Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation
With the advent of various casting process simulation techniques, it is possible to derive theoretically casting parameters, which can be further validated through experiments. In this paper, detailed simulation activities are carried out to determine the shrinkage characteristics of two Al–Si alloy...
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irk-123456789-1303352018-02-11T03:03:38Z Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation Santhi, Samavedam Sundarrajan, Srinivasan Фазовые превращения With the advent of various casting process simulation techniques, it is possible to derive theoretically casting parameters, which can be further validated through experiments. In this paper, detailed simulation activities are carried out to determine the shrinkage characteristics of two Al–Si alloys (US 413 and US A356) followed by validation through experimental studies. Production of defect-free castings requires good understanding of shrinkage characteristics. The influence of various process parameters on these characteristics determines the casting quality. Based on this, an extensive study is undertaken to comprehend the influence of various parameters. С появлением различных методов моделирования процесса литья появилась возможность теоретически оценить параметры литья, которые могут быть дополнительно проверены с помощью экспериментов. В данной работе было проведено детальное моделирование для определения характеристик усадки двух сплавов Al–Si (US 413 и US A356) с последующей проверкой с помощью эксперимента. Производство отливок без дефектов требует хорошего понимания характеристик усадки. Влияние различных параметров процесса на эти характеристики определяет качество отливки. Исходя из этого, было проведено обширное исследование, чтобы определить влияние различных параметров. З появою різних метод моделювання процесу лиття з’явилася можливість теоретично оцінити параметри лиття, які можуть бути додатково перевірені за допомогою експериментів. В даній роботі було проведено детальне моделювання для визначення характеристик усадки двох стопів Al–Si (US 413 і US A356) з подальшою перевіркою за допомогою експерименту. Виробництво виливків без дефектів потребує доброго розуміння характеристик усадки. Вплив різних параметрів процесу на ці характеристики визначає якість виливки. Виходячи з цього, було проведено цілу низку досліджень, щоб визначити вплив різних параметрів. 2017 Article Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation / Samavedam Santhi, Srinivasan Sundarrajan // Металлофизика и новейшие технологии. — 2017. — Т. 39, № 7. — С. 959-981. — Бібліогр.: 22 назв. — англ. 1024-1809 PACS: 07.05.Tp, 61.72.Qq, 64.70.dg, 81.05.Bx, 81.20.Hy, 81.30.Fb DOI: doi.org/10.15407/mfint.39.07.0959 http://dspace.nbuv.gov.ua/handle/123456789/130335 en Металлофизика и новейшие технологии Інститут металофізики ім. Г.В. Курдюмова НАН України |
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Фазовые превращения Фазовые превращения Santhi, Samavedam Sundarrajan, Srinivasan Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation Металлофизика и новейшие технологии |
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With the advent of various casting process simulation techniques, it is possible to derive theoretically casting parameters, which can be further validated through experiments. In this paper, detailed simulation activities are carried out to determine the shrinkage characteristics of two Al–Si alloys (US 413 and US A356) followed by validation through experimental studies. Production of defect-free castings requires good understanding of shrinkage characteristics. The influence of various process parameters on these characteristics determines the casting quality. Based on this, an extensive study is undertaken to comprehend the influence of various parameters. |
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Santhi, Samavedam Sundarrajan, Srinivasan |
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Santhi, Samavedam Sundarrajan, Srinivasan |
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Santhi, Samavedam |
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Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation |
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Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation |
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Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation |
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Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation |
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Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation |
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shrinkage estimation of cast al–si alloys through process simulation |
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Інститут металофізики ім. Г.В. Курдюмова НАН України |
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Shrinkage Estimation of Cast Al–Si Alloys through Process Simulation / Samavedam Santhi, Srinivasan Sundarrajan // Металлофизика и новейшие технологии. — 2017. — Т. 39, № 7. — С. 959-981. — Бібліогр.: 22 назв. — англ. |
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Металлофизика и новейшие технологии |
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2025-07-09T13:22:11Z |
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ФАЗОВЫЕ ПРЕВРАЩЕНИЯ
PACS numbers: 07.05.Tp, 61.72.Qq, 64.70.dg, 81.05.Bx, 81.20.Hy, 81.30.Fb
Shrinkage Estimation of Cast Al–Si Alloys Through Process
Simulation
Samavedam Santhi and Srinivasan Sundarrajan*
Mahatma Gandhi Institute of Technology,
500075 Hyderabad, India
*National Institute of Technology,
620015 Trichy, India
With the advent of various casting process simulation techniques, it is possi-
ble to derive theoretically casting parameters, which can be further validated
through experiments. In this paper, detailed simulation activities are carried
out to determine the shrinkage characteristics of two Al–Si alloys (US 413
and US A356) followed by validation through experimental studies. Produc-
tion of defect-free castings requires good understanding of shrinkage charac-
teristics. The influence of various process parameters on these characteris-
tics determines the casting quality. Based on this, an extensive study is un-
dertaken to comprehend the influence of various parameters.
