icmf

7/27/2019 ICMF

1/9

INTERNATIONAL CONFERENCE ON MATERIALS FOR THE FUTURE

COMPUTER SIMULATION OF SQUEEZE CASTING PROCESS

USING FLOW 3DVinay V.N

M.Tech (IC engines and Turbomachinery)

GovernmentEngineeringCollegeThrissur,Kerala.India

vinayvn90@gmail

Keywords: Squeeze casting, heat transfercoefficient,wall to fluid heat flux,Magnessiumalloy AM60

Abstract

The aim of this thesis to investigate

solidification process during SqueezeCasting of Magnesium alloy AM60. In

Squeeze Casting applied pressure plays an

important role. The main advantage of the

deployment of high pressure is that it

increases the heat transfer coefficients

between liquid metal and mold surface by

several orders of magnitude which enhances

cooling rates and solidification and produce a

fine grain structured castings preventing the

appearance of gas porosity/shrinkage

porosity. In this work, solidification processduring squeeze casting process of different

wall-thickness 5-step casting under different

pressure conditions is simulated using the

commercial CFD software FLOW-3D .The

thesis work attempted to simulate in a

systematic manner the heat transfer process

during Squeeze Casting of a 5 step.Casting

model with dimensions of 100303 mm,

Smt.Bindu M.D

Asst.Professor

Government Engineering College

Thrissur,[email protected].

Dr.S.Savithri , Senior Principal Scientist

CMS-PEET Dept. NIIST CSIR,Trivandrum

100 x 30 x 5 mm, 100 x 30 x 8 mm, 100 x

30 x12 mm, 100 x 30 x 20 mm accordingly.

The molten metal was allowed to fill the

cavity from the bottom by a cylindrical

shape sleeve with diameter 100 mm. The cast

material chosen for this simulation is

magnesium alloy AM60 and mold material

chosen is Steel AISI P20 Squeeze casting of

magnesium alloy AM60 was performed

under an applied pressure 0,30, 60 and 90

Mpa. This work is directed towards using

heat transfer coefficients at the metal/die

interface for simulating the solidificationprocess of different wall-thickness 5-step

casting under different pressure conditions

and generating time-temperature profile at

different locations..Hence for the present

study, the experimentally applied pressure is

incorporated into the simulation by

specifying heat transfer coefficient at the

metal-dieinterface.

I.INTRODUCTION

Squeeze casting, also known as liquid-metal

forging, is a process by which molten metal

solidifies under pressure within closed dies

positioned between the plates of a hydraulic

press.The applied pressure and the instant

contact of the molten metal with the die

surface produce a rapid heat transfercondition that yields a pore-free fine-grain

casting with mechanical properties

approaching those of a wrought product.

This enhancement is realized due to the esta-blishment of direct contact between the

liquid metal and the die wall.Owing to the

high heat flux at the boundaries, the

solidification is quickly achieved.Due to

the elimination of air gap between the

metal and die interface, the heat transfer

coefficient is increased, which enhancescooling rates and solidification. Simulation

is a very important method for

optimizing squeeze casting process. Since

casting is a transient process, during the

process, not only the metal itself changes itsphase from liquid to solid, but also the

7/27/2019 ICMF

2/9


casting-die heat transfer condition. The

changes of these two factors affect each

other. Generally, in casting simulation

model, any minor change in the

boundary conditions can significantly

affect the numerical prediction results.Therefore, to obtain reliable and valid

prediction through simulation, precisely

casting-die heat transfer condition must be

imposed.The numerical simulation has

increasingly become an effective tool in the

casting manufacturing, by which some

primitive and time-consuming procedures

for finding the appropriate set of process

parameters are avoided. However, Little

attention has been paid to variation of

casting thicknesses and hydraulic pressures.Actually, in the die casting practice, the

different thicknesses at different locations of

castings results in significant variation of the

heat transfer coefficients. Therefore, it

would be important to investigate the

influence of casting thickness, applied

pressure value, and process parameters on

the heat transfer coefficients.

