Effects of Reduced Pressure and Casting Design on Mold Filling in ExpendablePattern Casting Process of Thin Wall Aluminum Alloy Castings+1

Sadatoshi Koroyasu+2

Department of Mechanical and Precision Systems, School of Science and Engineering, Teikyo University, Utsunomiya 320-8551, Japan

The effects of reduced pressure and casting design on mold filling for thin wall aluminum alloy castings in the expendable pattern casting(EPC) process were investigated experimentally. Thin wall aluminum alloy plates were cast by the EPC process using several coats with differentpermeabilities. The fluidity length and melt velocity were measured. The application of the reduced pressure condition in the flask led to a largermelt velocity and longer melt fluidity length. There was no significant difference in the melt velocity depending on the casting design. Howeverin the high coat permeability region, the melt fluidity length in top pouring was longer than that in bottom pouring. The distances of melt flowstop were predicted based on the heat transfer from the molten metal to the mold through the coat using measured melt velocities. Except withtop pouring in the high coat permeability region, the predicted values more or less agreed with experimental fluidity length values.[doi:10.2320/matertrans.F-M2021843]

(Received April 1, 2021; Accepted July 2, 2021; Published August 20, 2021)

Keywords: expendable pattern casting, aluminum alloy, thin wall casting, fluidity length, coat permeability, reduced pressure, casting design

1. Introduction

The expendable pattern casting (EPC) process is veryattractive, particularly for the thin-wall castings with complexshapes such as automobile parts,1,2) because near net shapecastings are obtained. In the EPC process, the mold fillingtakes place along with the thermal decomposition of theexpendable polystyrene (EPS) pattern and discharge of thepyrolysate through the coat layer, which complicates themold filling mechanism, and the melt velocity is much lowerthan that for a cavity mold.3,4) In particular, in the EPCprocess of aluminum alloy castings, the melt temperature islower than that of cast iron, resulting in a lower thermaldecomposition rate of the EPS pattern and lower meltvelocity. Therefore, especially with thin wall castings, amisrun can easily occur due to temperature drop at themelt surface.5,6)

Recently, a relatively large number of investigations havebeen conducted on the mold filling for the EPC process, suchas the research by Maruyama et al.7,8) on molten cast iron.However, almost no studies have been reported on the meltfluidity in thin wall castings. Moreover, there are few moldfilling analysis systems that can exactly simulate the EPCprocess.9) Therefore, it is necessary to accumulate exper-imental data for a basis of accurate mold filling analysis.

In this study, the research on the mold filling in the EPCprocess has been conducted for aluminum alloy thin wallplate castings. Table 1 lists several previous major reportson this study. The effect of the coat permeability on the meltvelocity was examined by conducting casting experimentsusing several coats with different permeabilities (Ref. 10) inTable 1).10) Furthermore, the effects of the reduced pressureand casting design on the melt velocity were also considered(Ref. 11) in Table 1).11) However, in these reports, becausethe mold filling was completed in almost all conditions, noconsideration has been discussed on the melt fluidity length.

In previous studies,12,13) the effects of the coat perme-ability, pouring temperature, and expansion ratio of theEPS pattern on the melt fluidity length were examinedexperimentally. The relationship between the melt fluiditylength and melt velocity was discussed. Additionally,solidification analyses were carried out using the measuredmelt velocity values. During mold filling, the apparent meltviscosity increases with increasing the solid fraction owingto a temperature drop at the melt surface. As a result, themelt flow stops. The distance of melt flow stop was predictedby considering the above mentioned critical solid fractionfor melt fluidity. Furthermore, the calculated values werecompared with experimental values of the melt fluiditylength. When the coat permeability was larger thanapproximately 2, the melt velocity increased very little evenwith increasing the coat permeability. Therefore, the increasein the melt fluidity length was small.12) In addition, the effectof heat insulating coat on the melt fluidity length was notsignificant.13)

In this study, the effects of the reduced pressure in the flaskand casting design on the melt fluidity length in thin wallcastings, which have not been examined previously, werestudied experimentally. Furthermore, as in the previous study,the melt fluidity length values were predicted and comparedwith the experimental results. In the previous reports12,13)

and this report for the EPC process of aluminum alloy platecastings, the condition of the casting thickness of 5mm atwhich a misrun had occurred under many conditions, wasused to define thin wall castings.

