Tóm tắt Luận án Study on the influence of external gas assisted injection molding on the tensile strength of thin wall product

 MINISTRY OF EDUCATION AND TRAINING 
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY 
AND EDUCATION 
TRAN MINH THE UYEN 
STUDY ON THE INFLUENCE OF EXTERNAL GAS 
ASSISTED INJECTION MOLDING ON THE TENSILE 
STRENGTH OF THIN WALL PRODUCT 
SUMMARY OF THE THESIS 
Major: Mechanical Engineering 
Major code: 62520103 
HO CHI MINH CITY – YEAR 2020 
 The work is completed at Ho Chi Minh city University of 
Technology and Education 
Scientific Supervisor one: Assoc. Prof. Do Thanh Trung 
 Scientific Supervisor two: Assoc. Prof. Pham Son Minh 
The thesis will be defensed in front of the Council for 
Ph.D. evaluation of the Ho Chi Minh City University of 
Technology and Education on ............../2020 
The thesis can be found at: 
-The National Library of Vietnam 
-The Library of Ho Chi Minh City University of Technology and 
Education 
1 
Chapter 1. OVERVIEW 
1.1 Overview of plastic injection technology and mold temperature 
control 
In the production of plastic products, the resins are first dried to 
remove the moisture, then the it is fed into the feed hopper on the injection 
molding machine. From here, the plastic is transported by the screw to the 
heater for heating, causing the resin to turn from the solid state to a liquid 
state. When the plastic has melted completely, it will be injected by the 
screw through the runner system to fill the mold cavity. After the mold 
cavity is completely filled, the plastic product is cooled so that the plastic 
from the liquid form returns to its original solid form and is removed from 
the mold, ending a plastic product manufacturing cycle. 
- Additives
- New materials
- Screw
- Injection Pressure
- Injection speed
- Control
- Precision structure
- ...
Strength:
- Tensile
- Bending
- Fatigue
- ...
New processParameter optimization
- Environment
- The cost of materials 
when producing a 
large volume
- The price of the 
machine increases
- High operating costs
Limited equipment, 
technology. Example: Mold 
temperature <100 oC
Expand technology 
capabilities, but not 
increase costs too much
Parameter optimization 
- Mold material
- Mold processing materials
- Processing method / technology
- Mold design process
- ...
Depends heavily on:
- Metallurgical technology
- CAD / CAM-CNC technology
Mold Temperature
Injection pressure, speed
Time
Better performance than 
other parameters
Figure 1.1: Main researches in the field of injection mold technology 
2 
In the field of injection mold, studies in recent years mainly focus 
on four main directions as shown in Figure 1.1. 
In addition to the ability to improve the mechanical properties of 
plastic products, optimizing the mold temperature control is one of the most 
effective ways to improve the surface quality of plastic products. Therefore, 
the important goal of injection mold temperature control is: heat the mold 
surface to the required temperature, while ensuring that the injection cycle 
time is not too long. 
1.2 Overseas research situation 
In these studies, the induction heating method is combined with the 
cooling fluid to control the mold temperature. Heater by induction has 
outstanding advantages compared to other methods such as: 
-High heating rate. 
-The heating time can be as long as 20 s. 
-The injection molding can be applied as an attached module, which 
means there is no need to change the existing mold structure. 
In addition, in order to meet the heating requirements for complex 
surfaces, the method of gas heating has been studied and evaluated for 
effectiveness. The heating process for injection molding via hot air is 
underway as shown in figure 1.2. At the end of the injection molding cycle, 
the two mold plates open and the product is taken out (Figure 1.2 - Step 1). 
Then the movable plate will be moved to the heated position (Figure 1.2 - 
Step 2). At this step, hot air is injected into the mold cavity. Through the 
convection heat transfer process between the hot air and the mold surface, 
the heat energy of the hot air will increase the mold surface temperature to 
the required value. Finally, the hot air will stop spraying, and the two mold 
plates will close completely (figure 1.2 - Step 3). Next, the molten plastic is 
injected into the mold cavity. 
