The traditional die casting process follows four basic steps to reach the end result. How the traditional method works is the die is prepared, the metal is forced into the cavity, the casting is ejected from the mold, and then the shakeout begins. The shakeout is done to separate any excess metal from the final product, such as scrap. While the traditional die casting process works great for most manufacturers there are some variations to the process to help make the process more efficient.
Here is a look at the variations that one can find within traditional die casting methods.
- Semi-Solid – One of the best things about semi-solid die casting is that it allows for even thinner walls than regular die casting, but it also enables manufacturers to make parts that are even more complex. How semi-solid die casting varies from regular die casting is in regular casting aluminum is heated to its liquid form and then injected into the molds, with this type of casting aluminum is heated to a state that is between liquid and solid, making it slushy.
- Pore-Free – This method is used when the manufacturer does not want the casting to be porous. Something interesting to note is that this process only differs from the normal die casting process in one way; oxygen is added to the die before any castings are made. The oxygen is added to the mold to help remove any air from the cavity. Removing any oxygen inside the cavity causes oxides to form inside the cavity, which gets rid of any porosity caused by gases. Making a pore-free casting offers the advantage of greater strength, but they can also be welded or heat-treated, unlike other castings. The only metals that can be used to make pore-free castings are aluminum, lead, and zinc.
- Heated-Manifold Direct-Injection – This method is also known as runner-less or direct-injection. Unlike other die casting methods, this form is only used with zinc. How this method works is the liquid zinc is first injected into a heated manifold and then is injected into the cavity through mini-nozzles, which are also heated. One of the advantages to using this method over regular die casting is that it has a lower cost because it reduces the amount of scrap, but also the surface quality is also better due to the slower cooling off period.
- Acurad – This process was developed in the 1950s by General Motors and stands for accurate, reliable, and dense. The reason this process was created was to combine directional solidification and a stable fill to work with the faster cycle times of the traditional process. This development lead to four new technologies for die casting, flow and fill modeling, heat treatable/high integrity, indirect squeeze, and thermal analysis. The Acurad system used a bottom fill system along with a stable flow. In the beginning, this system was done by trial and error, but eventually computerized flow and fill replaced the human thought processes. This system was the first one designed that could handle low-iron aluminum and also was the first to introduce the double piston design, which was later changed to one piston that was used later on in the cycle to perform the same results more effectively than the double piston design.