Sinker EDM (Ram EDM)

A sinker EDM, also called ram or die-sinking EDM, erodes a cavity with sparks between a shaped electrode and the workpiece, both submerged in dielectric oil. The electrode, usually graphite or copper, is the negative of the shape wanted. As it sinks into the part, the sparks reproduce its form. There is no cutting force, and the hardness of the workpiece does not matter, only that it conducts.

This is how deep ribs, sharp internal corners and fine textures get into hardened mould and die steel, where a milling cutter would be too long, too thin or simply unable to reach. The electrodes themselves are milled first, on a machining center set up for graphite or copper. For shapes that go right through the part, a wire EDM needs no electrode at all.

Compare the X, Y and Z travels, the work tank size, and the heaviest workpiece and electrode the machine carries. An electrode changer and a C axis let a job run through several electrodes unattended. The generator's maximum current relates to the removal rate on large cavities, and its fine-finish settings matter for small, detailed work.