Keywords: shrinkage, cast aluminium alloys, casting mould, process simula-
tion, solid model, design of experiments.
З появою різних метод моделювання процесу лиття з’явилася можливість
теоретично оцінити параметри лиття, які можуть бути додатково переві-
рені за допомогою експериментів. В даній роботі було проведено детальне
моделювання для визначення характеристик усадки двох стопів Al–Si
(US 413 і US A356) з подальшою перевіркою за допомогою експерименту.
Виробництво виливків без дефектів потребує доброго розуміння характе-
ристик усадки. Вплив різних параметрів процесу на ці характеристики
визначає якість виливки. Виходячи з цього, було проведено цілу низку
досліджень, щоб визначити вплив різних параметрів.
Ключові слова: усадка стопу, ливарні алюмінійові стопи, ливарна форма,
Corresponding author: Samavedam Santhi
E-mail: santhi_samave@yahoo.com
Please cite this article as: Samavedam Santhi and Srinivasan Sundarrajan, Shrinkage
Estimation of Cast Al–Si Alloys through Process Simulation, Metallofiz. Noveishie
Tekhnol., 39, No. 7: 959–981 (2017), DOI: 10.15407/mfint.39.07.0959.
Ìåòàëëîôèç. íîâåéøèå òåõíîë. / Metallofiz. Noveishie Tekhnol.
2017, т. 39, № 7, сс. 959–981 / DOI: 10.15407/mfint.39.07.0959
Îттиски доступнû непосредственно от издателя
Ôотокопирование разрешено только
в соответствии с лицензией
2017 ÈÌÔ (Èнститут металлофизики
им. Ã. В. Êурдюмова ÍÀÍ Óкраинû)
Íапечатано в Óкраине.
959
mailto:santhi_samave@yahoo.com
960 Samavedam SANTHI and Srinivasan SUNDARRAJAN
симуляція процесу, модель твердого тіла, проєктування експериментів.
С появлением различнûх методов моделирования процесса литья появи-
лась возможность теоретически оценить параметрû литья, которûе могут
бûть дополнительно проверенû с помощью экспериментов. В данной ра-
боте бûло проведено детальное моделирование для определения характе-
ристик усадки двух сплавов Al–Si (US 413 и US A356) с последующей про-
веркой с помощью эксперимента. Производство отливок без дефектов тре-
бует хорошего понимания характеристик усадки. Влияние различнûх
параметров процесса на эти характеристики определяет качество отлив-
ки. Èсходя из этого, бûло проведено обширное исследование, чтобû опре-
делить влияние различнûх параметров.
Ключевые слова: усадка сплава, литûе алюминиевûе сплавû, литейная
форма, моделирование процессов, модель твёрдого тела, проектирование
экспериментов.
(Received June 29, 2017)
1. INTRODUCTION
Solidification of castings involves modification of phase with libera-
tion of latent heat from a moving liquid-solid boundary to mould and
then to atmosphere [1]. Casting process simulation programmes are
time and temperature dependent and more attention is being focused
on systematic aspects in production of castings such as studies of the
heat transfer mechanisms, by which castings solidify, and the rate, at
which solidification and shrinkage takes place [2].
Computer simulation of casting takes into account the qualitative
and quantitative consideration of the process parameters, boundary
conditions and their influence on quality of casting. Process parame-
ters and boundary conditions include casting type, mould material,
chemical composition of alloy considered, physical properties and in-
terfacial heat transfer coefficient between the existing boundaries.
The temperature history of all sites inside the casting are attained
by plotting the progress of solidification fronts (isothermal contours)
at different instants of time, and by identifying the last freezing re-
gions/sites [3]. The numerical simulation of casting solidification pro-
cedure has been done through Finite Difference Method (FDM).
The cast Al–Si alloys are the true workhorses of the aluminium alloy
casting industry because of their excellent casting characteristics and
good strength [4]. Shrinkage is the most significant discontinuity in
castings, and forms due to the contraction of liquid metal, transfor-
mation of liquid to the solid and contraction in the solid state [5]. This
shrinkage results in the form of voids like micro- and macroshrinkage
during solidification. Macroporosity or macroshrinkage occurs due to
entrapped liquid metal surrounded by solid. Y. Li states [6] that the
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 961
tendency for formation of shrinkage porosity is related to liquid to sol-
id volume fraction at the time of final solidification and solidification
temperature range of alloy. Shape and relevant wall thickness of a
casting are very important casting parameters that influence the
shrinkage porosity.
