki, odprava mehur~kov, forma iz silikonske gume, hitra izdelava orodij
1 INTRODUCTION
To reduce the time and the cost of product develop-
ment, rapid prototyping (RP) was developed.1 This offers
the potential to completely revolutionize the process of
manufacture. However, the features of the prototype do
not usually meet the needs of the end product with the
required material. Rapid tooling (RT) technologies are
then developed because it is the technology that uses RP
technologies and applies them to the manufacturing of
mold inserts.2 Since the importance of RT goes far
beyond component performance testing, RT is regarded
as an important method of reducing the costs and the
time to market in a new-product development process.
Several RT technologies are commonly available in
industry now. RT is divided into direct tooling and indi-
rect tooling.3 Direct tooling means fabricating mold
inserts directly from an RP machine, such as selective
laser sintering.4,5 Indirect tooling means fabricating the
mold insert by a master pattern fabricated using various
RP technologies. Soft tooling is used for low-volume
production. The materials used for soft tooling have low
hardness levels, such as silicone-rubber6 and epoxy-resin
composites.7 Conversely, hard tooling is associated with
higher volumes of production. Materials used for hard
tooling often have high hardness levels. Soft tooling is
easier to work with than tooling steels because these
tools are created from materials such as epoxy-based
composites with aluminum particles, silicone rubber or
low-melting-point alloys. It is well known that RT is
capable of replacing conventional steel tooling, saving
costs and time in the manufacturing process.8 Indirect
soft tooling is used more frequently in the development
of new products than direct tooling, because it is fast,
simple and cost-effective. It is a well-known fact that a
silicone rubber mold is employed frequently because it
has flexible and elastic characteristics, so that parts with
sophisticated geometries can be fabricated.9 A silicone-
rubber mold can be used for producing low-melting-
point metal parts, wax patterns and plastic parts. Air
bubbles in the silicone-rubber mold are one of the most
common types of defects, especially in the vicinity of the
master pattern. A silicone-rubber mold with air bubbles
appearing in the vicinity of the master pattern will
change the appearance and dimensional accuracy of the
part duplicated from this silicone-rubber mold using
vacuum casting. Conventionally, de-bubbling the air
bubbles with a purely manual operation mode depends
Materiali in tehnologije / Materials and technology 50 (2016) 6, 995–1000 995
UDK 677.017.7:678.84:678.032 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 50(6)995(2016)
significantly on the experiences of the operator. The
drawbacks of this method include human error and noise
pollution derived from the vacuum pump. A com-
mercially available automatic vacuum machine was
widely employed to degas in the manufacturing of sili-
cone-rubber molds, but the hardware is costly.10 In
addition, the programmable logic controller mode lacks
the flexibility to modify the program. Hence, developing
a low-cost and easy-to-operate automated de-bubbling
system is a major concern. To meet this requirement, the
objective of this work is to develop a low-cost and
high-efficiency automatic de-bubbling system with a
human-machine interface (HMI).11 Three vessels were
used for filling the liquid silicone rubber for de-bubbling.
The de-bubbling process sequences were investigated in
detail. The effect of the pressure-relief process in the
explosive phase on the de-bubbling efficiency for manual
and automatic modes was also analyzed. Trend equations
for predicting the balance phase duration and conver-
gence phase duration for three vessels were investigated.
The performance of the automatic de-bubbling system
developed was evaluated. Comparisons of the de-bubbl-
ing efficiencies for automatic and manual modes were
compared.
2 EXPERIMENTAL PART
Figure 1 shows a low-cost, automated de-bubbling
system with an HMI. This system consists of a photo-
electric sensor (EX-11EB; SUNX, Inc.), a programmable
logic controller (PLC) (FX 2N-32MR, Mitsubishi), an
HMI (GP37W2-BG41-24V; Pro-face, Inc.), an electro-
magnetic valve (SUG 15-24VDC; Chelic, Inc.) and an
electronic buzzer (TS2BCL; Tend, Inc.). A photoelectric
sensor (response time 0.5 ms) was used for detecting the
air bubbles during the de-bubbling process. A PLC was
used as a key component of the electric control module.
