What Is Die Casting vs. Injection Molding? The process of making a part is basically the same whether you are using die casting or injection molding. You create a die or mold in the form of the part you want to create. You then liquify the material and use extreme pressure to inject it into the die/mold. You then cool the die/mold with internal cooling lines and die spray on the die cavities. Finally, you open the die and remove the shot. Although there are some variations in technique, the major difference between die casting and injection molding is that die casting uses some kind of metal, often an aluminum alloy, as the raw material, while injection molding uses plastic or polymers.