2. SIMULATION PROCEDURE
Efficient design of experiments is an efficient approach for improving
a process to quickly obtain meaningful results and draw conclusions
about how factors or process parameters interact [7, 8] when more than
one factor is changing at a time. An orthogonal array would mean a
balanced design with equal weight age to each factor [9, 10]. MINITAB
software was used for experimental design [10].
2.1. Selection of Process Parameters
The parameters, which influence the shrinkage, are pouring tempera-
ture, casting shape, use of chills, alloy composition, type of mould
sand, presence of mould coat and pouring time [11].
Out of the above parameters, which influence the shrinkage, alloy
composition, bottom chill, shape of the casting, mould coat, and pour-
ing temperature, were considered as the process parameters for the
present investigation. Alloy composition affects the shrinkage charac-
teristics and mechanical properties of the cast product. To study the
influence of alloy composition, two alloys with chemical compositions
given in Table 1 (US 413 and US A356) were used.
TABLE 1. Chemical composition (wt.%).
Element US 413 US A356
Silicon
Iron
Copper
Manganese
Magnesium
Nickel
Zinc
Lead
Tin
Titanium
Others (each)
Others (total)
Aluminium
11.5
0.40
0.15
0.55
0.10
0.10
0.15
0.10
—
0.20
0.05
0.15
Balance
6.90
0.45
0.20
0.35
0.55
0.15
0.15
0.15
0.05
0.15
0.05
0.15
Balance
962 Samavedam SANTHI and Srinivasan SUNDARRAJAN
Rectangle, cube and cylinder were the three basic industrial casting
shapes considered for the present study. The rate of heat exchange de-
pends on thermo-physical properties of the liquid metal, casting
mould, wall thickness of casting and its shape. The dimensional details
of the casting are provided in Table 2.
Mould coatings provide smooth surfaces, improve the quality and
reduce the mould erosion [1, 12]. Pouring temperature [13] influences
fluidity, porosity, strength and structure of the casting. Pouring tem-
perature T (T is melting point +75°C) and T + 50°C of superheat was
considered. The bottom chill showed significant difference in the cast-
ing characteristics, and directional solidification can help in eliminat-
ing shrinkage porosity defects [14]. A mild steel (MS) chill was consid-
ered for the present study.
Table 3 shows the details of the factors and their levels (variables)
for the present study. An orthogonal array L36 (2
4
3
1) was used with
five factors (one process parameter with three levels and four process
parameters with two levels) and 36 runs for shrinkage simulation in-
vestigation, as shown in Table 4.
TABLE 2. Dimensional details of the casting shapes to determine shrinkage
characteristics.
Sl. No. Shape
Dimension,
mm
Pouring
position
Surface area,
cm2
Volume,
cm3
1 Rectangle 115×100×48
436.40 552.000
2 Cube 82×82×82
403.44 551.368
3 Cylinder ∅90×90
381.51 572.265
TABLE 3. Factors and their levels for shrinkage simulation studies.
Factor 1
Alloy
Factor 2
Chill
Factor 3
Pouring
temperature, °C
Factor 4
Mould coat
Factor 5
Casting
mould
Level 1 US A356
Mild
Steel (MS) T + 50 Graphite (GC) Cylinder
Level 2 US 413 No T No coating (NC) Cube
Level 3 — — — — Rectangle
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 963
3. CASTING PROCESS SIMULATION
3.1. Solid Model
Simulation studies on shrinkage characteristics of aluminium alloy
have been conducted using the Virtual casting commercial software
TABLE 4. L36 (2
4
3
1) orthogonal array for the simulation studies.
Simulation
run order Alloy Chill
Pouring
temperature, °C
Mould
coat
Casting
mould
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
MS
MS
MS
MS
MS
MS
MS
MS
MS
No
No
No
No
No
No
No
No
No
MS
MS
MS
MS
MS
MS
MS
MS
MS
No
No
No
No
No
No
No
No
No
T + 50
T + 50
T + 50
T + 50
T + 50
T + 50
T
T
T
T + 50
T + 50
T + 50
T
T
T
T
T
T
T
T
T
T
T
T
T + 50
T + 50
T + 50
T
T
T
T + 50
T + 50
T + 50
T + 50
T + 50
T + 50
GC
GC
GC
NC
NC
NC
GC
GC
NC
NC
NC
GC
GC
GC
GC
NC
NC
NC
NC
NC
NC
GC
GC
GC
NC
NC
NC
GC
GC
GC
NC
NC
NC
GC
GC
GC
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
964 Samavedam SANTHI and Srinivasan SUNDARRAJAN
[15]. The solid models for shrinkage simulations were created using
the SolidWorks software.
The solid models for shrinkage simulation are given in Fig. 1, along
with their respective chills where applicable.