An HMI was used for operating the automatic de-
bubbling system. The HMI consists of all the aspects of
the interaction and communication between the operators
and machines by using a graphical HMI unit. The
electromagnetic valve (on-off reaction time < 15 ms) was
used to break the vacuum automatically. An electronic
buzzer was used to alert the operator when the de-
bubbling process is completed. Considering the practical
requirements for the different operators, the de-bubbling
method of this system includes an automation mode and
a manual control mode. This system can be equipped
with manual and automatic modes. Three different volu-
mes (250 mL, 500 mL and 1000 mL) of vessels were
used for filling the liquid silicone rubber in this study.
The silicone rubber (KE-1310ST; ShinEtsu, Inc.) in the
liquid state was mixed with a hardener (CAT-1310S;
ShinEtsu, Inc). Generally, the curing agent and silicone
C.-C. KUO, C.-M. HUANG: A HIGH-EFFICIENCY AUTOMATIC DE-BUBBLING SYSTEM FOR LIQUID SILICONE RUBBER
996 Materiali in tehnologije / Materials and technology 50 (2016) 6, 995–1000
Figure 2: Brief flowchart of the automatic vacuum degassing process
using an HMI
Slika 2: Shema poteka postopka avtomatskega vakuumskega razpli-
njevanja s pomo~jo HMI
Figure 1: A low-cost, automated, de-bubbling system with an HMI
Slika 1: Stro{kovno ugoden in avtomatiziran sistem za odpravo me-
hur~kov s HMI
rubber in a weight ratio of 10:1 were mixed thoroughly
with a stirrer. After the de-bubbling process, the pressure
inside the vacuum machine was changed by breaking the
vacuum atmosphere. Thus, a silicone-rubber mold can be
fabricated with defects caused by the air bubbles derived
from the mixing process. To reduce the difference caused
by the different operators in the amount of air bubbles,
while mixing the liquid silicone rubber, an agitation
blade for mixing the liquid silicone rubber was designed
and fabricated. To confirm the center of the vessel is
aligned with the center of the agitation blade, a
positioning fixture was designed and fabricated. Figure
2 shows a brief flowchart of the automatic vacuum
degassing process using an HMI. Due to the
experimental limitations, the solenoid valve does not
work when the break vacuum duration is set less than
0.03 s. Thus, the break vacuum duration was set to be
0.03 s.
3 RESULTS AND DISCUSSION
The center of the vessel can be aligned with the
center of the agitation blade using the positioning fix-
ture. Figure 3 shows the three phases of the de-bubbling
process sequences. In general, the liquid silicone rubber
has a large number of air bubbles because of the mixing
reaction of the materials. As can be seen from this figure,
the first phase is the explosive phase, where the volume
of liquid silicone rubber is drastically increased because
the pressure in the vacuum chamber is lower than the
atmospheric pressure, as shown in Figure 4a. The
second phase is the balance phase, where the air bubbles
in the liquid silicone rubber are eliminated gradually, as
shown in Figure 4b. The final phase is the convergence
phase, where the number and the size of the air bubbles
in the liquid silicone rubber are eliminated significantly,
as shown in Figure 4c. Schematic illustrations of the
three phases of the de-bubbling process are shown in
Figure 5. A number of air bubbles less than 15 is defined
as the end of balance phase. In addition, no more air
bubbles inside the liquid silicone rubber is defined as the
end of convergence. A stopping vacuum of 120 s bet-
ween convergence phase and convergence phase is
required for reducing the convergence phase’s duration.
This is because air bubbles inside the liquid silicone
rubber can reach the top of the liquid silicone rubber
during 120 s. The air bubbles can be eliminated comple-
tely by an automatic de-bubbling system with an HMI
based on the criteria discussed above.