With this method, the mold surface temperature can be increased 
from 60 ° C to 120 ° C in 2 s. However, this heating will reach saturation 
when the heating time is longer than 4 s. The advantage of the “gas 
heating” method is the very high heating speed, and the product cycle time 
will be shortened. However, the design of the injection mold needs to be 
redesigned in order to integrate the heating system. 
3 
 Figure 1.2: Hot air heating process for plastic injection molding. 
1.3 Researches in our country 
Mold temperature control is only understood and implemented in the 
direction of cooling the mold or limiting the pressure drop of the plastic 
flow in the process of flowing into the mold, with the most important goal 
is to cool the mold in the shortest time. On the contrary, the problem of 
keeping the mold surface at high temperature during injection molding in 
order to improve product quality, especially products for the electronics 
industry and products requiring high precision, has begun to be noticed 
through the research topic of Assoc. Prof. Dang Van Nghin. Therefore, in 
general, the situation of manufacturing plastic products in Vietnam is 
stopping at the group of simple products with average quality, and mainly 
focusing on the consumer goods sector. In addition, the possibility of 
limiting defects for plastic products according to the mold temperature 
control method has not been considered and applied. 
1.4 Scientific problem still exists 
The hot air heating method has the following limitations: 
- Mold structure needs to be redesigned. 
- With the actual mold structure, the heating result for the mold 
surface is not good. 
Therefore, in order to increase the applicability of the hot air 
heating method for plastic injection molds, the research topic "Study on the 
influence of external gas assisted injection molding on the tensile strength 
of thin wall product " done in this thesis. 
1.5 The urgency of the subject 
Researching technology and manufacturing plastic injection 
equipment for the production process of engineering plastic products 
requiring high accuracy is a potential direction in the mold field in 
4 
particular and the industrial general accuracy. This technology will 
contribute to improving the product quality, expanding the technological 
capabilities of the plastic injection method, as well as creating a premise for 
more development of technical plastic products in Ho Chi Minh City. 
1.6 Scientific significance 
With the results of the thesis, the heating method for the mold surface 
will have a new and more efficient method of: 
- Heating zone control. 
- Improve mold heating speed. 
- Minimize the change of mold structure. 
- Increase the strength of weldline on thin-walled plastic products. 
1.7 Practical value 
Improving the quality of plastic products, as well as finding new 
technologies to improve the quality and output of plastic products are one 
of the urgent requirements for the plastic industry in Vietnam. Therefore, 
the topic "Study on the influence of external gas assisted injection molding 
on the tensile strength of thin wall product" is proposed to contribute to 
improving the quality of technical plastic products, especially for products 
are manufactured by injection molding technology. 
1.8 Research Purposes 
Through the heating method for injection molding with hot air 
from outside, the topic will focus on researching the following objectives: 
• Clarify the influence of key parameters on the gas heating process 
of the mold. 
• Find and evaluate simulation methods for mold heating process. 
• Evaluate the result of heating the mold cavity by hot air. 
• Applying heating method for mold cavity by hot air in enhancing 
the durability of thin-walled plastic products. 
1.9 Research subjects 
The thesis studies the feasible hot air heating model for injection 
molds with hot air injected from outside the mold. From there, study the 
effect of heating by this method on thin-walled thermoplastics products 
according to ASTM D638. 
1.10 Research tasks and topic limitations 
- The thesis only focuses on research method of heating by hot gas 
with gas source supplied from outside the mold. 
- The heating process, temperature and temperature field were 
investigated through experiment and simulation using ANSYS software. 
5 
- The process of plastic injection into the mold cavity is studied 
through experiment and simulation by Moldex3D software. 
- The hot air temperature varies between 200 ° C and 400 ° C. 
- Applied research for thin-walled plastic products with a thickness of 
from 0.4 mm to 0.8 mm. 
- The plastic materials studied are PA6 and PA6 + 30% GF. 
- Within the time limit and budget of the thesis, the author only 
focuses on the tensile strength of plastic products. 
- Laboratory equipment is provided by the mold laboratory of the 
HCMC University of Technology and Education. 