II. Strategy and Scope of Thesis

Recently Sun [3] has carried out extensive

experiments on squeeze casting process of a

different wall-thickness 5-step casting under

different pressure conditions. Squeeze

casting of magnesium alloy AM60 was

performed under an applied pressure 30, 60

and 90 MPa in a hydraulic press. With

measured temperatures, heat fluxes IHTCs

were evaluated using the polynomial curve

fitting method and numerical inversemethod. In this work, solidification process

during squeeze casting process is simulated

using the commercial CFD software FLOW-

3D for the same set of parameters for which

Sun [3] has carried out experiments. The

heat transfer coefficients needed for

metal/mold inteface is taken from the

polynomial fit developed by Sun [3]. The

scope of this thesis has been restricted to the

investigation of solidification process. In

squeeze casting applied pressure plays animportant role. The main advantage of the

deployment of high pressure is that it

enhances the heat transfer coefficients

between liquid metal and mold surface by

several orders of magnitude. This

enhancement is realized due to the

establishment of direct contact between theliquid metal and the die wall. This fact has

been proved experimentally by Sun [3]

where he has carried out extensive

experiments to record temperature profiles

during squeeze casting process of different

wall-thickness 5-step casting under different

pressure conditions. The alloy chosen for his

experiments was Magnesium alloy AM60

for the casting and steel die for the mold.

From the experimental data, he calculated

the heat transfer coefficients at the metal/dieinterface using inverse approach and by

polynomial fitting method. This work is

directed towards using these heat transfer

coefficients at the metal/die interface for

simulating the solidification process of

different wall-thickness 5-step casting under

different pressure conditions and to map the

temperature profiles at different locations

and try to compare the results between

simulation and experiments.

III.Flow 3D- An Overview

FLOW-3D is a powerful and highly accurate

commercial CFD software that gives

engineers valuable insight into many of the

physical processes. With special capabilities

for accurately predicting free-surface flows,

FLOW-3D is the ideal CFD software to use

in design phase as well as in improving

production processes [8].It employs

specially developed numerical techniques to

solve the equations of motion for fluids to

obtain transient, three-dimensional solutions

to multi-scale, multi-physics flow problems.

It is an easy-to-use simulation software

designed to accurately simulate filling and

solidification processes,pinpoint probable

defects and problems before casting,identify

viable designs more quickly,decrease the

number of design iterations,improve scraprates,reduce overall casting costs.

7/27/2019 ICMF

3/9


IV CASE STUDY

Experimental Results Reported By Sun Et

Al For Estimation Of Heat Transfer

Coefficient During Squeeze CastingProcess.

The experimental results of Sun et al [9] is

presented where they have done experiments

to record the thermal histories at certain

locations and how they calculated the heat

transfer coefficient between metal/die

interface by using polynomial extrapolation

method.Figure 1.1 shows the 3-D model of

5-step casting used for their experimental

study. It consists of 5 step casting, with

dimensions of 100 x 30 x3 mm, 100 x 30 x

5 mm, 100 x 30 x 8 mm, 100 x 30 x12 mm,100 x 30 x 20 mm accordingly

Figure 1.1 3-D model of 5-step casting with

round-shape gating system Sun et al.[ 9]

Configuration of die and installation of

measurement unit.

Figure 1.2 Configuration of the upper die

and the geometric installation of

Thermocouple and pressure transducers. Sun

et al. [ 9]

To measure the temperatures and

pressures at the casting-die interface

accurately and effectively, a special

thermocouple holder was developed. Ithosted 3 thermocouples simultaneously to

ensure accurate placement of thermocouples

in desired locations of each step. Figure 1.2

illustrates schematically the configuration of

the upper die (left and right parts) mounted

on the top ceiling of the press machine.

Pressures within the die cavity weremeasured using Kistler pressure transducers

6175A2 with operating temperature 850C

and pressures up to 200 MPa. As shown in

Figure 1.2, pressure transducers and

temperature thermocouples were located

opposite to each other so that measurements

from sensors could be directly correlated due

to the symmetry of the step casting. Five

pressure transducers and temperature

measuring unit were designated as PT1

through PT5, TS1 through TS5, respectively.

Determination Of IHTC by Polynomial

Curve Fitting Method.