Table 1: Time saving of the explosive phase for different volumes of
silicone rubber
Table 1: Prihranek ~asa pri eksplozivni fazi, pri razli~nih prostorninah
silikonske gume
Volume of
silicone
rubber (mL)
Percentage
of volume
(%)
Mode
Explosive
phase du-
ration (s)
Time
saving
(%)
350 70
Manual 5335
61.46
Automatic 2056
300 60
Manual 3952
81.12
Automatic 746
250 50
Manual 2883
82.59
Automatic 502
200 40
Manual 706
70.00
Automatic 233
150 30
Manual 283
61.48
Automatic 109
100 20
Manual 0
0
Automatic 0
Table 1 shows the time saving of the explosive phase
for different volumes of silicone rubber. As can be seen,
C.-C. KUO, C.-M. HUANG: A HIGH-EFFICIENCY AUTOMATIC DE-BUBBLING SYSTEM FOR LIQUID SILICONE RUBBER
Materiali in tehnologije / Materials and technology 50 (2016) 6, 995–1000 997
Figure 4: Schematic illustrations of the three phases of the de-bubbl-
ing process: a) explosive phase, b) balance phase and c) convergence
phase
Slika 4: Shematski prikaz treh faz postopka razplinjevanja: a) eksplo-
zivna faza, b) ravnote`na faza in c) konvergen~na faza
Figure 3: Three phases of the de-bubbling process: a) explosive phase, b) balance phase and c) convergence phase
Slika 3: Tri faze postopka razplinjevanja: a) eksplozivna faza, b) ravnote`na faza in c) konvergen~na faza
the maximum time saving of the explosive phase is about
81.12 %. The time savings of the explosive phase in-
crease with the increasing percentage of volume, ranging
from 30 % to 60 %. The time saving of the explosive
phase decreases when the percentage of volume exceeds
60 %. These results show that the vessel with a percent-
age of volume of 60% of silicone rubber is the optimum
value.
Figure 5 shows the sequential procedures of the
automatic de-bubbling process. Figure 6 shows the
sequential procedures of the de-bubbling process with
manual operation. It is obvious that the results for the
two operation modes are the same, showing no air
bubbles inside the liquid silicone rubber. This result
shows that the air bubbles inside the liquid silicone
rubber can be eliminated completely with the automatic
operation mode. This means the system can be used for
the production of a high-quality, bubble-free, silicone-
rubber mold.12
Precise determination the balance phase’s duration
and the convergence duration is an absolute requirement
for a high-efficiency, automatic, de-bubbling process.
Figure 7 shows the trend equations for the balance
duration and convergence duration for vessel volumes of
250 mL, 500 mL and 1000 mL. For a vessel volume of
250 mL, the balance phase’s duration (y) can be pre-
dicted from the trend equation of y = 3.316x – 30.8 by
the volume of silicone rubber (x). Note that the R2 repre-
sents the correlation coefficient. Generally, a higher R2
value (maximum value =1) means a better accuracy of
the trend equation.16 Six predicted equations for both the
balanced phase and the convergence phase are investi-
gated, and the maximum relative error of these equations
can be controlled within 6.34 %. This means that both
the balanced phase duration and the convergence phase
duration can be calculated from these equations.
To evaluate the performance of the automatic degass-
ing system developed, each test was carried out three
times with the mean and the deviation determined. Table
2 shows the time saving of the total degassing time for
three different volumes of silicone rubber. Figure 8
shows the total degassing time as a function of silicone
rubber for the manual and automatic operation modes.