1.11 Research methodology 
- Simulation of heating and plastic filling of mold cavity. 
- Experimenting the heating process and creating product samples 
corresponding to injection molding processes to investigate the effect of the 
heating step of the mold cavity on the tensile strength of thin-walled plastic 
products. 
 Research methods are implemented on the basis of existing equipment 
at HCMC University of Technology and Education such as: injection 
molding machine, thermometric equipment (infrared camera, temperature 
sensor, ... ) and common injection molds in Vietnam. 
1.12 Thesis structure 
 Chapter 1: Overview - Presenting issues related to research directions 
on injection mold technology, outstanding issues and giving research 
directions. 
 Chapter 2: Cơ sở lý thuyết - Focus on clarifying issues related to the 
heating process for plastic injection molds with hot air sprayed from the 
outside. 
 Chapter 3: Mô tả mô phỏng và thực nghiệm - The hot air heating 
process outside the mold, the plastic filling process of the mold cavity and 
the equipment used for the experiment are described in detail. 
 Chapter 4: Effect of heating parameters on the temperature distribution 
of the cavity surface - This chapter will show the effect of the heating 
parameters (including the insert thickness and the gap (distance) between 
the hot air nozzle and the mold cavity surface) to heating result by hot air. 
 Chapter 5: The effect of hot air heating method on the strength of thin-
walled plastic products - The effect of heating method on the tensile 
strength of thin-walled plastic products will be studied by simulation and 
experiment. 
 Chapter 6: Conclusion. 
6 
Chapter 2. THEORETICAL BASIS 
The design of experiments, as well as analysis of the results of the 
topic will be conducted on the basis of the following theories: 
- Plastic injection process. 
- Simulate the flow of plastic in a mold. 
- Plastic flow in sheet / box part. 
- Convection heat transfer. 
- Plastic Fountain Flow. 
- The effect of the "Frozen layer" on the plastic mold filling process. 
- Tensile strength according to ASTM D638. 
2.1 Plastic injection process 
The basic steps of the injection molding process are shown in 
Figure 2.1. The granular raw material is fed into the hopper and dropped 
into the cylinder. In the cylinder, with the reciprocating and translating 
motion of the screw, combined with the heating resistors outside the 
cylinder, the plastic material from the granular is heated to a plastic state 
and melted into a liquid in temperatures from 150 ° C to 320 ° C. Through 
the translating screw motion, molten plastic in the cylinder is pressed into 
the cavity through the nozzle. At the injection position, the plastic is 
completely liquid. After the whole cavity is filled, packing step will 
proceed. In this process, plastic will continue to be pressed into the mold 
cavity to compensate for the volume loss due to material shrinkage. The 
forming process is finished when the plastic material at the gate is 
completely frozen. Then, the temperature of the product will continue to 
decrease through the cooling step. When the whole product reaches the 
rejection temperature, the mold will open and the product will be removed. 
Figure 2.1: Plastic injection process 
2.2 Simulate plastic flow in a mold 
7 
Figure 2.2: Molecular structure (left) and plastic viscosity 
(right) 
Figure 2.3: Đường đặc tính dẻo của nhựa nhiệt dẻo 
Viscosity is the relationship between the flow resistance to the flow 
of a fluid. The viscosity of fluids such as water, oil, etc. is usually a 
constant value at a certain temperature. These fluids mostly follow 
Newton's theory of fluids. However, the viscosity of thermoplastics is 
very complex and non-Newtonian [109]. Unlike other conventional 
plastics, the viscosity of thermoplastics depends on their chemical 
structure, temperature (T) and pressure (P) as shown in Figure 2.2. 
According to a given chemical structure and formula, the viscosity of 
8 
thermoplastics depends mainly on temperature, shear rate and pressure. 
To understand the viscosity nature of thermoplastics, it is necessary to 
define shear stress and shear rate as shown in Figure 2.3. 
