aldc-12 die casting mold design

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J. Mater. Sci. Technol., Vol.24 No.3, 2008 383 Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation Young-Chan Kim 1), Chang-Seog Kang 1) , Jae-Ik Cho 1) , Chang-Yeol Jeong 1) , Se-Weon Choi 1) and Sung-Kil Hong 2) 1) Korea Institute of Industrial Technology, Gwangju, Korea 2) Chonnam National University, Gwangju, Korea [Manuscript received September 22, 2007] Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1 mm. Therefore, in this study, thin-walled die casting of aluminum (Al-Si-Cu alloy: ALDC 12) in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation (MAGMA soft) and actual casting experiment (Buhler Evolution B 53D). Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion. KEY WORDS: Aluminum casting alloy; Thin-wall die casting; Solidification simulation 1. Introduction Even though silicon-containing aluminum alloys are known to be one of the most important cast- ing alloys due to their superior casting characteristics and unique combination of mechanical and physical properties such as low density and price, moderately high strength, good castability [1,2,3,4] , manufacturing of thin-wall aluminum die casting components, less than 1.0 mm in thickness, is generally known to be very difficult task to achieve sufficient fluidity and feedability. This leads to the limited application of the aluminum alloy in the fields of materials indus- try for the housing of notebook computer and cellular phone, etc. High pressure die casting (HPDC) is an impor- tant process in the manufacturing of high volume and low cost components, such as automatic transmission housing and electric/electronic housing, an econom- ical and efficient method for producing components requiring low surface roughness and high dimensional accuracy [5] . During die casting process the molten aluminum alloy is injected into the die cavity at high velocity (30-100 m/s) and under high pressure (50-80 MPa) through complex gate and runner systems [6] . The geometric complexity of the dies strongly leads to three dimensional fluid flow with significant free sur- face fragmentation and splashing. The ordering in which various parts of the die was filled and the posi- tioning of the air vents are crucial to forming homo- geneous casting components with minimal entrapped void. This is influenced by the design of the gating system and the geometry of the die [7] . Therefore, the gating system has to be optimized for soundness of surface and no defect. Ph.D., to whom correspondence should be addressed, E-mail: [email protected]. Therefore, in this work simulations of filling and solidification analyses by using the MAGMA- soft were presented in order to find the optimal die design necessary to prevent defects. Moreover the optimal die casting conditions for producing 297 mm×210 mm×0.8 mm thin-walled aluminum components (Al-Si-Cu alloy: ALDC 12) was investi- gated by actual casting experiment (Buhler evolution B 53D) for 2 different gating systems: tangential and split type. 2. Experimental Numerical simulation offers a powerful and cost effective way to study the effectiveness of different die designs and filling processes, ultimately leading to improvements of both product quality and pro- cess productivity, including more effective control of the die filling and die thermal performance. It is im- portant for the various defects and incomplete filling phenomenon to be prevented. Thus, the time loss and economic expenses must be minimized [7] . For ac- quiring optimal gating system, computational solidi- fication simulation by using MAGMA soft with finite volume method (FVM) [8] is conducted. The solidifi- cation simulation is able to calculate the mold filling, solidification and the development of residual stresses caused during the casting process for three gating de- signs. The initial conditions and process parameters and the chemical compositions of casting alloy for this study are described in Tables 1 and 2. As shown in Table 1, the melt ladled was about 250 cm 3 and shot sleeve filling was less than 27% for both gating de- signs. Also, the initial temperature of the melt was 670 C. Plunger diameter and active length were 70 and 250 mm, respectively. The optimum number of meshes used in simulation was about 36 and 30 mil- lion.