2. Experimental Procedure

Figure 1 shows a schematic of the casting apparatus usedin this study, which is similar to that used in previousstudies.12,13) The steel molding flask was a cylindrical vesselwith an inside diameter of 200mm and depth of 300mm.The EPS pattern shown in Fig. 1 has a plate shape with awidth, height, and thickness of 70, 200, and 5mm,respectively, with a depth direction length of 70mm. Thecluster of the bottom pouring system was assembled with the

+1This Paper was Originally Published in Japanese in J. JFS 93 (2021) 121­127.

+2Corresponding author, E-mail: koroyasu@mps.teikyo-u.ac.jp

Materials Transactions, Vol. 62, No. 10 (2021) pp. 1569 to 1575©2021 Japan Foundry Engineering Society

EPS pattern, as shown in Fig. 1(a). The cluster of the toppouring system was also assembled using the EPS pattern ofthe same size, as shown in Fig. 1(b). The EPS pattern withexpansion ratio of 60 times (density = 18 kg·m¹3) wasmainly used. The EPS pattern with expansion ratio of 100times (density = 11 kg·m¹3) was also used for experimentson the effect of the casting design.

The runner is a plate EPS with a cross section of35 © 10mm and length of 135mm, which has an expansionratio of 60 times. The cross section of the ingate is 35 ©10mm. A ceramic tube (inside diameter and outside diameterof 25 and 35mm, respectively) was used as a sprue from thepouring basin to the runner. The length of the sprue was300mm for the bottom pouring (Fig. 1(a)) and 100mm forthe top pouring (Fig. 1(b)). The pouring basin is an insulatingsand mold with an inside diameter, depth, and thickness of80, 80, and 15mm, respectively. JIS No. 6 silica sand witha mode diameter of approximately 0.15mm (AFS grainfineness number 62) was poured into the flask.

As shown in Table 2, ten kinds of coats consisting of threemica base coats (A, B, and D) and seven kinds of silica basecoats (C, and E­J) were used. The values of coat permeabilityare in the range of 0.13­45, and are in accordance with JISmold permeability (JIS Z2603).14) These values weredetermined from the slopes of inter-coat differential pressuresplotted as a function of the air flow rate through the coatlayer.10) The coat layer of mica base coats (coats A, B, and D)generally has a high heat insulation characteristics not only alow permeability. After the EPS pattern was coated usinga dipping method, it was dried for 24 h in a drying furnace

at 323K. The coat thickness after drying was approximately1mm.

An aluminum alloy JIS AC2A (A319 equivalent) was usedas the casting material. It was melted in a high frequencyelectric induction furnace, after which it was cast directlyfrom the furnace. The pouring temperature was set atapproximately 973K. During the pouring process, the

Table 1 List of previous studies on mold filling in EPC process and this study.

Touch sensorExpendable pattern

Dry sand

Screen

to suctionpump

to recorder

Flask

Sprue

Pouring basin Plastic filmHgmanometer

φ200mm

200m

m

300m

m

(Ceramic tube)

5mm

Runner

10m

m Touch sensor

Expendable pattern

Dry sand

Screen

to suctionpump

to recorder

Flask

Sprue(Ceramic tube)

Pouring basin Plastic filmHgmanometer

φ200mm

200m

m

300m

m

5mm

10m

m

(a) Bottom pouring (b) Top pouring

Fig. 1 Schematic diagram of casting apparatus for measurement of mold filling.

Table 2 Test coats used in experiments.

