Available via license: CC BY-NC-ND 3.0
Content may be subject to copyright.
113
RESEARCH PAPERS
FACULTY OF MATERIALS SCIENCE AND TECHNOLOGY IN TRNAVA
SLOVAK UNIVERSITY OF TECHNOLOGY IN BRATISLAVA
10.1515/rput-2016-0046 2016, Volume 24, Number 38
IMPACT OF VISCOSITY ON FILLING THE INJECTION
MOULD CAVITY
Lukáš SATIN, Jozef BÍLIK
SLOVAK UNIVERSITY OF TECHNOLOGY IN BRATISLAVA,
FACULTY OF MATERIALS SCIENCE AND TECHNOLOGY IN TRNAVA,
INSTITUTE OF PRODUCTION TECHNOLOGIES,
ULICA JÁNA BOTTU 2781/25, 917 24 TRNAVA, SLOVAK REPUBLIC
e-mail: lukas.satin@stuba.sk, jozef.bilik@stuba.sk
Abstract
The aim of this paper is to look closer at the rheological properties of plastics and their
impact on technology in the plastics processing industry. The paper focuses on the influence of
viscosity of the material on filling the mould cavity. Four materials were tested with the settings
of process parameters with different viscosity. Using simulation software of Moldex3D, we can
see the effect of change in viscosity in the material to be filled.
Key words
injection mould, CAE analysis, viscosity, CAD model
INTRODUCTION
Rheology is the science that deals with the deformation of the material to which force is
applied. The term is most commonly used in the study of liquids and liquid-like materials, i.e.
all materials that flow. Rheology, however, also includes the study of deformation of solids that
occur for example when processing metal or moulding rubber. Two key words in the above
definition are rheology deformation and strength. To learn something about the rheological
properties of the material, you have to either measure the deformation resulting from the forces,
or to measure the force required to achieve the observed deformation. For a linear elastic
material or a Newtonian fluid, it is sufficient to have a general equation that describes how the
materials react to any type of deformation. Such an equation is called a constitutive or
rheological equation of state. However, for more complex materials such as molten plastic,
creation of constitutive equations is much more complex task that may require the results of
many types of experiments. Another aspect is the development of rheology of polymers, which
shows how the rheological properties behave in the affected structure (material composition,
temperature and pressure). In the case of more complex materials, a relationship can be
established, which shows how the specific rheological properties such as viscosity of the
treatment module affect the molecular structure, composition, temperature and pressure. The
Unauthenticated
Download Date | 5/3/17 11:22 AM
114
molten plastics in a fluid state are rheologically complex materials that can exhibit properties
such as viscous flow and elastic recoil. General constitutive equation has been developed
primarily for these materials, and the current state of knowledge of their rheological behaviour
is largely based on empirical research. This fact, on the one hand, complicates the description
and measurement of the rheological properties, but on the other hand, makes the plastic
rheology a relatively new and interesting science (1).
RHEOLOGICAL PROPERTIES
The rheological characteristics of the material features significantly influence the shape
and flow of the material. They also called flow properties. The mathematical representation is
the following flow curve, which expresses the ratio of shear stress and shear rate. The flow of
polymer materials during their processing is pseudoplastic and largely differs from the flow of
low molecular weight liquids (2). One of the main differences between the low molecular
weight fluids, which are also called Newtonian, and, high molecular compounds, which are
referred to as non-Newtonian, is viscosity. The physical Oxford dictionary is defined as the
viscosity value expressing the size of the internal friction in the liquid, measured as the amount
of force exerted per unit area of the resistance extending flow (3). More generally, the viscosity
is a material property that describes its resistance to creep. Liquid resists the movement of the
layers of particles with different speeds. It is also the most common rheological measurement
and the identification value, but it is a qualitatively different feature for the Newtonian and non-
Newtonian fluids. Mathematically, viscosity can be defined as the ratio of shear stress and shear
rate (4).
From the rheology point of view, fluids can be thus classified according to the viscosity as:
• Newtonian – liquids of low molecular weight -. To describe their rheological behaviour during
shear, Newton's law is applied. The viscosity of Newtonian materials is independent of time,
and speed shear deformation depends only on the temperature, pressure and molecular
properties of the test substance (5).