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Aldc-12 Die Casting Mold Design

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Page 1: Aldc-12 Die Casting Mold Design

J. Mater. Sci. Technol., Vol.24 No.3, 2008 383

Die Casting Mold Design of the Thin-walled Aluminum Case

by Computational Solidification Simulation

Young-Chan Kim1)†, Chang-Seog Kang1), Jae-Ik Cho1), Chang-Yeol Jeong1), Se-Weon Choi1)

and Sung-Kil Hong2)

1) Korea Institute of Industrial Technology, Gwangju, Korea

2) Chonnam National University, Gwangju, Korea

[Manuscript received September 22, 2007]

Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However,among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficultto achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1 mm.Therefore, in this study, thin-walled die casting of aluminum (Al-Si-Cu alloy: ALDC 12) in size of notebookcomputer housing and thickness of 0.8 mm was investigated by solidification simulation (MAGMA soft) andactual casting experiment (Buhler Evolution B 53D). Three different types of gating design, finger, tangentialand split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die castingwas possible with tangential and split type gating design because those gates allowed aluminum melt to flowinto the thin cavity uniformly and split type gating system was preferable gating design comparing to tangentialtype gating system at the point of view of soundness of casting and distortion generated after solidification.Also, the solidification simulation agreed well with the actual die-casting and the casting showed no castingdefects and distortion.

KEY WORDS: Aluminum casting alloy; Thin-wall die casting; Solidification simulation

1. Introduction

Even though silicon-containing aluminum alloysare known to be one of the most important cast-ing alloys due to their superior casting characteristicsand unique combination of mechanical and physicalproperties such as low density and price, moderatelyhigh strength, good castability[1,2,3,4], manufacturingof thin-wall aluminum die casting components, lessthan 1.0 mm in thickness, is generally known to bevery difficult task to achieve sufficient fluidity andfeedability. This leads to the limited application ofthe aluminum alloy in the fields of materials indus-try for the housing of notebook computer and cellularphone, etc.

High pressure die casting (HPDC) is an impor-tant process in the manufacturing of high volume andlow cost components, such as automatic transmissionhousing and electric/electronic housing, an econom-ical and efficient method for producing componentsrequiring low surface roughness and high dimensionalaccuracy[5].

During die casting process the molten aluminumalloy is injected into the die cavity at high velocity(30-100 m/s) and under high pressure (50-80 MPa)through complex gate and runner systems[6]. Thegeometric complexity of the dies strongly leads tothree dimensional fluid flow with significant free sur-face fragmentation and splashing. The ordering inwhich various parts of the die was filled and the posi-tioning of the air vents are crucial to forming homo-geneous casting components with minimal entrappedvoid. This is influenced by the design of the gatingsystem and the geometry of the die[7]. Therefore, thegating system has to be optimized for soundness ofsurface and no defect.

† Ph.D., to whom correspondence should be addressed,E-mail: [email protected].

Therefore, in this work simulations of fillingand solidification analyses by using the MAGMA-soft were presented in order to find the optimaldie design necessary to prevent defects. Moreoverthe optimal die casting conditions for producing297 mm×210 mm×0.8 mm thin-walled aluminumcomponents (Al-Si-Cu alloy: ALDC 12) was investi-gated by actual casting experiment (Buhler evolutionB 53D) for 2 different gating systems: tangential andsplit type.

2. Experimental

Numerical simulation offers a powerful and costeffective way to study the effectiveness of differentdie designs and filling processes, ultimately leadingto improvements of both product quality and pro-cess productivity, including more effective control ofthe die filling and die thermal performance. It is im-portant for the various defects and incomplete fillingphenomenon to be prevented. Thus, the time lossand economic expenses must be minimized[7]. For ac-quiring optimal gating system, computational solidi-fication simulation by using MAGMA soft with finitevolume method (FVM)[8] is conducted. The solidifi-cation simulation is able to calculate the mold filling,solidification and the development of residual stressescaused during the casting process for three gating de-signs. The initial conditions and process parametersand the chemical compositions of casting alloy for thisstudy are described in Tables 1 and 2. As shown inTable 1, the melt ladled was about 250 cm3 and shotsleeve filling was less than 27% for both gating de-signs. Also, the initial temperature of the melt was670◦C. Plunger diameter and active length were 70and 250 mm, respectively. The optimum number ofmeshes used in simulation was about 36 and 30 mil-lion.

