- Die casting machine
- Gravity die casting
- Advantages compared to sand molding
- Die casting process
Main drawback of sand molding process:
Mold needs to prepare for each casting produced.
The specialty of die casting process:
A “metallic mold” is used to prepare sand mold with which larger number of casting is made. The metallic mold is known as “die”.
Die casting process:
- Mold material: metal or alloy.
- Types of die casting process:
- Gravity Die casting (permanent molding).
- Pressures die casting.
- Cold chamber pressure Die casting
- Hot chamber die casting
- Unlike gravity die casting in pressure die casting the molten metal is forced into a permanent mold cavity under pressure.
- The pressure varies from 20 to 2000 kg/sq.cm. And is maintained till the solidification stage is reached. The weight is for the most part acquired by compacted air or using pressurized water.
- Die casting machines
- Die casting machines perform the following functions.
- Holding the two die halves firmly together. Closing the die
- Injection molten metal into the die casting mold
- Opening the die
- Ejecting the die casting out of die
Gravity Die casting
- The casting is called gravity die casting because the molten metal is poured into the mold under gravity only, no external pressure is applied to force the liquid metal into the mold cavity (opposite to die casting).
- Permanent molds are made of grey cast iron in two halves (having high resistance to thermal shocks), alloy steels (for very high temp. and withstanding surface erosion) or non-ferrous alloys.
- The inner surface of the molds is coated first with refractory and with lamp black or core oil. This is done in order to reduce the chilling effect on cast prevents the adherence of molten metal to the mold.
- Pouring cups, risers, gates, sprues are present in the mold.
- Compared to sand casting following are merits
- Closer dimensional tolerances.
- Smoother surface and better appearances.
- Fine-grained metal structure. (Because of the chilling effect.)
- Mass production is more economical.
- Low shrinkage and gas porosity.
Think – “climate toys can be delivered with this procedure.”
- Lasting mold costs were substantially more than sand for
- Suited for small/ medium-sized non-ferrous casting only.
- Several defects like stress and surface hardening may be produced due to surface chilling effect.
- Since the gating system is cut in mold halves, once machined, it cannot be changed.
- The extremely high temp of molten metal makes this method unsuitable for steel casting.
- Carburetor bodies.
- Refrigeration casting.
- Oil pump bodies.
- Connecting rods and automotive pistons.
- Typewriter segments, etc.