EDM Milling

EDM Milling: is the process in which complex shapes are machined using simple shaped electrode. The simple shaped electrodes are rotated at high speeds and follow specified paths in the workpiece like the end mills. This technique is very useful and it makes EDM very versatile like the mechanical milling process. This process solves the problem of manufacturing accurate complex shaped electrodes for die-sinking of three dimensional cavities. EDM milling improves flushing due to the high speed electrode rotation. Moreover, the tooling problems involved with complex shaped electrodes is eliminated by the use of simple shaped electrodes. The electrode wear can be optimized in EDM milling because of the rotational and contouring motions of the electrode. EDM contouring and planetary EDM techniques are quite similar to EDM milling except that in the former cases, the electrode rotation is not present in some cases where electrodes other than cylindrical shapes are used.

In the case of EDM milling or contouring EDM, three types of motions with cylindrical electrodes can be distinguished. They are EDM profiling, EDM pocketing and EDM grooving as shown in the fig . These motions need distinction unlike in mechanical milling operations because of the different sparking gaps involved with the motions. In EDM profiling, the electrode is moved along the outer or inner contour of the workpiece. For pocketing operations, the generated toolpath comprises of several parallel or equidistant tracks in order to generate large two dimensional cavities. EDM grooving is a technique similar to wire EDM where the electrode travels along the specified contour in the workpiece. 

EDM milling provides the most economic advantage where several electrodes would otherwise be used to produce a part by die-sinking EDM. An example is a piston for a circuit breaker mold, which required 50 electrodes for production by die-sinking EDM.

The need to manufacture electrodes resulted in an overall production time of 23 days for the part. EDM milling reduced this time to 11 days, with savings in electrode costs also cutting production cost. The figure below graphically compares the machining time of the slot usind Die-sinling and EDM milling. 

EDM milling has the potential to simplify the planning process, by eliminating several traditional steps used in CNC die-sinking. The table below gives the process planning steps in EDM milling.

The rotation of the electrode and the tool path generated optimizes the electrode wear. However, it does not mean that EDM milling completely eliminates the electrode wear or reduces it to miniscule amount of 1%. The simplicity of electrode now permits an easier investigation on electrode wear and allows us to focus the research on developing a mathematical algorithm and compensate for electrode.

The main limitation in the EDM process is that complex shapes with sharp corners cannot be machined because of the rotating electrode.