INDUSTRIAL MANUFACTURING PROCESS

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| Basic Principle | Types of EDM | Process Control | Application |

Processes control
Gap Control
EDM requires that a constant gap be maintained between the electrode and the workpiece to obtain maximum machining efficiency. Therefore, every precision EDM tool holder incorporates some form of servo control to maintain the proper gap spacing. The servo control can be an electro-hydraulic system or an electro-mechanical servo system. As cutting proceeds, the servo control system automatically advances the electrode at the rate required to keep the gap constant. If the gap becomes blocked with particles from the cut, the control system automatically retracts the electrode to allow the cutting area to clear, then returns the electrode to the cutting position.
Heat Affected Zone

The EDM process is a thermal process, some annealing of the workpiece can be expected in a zone just below the machined surface. This effect can be minimized by machining at lower rate, i.e. using a finish cut to remove the annealed material left by the previous high speed roughing cut.

In addition, not all the workpiece material melted by the discharge is expelled into the dielectric. The remaining melted material is quickly chilled, primarily by heat conduction into the bulk of the workpiece, resulting in an exceedingly hard surface.

 
Tool characteristics and Wear Ratio

Criteria for the tool material are the ready erosion of the work, minimisation of self-erosion, and cheapness and ease of formability. High melting-point materials and suitable polarity are thus important. Brass or copper are frequently used with RC circuits, whereas graphite is commonly employed with pulse circuits. To prevent taper on finishing operations from sparking at the side of the tool, the sides of the electrode are usually relieved.

 
Overcut

In the erosion process there naturally is an overcut which is the measure of the distance between the electrode and the wall of the surface being machined. The general rule is that the highest the melting point of the tool materials, the smaller the overcut.

 
Flushing

Although the main function of dielectric fluid is to serve as an insulator between tool and workpiece, it is also a coolant quenching the spark rapidly and cooling down the materials as well as flushing medium for chip removal. As it affects electrode wear, m.r.r. etc., effective filtering and flushing is essential.