|There are two basic types of die casting machines:
Hot chamber machines
are used primarily for zinc
and other low melting point alloys
that do not readily attack and erode metal pots, cylinders and plungers. The injection mechanism
of a hot chamber machine is immersed in the molten metal bath of a metal holding furnace. The furnace is attached to the machine by a metal feed system called a gooseneck. As the injection cylinder plunger rises, a port in the injection cylinder opens, allowing molten metal to fill the cylinder. As the plunger moves downward it seals the port and forces molten metal through the gooseneck and nozzle into the die cavity. After the metal has solidified in the die cavity, the plunger is withdrawn, the die opens and the casting is ejected.
These machines are then rated by how much clamping force they can apply. Typical sizes range from 400 to 4,000 short tons. Hot-chamber machines rely upon a pool of molten metal to feed the die. At the beginning of the cycle the piston of the machine is retracted, which allows the molten metal fill the "gooseneck". The gas or oil powered piston then forces this metal out of the gooseneck into the die. The advantages of this system include fast cycle times (approximately 15 cycles a minute) and the convenience of melting the metal in the casting machine. The disadvantages of this system are that high-melting point metals cannot be utilized and aluminum cannot be used because it picks up some of the iron while in the molten pool. Due to this hot-chamber machines are primarily used with zinc, tin, and lead based alloys.
Cold chamber machines
are used when the casting alloy cannot be used in hot-chamber machines; these alloys include aluminum, magnesium, copper, and zinc alloys with a large composition of aluminum. This machine works by melting the material, first, in a separate furnace. Then a precise amount of molten metal is transported to the cold-chamber machine where it is fed into an unheated shot chamber (or injection cylinder). This shot is then driven into the die by a hydraulic or mechanical piston. This biggest disadvantage of this system is the slower cycle time due to the need to transfer the molten metal from the furnace to the cold-chamber machine.
Cold chamber machines are used for alloys such as aluminum and other alloys with high melting points. The molten metal is poured into a "cold chamber," or cylindrical sleeve, manually by a hand ladle or by an automatic ladle. A hydraulically operated plunger seals the cold chamber port and forces metal into the locked die at high pressures.