3.2. Simulation Studies
Casting process simulations were carried out using Virtual Casting
software [15], which is a program for the simulation of the solidifica-
tion process of industrial castings using FDM.
Virtual casting software creates a virtual environment for casting
solidification, predicting and analysing the occurrence of shrinkage
defects. The input data for the casting process simulation are solid
model of the casting, material properties and boundary conditions.
Virtual Casting consists of three major processes: Pre-processing,
Solving the governing equations and Post-processing or visualization
of results. The simulation output/results were displayed as contour
plots of temperature, porosity, solid fraction (Fs), solidification time
and cooling rate.
For accurate results, the process simulation requires boundary con-
ditions. The boundary condition values described at the beginning of
the process were the thermal data of metal and casting mould, condi-
Fig. 1. Solid models for shrinkage studies: a—shrinkage, b—respective chills.
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 965
tions of heat exchange between the casting and individual parts of the
mould and between the mould and its surroundings.
The interfacial heat transfer coefficient is the rate of heat loss
through the metal/mould interfaces, which influence the casting char-
acteristics [16]. However, interfacial heat transfer coefficient is not a
simple material property and is dependent upon chemical, physical in-
terfacial conditions, mould and casting material properties and casting
geometry. The selection of interfacial heat transfer coefficient values,
as well as boundary conditions at the metal/mould interface, affects
the accuracy of the simulations. In the present investigations, interfa-
cial heat transfer coefficient values for conformity of computer simu-
lation and the experimental measurements were consistent. The ther-
mo-physical properties of US A356, US 413 alloys, silica sand and mild
steel chill for the casting process simulation [16–18] are given in Ta-
ble 5.
The solid model of shrinkage characteristic, which is imported in the
STL-file format (Fig. 2) as the solution domain, divides into small fi-
nite cells of casting and mould with a material identification. Bounda-
ry conditions were assigned at all material interfaces metal, mould and
mould coat.
The critical liquid fraction (a parameter used is the solvus in the
governing equations for calculation of porosity) is the value of liquid
fraction, below which a neighbouring cell does not feed to pay off for
shrinkage. During solidification at a particular location, liquid is
pulled in from neighbouring locations to pay off for solidification
shrinkage. If the neighbouring location has a high percentage of solid,
liquid cannot flow through it. The exit solid fraction is the total vol-
ume percent of solid, at which the simulation exits.
TABLE 5. Physical constants and properties of US A356, US 413 alloys, silica
sand and mild steel chill for casting simulation.
Sl. No. Parameter US A356 US 413 Sand MS Chill
1
2
3
4
5
6
7
Melting point, K
Thermal conductivity,
W/(mm⋅K)
Density of solid, g/cm3
Liquids temperature, K
Freezing range, K
Latent heat of fusion, J/kg
Specific heat, J/(kg⋅K)
934
0.159249
2.68496
886
400
388442
962.944
855
0.121338
2.65772
847
303.75
389112
1170
—
90.27×10−5
1.5219
—
—
—
1076.0076
—
4.5×10−2
7.84
—
—
—
460.548
8
Heat Transfer Coefficient, HTC, W/(m2⋅K)
Metal–mould
Metal–coating mould
35×10−4
15×10−4
25×10−4
12×10−4
—
—
—
—
966 Samavedam SANTHI and Srinivasan SUNDARRAJAN
For example, a value of 1 for the exit solid fraction means that the
simulation will be done until the casting is 100% solidified. The simu-
lation results for shrinkage are represented as contour plots of the lo-
cation and magnitude of porosity formed during the solidification at
particular location from the bottom of the casting for simulation run
order 30 in Fig. 3.
In Figures 3 and 4, the top portion shows the magnitude of porosity
formed during the solidification and the bottom portion depicts the lo-
cation of the porosity from the bottom of the casting.
Fig. 2. STL-file and boundary conditions.
Fig. 3. Typical contour plots showing the porosity distribution for simulation
30.
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 967
4. RESULTS AND DISCUSSION
The transformation from the liquid state to the solid state is accompa-
nied by a decrease in volume in most metals, leading to shrinkage and
porosity [1]. The tendency for the formation of shrinkage is associated
with both liquid and solid volume fraction and the solidification tem-
perature range of the particular alloy [1, 12]. Shrinkage occurs in me-
tallic materials during freezing and cooling.
Using the virtual casting software, macroshrinkage and mi-
croshrinkage for the 36 simulation runs were done. The contour plots
showing the location and magnitude of porosity formed during the so-
lidification for simulation number 13 is shown in Fig. 4, in 2D, which
is difficult to measure. Hence, 3D solid works software was used for
generating 3D model of the images. The large tolerance level (0.1 mm),
typical in foundry processes [19] was considered for the present study.