Temperarure
S
p
ec
if
ic
 v
o
lu
m
e
Amorphous plastic
Semi-crystalline plastic
Figure 2.4: The dependence of the specific volume on pressure 
and temperature corresponds to amorphous and semi-crystalline plastic. 
2.3 The effect of the "Frozen layer" on the plastic mold filling process 
During the plastic filling process of the mold cavity, due to the 
effect of heat transfer between the hot plastic and the mold cavity, the 
surface layer of the plastic flow will lose heat, reducing the temperature. 
Therefore, at the contact surface between the plastic and the mold cavity 
will form a Frozen layer. It is this rapid solidification that flows out of the 
resin will have the same characteristics as conventional flow. In the plastic 
injection field, the plastic flow in the mold cavity complies with the 
properties of the Fountain Flow with features such as: The plastic part at 
the center of the flow will flow faster than the plastic part near the mold 
cavity. In which, at the position in contact with the mold cavity, plastic is 
considered not flowing. The plastic at the beginning of the flow is pressed 
forward and rolled towards the cavity (figure 2.5). 
The result of this wall is: during the filling of the mold cavity, the 
plastic that is pressed i ... 
25 
5.2.2 PA6+30%GF plastic 
P
r
e
ss
u
r
e
 (
M
P
a
)
Packing time (s)
180 °C
150 °C
120 °C
90 °C
60 °C
Figure 5.8: Diagram comparing the pressure distribution at the mold 
cavity with different mold temperatures of 0.4 mm mesh thickness products 
P
r
e
ss
u
r
e
 (
M
P
a
)
Packing time (s)
180 °C
150 °C
120 °C
90 °C
60 °C
Figure 5.9: Diagram comparing the pressure distribution at the mold 
cavity with different mold temperatures of 0.6 mm mesh thickness products 
P
r
e
ss
u
r
e
 (
M
P
a
)
Packing time (s)
180 °C
150 °C
120 °C
90 °C
60 °C
Figure 5.10: Diagram comparing the pressure distribution at the mold 
cavity with different mold temperatures of 0.8 mm mesh thickness products 
26 
5.2.3 Results and discussions 
With the same injection conditions, when the temperature value of 
the insert changes from 60 ˚C to 180 ˚C, the change of the forming pressure 
over time is investigated through simulation methods using Moldex3D 
software. in 0.1 s to 1 s intervals corresponding to different product 
thickness cases (varying from 0.4 mm to 0.8 mm). The simulation results 
are compared with each other and the following conclusions are drawn: 
- With the value of packing pressure presented as in Figure 5.5 to 
figure 5.10, it can be seen the decrease of holding pressure over time from 
0.1 s to 1 s. In general, these results show that the higher the mold 
temperature, the longer the forming pressure will be, allowing more plastic 
to be pressed into the cavity. This can be explained by the solidification 
phenomenon of plastic when it comes into contact with the mold cavity. 
When the mold temperature is high, solidification tends to take place more 
slowly, so the resin will stay in a liquid state longer, and as a result the 
pressure applied at the weldline position is kept high in the range of longer 
time than in the case of low mold temperature. 
- In addition, when the product thickness is smaller, the packing 
pressure drops faster. This is because the plastic flow thickness is thin, the 
heat transferred out will be faster, and the solidification process will be 
faster than in the case of products with larger thickness. However, when 
applying a heating step to the cavity, the forming pressure can still be kept 
high, especially in the case of a 0.4 mm thick product as shown in Figure 
5.5 and Figure 5.8. 
- The results of this simulation also show that the method of heating 
the surface of the mold cavity with hot air has the ability to impact quite 
well on the change of holding pressure. This is one of the important bases 
for improving the durability of injection molding products. 
27 
5.3 Experiment on the effect of hot air heating method on product 
durability 
Weldline
Insert
Insert
Figure 5.11: Mold for the experimental process 
 In this section, to test the simulation results, as well as the results of 
the product's strength, the mold with the product is the tensile test bar used 
for the experiment process. Figure 5.11 shows a cavity plate with structure 
for inserting the insert into the mold cavity. 
