Aluminum is a metal that can be used in die casting to make parts easily. Many die casting techniques like permanent mold casting and sand casting are used for casting aluminum. Permanent mold casting is highly repeatable and helps to decrease the spin balancing processes and secondary machining operations. On the other hand, sand casting uses temporary molds that are made from wood or metal, making the tooling investment very low. However, per part prices are higher in the case of sand casting than permanent mold castings.
In the case of permanent mold casting techniques, the cycle times are short and this will decrease the per part price. However, tooling costs can be very high in this method. When compared to sand castings, permanent mold castings cool faster, offering a finer and uniform microstructure to the parts. This will help to boost the mechanical properties of the product by about twenty percent.
Gravity fed permanent metal molds is used these days to manufacture near net shaped parts from different alloys of aluminum. However, it is the duty of the die cast designer to ensure that it is profitable and possible to use permanent molds to manufacture the part. The die cast company should know the limits of the casting method to take full advantage of this die casting technique.
The Technique
Permanent molds can be used to manufacture many dimensionally repeatable parts. The permanent molds used in this technique are made from steel or iron, and are reused. Yet in the case of sand and investment castings, the molds are temporary and are destroyed during part removal.
In die casting methods, molten aluminum under very high pressure is injected into the die. Therefore, the die should be able to withstand the extreme pressures and temperatures, which increases the costs drastically for sand and investment casting, as the molds are destroyed in part removal.
Permanent mold castings can be offered with non-porous and uniform microstructures, but the qualities are very much dependent on foundry tooling design and solidification rates. These molds should be designed carefully with vents, sprues, and risers to offer smooth and controlled flow of the metal.
Placement and design of the gates and sprues is very important to ensure laminar flow of the metal into mold, as laminar flow will help to decrease the amount of gas entering the system. Presence of gas in the system will lead to voids in castings and permanent mold castings will help to limit this to minimum.