Types of Castings
Variants of the die casting process include low-pressure die casting, vacuum die casting, squeeze die casting, and semi-solid die casting. Depending on the material employed and the shape and size of the intended part, one die casting method may provide superior results over another.
Low-Pressure Die Casting
In low-pressure die casting, a riser tube connects the die directly to the molten metal bath located below. Once the machine operator pressurizes the chamber (between 20–100kPA), the molten metal moves upwards through the tube and into the mold. By eliminating the need for feeders, this die casting process yields a more sizable output compared to some other casting methods.
Low-pressure die casting is suitable for fabricating aluminum components and parts that are symmetric around an axis of rotation.
Vacuum Die Casting
Vacuum pressure casting (also referred to as VPC) is a newer die casting method that is ideal for projects requiring minimal porosity and enhanced strength. The casting process is similar to that of low-pressure die casting. However, while in low-pressure casting the die is positioned above the molten metal bath, in vacuum die casting the locations of the components are switched. This process alteration allows the tube to act as a vacuum and forces molten metal into the die cavity.
Squeeze Die Casting
Squeeze die casting allows manufacturers to cast alloys and metals with low fluidity. The casting process enables the fabrication of denser parts and products and is highly suitable for secondary heat treating stages.
During a squeeze casting operation, molten metal fills an open die. Once filled, the die squeezes shut around the molten metal and forces the material into the recessed areas of the molding, ensuring that every portion is adequately filled.
Semi-Solid Die Casting
Semi-solid die casting—also known as thixoforming— is similar to vacuum die casting in that the process tends to produce parts with maximum density and minimal porosity.
Semi-solid die casting relies on a machine to cut the workpiece into smaller slugs for melting. When the metal reaches a phase transition and begins to change from solid to liquid, a shot sleeve forces the metal into a mold cavity to harden into the desired shape.