The casting process is subdivided into two distinct subgroups:1 - Expendable mold casting(sand, plastic, shell, and investment (lost-wax technique) mouldings.) 2 - Nonexpendable mold casting(permanent, die, centrifugal, and continuous casting).Classification of die casting:(a)Gravity Die Casting (also called permanent mould process)

(b)Pressure Die Casting

Die Casting Process Flow (Image courtesy: wiki)

[Pressure-die casting][ pressure die Casting Techniques][Die cast Part of automobile][Die casting Fence fittings](Image courtesy: wiki)

(Hot Die Casting machine)

(Image courtesy: wiki)There are two basic types of die casting machines: (1)hot-chamber machines (2) cold-chamber machines

cold-die-casting machine(Image courtesy: wiki)

Table : Capabilities of major casting processes

Attribute/processsandinvestmentGravity diePressure dieMax. sizeSeveral tonsUpto 20 kgUpto 50 kgUpto 8 kgDim. tolerance>0.6 mm>0.1 mm>0.4 mm>.05 mmSurface finish>200 rms>60 rms>150 rms>30 rmsMin. thickness>6 mm>1.5 mm>4.5 mm>0.8 mmEconomic quantityAny no.>100>500>2500

( Cooling Curve for casting)(Image courtesy: wiki)Chvorinov's rule:

The local solidification time can be calculated using Chvorinov's rule, which is:

Structure:(Intermediate cooling rates from melt result in a dendritic microstructure. (Image courtesy: wiki)

Minimum wall thicknesses and minimum draft angles for die casting are :

MaterialMin. Thickness mm (in)Min. Draft Angle ()Aluminum alloys0.9 mm 0.5Zinc alloys0.6 mm 0.25Copper alloys (Brass)1.25 mm 0.7

Die casting materials:

Zinc: the easiest alloy to cast; high ductility; high impact strength; easily plated; economical for small parts; promotes long die life.

Aluminum: lightweight; high dimensional stability for complex shapes and thin walls;.

Magnesium: the easiest alloy to machine; excellent strength-to-weight ratio; lightest alloy commonly die cast.

Copper: high hardness; high corrosion resistance; highest mechanical properties of alloys die cast; excellent wear resistance.

Common aluminum alloys for die casting are summarized as follows:

MaterialSiliconCopperTensile Strength MPa (ksi)PropertiesAA 380 (UNSA03800)8.5 %3.5 %324 (47)Fair easy to fillAA 384 (UNS A03840)11 %4 %331 (48)Easy to fillAA 386 (UNS A03860)9.5 %0.6 %317 (46)Good corrosion resistanceAA 390 (UNS A03900)17 %4.5 %283 (41)Good wear resistance

Advantages:Excellent dimensional accuracySmooth cast surfaces (12.5 m rms). Thinner walls can be castInserts can be cast-in (such as threaded inserts, heating elements )Reduces or eliminates secondary machining operations. Rapid production rates. tensile strength as high as 415 MPa .

Disadvantages:Casting weight must be between 30 grams and 10 kg Casting must be smaller than 600 mm High initial cost. Limited to high-fluidity metals. A certain amount of porosity is common. Thickest section should be less than 13 mm A large production volume is needed to make this an economical .

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