The experimental process will use the following equipment: 
- Hot air system 
- Gas source 
- Thermal measuring equipment: Thermal couple and infrared camera 
5.3.1 Investigate the temperature field of the mold surface during the 
heating process for the insert 
Through the infrared camera, the temperature distribution at the 
mold surface is also collected and presented as shown in Figure 5.12 to 
Figure 5.16. These results show that the local heating ability of Ex-GMTC 
method is quite good. Specifically, the temperature is concentrated only at 
the location where the weldline appears, in addition, the temperature is kept 
low at other locations. This is one of the advantages of hot air heating in 
particular and surface heating in general. Because of this feature, after 
heating and the plastic is filled in the mold cavity, the cooling step for the 
mold cavity will be carried out easily with a very small high temperature 
zone compared to the entire mold plate volume. In addition, in terms of 
energy saving, the temperature distribution at the mold surface also shows 
that nearly all of the heat energy of the heating process is concentrated in 
the area to be heated, which indicates the efficiency of Ex-GMTC heating 
method is great. 
28 
Figure 5.12: The mold surface temperature when heated with the gas 
source 200 oC 
Figure 5.13: The mold surface temperature when heated with the gas 
source 250 oC 
29 
Figure 5.14: The mold surface temperature when heated with the gas 
source 300 oC 
Figure 5.15: The mold surface temperature when heated with the gas 
source 350 oC 
30 
Figure 5.16: The mold surface temperature when heated with the gas 
source 400 oC 
5.3.2 Test product durability with injection molding processes with 
different mold temperatures 
Tensile test results are synthesized and compared through 2 charts as 
shown in Figure 5.17 and Figure 5.18. This result shows a clear influence 
of the insert temperature and mesh thickness on the tensile strength of the 
product. 
+ For products made of PA6 plastic: 
- In the same cavity temperature (Figure 5.17): when the mesh thickness 
increases, the product's tensile capacity increases. At a temperature of 60 
ºC, with a mesh thickness of 0.4 mm, the corresponding tensile force is 7 
kgf, when the mesh thickness is increased to 0.6 mm, the tensile force 
increases to 7.5 kgf, an increase of 6.83%. However, the degree of tensile 
strength increase is more and more pronounced, especially in the area 
where the insert temperature is higher than 120 ºC. 
- In general, when the insert temperature increases from 30 ºC to 150 ºC, 
the tensile strength of the product improves markedly with all types of 
product thickness. However, the experimental results also show that the 
smaller the thickness, the higher percentage increase of strength will be. 
+ For products made of PA6 + 30% GF: due to the addition of glass 
fiber in the resin composition, these products have a higher tensile strength 
31 
than products made of PA6. Considering the same mold temperature of 30 
ºC and mesh thickness of 0.4 mm, the tensile strength of product made of 
PA6 is 1.75 MPa while product sample PA6 + 30% GF is 2.51 MPa. The 
phenomenon of durability of the product increased when injection molding 
with higher insert temperature also appeared with this composite material. 
Mold Temperature (°C)
 σ
t 
(M
P
a
)
Thickness h=0.4 mm
Thickness h=0.6 mm
Thickness h=0.8 mm
Figure 5.17: Tensile strength of thin wall products made of PA6 
Mold Temperature (°C)
σ
t 
(M
P
a
)
Thickness h=0,4 mm
Thickness h=0,6 mm
Thickness h=0,8 mm
Figure 5.18: Tensile strength of thin wall products made of PA6 + 30% GF 
32 
❖ To find regression equation on the relationship between tensile 
strength and mold temperature and product thickness by Minitab 
software of PA6 resin as follows: 
σt = 2,209 + 0,006T – 1,47h (5.1) 
 With σt: Tensile strength (MPa) 
T: Mold temperature (ºC) 
h: Thickness (mm) 
This regression equation was tested accuracy on Minitab software 
with the reliability of R-sq (ajd) = 92.95%. Therefore, this equation can be 
used to predict cases of PA6 plastic products with different temperatures 
and thickness. 
