Low pressure die casting is the die casting method by filling cavities with liquid metal under low pressure. It has been a common process used in our aluminum foundry to produce various cast aluminum parts in good quality.
Low Pressure Die Casting Process
In low pressure die casting, low pressure, other than gravity, is used to to fill molds with light metal especially aluminum alloys. In this process, a tool or die is designed and manufactured to the required shape of the component to be made. It is then mounted on a holding furnace and is connected to the molten metal by a feed tube or stalk. The furnace is pressurised by the introduction of air above the surface of the molten metal causing it to rise steadily in the stalk and quietly fill the mould. The air in the mould cavity is expelled through suitably positioned vents in the die and when the cavity is filled, solidification commences.
Molten metal is pushed into the die under low pressure. Once solidified, the pressure is released and any residual liquid in the tube or cavity flows back into the holding furnace for recycling. After cooling, the cast part is removed from the die, this process can be repeated many time to obtain the quantity ordered by customers.
Common Low Pressure Die Casting Alloys
Advantages of Low-Pressure Die Casting
Low pressure casting can use sand mold, metal mold, graphite mold, etc. The filling process is not only different from gravity die casting, sand casting, but also different from high pressure die casting. It has the following advantages:
- The pure metal liquid filling in the mold improves the purity of the casting. Because the slag generally floats on the surface of the liquid metal, and the low pressure die casting is filled by the liquid metal at the bottom of the crucible through the riser pipe, the possibility of the slag entering the mold cavity is completely avoided.
- The liquid metal filling is stable, which reduces or avoids the churning, impact and splashing phenomenon when filling liquid meta, thus reducing the formation of oxidizing slag.
- The filling of liquid metal under pressure can improve the fluidity of the liquid metal, which is conducive to creat casting with clear outline and smooth surface, and is more beneficial to the creat large thin-wall castings.
- The castings crystallize and solidify under pressure, and can be fully fed, and the casting structure is dense.
- In general, no riser is needed, and the uncongealed metal in the riser pipe can be reflux to the crucible for repeated use, so that the recovery rate of the metal liquid is greatly improved, the recovery rate can reach 90%
- Convenient production operation, high production efficiency, and easy to achieve mechanization & automation.
Low Pressure Die Casting Applications
Low pressure die casting is the earliest anti-gravity casting technology, which began to be used in industrial production in the 1940s. Today, low pressure die casting is mainly used in the production of aluminum castings and magnesium castings, such as, automotive wheel hub, cylinder block, cylinder head, piston, missile shell, impeller, wind wheel and other complex shaped castings. Besides, low pressure casting can also be applied to produce small copper alloy castings, such as pipe fittings, bathroom cock faucets, etc.