To evaluate the IHTC effectively,the

finite difference method (FDM) was

employed as follows based on the heat

transfer equations. Since the thickness of

each step is much smaller than the width or

length of the step, it can be assumed that

the heat transfer at each step is one-dimensional. The heat transfer across the

nodal points of the step casting and die is

shown in Figure 1.3. The temperatures

were measured at 2, 4, 6, 8 mm beneath

die surface and the heat flux transferred

to the die mould can be evaluated by heat

transfer equations.

Figure 1.3 One-dimensional heat transfer at

the interface between the casting and die,

where temperature measurements were

performed (Sun et al. [ 9])

7/27/2019 ICMF

4/9


Figure 1.4 5-step castings solidifying under

applied pressure 30, 60, and 90MPa. (Sun et

al., [9]

From the temperature versus time curves

obtained at each position inside the die,the temperature at the die surface (X0 =

0mm) can be extrapolated by using

polynomial curve fitting method. After the

completion of filling, by selecting a

particular time of solidification process,

the values of temperatures were read from

the temperature-time data at position X1,

X2, X3, and X4 as shown in Figure 1.3. A

polynomial curve with various measured

temperatures against distance X were

plotted and extrapolated by a polynomialtrend line. The temperature at the die surface

was determined by substituting the value of

X=0 in the polynomial curve fitting. The

polynomial equation thus obtained is given

below which predicts the temperature

values at various distances inside the die at

a chosen time.

y = 0.0635x3 + 0.1759x2 - 16.495x + 308.43

This procedure is repeated for a number

of time increments to get series of such

temperatures with corresponding times at

metal - die interface, at metal surface, die

surface, and at various positions inside the

die.

V. RESULTS & DISCUSSION

The simulation results of casting simulation

of 5 step casting using FLOW-3D software

is presented. The casting material chosen for

the 5 step casting is Magnesium alloy AM60

and the mold material chosen for the die is

steel. In this study only the solidification

sequence is simulated using FLOW-3D.

Since solidification phenomena is governed

by the energy equation along with phase

change, the applied pressure during squeeze

casting process can't be given as a directinput for the simulation.Hence for the

present study, the experimentally applied

pressure is incorporated into the simulation

by specifying heat transfer coefficient at the

metal/die interface. The 5 step casting is

imported in FLOW-3D as an .STL file. The

mold box of required dimensions is created

in FLOW-3D.The 5 step casting is initially

assumed to be filled of the casting material

at the pouring temperature. Then the whole

geometry is discretized into rectangularblocks. The total number of cells is around

2,45,000. At the metal/mold interface a

value for heat transfer coefficient is

specified.The thermophysical properties

used for simulation are shown in Table

(a)Thermo physical properties of

magnesium alloy AM60.

(b) Material properties of Steel AISI P20

used for simulation.

7/27/2019 ICMF

5/9


The heat transfer coefficient (hc/d) is

calculated according to the polynomial

expression given by Zhizhong Sun [3].

hc/d = ( 1996.6 + 169.56 P - 0.78 P2

)

where, hc/d is the heat transfer coefficient

across the casting/die interface (W/m2K),

The heat transfer coefficient (hc/d) is an

important factor which controls heat transfer

phenomena at the metal/die interface during

solidification process in squeeze casting.P is

the applied pressure (Mpa)

Since the applied pressure also increases

liquidus temperature, a linear relation

between the liquidus temperatures and

applied pressures was employed byZhizhong Sun [3]as:

TL=0.092P+Tmwhere TL is the liquidus temperature of

magnesium alloy AM60 under applied

pressures, P is the applied pressure

(MPa), Tm is the non-equilibrium

solidification temperature (615C) at 0

MPa.

A similar linear relation between the

solidus temperatures and applied pressures

was proposed by Zhizhong Sun :

Ts = 0.072 P + Ts,mwhere Ts is the solidus temperature of

magnesium alloy AM60 under applied

pressures, P is the applied pressure, Ts,m is

the solidus temperature (540C) at 0 MPa.

Table 1.1 below shows the values used for

the present simulation based on these

polynomial expressions.

