presented by: chandra bhan prajapati 2008amd2934
TRANSCRIPT
Presented by:
Chandra bhan prajapati
2008AMD2934
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)
Attribute/process
sand investment Gravity die Pressure die
Max. size Several tons
Upto 20 kg Upto 50 kg Upto 8 kg
Dim. tolerance >0.6 mm >0.1 mm >0.4 mm >.05 mm
Surface finish >200 rms >60 rms >150 rms >30 rms
Min. thickness >6 mm >1.5 mm >4.5 mm >0.8 mm
Economic quantity
Any no. >100 >500 >2500
Table : Capabilities of major casting processes
( 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)
MaterialMin. Thickness
mm (in)Min. Draft Angle (º)
Aluminum alloys0.9 mm
0.5
Zinc alloys0.6 mm
0.25
Copper alloys (Brass)1.25 mm
0.7
Minimum wall thicknesses and minimum draft angles for die casting are :
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.
Material Silicon CopperTensile Strength
MPa (ksi)Properties
AA 380(UNS A03800)
8.5 % 3.5 %324(47)
Fair easy to fill
AA 384(UNS A03840)
11 % 4 %331(48)
Easy to fill
AA 386(UNS A03860)
9.5 % 0.6 %317(46)
Good corrosion resistance
AA 390(UNS A03900)
17 % 4.5 %283(41)
Good wear resistance
Common aluminum alloys for die casting are summarized as follows:
Advantages:•Excellent dimensional accuracy•Smooth cast surfaces (1—2.5 μm rms). •Thinner walls can be cast•Inserts 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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