Post processing image is converted to the solid model part (SLD-part)
file format. The starting location of the shrinkage porosity was 80 mm
from bottom and spread up to 92 mm from the flat bottom. These con-
Fig. 4. Typical contour plots showing the porosity distribution for simula-
tion 13.
a b
Fig. 5. Constructed porosity of the simulation run order 13: a—84 mm from
bottom (volume is 15.49288 cm
3), b—88 mm from bottom (volume is 10.8578
cm3).
968 Samavedam SANTHI and Srinivasan SUNDARRAJAN
tour plot data were converted to solid model part (SLD-part) was shown
as constructed porosity in Fig. 5 (for 84 mm and 88 mm).
The shrinkage porosity distribution for simulation 13 between 80–
92 mm from the flat bottom was given in Table 6. The porosity distri-
bution obtained from the contour plot in all the four locations was
0.499. The amount of shrinkage porosity distribution in these regions
is given in Table 7.
The porosity distribution for all the 36 simulations was calculated in
similar way. Figure 6 gives the constructed porosity of simulation for
run 5 and 30 for rectangle (103 mm from bottom, volume is 10.399 cm
3
and 108 mm from bottom, volume is 9.4899 cm
3) and cube (68 mm from
bottom, volume is 6.02598 cm
3
and 72 mm from bottom, volume is
6.20088 cm
3) castings respectively.
The porosity distribution results for all the 36 simulations are given
in Table 8.
4.1. Solidification
When liquid metal enters a mould cavity, its heat is absorbed and
transferred through the mould wall as shown in Fig. 7. For eutectics
and pure metals, the solidification continues layer by layer starting
from the mould wall and gradually moving inwards [21]. The progress-
ing layer between the liquid and solid is called the solidification front.
TABLE 6. Shrinkage porosity distribution—Simulation 13.
Sl. No. Distance from the flat bottom, mm Volume, cm
3
1
2
3
4
80
84
88
92
15.49288
10.63793
10.85780
15.55000
Total volume 52.53861
TABLE 7. Amount of Shrinkage porosity—Simulation 13.
Total volume of shrinkage porosity
distribution, cm
3 52.53861
Amount of shrinkage porosity
distribution in the four regions, cm
3 52.53861×0.499 = 26.21677
Amount of shrinkage porosity
in the casting, cm
3 26.21677/572.265 = 0.045812
Percentage shrinkage porosity
in the casting 4.5812
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 969
As this front solidifies, it contracts in volume, and draws liquid metal
from the inner part of the casting (opposite to the mould wall).
When the solidification front reaches the innermost region or the
thickest part of the casting, there is no liquid metal left to compensate
the shrinkage, and as a result, a void space called shrinkage cavity is
formed.
When liquid metal enters into the mould cavity, its heat is removed
and transferred through the mould wall. Most of the cast alloys do not
have distinct melting point. Only pure metals and eutectic alloys solid-
ify at a constant temperature. However, cast alloys solidify over a
Fig. 7. Solidification of casting in a mould.
Fig. 6. Shows constructed porosity of simulation for run: a—30, rectangle
casting; b—5, cube casting.
970 Samavedam SANTHI and Srinivasan SUNDARRAJAN
range of temperatures. The range between the liquidus line and solidus
line is known as the freezing range Rf = Tliq − Tsol, where Tliq is liquidus
temperature and Tsol is solidus temperature as shown in Fig. 8.
Solidification proceeds layer-by-layer in short freezing range
(US 413) alloys, which behave like pure metals and eutectics. Solidifi-
cation is initiated at a large number of nucleation sites, in case of long
TABLE 8. Porosity distribution for all 36 simulations.
Simulation
run order Alloy Chill
Pouring
temperature, °C
Mould
coat
Casting
mould
Shrinkage
porosity, %
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US A356
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
US 413
MS
MS
MS
MS
MS
MS
MS
MS
MS
No
No
No
No
No
No
No
No
No
MS
MS
MS
MS
MS
MS
MS
MS
MS
No
No
No
No
No
No
No
No
No
T + 50
T + 50
T + 50
T + 50
T + 50
T + 50
T
T
T
T + 50
T + 50
T + 50
T
T
T
T
T
T
T
T
T
T
T
T
T + 50
T + 50
T + 50
T
T
T
T + 50
T + 50
T + 50
T + 50
T + 50
T + 50
GC
GC
GC
NC
NC
NC
GC
GC
NC
NC
NC
GC
GC
GC
GC
NC
NC
NC
NC
NC
NC
GC
GC
GC
NC
NC
NC
GC
GC
GC
NC
NC
NC
GC
GC
GC
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
Cylinder
Cube
Rectangle
3.473
2.845
2.628
3.500
3.162
2.700
3.850
3.250
2.800
3.800
3.240
2.895
4.582
3.300
3.100
4.515
3.500
3.130
3.380
2.900
2.180
3.340
2.880
2.190
3.040
2.610
2.000
3.400
2.710
2.290
3.350
2.640
2.100
3.300
2.600
2.120
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 971
freezing range alloys and grains grows until the neighbouring grains
hinder them. Freezing rate is greatly affected by the cooling rate and
thermal gradients inside the casting, which are influenced by varying
process parameters.
