Workshop of Advances and Opportunities for International Collaborative Research and Development in Solidification Processing and in Metal Processing

ADJUSTED PRESSURE CASTING ADJUSTED PRESSURE CASTING TECHNIQUE AND ITS APPLICATIONS TECHNIQUE AND ITS APPLICATIONS

IN CHINAIN CHINA

Weidong HUANGState Key Laboratory of Solidification ProcessingNorthwestern Polytechnical UniversityXi’an, P.R. China

2004-12-13 Xi’an, China

SKLSPHistory

Founded in 1989 on the basis of the Casting Division of the Dept. Materials Sci. and Eng., NPU, financially supported by the Chinese Ministry of Science and Technology

1987, Ranked first of all the Casting Divisions in Chinese universities in a evaluation by the Chinese Ministry of Education

2003, Ranked seventh of the 19 State Key Lab. in materials field in a evaluation by the Chinese Ministry of Science and Technology

2004-12-13 Xi’an, China

RESEARCH FIELDS

Fundamentals of solidification processing

Advanced solidification technology

Advanced materials

2004-12-13 Xi’an, China

FUNDAMENTAL RESEARCH OF SOLIDIFICATIONInterface pattern formation during

solidificationRapid solidificationHeat, mass and momentum transfer

during solidificationSemi-solid processing microstructure

ADVANCED SOLIDIFICATION TECHNOLOGYCasting

Thin wall castings with complicated shape Al, Mg, Ni based alloys

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ADVANCED SOLIDIFICATION TECHNOLOGYDirectional Solidification

Super-high temperature gradient -1000 ℃/cmSuper-thin columnar crystals

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ADVANCED SOLIDIFICATION TECHNOLOGYContinuous casting of single crystal metals

High conductivity and good signal transmission performance High elongation and easy to be drawn into thin wire

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ADVANCED SOLIDIFICATION TECHNOLOGYLaser rapid forming

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ADVANCED MATERIALSMagnisium alloy processing

ADVANCED MATERIALSFunctional crystals

Benzophenone－organic crystal for nonlinear optics

Hg1-xMnxTe －Semiconductcrystal of II-VI compound

ADJUSTED PRESSURE CASTING —— APCA new counter pressure casting

technique

Pressure changes from vacuum to positive pressure under control

Mold filling is much more smooth and the casting is easier to solidify directionally

Suitable for lagre sized and very thin wall casting with high strength and plasticity

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

BackgroundBackgroundCharacteristics of aerospace components:Characteristics of aerospace components:– Thin wall– Large scale– Complicated form– very high requirement for mechanical performance

Two key points in casting:Two key points in casting:– Filling capacity– Solidification sequence

2004-12-13 Xi’an, China

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

Traditional techniqueTraditional techniqueCounter Pressure Casting——CPC

Sketch map of CPC system1.Pressure vessel,

2.Pressure controlling, 3.Upper chamber, 4.Mould,

5.Liquid metal, 6. attemperator,7.Lower chamber.

Pressure control for CPC process（Decrease pressure method）

P1: Pressure in the upper chamber,P2: Pressure in the lower chamber.

2004-12-13 Xi’an, China

High pressured gas hinders the filling process, thus it is High pressured gas hinders the filling process, thus it is difficult to fill the part with thin walls;difficult to fill the part with thin walls;

Gas in the mould needs to be evacuated, which demands Gas in the mould needs to be evacuated, which demands better permeability of the mould;better permeability of the mould;

More gases dissolves in the liquid metal under high pressure, More gases dissolves in the liquid metal under high pressure, which reduces the stability of the castings;which reduces the stability of the castings;

Drawbacks of CPC technique Drawbacks of CPC technique

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

2004-12-13 Xi’an, China

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

Adjusted Pressure Casting techniqueAdjusted Pressure Casting techniqueAPC – invented in 1987 at NPU

Sketch map of APC system1.Pressure vessel,

2.Positive pressure controller, 3.Upper chamber, 4.Mould,

5.Negaitive pressure controller, 6. Vacuumed vessel, 7.Liquid metal, 8. Attemperator, 9.Lower chamber.

Pressure control for APC processP1: Pressure in the upper chamber,P2: Pressure in the lower chamber.

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Advantages of APC techniqueAdvantages of APC technique11

11、、Vacuum processVacuum process：：The two chambers are evacuated and maintained before the filling process.

– Gases dissolved in the liquid metal can be separated out under vacuum environment, the gas content of the casting can be reduced remarkably;

– Reduce gases and moisture of the mold surface, avoid the formation of intrusive blowholes;

– Reduce oxidation of metals, ensures the cleanness of the metal.

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

2004-12-13 Xi’an, China

Advantages of APC techniqueAdvantages of APC technique22

22、、Filling processFilling process：：Pressure of lower chamber is increased and liquid metal is injected into the vacuum cavity.

– No hindrance from gases in the cavity to the mould filling, enhances the filling capacity;

– Easier to get smooth filling process and favorable temperature field;

– No need for gas evacuation in the cavity, reduces demands for the permeability of casting mold.

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

2004-12-13 Xi’an, China

Advantages of APC techniqueAdvantages of APC technique33

33、、Solidification processSolidification process：：

Pressures of both chambers are rapidly increased simultaneously at the end of filling process.– Gas separation from the melt is prohibited in the solidification process, prevent the formation of pinholes;

– Shrinkages formed earlier can be crashed, fused and refilled under high pressure during solidification.

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

2004-12-13 Xi’an, China

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

Improvement of APC technique on the Improvement of APC technique on the mechanical properties of specimensmechanical properties of specimens

(a) (b)Mechanical property achieved by different casting method for A356 alloy.

a. tensile strength of specimens by gravity casting and APC technique,b. elongation of specimens by gravity casting and APC technique.

2004-12-13 Xi’an, China

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

Fracture Microstructures of the specimensFracture Microstructures of the specimens

(a) (b)SEM photograph of the fractures by different casting methods

a. Gravity casting b. APC casting

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ADJUSTED PRESSURE CASTING TECHNIQUE——APC

Equipment for APC systemEquipment for APC system

2004-12-13 Xi’an, China

ADJUSTED PRESSURE CASTING TECHNIQUE——APC

Samples of APC CastingSamples of APC Casting

2004-12-13 Xi’an, China

CONCLUSIONS

APC technique is highly applicable to the APC technique is highly applicable to the manufacture of aerospace components.manufacture of aerospace components.

Successfully applications of APC technique in Successfully applications of APC technique in manufacture of aluminum components have been manufacture of aluminum components have been made in China.made in China.

2004-12-13 Xi’an, China

THANK YOU FOR YOUR ATTENTION

2004-12-13 Xi’an, China