• Non-Newtonian - high-molecular liquids, the flow of which is independent of time. Their
viscosity is not constant, but depends on the strain rate. Description of their behaviour is
possible using various mathematical models. The flow properties of non-Newtonian fluids are
described by rheogram.
• The behaviour during the flow of non-Newtonian substances can be subdivided into:
- Viscoplastic,
- Dilatant.
The Newtonian fluid behaviour can be caused by several factors related to the structural
reorganization of the molecules of the material as a result of the material flow. The polymeric
substances and compounds are the cause of reducing the viscosity of highly anisotropic
arrangement of chains (7).
FACTORS INFLUENCING THE RHEOLOGICAL PROPERTIES
• Shear stress - represents the ratio of the shear force acting on a unit area,
• Shear rate - change of shear strain versus time,
• Temperature - significantly affects viscosity,
• Pressure - affects the free volume between the particles,
• Molecular weight and structure - the arrangement of the macromolecules of the melt
depends on the behaviour of the plastics,
• Additives - chemical composition of the material affects its behaviour during processing (4).
Unauthenticated
Download Date | 5/3/17 11:22 AM
115
IMPORTANCE OF RHEOLOGICAL PROPERTIES IN THE SIMULATION
OF INJECTION
The first injection of plastics into the mould always precedes the simulation, which should
identify possible problems and shortcomings caused by the parameters selected, as well as the
choice of material. The simulation parameters are important, as well as injection of the selected
material, and thus on the most accurate simulation of the outputs it is necessary to select the
values, including the rheological properties so as to achieve the best quality and the final shape
of the product.
For the purposes of determining the rheological impact of its properties to the resulting
shape of the second burst, we will compare the simulation results for four different polymeric
materials used for the injection under the same conditions in the mould cavity of the same shape.
DRAFT MODEL COMPONENTS
As a model for simulation of the injection component, we proposed a flat rectangular shape,
wherein the holes are rectangular. These are important to evaluate and compare the degree of
filling the moulds. We constructed the model components in SolidWorks CSG method. First,
we sketched a rectangle 150x46 mm in draw mode. We then pull it out to a ofmade parts can
be seen in Figure 1. The finished component- was exported into the STEP format.
Fig. 1 A designed 3D model part in SolidWorks
SELECTION AND MATERIAL PARAMETERS
Material
Density [g.c-3]
Modulus of
elasticity [MPa]
Yield strength
[MPa]
Melt
temperature
[°C]
Pour point [°C]
PA66
Ultramid
1003-2
1.14
3000
85
280-305
252
PC ST5201V
1.20
2400
66
280-320
163
PC XQ83619
1.32
2800
65
280-300
160
POM
Ultraform
E3320
1.40
2700
64
180-220
170
Table 1 Basic characteristics of selected
materials
Unauthenticated
Download Date | 5/3/17 11:22 AM
116
Fig. 2 Graphical representation of the medium viscosity materials
MACHINE SELECTION AND INJECTION PARAMETERS
The machine suitable for the production of parts- was designed based on the parameters
chosen from Injection machine Engel ES 200/65. In the SolidWorks program, we found that
the volume part was 8.8 cm-3, the dimensions were 150x46 mm and the height 4 mm.
Comparison of these values with the values in Table 2 shows, that in the case of one-
dimensional form, the machine clearly meets the specifications required for the production of
the proposed part.
Table 2 Basic parameters of the selected injection moulding machine
Parameter
Value
Unit
Clamping force
650
Kn
Screw diameter
25
mm
Maximum injection volume
68
cm3
Diameter of central ring
125
mm
ejectors
100
mm
Size of clamping plate
570x552
mm
Maximum range
430
mm
Height of mould
150
mm
Unauthenticated
Download Date | 5/3/17 11:22 AM
117
SIMULATION OF INJECTION IN MOLDEX 3D ENVIRONMENT
Simulation of injection moulding to form was implemented in the environment of Moldex
3D R13.0. The Moldex 3D CAE software is designed to execute simulation of injection
moulding. It offers a wide range of analyses for different processing of liquid plastics. The
simulation takes place on the finite element model that can be constructed directly in the
environment of Moldex-in, or we can use the model exported from any CAD software in STEP
format.