4.2. Influence of Process Parameters
4.2.1. Casting Mould
Progress of solidification is influenced by size, shape and thickness of
the casting [18, 20]. Macrocavities decrease with casting shape chang-
es from thick cylinder to thin rectangle castings. The shape of the cast-
ing influences the solidification of the casting in localized areas be-
cause the edges play a significant role in the heat extraction. The edges
of the test casting, combined with the relative composition of the alloy,
decide the variation in formation of macrocavities. The solidification
time is inversely proportional to surface area of the casting [22].
Relative solidification time affects the macrocavities (with in-
creased solidification time, the macrocavities increase). Solidification
time is higher in cylindrical shape castings (which have the least sur-
face area of the three casting shapes considered for the present study)
[22], which promoted maximum macrocavities. The influence of cast-
ing shape on shrinkage porosity is shown for the two alloys US A356
and US 413 in Figs. 9 and 10. The numbers 1–6 on the X-axis in the
Figs. 9 and 10 were percentage shrinkage values obtained for six simu-
lation runs conducted for each casting mould.
4.2.2. Chill
Bottom chills reduced the shrinkage porosity for all the shapes of cast-
ings (rectangle, cube and cylinder). Bottom chill extracts heat locally.
However, there was an increased rate of heat extraction from the liq-
Fig. 8. Freezing range of alloys.
972 Samavedam SANTHI and Srinivasan SUNDARRAJAN
uid metal and compensation of solidification shrinkage as the pouring
time of molten metal increased, giving a reduction in shrinkage porosi-
ty.
The rate of heat extraction and the temperature gradients inside the
solidifying metal influenced the solidification. Changes in tempera-
ture gradient by the presence of chill had no effect on macrosolidifica-
Fig. 9. Influence of casting mould on shrinkage—US A356.
Fig. 10. Influence of casting mould on shrinkage—US 413.
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 973
tion and hence macrocavities were not influenced. Chills promoted
steeper temperature gradients in the solidifying metal and increased
the feeding capacity, thus reducing internal porosity and pore size.
The influence of a bottom chill on the shrinkage porosity is given in
Fig. 11.
4.2.3. Pouring Temperature
Pouring temperature is an important parameter in foundries for man-
ufacturing quality castings. In order to study the influence of pouring
temperature on shrinkage porosity, pouring temperature, T, and
T + 50°C were considered. Superheat is the additional heat essential for
melting, which increases the fluidity and provides the allowance for
heat losses before they are in their final position in the mould. In-
creased pouring temperature results in lower rate of heat extraction by
the mould, hence higher pouring temperature led to decreased macro-
cavities and internal porosity as shown in Fig. 12.
4.2.4. Mould Coat
In order to study the effect of mould coating on shrinkage porosity,
moulds with and without graphite coatings were considered. Mould
coatings provide smooth casting surfaces and influence the thermal
gradient by promoting the directional solidification. Mould coatings
Fig. 11. Influence of chill on shrinkage.
974 Samavedam SANTHI and Srinivasan SUNDARRAJAN
allow a passageway for feed metal to flow into the solidifying structure
and compensated for normal metal shrinkage during solidification.
There was decreased shrinkage porosity for all the three types of cast-
ing shapes in graphite-coated moulds as shown in Fig. 13.
Fig. 12. Influence of pouring temperature on shrinkage.
Fig. 13. Influence of mould coat on shrinkage.
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 975
4.2.5. Interaction Plots
The importance of interactions among influencing factors are illus-
trated using interaction plots. The effect of one factor is dependent
upon the other. To study interaction effects between the process pa-
rameters, it is necessary to vary all the factors simultaneously. If the
process parameters are more than three, then, the interaction plot can
be displayed in the form of matrix. The plot has one panel for each pair
of factors in the data set.
Parallel lines in the interaction plot imply no interaction between
the influencing factors. Increased departure from parallel plots im-
plies stronger interaction effects.
A significant amount of interaction was observed between the pro-
cessing parameters. The interaction and main effects plot (given in
Figs. 14 and 15) for shrinkage indicate that there was a strong interac-
tion among all the influencing factors, when considering the levels
(variables). Thus, the alloy, bottom chill, mould coat, casting shape
Fig. 14. Interaction plots of processing parameters on shrinkage.
Fig. 15. Plots showing the processing parameters on shrinkage.