❖ To find regression equation on the relationship between tensile 
strength and mold temperature and product thickness by Minitab 
software of PA6 + 30% GF resin as follows: 
σt = 3,317 + 0,006T – 2,335h (5.2) 
This regression equation tests the accuracy on Minitab software 
with the reliability of R-sq (ajd) = 93.28%. Therefore, this equation can be 
used to predict the case of PA6 + 30% GF plastic products with different 
temperatures and thickness. 
5.4 Conclusion 
- The results of simulating the heating process for the insert shows that high 
temperatures are concentrated at the surface of the insert, at the position of 
creating a mesh grid for plastic products. 
- The results of the temperature change at the surface of the insert show that 
corresponding to the temperature values of the hot air stream, the surface 
temperature of the mold cavity will increase very rapidly in the first 5 s of 
the heating process. Then, over the next 10 s, the temperature at the mold 
surface will slow down. 
- The molding plastic filling process was investigated through Moldex3D 
software. Simulation results show the reduction of forming pressure over 
time from 0.1 s to 1 s. 
- Cases of using the hot air heating step show that the forming pressure can 
still be kept high, especially in the case of 0.4 mm thick products. 
- The results of the temperature distribution of the mold surface show that 
the local heating ability of the Ex-GMTC method is quite good. 
- The results of pulling plastic products into thin wall were synthesized and 
compared with 2 types of plastic, PA6 and PA6 + 30%GF. This result 
shows a clear influence of the insert plate temperature and mesh thickness 
on the product's tensile capacity. 
33 
Chapter 6. CONCLUSION 
- Through simulation and experimentation, the results showed: 
• The thickness of the insert has a great influence on the heating rate, 
as well as the temperature distribution on the surface of the mold cavity. 
• The gap between the hot air nozzle and the mold surface also has 
an influence on the speed and temperature distribution. 
• The simulation also shows that the hot air injection method from 
outside can be analyzed first, in order to choose the optimal parameters 
depending on the product shape and injection mold structure. 
- With the thin-walled products, the results in the thesis show that high 
temperatures are concentrated only at the surface of the insert, at the 
position of creating a mesh grid for plastic products. This is also one of the 
outstanding advantages of the hot air heating method. 
- The heating process shows that the temperature of the surface of the mold 
will increase very quickly in the first 5 s of the heating process. Then, over 
the next 10 s, the temperature at the mold surface will slow down, and after 
20 s, the temperature of the mold surface will remain stable. 
- The case of using hot air heating step shows that the forming pressure can 
still be kept high, especially in the case of 0.4 mm thick products. 
- The results of the temperature distribution of the mold surface show that 
the local heating ability of the Ex-GMTC method is quite good. 
- The results of tensile test on thin-walled plastic products show positive 
effects of mold temperature and mesh thickness on the product's tensile 
capacity. In particular, the experimental results also show that the smaller 
the thickness, the higher percentage increase of the strength will be. 
34 
APPENDIX: PUBLISHED PAPERS 
1. Pham Son Minh, Tran Minh The Uyen, Dang Minh Phung and Thanh 
Trung Do, A study of temperature control for the pulsed cooling of 
injection molding process, The 2nd international conference on green 
technology and sustainable development, 2014, Vol. 1, pp. 81-85. 
2. Trần Minh Thế Uyên, Phạm Sơn Minh, Đỗ Thành Trung, Trần Văn 
Trọn và Phan Thế Nhân, Ảnh hưởng của áp suất phun đến chiều dài 
dòng chảy của nhựa lỏng trên sản phẩm phun ép nhựa, Tạp chí Cơ khí 
Việt Nam, 2014, Số 7, tr. 60-63. 
3. Pham Son Minh and Tran Minh The Uyen, Numerical study on flow 
length in injection molding process with high-speed injection molding, 
International Journal of Mechanical Engineering and Applications, 
2014, Vol. 2, pp. 58-63. 