S. Koroyasu1570

distance from the bottom of the pouring basin to the meltsurface was maintained at approximately 50mm. Thepouring operation was continued until the height of the meltsurface in the basin changed, either due to the complete moldfilling or melt flow stop. As a result, the melt head duringmold filling exhibits similar values under each experimentalcondition in both casting designs. During mold filling, themelt head at the melt surface decreases from approximately350 to 150mmAl with the bottom pouring, whereas itincreases from approximately 150 to 350mmAl with thetop pouring. An atmospheric pressure and reduced pressureof 13.3 kPa (differential pressure with respect to atmosphericpressure) were applied in the flask during the pouring processand mold filling. However, when the coat permeabilitywas 0.41 (coat C) and 1.7 (coat F), experiments were carriedout in detail under five different reduced pressure conditions(0, 3.3, 6.7, 10, and 13.3 kPa). The pressure in the flask wasreduced by aspiration using a suction port on the flask side.A plastic film was used to cover the top of the flask andmaintain the reduced pressure in the flask.

In this study, the melt fluidity was evaluated by measuringthe melt fluidity length. In order to measure the melt arrivaltime in the flow direction, five touch sensors7,8) for the moltenmetal were inserted into the EPS pattern at distances of 10,55, 100, 145, and 190mm from the ingate, as shown inFigs. 2(a) and 2(b) for both bottom and top pourings. Thetouch sensors are tungsten wires with diameters of 0.5mm,which passed through the center of the 70mm wide EPSpattern. The voltage across the resistance in Fig. 2 increasesin a stepwise fashion, every time the molten metal contacts atouch sensor. The melt arrival time was defined as the voltagerise time in this voltage-time chart. The average melt velocitywas defined with respect to the time when the molten metalreached the touch sensor finally.

3. Analytical Procedure12,13)

The case where the molten aluminum alloy replaces in theEPS pattern of a semi-infinite plate using the bottom pouringsystem as shown in Fig. 3, was considered. In this analysis,the melt velocity was assumed to be constant. Furthermore,the heat release from molten metal was assumed to be the

only heat transfer to the dry sand mold through the coat layer.In Fig. 3, x is the distance from the center of the molten metalin the thickness direction, and y is the distance from the inletof the molten metal. In this case, the conductive heat transferfrom the molten metal to the mold through the coat, can beformulated as:

Molten metal: μ1c1@T1@t

¼ ­ 1

@2T1@x2

þ @2T1@y2

� �ð1Þ

Coat: μ2c2@T2@t

¼ ­ 2

@2T2@x2

þ @2T2@y2

� �ð2Þ

Mold: μ3c3@T3@t

¼ ­ 3

@2T3@x2

þ @2T3@y2

� �ð3Þ

where t is the time, T is the temperature, ­, c, and μ are thethermal conductivity, specific heat, and density, respectively.For numerical calculations, the finite differential method wasused. The temperature recovery method15) was used to dealwith the latent heat of solidification. The linear approx-imation between the solid fraction fS and temperature of meltT, can be written as follows:15)

T ¼ TL � ðTL � TSÞfS ð4Þwhere TL and TS are the liquidus and solidus temperatures,respectively. The melt flow stop was determined from thetime when the solid fraction at the center of melt surfacewas 0.52.16) The flow length under this condition was definedas the distance of melt flow stop. Table 3 shows the mainphysical properties used for calculations. The JIS AC2Avalues17) were used for the physical properties of the moltenaluminum alloy. The values previously measured by authors

EPSpattern

Tungstenwire

V

Drybattery

Diode

190mm

145mm

100mm

55mm

10mm

1kΩRunner

10mm

55mm

100mm

145mm

190mm

Tungstenwire

EPSpattern

Drybattery

Diode

VRunner

1kΩ

(a) Bottom pouring (b) Top pouring

Fig. 2 Schematic diagram of melt touch sensor.

x

Coat

Ti=const. d/2

Mold

0

y

T1,λ1,ρ1,c1 T3,λ3,ρ3,c3

δ

Molten metal

∂T /∂y = 0

∂T /∂y = 0

∂T /∂

x = 0

∂T /∂

x = 0

T2λ2ρ2c2

Ld/2u

Fig. 3 Heat conduction model and coordinate system.

