conventional machining process utilize the ability of the cutting tool to stress the material beyond the yield point to start the material removal process. This requires that the cutting tool material be harder than the workpiece material. The advent of harder materials for aerospace applications have made the removal process by conventiional methods very difficult as well as time consuming since the material removal rate reduces with an increase in hardness of the work material. Hence machining process with utilize other methods such as electro-chemical processes for material removal have been developed. These processes are termed as unconventional or non-traditional machining methods.

   New materials which have high strength to weight ratio, heat resistance and hardness such as nimonic alloys, alloys with alloying elements such as tungsten, molybdenum and columbium are difficult to machine by the traditinal methods. The complex shapes in these materials are either difficult to machine or time consuming by the traditional methods. In such cases, the application of the  non-traditional machining processes finds extensive use. Further, in some applications a very high accuracy is desired besides the complexity of the surface to be machined. These processes are not meant to replace the conventional processes but to supplement them. 

   There are a number of unconventional processes. They are:

   (i)Electri Discharge Machining (EDM)

   (ii)Electro Chemical machining (ECM)

   (iii)Electro Chemical Grinding (ECG)

   (iv)Ultrasonic Machining (USM)

   (v) Laser Beam Machining (LBM)

   (vi)Chemical Machining (CHM)

   (vii)Abrasive Jet Machining (AJM)

   (viii)Water Jet Machining（WJM）

  （ix）Plasma Arc Machining (PAM)