Gravity Die Casting is a permanent mold casting method in which the molten metal is poured from a vessel into the mold cavity for the die casting process. The mold cavity fills with no force other than gravity only, and the filling of molten metal material can be controlled by tilting the die part. Compared with traditional pressure die casting, gravity die casting process makes molten metal arrives in the mold that sand cores can be utilized to make internal voids, yet this is not feasible for pressure die casting.
During the gravity die casting method conducted by gravity die casting machines, the molten metal is poured into the mold from the above, which fills from the bottom up by the gravity die casting machine. It is achieved purely under gravitational force. However, in pressure die casting, the molten metal is injected into the mold under considerable pressure ranging from 1500 and 25,400 psi as the general pressure values. This pressure of injection is maintained until the casting solidifies. In the gravity die casting machine, there is not such mechanism, so the method is basically the same but at the end gravity die casting machine does not use pressure to finish the casting but simply let the gravity to make it happen.
For this reason, if one consider for the long run production operation, the pressure filling die can be injected with pressured materials in a very quickly manner, coupled with the highly automated working mechanism, so the productivity and the overall circumstances can be controlled well under the automation control. If compared with the gravity die casting machines, this automated molten metal delivery of course costs more to settle and due to many complicated technical issues, so pressure die casting molds need to be manufactured by hardened steel coupled with internal cooling channels to well dissipate the accumulated heat, otherwise, the heat may cause unwanted effects.
With this respect, components of gravity die casting machines and the gravity die casting molds can be made of cast iron instead. The lower cycling rates of gravity die casting machines do not have accumulated heat issues in the mold part, and the chilling of the casting is good. Moreover, gravity die casting machines also has the advantages that the sand cores could be utilized to generate inner voids.
Gravity die casting machines exist for a long time, and this is a very old design of casting that has been used for centuries by iron workers in the old days. The accuracy of gravity die casting machines cannot keep up with pressured counterparts, because the fast filling of the mold with molted metal materials permit the pressure die casting method to achieve very smooth and complicated profile castings which are highly accurate in dimension. Plus, due to the high pressure, the walls can be thinner for sure if compared to the walls made by gravity die casting machines. The slower speed of molten material poured into the die indicates that the folding is lesser and the turbulences happened inside the cavity would make further inaccuracies. At the same time, since the pour manner by gravity die casting machines are uniquely with less air trapped in the casting process, gravity die casting machines need less following heat treatment of the casted.
Although gravity die casting machines is designed with some inconvenience compared to the pressured counterparts, this method still exists for some reasons. The greatest two reasons are: Expenses and flexibility. As the pressure measure’s setting involves a lot of pre-setting stuff to be done, there are many prerequisite equipment need to be settled down first. To the case of gravity die casting machines, since gravity is the cause of the forming process, so this part does not cost much. Furthermore, the gravity die casting machines contains more flexibility in the designs by themselves. Sometimes, people may use gravity die casting machines to do some trial casting first, then after all the manufacturing settings are all set into stable features, they may turn their method to pressure die casting method, since this one can promise high productivity and better quality. So it is up to users’ choice to choose whether to use gravity die casting machines or pressure die casting machines.
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