Table 3 Physical properties used in calculations.

Effects of Reduced Pressure and Casting Design on Mold Filling in Expendable Pattern Casting Process of Thin Wall Aluminum Alloy Castings 1571

were used for the thermal conductivity and bulk density ofthe dry sand packed bed.18) The literature data18) was used forthe specific heat of the sand mold. The values measured byauthors12,13) were used for thermal conductivities of the coatlayer.19) The heat transfer coefficient at the molten metal-coatinterface was assumed h = 350W·m¹2·K¹1.5,6) The correla-tion line of the measured melt velocity in this work wasused for the melt velocity at the ingate. During mold fillinguntil melt flow stop, a constant value of the melt velocity wasused.

4. Experimental Results and Discussion

Figure 4 shows the experimental values of the melt fluiditylength for a bottom pouring. These values are shown as afunction of the coat permeability, with the degree of reducedpressure as a parameter. As shown in Table 2, heat insulatingcoats are included in the low coat permeability region.However, a previous report13) showed that the effect of heatinsulating coat on the melt fluidity length was not significant.Therefore, these experimental values were shown withoutdistinction from normal coats. A fluidity length of 200mm,shown as the dotted line in Fig. 3, indicates completed moldfilling. The use of a high permeability coat or reducedpressure condition led to a higher melt fluidity length. Ata reduced pressure condition of 13.3 kPa, when the coatpermeability is larger than approximately 2 (K > 2), themold filling is completed. Therefore, the effect of the coatpermeability on the fluidity length cannot be examined. Withthe non-reduced pressure condition, even when the coatpermeability is larger than approximately 2 (K > 2), the meltfluidity length does not increase significantly with increasingcoat permeability. The rate of increase in the melt fluiditylength decreases compared to the low coat permeabilityregion (K < 2). It is considered that the melt flow stopdepends on the increase in the solid fraction due to thetemperature drop at the melt surface. Furthermore, thetemperature drop at the melt surface is dependent on themelt velocity, which in turn is related to the heat releasetime during mold filling. The relationship between the meltfluidity length and melt velocity was examined in thefollowing.

Figure 5 shows the experimental values of the meltvelocity u obtained when measuring the melt fluidity lengthas shown in Fig. 4. These values are shown as a function ofthe coat permeability K, with the degree of reduced pressureas a parameter. The melt velocity increases with increasingcoat permeability. The use of a reduced pressure conditionled to higher melt velocities. As the melt velocity increases,the heat release time of the melt becomes shorter, resultingin a lower temperature drop at the melt surface. This resultqualitatively agrees with the result of the melt fluidity lengthshown in Fig. 4. Under the non-reduced and reducedconditions, respectively, when the coat permeability is lessthan approximately 2 (K < 2), the melt velocity increasesrelatively monotonously with increasing coat permeability.However, when the coat permeability is larger thanapproximately 2 (K > 2), the rate of increase in the meltvelocity is reduced. This result also qualitatively agrees withthe consideration that the melt fluidity length depends onmelt velocity, as described above.