Four sets of solidification simulation was

first carried out which corresponds to four

different pressure values viz. 0 Mpa, 30Mpa, 60 MPa and 90 Mpa. Hence

accordingly different heat transfer

coefficients were used for the solidification

simulation. The values shown in above table

1.1 is used in FLOW-3D for specifying the

heat transfer coefficient value at the

metal/die interface. During solidification, thetemperature of the liquid metal in the casting

starts to reduce and once the temperature

reaches below the liquidus temperature

solidification starts and it continues till the

temperature of the cast metal reaches solidus

temperature. Below the solidus temperature

there is no phase change, but the temperature

decreases further. The heat dissipated by the

hot liquid metal is transferred to the mold

material at the metal/die interface and the

mold material gets heated up.Table 1.2 below shows the total

solidification time of the 5-step casting

obtained by the simulation for different

applied pressures. It can be seen from the

table that the total solidification time reduces

as pressure increases. This is because of the

higher heat transfer coefficient values for

higher pressures at the metal/die interface.

Temperature profiles at differentlocations of the casting

Figure. 1.5 shows a typical cooling curve at

five different locations of the 5-step casting

when the applied pressure is 0 MPa. That

means value of around 2000 W/m2K is

chosen for the heat transfer coefficient value

at the metal/die interface. The initial

temperature of the liquid metal is around

720C and that of mold materials is around

210C. It can be observed clearly, the slope

7/27/2019 ICMF

6/9


of the cooling curve corresponding to step 1

is much steeper than that of the cooling

curve corresponding to step 5. This is

because step 1 is the thinnest part of the 5

step casting and hence the heat is dissipated

fast, whereas step 5 corresponds to thethickest part of the 5-step casting and the

heat dissipation is slower. It can also be

observed that step1 has solidified

completely in 10 seconds whereas step 5 has

taken almost 35 seconds to solidify.

Figure 1.5 Cooling curves at different

locations of the 5 step casting (P 0 Mpa)

Figure 1.6 shows the temperature profile at

the mold locations corresponding to the

applied pressure of 0 Mpa. It can be

observed that the temperature at the moldlocations increases upto a certain time and

then starts cooling down. The temperatures

increases from 210C to approximately

380C near the thicker locations (step 5 of

the 5 step casting)

Figure 1.6 Temperature profile at

differentlocations of the 5 step casting (P 0

Mpa).

Figure 1.6 shows the cooling curve

corresponding to casting location step 5 fordifferent applied pressures. It can be

observed that there is not much of a

difference in the slope of the cooling curve

when the pressure changes from 30 MPa to

90 MPa eventhough the heat transfer

coefficient almost doubles up for these

pressures. The total solidification time alsohas reduced tremendously. The

solidification time has reduced from 35

seconds to almost 15 seconds.

Figure 1.6 Cooling curves at location step

5 for different applied pressures.

Figure 1.7 shows the Temperature profile

corresponding to casting location step 5 for

different applied pressures. It can be

observed that the temperatures increases

from 210C to approximately 420C inmold temperature curve when the pressure

changes from 30 MPa to 90 MPa.

Figure 1.7 Temperature profile at location

step 5 for different applied pressures

A typical solidification simulation sequence

is depicted in Figure 1.5 where the 2-D

contour plots of temperature profile and

0

100

200

300

400

500

600

700

800

0 20 40 60 80

Temperature(oC)

Time (s)

Step 5

Step 4

Step 3

Step 2

Step 1

0

50

100

150

200

250

300

350

400

0 20 40 60 80

Walltemperature(oC)

Time (s)

Step 5

Step 4

Step 3

Step 2

Step 1

0

200

400

600

800

0.00 50.00 100.00

Temperature(C)

time (s)

0 Mpa

30 Mpa

60 Mpa

90 Mpa

0

100

200

300

400

500

0.00 50.00 100.00W

alltemperature(C)

time (s)

0 Mpa

30 Mpa

60 Mpa

90 Mpa

7/27/2019 ICMF

7/9


solid fraction profile are shown for an

applied pressures. (0,30.60,90Mpa) at t=30s

A typical solidification simulation sequence

is depicted in Figure 1.6 where the 2-Dcontour plots Solid fraction plots for various

applied pressures 0 , 30 , 60 , 90 Mpa at t=

40 s

2-D contour plots of wall to fluid heat flux

profile are shown for an applied pressures.(0.30.60.90 mpa)

7/27/2019 ICMF

8/9


CONCLUSION

An investigation into the solidification

process during squeeze casting of

magnesium alloy AM60 in a different wall-

thickness 5-step was performed under an

applied pressure 0 ,30, 60 and 90 MPa.