4. Huỳnh Đỗ Song Toàn, Trần Minh Thế Uyên, Nguyễn Danh Kiên và 
Lê Hiếu Giang, Nâng cao độ chính xác kích thước sản phẩm nhựa 
thành mỏng bằng phương pháp kết hợp mô phỏng và thực nghiệm, Tạp 
chí Khoa học Giáo dục Kỹ thuật Trường ĐH SPKT TP.HCM, 2015, Số 
32, tr. 42-45. 
5. Phạm Sơn Minh, Đỗ Thành Trung, Lê Tuyên Giáo và Trần Minh Thế 
Uyên, Nghiên cứu quá trình gia nhiệt bằng khí nóng cho khuôn phun 
ép tạo sản phẩm dạng lưới, Tạp chí Khoa học Giáo dục Kỹ thuật 
Trường ĐH SPKT TP. HCM, 2015, Số 32, tr. 46-51. 
6. Huỳnh Đỗ Song Toàn, Trần Minh Thế Uyên, Võ Bá Anh Đại và Lê 
Hiếu Giang, Phân tích gia nhiệt và làm nguội bằng nước trong khuôn 
ép phun một số sản phẩm khác nhau, Tạp chí Khoa học Giáo dục Kỹ 
thuật Trường ĐH SPKT TP. HCM, 2015, Số 33, tr. 44-50. 
7. Phạm Sơn Minh, Đỗ Thành Trung, Trần Minh Thế Uyên và Phan Thế 
Nhân, Ảnh hưởng của chiều dày sản phẩm và nhiệt độ khuôn đến độ 
cong vênh của sản phẩm nhựa polypropylene dạng tấm, Hội nghị Khoa 
học và Công nghệ Toàn quốc về Cơ khí lần thứ IV, TP. HCM, 2015, 
Tập 2, tr. 536 – 543. 
8. Thanh Trung Do, Pham Son Minh, Tran Minh The Uyen and Pham 
Hoang The, Numerical study on the flow length in an injection molding 
process with an external air-heating step, International Journal of 
Engineering Research and Application, 2017, Vol. 7, pp. 85-89. 
9. Thanh Trung Do, Tran Minh The Uyen and Pham Son Minh, Study 
on the external gas-assisted mold temperature control for thin wall 
injection molding, International Journal of Engineering Research and 
Application, 2017, Vol. 7, pp. 15-19. 
35 
10. Pham Son Minh, Thanh Trung Do, Tran Minh The Uyen and Phan 
The Nhan, A study on the welding line strength of composite parts with 
various venting systems in injection molding process, Key Engineering 
Materials, 2017, Vol. 737, pp. 70-76. (SCOPUS). 
11. Pham Son Minh and Tran Minh The Uyen, Numerical study on the 
heliacal cooling channel for injection molding process, International 
Journal of Innovative Science, Engineering & Technology, 2018, Vol. 
5(2), pp. 86-91. 
12. Pham Son Minh, Thanh Trung Do and Tran Minh The Uyen, The 
feasibility of external gas-assisted mold-temperature control for thin-
wall injection molding, Advances in Mechanical Engineering, 2018, 
Vol. 10 (10), pp. 1-13. (SCIE). 
13. Pham Son Minh, Tran Minh The Uyen, Tran Anh Son and Huynh 
Duc Thuan, Study on the temperature distribution of core plates during 
injection molding, International Journal of Engineering Inventions, 
2018, Vol. 7 (10), pp. 24 – 29. 
14. Minh The Uyen Tran, Son Minh Pham and Thanh Trung Do, 
Experimental study on external air heating for an injection molding 
process, ICSSE2019, 2019, pp. 681-685. 
15. Tran Minh The Uyen, Le Tuyen Giao, Thanh Trung Do and Pham 
Son Minh, Numerical study on local heating for thin-walled product by 
external air heating, Materials Science Forum, 2019, Vol. 971, pp. 21-
26. (SCOPUS). 
16. Tran Minh The Uyen, Nguyen Truong Giang, Thanh Trung 
Do, Tran Anh Son and Pham Son Minh, External Gas-
Assisted Mold Temperature Control Improves Weld Line 
Quality in the Injection Molding Process, Materials, 2020, 
Vol. 13, pp. 1-19. (SCIE).