The solid and dashed lines in Fig. 4 represent thecalculated distances of melt flow stop. For this calculation,the value of the melt velocity u is required. Therefore, theexperimental values of the melt velocity u shown in Fig. 5,were divided into two regions, namely, the region for whichthe coat permeability is less than 2 (K < 2) and that with(K > 2). The linear approximations in each region were usedfor the melt velocity u. The solid and dashed lines in Fig. 5represent the correlation lines of the melt velocity for thenon-reduced and reduced pressure conditions, respectively.As described above, since the effect of the heat insulatingcoat on the melt fluidity length was not significant,13) thecalculated values of melt flow stop distance were not distinctfrom those for normal coats. Except under the reducedpressure condition and region where the coat permeability islarger than approximately 2 (K > 2), the experimental valuesof melt fluidity length more or less agree with the calculatedvalues. As a result, when the melt velocity is known, the meltfluidity length can be estimated. The effect of the reducedpressure on the melt fluidity length seems to be examinedalmost quantitatively using the change in the melt velocity.

Figure 6 shows the experimental values of the melt fluiditylength for a bottom pouring, as a function of the degree ofreduced pressure, with the coat permeability of K = 0.41 and

10-1 100 101 1020

50

100

150

200

Coat permeability K

Flui

dity

leng

th L

F/m

mCasting thickness = 5mm

Key Line Reduced(calcd.) pressure

0 kPa13.3 kPa

Pouring temp.= 973K

0kPa

Reduced pressure:13.3kPa

(K < 2)

Max.length

Fig. 4 Effects of coat permeability and reduced pressure on melt fluiditylength.

10-1 100 101 1020

20

40

60

80

Coat permeability K

Mel

t vel

ocity

u/m

m·s

-1

Casting thickness = 5mm

Reduced

13.3kPa

Pouring temp.=973K

0kPa

pressure=Correlation line

(K < 2)

Fig. 5 Effects of coat permeability and reduced pressure on melt velocity.

S. Koroyasu1572

1.7. The use of a high permeability coat or reduced pressurecondition increases the melt fluidity length, similar to theresults in Fig. 4. The melt fluidity length increases almostlinearly with increasing the degree of reduced pressure.

Figure 7 shows the experimental values of the meltvelocity u obtained when measuring the melt fluidity lengthas shown in Fig. 6, as a function of the degree of reducedpressure, with the coat permeability of K = 0.41 and 1.7. Themelt velocity u increases almost linearly with increasing thedegree of reduced pressure. As a result, it may be consideredthat the melt fluidity length shown in Fig. 6 also increasedalmost linearly with respect to the degree of reduced pressure.The solid lines in Fig. 6 represent the calculated values ofthe melt flow stop distance. As values of the melt velocity uwere required for this calculation, the values derived fromthe linear approximations of the measured melt velocities inFig. 7, were used. The calculated values of the melt flow stopdistance are more or less in agreement with the experimentalvalues of the melt fluidity length. The dashed lines in Fig. 7represent the calculated values of melt velocity based onthe mold filling model4) in a previous study, which are largerthan the experimental values. Therefore, the values of themelt fluidity length calculated using the mold filling modelshown by the dashed lines in Fig. 6, are larger than theexperimental values.

Figure 8 shows the experimental values of the melt fluiditylength for a non-reduced pressure condition. These values areshown as a function of the coat permeability, with the castingdesign as a parameter. When the coat permeability is less thanapproximately 2 (K < 2), the melt fluidity length increaseswith increasing the coat permeability. However, the effectof the casting design on the melt fluidity length is notsignificant. On the other hand, when the coat permeability islarger than approximately 2 (K > 2), the melt fluidity lengthfor a top pouring is larger than that for a bottom pouring.Furthermore, the mold filling for a top pouring is completedunder the conditions in this work.

Figure 9 shows the experimental values of the meltvelocity u obtained when measuring the melt fluidity lengthas shown in Fig. 8. These values are shown as a functionof the coat permeability K, with the casting design as aparameter. In the range of coat permeability in thisexperiment, the effect of the casting design on the meltvelocity is not significant. In contrast to this result, whenthe coat permeability is larger than approximately 2 (K > 2),the melt fluidity length for the top pouring is larger than thatfor the bottom pouring, as shown in Fig. 8. The discussionfor this phenomenon may be as follows.