976 Samavedam SANTHI and Srinivasan SUNDARRAJAN
and pouring temperature influence the shrinkage. The difference in
the vertical position of the plotted points indicates greater magnitude
of the effect, hence the bottom chill factor is considered more signifi-
cant in influencing shrinkage.
5. EXPERIMENTAL VALIDATION STUDIES
Experiments were conducted to validate the casting process simulation
results. To evaluate the influence of process parameters, six experi-
ments were conducted (given in Table 9), and a schematic diagram of
the testing arrangement for cube casting is shown in Fig. 16. These ex-
periments were designated as experiments run order 1 to 6. The pre-
pared moulds, overflow core and pouring basins for three casting
shapes are shown in Fig. 17. The overflow core was placed over the
mould in order to ensure that only a fixed quantity of metal was poured
into the mould each time.
5.1. Moulding, Melting and Pouring
Moulds were prepared using green sand process. The sand composition
TABLE 9. Conditions for validation experiments.
Experiment
run order Alloy Chill
Pouring
temperature, °C Mould coat Casting shape
1
2
3
4
5
6
US A356
US A356
US A356
US 413
US 413
US 413
MS
MS
MS
MS
No
MS
T + 50
T + 50
T
T
T + 50
T
NC
GC
NC
NC
GC
NC
Cylinder
Cube
Rectangle
Rectangle
Cube
Rectangle
Fig. 16. The assembled mould for volume deficit experiment.
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 977
was silica sand with 5–6 wt.% Bentonite and 5–8 wt.% water. Moulds
were prepared with slight ramming. The patterns stripped after
3 hours. The alloy was melted in an electric resistance furnace of capac-
ity 20 kg provided with mild steel crucible. Temperature was measured
with a K-type thermocouple.
The furnace was turned off and the crucible was lifted and put in a
tilting device. The metal was tapped into a smaller crucible for pouring
into the mould. Figure 18 shows the solidified castings of the valida-
tion experiments.
Low-magnification examination of cast components reveals porosi-
ty, shrinkage. Unetched condition generally discloses the porosity and
shrinkage defects. During solidification of casting, if a region in the
casting receives insufficient amount of liquid metal, then, the liquid in
this region solidifies either in the form of shrinkage/pore. Structure
consists of a network of silicon particles (sharp and grey), formed in
the interdendritic aluminium-silicon eutectic, for alloy US A356, as
sand cast is shown in Fig. 19, while the structure consists of eutectic
Fig. 17. Schematic diagram for the volume deficit experiment for cube shape
casting.
Fig. 18. Solidified castings from the validation experiments.
978 Samavedam SANTHI and Srinivasan SUNDARRAJAN
silicon (grey constituent) for alloy US 413, as sand cast is shown in
Fig. 20 at 50× magnification.
5.2. Shrinkage Porosity Calculations for the Validation Experiments
Shrinkage porosity calculations for the validation experiments were
done using Archimedes principle. The shrinkage porosity values for
the six validation experiments are given at Table 10.
5.3. Comparison of Simulation and Experimental Studies
To establish the strength of association between the casting process
simulation and experimental validation studies, correlation co-
efficient between the two results is calculated using the formula:
( ) ( )2 22 2
correlation( ) ,
N XY X Y
r
N X X N Y Y
−
=
− −
∑ ∑ ∑
∑ ∑ ∑ ∑
Fig. 19. Alloy US A356, as sand cast.
Fig. 20. Alloy US 413, as sand cast.
SHRINKAGE ESTIMATION OF CAST Al–Si ALLOYS THROUGH SIMULATION 979
where N is number of values (casting shape), X is shrinkage value of
casting process simulation, Y is shrinkage value of experimental vali-
dation study.
The correlation coefficient value obtained was 0.9389 indicating a
strong, positive relationship between casting process simulation and
validation experiments for US 413 alloy as shown in Fig. 21.
The value of correlation coefficient for US A356 alloy was calculated
similarly and is equal to 0.9353, indicating a strong association be-
tween the two studies.
The simulation results are in agreement with validation experi-
ments data.
The casting process simulation results are in agreement with valida-
tion experiments, however minor variation is observed. During solidi-
fication, the mould cavity continuously changes the properties of liq-
TABLE 10. Shrinkage porosity values for the six validation experiments.
Experiment
run order Alloy Chill
Pouring
temperature, °C
Mould
coat
Casting
mould
Shrinkage
porosity, %
1
2
3
4
5
6
US A356
US A356
US A356
US 413
US 413
US 413
MS
MS
MS
MS
No
MS
T + 50
T + 50
T
T
T + 50
T
NC
GC
NC
NC
GC
NC
Cylinder
Cube
Rectangle
Rectangle
Cube
Rectangle
2.84
2.65
2.63
2.11
2.07
1.90
Fig. 21. Shrinkage porosity: simulation and experimental studies.
