Casting is a 7,000 year old process in which a liquid material is poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. Some molds can be made in two halves and a core added if the cast needs to be hollow in a certain place.
The solidified part is then ejected or broken out of the mold to complete the process. Once cooled the cast part is then normally machined to remove excess material before it can be called a finished product.
Hot-chamber die casting 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 to fill the “gooseneck”. The pneumatic or hydraulic 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 it is limited to use with low melting point metals and that aluminium cannot be used because it picks up some of the iron while in the molten pool. Therefore, 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 include aluminium, zinc alloys with a large composition of aluminium, magnesium and copper.
The process for these machines start with melting the metal 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.
The 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.