0 5 10 150

50

100

150

200

Reduced pressure /kPa

Flui

dity

leng

th L

F/m

m·s

-1Casting thickness = 5mm

Coat permeability =

Pouring temp.= 973K

Calculated

0.41

1.7

Calculated(by mold filling model)

Fig. 6 Effect of reduced pressure degree on melt fluidity length.

0 5 10 150

50

100

Reduced pressure /kPa

Mel

t vel

ocity

u/m

m·s

-1 Casting thickness = 5mm

Coat permeability =

Pouring temp.= 973K

0.41

1.7

Calculated(by mold filling model)

Fig. 7 Effect of reduced pressure degree on melt velocity.

10-1 100 101 1020

50

100

150

200

Coat permeability K

Flui

dity

leng

th L

F/m

m

Casting thickness = 5mm

Key CastingdesignBottomTop

Calculated

Pouring temp.=973K Max.length

(K < 2)

Fig. 8 Effects of coat permeability and casting design on melt fluiditylength for EPS expansion ratio of 60 times.

10-1 100 101 1020

20

40

60

80

Coat permeability K

Mel

t vel

ocity

u/m

m·s

-1

Casting thickness = 5mm

Key CastingdesignBottomTop

Correlation line

Pouring temp.=973K

(K < 2)

Fig. 9 Effects of coat permeability and casting design on melt velocity forEPS expansion ratio of 60 times.

Effects of Reduced Pressure and Casting Design on Mold Filling in Expendable Pattern Casting Process of Thin Wall Aluminum Alloy Castings 1573

Figure 10 shows examples of the castings appearance withthe bottom pouring and top pouring. This figure shows thedifference in the melt surface shape at the melt flow stop withrespect to the casting design. The casting with the bottompouring has a flat melt surface as shown in Fig. 10(a).However, with the top pouring, a local melt preceding flowwas observed in many castings, as shown in Fig. 10(b).

Figure 11 shows a schematic diagram of the mold fillingwith the top pouring, which shows a local melt precedingflow as shown in Fig. 10(b). In this case, the heat transferoccurs perpendicular to the melt flow as shown in Fig. 11,which results in an increase in the melt surface temperaturein a different position from where the melt flow preceded. Asa result, it seems that the melt fluidity length increases. Withincreasing the coat permeability, since the melt velocityincreases, the turbulence of the melt flow also increases.Thus, the heat transfer perpendicular to the melt flow seemsto be more remarkable.

The line in Fig. 8 represents the calculated melt flow stopdistances. In this calculation, the melt velocity used wasderived from the linear approximation of measured meltvelocities in Fig. 9. With the bottom pouring, the calculatedvalues of the melt flow stop distance more or less agreewith the experimental values of the melt fluidity length.When the coat permeability is larger than approximately 2(K > 2), the measured values of the melt fluidity length withthe top pouring were larger than those with the bottompouring. Therefore, these measured values are also largerthan the calculated values of the melt flow stop distance.

Figure 12 shows the experimental values of the meltfluidity length for a non-reduced pressure condition and EPSexpansion ratio of 100 times. These values are shown as afunction of the coat permeability, with the casting design as

a parameter. When the coat permeability is larger thanapproximately 2 (K > 2), with both the bottom and toppouring, the mold filling is completed under the conditions inthis experiment. Therefore, the effect of the casting design onthe melt fluidity length cannot be examined in this region.When the coat permeability is less than approximately 2(K < 2) and larger than approximately 0.4 (K > 0.4), themelt fluidity length for the top pouring is larger than that forthe bottom pouring, and the mold filling is completed. This issimilar to the result with an EPS expansion ratio of 60 timesand coat permeability of above approximately 2 (K > 2),as shown in Fig. 8. It seems that the melt fluidity lengthincreased due to the local melt preceding flow, as shown inFig. 10(b). Because the melt velocity with an EPS expansionratio of 100 times is higher than that with an expansion ratioof 60 times, the melt fluidity length seems to have increasedin the lower coat permeability region.

