Contents

III. How to design electrodes

⇒ "Ⅰ. About electric discharge machining"

⇒ "II. How to set machining conditions"

3. Classification of rough / semi-finish / finish

The electrodes are made with distinguishing for rough machining, for middle finishing and for finishing.
Rough electrode intends to process until an approximate machining shape with leaving around 0.1-0.5mm of the machining shape is formed. Electrode design to get high machining speed is important. When the approximate shape has already been formed in the previous process such as cutting, making rough electrodes may be omitted.

Finishing electrodes are used in the stage of machining after the formation of rough shape by rough machining. Electrode design to get required machining surface roughness and machining accuracy is important.

Middle finish electrode is designed as an intermediate electrode on electrode reduction between a rough electrode and a finish electrode, and it is made only when needed. The case when making middle electrode is necessary is firstly when electrode reduction amount becomes big as a result that machining speed of rough electrodes is made of great importance. In a large electrode reduction, middle finish electrode is necessary because the burden of the finish electrode becomes big for a large shape difference at the time of machining. Second case is when electrode reduction amount becomes small as a result of emphasizing the shape accuracy of finishing electrode. In small electrode reduction, machining speed is slow, and a middle finish electrode is necessary because machining speed becomes slow even if it is after the rough machining.

The aim to make a middle finish electrode is when the value of "electrode reduction amount of rough electrode"/"electrode reduction amount of finish electrode" is more than 4 times. For example, when electrode reduction amount of rough electrode is 0.3mm and electrode reduction amount of finish electrode is 0.07mm, it is 4.3 times, and a middle finish electrode is necessary. Also, if you do not use a middle finish electrode in such a case, the machining time with the finish electrodes may get longer, or adversely, defectives of finish surface become easy to occur because it is required machining near to the limit with rough electrodes.