Pressure Die Casting is a metal vacuum casting process that is characterized by forcing molten metal under high pressure into a mould cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter and tin based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.
The die casting method is especially suited for applications where a large quantity of small to medium sized parts are needed with good detail, a fine surface quality and dimensional consistency. This level of versatility has placed die castings among the highest volume products made in the metalworking industry
There are four major steps in the die casting process.
First, the mold is sprayed with lubricant and closed. The lubricant both helps control the temperature of the die and it also assists in the removal of the casting.
Molten metal is then shot into the die under high pressure; between 10-175 MPa (1,500-25,000 psi).
Once the die is filled the pressure is maintained until the casting has solidified. The die is then opened and the shot (shots are different from castings because there can be multiple cavities in a die, yielding multiple castings per shot) is ejected by the ejector pins.
Finally, the scrap, which includes the gate, runners, sprues and flash, must be separated from the casting(s). This is often done using a special trim die in a power press or hydraulic press.
Pressure die casting is a process where metal is melted and forced into steel dies. The metal hardens into the desired shape. Molten metal is injected into a die cavity through a channel by movement of a plunger. After a preset solidification time, the plunger reverses direction, the part is ejected, and the machine is ready for the next cycle.
In hot chamber casting a plunger traps a certain volume of molten metal and forces it into the die cavity through a gooseneck and nozzle. Metals having low melting points such as zinc, copper, magnesium and lead are cast using hot chamber die casting.
In cold vacuum casting chamber, molten metal is poured into the injection cylinder. The metal is forced into the die cavity at high pressures. High melting point of aluminum machining alloys and copper are normally cast using cold chamber die casting.
Secondary operations to produce features not readily castable, such as CNC machining, drilling & tapping holes, polishing, plating, buffing, or painting are available.
Some examples of use of die casting include engine blocks, toy components, bushings, levers, gears, and assorted parts used in the automotive, aerospace and medical industries, etc.
Excellent dimensional accuracy (dependent on casting material, but typically 0.1 mm for the first 2.5 cm (0.005 in. for the first inch) and 0.02 mm for each additional centimeter (0.002 in. for each additional inch)
Smooth cast surfaces (1—2.5 μm (40—100 μin.) rms)
Thinner walls can be cast as compared to sand and permanent mold casting (approximately 0.75 mm (0.030 in.)
Rapid production rate