980 Samavedam SANTHI and Srinivasan SUNDARRAJAN
uid and solid phases due to interactions between metal-mould, metal-
ambient and mould-ambient. Exactly envisaging the change in proper-
ties during solidification is very difficult in virtual environment (cast-
ing simulations). Interfacial heat transfer coefficient (h) is one of the
critical properties of casting process simulation. Although mould and
interface are considered as one and the same, certain mechanisms oc-
cur and change the h value during the casting process. It is necessary
to obtain precise experimental data for mould coat, to study the effect
of heat transfer coefficient accurately. Due to the above factors, there
could be minor variation between the study results of casting process
simulation and validation experiments.
6. CONCLUSION
For casting process simulation and experimental validation studies,
the correlation coefficient value obtained is observed to be close to +1
indicating a positive relationship between them. The thermal insula-
tion properties of the mould coating played a vital role in shrinkage of
the casting. The mould coating was designed to absorb the gaseous
products formed at the metal front thereby reducing the shrinkage.
Shrinkage decreased with changed casting shape, from cylinder to rec-
tangle castings. Higher pouring temperature resulted in lower rates of
heat extraction by the mould, thereby decreasing macro- and mi-
croshrinkage. Chill promoted faster temperature gradient in the solid-
ifying metal and increase its feeding capacity thereby reducing
shrinkage.
ACKNOWLEDGEMENTS
The authors thank the Directorate of Engineering and the Director,
DRDL for providing support and permission for carrying out this R&D
work.
REFERENCES
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19. J. Nukaga, S. Kitazawa, and H. Kamimura, NDT & E International, 41, Iss. 7:
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1951) (New York, USA: AIME: 1951), p. 24.
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(New York, USA: McGraw-Hill: 1967).
https://doi.org/10.1016/j.ndteint.2008.04.003
https://doi.org/10.1016/j.ndteint.2008.04.003
2. simulation procedure
2.1. Selection of Process Parameters
3. CASTING PROCESS SIMULATION
3.1. Solid Model
4.2. Influence of Process Parameters
4.2.1. Casting Mould
4.2.2. Chill
4.2.3. Pouring Temperature
4.2.4. Mould Coat
4.2.5. Interaction Plots
5. Experimental validation studies
5.1. Moulding, Melting and Pouring
5.3. Comparison of Simulation and Experimental Studies
AcknowledgementS
REFERENCES
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/HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. Stvoreni PDF dokumenti mogu se otvoriti Acrobat i Adobe Reader 5.0 i kasnijim verzijama.)
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/NLD (Gebruik deze instellingen om Adobe PDF-documenten te maken die zijn geoptimaliseerd voor prepress-afdrukken van hoge kwaliteit. De gemaakte PDF-documenten kunnen worden geopend met Acrobat en Adobe Reader 5.0 en hoger.)
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/ENU (Use these settings to create Adobe PDF documents best suited for high-quality prepress printing. Created PDF documents can be opened with Acrobat and Adobe Reader 5.0 and later.)
>>
/Namespace [
(Adobe)
(Common)
(1.0)
]
/OtherNamespaces [
<<
/AsReaderSpreads false
/CropImagesToFrames true
/ErrorControl /WarnAndContinue
/FlattenerIgnoreSpreadOverrides false
/IncludeGuidesGrids false
/IncludeNonPrinting false
/IncludeSlug false
/Namespace [
(Adobe)
(InDesign)
(4.0)
]
/OmitPlacedBitmaps false
/OmitPlacedEPS false
/OmitPlacedPDF false
/SimulateOverprint /Legacy
>>
<<
/AddBleedMarks false
/AddColorBars false
/AddCropMarks false
/AddPageInfo false
/AddRegMarks false
/ConvertColors /ConvertToCMYK
/DestinationProfileName ()
/DestinationProfileSelector /DocumentCMYK
/Downsample16BitImages true
/FlattenerPreset <<
/PresetSelector /MediumResolution
>>
/FormElements false
/GenerateStructure false
/IncludeBookmarks false
/IncludeHyperlinks false
/IncludeInteractive false
/IncludeLayers false
/IncludeProfiles false
/MultimediaHandling /UseObjectSettings
/Namespace [
(Adobe)
(CreativeSuite)
(2.0)
]
/PDFXOutputIntentProfileSelector /DocumentCMYK
/PreserveEditing true
/UntaggedCMYKHandling /LeaveUntagged
/UntaggedRGBHandling /UseDocumentProfile
/UseDocumentBleed false
>>
]
>> setdistillerparams
<<
/HWResolution [2400 2400]
/PageSize [612.000 792.000]
>> setpagedevice
|