Figure 13 shows the experimental values of the meltvelocity u obtained when measuring the melt fluidity lengthas shown in Fig. 12. These values are shown as a functionof the coat permeability K, with the casting design as aparameter. The effect of the casting design on the meltvelocity is not so significant. In Fig. 13, the correlation lineof the melt velocity for an EPS expansion ratio of 60 times

(a) Bottom pouring (b) Top pouring

Fig. 10 Examples of casting appearance with bottom pouring and toppouring.

HeatHeat

Molten metal

CoatCoat

Drysand

Drysand

EPSpattern

Fig. 11 Schematic diagram of melt flow with local melt preceding for toppouring.

10-1 100 101 1020

50

100

150

200

Coat permeability K

Flui

dity

leng

th L

F/m

m

Casting thickness = 5mm

Key CastingdesignBottomTop

Calculated

Expansion ratio = 100 Max.length

(K < 2)

(0.4 < K < 2)(ratio:100)

Calculated(ratio:60)

Fig. 12 Effects of coat permeability and casting design on melt fluiditylength for EPS expansion ratio of 100 times.

10-1 100 101 1020

50

100

150

Coat permeability K

Mel

t vel

ocity

u/m

m·s

-1

Casting thickness = 5mm

Key CastingdesignBottomTop

Correlation lineExpansion ratio = 100

(K < 2)

(ratio:100)

Correlation line(ratio:60)

Fig. 13 Effects of coat permeability and casting design on melt velocity forEPS expansion ratio of 100 times.

S. Koroyasu1574

shown in Fig. 9, is included for comparison. The meltvelocity for an EPS expansion ratio of 100 times isconsiderably higher than that for expansion ratio of 60 times.

The line shown in Fig. 12 represents the calculated valuesof the melt flow stop distance. The melt velocity used in thiscalculation was derived from the linear approximation ofmeasured melt velocities in Fig. 13. When the coatpermeability is larger than approximately 2 (K > 2), thecalculated values of the melt flow stop distance are also largerthan 200mm. Therefore, the calculated and measured valuesof the melt fluidity length were compared in the region wherethe coat permeability is less than approximately 2 (K < 2).With the bottom pouring, the calculated values of the meltflow stop distance more or less agree with the experimentalvalues of the melt fluidity length. However, with the toppouring, the measured values of the melt fluidity length werelonger than that with the bottom pouring. Therefore, themeasured values of the melt fluidity length also longer thanthe calculated values of the melt flow stop distance. InFig. 12, the calculated values of the melt flow stop distancefor an EPS expansion ratio of 60 times shown in Fig. 8, arealso included for comparison. When the coat permeabilityis limited to less than approximately 2 (K < 2), the meltfluidity length for an EPS expansion ratio of 100 times isconsiderably larger than that for a ratio of 60 times. Thisresult seems to be because the melt velocity shown in Fig. 13is considerably higher than that for an EPS expansion ratioof 60 times.

5. Conclusion

The effects of the reduced pressure and casting design onthe mold filling for thin wall aluminum alloy castings in theEPC process were investigated. Aluminum alloy plates werecast using several kinds of coats with different permeabilities.The melt fluidity lengths and melt velocities were measured.

The following conclusions were obtained under theconditions in this work.(1) The use of a reduced pressure condition led to a higher

melt velocity and melt fluidity length.(2) There was no significant difference in the melt velocity

with respect to the casting design. However in the highcoat permeability region, the melt fluidity length in toppouring was longer than that in bottom pouring.

(3) Except with the top pouring in the high coatpermeability region, the predicted values of the meltflow stop distance more or less agreed withexperimental values of the melt fluidity length.

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Effects of Reduced Pressure and Casting Design on Mold Filling in Expendable Pattern Casting Process of Thin Wall Aluminum Alloy Castings 1575