You my check for some brittle polymers. Specially thermosetting polymers.

This question can not be easily answered.

First, they require an additional electrode through which electric discharge is ignited for electrically non-conductive materials. This additional electrode may e.g. be a coating of non-conductive material. This layer is destroyed during discharge and must be newly formed simultaneously for the wide discharges. The removal is thus not only on the base points of the discharge, but is bewrikt through the entire plasma channel (part of the discharge). Thus, the calculation of the melting and evaporation volume is more difficult. Next, it should be noted that evaporation, melting, and "recrystallization" of many electrically non-conductive materials proceed differently than for metals and metallic alloys.

Second, the question of efficiency is difficult and easy at the same. If no other processing possibility, then the efficiency is very good. Are there comparable processing method must then be compared. In many plastic materials I can imagine competitive process. Whether the high machining accuracy, can be achieved as with the metals must be tested, as well as the surface quality.

Adapted machines, there is no, because most studies are performed on standard machines or university test facilities. A compilation of all ED processed electrically non-conductive materials, I do not know, and will be hard to create them too, because publications are only a part of the real tests.

Here is an article on low conductive material machining on WEDM. You can refer this for more clarity on the topic.

Chapter Experimental Study on Improving Material Removal Rate and Su...