As can be seen, a reduction in the degassing time of at
least 42 % can be observed using the automatic degass-
ing system with a human-machine interface. It is obvious
that there is an increase in time saving of degassing with
an increase in the volume of silicone rubber. Three
phases are important for the degassing process, but the
explosive phase is the most critical one. This is because
the pressure-relief process in the automatic operation
mode is significantly different from that in the manual
operation mode, as shown in Figure 9. The recovery
C.-C. KUO, C.-M. HUANG: A HIGH-EFFICIENCY AUTOMATIC DE-BUBBLING SYSTEM FOR LIQUID SILICONE RUBBER
998 Materiali in tehnologije / Materials and technology 50 (2016) 6, 995–1000
Figure 6: Sequential procedures of the de-bubbling process with the
manual de-bubbling mode: a) liquid silicone rubber before de-bubbl-
ing process, b) explosive phase, c) balance phase, d) pause 120 s,
e) convergence phase and f) de-bubbling process was completed
Slika 6: Sekven~ni postopki postopka razplinjevanja pri ro~nem vo-
denju razplinjevanja: a) teko~a silikonska guma pred razplinjevanjem,
b) eksplozivna faza, c) ravnote`na faza, d) pavza 120 s, e) konver-
gen~na faza in f) zaklju~en postopek razplinjevanja
Figure 5: Sequential procedures of the automatic operation mode:
a) liquid silicone rubber before de-bubbling process, b) explosive
phase, c) balance phase, d) pause 120 s, e) convergence phase and
f) de-bubbling process was completed
Slika 5: Sekven~ni postopki pri avtomatskem na~inu dela: a) teko~a
silikonska guma pred razplinjevanjem, b) eksplozivna faza, c) ravno-
te`na faza, d) pavza 120 s, e) konvergen~na faza in f) zaklju~en
postopek razplinjevanja
time needed for the pressure of the chamber reaching the
degassing pressure with the automatic operation mode is
shorter than that with the manual operation mode. Based
on the experimental results, the advantages of this sys-
tem include saving labor, reducing the human error of
the operator and a higher degassing efficiency. This
system has broad application prospects in the develop-
ment of new products using a silicone-rubber mold.
4 CONCLUSIONS
A low-cost, high-efficiency degassing system has
been designed, implemented and tested in this study. The
entire degassing-process sequences consist of the
explosive phase, the balance phase and the convergence
phase. The automatic degassing method provides three
decisive advantages compared with the manual degass-
ing method. The explosive phase has been proved to be a
key process for a high-efficiency degassing process. A
reduction of the degassing time by at least 42 % can be
gained. This system has broad application prospects in
the development stage for new products using rapid-tool-
ing technology.
Acknowledgement
This work was financially supported by the Ministry
of Science and Technology of Taiwan under contract
nos. NSC 102-2221-E-131-012 and NSC 101-2221-
E-131-007.
C.-C. KUO, C.-M. HUANG: A HIGH-EFFICIENCY AUTOMATIC DE-BUBBLING SYSTEM FOR LIQUID SILICONE RUBBER
Materiali in tehnologije / Materials and technology 50 (2016) 6, 995–1000 999
Table 2: Time saving of the total degassing time for three different volumes of silicone rubber
Tabela 2: Prihranek ~asa od vsega ~asa razplinjevanja, pri treh razli~nih prostorninah silikonske gume
Volume of silicone
rubber (mL) Mode
Explosive
phase duration
(s)
Balance phase
duration (s) Pause (s)
Convergence
phase duration (s) Total (s)
Time saving
(%)