First, we imported the model that we had created in SolidWorks. We then selected the
appropriate solver for 3D solid model and chose the method of injection technology. After that,
we chose the material and process parameters of injection. In the middle of the shorter sidewall
inlet point we placed a small diameter. Finally, we ran the analysis. We repeated this process
four times, which was due to the fact that the model and the parameters of the simulation were
the same of each for the materials selected.
EVALUATION OF THE SIMULATION
Conditions of melt are compared at the end of the injection moulding cycle of about 4
seconds. After this period, melt solidifies under a constant pressure of 5.0 MPa, so that the
extension of the injection time is not relevant. The actual injection cycle times are slightly
different, the order of a hundredth of a second, as we chose the same time for all materials, in
order to unify the evaluation results.
First, check the value of simulation, shear rate and shear stress.
Fig. 3 Shear rate and shear stress in the component cross section
of the Ultramid10032 material
Ultramid 1003-2 reaches the shear maximal speed 65381.1 s-1, which is on the edge of flow
apertures, and sliding pressure in this place is 0.8 MPa. That makes viscidity approximately 12
Pas.
Unauthenticated
Download Date | 5/3/17 11:22 AM
118
Fig. 4 Shear rate and shear stress in the component cross section of the PC ST5201V material
PC ST5201V reaches shear maximal speed 60634.3 s-1, which is on the edge of flow apertures,
and sliding pressure in this place is 3.87 MPa. That makes viscidity approximately 64 Pas.
Fig. 5 Shear rate and shear stress in the component cross section of the PC XQ83619 material
PC XQ83619 reaches the shear maximal speed of 63550.7 s-1 which is on the edge of flow
apertures, and sliding pressure in this place is 2.175 MPa. That makes viscidity approximately
34 Pas.
Fig. 6 Shear rate and shear stress in the component cross section of the POM UltramidE3320
material
POM UltramidE3320 reaches the shear maximal speed of 86457.6 s-1, which is on the edge of
flow apertures, and sliding pressure in this place is 3.387 Pa. That makes viscidity
approximately 39 Pas.
Unauthenticated
Download Date | 5/3/17 11:22 AM
119
The biggest viscosity has material PC_ST5201V and in the selected area approximately 64 Pas.
Therefore it has the highest assumption to fill the component the least, and right after is followed
by material POM UltramidE3320, which has in given point viscosity 39 Pas. The PC_XQ83619
material with viscidity 34 Pas could be filled better. Out of mentioned materials in the given
area, the lowest viscosity was that of plastic Ultramid 1003-2 approximately 12 Pas. Simulation
of fillings revealed how the components were really filled.
Figure 7 shows that the material filled almost 66% of the mould cavity. The four materials
of the selected PA66 Ultramid 1003-2 with lowest viscosity, we can therefore expect that the
mould will be filled to substantially greater extent than the other three parts. This supposition
was confirmed by simulation. Figure 8 shows the state of filling the mould with ST5201V PC
material, which filled approximately 30 % of the total form. Since this material has a
considerably higher viscosity than Ultramid PA66 1003-2, we assumed that it fills the form in
the lower range.
Figure 9 shows the material of XQ83619 PC that filled the mould at about 33 %; only
slightly more than ST5201V PC. We could conclude that, despite the different nature of the two
medium viscosity of polycarbonates, there is the minimum difference in the flow and filling. It
is a more important factor than the character of viscosity value or viscosity values. The rate of
filling the mould POM Ultraform E3320 is shown in Figure 10. We see the result of
Fig. 7 Status PA66 Ultramid 1003-2 in the mould
cavity at the end of the injection cycle
Fig. 8 Status of the PC ST5201V melt in the
mould cavity at the end of the injection cycle
Fig. 9 Status PC XQ83619 in the mold cavity
at the end of the injection cycle
Fig. 10 Status POM Ultraform E3320 in the
mold cavity at the end of the injection cycle
Unauthenticated
Download Date | 5/3/17 11:22 AM
120
significantly higher viscosity compared to other materials used to fill the mould at the lowest
rate, only about 23 %. Compared to PC material of XQ83619 or ST5201V PC, there is not as
rapid decline as compared with those of polycarbonate and polyamide PA66, even though the
different values of medium viscosity are comparable.