Page 2: Aldc-12 Die Casting Mold Design

384 J. Mater. Sci. Technol., Vol.24 No.3, 2008

Table 1 Process parameters for computational solidification simulation

Tangential type Split type

Geometry data Molten metal ladled 242.957 cm3 258.084 cm3

In-gate area 1.496 cm2 2.253 cm2

Projected area 804.126 cm2 823.517 cm2

Characteristic wall thickness 0.8 mm 0.8 mm

Quality 60 MPa 60 MPa

Sleeve data Plunger diameter 70 mm 70 mm

Active length 250 mm 250 mm

Shot sleeve filling 25.252 % 26.825 %

Plunge area 4310.913 mm2 4310.913 mm2

shot sleeve volume 1077.728 cm3 1077.728 cm3

Process data Slow shot velocity 0.35 m/s 0.35 m/s

Theoretical filling time 8.830 ms 8.830 ms

Fast shot velocity 2.2 m/s 3.2 m/s

Cavity filling time 9.272 ms 6.354 ms

Velocity at in-gate 56.596 m/s 54.664 m/s

Table 2 The chemical compositions of ALDC12 alloy (in wt pct)

Alloy Cu Si Mg Zn Fe Mn Ni Sn Al

ALDC12 1.5–3.5 9.6–12.0 0.3 1.0 0.8 0.5 0.5 0.3 Bal.

Fig.1 Schematic illustration of finger type gating system: (a) case 1, (b) case 2

Fig.2 Temperature distribution of finger type gating system: (a) case 1, (b) case 2

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J. Mater. Sci. Technol., Vol.24 No.3, 2008 385

Fig.3 Schematic illustration of tangential type gating system: (a) case 3, (b) case 4

Fig.4 Temperature distribution of tangential type gating system: (a) case 3, (b) case 4

3. Results and Discussion

3.1 Results of temperature distribution

For the decision of optimal gating system, thefilling simulation was conducted for 3 different gat-ing designs: finger, tangential and split type. First,the finger type gating system has the merits that aremaintenance of the melt temperature and distribu-tion of the melt. As shown in Fig.1, two cases forshape and size of runner and gate were investigated.Figure 2 shows the temperature distribution and fill-ing patterns. Both case 1 and 2 had the melt withtemperature below liquidus after passing through theingate and at that point the melt wasn’t able to formthe uniform melt flow. And finger type gating systemwas very difficult to control approach time at ingatearea.

The tangential type gating system has no inter-ference during filling, continuous and directional meltflow. Figure 3 shows tangential type gating designs,with extended ingate and 85% length compared tothe end line of casting. The results of case 3 showedthat the melt injected dropped the temperature at thelast filling area but it didn’t separate with the mainstream. On the other hand, in the case 4 the cavitywas filled with melt above the liquidus temperature

but it occurred back flow near gate because metalpressure didn’t affect the casting by the short ingatelength as shown in Fig.4. The back flow might causesurface defects.

The split type gating system is easy to control theapproach time at ingate area and minimize the dis-tortion of casting after trimming. Two cases were in-vestigated for the size and shape of the ingate. Figure5 shows split type gating designs with 4 and 6 verti-cal runners. As shown in Fig.6, the case 5 shows themelt introduced separately in cavity with thin-wall iscooled strongly. It may cause the misrun and defectslike flow line and flow mark. The case 6 with 6 ver-tical runners minimizing the distance among ingateshad the effect of minimizing for drop temperature,maintained continuous flow during filling.

Three different types gating design were used andthe results showed that the sound thin-walled die cast-ing was possible with tangential and split type gatingdesign because those gates allowed aluminum meltflow to into the thin-wall cavity uniformly.

