Introduction of Die Casting Machines

22 Jan Introduction of Die Casting Machines

As you know, Die casting is a metal manufacturing process that molten metal was molded into a mould tooling cavity by die casting machine through high pressure. Die casting machines, large or small, vary fundamentally only in the method used to inject molten metal into the die.

Basically there are two types of die casting machines in the casting industry, they are hot-chamber machines and cold-chamber machines.These are rated by how much clamping force they can apply. Typical ratings are between 400 and 4,000 st. Most machines use toggle type mechanisms actuated by hydraulic cylinders or air pressure to achieve locking. Others use direct acting hydraulic pressure. Safety interlock systems are used to prevent the die from opening during the casting cycles.

HOT CHAMBER MACHINES

Hot-chamber die casting, also known as gooseneck machines, rely upon a pool of molten metal to feed the die. Hot chamber machines are used primarily for zinc, and low melting point alloys which do not readily attack and erode metal pots, cylinders and plungers.

In the hot chamber machine, the injection mechanism is immersed in molten metal in a furnace attached to the machine. As the plunger is raised, a port opens allowing molten metal to fill the cylinder. As the plunger moves downward sealing the port, it forces molten metal through the gooseneck and nozzle into the die. After the metal has solidified, the plunger is withdrawn, the die opens, and the resulting casting is ejected.

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

Hot chamber machines are rapid in operation. Cycle times vary from less than one second for small components weighing less than one ounce, to thirty seconds for a casting of several pounds. Dies are filled quickly (normally between five and forty milliseconds) and metal is injected at high pressures (1,500 to over 4,500 psi).

COLD CHAMBER MACHINES

Cold chamber die casting machine would be 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. 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.

Cold chamber machine is different from hot chamber machines primarily in one respect; the injection plunger and cylinder are not submerged in molten metal. The molten metal is poured into a “cold chamber” through a port or pouring slot by a hand or automatic ladle. A hydraulically operated plunger, advancing forward, seals the port forcing metal into the locked die at high pressures. Injection pressures range from 3,000 to over 10,000 psi for both aluminum and magnesium alloys, and from 6,000 to over 15,000 psi for copper-based alloys.

The operation of a “cold chamber” machine is a little slower than a “hot chamber” machine because of the ladling operation. A cold chamber machine is used for high melting point casting alloys because plunger and cylinder assemblies are less subject to attack since they are not submerged in molten metal.

In a cold chamber machine, more molten metal is poured into the chamber than is needed to fill the die cavity. This helps sustain sufficient pressure to pack the cavity solidly with casting alloy.

After reading the introduction of die casting machine above, I think you should have some basic knowledge about die casting manufacturing process and die casting machines. Once you have any die casting project to run, please don’t hesitate to contact us, and we will provide you most precision casting with low cost solution.