Simulation of filling has confirmed the assumption that component with material Ultramid
1003-2 is filled the most. Also was confirmed that materials POM UltramidE3320 and PC
ST5201V fill the component the least.
Fig. 11 Temperatures of the inlets at the end of the injection cycle
In Figure 11, we can see the average temperature of the inlet 4 for all the materials at the
end of the injection cycle. When comparing the values as indicated in Table 1, we can conclude
that, in all four cases, the material is below the melting temperature. Holding pressure is
therefore not possible, and the state of filling the mould with material is finite. Comparing the
preceding figures and their recovery in relation to the viscosity of each material, we can say
that the viscosity, as the most important rheological property of the plastic melt during the
injection moulding process, has a significant impact on the flow of material as well as the degree
of filling the moulds. The complete filling of the mould was not achieved in either case; the
solution could be in changing either the shape of parts and injection parameters, or selecting
suitable materials with lower viscosity. We estimate that material with about half the size of
medium viscosity value, such as Ultramid PA66 material 1003-2, would be able to fill up the
form without changing either the form of parts or injection parameters.
CONCLUSION
Based on this simulation, we can study how the rheological properties of four different
types of plastics are affected by using the same mould cavity and injection parameters of the
final parts. We found that the Ultramid PA66 1003-2 material with the lowest viscosity reached
the top speed of melt flow rate. When comparing XQ83619 PC and PC ST5201V, we can
conclude that both the ratio of the viscosities and the degree of filling the moulds are not directly
proportional; to determine their relationship would require a large number of simulations. The
results of the simulations carried out, however, clearly show that the viscosity of the molten
material significantly affects the final product injection and is an important parameter that
should be considered when selecting the material for injection moulding.
Unauthenticated
Download Date | 5/3/17 11:22 AM
121
Acknowledgement
The article was written within the project of the European Union Structural funds ITMS
26220120013: “Centre of Excellence of 5- axis Machining”. Article was also supported by the
research project of KEGA 032STU-/2014 called “Blended Learning principles implementation
into teaching of programming of CNC machine tools with advanced kinematic structure” and
also by the Grant scheme for Support of Young Researchers No. 1350 called LATEXMA and
VEGA Grant No. 1/0122/16 of the Grant Agency of the Slovak Republic Ministry of Education.
References:
1. DEALY J., WISSBRUN, K., 1990. Melt rheology and its role in plastics processing. New
York: Van Nostrand Reinhold, 665 s. ISBN 13-978-1-4615-9740-7.
2. ZEMAN, L. 2009. Injection moulding. BEN – technical documents. Praha, 238 p. ISBN
978-80-7300-250.
3. OXFORD DICTIONARIES. Definition of viscosity. [Online] 2016. [cit. 2016-4-3].
Available on Internet: https://www.oxforddictionaries.com/definition/english/viscosity
4. JAHNÁTEK, Ľ., GROM, J., NÁPLAVA, A., 2005. Theory and technology of processing
plastics. Bratislava: Slovak University of Technology, 188 p. ISBN 80-227-2256-1.
5. UNIVERZITA TOMÁŠA BAŤU V ZLÍNE. The flow behavior of polymer melts -
rheological models. Institute of physics and Materials Engineering UTB. [Online] 2010. [cit.
2015-29-11]. Available on Internet: http://ufmi.ft.utb.cz/texty/fyzika_pol/FP_02.pdf
6. VAVRO, K., PECIAR, M. 1998. Process engineering I. Bratislava, Vydavateľstvo STU,
1998. ISBN 80-227-1030-X.
7. RHEOSENSE. Viscosity of Newtonian and non-Newtonian Fluids. [Online] 2016. [cit.
2016-5-2]. Available on Internet: http://www.rheosense.com/applications/viscosity/
newtonian-non-newtonian
ORCID:
Jozef Bílik 0000-0001-7828-8583
Unauthenticated
Download Date | 5/3/17 11:22 AM