3.2 Results of air entrapment, residual stress, dis-placement and casting experiment

It was found that tangential type gating system

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386 J. Mater. Sci. Technol., Vol.24 No.3, 2008

with extended ingate and split type gating system ex-hibited quite uniform melt flow throughout the filling

Fig.5 Schematic illustration of split type gating system: (a) case 5, (b) case 6

Fig.6 Temperature distribution of split type gating system: (a) case 5, (b) case 6

Fig.7 Results of air entrapment; (a) tangential type gating system, (b) split type gating system

of the cavity. So these two gating designs were se-lected to study the solidification and stress simula-tion. The defects were predicted by air entrapment.As shown in Fig.7, the tangential type gating de-sign showed higher back pressure (about 1 MPa) andair volume than split type, which might result in airporosity. On the other hand, split type gating design

had little air pocket, so the location of overflow hasto be corrected.

Since thin-walled aluminum housing fabricated inthis work was only 0.8 mm in thickness, the residualstress and replacement after trimming are very impor-tant factors to its mass production. Figure 8 showsthe results of residual stress and replacement after

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J. Mater. Sci. Technol., Vol.24 No.3, 2008 387

trimming. Results of residual stress were both tan-gential and split type design, but the cold crack wasless possible to occur after solidification. Moreoverthe value after trimming was nearly zero. Results ofreplacement after trimming (Fig.9) showed tangential

type and split type had each displacement of 0.8 mmand 0.7 mm for x-direction after trimming. It waspredicted that this displacement was caused by ma-chining of the runner.

Fig.8 Results of residual stress: (a) tangential type gating system, (b) split type gating system

Fig.9 Results of replacement after trimming: (a) tangential type gating system, (b) split type gating system

Fig.10 Results of actual casting experiment: (a) tangential type gating system, (b) split type gating system

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388 J. Mater. Sci. Technol., Vol.24 No.3, 2008

For the comparison with results of computa-tional solidification simulation and actual casting, thesilicon-containing aluminum casting alloy, ALDC 12,was cast by using a high speed die casting machinewith both tangential and split type gating systems.As shown in Fig.10, defects including misrun andcracks were observed in the specimens in the tangen-tial type gating system while the split type resultedin sound casting with the highest injection speed of4.5 m/s.

4. Conclusions

(1) It was necessary for minimizing temperaturedrop, maintenance of continuous flow during filling tocontrol defects.

(2) The results of computational solidification sim-ulation showed that split type gating system waspreferable gating design to tangential type at thepoint of view of flow pattern and distortion generatedafter solidification.

(3) The results of solidification simulation agreedvery well with those of actual die casting.

AcknowledgementsThis work was supported by Korea Institute of Indus-

trial Technology and Gwangju Metropolitan City underThe Advanced Elements and Materials Industry Develop-ment Program.

REFERENCES

[1 ] The Japan Inst. of Light Metals, Microstructure andProperties of Aluminum Alloys, 1991, 233.

[2 ] G.K.Sigworth: AFS Trans., 1983, 91, 7.[3 ] O.Madelaine-Dupuich and J.Stolarz: Mater. Sci. Fo-

rum, 1996, 217-222, 1343.[4 ] John E. Gruzleski, Bernard M. Closset: The Treat-

ment of Liquid Aluminum-Silicon Alloys, AFS, 1990,13.

[5 ] Matthew S. Dargusch: J. Mater. Process. Technol.,2006, 180, 37.

[6 ] P.Hairy and M.Richard: in Proceedings of the 19thInternational Die-Casting Congress and Exposition,NADCA, 1997.

[7 ] P.W.Cleary et al.: Applied Mathematical Modeling,2006, 30, 1406.

[8 ] J.K.Lee, J.K.Choi and C.P.Hong: J. KFS, 1998, 18,555.

[9 ] S.Chellapillar: MS Thesis, the Ohio State University,Ohio, 1997.