Vacuum die casting:
The major problem of die casting is that the air left in the cavity when the die is closed. Also back pressure exists on the molten metal in the die cavity. It can be overcome by evacuating the air from the die after the die is closed and metal is injected.
Adv:- Metal enters much faster – less filling time
No porosity
Parts exposed to air after solidification so no oxidation.
High tolerance
Fine microstructure
These are of two types:
(a) Hot chamber die casting
(b) Cold chamber die casting
(a) Hot chamber die casting:
A Gooseneck is used for pumping of the liquid metal in to the die cavity. It is made up of grey C.I., ductile iron, cast steel. A plunger made up of alloy C.I., hydraulic operated moves up in the gooseneck to uncover the entry port for the entry of liquid metal into the gooseneck.
(b) Cold chamber process:
- Used for zinc, lead and tin (low melting temp. alloys)
- Operation same as hot chamber
- Molten metal is poured in to shot chamber of m/c by either manually or by hand ladle / auto ladle.
Adv: complex casting
Small thickness
High production rate (200 pieces/hr)
Good surface finish (1 micron)
Closer dimension tolerance
Long life of die
Economic
Limitation: maximum size
Not all materials
Air trapped
Application: carburettors
Crank cases
Magnetos
Automobile parts
The major problem of die casting is that the air left in the cavity when the die is closed. Also back pressure exists on the molten metal in the die cavity. It can be overcome by evacuating the air from the die after the die is closed and metal is injected.
Adv:- Metal enters much faster – less filling time
No porosity
Parts exposed to air after solidification so no oxidation.
High tolerance
Fine microstructure
These are of two types:
(a) Hot chamber die casting
(b) Cold chamber die casting
(a) Hot chamber die casting:
A Gooseneck is used for pumping of the liquid metal in to the die cavity. It is made up of grey C.I., ductile iron, cast steel. A plunger made up of alloy C.I., hydraulic operated moves up in the gooseneck to uncover the entry port for the entry of liquid metal into the gooseneck.
(b) Cold chamber process:
- Used for zinc, lead and tin (low melting temp. alloys)
- Operation same as hot chamber
- Molten metal is poured in to shot chamber of m/c by either manually or by hand ladle / auto ladle.
Adv: complex casting
Small thickness
High production rate (200 pieces/hr)
Good surface finish (1 micron)
Closer dimension tolerance
Long life of die
Economic
Limitation: maximum size
Not all materials
Air trapped
Application: carburettors
Crank cases
Magnetos
Automobile parts
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