To begin, a steel mold capable of rapidly manufacturing tens of thousands of castings must be constructed in at least two pieces to allow for casting removal. These portions are firmly installed in a machine and are configured in such a way that one is fixed (fixed die half) and the other is movable (injector die half). To begin the casting cycle, the die casting machine clamps the two die halves securely together. Molten metal is pumped into the cavity of the die, where it immediately hardens. After drawing apart the die halves, the casting is expelled. Die casting dies can be simple or complicated, including moving slides, cores, or other components depending on the casting's complexity.
Die casting's whole cycle is by far the quickest method known for creating precision non-ferrous metal pieces. This is in stark contrast to sand casting, where each casting requires a fresh sand mold. While the permanent mold technique does not use sand and instead employs iron or steel molds, it is significantly slower and less accurate than die casting.
TYPES OF DIE CASTING MACHINES
Regardless of the equipment utilized, it is critical to secure die halves, cores, and/or other moving elements during the casting cycle. The clamping force of the machine is generally determined by (a) the projected surface area of the casting (as measured at the die parting line) and (b) the pressure utilized to feed metal into the die. To lock the majority of machines, toggle type mechanisms are used, which are activated by hydraulic cylinders (or occasionally by air pressure). Others make use of hydraulic pressure that acts directly on the piston. To prevent the die from opening during the casting cycle, safety interlock mechanisms are utilized.
Die casting machines, whether big or tiny, are basically identical save for the technique by which molten metal is injected into the die. These machines are categorised and categorized as either hot chamber die casting machines or cold chamber die casting machines.
MACHINES FOR HEATING CHAMBERS
Hot chamber machines are typically used for zinc and low melting point alloys that are resistant to attack and eroding metal pots, cylinders, and plungers. The advancement of technology and the introduction of new, higher-temperature materials have increased the equipment's application to magnesium alloys.
The injection mechanism of the hot chamber machine is immersed in molten metal in a furnace attached to the machine. When the plunger is lifted, a port in the cylinder opens, enabling molten metal to fill it. As the plunger descends, it seals the port and drives molten metal into the die via the gooseneck and nozzle. The plunger is removed once the metal has solidified, the die is opened, and the resultant casting is expelled.
Hot chamber machines operate at a high rate of speed. Cycle durations range from under a second for tiny components weighing less than an ounce to thirty seconds for large castings weighing several pounds. Die filling occurs rapidly (often between five to forty milliseconds) and metal is introduced at high pressures (1,500 to over 4,500 psi). Modern technology, on the other hand, allows for precise control of these variables, resulting in castings with fine detail, tight tolerances, and great strength.
MACHINES FOR COLD CHAMBERS
Cold chamber machines are distinguished from hot chamber machines principally by the absence of molten metal around the injection plunger and cylinder. A manual or motorized ladle pours the molten metal into a "cold chamber" via a port or pouring slot. A forward-moving hydraulic plunger closes the port, driving metal into the locked die at high pressures. Aluminum and magnesium alloys are injected at pressures ranging from 3,000 to over 10,000 psi, while copper-based alloys are injected at pressures ranging from 6,000 to over 15,000 psi.
A cold chamber machine pours more molten metal into the chamber than is required to completely fill the die cavity. This assists in maintaining adequate pressure to completely fill the cavity with casting alloy. Excess metal is evacuated with the casting and is considered part of the shot.
Due to the ladling action, a "cold chamber" machine operates slightly slower than a "hot chamber" machine. A cold chamber machine is used to cast alloys with a high melting point since the plunger and cylinder assemblies are not immersed in molten metal.