Die casting is a technique which has been in vogue since the last 250 to 300 years. Forging is a classic technique which has extensively been used since the ancient period both in Asia and Europe. Die casting requires a machine to press dies out of casting sand then a foundry to raise the metal to such a high temperature that it liquefies and at last pour the metal. It may create a sword but till now the swords are considered at the same time a weapon and an art piece with all the grains in it that the master swordsmiths incorporate in the metal after a lot of cutting folding twisting and turning. these grains will not be available if swords are made in dies. again the process of cuts and folds and strikes makes the steel uniform throughout in carbon content and adds extra plasticity to the material which will never be achieved in the cast piece even after a series of quenching and tempering. moreover forging allows us mix more than one quality of steel together retaining their basic properties. whereas cast iron is allover homogeneous. 
the Japanese katana or the samurai swords are an example of the above process of forging where hard high carbon steel is combined with low carbon soft steel to produce a one of its kind blade which is at the same time so strong as to knock a tree down and so sharp as to slice a human being from head to groin in a single blow. the strength of the blade is due to the hard steel and the razor edge is the consequence of the soft steel which had made the katana one of the deadliest weapons in the pre firearms age.
so forging is a technique which allows steel to be used not only as a metal for making implements but also it allows the smith add a touch of artistic and asthetic value to the implement which the foundry can never do. moreover the forged materials go through a cycle of quenching and annealing which causes them to become flexible and strong at the same time which is a quality the rapier is supposed to have. Even in modern times we use forges for different implement making than diecasting them.