The EDM of nitrided forging dies is one of the most demanding tasks that Peugeot undertakes with its ONA EDM machines. This type of part is a good example of how die sinking EDM is used for the machining of large surface areas.
The nitriding process can significantly increase the useful life of stamping dies used to shape forged parts. Nitriding increases surface hardness and resistance to wear with a considerable dimensional stability due to the surface of the die being enriched with nitrogen and the formation of nitrides.
Despite the benefits of nitriding, the process does not prevent the die from being damaged during use, which means that it has to be reconstructed and re-machined in order to recover the initial shape. The same die can be rebuilt several times during its useful life. EDM is regarded as the best machining solution for regenerating the die because its high level of surface hardness after the nitriding process makes the use of other machining techniques impractical. EDM is also used in the initial machining of the new die, when the surface to be machined has not yet been nitrided, since machining by milling leads to problems in the vertical faces due to the vibration which occurs in the milling cutter.
The iron nitride coating on the nitrided dies requires the use of EDM machines that are equipped with high- amperage generators. ONA die sinking machines from the NX series have the optional feature of generators of up to 400 amps. These make it possible to efficiently machine the nitrided surface, obtaining high initial volume in the roughing phase and achieving a homogeneous final roughness on large surface areas.