The pressure applied during squeeze castingprocess affects the solidifications sequence

in three ways (a) it increases the heat

transfer rate (b) It increases the liquidus and

solidus temperature (c) It doesn't affect the

freezing range of the alloy that much. The

cooling rates increased with the increasing

heat transfer coefficients thereby reducing

the solidification time. Temperature profiles

at different locations of the casting versus

time graphs were obtained. It can be

observed clearly, the slope of the coolingcurve corresponding to step 1 is much

steeper than that of the cooling curve

corresponding to step 5 at five different

locations of the 5-step casting when different

pressure is applied, because step 1 is the

thinnest part of the 5 step casting and hence

the heat is dissipated fast, whereas step 5

corresponds to the thickest part of the 5-step

casting and the heat dissipation is slower. It

can be observed that the temperature at the

mold locations increases upto a certain time

and then starts cooling down. The cooling

curve corresponding to casting location at

each step for different applied pressures is

plotted. There is not much of a difference in

the slope of the cooling curve when the

pressure changes from 30 MPa to 90 MPa

eventhough the heat transfer coefficient

almost doubles up for these pressures.The

total solidification time also has reduced

tremendously. From steps 1, 2, 3, 4, to 5with applied pressure wall to fluid heat flux

increases as the step become thicker due to

the large difference in temperatures between

the melt and the die with thick cavity section

as well as relatively high localized pressure.

REFERENCES

7/27/2019 ICMF

9/9


[1] K.Sukumaran, K.K Ravikumar,

S.G.K.Pillai,T.P.D Rajan, M.Ravi, B.C Pai

(2008). Studies on Squeeze Casting Of Mg

Alloy And 2124 10 % Si-Cp Metal Matrix

Composite, Journal of Materials Science &

Engineering.[2] M.R. Ghomashchi, A. Vikhrov(2000)Squeeze casting: an overview, Journal of

Materials Processing Technology, Vol

101,1-9

[3] Zhizhong Sun (2012) Modeling AndExperimental Study On Heat Transfer In

Squeeze Casting Of Magnesium Alloy AM60

And Aluminum Alloy A443. Journal of

Materials Processing Technology CANMET

Materials, Natural Resources Canada.

[4] M.R.Barkhudarov (1995).EnhancementsTo Heat Transfer And Solidification

Shrinkage Models In Flow -3 D ,1-18.

[5] S.W Youn, C.G Kang, P.K Seo (2004).

Thermal Fluid/ Solidification Analysis Of

Automobile Part By Horizontal Squeeze

Casting Process And Experimental

Evaluation, Journal of Materials Processing

Technology , Vol 186, 174-178.

[6]L.J.Yang (2003) The Effect Of

Solidification Time In Squeeze Casting Of

Aluminium And Zinc Alloys. Journal of

Materials Processing Technology, Vol 192-193,114-120.

[7] C.A.Santos, J.M.V Quaresma, A.Garcia

(2001). Determination Of Transient

Interfacial Heat Transfer Coefficient In

Chill Mold Castings, Journal of alloys

compd .319,174-186

[8] Flow 3D Version 9.2 User Manual ,Flow

Science ,Inc.(2007)

[9]Zhizhong Sun, Henry Hu, Xiaoping Niu

Determination of heat transfer coefficients

by extrapolation and numerical inversemethods in squeezecasting of magnesium

alloy AM60 . Proceedings of the 7th

International Conference on Computational

Heat and Mass Transfer(ICCHMT-7),

Istanbul, Turkey, ( July 18-22,2011).

icmf

Documents