110
Manual 1642 338 120 237 2337
45.64
Automatic 583 334 120 233 1270
240
Manual 1415 509 120 427 2471
42.24
Automatic 416 496 120 396 1428
430
Manual 1409 530 120 465 2525
42.07
Automatic 406 508 120 428 1462
Figure 8: Total degassing time as a function of silicone-rubber vol-
ume for manual and automatic operation modes
Slika 8: Celotni ~as razplinjevanja (v odvisnosti od volumna) silikon-
ske gume pri avtomatskem in ro~nem na~inu upravljanja
Figure 9: Schematic illustrations of the pressure relief process in the
explosive phase: a) manual operation mode and b) automatic operation
mode
Slika 9: Shematski prikaz postopka spro{~anja tlaka v eksplozivni
fazi: a) ro~ni na~in vodenja in b) avtomatski na~in vodenja
Figure 7: Trend equations of: a) balance phase duration and b) con-
vergence phase duration for vessel volumes of 250 mL, 500 mL and
1000 mL
Slika 7: Trend ena~b za: a) trajanje ravnote`ne faze in b) trajanje kon-
vergen~ne faze pri prostornini posode 250 mL, 500 mL in 1000 mL
5 REFERENCES
1 M. Laub, H. P. Jennissen, Identification of the anthelix motif in the
TGF-b superfamily by molecular 3D-Rapid Prototyping, Material-
wissenschaft und Werkstofftechnik, 34 (2003) 12, 1113–1119,
doi:10.1002/mawe.200300715
2 A. Iftikhar, M. Khan, K. Alam, S. H. I. Jaffery, L. Ali, Y. Ayaz, A.
Khan, Turbine blade manufacturing through rapid tooling (RT)
process and its quality inspection, Materials and Manufacturing
Processes, 28 (2013) 5, 534–538, doi:10.1080/10426914.2012.
746698
3 D. K. Pal, B. Ravi, Rapid tooling route selection and evaluation for
sand and investment casting, Virtual and Physical Prototyping Jour-
nal, 2 (2007) 4, 197–207, doi:10.1080/17452750701747088
4 S. Singh, V. S. Sharma, A. Sachdeva, S. K. Sinha, Optimization and
analysis of mechanical properties for selective laser sintered poly-
amide parts, Materials and Manufacturing Processes, 28 (2013) 2,
163–172, doi:10.1080/10426914.2012.677901
5 J. Liu, H. Hu, P. Li, C. Shuai, S. Peng, Fabrication and characte-
rization of porous 45S5 glass scaffolds via direct selective laser
sintering, Materials and Manufacturing Processes, 28 (2013) 6,
610–615, doi:10.1080/10426914.2012.736656
6 D. Juarez, R. Balart, T. Boronat, M. J. Reig, S. Ferrandiz, Validation
of the use of SEBS blends as a substitute for liquid silicone rubber in
injection processes, Materials and Manufacturing Processes, 28
(2013) 11, 1215–122, doi:10.1080/10426914.2013.811732
7 R. Azim, M. T. Islam, Design of a wideband planar antenna on an
epoxy-resin-reinforced woven-glass material, Mater. Tehnol., 49
(2015) 2, 193–196, doi:10.17222/mit.2013.169
8 C. C. Kuo, A cost-effective approach to the rapid fabrication of func-
tional metal prototypes, Mater. Tehnol., 48 (2014) 4, 581–585
9 C. C. Kuo, C. Y. Lin, Development of bridge tooling for fabricating
mold inserts of aspheric optical lens, Materialwissenschaft und
Werkstofftechnik, 42 (2011) 11, 1019–1024, doi:10.1002/mawe.
201100819
10 Y. Tang, W. K. Tan, J. Y. H. Fuh, H. T. Loh, Y. S. Wong, S. C. H.
Thian, L. Lu, Micro-mould fabrication for a micro-gear via vacuum
casting, Journal of Materials Processing Technology, 192-193
(2007), 334–339, doi:10.1016/j.jmatprotec.2007.04.098
11 A. Jakli~, F. Vode, R. Robi~, F. Perko, B. Strmole, J. Novak, J. Trip-
lat, The implantation of an online mathematical model of slab
reheating in a posher-type furnace, Mater. Tehnol., 39 (2005) 6,
215–220
12 C. C. Kuo, Y. J. Wang, Development of a micro-hot embossing mold
with high replication fidelity using surface modification, Materials
and Manufacturing Processes, 29 (2014) 9, 1101–1110, doi:10.1080/
10426914.2014.912312
C.-C. KUO, C.-M. HUANG: A HIGH-EFFICIENCY AUTOMATIC DE-BUBBLING SYSTEM FOR LIQUID SILICONE RUBBER
1000 Materiali in tehnologije / Materials and technology 50 (2016) 6, 995–1000